JP4784474B2 - Optical disc apparatus and focus position control method - Google Patents

Description

  The present invention relates to an optical disc apparatus and a focus position control method, and is suitable for application to, for example, a standing wave recording type optical disc apparatus.

  2. Description of the Related Art Conventionally, in an optical disc apparatus, a light beam is irradiated onto an optical disc such as a CD (Compact Disc), a DVD (Digital Versatile Disc), and a Blu-ray Disc (registered trademark, hereinafter referred to as BD), and the reflected light is read. Thus, information that can be reproduced is widely used.

  Further, in such a conventional optical disc apparatus, information is recorded by irradiating the optical disc with a light beam and changing the local reflectance of the optical disc.

  For this optical disc, the size of the light spot formed on the optical disc is given by approximately λ / NA (λ: wavelength of the light beam, NA: numerical aperture), and the resolution is also known to be proportional to this value. It has been. For example, Non-Patent Document 1 shows details of a BD that can record data of approximately 25 [GB] on an optical disk having a diameter of 120 [mm].

  By the way, various kinds of information such as various contents such as music contents and video contents, or various data for computers are recorded on the optical disc. In particular, in recent years, the amount of information has increased due to higher definition of video and higher sound quality of music, and an increase in the number of contents to be recorded on one optical disc has been demanded. It is requested.

  In view of this, there has also been proposed a method of increasing the recording capacity of one optical disc by overlapping recording layers in one optical disc (see, for example, Non-Patent Document 2).

  On the other hand, an optical disk apparatus using a hologram has been proposed as a method for recording information on the optical disk (see, for example, Non-Patent Document 3).

  For example, as shown in FIG. 1, an optical disc apparatus 1 is a material containing a monomer that undergoes a polymerization reaction due to, for example, irradiated light intensity and contains a monomer to be polymerized, and a material (photopolymer) whose refractive index changes depending on the concentration distribution of the polymer. A light beam is once condensed from the optical head 7 in the optical disk 8 made of a material, etc., and then once again in the reverse direction using the reflection device 9 provided on the back side (lower side in FIG. 1) of the optical disk 8. The light beam is condensed at the same focal position.

  The optical disc apparatus 1 emits a light beam composed of laser light from a laser 2, modulates the light wave by an acousto-optic modulator 3, and converts it into parallel light by a collimator lens 4. Subsequently, the light beam passes through the polarization beam splitter 5, is converted from linearly polarized light to circularly polarized light by the quarter wavelength plate 6, and then enters the optical head 7.

  The optical head 7 is adapted to record and reproduce information. The optical head reflects a light beam by a mirror 7A, condenses it by an objective lens 7B, and is rotated by a spindle motor (not shown). 8 is irradiated.

  At this time, the light beam is once focused inside the optical disc 8, then reflected by the reflecting device 9 disposed on the back side of the optical disc 8, and from the back side of the optical disc 8 to the same focal point inside the optical disc 8. Focused. Incidentally, the reflection device 9 includes a condenser lens 9A, a shutter 9B, a condenser lens 9C, and a reflection mirror 9D.

  As a result, as shown in FIG. 2 (A), a standing wave is generated at the focal position of the light beam, and the light spot size is formed in a shape in which two cones are bonded together on the bottom surfaces. A recording mark RM made up of small interference fringes (holograms) is formed. Thus, the recording mark RM is recorded as information.

  When a plurality of recording marks RM are recorded in the optical disk 8, the optical disk apparatus 1 rotates the optical disk 8 and arranges the recording marks RM along a concentric or spiral track to form one mark recording layer. And by adjusting the focal position of the light beam, each recording mark RM can be recorded so that a plurality of mark recording layers are stacked.

  As a result, the optical disc 8 has a multilayer structure having a plurality of mark recording layers therein. For example, in the optical disc 8, as shown in FIG. 2B, the distance (mark pitch) p1 between the recording marks RM is about 1.5 [μm], and the distance (track pitch) p2 between the tracks is about 2 [μm]. The distance p3 between the layers is about 22.5 [μm].

  Further, when reproducing information from the disc 8 on which the recording mark RM is recorded, the optical disc apparatus 1 closes the shutter 9B of the reflection device 9 so that the light beam is not irradiated from the back side of the optical disc 8.

  At this time, the optical disc apparatus 1 irradiates the recording mark RM in the optical disc 8 with the optical beam by the optical head 7 and causes the reproducing light beam generated from the recording mark RM to enter the optical head 7. The reproduction light beam is converted from circularly polarized light to linearly polarized light by the quarter wavelength plate 6 and reflected by the polarizing beam splitter 5. Further, the reproduction light beam is condensed by the condenser lens 10 and irradiated to the photodetector 12 through the pinhole 11.

At this time, the optical disc apparatus 1 detects the light amount of the reproduction light beam by the photodetector 12 and reproduces information based on the detection result.
Y. Kasami, Y. Kuroda, K. Seo, O. Kawakubo, S. Takagawa, M. Ono, and M. Yamada, Jpn. J. Appl. Phys., 39, 756 (2000) I. Ichimura et al, Technical Digest of ISOM'04, pp52, Oct. 11-15, 2005, Jeju Korea RR Mcleod er al., “Microholographic multilayer optical disk data storage,” Appl. Opt., Vol. 44, 2005, pp3197

  By the way, in the conventional optical disc apparatus corresponding to CD, DVD, or BD, surface rotation or eccentricity may occur in the rotated optical disc, but focus control, tracking control, etc. are performed based on the detection result of the light beam. By performing various controls, the target track can be accurately irradiated with the light beam.

  Further, in the optical disc apparatus 1 shown in FIG. 1, in order to form a standing wave, the focal positions of the light beams emitted from both sides of the optical disc 8 must be matched accurately. For this reason, in the optical disc apparatus 1, it is necessary to control and drive the objective lens 7B and the condenser lens 9A separately in accordance with surface blurring, eccentricity, and the like that occur in the optical disc 8.

  However, the optical disc apparatus 1 shown in FIG. 1 does not have a configuration that can specifically perform such focus control and tracking control, and cannot accurately irradiate the target mark position with the light beam. Further, in the optical disc apparatus 1, a position control method using reflected light as in a conventional optical disc cannot be applied.

  That is, the optical disk apparatus 1 cannot accurately focus the light beam at a desired position in the optical disk 8, and there is a possibility that information cannot be recorded or reproduced correctly.

  The present invention has been made in view of the above points, and an object of the present invention is to propose an optical disc apparatus and a focus position control method for recording or reproducing a recording mark representing information on an optical recording medium with high accuracy.

  In order to solve this problem, in the optical disc apparatus of the present invention, both sides of the optical recording medium in the form of a disc through the first and second objective lenses corresponding to the first and second lights emitted from the light source, respectively. In the optical disc apparatus for irradiating the same target recording mark position from the first, the first focal point moving unit that moves the focal position of the first light, and the amount of deviation of the focal position of the first light from the recording mark position are detected. Then, a mark position deviation signal generation unit that generates a mark position deviation signal according to the detection result, and a first light focus position is moved to the recording mark position based on the mark position deviation signal. A first drive control unit that controls the focus moving unit, a second focus moving unit that moves the focal position of the second light, and a deviation amount of the focal position of the second light with respect to the focal position of the first light Detect The focal position of the second light matches the focal position of the first light based on the focal position deviation signal generation unit that generates the focal position deviation signal according to the detection result, the mark position deviation signal, and the focal position deviation signal. And a second drive control unit for controlling the second focal point moving unit.

  Accordingly, since the focal position of the second light can be moved in the same direction as the focal position of the first light according to the mark position deviation signal, the second light with respect to the focal position of the first light can be moved. The amplitude of the focal position deviation signal can be reduced by reducing the focal position deviation amount. As a result, the focus position of the second light can be made to follow the focus position of the first light based on the focus position shift signal having a small amplitude, and therefore the focus position of the second light can be determined with high accuracy. Can be matched to the focal position of the light.

  In the focus control method of the present invention, the first and second lights emitted from the light source are targeted from both sides of the optical recording medium in the form of a disk via the corresponding first and second objective lenses, respectively. A first focus that moves the focal position of the first light based on a mark position deviation signal that represents the deviation amount from the focal position of the first light with respect to the recording mark position when irradiating the same recording mark position. By driving the moving unit, a first focal position moving step for moving the focal position of the first light to the recording mark position, and a deviation amount of the focal position of the second light with respect to the focal position of the first light are set. A focal position deviation signal generating step for detecting and generating a focal position deviation signal, and driving a second focal point moving unit for moving the focal position of the second light based on the mark position deviation signal and the focal position deviation signal. By Was the focal position of the second light to a first provided and the second focus position moving step for matching the focal position of the light.

  Accordingly, since the focal position of the second light can be moved in the same direction as the focal position of the first light according to the mark position deviation signal, the second light with respect to the focal position of the first light can be moved. The amplitude of the focal position deviation signal can be reduced by reducing the focal position deviation amount. As a result, the focus position of the second light can be made to follow the focus position of the first light based on the focus position shift signal having a small amplitude, and therefore the focus position of the second light can be determined with high accuracy. Can be matched to the focal position of the light.

  In the present invention, the first and second lights emitted from the light source are incident on a disk-shaped optical recording medium through the same objective lens, and the optical recording of the first or second light is performed. When irradiating one target light reflected by the reflective film of the medium and the other light before reaching the reflective film to the same target recording mark position from opposite directions, the optical recording medium Driving the first focal point moving unit that moves the focal point position of the first light based on the movement amount signal representing the movement amount from the current recording mark position to the next recording mark position. The focus position of the light is moved to the recording mark position, the shift amount of the focus position of the second light with respect to the focus position of the first light is detected, a focus position shift signal is generated, the shift amount signal and the focus position shift signal Move the focus position of the second light based on By driving the second focus movement unit to and so as to coincide the focal position of the second light to the focal position of the first light.

  Accordingly, since the focal position of the second light can be moved in the same direction as the focal position of the first light according to the mark position deviation signal, the second light with respect to the focal position of the first light can be moved. The amplitude of the focal position deviation signal can be reduced by reducing the focal position deviation amount. As a result, the focus position of the second light can be made to follow the focus position of the first light based on the focus position shift signal having a small amplitude, and therefore the focus position of the second light can be determined with high accuracy. Can be matched to the focal position of the light.

  According to the present invention, since the focal position of the second light can be moved in the same direction as the focal position of the first light in accordance with the mark position deviation signal, the second position with respect to the focal position of the first light. The amount of deviation of the focal position of the light can be reduced to reduce the amplitude in the focal position deviation signal. As a result, the focus position of the second light can be made to follow the focus position of the first light based on the focus position shift signal having a small amplitude, and therefore the focus position of the second light can be determined with high accuracy. Therefore, it is possible to realize an optical disc apparatus and a focal position control method for recording or reproducing a recording mark representing information on an optical recording medium with high accuracy.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

(1) First Embodiment (1-1) Configuration of Optical Disc First, an optical disc 100 used as an optical recording medium in the present invention will be described. As shown in the external view in FIG. 3A, the optical disc 100 as a whole is formed in a disk shape having a diameter of about 120 [mm], similar to the conventional CD, DVD and BD, and has a hole 100H at the center. Is formed.

  Further, as shown in the cross-sectional view of FIG. 3B, the optical disc 100 has a recording layer 101 for recording information in the center, and the recording layer 101 is sandwiched from both sides by the substrates 102 and 103. It is configured.

  Incidentally, the thickness t1 of the recording layer 101 is about 0.3 [mm], and the thicknesses t2 and t3 of the substrates 102 and 103 are both about 0.6 [mm].

  The substrates 102 and 103 are made of, for example, a material such as polycarbonate or glass, and both of them transmit light incident from one surface to the opposite surface with high transmittance. Further, the substrates 102 and 103 have a certain degree of strength and play a role of protecting the recording layer 101. In addition, about the surface of the board | substrates 102 and 103, unnecessary reflection may be made to be prevented by anti-reflective coating.

  Similar to the optical disc 8 (FIG. 1), the recording layer 101 is made of a photopolymer whose refractive index changes depending on the intensity of irradiated light, and responds to a blue light beam having a wavelength of 405 [nm]. As shown in FIG. 3B, when the two first blue light beams Lb1 and Lb2 having relatively strong intensities interfere in the recording layer 101, the recording layer 101 is not fixed. A standing wave is generated, and an interference pattern having properties as a hologram as shown in FIG. 2A is formed.

  The optical disc 100 also has a reflection / transmission film 104 at the boundary surface between the recording layer 101 and the substrate 102. The reflection / transmission film 104 is made of a dielectric multilayer film or the like, and transmits the first blue light beam Lb1, the second light blue beam Lb2, and the blue reproduction light beam Lb3 having a wavelength of 405 [nm] and has a wavelength of 660 [nm]. It has wavelength selectivity such as reflecting a red light beam.

  The reflection / transmission film 104 forms a tracking servo guide groove. Specifically, a spiral track is formed by lands and grooves similar to a general BD-R (Recordable) disk. Yes. This track is given an address consisting of a series of numbers for each predetermined recording unit, and the track on which information is recorded or reproduced can be specified by the address.

  Note that pits or the like may be formed in the reflective / transmissive film 104 (that is, the boundary surface between the recording layer 101 and the substrate 102) instead of the guide grooves, or the guide grooves and pits may be combined.

  When the red light beam Lr1 is irradiated from the substrate 102 side, the reflection / transmission film 104 reflects this toward the substrate 102 side. Hereinafter, the light beam reflected at this time is referred to as a red reflected light beam Lr2.

  The red reflected light beam Lr2 is used for focusing the focus Fr of the red light beam Lr1 collected by a predetermined objective lens OL1 on a target track (hereinafter referred to as a target mark position) in an optical disc apparatus, for example. It is assumed that the objective lens OL1 is used for position control (that is, focus control and tracking control).

  In the following, the surface on the substrate 102 side of the optical disc 100 is referred to as a guide surface 100A, and the surface on the substrate 103 side of the optical disc 100 is referred to as a recording light irradiation surface 100B.

  In practice, when information is recorded on the optical disc 100, as shown in FIG. 3B, the red light beam Lr1 is collected by the position-controlled objective lens OL1, and the target track of the reflective / transmissive film 104 is recorded. (Hereinafter referred to as the target mark position).

Further, the first blue light beam Lb1 that shares the optical axis Lx with the red light beam Lr1 and is condensed by the objective lens OL1 passes through the substrate 102 and the reflection / transmission film 104, and the desired track in the recording layer 101. It is focused at a position corresponding to the back side (i.e. the substrate 103 side) of the. At this time, the first focal point Fb1 of the first blue light beam Lb1 is located farther than the focal point Fr on the common optical axis Lx with reference to the objective lens OL1.

  Further, the second blue light beam Lb2 having the same wavelength as the first blue light beam Lb1 and sharing the optical axis Lx is equivalent to the objective lens OL1 from the opposite side of the first blue light beam Lb1 (that is, the substrate 103 side). The light is condensed and irradiated by an objective lens OL2 having the following optical characteristics. At this time, the second focal point Fb2 of the second blue light beam Lb2 is positioned at the same position as the first focal point Fb1 of the first blue light beam Lb1 by controlling the position of the objective lens OL2. .

  As a result, on the optical disc 100, the recording mark RM having a relatively small interference pattern is recorded as a minute hologram at the position of the first focus Fb1 and the second focus Fb2 corresponding to the back side of the target mark position in the recording layer 101. The

  At this time, in the recording layer 101, a recording mark RM is formed at a portion where the first blue light beam Lb1 and the second light blue beam Lb2, both of which are converged light, overlap and have a predetermined intensity or more. For this reason, as shown in FIG. 2 (A), the recording mark RM generally has a shape in which two cones are bonded to each other at the bottom surfaces, and a central portion (a portion where the bottom surfaces are bonded together). Is slightly constricted.

  Incidentally, regarding the recording mark RM, with respect to the diameter RMr of the constricted portion at the center, the wavelength of the first blue light beam Lb1 and the second light blue beam Lb2 is λ [m], and the numerical apertures of the objective lenses OL1 and OL2 are NA. Then, it calculates | requires by the following (1) Formula.

The height RMh of the recording mark RM can be obtained by the following equation (2), where n is the refractive index of the recording layer 101 .

  For example, when the wavelength λ is 405 [nm], the numerical aperture NA is 0.5, and the refractive index n is 1.5, the diameter RMr = 0.97 [μm] from the formula (1) and the height from the formula (2). RMh = 9.72 [μm].

  Further, the optical disc 100 is designed such that the thickness t1 (= 0.3 [mm]) of the recording layer 101 is sufficiently larger than the height RMh of the recording mark RM. For this reason, the optical disc 100 records the recording mark RM while switching the distance from the recording reflective film 104 in the recording layer 101 (hereinafter referred to as depth), as shown in FIG. In addition, it is possible to perform multilayer recording in which a plurality of mark recording layers are stacked in the thickness direction of the optical disc 100.

  In this case, the depth of the recording mark RM is changed by adjusting the depths of the focal points Fb1 and Fb2 of the blue light beams Lb1 and Lb2 in the recording layer 101 of the optical disc 100. For example, in the optical disc 100, when the distance p3 between the mark recording layers is set to about 15 [μm] in consideration of the mutual interference between the recording marks RM, about 20 mark recording layers are formed in the recording layer 101. can do. The distance p3 may be set to various values other than about 15 [μm] in consideration of the mutual interference between the recording marks RM.

  On the other hand, in the optical disc 100, when the information is reproduced, the red light beam Lr1 collected by the objective lens OL1 is focused on the target mark position of the reflection / transmission film 104 when the information is recorded. The position of the objective lens OL1 is controlled.

  Further, in the optical disc 100, the first focal point Fb1 of the first blue light beam Lb1 transmitted through the substrate 102 and the reflective / transmissive film 104 through the same objective lens OL1 corresponds to the “back side” of the target mark position in the recording layer 101. In addition, the focus is set to a position (hereinafter, referred to as a target mark position) that is a target depth.

  At this time, the recording mark RM recorded at the position of the first focal point Fb1 generates a blue reproduction light beam Lb3 from the recording mark RM recorded at the target mark position due to the property as a hologram. The blue reproduction light beam Lb3 has the same optical characteristics as the second blue light beam Lb2 irradiated when the recording mark RM is recorded, and is in the same direction as the second blue light beam Lb2, that is, the recording layer 101. It progresses while diverging from the inside to the substrate 102 side.

  As described above, the optical disk 100 uses the red light beam Lr1 for position control, the first blue light beam Lb1 for information recording, and the second blue light beam Lb2 for recording information. The recording mark RM is formed as the information at the position where the first focal point Fb1 and the second focal point Fb2 overlap, that is, the target mark position behind the target mark position in the reflective / transmissive film 104 and the target depth. Yes.

  Further, when the recorded information is reproduced, the optical disc 100 uses the position-control red light beam Lr1 and the information reproduction first blue light beam Lb1, so that the position of the first focus Fb1, that is, the target mark A blue reproduction light beam Lb3 is generated from the recording mark RM recorded at the position.

(1-2) Configuration of Optical Disc Device Next, the optical disc device 20 corresponding to the optical disc 100 described above will be described. As shown in FIG. 4, the optical disc apparatus 20 is configured to perform overall control by a control unit 21.

  The control unit 21 is mainly configured by a CPU (Central Processing Unit) (not shown), reads various programs such as a basic program and an information recording program from a ROM (Read Only Memory) (not shown), and stores them in a RAM (Random) (not shown). Various processes such as an information recording process are executed by expanding in (Access Memory).

  For example, when the control unit 21 receives an information recording command, recording information, and recording address information from an external device (not shown) with the optical disc 100 loaded, the control unit 21 represents the amount of movement of the first objective lens based on the recording address information. A movement amount signal is generated, the movement amount signal and a drive command are supplied to the drive control unit 22, and recording information is supplied to the signal processing unit 23. Incidentally, the recording address information is information indicating an address at which the recording information is to be recorded among the addresses given to the recording layer 101 of the optical disc 100.

  The drive control unit 22 drives and controls the spindle motor 24 in accordance with the drive command to rotate the optical disc 100 at a predetermined rotation speed, and controls the sled motor 25 to drive the optical pickup 26 with the moving shafts 25A and 25B. Are moved to a position corresponding to the recording address information in the radial direction of the optical disc 100 (that is, the inner circumferential direction or the outer circumferential direction).

  The signal processing unit 23 generates a recording signal by performing various signal processing such as predetermined encoding processing and modulation processing on the supplied recording information, and supplies the recording signal to the optical pickup 26.

  As shown in FIG. 5, the optical pickup 26 has a substantially U-shaped side surface. As shown in FIG. 3B, the optical pickup 26 irradiates the optical disc 100 with a light beam focused on both sides. Has been made to get.

  The optical pickup 26 performs focus control and tracking control based on the control of the drive control unit 22 (FIG. 4), so that the track indicated by the recording address information in the recording layer 101 of the optical disc 100 (hereinafter referred to as the target mark position). The recording mark position of the light beam is aligned with the recording mark RM according to the recording signal from the signal processing unit 23 (details will be described later).

  When the control unit 21 receives, for example, an information reproduction command and reproduction address information indicating the address of the recording information from an external device (not shown), the control unit 21 supplies the drive command to the drive control unit 22 and also reproduces the reproduction processing command. Is supplied to the signal processing unit 23.

  As in the case of recording information, the drive control unit 22 controls the spindle motor 24 to rotate the optical disc 100 at a predetermined rotational speed, and controls the sled motor 25 to control the optical pickup 26 for reproduction addressing. Move to a position corresponding to the information.

  The optical pickup 26 performs focus control and tracking control based on the control of the drive control unit 22 (FIG. 4), so that light is applied to the track (that is, the target mark position) indicated by the reproduction address information in the recording layer 101 of the optical disc 100. The recording mark position of the beam is aligned, and a light beam having a predetermined light amount is irradiated. At this time, the optical pickup 26 detects the reproduction light beam generated from the recording mark RM of the recording layer 101 in the optical disc 100 and supplies a detection signal corresponding to the amount of light to the signal processing unit 23 (details). Will be described later).

  The signal processing unit 23 generates reproduction information by performing various signal processing such as predetermined demodulation processing and decoding processing on the supplied detection signal, and supplies the reproduction information to the control unit 21. In response to this, the control unit 21 sends the reproduction information to an external device (not shown).

  As described above, the optical disc apparatus 20 controls the optical pickup 26 by the control unit 21 to record information at the target mark position in the recording layer 101 of the optical disc 100 and reproduce information from the target mark position. ing.

(1-3) Configuration of Optical Pickup Next, the configuration of the optical pickup 26 will be described. As schematically shown in FIG. 6, the optical pickup 26 is provided with a large number of optical components, and is roughly divided into a guide surface position control optical system 30, a guide surface information optical system 50, and a recording light irradiation surface optical system 70. It is comprised by.

(1-3-1) Configuration of Guide Surface Red Optical System The guide surface position control optical system 30 irradiates the guide surface 100A of the optical disc 100 with the red light beam Lr1, and the optical disc 100 emits the red light beam Lr1. The reflected red light beam Lr2 is received.

  In FIG. 7, the laser diode 31 of the guide surface position control optical system 30 can emit red laser light having a wavelength of about 660 [nm]. In practice, the laser diode 31 emits a red light beam Lr1 having a predetermined amount of light, which is a divergent light, based on the control of the control unit 21 (FIG. 4) and makes it incident on the collimator lens 32. The collimator lens 32 converts the red light beam Lr1 from diverging light to parallel light and makes it incident on the non-polarizing beam splitter 34 via the slit 33.

  The non-polarizing beam splitter 34 transmits the red light beam Lr1 at a rate of about 50% on the reflection / transmission surface 34A and makes it incident on the correction lens 35. The correction lenses 35 and 36 cause the red light beam Lr1 to diverge once and then converge to enter the dichroic prism 37.

  The reflection / transmission surface 37S of the dichroic prism 37 has so-called wavelength selectivity in which the transmittance and the reflectance differ depending on the wavelength of the light beam, and transmits the red light beam at a rate of approximately 100%. Is reflected at a rate of almost 100%. Therefore, the dichroic prism 37 transmits the red light beam Lr1 through the reflection / transmission surface 37S and makes it incident on the first objective lens 38.

  The first objective lens 38 condenses the red light beam Lr1 and irradiates it toward the guide surface 100A of the optical disc 100. At this time, as shown in FIG. 3B, the red light beam Lr1 is transmitted through the substrate 102 and reflected by the reflective / transmissive film 104, and becomes a red reflected light beam Lr2 that goes in the opposite direction to the red light beam Lr1.

  Incidentally, the first objective lens 38 is designed to be optimized for the first blue light beam Lb1, and the red light beam Lr1 is related to the optical distance between the slit 33, the correction lenses 35 and 36, and the like. The lens functions as a condenser lens having a numerical aperture (NA) of 0.41.

  Thereafter, the red reflected light beam Lr2 sequentially passes through the first objective lens 38, the dichroic prism 37, and the correction lenses 36 and 35 to be converted into parallel light, and then enters the non-polarizing beam splitter 34.

  The non-polarizing beam splitter 34 irradiates the mirror 40 by reflecting the red reflected light beam Lr2 at a ratio of about 50%, and reflects the red reflected light beam Lr2 again by the mirror 40, and then collects the condensing lens 41. To enter.

  The condensing lens 41 converges the red reflected light beam Lr2 and gives astigmatism by the cylindrical lens 42, and then irradiates the red photodetector 43 with the red reflected light beam Lr2.

  By the way, in the optical disk apparatus 20, there is a possibility that surface blurring or the like occurs in the rotating optical disk 100, so that the relative position of the target mark position with respect to the guide surface position control optical system 30 may vary.

  For this reason, in order to make the focal point Fr (FIG. 3B) of the red light beam Lr1 follow the target mark position in the guide surface position control optical system 30, the focal point Fr is a focus direction that is in the proximity direction or the separation direction with respect to the optical disc 100. It is necessary to move in the tracking direction which is the direction of the optical disk 100 and the direction of the inner circumference or the outer circumference of the optical disc 100.

  Therefore, the first objective lens 38 can be driven in the biaxial direction of the focus direction and the tracking direction by the first actuator 38A.

  Further, in the guide surface position control optical system 30 (FIG. 7), the focusing lens 41 is in a focused state when the red light beam Lr1 is collected by the first objective lens 38 and applied to the reflection / transmission film 104 of the optical disc 100. Thus, the optical positions of the various optical components are adjusted so that the red reflected light beam Lr2 is condensed and reflected in the focused state when the red photodetector 43 is irradiated.

  As shown in FIG. 8, the red photodetector 43 has four detection areas 43A, 43B, 43C, and 43D that are divided in a lattice pattern on the surface irradiated with the red reflected light beam Lr2. Incidentally, the direction (vertical direction in the figure) indicated by the arrow a1 corresponds to the traveling direction of the track when the red light beam Lr1 is irradiated onto the reflective / transmissive film 104 (FIG. 3).

  The red photodetector 43 detects a part of the red reflected light beam Lr2 by the detection areas 43A, 43B, 43C, and 43D, and generates detection signals SDAr, SDBr, SDCr, and SDDr according to the amount of light detected at this time, respectively. These are sent to the signal processing unit 23 (FIG. 4).

  The signal processing unit 23 performs focus control by a so-called astigmatism method, calculates a red focus error signal SFEr according to the following equation (3), and supplies this to the drive control unit 22.

  The red focus error signal SFEr represents the amount of deviation between the focal point Fr of the red light beam Lr1 and the reflective / transmissive film 104 of the optical disc 100.

  The signal processing unit 23 performs tracking control by a so-called push-pull method. The signal processing unit 23 calculates a red tracking error signal STEr according to the following equation (4) and supplies it to the drive control unit 22.

  The red tracking error signal STEr represents the amount of deviation between the focal point Fr of the red light beam Lr1 and the target mark position on the reflection / transmission film 104 of the optical disc 100.

  The drive control unit 22 generates a focus drive signal SFDr based on the red focus error signal SFEr, and supplies the focus drive signal SFDr to the first actuator 38A, so that the red light beam Lr1 is reflected and transmitted by the reflective / transmissive film 104 of the optical disc 100. The first objective lens 38 is feedback-controlled (that is, focus control) so as to be in focus.

  Further, the drive control unit 22 generates a tracking drive signal STDr based on the red tracking error signal STEr and supplies the tracking drive signal STDr to the first actuator 38A, whereby the red light beam Lr1 is reflected / transmitted by the optical disc 100. The first objective lens 38 is feedback-controlled (that is, tracking control) so as to focus on the target mark position at 104.

  As described above, the guide surface position control optical system 30 irradiates the reflection / transmission film 104 of the optical disc 100 with the red light beam Lr1 and supplies the signal processing unit 23 with the light reception result of the red reflection light beam Lr2 that is the reflection light. Has been made. In response to this, the drive control unit 22 performs focus control and tracking control of the first objective lens 38 so that the red light beam Lr1 is focused on the target mark position of the reflection / transmission film 104.

(1-3-2) Configuration of Guide Surface Blue Optical System The guide surface information optical system 50 is configured to irradiate the guide surface 100A of the optical disc 100 with the first blue light beam Lb1, and also to the optical disc 100. The second blue light beam Lb2 or the blue reproduction light beam Lb3 incident from the first light beam is received.

(1-3-2-1) Irradiation with Blue Light Beam In FIG. 9, the laser diode 51 of the guide surface information optical system 50 is configured to emit blue laser light having a wavelength of about 405 [nm]. In practice, the laser diode 51 emits a blue light beam Lb0 made of divergent light based on the control of the control unit 21 (FIG. 4) and makes it incident on the collimator lens 52. The collimator lens 52 converts the blue light beam Lb0 from diverging light into parallel light and makes it incident on the half-wave plate 53.

  At this time, the blue light beam Lb0 is incident on the surface 55A of the polarization beam splitter 55 after the polarization direction is rotated by a predetermined angle by the half-wave plate 53 and the intensity distribution is shaped by the anamorphic prism 54.

  The polarization beam splitter 55 reflects or transmits the light beam on the reflection / transmission surface 55S at a different rate depending on the polarization direction of the light beam. For example, the reflection / transmission surface 55S reflects a p-polarized light beam at a rate of approximately 50%, transmits the remaining 50%, and transmits an s-polarized light beam at a rate of approximately 100%.

  Actually, the polarization beam splitter 55 reflects the p-polarized blue light beam Lb0 at a rate of about 50% by the reflection / transmission surface 55S, and makes it incident on the quarter-wave plate 56 from the surface 55B, and the remaining 50 % Is transmitted and is incident on the shutter 71 from the surface 55D. Hereinafter, the blue light beam reflected by the reflection / transmission surface 55S is referred to as a first blue light beam Lb1, and the blue light beam transmitted through the reflection / transmission surface 55S is referred to as a second blue light beam Lb2.

  The quarter-wave plate 56 converts the first blue light beam Lb1 from linearly polarized light to circularly polarized light and irradiates the movable mirror 57, and is reflected by the movable mirror 57, and the first blue light beam Lb1 is linearly converted from circularly polarized light. The light is converted into polarized light and again incident on the surface 55B of the polarization beam splitter 55.

  At this time, the first blue light beam Lb1 is converted from p-polarized light to left-circularly polarized light, for example, by the ¼ wavelength plate 56, and is converted from left-circularly polarized light to right-circularly polarized light when reflected by the movable mirror 57. Again, the ¼ wavelength plate 56 converts the right circularly polarized light into s polarized light. That is, the polarization direction of the first blue light beam Lb1 differs between when it is emitted from the surface 55B and when it is incident on the surface 55B after being reflected by the movable mirror 57.

  The polarization beam splitter 55 transmits the first blue light beam Lb1 as it is through the reflection / transmission surface 55S according to the polarization direction (s-polarized light) of the first blue light beam Lb1 incident from the surface 55B, and polarized from the surface 55C. The beam is made incident on the beam splitter 58.

  As a result, the guide surface information optical system 50 extends the optical path length of the first blue light beam Lb1 by the polarizing beam splitter 55, the quarter wavelength plate 56, and the movable mirror 57.

  The reflection / transmission surface 55S of the polarizing beam splitter 58 reflects, for example, a p-polarized light beam at a rate of about 100% and transmits an s-polarized light beam at a rate of about 100%. In practice, the polarization beam splitter 58 transmits the first blue light beam Lb1 as it is through the reflection / transmission surface 58S, and converts the linearly polarized light (s-polarized light) into circularly polarized light (right circularly polarized light) by the quarter wavelength plate 59. The incident light is incident on the relay lens 60.

  The relay lens 60 converts the first blue light beam Lb1 from parallel light into convergent light by the movable lens 61, and converts the first blue light beam Lb1 that has become divergent light after convergence into the converged light again by the fixed lens 62. , And is incident on the dichroic prism 37.

  Here, the movable lens 61 is moved in the optical axis direction of the first blue light beam Lb1 by the actuator 61A. In practice, the relay lens 60 changes the convergence state of the first blue light beam Lb1 emitted from the fixed lens 62 by moving the movable lens 61 by the actuator 61A based on the control of the control unit 21 (FIG. 4). Has been made to get.

  The dichroic prism 37 reflects the first blue light beam Lb1 by the reflection / transmission surface 37S in accordance with the wavelength of the first blue light beam Lb1, and makes it incident on the first objective lens 38. Incidentally, when the first blue light beam Lb1 is reflected by the reflection / transmission surface 37S, the polarization direction of the circularly polarized light is inverted, and is converted from, for example, right circularly polarized light to left circularly polarized light.

  The first objective lens 38 condenses the first blue light beam Lb1 and irradiates the guide surface 100A of the optical disc 100 with it. Incidentally, the first objective lens 38 acts as a condensing lens having a numerical aperture (NA) of 0.5 with respect to the first blue light beam Lb1 due to the optical distance to the relay lens 60 and the like. .

  At this time, the first blue light beam Lb1 passes through the substrate 102 and the reflective / transmissive film 104 and is focused in the recording layer 101 as shown in FIG. 3B. Here, the position of the first focal point Fb1 of the first blue light beam Lb1 is determined by the convergence state when it is emitted from the fixed lens 62 of the relay lens 60. That is, the first focus Fb1 moves to the guide surface 100A side or the recording light irradiation surface 100B side in the recording layer 101 according to the position of the movable lens 61.

  Specifically, the guide surface information optical system 50 is designed so that the moving distance of the movable lens 61 and the moving distance of the first focal point Fb1 of the first blue light beam Lb1 are substantially proportional to each other. Is moved by 1 [mm], the first focal point Fb1 of the first blue light beam Lb1 is moved by 30 [μm].

  In practice, the guide surface information optical system 50 has the first focal point Fb1 of the first blue light beam Lb1 in the recording layer 101 of the optical disc 100 when the position of the movable lens 61 is controlled by the control unit 21 (FIG. 4). The depth d1 (that is, the distance from the reflection / transmission film 104) of (FIG. 3B) is adjusted.

  The first blue light beam Lb1 becomes divergent light after converging to the first focal point Fb1, passes through the recording layer 101 and the substrate 103, is emitted from the recording light irradiation surface 100B, and enters the second objective lens 79 ( Details will be described later).

  Thus, the guide surface information optical system 50 irradiates the first blue light beam Lb1 from the guide surface 100A side of the optical disc 100 to position the first focal point Fb1 of the first blue light beam Lb1 in the recording layer 101, Further, the depth d1 of the first focus Fb1 is adjusted according to the position of the movable lens 61 in the relay lens 60.

(1-3-2-2) Reception of Blue Light Beam By the way, the optical disc 100 transmits the second blue light beam Lb2 irradiated from the second objective lens 79 of the recording light irradiation surface optical system 70 to the recording light irradiation surface 100B. The light is emitted as diverging light from the guide surface 100A (details will be described later). Incidentally, the second blue light beam Lb2 is configured to be circularly polarized light (for example, right circularly polarized light).

  At this time, in the guide surface information optical system 50, as shown in FIG. 10, the second blue light beam Lb2 is converged to some extent by the first objective lens 38, then reflected by the dichroic prism 37, and incident on the relay lens 60. The Incidentally, when the second blue light beam Lb2 is reflected on the reflection / transmission surface 37S, the polarization direction of the circularly polarized light is inverted, and is converted from, for example, right circularly polarized light to left circularly polarized light.

  Subsequently, the second blue light beam Lb2 is converted into parallel light by the fixed lens 62 and the movable lens 61 of the relay lens 60, and further from the circularly polarized light (left circularly polarized light) to the linearly polarized light (p polarized light) by the quarter wavelength plate 59. And then incident on the polarization beam splitter 58.

  The polarization beam splitter 58 reflects the second blue light beam Lb2 according to the polarization direction of the second blue light beam Lb2 and makes it incident on the condensing lens 63. The condensing lens 63 condenses the second blue light beam Lb2 and irradiates the photodetector 64 with it.

  Incidentally, each optical component in the guide surface information optical system 50 is arranged so that the second blue light beam Lb2 is focused on the photodetector 64.

  The photodetector 64 detects the light amount of the second blue light beam Lb2, generates a reproduction detection signal SDp according to the light amount detected at this time, and supplies this to the signal processing unit 23 (FIG. 4).

  However, the reproduction detection signal SDp generated according to the amount of the second blue light beam Lb2 in the photodetector 64 at this time has no particular application. For this reason, the signal processing unit 23 (FIG. 4) is not particularly subjected to signal processing although the reproduction detection signal SDp is supplied.

  On the other hand, when the recording mark RM is recorded on the recording layer 101, the optical disc 100 has a hologram when the first focal point Fb1 of the first blue light beam Lb1 is focused on the recording mark RM as described above. Therefore, the blue reproduction light beam Lb3 is generated from the recording mark RM.

  This blue reproduction light beam Lb3 is a reproduction of the light beam irradiated in addition to the first blue light beam Lb1 when the recording mark RM is recorded, that is, the second blue light beam Lb2 on the principle of hologram. It becomes. Therefore, the blue reproduction light beam Lb3 is finally irradiated onto the photodetector 64 by passing through the same optical path as the second blue light beam Lb2 in the guide surface information optical system 50.

  Here, each optical component in the guide surface information optical system 50 is arranged so that the second blue light beam Lb2 is focused on the photodetector 64 as described above. Therefore, the blue reproduction light beam Lb3 is focused on the photodetector 64 in the same manner as the second blue light beam Lb2.

  The photodetector 64 detects the light amount of the blue light beam Lb3, generates a reproduction detection signal SDp according to the light amount detected at this time, and supplies it to the signal processing unit 23 (FIG. 4).

  In this case, the reproduction detection signal SDp represents information recorded on the optical disc 100. Therefore, the signal processing unit 23 generates reproduction information by performing predetermined demodulation processing, decoding processing, and the like on the reproduction detection signal SDp, and supplies the reproduction information to the control unit 21.

  As described above, the guide surface information optical system 50 receives the second blue light beam Lb2 or the blue reproduction light beam Lb3 incident on the first objective lens 38 from the guide surface 100A of the optical disc 100, and receives the light reception result as a signal processing unit. 23.

(1-3-3) Configuration of Recording Light Irradiation Surface Optical System The recording light irradiation surface optical system 70 (FIG. 6) irradiates the recording light irradiation surface 100B of the optical disc 100 with the second blue light beam Lb2. In addition, the first blue light beam Lb1 irradiated from the guide surface information optical system 50 and transmitted through the optical disc 100 is received.

(1-3-3-1) Irradiation of Blue Light Beam In FIG. 10, as described above, the polarization beam splitter 55 of the guide surface information optical system 50 reduces the blue light beam Lb0 that is p-polarized light on the reflection / transmission surface 55S. The light is transmitted at a rate of 50%, and is incident on the shutter 71 from the surface 55D as the second blue light beam Lb2.

  The shutter 71 is configured to block or transmit the second blue light beam Lb2 based on the control of the control unit 21 (FIG. 4). When the shutter 71 transmits the second blue light beam Lb2, the shutter 71 passes to the polarization beam splitter 72. Make it incident.

  Incidentally, as the shutter 71, for example, a mechanical shutter that blocks or transmits the blue light beam Lb2 by mechanically moving a blocking plate that blocks the blue light beam Lb2, or a blue shutter that changes the voltage applied to the liquid crystal panel. A liquid crystal shutter or the like that blocks or transmits the light beam Lb2 can be used.

  The reflection / transmission surface 72S of the polarization beam splitter 72 transmits, for example, a p-polarized light beam at a rate of about 100% and reflects an s-polarized light beam at a rate of about 100%. In practice, the polarization beam splitter 72 transmits the p-polarized second blue light beam Lb2 as it is, reflects it by the mirror 73, and then converts it from linearly polarized light (p-polarized light) to circularly polarized light (left-handed) by the quarter wavelength plate 74. After being converted into circularly polarized light, the light is incident on the relay lens 75.

  The relay lens 75 is configured in the same manner as the relay lens 60, and includes a movable lens 76, an actuator 76A, and a fixed lens 77 corresponding to the movable lens 61, the actuator 61A, and the fixed lens 62, respectively.

  The relay lens 75 converts the second blue light beam Lb2 from parallel light into convergent light by the movable lens 76, and converts the second blue light beam Lb2 that has become divergent light after convergence into the converged light again by the fixed lens 77. Then, the light is incident on a mirror 78 (for example, a galvano mirror, hereinafter referred to as a variable angle mirror) that can change the angle.

  Similarly to the relay lens 60, the relay lens 75 moves the movable lens 76 by the actuator 76A based on the control of the control unit 21 (FIG. 4), thereby converging the second blue light beam Lb2 emitted from the fixed lens 77. The state can be changed.

  The variable angle mirror 78 reflects the second blue light beam Lb 2 and makes it incident on the second objective lens 79. Incidentally, when the second blue light beam Lb2 is reflected, the polarization direction of the circularly polarized light is reversed, and is converted from, for example, left circularly polarized light to right circularly polarized light.

  The angle variable mirror 78 can change the angle of the reflecting surface 78A, and the angle of the reflecting surface 78A is adjusted according to the control of the control unit 21 (FIG. 4), so that the second blue light beam Lb2 is adjusted. The traveling direction can be adjusted to a tangential direction which is a direction rotating around the tracking direction of the optical disc 100.

  The second objective lens 79 is configured integrally with the second actuator 79A, and, like the first objective lens 38, the second actuator 79A allows the focus direction, which is the approaching direction or the separation direction to the optical disc 100, and the optical disc. 100 can be driven in a biaxial direction with a tracking direction which is an inner peripheral side direction or an outer peripheral side direction.

  The second objective lens 79 condenses the second blue light beam Lb2 and irradiates the recording light irradiation surface 100B of the optical disc 100. This objective lens has optical characteristics similar to those of the first objective lens 38, and the numerical aperture (NA) of the second blue light beam Lb2 depends on the optical distance to the relay lens 75 and the like. It will act as a 0.5 condenser lens.

  At this time, the second blue light beam Lb2 is transmitted through the substrate 103 and focused into the recording layer 101 as shown in FIG. Here, the position of the second focal point Fb2 of the second blue light beam Lb2 is determined by the convergence state when the relay lens 75 is emitted from the fixed lens 77. That is, the second focal point Fb2 moves to the guide surface 100A side or the recording light irradiation surface 100B side in the recording layer 101 according to the position of the movable lens 76, similarly to the first focal point Fb1 of the first blue light beam Lb1. become.

  Specifically, in the recording light irradiation surface optical system 70, like the guide surface information optical system 50, the moving distance of the movable lens 76 and the moving distance of the second focal point Fb2 of the second blue light beam Lb2 are approximately proportional. For example, when the movable lens 76 is moved by 1 [mm], the second focal point Fb2 of the second blue light beam Lb2 is moved by 30 [μm].

  In practice, the recording light irradiation surface optical system 70 controls the recording of the optical disk 100 by controlling the position of the movable lens 61 in the relay lens 75 together with the position of the movable lens 61 in the relay lens 60 by the control unit 21 (FIG. 4). The depth d2 of the second focal point Fb2 (FIG. 3B) of the second blue light beam Lb2 in the layer 101 is adjusted.

  At this time, in the optical disc apparatus 20, the first objective lens in the recording layer 101 when it is assumed by the control unit 21 (FIG. 4) that no surface blur or the like has occurred in the optical disc 100 (that is, in an ideal state). The second focal point Fb2 of the second blue light beam Lb2 when the second objective lens 79 is at the reference position is aligned with the first focal point Fb1 of the first blue light beam Lb1 when the lens 38 is at the reference position. Has been made.

  The second blue light beam Lb2 is focused at the second focal point Fb2, and then passes through the recording layer 101, the reflective / transmissive film 104, and the substrate 102 while diverging, and is emitted from the guide surface 100A to the first objective lens 38. It is designed to be incident.

  In this way, the recording light irradiation surface optical system 70 irradiates the second blue light beam Lb2 from the recording light irradiation surface 100B side of the optical disc 100, and sets the second focal point Fb2 of the second blue light beam Lb2 in the recording layer 101. The depth d2 of the second focal point Fb2 is adjusted according to the position of the movable lens 76 in the relay lens 75.

(1-3-3-2) Reception of Blue Light Beam By the way, as described above, the first blue light beam Lb1 irradiated from the first objective lens 38 of the guide surface information optical system 50 (FIG. 9) is an optical disc. After once converging in the 100 recording layers 101, it becomes divergent light and enters the second objective lens 79.

  At this time, in the recording light irradiation surface optical system 70, the first blue light beam Lb 1 is converged to some extent by the second objective lens 79, then reflected by the angle variable mirror 78 and incident on the relay lens 75. Incidentally, when the first blue light beam Lb1 is reflected by the reflecting surface 78S, the polarization direction of the circularly polarized light is inverted, and is converted from, for example, left circularly polarized light to right circularly polarized light.

  Subsequently, the first blue light beam Lb1 is converted into parallel light by the fixed lens 62 and the movable lens 61 of the relay lens 75, and further from the circularly polarized light (right circularly polarized light) to the linearly polarized light (s polarized light) by the quarter wavelength plate 74. Then, the light is reflected by the mirror 73 and then incident on the polarization beam splitter 72.

  The polarization beam splitter 72 reflects the first blue light beam Lb1 according to the polarization direction of the first blue light beam Lb1 and makes it incident on the condenser lens 80. The condensing lens 80 converges the first blue light beam Lb1 and gives astigmatism by the cylindrical lens 81, and then irradiates the blue photodetector 82 with the first blue light beam Lb1.

  The blue photodetector 82 generates a detection signal according to the amount of light of the received first blue light beam Lb1, and supplies the detection signal to the drive control unit 22 via the signal processing unit 23. The drive control unit 22 executes servo control in the recording light irradiation surface optical system based on this detection signal. The servo control in this recording light irradiation surface optical system will be described later.

(1-3-4) Adjustment of Optical Path Length By the way, as described above, the optical pickup 26 of the optical disc apparatus 20 records the first blue color from the blue light beam Lb0 by the polarization beam splitter 55 (FIG. 9) as described above. By separating the light beam Lb1 and the second light blue beam Lb2 and causing the first blue light beam Lb1 and the second light blue beam Lb2 to interfere with each other in the recording layer 101 of the optical disc 100, a target in the recording layer 101 is obtained. A recording mark RM is recorded at the mark position.

  The laser diode 51 that emits the blue light beam Lb0 has a recording mark RM as a hologram correctly recorded on the recording layer 101 of the optical disc 100 in accordance with general hologram forming conditions. The length needs to be equal to or larger than the hologram size (that is, the height RMh of the recording mark RM).

  In practice, in the laser diode 51, like a general laser diode, the coherent length is a value obtained by multiplying the length of a resonator (not shown) provided in the laser diode 51 by the refractive index of the resonator. Therefore, it is considered to be approximately 100 [μm] to 1 [mm].

  On the other hand, in the optical pickup 26, the first blue light beam Lb1 passes through the optical path in the guide surface information optical system 50 (FIG. 9), is irradiated from the guide surface 100A side of the optical disc 100, and the second blue light beam Lb2 is emitted. The light is irradiated from the recording light irradiation surface 100B side of the optical disc 100 through the optical path in the recording light irradiation surface optical system 70 (FIG. 10). That is, in the optical pickup 26, since the optical paths of the first blue light beam Lb1 and the second blue light beam Lb2 are different from each other, there is a difference in the optical path length (that is, the length of the optical path from the laser diode 51 to the target mark position). Will occur.

  Further, in the optical pickup 26, as described above, the depth of the target mark position (target depth) in the recording layer 101 of the optical disc 100 is adjusted by adjusting the positions of the movable lenses 61 and 76 in the relay lenses 60 and 75. It has been made to change. At this time, the optical pickup 26 changes the optical path lengths of the first blue light beam Lb1 and the second blue light beam Lb2 by changing the depth of the target mark position.

  However, in order to form an interference pattern in the optical pickup 26, the difference in the optical path length between the first blue light beam Lb1 and the second light blue beam Lb2 depends on the general hologram formation conditions. [Μm] to 1 [mm]) or less.

  Therefore, the control unit 21 (FIG. 4) adjusts the optical path length of the first blue light beam Lb1 by controlling the position of the movable mirror 57. In this case, the control unit 21 uses the relationship between the position of the movable lens 61 in the relay lens 60 and the depth of the target mark position, and moves the movable mirror 57 according to the position of the movable lens 61, thereby The optical path length of one blue light beam Lb1 is changed.

  As a result, in the optical pickup 26, the difference in optical path length between the first blue light beam Lb1 and the second light blue beam Lb2 can be suppressed to a coherent length or less, and a good hologram is formed at the target mark position in the recording layer 101. The recording mark RM can be recorded.

  As described above, the control unit 21 of the optical disc device 20 controls the position of the movable mirror 57, thereby reducing the difference in optical path length between the first blue light beam Lb1 and the second light blue beam Lb2 in the optical pickup 26 to be equal to or less than the coherent length. As a result, a good recording mark RM can be recorded at the target mark position in the recording layer 101 of the optical disc 100.

(1-4) Recording and Reproducing Information (1-4-1) Recording Information on Optical Disc When recording information on the optical disc 100, the control unit 21 (FIG. 4) of the optical disc apparatus 20 is externally connected as described above. When an information recording command, recording information, and recording address information are received from a device (not shown) or the like, a movement amount signal based on the driving command and recording address information is supplied to the drive control unit 22 and the recording information is transmitted to the signal processing unit 23. To supply.

  At this time, the drive controller 22 causes the guide surface position control optical system 30 (FIG. 7) of the optical pickup 26 to irradiate the red light beam Lr1 from the guide surface 100A side of the optical disc 100, and the reflected red light beam Lr2 as the reflected light. Based on the detection result, the focus control and tracking control (that is, position control) of the first objective lens 38 are performed, so that the focus Fr of the red light beam Lr1 follows the target mark position corresponding to the recording address information.

  Further, the control unit 21 causes the guide surface information optical system 50 (FIG. 9) to irradiate the first blue light beam Lb1 from the guide surface 100A side of the optical disc 100. At this time, the first focal point Fb1 of the first blue light beam Lb1 is condensed by the position-controlled first objective lens 38, thereby being positioned behind the target mark position.

  Furthermore, the control unit 21 adjusts the depth d1 of the first focal point Fb1 (FIG. 3B) to the target depth by adjusting the position of the movable lens 61 in the relay lens 60. As a result, the first focal point Fb1 of the first blue light beam Lb1 is adjusted to the target mark position.

On the other hand, the control unit 21 controls the shutter 71 of the recording light irradiation surface optical system 70 (FIG. 10) to transmit the second blue light beam Lb2, and the second blue light beam Lb2 is transmitted to the recording light irradiation surface of the optical disc 100. Irradiate from the 100B side.

  Further, the control unit 21 adjusts the position of the movable lens 76 in the relay lens 75 in accordance with the position of the movable lens 61 in the relay lens 60, whereby the depth d2 of the second blue light beam Lb2 (FIG. 3B). Adjust. As a result, the second blue light beam Lb2 has the depth d2 of the second focal point Fb2 set to the depth d1 of the first focal point Fb1 in the first blue light beam Lb1 when it is assumed that surface blurring has not occurred in the optical disc 100. Combined.

  Furthermore, the control unit 21 causes the drive control unit 22 to perform focus control and tracking control of the second objective lens 79 and tangential control (that is, position control) of the angle variable mirror 78 by a servo control process in a recording light irradiation surface optical system described later. ).

  As a result, the second focal point Fb2 of the second blue light beam Lb2 is aligned with the position of the first focal point Fb1 in the first blue light beam Lb1, that is, the target mark position.

  In addition, the control unit 21 adjusts the position of the movable mirror 57 in accordance with the position of the movable lens 61 in the relay lens 60, so that the optical path length difference between the first blue light beam Lb1 and the second light blue beam Lb2 is less than or equal to the coherent length. suppress.

  Thus, the control unit 21 of the optical disc apparatus 20 can form a good recording mark RM at the target mark position in the recording layer 101 of the optical disc 100.

  By the way, the signal processing unit 23 (FIG. 4) generates a recording signal representing binary data having a value “0” or “1” based on recording information supplied from an external device (not shown) or the like. In response to this, the laser diode 51 emits the blue light beam Lb0 when the recording signal has the value “1”, for example, and does not emit the blue light beam Lb0 when the recording signal has the value “0”. .

  As a result, the optical disc apparatus 20 forms the recording mark RM at the target mark position in the recording layer 101 of the optical disc 100 when the recording signal has the value “1”, and at the target mark position when the recording signal has the value “0”. Since the recording mark RM is not formed, the value “1” or “0” of the recording signal can be recorded at the target mark position depending on the presence or absence of the recording mark RM. The recording layer 101 can be recorded.

(1-4-2) Reproduction of Information from Optical Disc When reproducing information from the optical disc 100, the control unit 21 (FIG. 4) of the optical disc apparatus 20 guides the guide surface position control optical system 30 of the optical pickup 26 (FIG. 7). Irradiates the red light beam Lr1 from the guide surface 100A side of the optical disc 100, and based on the detection result of the red reflected light beam Lr2 that is the reflected light, the drive control unit 22 performs focus control and tracking control of the first objective lens 38. (That is, position control) is performed.

  Further, the control unit 21 causes the guide surface information optical system 50 (FIG. 9) to irradiate the first blue light beam Lb1 from the guide surface 100A side of the optical disc 100. At this time, the first focal point Fb1 of the first blue light beam Lb1 is condensed by the position-controlled first objective lens 38, thereby being positioned behind the target mark position.

  Incidentally, the control unit 21 is configured to prevent erroneous erasure of the recording mark RM by the first blue light beam Lb1 by suppressing the emission power of the laser diode 51 during reproduction.

  Furthermore, the control unit 21 adjusts the depth d1 of the first focal point Fb1 (FIG. 3B) to the target depth by adjusting the position of the movable lens 61 in the relay lens 60. As a result, the first focal point Fb1 of the first blue light beam Lb1 is adjusted to the target mark position.

  On the other hand, the control unit 21 controls the shutter 71 of the recording light irradiation surface optical system 70 (FIG. 10) and blocks the second blue light beam Lb2, thereby irradiating the optical disk 100 with the second blue light beam Lb2. I won't let you.

  That is, the optical pickup 26 irradiates the recording mark RM recorded at the target mark position in the recording layer 101 of the optical disc 100 only with the first blue light beam Lb1 as so-called reference light. In response to this, the recording mark RM acts as a hologram, and generates a blue reproduction light beam Lb3 as so-called reproduction light toward the guide surface 101A. At this time, the guide surface information optical system 50 detects the blue reproduction light beam Lb3 and generates a detection signal corresponding to the detection result.

  Thus, the control unit 21 of the optical disc apparatus 20 generates the blue reproduction light beam Lb3 from the recording mark RM recorded at the target mark position in the recording layer 101 of the optical disc 100, and receives the blue reproduction light beam Lb3. It is possible to detect that it is recorded.

  Here, when the recording mark RM is not recorded at the target mark position, the optical disk device 20 does not generate the blue reproduction light beam Lb3 from the target mark position. A detection signal indicating that the beam Lb3 has not been received is generated.

  In response to this, the signal processing unit 22 recognizes whether the blue reproduction light beam Lb3 is detected based on the detection signal as a value “1” or “0”, and generates reproduction information based on the recognition result. To do.

  Thereby, in the optical disc apparatus 20, when the recording mark RM is formed at the target mark position in the recording layer 101 of the optical disc 100, the blue reproduction light beam Lb3 is received, and the recording mark RM is formed at the target mark position. By not receiving the blue reproduction light beam Lb3 when there is not, it is possible to recognize whether the value “1” or “0” is recorded at the target mark position, and as a result, recording is performed on the recording layer 101 of the optical disc 100. Information can be reproduced.

(1-5) Servo Control in Recording Light Irradiation Surface Optical System (1-5-1) Principle Next, servo control executed during the recording process described above based on the detection signal generated by the blue photodetector 82 The principle of processing will be described.

  In the optical pickup 26, in order to form a standing wave, it is necessary to match the second focal point Fb2 of the second blue light beam Lb2 with the first focal point Fb1 of the first blue light beam Lb1. Therefore, in the recording light irradiation surface optical system 70, as servo control processing, focus control and tracking control for driving the second objective lens 79 and tangential control for driving the angle variable mirror 78 are executed.

  On the other hand, the guide surface position control optical system 30 drives the first objective lens 38 based on the red focus error signal SFEr and the red tracking error signal STEr as described above. These red focus error signal SFEr and red tracking error signal STEr represent the amount of deviation of the red light beam Lr1 from the target track position in the reflective / transmissive film 104.

However, since the first blue beam Lb1 is irradiated through the same first objective lens 38 as the red light beam Lr1, the optical axis of the first blue beam Lb1 is in the tracking direction with the optical axis of the red light beam Lr1. Therefore, the red tracking error signal STEr represents the amount of shift in the tracking direction with respect to the target mark position of the first focus Fb1.

  Further, the drive control unit 22 sets the depth d1 from the reflection / transmission film 104 as a target mark position with respect to the first focus Fb1, and relays the first focus Fb1 by the depth d1 from the focus position of the red light beam Lr1. The lens 60 controls. Therefore, the amount of deviation of the red light beam Lr1 from the reflection / transmission film 104 represents the amount of deviation of the first focus Fb1 up to the depth d1, and represents the defocus of the red light beam Lr1 with respect to the reflection / transmission film 104. The red focus error signal SFEr represents the shift amount of the first focus Fb1 with respect to the target mark position as it is.

  Therefore, the drive control unit 22 drives the first objective lens 38 in the focus direction and the tracking direction based on the red focus error signal SFEr and the red tracking error signal STEr, thereby causing the first blue light beam to reach the target mark position on the optical disc 100. Lb1 can be irradiated.

  Here, since the optical disc 100 has eccentricity, bending, and the like, and the position of the target mark position changes sequentially, the target of the first focus Fb1 is not changed unless the first focus Fb1 is moved following the target mark position. A deviation from the mark position (hereinafter referred to as a mark position deviation) occurs. Further, the mark position shift also occurs depending on vibration or the like when the optical disc 100 is rotated at high speed.

  As shown in FIG. 11, since the mark position deviation due to the eccentricity or bending of the optical disk 100 occurs in one cycle for one rotation of the optical disk 100, the red focus error signal SFEr and the red tracking error signal STEr include A low-frequency component having a large amplitude corresponding to one cycle is generated for one rotation of the optical disc 100. In FIG. 11, the red focus error signal SFEr and the red tracking error signal STEr acquired when the first objective lens 38 is stopped are shown.

  On the other hand, the mark position shift caused by the vibration of the optical disc 100 is generated at a high speed according to the vibration accompanying the high-speed rotation. Therefore, a high-frequency component having a small amplitude is generated in the red focus error signal SFEr and the red tracking error signal STEr. .

  Accordingly, the drive control unit 22 performs the feedback process using the red focus error signal SFEr and the red tracking error signal STEr, which is a combination of the low frequency component and the high frequency component, so as to eliminate the mark position deviation. Drive.

  Here, the optical disc apparatus 20 uses the detection signal generated from the blue photodetector 82 (FIG. 9) of the recording light irradiation surface optical system 70 to cause the signal processing unit 23 to perform the second focus on the first focus Fb1 in the recording layer 101. The amount of Fb2 deviation (hereinafter referred to as focal position deviation) can be calculated as a blue focus error signal SFEb and a blue tracking error signal STEb (details will be described later).

  Therefore, as in the virtual optical disc apparatus 20R shown in FIG. 12, the servo system of the first objective lens 38 and the servo system of the second objective lens 79 are formed independently, and the blue focus error signal SFEb and the blue objective error signal SFEb When feedback processing is executed using the tracking error signal SFEb, the second focus Fb2 can follow the first focus Fb1 by driving the second objective lens 79 so as to eliminate this focal position shift. It is theoretically possible to make the second focus Fb2 coincide with the first focus Fb1.

However, due to the characteristics of servo control, the optical disc apparatus 20 causes the second focus Fb2 to move faster than the first focus Fb1 so that the second focus Fb2 follows the first focus Fb1 by feedback processing. It becomes necessary to drive the lens 79. That is, in the optical disc apparatus 20, the high-speed response in the servo system of the second objective lens 79 must be set much higher than the high-speed response in the servo system of the first objective lens 38.

  Here, the optical disc apparatus 20 rotates the optical disc 100 at a very high speed. The optical disc apparatus 20 has a first focus when the optical disc 100 is rotated at a rotational speed exceeding 5000 [rpm], for example, as in a current DVD (Digital Versatile Disc) -ROM (Read Only Memory) drive. In order to eliminate the mark position shift of Fb1, the feedback processing using the red focus error signal SFEr and the red tracking error signal STEr is already driven in a state close to the limit of the servo system performance of the first objective lens 38. Yes. For this reason, it is technically difficult to provide the servo system of the second objective lens 79 with higher high-speed response.

Accordingly, when the high-speed response of the servo system of the first objective lens 38 and the high-speed response of the servo system of the second objective lens 79 are set to be equal, the optical disc device 20R oscillates the servo system of the second objective lens 79. As a result, the servo processing is forced to stop, and errors such as so-called servo jumps occur frequently.

  Also, setting the rotation speed of the optical disc 100 to be low is not preferable because it means that the recording and reproduction speed of information is reduced.

  Here, since the first objective lens 38 (FIG. 9) and the second objective lens 79 have substantially the same configuration and have symmetry, as shown in FIG. 13, the optical disc 100 has a skew or the like. If not, the focal point FB2 can be made to coincide with the first focal point Fb1 by driving the second objective lens 79 in the same direction as the first objective lens 38 and by the same amount of movement.

  Incidentally, in the optical disc apparatus 20, since not only the first objective lens 38 and the second objective lens 79 but also the first actuator 38A and the second actuator 79A have the same configuration, the same drive control signal is supplied. Thus, the first objective lens 38 and the second objective lens 79 can be driven in the same manner, and the second objective lens 79 can be driven in the same manner as the first objective lens 38 without performing complicated calculations. .

  Therefore, in the optical disk device 20 of the present embodiment, the second objective lens 79 is driven in the same manner as the first objective lens 38 by using the feedback signal of the first objective lens 38 as a feedforward signal for the second objective lens 79. I will let you.

  As a result, the second focus Fb2 can be moved to match the second focus Fb2 and the first focus Fb1 in accordance with the movement of the first focus Fb1, and the second objective lens 79 can be obtained. The high-speed response of the servo system can be set to the same high-speed response as the servo system of the first objective lens 38.

  By the way, in the optical disk apparatus 20, the second blue light beam irradiated from the recording light irradiation surface side that is the back surface thereof with respect to the first focal point Fb1 by the first blue light beam Lb1 irradiated from the guide surface side of the optical disk 100. Since it is necessary to match the second focus Fb2 by Lb2, there is a factor that the second focus Fb2 shifts from the first focus Fb1 in addition to the mark position shift described above.

  That is, when a skew occurs due to the deflection of the optical disc 100, the first blue light beam Lb1 and the second blue color with respect to the surface of the optical disc 100 due to refraction when entering the optical disc 100, as shown in FIG. The optical axes of the light beam Lb2 are inclined in opposite directions.

  Therefore, the optical disc apparatus 20 simply drives the second objective lens 79 in the same manner as the first objective lens 38 so as to align the first focus Fb1 with the target mark position, and the second focus Fb2 relative to the position of the first focus Fb1. The positions cannot be matched and a focal position shift occurs.

  The same applies to the case where the optical disc 100 has a non-uniform film thickness and the thickness from the reflection / transmission film 104 to the recording light irradiation surface 100B changes. For example, as shown in FIG. When the thickness is larger than 0.6 mm, the optical path length of the second blue light beam Lb2 in the optical disc 100 changes according to the distance from the position of the first focal point Fb1 to the surface of the recording light irradiation surface 100B of the optical disc 100. Therefore, a focus position shift occurs.

  Note that these focal position shifts caused by skew and film thickness unevenness are all caused by refraction in the optical disk 100 and are smaller than mark position deviations caused by bending of the optical disk 100 or the like. .

Therefore, in the optical disc apparatus 20 of the present embodiment, not only the second objective lens 79 is driven in the same manner as the first objective lens 38 by the feedforward process, but also the second objective lens 79 is driven by the feedback process and remains slightly. By eliminating the focus position shift, the second focus Fb2 is made to coincide with the first focus Fb1 with high accuracy.

(1-5-2) Specific Processing Content of Servo Control Processing Next, specific processing content of the servo control processing in the recording light irradiation surface optical system 70 will be described.

  As shown in FIG. 16, in the optical disc apparatus 20 according to the present embodiment, a red photodetector 43 is provided as a servo system for the first objective lens 38 via a signal processing unit 23 and amplifiers APf1 and APt1 as drive control units 22. It is connected to the first actuator 38A.

  Further, the second objective lens 79 has a feedback system and a feedforward system as a servo system. As a feedback system, a blue photodetector 82 passes through the signal processing unit 23 and amplifiers APf2 and APt2 as the drive control unit 22. As a feedforward system for the second objective lens 79, amplifiers APf3 and APt3 as the drive control unit 22 are connected between the red photodetector 43 and the second actuator 79A. .

  In FIG. 16, in the optical disc apparatus 20, the first objective lens 38, the first actuator 38A, the red photodetector 43, the second objective lens 79, the second actuator 79A, the blue photodetector 82, the cylindrical lens 80, and the amplifier APf1. , APt1, APf2, APt2, APf3 and APt3, only the polarization beam splitters 58 and 72, and the signal processing unit 23 are shown, and other optical components are omitted for convenience. Similarly, in the following drawings, only the optical components necessary for the description of the optical disc apparatus 20 are shown, and other optical components are omitted for convenience.

  The signal processing unit 23 uses the detection signals SDAr, SDBr, SDCr, and SDDr supplied from the red photodetector 43 as described above, and the red focus error signal SFEr and the red tracking error signal according to the equations (3) and (4). STEr is generated and supplied to the amplifiers APf1 and APt1 and the amplifiers APf3 and APt3.

  The amplifiers APf1 and APt1 amplify the red focus error signal SFEr and the red tracking error signal STEr as feedback processing to generate drive control signals SFDr and STDr, and supply them to the first actuator 38A, thereby supplying the first objective lens. 38 is driven in the focus direction and the tracking direction.

  On the other hand, the amplifiers APf3 and APt3 amplify the red focus error signal SFEr and the red tracking error signal STEr respectively with a predetermined gain as feedforward processing, and generate amplified signals SFG and STG.

  Further, the optical disc apparatus 20 generates a blue focus error signal SFEb and a blue tracking error signal STEb that indicate the amount of focus position shift according to the amount of light received by the blue photodetector 82 of the first blue light beam Lb1, and this focus position shift is detected. Execute the feedback process to cancel.

  That is, as shown in FIG. 17, the blue photodetector 82 has four detection areas 82A, 82B, and 82C that are divided in a lattice pattern on the surface irradiated with the first blue light beam Lb1, as with the red photodetector 43. And 82D. Incidentally, the direction indicated by the arrow a2 (the horizontal direction in the figure) corresponds to the track traveling direction in the reflective / transmissive film 104 (FIG. 3) when the first blue light beam Lb1 is irradiated.

  Here, as shown in FIG. 16, the blue light detector 82 is irradiated from the guide surface side of the optical disc 100 via the first objective lens 38 and the first blue light that has passed through the optical disc 100 and the second objective lens 79. The beam Lb1 is received.

  As shown in FIG. 18A, when the first focal point Fb1 and the second focal point Fb2 coincide with each other, as shown in FIG. 18B, the optical axis of the first blue light beam Lb1 and the second blue color are obtained. Since the optical axis of the light beam Lb2 completely coincides, a spot Q on a substantially perfect circle is formed at the center of the blue photodetector 82.

  On the other hand, as shown in FIG. 19A, when the first focal point Fb1 and the second focal point Fb2 do not match and there is a deviation in the focus direction (X-axis direction), as shown in FIG. In addition, since the distance from the first focal point Fb1 of the first blue beam Lb1 to the blue photodetector 82 (FIG. 9) is shifted and aberration occurs in the cylindrical lens 80 by the astigmatism method, the blue photodetector 82 has an elliptical shape. A spot Q is formed.

  Therefore, the optical disk device 20 can match the second focal point Fb with the first focal point Fb1 with high accuracy by driving the second objective lens 79 so that the spot Q is almost a perfect circle.

  On the other hand, as shown in FIG. 20A, when the first focal point Fb1 and the second focal point Fb2 do not coincide with each other and a deviation occurs in the tracking direction (Y-axis direction), as shown in FIG. Since the optical axis of the first blue light beam Lb1 and the optical axis of the second blue light beam Lb2 are deviated, the spot Q on a substantially perfect circle is formed in the blue photodetector 82 in a state deviated in the a2 direction.

  Therefore, the optical disk device 20 can match the second focus Fb with the first focus Fb1 with high accuracy by driving the second objective lens 79 so that the spot Q is substantially at the center of the blue photodetector 82.

  In FIG. 21, the optical pickup 26 is shown as an XZ plane in a state where portions other than the portion surrounded by a broken line are rotated by 90 ° from FIGS. As shown in FIG. 21A, when the first focal point Fb1 and the second focal point Fb2 do not coincide with each other and a deviation occurs in the tangential direction (Z-axis direction), as shown in FIG. Since the optical axis of the first blue light beam Lb1 and the optical axis of the second blue light beam Lb2 are deviated, the spot Q on a substantially perfect circle is formed in the blue photodetector 82 in a state deviated in a direction perpendicular to the a2 direction. Is done.

  Therefore, the optical disk device 20 can match the second focal point Fb to the first focal point Fb1 with high accuracy by driving the variable angle mirror 78 so that the spot Q is approximately at the center of the blue photodetector 82.

  As described above, in the optical disc apparatus 20, if the second focal point Fb2 is moved in three directions of the X-axis direction (focus direction), the Y-axis direction (tracking direction), and the Z-axis direction (tangential direction) by feedback processing, The second focus Fb2 can be matched with the first focus Fb1 with high accuracy.

  In practice, the blue photodetector 82 detects a part of the first blue light beam Lb1 by the detection regions 82A, 82B, 82C and 82D, respectively, and detects the detection signals SDAb, SDBb, SDCb and SDDb according to the detected light quantity. Are generated and sent to the signal processing unit 23 (FIG. 4).

  The signal processing unit 23 performs focus control by a so-called astigmatism method. The signal processing unit 23 calculates a blue focus error signal SFEb according to the following equation (5), and supplies the blue focus error signal SFEb to the amplifier APf2 as the drive control unit 22. Supply.

  This blue focus error signal SFEb represents the amount of shift in the focus direction between the first focal point Fb1 of the first blue light beam Lb1 and the second focal point Fb2 of the second blue light beam Lb2.

  The signal processing unit 23 performs tracking control using a push-pull signal. The signal processing unit 23 calculates a blue tracking error signal STEb according to the following equation (6), and this is used as an amplifier APt2 as the drive control unit 22. To supply.

  This blue tracking error signal STEb represents the amount of shift in the tracking direction between the first focal point Fb1 of the first blue light beam Lb1 and the second focal point Fb2 of the second blue light beam Lb2.

  As described above, the low-frequency component having a large amplitude is mainly caused by the mark position shift, and the focus position shift due to the mark position shift can be eliminated in advance by the feedforward process. In the SFEb and the blue tracking error signal STEb, a focal position shift due to skew and film thickness unevenness mainly appears. Although these focal position deviations may appear as low frequency components, they are based on minute changes in the optical axis or optical path length in the optical disc 100, and their amplitude is minute compared to the mark position deviation.

  Therefore, as shown in FIG. 22, the blue focus error signal SFEb and the blue tracking error signal STEb have almost no large amplitude of low frequency components, unlike the above-described red focus error signal SFEr and red tracking error signal STEr. become. Note that FIG. 22 shows the blue focus error signal SFEb and the blue tracking error signal STEb that are acquired in a state where the second objective lens 79 is stopped.

  Accordingly, since the drive control unit 22 can set the gains of the amplifiers APf2 and APt2 in accordance with the high frequency component, it is possible to prevent the feedback system from oscillating and to follow the second focus Fb2 with respect to the first focus Fb1. Can be improved.

  Furthermore, the signal processing unit 23 also generates a tangential error signal necessary for tangential control. The signal processing unit 23 performs tangential control using a push-pull signal. The signal processing unit 23 calculates a blue tangential error signal SNEb according to the following equation (7), and uses the blue tangential error signal SNEb as an amplifier as the drive control unit 22. Supply to APn.

  The blue tangential error signal SNEb represents the amount of deviation in the tangential direction between the first focal point Fb1 of the first blue light beam Lb1 and the second focal point Fb2 of the second blue light beam Lb2.

  The drive control unit 22 amplifies the blue focus error signal SFEb with a predetermined gain by the amplifier APf2 and superimposes the blue focus error signal SFEb on the amplification signal SFG supplied from the amplifier APf3, thereby generating the focus drive control signal SFDb. By supplying this to the second actuator 79, the second objective lens 79 is driven in the focus direction, and the second focus Fb2 is moved in the focus direction.

  As a result, as shown in FIG. 23, the drive control unit 22 feeds the second objective lens in the same direction as the first objective lens 38 by feedforward processing in accordance with driving the first objective lens 38 in the focus direction. While driving 79, the second objective lens 79 can be driven so as to eliminate the focal position shift in the focus direction by feedback processing.

  In addition, the drive control unit 22 amplifies the blue tracking error signal STEb with a predetermined gain by the amplifier APt2, and superimposes the blue tracking error signal STEb on the amplification signal STG supplied from the amplifier APt3 to thereby generate the second focus drive control signal STDb. Then, the second objective lens 79 is driven in the tracking direction and the second focal point Fb2 is moved in the tracking direction.

  As a result, as shown in FIG. 24, when the first objective lens 38 is driven in the tracking direction, the drive control unit 22 drives the second objective lens 79 in the same direction as the first objective lens 38. The second objective lens 79 can be driven so as to correct the focal position deviation in the tracking direction.

  As described above, the optical disc device 20 performs the second drive by superimposing the blue focus error signal SFEb on the red focus error signal SFEr for accurately irradiating the first focus Fb1 to the target mark position as the servo control process. By generating the control signal SFDb, the second objective lens 79 is moved in the same direction as the first objective lens 38 by feedforward processing, and the remaining minute focal position deviation is eliminated by feedback processing. As a result, the amount of movement of the second objective lens 79 as feedback processing can be reduced, and the second focus Fb2 can be matched with the first focus Fb1 with high accuracy without greatly improving the performance of the second actuator 79A. be able to.

  Further, the drive control unit 22 amplifies the blue tangential error signal SNE to generate a tangential drive control signal SNDb, and supplies the generated tangential drive control signal SNDb to the angle variable mirror 78, thereby driving the angle variable mirror 78 and the second focus. Fb2 is moved in the tangential direction.

  As a result, the drive control unit 22 can drive the variable angle mirror 78 so as to correct the focal position shift in the tangential direction.

  In this way, the optical disk apparatus 20 drives the second objective lens 79 and the angle variable mirror 78 to move the second focal point Fb2 in three directions of the focus direction, the tracking direction, and the tangential direction. Fb2 can be matched with the first focus Fb1.

(1-6) Operation and Effect In the above configuration, the optical disc apparatus 20 moves from the first focus Fb1 that is the focus position of the first blue light beam Lb1 as the first light to the target mark position that is the recording mark position. The first objective lens 38 is controlled so as to move the first focal point Fb1 to the target mark position by driving the first objective lens 38 based on the red focus error signal SFEr which is a mark position deviation signal representing the deviation amount. Then, the blue focus error signal SFEb and the red focus error signal SFEr, which are focus position shift signals indicating the shift amount of the second focus Fb2, which is the focus position of the second blue light beam Lb2 as the second light, with respect to the first focus Fb1. By driving the second objective lens 79 so that the second focal point Fb2 coincides with the first focal point Fb1. The second objective lens 79 was controlled.

  As a result, the optical disc apparatus 20 reflects the amount of movement of the first objective lens 38 that is driven so as to eliminate the deviation amount to the target mark position by the feedback processing on the second objective lens 79 as feedforward processing. Therefore, unlike the conventional method of further feedback processing the amount of movement of the first objective lens 38 driven by the feedback processing, the feed-forward system of the second objective lens 79 is compared with the servo system of the first objective lens 38. However, high-speed response is not required. Since the amplitude of the blue focus error signal SFEb used as the focal position deviation amount during the feedback process can be reduced, the feedback system of the second objective lens 79 has a higher response speed than the servo system of the first objective lens 38. Sex is not required. As a result, the followability of the second focus Fb2 with respect to the first focus Fb1 is improved without setting the high-speed response as the servo system of the second objective lens 79 much higher than that of the servo system of the first objective lens 38. be able to.

  Further, the optical disc apparatus 20 differs from the case where the second objective lens 79 is driven much faster than the first objective lens 38 in order to follow the first objective lens 38 driven by the feedback process by the feedback process. Since it is only necessary to eliminate the slight remaining focal position deviation while driving almost the same as the objective lens 38, it may be driven slightly faster than the second objective lens 38 at the maximum. The high-speed response of the system can be set to a high-speed response equivalent to that of the servo system of the first objective lens 38.

  Unlike the case of following the first objective lens 38 driven by feedback processing, the optical disc apparatus 20 further increases the large amplitude of the low-frequency component included in the red focus error signal SFEr in the blue focus error signal SFEr. In addition, the second focus Fb2 can follow the first focus Fb1 only by driving the second objective lens 79 within the same driving range as the first objective lens 38.

  The optical disc apparatus 20 moves the second focus Fb2 by the same direction and the same movement amount as the first focus Fb1 based on the red focus error signal SFEr.

  As a result, the same movement as the movement for eliminating the mark position deviation that causes the first focus Fb1 to deviate from the target mark position can be made the second focus Fb2 by the feedforward process, and thus the blue focus error signal SFEb. Can be limited to only a focal position shift with a small amount of movement generated according to the skew and film thickness unevenness of the optical disc 100. This focal position deviation is particularly small in amplitude at a low frequency component as compared with the mark position deviation, so that the blue focus error signal SFEb is mainly composed of only a high frequency component. Since the amplification ratio of the amplifier APf2 can be set, the servo system of the second objective lens 79 can be properly converged and the accuracy of the feedback processing can be improved.

  Further, in the optical disc apparatus 20, the first objective lens 38 and the second objective lens 79 are configured to have the same configuration, so that the first objective lens 38 and the second objective lens 79 are based on the red focus error signal SFEr. Similarly, the second focus Fb2 can be moved by the same direction and the same movement amount as the first focus Fb1 without performing complicated calculations, and the servo system of the second objective lens 79 can be simplified. be able to.

  Further, the optical disc apparatus 20 generates a blue focus error signal SFEb representing the amount of deviation of the second focus Fb2 from the first focus Fb1 based on the first blue light beam Lb1 transmitted through the optical disc 100 and the second objective lens 79. As a result, unlike the focus error signal based on the light beam irradiated to different recording mark positions, the amount of focus position deviation can be directly expressed by the blue focus error signal SFEb. It is possible to match the first focus Fb1 with high accuracy.

  The optical disc device 20 generates a blue focus error signal SFEb, a blue tracking error signal STEr, and a tangential error signal SNEb, and uses the second objective lens 79 and the angle variable mirror 78 to focus, track, and tangentially. Since the second focal point Fb2 can be moved with respect to the second focal point Fb2, the second focal point Fb2 can be made to coincide with the first focal point Fb1 with higher accuracy than the method of moving only the two directions of the focus direction and the tracking direction. .

  Furthermore, the optical disc apparatus 20 classifies the focus position shift that must be eliminated by feedback processing into a low-frequency component mainly generated due to the mark position shift and a high-frequency component generated due to other factors, By feeding the second objective lens 79 in accordance with the focus drive control signal SFDb generated by amplification at a ratio corresponding to each characteristic, a feedforward system that mainly eliminates low-frequency components and mainly high-frequency components The feedback system that solves the problem can be converged efficiently.

  According to the above configuration, the second focus Fb2 is moved in the same manner as the first focus Fb1 by the feedforward process to reduce the low-frequency focal position shift having a large amplitude, and the shift amount is converged by the feedback process. By driving the second objective lens 79 and eliminating the focal position deviation of the second focal point Fb2 with respect to the first focal point Fb1, the factor causing the focal position deviation is mainly limited to a high-frequency component having a small amplitude, and feedback. Since the amplification factor of the amplifier APf2 at the time of processing can be matched with this high-frequency component, the high-speed responsiveness regarding the feedback processing of the second objective lens 79 is improved and the followability of the second focus Fb2 to the first focus Fb1 is improved. Thus, an optical data recording / reproducing recording mark representing information on an optical recording medium can be performed with high accuracy. It can be realized disk apparatus and a focus position control method.

(2) Second Embodiment In the first embodiment described above, the reflection control film 104 is irradiated with the servo-controlled red light beam Lr1, while the blue light beam Lb emitted from the laser diode 51 is irradiated with two. The first blue light beam Lb1 is irradiated from the guide surface side and the second blue light beam Lb2 is irradiated from the recording light irradiation surface on the back side of the guide surface of the optical disc 100, so that a standing wave is generated. The interference pattern was recorded as a recording mark RM.

  In the optical disc apparatus 20 according to the present embodiment described with reference to FIGS. 25 to 29, the blue light beam Lb is divided into three blue light beams LbA, LbB, and LbC, and three blue lights from one surface side of the optical disc 200 are obtained. Irradiate the beam Lb. For convenience of explanation, portions corresponding to those of the first embodiment described with reference to FIGS. 1 to 24 are denoted by the same reference numerals.

  Further, here, like the reflective / transmissive film 104 of the optical disc 100, the reflective film 204 is formed with a track in which guide grooves are arranged in a spiral shape or a concentric shape, and is used as a position index when performing tracking control. It is assumed that

  Incidentally, in the optical disk 200, the substrate 201 is not necessarily required. In this case, the back surface reflection of the optical disk 200 may be used as the reflective film 204. It is also possible to prevent unnecessary reflection by applying a non-reflective coating on the surface of the disk.

(2-1) Configuration of Optical Disc Device The optical disc device 120 according to the second embodiment has the same configuration as the optical disc device 20 (FIG. 4) according to the first embodiment, and thus description thereof is omitted. To do.

  In FIG. 25 corresponding to FIG. 6, the optical pickup 126 according to the second embodiment includes a plurality of recording marks formed of relatively small holograms that form a standing wave in the recording layer of the optical disc 200 by interference of a light beam. It has a configuration that is partially similar to that of the first embodiment in that it is recorded.

  However, this optical pickup 126 is greatly different from the optical pickup 26 according to the first embodiment (FIG. 6) in that the optical beam is irradiated only from one side of the optical disc 200.

  At the time of recording, the optical pickup 126 uses a blue light beam Lb that is linearly polarized light emitted from the same laser diode as a blue light beam LbC for tracking and focus servo, and blue light beams LbA and LbB for hologram recording. Split into light beams of books. On the other hand, the optical pickup 126 is divided into two light beams, a light beam LbC for tracking and focus servo and a blue light beam LbA for reading holograms during reproduction.

  First, the blue light beam LbC used for tracking and focus servo during recording and reproduction will be described. The laser diode 131 emits a blue light beam Lb having a wavelength of 405 [nm] and enters the collimator lens 132. The collimator lens 132 converts the blue light beam Lb into parallel light and then enters the beam splitter 133.

  The beam splitter 133 reflects most of the blue light beam Lb, while the remaining part is transmitted as the blue light beam LbC and is incident on the objective lens 137 via the mirror 134 and the polarization beam splitters 135 and 136.

  The objective lens 137 collects the blue light beam LbC and irradiates it on the reflection film 204 of the optical disc 200 (FIG. 26). Further, the objective lens 137 receives the blue light beam LbC reflected by the reflecting film 204 and makes it incident on the beam splitter 133 sequentially through the polarization beam splitters 136 and 135 and the mirror 134 so as to follow the original path in reverse. .

  The beam splitter 133 reflects the blue light beam LbC, deflects the angle by 90 °, and irradiates the photodetector 160 via the condenser lens 158 and the cylindrical lens 159. Similar to the photo detector 43 (FIG. 8), the photo detector 160 having the detection region divided into four generates a detection signal corresponding to the amount of received light of the blue light beam LbC and supplies it to the signal processing unit 23.

  The signal processing unit 23 generates the focus error signal SFEr and the tracking error signal STEr according to the above-described equations (3) and (4) based on the detection signal, and sends them to the drive control unit 22. The drive control unit 22 generates a focus drive control signal SFDr and a tracking drive control signal STEr based on the focus error signal SFEr and the tracking error signal STEr, and supplies them to a biaxial actuator 137A (not shown), whereby the objective lens 137 is driven in the focus direction and the tracking direction.

  Next, the blue light beam LbA used when recording standing waves will be described. The beam splitter 133 makes most of the reflected blue light beam Lb incident on the half-wave plate 142. The half-wave plate transmits approximately half of the incident blue light beam Lb as it is, while changing the polarization direction of the remaining approximately half by 90 ° and makes it incident on the polarization beam splitter 143.

  The polarization beam splitter 143 transmits about half of the blue light beam LbA and enters the movable angle variable mirror 144 that deflects the direction of the blue light beam LbA. The variable angle mirror 144 changes the angle by reflecting the blue light beam LbA and makes it incident on the liquid crystal panel 145.

  The liquid crystal panel 145 corrects the spherical aberration of the blue light beam LbA and the coma caused by the tilt of the disk, and makes it incident on the quarter-wave plate 146. The quarter wavelength plate converts linearly polarized light into, for example, right circularly polarized light, and enters the polarizing beam splitter 136 through the movable lens 148 and the fixed lens 149 of the first relay lens 147 in order.

  The first relay lens 147 moves the focal point FbA of the blue light beam LbA in the focus direction by driving the movable lens 148 and controlling the distance between the movable lens 148 and the fixed lens 149, and from the reflective film 204. The distance of the focal point FbA is adjusted.

  The polarization beam splitter 136 reflects the blue light beam LbA, deflects its direction by 90 °, and makes it incident on the objective lens 137. The objective lens 137 focuses the blue light beam LbA and irradiates the target mark position in the recording layer 201 of the optical disc 200.

  Next, the blue light beam LbB used at the time of recording a standing wave similarly to the blue light beam LbA will be described. Since most of the optical components on the optical path of the blue light beam LbB play the same role as the blue light beam LbA described above, the description of the overlapping parts is omitted.

  The polarization beam splitter 143 reflects the remaining half of the blue light beam Lb into a blue light beam LbB, and enters the optical compensator 152 through the liquid crystal panel 150 and the half-wave plate 151. The optical compensator 152 makes the optical path length of the blue light beam LbB coincide with the blue light beam LbA using the difference in refractive index, and then enters the polarization beam splitter 153.

  The polarization beam splitter 153 causes the blue light beam LbB to enter the polarization beam splitter 135 through the quarter wavelength plate 154, the movable lens 156 of the second relay lens 155, and the fixed lens 157 in this order.

  The polarization beam splitter 135 reflects the blue light beam LbB, deflects the direction by 90 °, and enters the objective lens 137 through the deflection beam splitter 136. The objective lens 137 is configured to match the focal point FbB formed after the blue light beam LbB is reflected by the reflecting film 204 and turned back to the target mark position in the recording layer 201.

  As a result, as shown in FIG. 25, the optical pickup 126 forms a standing wave in the recording layer 202 of the optical disc 200 by the blue light beam LbA and the blue light beam LbB forming a standing wave at the target mark position. The interference pattern can be recorded as the recording mark RM.

  The optical pickup 126 drives the objective lens 137 so that the blue light beam LbC is focused on the target mark position in the reflective film 204, and the positions of the focal points FbA and FbB of the blue light beams LbA and LbB are set to the first relay lens 147 and The second relay lens 155 controls the focus direction.

  The optical pickup 126 controls the blue light beams LbA, LbB, and LbC by the objective lens 137 in the tracking direction, and controls the blue light beam LbA by the angle variable mirror 144 when a focal position shift occurs according to a skew or the like. By doing so, the focal points FbA and FbB are made to coincide with the target mark position.

  The objective lens 137 condenses the blue light beam LbA (shown by a broken line) reflected by the reflective film 204 and makes it incident on the polarization beam splitter 136. At this time, the polarizing beam splitter 136 transmits the blue light beam LbA that has been left-circularly polarized by being reflected by the reflecting film 201 and enters the polarizing beam splitter 135.

  The deflecting beam splitter 135 reflects the blue light beam LbA and makes it incident on the beam splitter 153 via the second relay lens 155 and the half-wave plate 154. The beam splitter 153 reflects the blue light beam LbA, changes its direction by 90 °, and enters the photodetector 163 through the condenser lens 161 and the cylindrical lens 162 in order.

  Similar to the photodetector 43 (FIG. 8), the photodetector 160 having a detection region divided into four generates a detection signal corresponding to the amount of received light of the blue light beam LbA, and supplies the detection signal to the signal processing unit 23, as in the photodetector 82.

  The signal processing unit 23 generates the focus error signal SFEb and the tracking error signal STEb in accordance with the above-described equations (5) and (6), and sends them to the drive control unit 22.

  On the other hand, the objective lens 137 condenses the blue light beam LbB (shown by a broken line) reflected by the reflective film 204 and makes it incident on the polarization beam splitter 136. At this time, the polarization beam splitter 136 reflects the blue light beam LbB that has been right-circularly polarized by being reflected by the reflection film 204 and makes it incident on the first relay lens 147.

  The first relay lens 147 transmits the blue light beam LbB and makes it incident on the polarization beam splitter 143 via the quarter wavelength plate 146, the liquid crystal panel 145, and the angle variable mirror 144. The polarization beam splitter reflects the blue light beam LbB, changes its direction by 90 °, and makes it incident on the photodetector 166 via the condenser lens 164 and the pinhole plate 165.

  The photodetector 166 is for detecting the amount of received light of the blue light beam LbB during the reproduction process, and does not execute signal processing during the recording process.

  On the other hand, in the reproduction process, the optical pickup 126 blocks the blue light beam LbB with the shutter added to the optical compensator 152 and irradiates the recording layer 201 of the optical disc 200 with only the blue light beam LbA. At this time, the blue light beam LbA is emitted to the recording mark RM, thereby generating reproduction light. This reproduced light is guided to the photodetector 166 as a blue light beam LbB by following the same optical path as when guided to the objective lens 137 in the opposite direction.

  At this time, the pinhole plate 165 provided in the front stage of the photodetector 166 blocks the defocused return light reflected by the reflective film 201 when the recording mark RM is not recorded, and causes the photodetector 166 to remove the recording mark RM from the recording mark RM. Only the blue light beam LbB is made incident. The photodetector 166 detects the amount of received light of the blue light beam LbB and generates a reproduction RF signal by the signal processing unit 23.

(2-2) Servo Control Processing Also in this embodiment, the servo control processing is executed as in the first embodiment described above.

  Here, the objective lens 137 is driven so that the blue light beam LbC is focused on a desired reflection position in the reflection film 201. The objective lens 137 irradiates the blue light beams LbA, LbB, and LbC to the same position in the tracking direction. On the other hand, since the optical pickup 126 needs to match the focal points FbA and FbB of the blue light beams LbA and LbB with the target mark positions, respectively, the blue light beam LbA and the second relay lens 155 are used. LbB is controlled in the focus direction.

  Further, in the optical pickup 126, the blue light beam LbA is controlled in the tracking direction by the angle variable mirror 144 in order to match the focal points LbA and LbB when the focal position shift occurs according to the skew or the like.

  Here, in the optical pickup 126, the second relay lens 155 controls the second relay lens 155 based on the movement amount signal representing the movement amount from the current target mark position to the next target mark position supplied from the control unit 21 (FIG. 4). The focal point FbB is moved. Further, since the second focus error signal SFEb is generated according to the amount of light received by the photodetector 163, it is possible to drive the first relay lens 147 by feedback processing and move the focus FbA so as to follow the focus FbB. It is. However, in this case, it becomes necessary to drive the first relay lens 147 much faster than the second relay lens 155.

  Therefore, in the present embodiment, the focus drive control signal SFDb is generated by superimposing the movement amount signal supplied from the control unit 21 and the second focus error signal SFEb.

  That is, as shown in FIG. 27, in the optical pickup 126, the amplifier APf1 as the drive control unit 22 is connected to the second relay lens 155. The photodetector 163 is connected to the first relay lens 147 via the amplifier APf2, and the amplifier APf3 serving as the drive control unit 22 is connected between the amplifier APf2 and the second relay lens 155. In FIG. 27, for the sake of convenience, only the optical components and the like necessary for the description are shown in the optical disk device 126, and other optical components and the like are omitted. The same applies to the following figures.

  When the movement amount signal is supplied from the control unit 21 by the amplifier APf1, the drive control unit 22 amplifies the recording address information to generate the focus drive control signal SDFbA, and supplies this to the first relay lens 147. . As a result, the drive control unit 22 drives the first relay lens 147 by moving the movable lens 148 of the first relay lens away from or in the proximity of the fixed lens 149, and the focal point FbA of the blue light beam LbA is driven. Move in the focus direction.

  The drive control unit 22 amplifies the second focus error signal SFEb generated by the amplifier Af2 according to the amount of light received by the photodetector 163, and amplifies the movement amount signal by the amplifier APf3. Further, the drive control unit 22 generates a focus drive control signal SDFbB by superimposing the amplified second focus error signal SFEb and the movement amount signal, and supplies this to the second relay lens 155. As a result, the drive control unit 22 can drive the second relay lens 155 in the same manner as the first relay lens 155 by moving the movable lens 156 according to the focus drive control signal SDFbB, and FIG. As shown, the focal point FbB is made to follow the focal point FbA, and the focal point FbB is made to coincide with the focal point FbA with high accuracy.

  As described above, in the optical disc apparatus 20, the movement of the first relay lens 147 is reflected on the second relay lens 155 in advance by feedforward processing, and the remaining focus corresponding to the skew or the like based on the second focus error signal SFEb. Since the position shift is eliminated, the feedback system of the second relay lens 155 has a higher speed response than the method of eliminating all the focal position shifts including the moving amount of the first relay lens 147 by the feedback process. It can be set later, and the configuration of the optical disc apparatus 20 can be simplified.

(2-3) Operation and Effect According to the configuration described above, the optical disc apparatus 20 performs the first operation by feedforward processing based on the movement amount signal indicating the movement amount from the current target mark position to the next target mark position. By controlling the first relay lens 147 which is a focus moving unit, the shift amount signal and the shift of the focus FbB which is the second focus with respect to the focus FbA while moving the focus FbA which is the first focus to the next target mark position. Based on the second focus error signal SFEb representing the amount, the focus FbB is made to coincide with the focus FbA by feedback processing.

  As a result, the amplitude of the second focus error signal SFEb can be suppressed, the load that the second relay lens 155 follows the first relay lens 147 is reduced, and the optical disc 100 is skewed or uneven in thickness. Even if it exists, since the focus position shift can be eliminated, the focus FbB can be matched with the focus FbA with high accuracy.

  According to the above configuration, the optical disc apparatus 20 not only eliminates the target mark deviation by similarly moving the focus FbA and the focus FbB based on the movement amount signal, but also eliminates the generated focal position deviation. Therefore, the focal point FbB can be matched with the focal point FbA with high accuracy, and thus an optical disc apparatus and a focal position control method for recording or reproducing a recording mark representing information on an optical recording medium with high accuracy can be realized.

(3) Other Embodiments In the above-described embodiments, the case where the drive control signal SFDb is calculated by superimposing the red focus error signal SFEr and the blue focus error signal SFEb at a predetermined ratio has been described. However, the present invention is not limited to this, and the drive control signal SFDb may be calculated using various calculation methods based on the red focus error signal SFEr and the blue focus error signal SFEb.

  In the above-described embodiment, the first focus Fb1 and the second focus Fb2 are similarly moved based on the red focus error signal SFEr, and further the second focus Fb2 is set based on the blue focus error signal SFEb. Although the case where the focal position deviation is eliminated by moving the lens has been described, the present invention is not limited to this, and the ratio of overlapping the red focus error signal SFEr and the blue focus error signal SFEb can be freely changed. .

  For example, the second focus Fb2 may be moved by 0.8 times the first focus Fb1, and the second focus Fb2 may be moved based on the blue focus error signal SFEb. Even in this case, the feedback processing load of the second objective lens 79 can be reduced as in the above-described embodiment. Further, the feedback system can be converged more efficiently by optimizing the gain of the amplifier APf3 to a low frequency component and optimizing the gain of the amplifier APf2 to a high frequency component.

  Further, in the above-described embodiment, the case where the feedforward process is executed using the red focus error signal SFEr and the red tracking error signal STEr has been described. However, the present invention is not limited to this, for example, the first focus When detecting the amount of deviation of the Fb1 relative to the tilt direction (the radial direction that is the tangential direction or the track normal direction) and controlling the tilt of the first objective lens 38 or the optical disc 100, the amount of deviation is used in the tilt direction. A feedforward process can be executed.

  Further, in the above-described embodiment, the case where the drive control signal SFDb is generated based on the red focus error signal STFr and the blue focus error signal SFTb by the amplifiers APf2 and APf3 as the drive control unit 22 has been described. The present invention is not limited to this. For example, the drive control signal SFDb may be generated by a DSP (Digital Signal Processor).

  Further, in the above-described embodiment, the case where the red focus error signal SFEr and the red tracking error signal SFEr are generated by the push-pull method has been described. Thus, the red focus error signal SFEr and the red tracking error signal SFEr may be generated.

  Furthermore, in the above-described embodiment, the case where the blue focus error signal SFEb and the blue tracking error signal STEb are generated from the detection signal detected by the photodetector 82 according to the equations (5) and (6) has been described. The present invention is not limited to this, and the blue focus error signal SFEb and the blue tracking error signal STEb may be generated by various other methods and calculation methods.

  Further, in the above-described embodiment, the case where the blue focus error signal SFEb and the blue tracking error signal STEb are generated based on the first blue light beam Lb1 transmitted through the optical disc 100 and the second objective lens 79 has been described. However, the present invention is not limited to this, and the blue focus error signal SFEb and the blue tracking error signal STEb may be generated based on the second blue beam Lb2 transmitted through the optical disc 100 and the first objective lens 38. The blue focus error signal SFEb and the blue tracking error signal STEb may be generated by various methods.

  Further, in the above-described embodiment, the case where the first blue light beam LB1 and the second blue light beam LB2 are emitted from the laser diode 51 that is the same light source has been described, but the present invention is not limited thereto. Instead, they may be emitted from different light sources.

  Further, in the above-described embodiment, the case where the first blue light beam LB1 and the second blue light beam LB2 form a standing wave to record a minute hologram as a recording mark has been described. However, the present invention is not limited to this, and the first blue light beam LB1 and the second blue light beam LB2 may record simple recording marks having no interference pattern.

  Further, in the above-described embodiment, the case where the first blue light beam LB1 and the second blue light beam LB2 form a constant wave is described, but the present invention is not limited to this, and the first blue light beam Reproduction light may be formed from the recording mark RM of the optical disc 100 by the beam LB1 and the second blue light beam LB2.

  Further, in the above-described embodiment, the case where the blue light beam Lb0 of 405 [nm] is used for recording and reproduction has been described. However, the present invention is not limited to this, and has other various wavelengths. A light beam may be used.

  Further, in the above-described embodiment, the second objective lens 79 is in the focus direction which is the thickness direction of the optical disc 100, the tracking direction which is the radial direction of the optical disc 100, and the tangential direction perpendicular to the focus direction and the tracking direction. However, the present invention is not limited to this. For example, the control may be performed only in the tracking direction and the focus direction.

  Furthermore, in the above-described embodiment, the case where the first objective lens 38 and the second objective lens 79 are configured to be equivalent to each other has been described. However, the present invention is not limited thereto, and may be configured differently. May be.

  Further, in the above-described embodiment, the case where the servo system of the first objective lens 38 and the servo system of the second objective lens 79 have the same high-speed response has been described, but the present invention is not limited to this. For example, the high-speed response of the servo system of the second objective lens 79 may be set higher than the high-speed response of the servo system of the first objective lens 38.

  Further, as described above, the first embodiment and the second embodiment have different configurations in various points, but they can be appropriately combined. For example, the optical disc apparatus 20 of the first embodiment may superimpose the red tracking error signal STEr and the blue tracking error signal STEb for tracking control only, and does not drive the second objective lens 79 in the tangential direction. Also good.

  Further, in the above-described embodiment, the case where the second focal position Fb2 is moved by the second objective lens 79 has been described. However, the present invention is not limited to this, and the second relay is used as the second focal point moving unit. The lens 60 and the second objective lens 79 may be combined to control the focus direction of the second focal position FB2, and in addition to the second objective lens 79, the second focal point is obtained using an optical component such as a variable angle mirror. The tracking direction of the position Fb2 may be controlled.

  Furthermore, in the above-described embodiment, the case where the optical disk 100 having a disk shape is used has been described. However, the present invention is not limited to this, and volume recording having a card shape or a die shape instead of the optical disk 100. A medium may be used.

  Further, in the above-described embodiment, the first objective lens 38 as the first focus movement unit, the drive control unit 22 as the first drive control unit and the second drive control unit, and the second focus movement. The case where the optical disc apparatus 20 is configured by the second objective lens 79 as the unit and the signal processing unit 23 as the focal position deviation signal generation unit has been described. However, the present invention is not limited to this, and other various circuit configurations are used. The first focus movement unit, the first drive control unit, the second focus movement unit, the second drive control unit, and the focus position deviation signal generation unit are configured to constitute the optical disc apparatus of the present invention. Anyway.

  The optical disk device and the focal position control method of the present invention can be used for various electronic devices on which the optical disk device is mounted, for example.

It is a basic diagram which shows the structure of the conventional standing wave recording-type optical disk apparatus. It is a basic diagram which shows the mode of formation of a hologram. It is a basic diagram which shows the structure of the optical disk by one embodiment of this invention. 1 is a schematic diagram illustrating a configuration of an optical disc device according to an embodiment of the present invention. It is a basic diagram which shows the external appearance structure of an optical pick-up. It is a basic diagram which shows the structure of an optical pick-up. It is a basic diagram which shows the optical path of a red light beam. It is a basic diagram which shows the structure of the detection area | region in the photodetector for red. It is a basic diagram which shows the optical path (1) of a blue light beam. It is a basic diagram which shows the optical path (2) of a blue light beam. It is a basic diagram which shows a red focus error signal and a red tracking error signal. It is an approximate line figure used for explanation of conventional servo control. It is a basic diagram which shows the symmetry of a 1st objective lens and a 2nd objective lens. It is a basic diagram which shows the focus position shift by skew. It is a basic diagram which shows the focus position shift by film thickness nonuniformity. It is a rough-line perspective view which shows the servo control by 1st Embodiment. It is a basic diagram which shows the structure of the detection area | region in the photodetector for blue. It is an approximate line figure used for explanation when a focus agrees. It is a basic diagram with which it uses for description of the focus position shift | offset | difference of a focus direction. It is a basic diagram with which it uses for description of the focus position shift of a tracking direction. It is a basic diagram with which it uses for description of the focus position shift | offset | difference of a tangential direction. It is a basic diagram which shows a blue focus error signal and a blue tracking error signal. It is an approximate line figure used for explanation of control of a tracking direction. It is a basic diagram with which it uses for description of control of a focus direction. It is a basic diagram which shows irradiation of the light beam with respect to an optical disk. It is a basic diagram which shows the structure of the optical pick-up by 2nd Embodiment. It is a basic diagram with which it uses for description of the focus control (1) by 2nd Embodiment. It is a basic diagram with which it uses for description of the focus control (2) by 2nd Embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 20 ... Optical disk apparatus, 21 ... Control part, 22 ... Drive control part, 23 ... Signal processing part, 26 ... Optical pick-up, 30 ... Guide surface position control optical system, 31, 51 ... Laser diode, 37, 55, 58, 72 ... Polarizing beam splitter, 38, 79 ... Objective lens, 38A, 79A ... Actuator, 43 ... Red detector, 64 ... Photo detector, 82 ... Blue detector, 50 ... Guide surface information optical system, 56... 1/4 wavelength plate, 57... Movable mirror, 60, 75... Relay lens, 61, 76. Shutter, 78 ... Variable angle mirror, 100 ... Optical disk, 101 ... Recording layer, 102, 103 ... Substrate, 104 ... Reflecting and transmitting film, Lr1 ... Red light beam, r2: Red reflected light beam, Lb0: Blue light beam, Lb1: First blue light beam, Lb2: Second blue light beam, Lb3: Blue reproduction light beam, Fr: Focus, Fb1: First 1 focus, Fb2 ... 2nd focus, RM ... record mark.

Claims (16)

An optical disc apparatus that irradiates the same target recording mark position from both sides of a disc-shaped optical recording medium through corresponding first and second objective lenses, respectively, with first and second light emitted from a light source. In
A first focal point moving unit that moves a focal position of the first light;
A mark position deviation signal generating unit that detects a deviation amount of the focal position of the first light with respect to the recording mark position, and generates a mark position deviation signal according to the detection result;
A first drive control unit that controls the first focus moving unit to move the focal position of the first light to the recording mark position based on the mark position deviation signal;
A second focus moving section for moving the focal position of the second light;
A focal position deviation signal generation unit that detects a deviation amount of the focal position of the second light with respect to the focal position of the first light, and generates a focal position deviation signal according to the detection result;
Based on the mark position shift signal and the focus position shift signal, a second focus moving unit that controls the second focus moving unit to match the focus position of the second light with the focus position of the first light. An optical disc apparatus comprising: a drive control unit. The first and second lights are
A minute hologram emitted from the same light source and recorded by the standing wave is recorded at the recording mark position.
The optical disc apparatus according to claim 1. The first focal point moving unit is
The focal position of the first light is moved by driving the first objective lens,
The second focal point moving unit is
The focal position of the second light is moved by driving the second objective lens.
The optical disc apparatus according to claim 1. The second objective lens is
It has the same configuration as the first objective lens
The optical disc apparatus according to claim 1. The second drive control unit includes:
Based on the mark position shift signal, the second focus position is moved in the same direction and by the same amount as the focus position of the first light, and the second light position is changed based on the focus position shift signal. The focal position is matched with the focal position of the first light.
The optical disc apparatus according to claim 1.   The second objective lens is
  It has the same configuration as the first objective lens,
  The second drive control unit includes:
  Based on the mark position deviation signal, the second objective lens is further driven on the basis of the focal position deviation signal while driving the second objective lens in the same direction and with the same movement amount as the first objective lens. By driving, the focal position of the second light is matched with the focal position of the first light.
The optical disc apparatus according to claim 1. The second drive control unit includes:
Based on the mark position deviation signal, the second focal position is moved in the same direction as the focal position of the first light at a ratio corresponding to the movement amount of the focal position of the first light. Based on the focal position deviation signal, the focal position of the second light is matched with the focal position of the first light.
The optical disc apparatus according to claim 1. The focal position deviation signal generator is
Based on the first light transmitted through the optical recording medium and the second objective lens, a shift amount of the focal position of the second light with respect to the focal position of the first light is detected.
The optical disc apparatus according to claim 1. The focal position deviation signal generator is
Based on the second light transmitted through the optical recording medium and the first objective lens, a shift amount of the focal position of the second light with respect to the focal position of the first light is detected.
The optical disc apparatus according to claim 1. The mark misalignment signal generator is
Third light emitted from another light source is applied to the optical recording medium from the first objective lens, and return light is reflected by the third light reflected by the optical recording medium. Thus, the amount of deviation of the focal position of the first light from the recording mark position is detected.
The optical disc device according to claim 8. The mark displacement signal is
A deviation amount in a focus direction which is a thickness direction of the optical recording medium or a tracking direction which is a radial direction of the optical recording medium with respect to the recording mark position of the focal position of the first light.
The optical disc apparatus according to claim 1. The focal position deviation signal generator is
The second direction is defined in three directions: a focus direction that is a thickness direction of the optical recording medium, a tracking direction that is a radial direction of the optical recording medium, and a tangential direction that is perpendicular to the focus direction and the tracking direction. Detecting a shift amount of the focal position with respect to the first focal position;
The second focal point moving unit is
The focal position of the second light is moved in three directions: the focus direction, the tracking direction, and the tangential direction.
The optical disc apparatus according to claim 1. First and second light emitted from a light source is incident on a disc-shaped optical recording medium through the same objective lens, and the reflective film of the optical recording medium out of the first and second lights. In the optical disc apparatus that irradiates one of the light reflected by the light and the other light before reaching the reflective film to the same target recording mark position from opposite directions,
A first focal point moving unit that moves a focal position of the first light;
The focus position of the first light is moved to the recording mark position on the basis of a movement amount signal representing the movement amount from the current recording mark position of the optical recording medium to the next recording mark position. A first drive control unit for controlling the first focus moving unit;
A second focus moving section for moving the focal position of the second light;
A focal position deviation signal generation unit that detects a deviation amount of the focal position of the second light with respect to the focal position of the first light and generates a focal position deviation signal;
Based on the movement amount signal and the focus position shift signal, a second drive that controls the second focus moving unit to match the focus position of the second light with the focus position of the first light. An optical disc device having a control unit. The first focal point moving unit is
A first relay lens comprising a pair of movable lens and fixed lens;
The second focal point moving unit is
The second relay lens is composed of a pair of movable lens and fixed lens.
The optical disc apparatus according to claim 13. When irradiating the first and second light emitted from the light source to the same target recording mark position from both sides of the disk-shaped optical recording medium via the corresponding first and second objective lenses, respectively. In the focal position control method for the first and second lights,
By driving a first focus moving unit that moves the focus position of the first light based on a mark position shift signal that represents a shift amount from the focus position of the first light with respect to the recording mark position, A first focal position moving step for moving the focal position of the first light to the recording mark position;
A focal position deviation signal generating step for detecting a deviation amount of the focal position of the second light with respect to the focal position of the first light and generating a focal position deviation signal;
By driving a second focus moving unit that moves the focus position of the second light based on the mark position shift signal and the focus position shift signal, the focus position of the second light is changed to the first position. A focus position control method comprising: a second focus position moving step for matching the focus position of light. The first and second lights emitted from the light source are incident on a disc-shaped optical recording medium through the same objective lens, and the first or second light is reflected by the reflective film of the optical recording medium. When the reflected one light and the other light before reaching the reflection film are irradiated to the same target recording mark position from opposite directions, the first and second lights are irradiated. In the focus position control method,
Based on a movement amount signal representing a movement amount from the current recording mark position of the optical recording medium to the next recording mark position, a first focus moving unit that moves the focal position of the first light is driven. A first focal position moving step for moving the focal position of the first light to the recording mark position;
A focal position deviation signal generating step for detecting a deviation amount of the focal position of the second light with respect to the focal position of the first light and generating a focal position deviation signal;
By driving a second focus moving unit that moves the focus position of the second light based on the movement amount signal and the focus position shift signal, the focus position of the second light is changed to the first light. A focal position control method comprising: a second focal position moving step for matching the focal position of the second focal position.

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