JP2005251291A - Recording and reproducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a recording and reproducing device in which a recording medium can be accurately irradiated by a light to be used for recording and reproducing the information. <P>SOLUTION: An object light 50 is converged by an objective lens 310, and a reference light 51 is deflected by a hologram element 312, and by the both lights, an information recording area 106 of a hologram recording medium 1 is irradiated. The reference light 51 rotates around an optical axis of the object light 50. By a detection light 52 transmitted through the objective lens 310, a servo information area 107 is irradiated. The positional information is detected by a photodetector 314 for servo in accordance with a reflected light of the detection light 52. By an actuator 320, the objective lens 310 and the hologram element 312 are controlled for moving to the focusing control direction or tracking control direction in accordance with a focusing drive signal and a tracking drive signal which are produced on the basis of the positional information. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a recording / reproducing apparatus that records information on a hologram memory medium and reproduces the recorded information.

  In recent years, rewritable optical discs such as phase change type and magneto-optical type are widely used as information recording media. In order to further increase the recording density of these optical discs, techniques such as reducing the beam spot diameter and shortening the distance between adjacent tracks or adjacent bits are required.

  As described above, the density of optical discs is increasing year by year. However, since the above optical disc records data in a plane, the recording density is limited to the diffraction limit of light, and physical recording of high density recording is performed. Approaching the limit. Therefore, in order to further increase the capacity, three-dimensional (volume type) multiplex recording including the depth direction is required.

  Therefore, a hologram memory having both a large capacity derived from a three-dimensional multiple recording area and a high speed derived from a two-dimensional batch recording / reproducing system has attracted attention as a next-generation computer file memory. Hologram memory, for example, irradiates a recording medium formed by sandwiching a recording layer made of a photopolymer or the like between two glass plates with object light corresponding to recording information and reference light, and is generated by both lights The recorded interference fringes are recorded as a change in the refractive index of the recording material. When reproducing the information, only the reference light is irradiated to the recorded interference fringes, and the recorded information is based on the diffracted light of the reference light. The optical information corresponding to is extracted.

  Since this hologram memory can multiplex-record a plurality of two-dimensional data in the same area, it has been attracting attention as a terabyte memory having a huge recording capacity while having the same shape as a CD or the like. With respect to a reproducing apparatus for such a hologram memory, for example, as shown in Patent Document 1, a technique for writing a positioning signal as hologram information separately from a data signal has been proposed.

Japanese Patent Application Laid-Open No. 2004-228561 provides an address servo area in which positioning information for controlling the positions of object light and reference light is provided on a recording medium, and positions the object light and reference light based on this information. Is described. Patent Document 3 describes a technique for deflecting an incident light beam by relatively rotating a pair of wedge-shaped prisms using a rotating mechanism, and recording data on a recording medium in a multiplexed manner.
JP 2000-268380 A JP 10-124872 A JP 2000-338846 A

    However, although the technique described in Patent Document 1 can record data on the entire surface of a recording medium, for example, when reproducing data in different drive devices, the deviation of the spindles of the respective drive devices. The center amount is different, and the amount of eccentricity changes every time the recording medium is chucked. Therefore, there is a problem that compatibility between apparatuses is poor and accurate positioning control is difficult.

  In the technique described in Patent Document 2, since the address / servo areas are provided at predetermined intervals, the recording area is reduced. Further, since the sampled servo system is used as the servo system, there is a problem that it is necessary to move the recording medium at a high speed and there is a limitation in recording and reproduction time. Further, in the technique described in Patent Document 3, since a pair of wedge prisms is used, two parts are required, and two rotation driving units for rotating the parts are required, which complicates the apparatus. And there was a problem of increasing the size.

  The present invention has been made in view of the above-described problems, and provides a recording / reproducing apparatus capable of accurately irradiating a recording medium with light used for recording and reproducing information. Objective. It is a second object of the present invention to provide a recording / reproducing apparatus capable of detecting a servo signal regardless of the moving speed of the recording medium and performing multiplex recording of data without increasing the size of the apparatus. .

  The present invention has been made to solve the above problems, and the invention according to claim 1 irradiates an optical recording medium with object light and reference light, and interferes with the information of the object light on the optical recording medium. In a recording / reproducing apparatus that records information as a fringe, irradiates the interference light with the reference light, and reproduces information based on the diffracted light of the reference light, the object light is condensed by an objective lens, and information is recorded Object light irradiation means for condensing the object light on the information recording area on the optical recording medium, and rotation irradiation for rotating the reference light around the optical axis of the objective lens and irradiating the information recording area Means, a wavefront converting means for converting the wavefront of the reference light into a non-planar wave, and a detection light irradiating means for irradiating a detection information for position detection on a servo information area different from the information recording area on the optical recording medium And by the detection light Based on the detection result of the position, a recording and reproducing apparatus characterized by comprising a control means for controlling the irradiation position of the object light and the reference light.

  In the servo information area different from the information recording area on the optical recording medium, for example, a concave portion or a convex portion is formed, and is distinguished from the information recording area. The object light irradiation means condenses the object light to which the information to be recorded is added by the objective lens and irradiates the information recording area of the optical recording medium. The rotation irradiating means rotates the reference light for forming the interference fringes and reproducing the information about the optical axis of the objective lens that collects the object light and irradiates the information recording area. The object recording light and the reference light are irradiated to the information recording areas from the same main surface side or different main surface sides of the optical recording medium, respectively.

  The detection light irradiation means irradiates the detection light to a servo information area different from the information recording area irradiated with the object light and the reference light. The detection light has, for example, position information in a direction parallel to the recording surface of the optical recording medium or in the normal direction of the recording surface, and the control unit irradiates the object light and the reference light based on the position information. To control.

  According to a second aspect of the present invention, there is provided the recording / reproducing apparatus according to the first aspect, wherein the detection light irradiating means includes the information recording area on the optical recording medium by the objective lens that focuses the object light. And the optical axis of the object light incident on the objective lens and the optical axis of the detection light are non-parallel.

  The detection light is focused on the servo information recording area by an objective lens that focuses the object light. For example, the optical axis of the object light incident on the objective lens and the optical axis of the detection light become non-parallel depending on the setting of the position of the optical component arranged in the optical path of the detection light.

  According to a third aspect of the present invention, in the recording / reproducing apparatus according to the first or second aspect, the object light, the reference light, and the detection light are generated by the same light source.

  According to a fourth aspect of the present invention, in the recording / reproducing apparatus according to any one of the first to third aspects, a polarization direction of the object light and the reference light and a polarization direction of the detection light are orthogonal to each other. It is characterized by that.

  A fifth aspect of the present invention is the recording / reproducing apparatus according to any one of the first to fourth aspects, wherein the servo information area is formed with a concave portion or a convex portion. .

  According to a sixth aspect of the present invention, in the recording / reproducing apparatus according to any one of the first to fifth aspects, the control means further includes the objective lens based on a position detection result by the detection light. The position of the objective lens and the wavefront conversion means is controlled by integrally moving the wavefront conversion means in the normal direction of the main surface of the optical recording medium.

  According to a seventh aspect of the present invention, in the recording / reproducing apparatus according to any one of the first to fifth aspects, the control unit further includes the objective lens based on a position detection result by the detection light. The position of the objective lens and the wavefront conversion means is controlled by integrally moving the wavefront conversion means in a direction parallel to the main surface of the optical recording medium.

  According to an eighth aspect of the present invention, in the recording / reproducing apparatus according to any one of the first to fifth aspects, the control means further includes the objective lens based on a position detection result by the detection light. By moving the entire optical system including the object light irradiation means, the rotation irradiation means, the wavefront conversion means, and the detection light irradiation means integrally in the normal direction of the main surface of the optical recording medium, The irradiation position of the object light and the reference light is controlled.

  According to a ninth aspect of the present invention, in the recording / reproducing apparatus according to any one of the first to fifth aspects, the control means further includes the objective lens based on a position detection result by the detection light. By moving the entire optical system including the object light irradiation means, the rotation irradiation means, the wavefront conversion means, and the detection light irradiation means integrally in a direction parallel to the main surface of the optical recording medium, The irradiation position of the object light and the reference light is controlled.

  A tenth aspect of the present invention is the recording / reproducing apparatus according to any one of the first to ninth aspects, wherein a plurality of information on the object light is recorded in the same area of the optical recording medium. As described above, a combination of the peristaltic multiplexing method and the shift multiplexing method is used.

  According to the present invention, the position information is detected by the detection light, and based on the position information, the irradiation position on the recording medium of the light used for recording and reproducing the information is controlled. The effect that the light used for reproduction can be accurately irradiated onto the recording medium is obtained. Further, the servo signal can be detected regardless of the moving speed of the recording medium, and the effect that multiple recording of data can be performed without increasing the size of the apparatus is also obtained.

  The best mode for carrying out the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a recording / reproducing apparatus according to an embodiment of the present invention. In the figure, reference numeral 1 denotes a hologram recording medium (optical recording medium) on which information is recorded by interference fringes formed by object light and reference light. A spindle motor 2 rotates the hologram recording medium 1 at a constant linear velocity, for example, when the outer shape of the hologram recording medium 1 is a disk. The number of rotations is controlled by the output of the driver IC 7.

  An optical pickup 3 is an optical component (not shown) such as a laser light source, a collimator lens, an objective lens, and a polarization beam splitter (object light irradiation means, rotation irradiation means, detection light irradiation means, wavefront conversion means), focusing actuator ( Control means), a tracking actuator (control means), and a two-dimensional light detection array as a light receiving element. The objective lens is driven in the thickness direction of the hologram recording medium 1 by a focusing actuator, and is driven in the in-plane direction of the recording surface of the hologram recording medium 1 by a tracking actuator.

  A feed motor (control means) 4 is a mechanism for sending the optical pickup 3 from the inner periphery to the outer periphery of the hologram recording medium 1, for example. The feed motor 4 controls the position of the optical pickup 3 based on the drive signal of the tracking actuator. Reference numeral 5 denotes a signal processing IC which receives a data reproduction signal, an address signal, a spindle control signal, a focus error signal, and a track error signal based on the return light from the hologram recording medium 1 incident on a light receiving element such as a two-dimensional photodetection array. Generate. Further, the signal processing IC 5 generates a focusing drive signal and a tracking drive signal based on the generated focus error signal and track error signal, and outputs them to the driver IC 7 together with the spindle control signal.

  The address signal is a signal for detecting a physical address on the hologram recording medium 1 detected based on the data reproduction signal. The spindle control signal is a signal for controlling the rotation of the spindle motor 2, and is a signal based on the address signal. The focus error signal is a signal for detecting a focus shift of the irradiation laser in the optical pickup 3, and the track error signal is a signal for detecting a track shift of the irradiation laser in the optical pickup 3. The focus error signal is generated by the astigmatism method or the like based on the return light output obtained by the light receiving element in the optical pickup 3, for example. The track error signal is generated by, for example, a push-pull method.

  Reference numeral 6 denotes a CPU (Central Processing Unit), which controls the entire apparatus based on a control program stored in a ROM (ROM: Read Only Memory) (not shown). In the present embodiment, the CPU 6 controls various servo operations related to information recording and reproduction operations on the hologram recording medium 1.

  The driver IC 7 amplifies the focusing drive signal, the tracking drive signal, and the spindle control signal input from the signal processing IC 5 to desired magnitudes, and supplies them to the focusing actuator, tracking actuator, and spindle motor 2, respectively. Further, the feed motor drive signal generated from the tracking drive signal is amplified to a desired magnitude and supplied to the feed motor 4.

  FIG. 2 is a cross-sectional structure diagram showing a cross-sectional structure of the hologram recording medium 1. In the figure, reference numeral 100 denotes a substrate having a concave (convex) portion formed in advance. On the substrate 100, a semi-transmissive film layer 101, a protective layer 102, a recording layer 103, and a protective layer 104 are stacked in this order, and the protective layer 104 is covered with the substrate 105. The recording layer 103 can be expected to have high reading (reproduction) efficiency, recording and erasing can be repeated, and there is no deterioration in characteristics due to the recording layer 103. Multiple recording is possible and high resolution can be expected. A single crystal or the like is used.

  The distance A between the concave (convex) portions is approximately 100 to 500 (μm) depending on the optical system, and the interval B between the convex (concave) portions is approximately 0.1 to 2 (μm) although it depends on the optical system. ) A flat area between the concave (convex) parts is the information recording area 106, and a concave (convex) part is the servo information area 107. Reference numerals 108 and 109 denote main surfaces of the hologram recording medium 1. The outer shape of the hologram recording medium 1 may be a disk type or a card type.

  FIG. 3 is a schematic configuration diagram showing a schematic configuration of the optical system 30 provided in the optical pickup 3. In the figure, reference numeral 301 denotes a laser serving as a light source. Reference numeral 302 denotes a lens such as a collimator lens, which converts light emitted from the laser 301 into parallel rays. A beam splitter 303 transmits and reflects light transmitted through the lens 302 in accordance with transmission / reflection characteristics. A polarizing beam splitter 304 transmits P-polarized light (vibration direction is parallel to the incident surface) and reflects S-polarized light (vibration direction is perpendicular to the incident surface).

  Reference numeral 305 denotes a half-wave plate that emits light by rotating the polarization plane of incident light. Reference numeral 306 denotes deflection means, which includes a beam splitter 306a and a deflection surface 306b. A spatial light modulator 307 adds two-dimensional data to the transmitted light. Reference numeral 308 denotes a half-wave plate. A composite polarization beam splitter 309 includes polarization beam splitters 309a and 309b. Reference numeral 310 denotes an objective lens (detection light irradiation means) that collects object light and detection light and irradiates the hologram recording medium 1.

  Reference numeral 312 denotes a hologram element (wavefront conversion means) that simultaneously has a condensing function and an effect of spatially randomizing the phase and amplitude of the light beam. Details of the hologram element 312 will be described later. Reference numeral 313 denotes a condensing lens having a condensing function. Reference numeral 314 denotes a two-dimensional photodetection array that detects two-dimensional data included in reflected light of reference light to which reproduction information is added during reproduction. Reference numeral 315 denotes a condenser lens. Reference numeral 316 denotes a cylindrical lens. A servo light receiving element 317 detects position information used for position control of the object light and the reference light based on the reflected light of the detection light for position detection.

  320 is an actuator having a function as the above-described focusing actuator and tracking actuator. The deviation between the object light and the reference light is detected as a focus error signal and a track error signal based on the output of the servo light receiving element 317, and the actuator 320 performs a focusing drive signal and tracking based on the focus error signal and the track error signal. Based on the drive signal, the objective lens 310 and the hologram element 312 are moved in the focusing control direction (normal direction of the recording surface; vertical direction in FIG. 3) or the tracking control direction (in-plane direction orthogonal to the concave portion or convex portion of the recording surface). The left and right directions in FIG. 50 is object light, 51 is reference light, and 52 is detection light.

  The optical system 30 is an optical system based on a peristortic multiplexing system (described later) in which the trajectory of the reference light 51 rotates around the optical axis of the object light 50 so as to draw a cone. In the peritropic multiplexing method, by rotating the reference beam 51, a plurality of pieces of information can be multiplexed and recorded in the same recording area. The deflection unit 306, the objective lens 310, and the hologram element 312 rotate as a unit (rotation irradiation unit). For example, a stepping motor or the like can be used as the rotating means for this purpose.

  Next, the irradiation method of the object light, the reference light, and the detection light according to the present embodiment will be described. The object light is light to which information to be recorded on the hologram recording medium 1 is added. The reference light is irradiated on the information recording area 106 of the hologram recording medium 1 together with the object light at the time of recording information to generate interference fringes, and is irradiated on the information recording area 106 of the hologram recording medium 1 at the time of reading information. This light is diffracted light including reproduction information. The detection light is applied to the servo information area 107 of the hologram recording medium 1 and is used for detecting position information for position control of the object light and the reference light.

  Light emitted from the laser 301 (for example, S-polarized light) is converted into parallel light by the lens 302 and passes through the beam splitter 303. This light is reflected by the polarization beam splitter 304, converted to P-polarized light by the half-wave plate 305, and separated into transmitted light and reflected light by the beam splitter 306a. The light that has passed through the beam splitter 306 a is given two-dimensional data by the spatial light modulator 307, passes through the half-wave plate 308 in the P-polarized state, passes through the polarizing beam splitter 309 a, and passes through the objective lens 310. The object light 50 is condensed near the recording layer 103 in the information recording area 106 of the hologram recording medium 1. The transmission / reflection characteristics of the beam splitter 303 are, for example, 80% transmittance and 20% reflectance (non-polarized light), and the transmission / reflection characteristics of the beam splitter 306a are, for example, 50% transmittance and 50% reflectance (non-polarized light). is there.

  The light reflected by the beam splitter 306a is reflected by the deflecting surface 306b, and the hologram element 312 makes the phase and amplitude of the light beam spatially random, and enters the information recording area 106 where the object light 50 is irradiated. The reference light 51 is irradiated from the same main surface 108 side as the object light 50. In the recording layer 103 of the information recording area 106 of the hologram recording medium 1, the object beam 50 and the reference beam 51 interfere with each other, and interference fringes are volume-recorded. The amount of the object light 50 can be arbitrarily set by rotating the half-wave plate 308 around the optical axis. The amount of light may be selected so that the interference fringe pattern is clearest.

  When reproducing the recorded information, the half-wave plate 308 is rotated around the optical axis so that only the S-polarized light component is emitted from the half-wave plate 308. All of this light is reflected by the polarization beam splitter 309a and is not irradiated onto the hologram recording medium 1. As a result, only the P-polarized reference light 51 is applied to the recording layer 103 of the information recording area 106 where the interference fringes are recorded. This light is diffracted by the recording layer 103 and reflected by the semi-transmissive film layer 101. The reflected light passes through the objective lens 310 and the polarization beam splitter 309a.

  The light that has passed through the beam splitter 306a is converted to S-polarized light by the half-wave plate 308 and passes through the spatial light modulator 307 and the beam splitter 306a. This light is again converted to P-polarized light by the half-wave plate 305, passes through the polarizing beam splitter 304 and the condenser lens 313, and enters the two-dimensional light detection array 314. The two-dimensional photodetection array 314 reproduces two-dimensional data based on this light. When reproducing the recorded data, it is desirable that the spatial light modulator 307 be in a totally transmissive state or removed from the optical path.

  Further, part of the light emitted from the laser 301 and converted into parallel light by the lens 302 is reflected by the beam splitter 303. The S-polarized light is reflected by the polarization beam splitters 309 b and 309 a and enters the objective lens 310. The optical axis of the light incident on the objective lens 310 is set so as to be shifted by a minute angle from the optical axis of the object light 50 by reflection optical components (beam splitter 303, polarization beam splitters 309b and 309a, etc.) in the optical path. . The light condensed by the objective lens 310 enters the servo information area 107 of the hologram recording medium 1 as the detection light 52.

  The light modulated by the concave (convex) portion formed in the servo information area 107 is reflected by the semi-transmissive film layer 101 and is made into substantially parallel light again by the objective lens 310. This light is reflected by the polarization beam splitters 309 a and 309 b and passes through the beam splitter 303. Subsequently, this light is collected by a condenser lens 315, given astigmatism by a cylindrical lens 316, and enters a servo light receiving element 317. The servo light receiving element 317 detects position information based on this light.

  Next, positioning control of the irradiation position of the object light 50 and the reference light 51 in the present embodiment will be described. When the hologram recording medium 1 is a portable medium, the positions of the focusing control direction and the tracking control direction of the object light 50 and the reference light 51 irradiated on the recording layer 103 are not determined between the recording and reproducing apparatuses. Further, even in the same recording apparatus, when the hologram recording medium 1 is rotated (moved) for recording / reproduction, the focusing control direction of the object light 50 and the reference light 51 irradiated on the recording layer 103 due to surface deflection and eccentricity. In addition, the position in the tracking control direction is shifted.

  In order to prevent this, the tracking control direction and the focusing control are performed based on the reflected light of the detection light 52 irradiated to the servo information area 107 by the track detection method, the focus detection method, and the address detection method that are generally used for optical disks. A positional deviation in the direction and a position in the in-plane direction orthogonal to the tracking control direction are detected. The tracking control direction can be detected by, for example, the push-pull method, and the focusing control direction can be detected by the astigmatism method, and the in-plane direction orthogonal to the tracking control direction is detected based on the address information configured in the servo information area 107. can do.

  A focus error signal and a track error signal are generated by the signal processing IC 5 based on the return light of the detection light 52 detected by the servo light receiving element 317, and a focusing drive signal and tracking are generated based on the focus error signal and the track error signal. A drive signal is generated. The actuator 320 controls the movement of the objective lens 310 and the hologram element 312 in the focusing control direction or the tracking control direction based on the focusing drive signal and the tracking drive signal. Thereby, the object beam 51 and the reference beam 52 can be irradiated to a desired position. At this time, when the movement amount is large, it is necessary to control the movement of the condenser lens 313 in the optical axis direction and the direction orthogonal to the optical axis in order to accurately form an image on the two-dimensional light detection array 314. There is also.

  The entire optical system 30 is controlled to move in the focusing control direction or the tracking control direction based on the focusing drive signal and the tracking drive signal generated based on the return light of the detection light 52 detected by the servo light receiving element 317. May be. Thereby, the object light 51 and the reference light 52 can be irradiated to a desired position. When the entire optical system 30 is moved, the image on the two-dimensional light detection array 314 is not shifted.

  Next, a multiplexing method when data is multiplexed and recorded on the hologram recording medium 1 will be described. There are several types of multiplexing systems. Here, the peritropic multiplexing system and the shift multiplexing system will be described. The peritropic multiplexing method is a method in which a plurality of data is multiplexed and recorded in the same recording area while rotating the reference light within a conical surface having the hologram recording medium 1 as a vertex. The shift multiplexing method is a method of recording data while shifting a data recording area by a minute amount.

  Hereinafter, the peritropic multiplexing method will be described with reference to FIG. For example, when two patterns of different two-dimensional data (for example, data a to data d) are recorded at the same location, four types of different two-dimensional data are sequentially given to the object light. In the figure, 31a to 31d are object lights corresponding to data a to data d, respectively. Reference numerals 32a to 32d are reference lights corresponding to the object lights 31a to 31d, respectively.

  The reference beams 32a to 32d are recorded at the point where the optical axis 40 of the objective lens 10 for irradiating the object beam and the recording layer of the hologram recording medium 1 intersect (data is recorded as interference fringes around this point). ) As the apex of the cone. When recording the data a, the object light 31a and the reference light 32a are caused to interfere with each other, the interference fringes are recorded on the recording layer, and when the data b is recorded, the object light 31b and the reference light 32b are caused to interfere with each other. When recording the interference fringes on the recording layer and recording the data c, the object light 31c and the reference light 32c are caused to interfere with each other, the interference fringes are recorded on the recording layer, and the data d is recorded. It is only necessary to cause the light 31d and the reference light 32d to interfere with each other to record interference fringes on the recording layer.

  When data is reproduced, diffracted light corresponding to the data a can be obtained by irradiating the data recording position with the reference light 32a, and if the light is converted into an electrical signal by a two-dimensional photodetector or the like, the original is obtained. 2D data is obtained. Similarly, by irradiating the recording layer with the reference light used at the time of data recording, diffracted light corresponding to each data can be obtained.

  The following [Equation 1] is an expression representing the Bragg angle in peritropic multiplexing. In [Expression 1], L is the thickness of the recording layer of the hologram recording medium 1, λ is the wavelength of light, θr is the incident angle of the reference light to the hologram recording medium 1, and θs is the hologram recording medium 1. Is the angle of incidence of the object light on. For example, if L = 200 (μm), λ = 500 (nm), θr = 50 (deg), and θs = 0 (deg), Δψ to 5.3 (deg). In the case of this condition, the reference light is rotated around the optical axis 40 every 6 °, and 60 (360/6) multiplexing can be performed in the same region.

  Hereinafter, the shift multiplexing method will be described with reference to FIG. The shift multiplexing method is a method of recording data while shifting a data recording area by a minute amount. In order to perform shift multiplexing, it is necessary to make the reference light a spherical wave or make the phase, amplitude, traveling direction, etc. of the reference wave spatially random. It is assumed that each area in which data is recorded in the shift multiplexing method overlaps with other areas.

  A certain area is irradiated with object light 33a (object light corresponding to data a), the object light 33a and reference light 34a are caused to interfere, and a hologram 35a is recorded. Subsequently, after the recording position is shifted by a small amount, the object light 33b (object light corresponding to the data b) is irradiated, the object light 33b and the reference light 34b are caused to interfere, and the hologram 35b is recorded. Thereafter, the data is multiplexed and recorded while sequentially shifting the recording position. When reproducing data, if the position of the recorded hologram 35a is irradiated with the reference light 34a, diffracted light can be obtained only from the hologram 35a recorded at that position by the reference light 34a. Dimension data can be reproduced.

  A combination of the above two types of multiplexing methods, the peritrophic multiplexing method and the shift multiplexing method, enables a large number of multiplexed recordings and realizes a recording / reproducing apparatus capable of recording a large amount of data. can do. When performing data recording by the shift multiplexing method, for example, the spot of the object beam and the reference beam may be shifted in the in-plane direction of the recording surface by the tracking actuator described above.

  Next, a method for making the reference light a non-planar wave will be described. In order to perform shift multiplexing, it is necessary to make the wavefront of the reference light completely random in the light beam or to make it a spherical wave. This is because if there is a correlation between the wavefronts of the reference light before and after the shift of the object light and the reference light, the data recorded in the overlapped area before and after the shift are reproduced simultaneously.

  Hereinafter, a method for converting the reference light into a non-plane wave will be described with reference to FIGS. FIG. 4 shows an example of means for spatially and randomly converting the phase, amplitude, and traveling direction of the reference light. In the figure, reference numeral 321 denotes a wavefront conversion element having the above function. A structure for converting the wavefront is formed in the region 321a of the wavefront conversion element 321 that is irradiated with the object light and the reference light.

  The black B, gray G, and white W regions irregularly arranged in the region 321a represent optically different regions. The light transmitted (reflected) through the region 321a is converted into light having a spatially random phase. Or each area | region of black B, gray G, and white W represents the area | region from which the transmittance | permeability (reflectance) differs. The light transmitted (reflected) through this region is converted into light having a spatially random amplitude (intensity). Or each area | region of black B, gray G, and white W represents the area | region formed so that an incident angle (reflection angle) may differ with respect to the transmitted (reflected) light. The light transmitted (reflected) through this region is converted into light whose traveling direction is spatially random.

  In this example, each example has been described in three stages of black, gray, and white. However, there are many stages, and the smaller each area, the higher the degree of randomness, such as the phase and amplitude of light, and so on. Crosstalk during playback is reduced.

  FIG. 5 shows an example in which the phase, amplitude (intensity), or traveling direction of the reference light is spatially randomly converted by using a hologram, or the reference light is converted from a plane wave to a spherical wave. In FIG. 5, reference numeral 62 denotes a light beam transmitted (reflected) through the wavefront conversion element 321 or light transmitted through the lens. This light beam 62 is light of a spherical wave or light whose phase, amplitude (intensity), or traveling direction is spatially randomly converted. Interference fringes generated by causing the light beam 62 to interfere with the reference light 61 as object light are recorded, and a hologram 63 is produced in the hologram element 312 in FIG. When the hologram 63 is irradiated with the reference light 64 as shown in FIG. 6, a light beam 65 equivalent to the light beam 62 and having the opposite traveling direction is generated (phase conjugate reproduction).

  In order to combine the functions of the hologram, an optical element that spatially and randomly converts the phase and amplitude (intensity) of object light and a light beam 62 that is transmitted (reflected) through a lens are used. Interference fringes generated by causing the light beam 62 and the reference light 61 to interfere with each other are recorded to produce a hologram 63. When the hologram 63 is irradiated with the reference light 64, a composite random light beam 65 equivalent to the light beam 62 and having the opposite traveling direction is generated (phase conjugate reproduction). When the hologram element 312 is mass-produced, it can be mass-produced inexpensively with good reproducibility by transferring the hologram pattern to a mold and further transferring it to glass, resin or the like.

  In the above-described embodiment, the object light and the reference light are irradiated from the same main surface side of the hologram recording medium 1, but both are irradiated from different main surface sides. Also good.

  3 does not need to be a prism, and as shown in FIG. 7, flat mirrors 306c and 306d may be opposed to each other and may be integrally held by a holder.

  As described above, according to the present embodiment, different recording / reproducing operations are performed by detecting position information using detection light and controlling the irradiation position of object light and reference light on the recording medium based on the position information. Even if there is surface wobbling or eccentricity between apparatuses or recording media, information can be recorded or reproduced at an appropriate recording position in the state of optimal irradiation light on the recording surface. Further, since the control area is irradiated with the detection light without irradiating the recording area, high-quality recording and reproduction can be performed. Furthermore, servo signals can be detected regardless of the moving speed of the recording medium, and multiple recording of data can be performed without increasing the size of the apparatus.

  Further, by providing means for rotating the reference light around the optical axis of the object light, data recording and reproduction can be performed by the peritropic multiplexing method. Further, by providing wavefront conversion means (hologram element 312) for converting the wavefront of the reference light into a non-planar wave, data recording and reproduction by the shift multiplexing method can be performed. Therefore, it is possible to realize an optical system that records and reproduces a large amount of data.

  Further, by condensing the detection light for detecting the position of the object light with the same objective lens as the object lens for condensing the object light, it is possible to reduce the size and cost of the apparatus. Further, by making the optical axis of the object light incident on the same objective lens non-parallel to the optical axis of the detection light, the object light and the detection light can be irradiated to different areas on the recording surface. Furthermore, by using the same light source as the light source for the object light, the reference light, and the detection light, it is possible to reduce the size and cost of the apparatus.

  In the present embodiment, the object light and the reference light are P-polarized light, and the detection light is S-polarized light. Thus, by making the polarization directions of the object light, the reference light, and the detection light orthogonal, the detection light does not become noise of the object light during information recording. Furthermore, since the reproduction light and the detection light can be separated by the polarization optical element, the detection light that becomes a noise component of the reproduction light at the time of reproduction can be cut.

  In addition, by providing a concave or convex portion in the servo information area of the recording medium, when the detection light is irradiated to that area, the light is diffracted and a push-pull signal can be detected. Can be detected.

  Further, by integrally moving the objective lens and the wavefront conversion means in the focusing control direction, the object light and the reference light can be controlled to the optimum positions in the direction perpendicular to the recording surface of the recording medium. Further, by integrally controlling the objective lens and the wavefront conversion means in the tracking control direction, the object light and the reference light can be controlled to the optimum positions in the direction parallel to the recording surface of the recording medium.

  Further, the whole optical system including the objective lens, the rotation irradiation unit, the wavefront conversion unit, and the like is integrally moved and controlled in the focusing control direction, so that the object light and the reference light can be obtained in the direction perpendicular to the recording surface of the recording medium. It can be controlled to an optimal position. In this case, the image on the two-dimensional photodetector is not blurred with this control. Furthermore, the entire optical system including the objective lens, rotation irradiation means, and wavefront conversion means is integrally moved and controlled in the tracking control direction, so that object light and reference light are optimized in a direction parallel to the recording surface of the recording medium. It is possible to control the position. In this case, the image on the two-dimensional photodetector does not shift with this control.

  In addition, the data recording capacity can be increased by multiplex recording data by combining the peritropic multiplexing method and the shift multiplexing method.

  As described above, the embodiments of the present invention have been described in detail with reference to the drawings, but the specific configuration is not limited to these embodiments, and includes design changes and the like within a scope not departing from the gist of the present invention. It is.

It is a block diagram which shows the structure of the recording / reproducing apparatus by one Embodiment of this invention. FIG. 2 is a cross-sectional structure diagram showing a cross-sectional structure of a hologram recording medium 1 in the same embodiment. It is a schematic block diagram which shows schematic structure of the optical system 30 with which the optical pick-up 3 by the same embodiment is provided. FIG. 4 is a reference diagram illustrating an example of means for spatially and randomly converting the phase, amplitude, and traveling direction of reference light in the embodiment. FIG. 6 is a reference diagram illustrating a method for producing a hologram 63 that spatially and randomly converts the phase, amplitude, or traveling direction of reference light in the embodiment. FIG. 6 is a reference diagram showing a method of generating random light 65 in which the phase, amplitude, or traveling direction of reference light is spatially random in the embodiment. It is a schematic block diagram which shows the other structural example of the deflection | deviation means 306 by the embodiment. It is a reference figure for demonstrating the principle of the data recording by a peritropic multiplexing system. It is a reference figure for demonstrating the principle of the data recording by a shift multiplexing system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Hologram recording medium, 2 ... Spindle motor, 3 ... Optical pick-up, 4 ... Feed motor, 5 ... Signal processing IC, 6 ... CPU, 7 ... Driver IC, 30 ... Optical system, 31a, 31b, 31c, 31d, 33a, 33b, 50 ... Object light, 32a, 32b, 32c, 32d, 34a, 34b, 51, 61, 64 ... Reference light, 35a 35b, 63 ... hologram, 40 ... optical axis, 52 ... detection light, 62, 65 ... luminous flux, 100, 105 ... substrate, 101 ... transmission film layer, 102, 104 ... Protective layer, 103 ... Recording layer, 106 ... Information recording area, 107 ... Servo information area, 108, 109 ... Main surface, 301 ... Laser, 302 ... Lens, 303, 306a ... BEAMS Ritter, 304, 309a, 309b ... Polarizing beam splitter, 305, 308 ... Half-wave plate, 306 ... Deflection means, 306b ... Deflection surface, 306c, 306d ... Flat plate mirror, 307 ... Spatial light modulator, 309 ... Compound polarization beam splitter, 310 ... Objective lens, 312 ... Hologram element, 313, 315 ... Condensing lens, 314 ... Two-dimensional light detection Array, 316 ... Cylindrical lens, 317 ... Light receiving element for servo, 320 ... Actuator, 321 ... Wavefront conversion element, 321a ... area.

Claims (10)

Based on the diffracted light of the reference light, irradiating the optical recording medium with object light and reference light, recording the information of the object light on the optical recording medium as interference fringes, irradiating the interference light with the reference light In a recording / reproducing apparatus for reproducing information,
Object light irradiating means for condensing the object light by an objective lens and condensing the object light on an information recording area on the optical recording medium on which information is recorded;
Rotating irradiation means for rotating the reference light around the optical axis of the objective lens and irradiating the information recording area;
Wavefront converting means for converting the wavefront of the reference light into a non-planar wave;
Detection light irradiation means for irradiating a servo information area different from the information recording area on the optical recording medium with detection light for position detection;
Control means for controlling the irradiation position of the object light and the reference light based on the detection result of the position by the detection light;
A recording / reproducing apparatus comprising: The detection light irradiating means condenses the detection light on a servo information area different from the information recording area on the optical recording medium by the objective lens that condenses the object light,
The recording / reproducing apparatus according to claim 1, wherein an optical axis of the object light incident on the objective lens and an optical axis of the detection light are non-parallel.   The recording / reproducing apparatus according to claim 1, wherein the object light, the reference light, and the detection light are generated by the same light source.   4. The recording / reproducing apparatus according to claim 1, wherein a polarization direction of the object light and the reference light and a polarization direction of the detection light are orthogonal to each other.   The recording / reproducing apparatus according to any one of claims 1 to 4, wherein a concave portion or a convex portion is formed in the servo information area.   The control means further moves the object lens and the wavefront conversion means integrally in the normal direction of the main surface of the optical recording medium based on the detection result of the position by the detection light. 6. The recording / reproducing apparatus according to claim 1, wherein an irradiation position of the reference light is controlled.   The control means further moves the object light and the wavefront conversion means integrally in a direction parallel to the main surface of the optical recording medium based on the position detection result by the detection light. 6. The recording / reproducing apparatus according to claim 1, wherein an irradiation position of the reference light is controlled.   The control means further includes an entire optical system including the objective lens, the object light irradiation means, the rotation irradiation means, the wavefront conversion means, and the detection light irradiation means based on the position detection result by the detection light. The irradiation position of the object light and the reference light is controlled by moving integrally in the normal direction of the main surface of the optical recording medium. The recording / reproducing apparatus described in 1.   The control means further includes an entire optical system including the objective lens, the object light irradiation means, the rotation irradiation means, the wavefront conversion means, and the detection light irradiation means based on the position detection result by the detection light. 6. The irradiation position of the object light and the reference light is controlled by integrally moving in a direction parallel to the main surface of the optical recording medium. The recording / reproducing apparatus described in 1. 10. The peritropic multiplexing method and the shift multiplexing method are combined as a multiple recording method for recording a plurality of information on the object light in the same area of the optical recording medium. The recording / reproducing apparatus according to the section.

Images