JP3582291B2 - Optical pickup device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical pickup device for recording or reproducing information by light.
[0002]
[Prior art]
In recent years, the technology of recording and reproducing information using light has made remarkable progress. Optical devices dedicated to reading out pre-recorded audio, text and image data, so-called compact discs, CD-ROMs, laser discs, etc., each of which is at a mature stage in both basic technology and market . In recent years, the range of use for secondary storage devices of computers, rewritable filing devices, and the like has been increasing. In addition, high-numerical-aperture objective lenses and the large-capacity optical disk drive using short-wavelength lasers, which will play a key role in the future market, are now in full swing with the aim of technological improvements, market expansion, and market share acquisition. We are heading. What supports these technological developments is market demand, but it can be said that many peripheral technologies such as semiconductor laser technology, optical technology, medium technology, signal processing technology, and precision processing technology contribute greatly. In the future, with the development of technology and the expansion of the market scale, the optical disk device is expected to establish its position as a data storage device for images and character information.
[0003]
Also, there are optical disc standards that have their own characteristics. This stems from the demands on performance and the timing of technological advances, but the fact that many optical disc standards coexist, that is, sacrificing compatibility, is a matter of handling and expanding the market size. And it becomes minus. In particular, CDs (compact discs) and DVDs (digital versatile discs), each of which constitutes a large market scale at home and have an appearance similar to that of a 12 cm diameter disc, are directly optically compatible. DVD discs cannot be played on a CD player due to the lack of performance, and vice versa. This is due to the difference in the substrate thickness of the disc (1.2 mm for CD, 0.6 mm for DVD), the difference in the numerical aperture of the objective lens, the difference in the wavelength of the laser beam used, etc., in order to make the DVD higher in density than the CD. .
[0004]
There is a great demand in the market for one optical disc drive to be able to use two different standards of CD and DVD. Therefore, several methods for obtaining compatibility using an optical pickup device having an unprecedented special optical system have been proposed, and some of them are being put to practical use.
[0005]
Hereinafter, a device using a conventional CD / DVD compatible optical pickup device will be described with reference to the drawings. FIG. 9 illustrates an optical pickup device using a bifocal objective lens that can realize independent focal points for a CD and a DVD with a single objective lens using a hologram technique. In FIG. 1, a light beam emitted from a semiconductor laser 1 which is a light source is converted into a substantially parallel light beam by a collimator lens 2, passes through a prism 3, and is focused on a recording surface 6 of an optical disk 5 by an objective lens 4. In this case, a pattern of the hologram 7 having a function of condensing a light beam at a position different from the focal point determined by the original boundary surface shape is provided by separating a part of the incident light on a part of the incident surface of the objective lens 4. The luminous flux condensed by the hologram 7 is applied to the CD and DVD, and the luminous flux is condensed by the hologram 7 under the maximum aperture of the objective lens 4 for the DVD. Each is used for a thick CD. Further, the luminous flux reflected by each recording surface 6 receives the return light separating action of the prism 3, passes through the condenser lens 8 and the cylindrical lens 9, reaches the photodetector 10, reproduces recording, and reproduces a servo signal. Perform detection. The correction of the spherical aberration caused by the difference in the substrate thickness can be realized by the function of the hologram 7. However, the CD is over-specified in that a high numerical aperture and a short wavelength light beam are used. The aperture is narrowed to meet the specifications of CD playback. By using a bifocal objective lens based on the hologram technology, a CD and a DVD, which are originally optically incompatible, can be used with one pickup, that is, one drive device, as if they were apparently compatible. In addition, the number of parts can be basically handled without increasing the number of parts.
[0006]
Next, a technique for using optical disks having different substrate thicknesses by another method will be described with reference to FIG. In the figure, the configurations of the semiconductor laser, the optical prism, and the light detection unit are almost the same as those of the method using the bifocal objective lens described above. It has a mechanism for switching an independent dedicated objective lens corresponding to a disk, and is a method called a so-called twin objective lens system. As shown in the figure, a mechanism for taking in and out a first objective lens 12 corresponding to a thin optical disk substrate 11 and a second objective lens 14 corresponding to a thick optical disk 13 in a light beam is provided, and an objective lens support called a bobbin 15 is provided. Each objective lens is mounted on the housing. By rotating the bobbin 15 around the rotation axis 16, each objective lens can be easily switched. Compared with the bifocal system, the use of the dedicated objective lenses enables the signal quality to be ensured and the simple but stable operation to be realized. In addition, a reproduction signal having a high C / N ratio can be obtained regardless of the light use efficiency of the dedicated device. When the objective lens is switched, it is necessary to confirm the corresponding disk, the incident light flux of the objective lens, or the basic position with respect to the photodetector 10.
[0007]
Now, another method will be described with reference to FIG. This method is based on the optically most basic concept of inserting a correction plate 17 made of a parallel-plate dielectric into the gap between the objective lens 4 and the thin optical disk substrate 11, and as shown in FIG. In the case of reproduction, in order to optically correspond to that of the thick optical disk substrate 13, a correction plate 17 corresponding to the substrate thickness difference is inserted at the position shown in the figure, so that spherical aberration caused by the substrate thickness difference can be corrected. The correction plate 17 is removed when reproducing a CD having a large substrate thickness. Stable operation can be expected with almost no reduction in light use efficiency. In addition, in the case of a CD having a large substrate thickness and a relatively low recording density, it is necessary to insert an aperture limiting aperture 18 immediately before the entrance pupil of the objective lens 4 in order to prevent the luminous flux from being excessively narrowed. A removal / insertion mechanism (not shown) for this purpose is also installed. The operation of the light detection unit 10 is the same as the method described above.
[0008]
Next, two methods for obtaining compatibility by switching the effective numerical aperture of the objective lens will be described. First, the first method will be described with reference to FIG. In this figure, the limiting aperture plate 19 for switching the numerical aperture is inserted and removed just before the light enters the objective lens 4 or in the substantially parallel light beam. It is condensed on the recording surface 6 as a light spot with the same high numerical aperture. In this case, it corresponds to a high-density optical disk having a thin substrate 11. When this light beam is incident on a thick-type optical disc with a different substrate thickness, the focused spot is narrowed down to the diffraction limit due to the effect of spherical aberration proportional to the cube of the ray height caused by the increased substrate. It has a large adverse effect on the detection of a recording pit (not shown) and the tracking operation. When a limiting aperture plate 19 having an arbitrary aperture is inserted, the diameter of the light beam incident on the objective lens 4 is reduced, the effective numerical aperture is reduced, and the spot becomes larger in terms of diffraction theory. Is more dominant, and the light condensing performance of the spot can be greatly improved by restricting the component having a large ray height, that is, the outer peripheral portion of the light beam. It can detect the recording pits of the optical disk and realize tracking by a normal operation.
[0009]
Further, a second method based on aperture restriction will be described with reference to FIG. In the figure, a shutter mechanism 20 made of a liquid crystal is provided at an arbitrary position in a substantially parallel light beam, and the aperture is released and restricted by turning on and off electrically (voltage) for control. Things. The use of the liquid crystal shutter mechanism 20 does not require a mechanical operation, and realizes operation stability and high-speed switching. Other mechanisms and operations are in accordance with the above-described first method.
[0010]
[Problems to be solved by the invention]
However, in the compatible optical pickup device corresponding to CDs and DVDs having different substrate thicknesses of the optical disk described above, a bifocal objective lens is used. In the compatible optical pickup device, limited light intensity from a laser is separated by a hologram element in a forward optical system. Therefore, the light use efficiency is reduced, and the return light intensity to the photodetector is also reduced due to the same effect in the return optical system, so that the C / N ratio is generally reduced as compared with other methods. In addition, unnecessary stray light due to the diffraction action of the hologram element is generated in a relatively large amount, and there arises a problem that a countermeasure for removing the stray light and a complicated light detection unit are caused. Since an optical recording apparatus having a data recording function requires a light spot having a higher light intensity than that for reproduction only, it is difficult to use a method using a bifocal objective lens having a relatively low light use efficiency. Absent. In addition, it is considered that the hologram element is configured directly on the objective lens or externally. However, in both cases, the manufacturing cost increases, and in the case of integration, the life of the mold is generally short and the unit price of the objective lens is low. Will be expensive.
[0011]
Next, in the case of an optical pickup device using a dedicated twin objective by rotating a bobbin, the use efficiency of light and the like are more advantageous than the bifocal objective method, but the pickup is required to hold two objective lenses. Since the mechanism and the electrical configuration of the movable part are large and heavy and complicated, and it is necessary to secure a space for holding the rotating shaft in the lower part, a thin optical pickup / drive is generally required by the market. The device is difficult to implement. Further, at the time of lens switching, it is necessary to confirm and hold a basic position with respect to the incident light beam or the photodetector, which complicates the configuration and operation.
[0012]
In addition, a method of inserting a dielectric plate made of a parallel flat plate for correcting spherical aberration at the time of reproducing a DVD with a thin substrate and removing the CD in the case of a CD with a thick substrate requires a mechanism for removing and inserting the plate. The insertion greatly limits the working distance of the objective lens, and causes problems such as a crash due to the runout of the disk and a limitation of the operating range. Also, the numerical aperture of the DVD-compatible objective lens is about 0.15 larger than that of the CD-compatible one, and the laser wavelength of the light source is short. This adversely affects the reproduction operation. In order to avoid this, it is necessary to insert an aperture limiting aperture just before or immediately after the objective lens only at the time of CD operation, and it is necessary to effectively reduce the numerical aperture to correspond to CD, and switch with an increase in the number of parts A mechanism is required, which complicates the configuration.
[0013]
Further, in the first method based on the aperture restriction, the two must be driven integrally in order to correct the deviation between the center of the aperture of the plate and the optical axis of the objective lens, and the configuration including the switching mechanism is difficult. . In the method using the second liquid crystal shutter, the shutter mechanism is relatively large, and if it is mounted on an optical pickup unit for accessing an arbitrary position on an optical disk, the weight becomes heavy and the access performance is reduced. Therefore, the manufacturing cost is relatively high.
[0014]
SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems. The present invention solves the above-mentioned problems by comparing the difference in the substrate thickness and the track between an optical disk such as a DVD using a thin substrate thickness and a conventional optical disk such as a CD having a standard (relatively thick) thickness. It is an object of the present invention to provide an optical pickup device capable of more effectively avoiding instability of operation caused by a difference in pitch and the like and complexity of a mechanism.
[0015]
[Means for Solving the Problems]
In the optical pickup device of the present invention, laser beams emitted from two semiconductor lasers are converted into two substantially parallel light beams by two collimator lenses, and the laser beams emitted from the collimator lenses are combined and separated. The means are superimposed and emitted in the same direction and projected onto an optical recording medium via an objective lens, and the combining / separating means couples the reflected return light of the two laser lights from the optical recording medium to the two collimator lenses. The reflected return light is separated in the direction, and the separated reflected return light is separated from the optical system from the semiconductor laser to the combining / separating means by a light separating means and detected by a photodetector. According to the present invention, a device capable of recording and reproducing information on and from two types of optical recording media without having a mechanical drive portion and without attenuating the signal level can be configured compactly.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
The invention according to claim 1 of the present invention is directed to a conductor laser that emits laser light, two collimator lenses that convert laser light emitted from the two semiconductor lasers into two substantially parallel light beams, respectively, The laser beams of substantially parallel light beams emitted from the collimator lenses are superimposed and emitted in the same direction, and the reflected return light of the two laser beams emitted in the same direction is separated in the direction of the two collimator lenses. A combining / separating unit that emits the laser beams from the combining / separating unit, and an objective lens that converges two laser beams emitted from the combining / separating unit in the same direction on a recording surface of an optical recording medium; Return light separating means for separating reflected return light of two laser lights from the recording surface which are separately emitted from the optical system from the semiconductor laser to the combining / separating means , And an optical detector having a function of photoelectric conversion of the return light separated by the separating meansThe two semiconductor lasers are arranged very close to each other, emit light beams at different wavelengths λ1 and λ2, and the emission directions are defined at an angle θ of π / 20 <θ <π / 4.With such a configuration, the optical paths of two semiconductor lasers are overlapped, and an optical pickup device having two functions can be compactly realized by one objective lens. Things.Further, it has an effect of making the configuration of the light source portion compact.
[0017]
In the invention according to claim 2 of the present invention, the synthesizing / separating means is formed of an optical semi-permeable film, and the two laser beams incident on the optical semi-permeable film are reflected or transmitted to overlap in the same direction. The optical pickup device according to claim 1, which emits light or separates light in different directions to emit light from the two semiconductor lasers. Combining / separating means formed of an optical semi-permeable membrane based on the difference in wavelength between two laser beams selectively performs reflection or transmission so that two laser beams or reflected return light can be superimposed and separated. Having.
[0018]
According to a third aspect of the present invention, the synthesizing / separating means is formed of a diffraction grating, and the two laser beams incident on the diffraction grating are reflected or transmitted so as to be superposed in the same direction and emitted, or to be emitted in different directions. 2. The optical pickup device according to claim 1, wherein the wavelengths of the two laser beams emitted from the two semiconductor lasers are different from each other. The combining / separating means formed by the diffraction grating selectively reflects or transmits based on the difference between the two laser beams or the reflected return light so that the two laser beams or the reflected return light can be overlapped and separated.
[0019]
According to a fourth aspect of the present invention, the combining / separating means includes a prism having a plurality of entrance / exit surfaces, and an optical semi-permeable membrane or a diffraction grating is provided inside or outside the prism. The optical pickup device according to claim 1, wherein the optical semi-permeable membrane or the diffraction grating is accurately and stably arranged inside or outside the prism. Thus, there is an effect that the combining / separating operation by the combining / separating means can be performed more reliably.
[0021]
Claims of the invention5In the invention described in (2), the optical semi-permeable film is formed of a wavelength selection film composed of a dielectric multilayer film, and reflects the light beam of wavelength λ1 of the two light beams and transmits the light beam of wavelength λ2. Has the effect of separating
[0022]
Claims of the invention6According to the invention described in the above, at least one of the two incident surfaces of the prism has an anamorphic function of changing the magnification of only one arbitrary direction of the cross section of the incident light beam, so that the elliptical cross-sectional light beam from the semiconductor laser is A product that approaches a circular cross-section luminous flux that improves the light collection quality
Having
[0023]
Claims of the invention7According to the invention described in (1), since the return light separating means is constituted by a hologram element utilizing a diffraction effect of light, the peripheral portion of the photodetector can be configured more compactly.
[0024]
Claims of the invention8The two semiconductor lasers, the return light separating means, and the photodetector are integrally formed in one package module.,The peripheral portion of the photodetector can be configured compactly, and has the effect of simplifying the optical and mechanical adjustments.
[0025]
Claims of the invention9The invention described in (1) is characterized in that the optical semi-permeable film is provided with an aperture for restricting a light beam of a peripheral portion having a high light height of the wavelength λ2 on a surface on the semiconductor laser side emitting the wavelength λ2. Has the function of suppressing the spherical aberration of the condensed spot on the recording surface.
[0026]
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Embodiment 1)
FIG. 1 is a configuration diagram of an optical system of an optical pickup device described in Embodiment 1 of the present invention. In the figure, an optical pickup device according to an embodiment of the present invention includes two semiconductor lasers that independently emit visible light λ1 and infrared light λ2 having different wavelengths, respectively, and light emitted from the two semiconductor lasers 21A and 21B. Collimator lenses 22A and 22B for converting the light beams of the visible light λ1 and the infrared light λ2 into two substantially parallel light beams, respectively, and the visible light λ1 and the infrared light respectively emitted from the two collimator lenses 22A and 22B. This prism 23 is formed by installing a prism 23 composed of one block having two incident surfaces 23A and 23B on which a substantially parallel light beam of λ2 is incident, and an optical semi-permeable film made of a dielectric multilayer film or the like inside the prism 23. The wavelength selection film 24 which superimposes and emits substantially two light beams of the two visible lights λ1 and infrared lights λ2 by the reflection and transmission actions of the optical semi-permeable film, An objective lens 27 for converging the light beam emitted from the exit surface 25 of the optical system 23 onto the recording surface of the optical disk, and returning the reflected light from the recording surface of the optical disk to the optical path from the semiconductor lasers 21A and 21B to the optical recording surface. And hologram elements 28A and 28B serving as return light separating means for separating the light, and photodetectors 29A and 29B having a function of photoelectrically converting the return light separated by the hologram elements 28A and 28B.
[0027]
First, the optical action by the light beam of wavelength λ1 will be described. The light beam emitted from the semiconductor laser 21A is incident on the dedicated collimator lens 22A while being diffused, is converted into a substantially parallel light beam, and is incident on the incident surface 23A of the prism 23. The angle (incident angle) β of the incident surface with respect to the incident light beam can take an arbitrary angle in the range of π / 4π <β <π / 2. In the first embodiment, the light enters the prism 23 at an angle of about 65 degrees. By doing so, it is generally possible to improve the cross-sectional intensity of a semiconductor laser having an elliptical intensity distribution to a circular distribution, to narrow down a light spot due to diffraction, and to improve light use efficiency. Can be. Such an optical form is called an anamorphic optical system, and can change the intensity distribution of the light beam cross section in only one arbitrary direction.
[0028]
The wavelength selection film 24 formed inside the prism 23 transmits visible light and reflects infrared light. The wavelength selection film 24 transmits the visible light λ 1, exits from the exit surface 25 of the prism 23, and further folds the light beam toward the front side of the paper by the flip-up mirror 26 and emits the light beam toward the objective lens 27. The incident light is focused on the recording surface (not shown) of the optical disk by the converging action of the objective lens 27. This condensed spot is imaged as a minute spot having a physical limit defined by the numerical aperture of the objective lens 27 called a so-called diffraction limit and the incident wavelength, and pit information of the optical disc recorded on the recording surface at high density. Can be picked up.
[0029]
Further, the reflected light including the pit reproduction information reflected on the recording surface and servo signals for focusing, tracking, and the like is converted again by the objective lens 27 into substantially parallel light. In addition, a tracking control in the optical axis direction to always follow a spot (not shown) with a spot, which will be described later, that is, a focusing operation for canceling the vertical shake of the optical disk substrate, and a tracking operation in the radial direction of the disk, It contains the optical information necessary for the tracking operation for canceling the deviation of the recording pit train or the rotation axis of the track and the disk, and the pit information as described above. Further, the light flux enters the prism 23 again and is transmitted through the wavelength selection film 24 in the same manner as described above, and the light beam passes through the prism 23 and returns to the collimator lens 22A again. Further, while receiving the converging function of the collimator lens 22A, the hologram element 28A provided between the semiconductor laser 21A and the collimator lens 22A undergoes a return light separating action due to diffraction, and a dedicated light installed near the semiconductor laser 21A. The light enters the photodetector 29A. The photodetector 29A is composed of a plurality of photodetection sensor areas (not shown), and converts the behavior of the incident light beam into a signal obtained by photoelectrically converting the intensity of incident light from each sensor into a current or voltage electric signal. A focus error signal, a tracking error signal, and a reproduction signal can be obtained by performing the calculation. In the first embodiment, the spot size method is used for detecting the focusing error signal, and the push-pull method using one beam or the phase difference method is used for detecting the tracking error signal.
[0030]
Here, this error signal detection will be described in detail with reference to FIGS. First, as for the focusing operation, a focusing error signal is detected by the knife edge method as described above, and the reflected return light from the recording surface is reflected by a photodetector by the return light separating action by diffraction of the hologram as shown in FIG. Diffracted to 29A. FIG. 3 shows an enlarged view of the light receiving portion of the photodetector 29A and a change accompanying the defocusing of the imaging pattern of the return light. FIG. 3B shows a pattern when the recording surface of the optical disc is focused. In the figure, a focus error signal FE is obtained by a differential output of the sum of the outputs of the central two light receiving units B and C of the four rectangular light receiving units and the sum of the outputs of the light receiving units A and D on both sides. Can be.
[0031]
That is, FE = (B + C)-(A + D). In the case of focusing, adjustment is made in advance so that the differential output becomes zero. Further, if defocusing is performed in a direction in which the distance between the objective lens 27 and the recording surface is increased, the spot pattern on the photodetector becomes small as shown in FIG. 7A, and the focus error signal FE increases as a positive value. On the other hand, when approaching the opposite, as shown in FIG. 3C, the output increases as a negative value. The direction of defocusing can be known from the sign of the error signal output, and the defocus amount can be known from the absolute value of the output, and this signal is finally fed back to the objective lens actuator (not shown) to follow the focus direction. Can be realized.
[0032]
FIG. 4 shows a characteristic curve of the error signal with respect to the defocus amount. The figure is generally called an S-shaped signal curve of focus or simply an S-shape from the shape, and the characteristics of the focus error signal can be visually recognized from this figure.
[0033]
Now, the tracking operation will be described. In FIG. 3, the pattern of the incident spot of the photodetector is formed by the 0th-order diffracted light diffracted by the pit row on the recording surface and the ± 1st-order diffracted lights condensed on both sides thereof. The ± first-order diffracted light partially overlaps the zero-order diffracted light on the photodetector 29A. (The hatched portions) The overlapping portions interfere with each other and are lower than the intensity of the 0th-order diffracted light. When the light spot on the recording surface of the optical disk is located along the center of the recording pit row (on-track state / not shown), the light intensity of the overlapping portions is balanced with each other, and the light spot is recorded. When deviating from the pit row, the balance of the ± 1st-order diffracted light is lost, that is, the balance of the light intensity of the overlapping portion is lost. Therefore, the tracking error signal TE can be obtained from the differential signal of TE = (A + B)-(C + D) at the center dividing line of the four light receiving sections of the photodetector. As in the case of focusing, this error signal is finally fed back to the tracking actuator, so that the tracking operation in the track direction can be realized. FIG. 5 shows a characteristic curve of the displacement amount of the light spot with respect to the recording pit row and the track error signal. As shown in the figure, the shape of the track is generally called an S-shaped signal curve of the track, or simply S-shaped, and the track error signal can be visually recognized from the figure.
[0034]
Further, the operation of reproducing recorded pits recorded on the recording surface of the optical disc will be described. In the photodetector of FIG. 3, the reproduction signal RF can be obtained by the total output of the four light receiving units, that is, RF = A + B + C + D.
[0035]
The description related to the detection of the error signal of focusing and tracking and the detection of the reproduction signal of the recording pit has been described above. However, in the first embodiment of the present invention, the operation can be compactly performed by each of the above methods. However, the detection of each error signal is not limited to the above method.
[0036]
Next, the optical action of the infrared light flux and the wavelength λ2 will be described. In the figure, the divergent light beam emitted from the semiconductor laser 21B is converted into a substantially parallel light beam by the action of the collimator lens 22B in the same manner as before. Further, the same light beam that is incident from the incident surface 23B of the prism 23 that provides an anamorphic function and is infrared light is reflected by the function of the wavelength selection film 24. The light beam emitted from the emission surface 25 follows the light path of the visible light and propagates along an optical path overlapping both the center of the light beam, and is reflected by the flip-up mirror 26 toward the upper part of the sheet of paper. (Illustrated).
[0037]
Although not described above, the present optical disk has a substrate thickness of 1.2 mm such as a compact disk and a track pitch of 1.6 μm, and the optical disk described above has a substrate thickness of 0.6 mm and a track pitch of 0.74 μm. It corresponds to a high-density optical disk called DVD.
[0038]
Further, the reflected return light reflected on the recording surface of the optical disk returns to the objective lens 27 again, is converted into a substantially parallel light beam, enters the prism 23, is reflected by the same surface under the action of the wavelength selection film 24, and is reflected on the same surface. Out of the light incident surface 23B, and is incident on the second photodetector 29B by the hologram element 28B provided between the collimator lens 22B and the semiconductor laser 21B while receiving the convergence of the collimator lens 22B. Here, focusing, tracking, and reproduction light information are detected by an independent photodetector 29B by a detection method similar to that of the optical system using the wavelength λ1 of visible light described above.
[0039]
The objective lens 27 used in the first embodiment has a numerical aperture of 0.6 capable of reproducing high-density pits for DVD, and is considerably larger than that of CD. If the objective lens 27 is used as it is for a CD having a large substrate thickness, a component having a high ray height away from the optical axis of the objective lens 27 is significantly affected by spherical aberration due to an increase in the substrate thickness. Degrades the quality of the imaging spot. The quality of the imaged spot can be improved by cutting off the component having a high ray height, that is, the component around the light beam. For this purpose, an aperture 30 having an elliptical cross-section similar to a light beam capable of performing necessary light shielding is provided in a gap between the incident surface 23B of the prism 23 and the collimator lens 22B. Alternatively, it may be installed on the near side when viewed from the light source side of the wavelength λ2 of the wavelength selection film 24 inside the prism 23, or on the incident surface 23B.
[0040]
Although the numerical aperture of the objective lens 27 is effectively limited, the numerical aperture of the objective lens originally used for the CD is smaller than the objective lens for the DVD used in the first embodiment, and the light-collecting characteristics are improved. There is not much effect. By providing the aperture, the influence of spherical aberration can be significantly improved.
[0041]
Further, various optical signals detected by the photodetectors 29A or 29B are photoelectrically converted as described above, and then sent to a signal processing unit (not shown) to further reproduce information of the disk and follow the optical disk of the objective lens 27. The operation signal is fed back to the focus and tracking actuators for performing the operation, and is used to realize stable driving of the optical pickup.
[0042]
Now, the semiconductor laser 21A, the semiconductor laser 21B, the photodetector 29A, the photodetector 29B, the hologram element 28A, and the hologram element 28B are in a module form, as shown in FIG. . This module has already been optically and mechanically aligned before being mounted on the optical pickup device. By doing so, the assemblability during mass production of the optical pickup can be improved, This can be strengthened against a large positional deviation. Further, electrical parts such as the semiconductor lasers 21A and 21B and the photodetectors 29A and 29B can be arranged in a concentrated manner, which contributes to downsizing of the optical pickup device.
[0043]
(Embodiment 2)
Embodiment 2 of the present invention will be described with reference to FIG. In the above-described first embodiment, the method using the luminous flux bending by the two anamorphic surfaces and the prism having the wavelength selection film inside improves the light use efficiency or uses a collimator lens having a relatively short focal length. Although a compact optical system can be realized, the anamorphic surface is not always an essential component. The optical pickup device according to the second embodiment eliminates the anamorphic surface, superimposes the light beams from the two light sources through the wavelength selection film on the objective lens by the following configuration, and makes the two types of optical discs Each can be addressed.
[0044]
In FIG. 7, similarly to the first embodiment, light beams emitted from two mutually adjacent semiconductor lasers 31A and 31B having different wavelengths enter collimator lenses 32A and 32B corresponding to the light beams, respectively, and become substantially parallel light beams. After that, the light beam on the short wavelength side enters from the incident surface 33A, is bent by the internal reflection surface 34, passes through the wavelength selection film 35, and is bent by the flip-up mirror 36 to the front side of the paper surface, thereby condensing the objective lens 37. Upon receiving the light, it forms an image as a minute spot on a recording surface (not shown) of an optical disk having a relatively thin substrate, and is used for reading or writing recorded data. The configuration and operation relating to the processing of the reflected return light on the recording surface are the same as in the first embodiment, and will not be described here.
[0045]
Further, the light beam on the long wavelength side enters from the incident surface 33B, is propagated to the flip-up mirror 36 side by the reflection action of the wavelength selection film 35 formed immediately after, and is bent toward the front side of the paper as before, The light is condensed on the recording surface of the optical disk having a relatively thick substrate by the light condensing action of the objective lens 37. An aperture 38 having an effect of further suppressing spherical aberration is provided on the incident surface 33B.
[0046]
(Embodiment 3)
Embodiment 3 of the present invention will be described with reference to FIG. The optical pickup device according to the third embodiment includes semiconductor lasers 41A and 41B (corresponding to 21A and 21B), collimator lenses 42A and 42B (corresponding to 22A and 22B), and a prism 43 (23) as in the first embodiment. ), A wavelength selection film 44 (corresponding to 24), an objective lens 47 (corresponding to 27), hologram elements 48A and 48B (corresponding to 28A and 28B), and photodetectors 49A and 49B (corresponding to 29A and 29B). The wavelength selection film 44 is provided in common and has a different configuration and operation. The wavelength selection film 44 is formed by arranging a diffraction grating having a lattice constant d on the outer surface of the prism 43, and converts the visible light λ1 and the infrared light λ2 incident from the incident surfaces 43A and 43B of the prism 43. In this configuration, light is emitted at a diffraction angle corresponding to the wavelength.
[0047]
Next, the optical operation of the third embodiment based on the above configuration will be described. As in the first and second embodiments, visible light λ1 and infrared light λ2 are emitted from the semiconductor lasers 41A and 41B, and are emitted as substantially parallel light beams by the collimator lenses 42A and 42B. The visible light λ1 and the infrared light λ2 of the substantially parallel light flux enter from the incident surfaces 43A and 43B of the prism 43, and the incident visible light λ1 enters the wavelength selection film 44 of the diffraction grating at an angle i1 and a diffraction angle θ1. And the infrared light λ2 enters the wavelength selection film 44 of the diffraction grating at an angle i2 and is emitted at a diffraction angle θ2 (θ1 = θ2).
[0048]
That is, d (sini1−sinθ1) = m · λ1 for the visible light λ1, and d (sini2−sinθ2) = m · λ2 for the infrared light λ2. Here, m is the order of the diffracted light. The diffraction angle θ1 and the diffraction angle θ2 can be made equal by appropriately setting the lattice constant d, the incident angles i1 and i2, and the wavelengths λ1 and λ2. By making the diffraction angles θ1 and θ2 equal, the visible light λ1 and the infrared light λ2 can be superimposed and emitted in the same direction.
[0049]
After the superimposed visible light λ1 and infrared light λ2 are emitted from the prism 43, they operate and have the same effects as in the first and second embodiments.
[0050]
【The invention's effect】
As is clear from each of the above embodiments, according to the present invention, two light sources having different wavelengths are arranged very close to each other, and each of the light sources has an angle in the emission direction and is incident on each dedicated collimator lens. By reflecting or transmitting the wavelength selection film in the prism, the exit optical path from the prism is overlapped and made incident on the objective lens to perform recording reproduction or recording, and the reflected return light from the recording surface is reflected by the hologram element. By separating it into a detector and configuring the semiconductor laser, hologram element, and photodetector in an integrated module, it is possible to realize a light-up device that is compatible with two types of optical discs and that is more compact. It can realize the incorporation of equipment, reduction of power consumption, improvement of access speed, and the like.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an optical system of an optical pickup device described in Embodiment 1 of the present invention.
FIG. 2 is a partial view of an optical pickup device illustrating the first embodiment of the present invention;
FIG. 3 is a partial view of an optical pickup device illustrating the first embodiment of the present invention;
FIG. 4 is a diagram for explaining the operation of the optical pickup device according to the first embodiment of the present invention;
FIG. 5 is a diagram for explaining the operation of the optical pickup device according to the first embodiment of the present invention;
FIG. 6 is a partial view of an optical pickup device according to the first embodiment of the present invention.
FIG. 7 is a configuration diagram of an optical system of an optical pickup device according to a second embodiment of the present invention;
FIG. 8 is a configuration diagram of an optical system of an optical pickup device according to a third embodiment of the present invention;
FIG. 9 is a configuration diagram of an optical system illustrating a conventional optical pickup device.
FIG. 10 is a configuration diagram of an optical system illustrating a conventional optical pickup device.
FIG. 11 is a configuration diagram of an optical system illustrating a conventional optical pickup device.
FIG. 12 is a configuration diagram of an optical system illustrating a conventional optical pickup device.
FIG. 13 is a configuration diagram of an optical system illustrating a conventional optical pickup device.
[Explanation of symbols]
1,21A, 21B, 31A, 31B, 41A, 41B Semiconductor laser
2,22A, 22B, 32A, 32B, 42A, 42B Collimator lens
3,23,43 prism
4,27,37 objective lens
5 Optical disk
6 Recording surface
7 Hologram
8 Condensing lens
9 Cylindrical lens
10, 29A, 29B, 49A, 49B Photodetector
11 Thin optical disc substrate
12 First objective lens
13 Thick optical disc substrate
14 Second objective lens
15 Bobbin
17 Correction plate
18 Aperture limiting aperture
19 Restricted aperture plate
20 Shutter mechanism
24, 35, 44 Wavelength selective film
25 Exit surface
26,36 flip up mirror
28A, 28B, 48A, 48B hologram element
30,38 aperture
33A, 33B, 43A, 43B Incident surface
34 Internal reflective surface

Claims (9)

A conductor laser for emitting laser light, two collimator lenses for converting laser light emitted from the two semiconductor lasers into two substantially parallel light beams, and substantially parallel light beams emitted from the collimator lens, respectively Combining / separating means for superimposing the two laser beams and emitting the same in the same direction, and separating and returning the reflected return lights of the two laser beams emitted in the same direction toward the two collimator lenses; and An objective lens for converging two laser beams superimposed and emitted in the same direction from the separating means on the recording surface of the optical recording medium; Return light separating means for separating the reflected return light of the two laser beams from the optical system from the semiconductor laser to the combining / separating means, and separated by the separating means. And an optical detector having a function of photoelectric conversion of the return light was,
The two semiconductor lasers becomes disposed in close proximity to one another, injecting a light beam into different wavelengths .lambda.1, and λ2, respectively, that have been defined injection direction at an angle theta consisting π / 20 <θ <π / 4 from each other An optical pickup device, characterized in that: The synthesizing / separating means is formed of an optical semi-permeable film, and reflects or transmits two laser beams incident on the optical semi-permeable film and emits them in the same direction by superimposing them, or separates and emits them in different directions. The optical pickup device according to claim 1, wherein: The synthesizing / separating means is formed by a diffraction grating, and reflects or transmits two laser beams incident on the diffraction grating and emits them by overlapping in the same direction or by separating and emitting in different directions. The optical pickup device according to claim 1. 2. The optical pickup according to claim 1, wherein the combining / separating unit includes a prism having a plurality of entrance / exit surfaces, and an optical semi-permeable film or a diffraction grating is provided inside or outside the prism. apparatus. The optical semi-permeable film is formed of a wavelength selection film composed of a dielectric multilayer film, and has a function of reflecting a light beam of wavelength λ1 of the two light beams and transmitting a light beam of wavelength λ2. The optical pickup device according to claim 2 . At least one surface of the two incident-exit surface of the prism, any one of claims 4, 5, characterized in that it comprises an anamorphic action of zooming only any one direction of the incident beam cross-section the optical pickup device according to. The optical pickup device according to any one of claims 1 to 6, wherein the return light separating means includes a hologram element that utilizes a diffraction effect of light. The optical pickup according to any one of claims 1 to 7 , wherein the two semiconductor lasers, the return light separating unit, and the photodetector are integrally formed in one package module. apparatus. 5. The optical semi-permeable film further comprising an aperture for restricting a light beam of a peripheral part having a high light height of the wavelength [lambda] 2 on a surface on the side of the semiconductor laser emitting the wavelength [lambda] 2. 9. The optical pickup device according to any one of items 8 to 8 .

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