JP4625788B2 - Optical pickup and optical disc apparatus - Google Patents

Description

  The present invention relates to a technique for recording or reproducing an information signal of an optical disc.

  An optical disc device is an information recording / reproducing device characterized by non-contact, large capacity, high-speed access, and low-cost media. Utilizing these features, it can be used as a digital audio signal recording / reproducing device or as an external storage device of a computer. Has been.

  At present, optical discs are roughly classified into first and second discs having different specifications such as the oscillation wavelength used by the semiconductor laser and the substrate thickness of the optical disc. The first optical disk has a disk substrate thickness of 0.6 mm such as DVD, DVD-ROM, DVD-RAM, DVD-R, and DVD-RW, and the oscillation wavelength of the semiconductor laser optimum for recording and reproduction is about 660 nm. It is. The second optical disk has a disk substrate thickness of 1.2 mm such as CD, CD-ROM, CD-R, CD-RW, etc., and the oscillation wavelength of the semiconductor laser optimum for recording / reproduction is about 785 nm. For this reason, the optical pickup for DVD, which is the first optical disk, is mounted with a semiconductor laser having two oscillation wavelengths of about 785 nm and about 660 nm in consideration of compatibility with the already widely used CD-based second optical disk. Things have become mainstream.

  Hereinafter, for the sake of simplicity of explanation, various types of optical discs of the first specification having a disc substrate thickness of 0.6 mm are referred to as DVD-type optical discs, and those of various types of optical discs having the disc specification of 1.2 mm. This is called a CD-based optical disk, the first semiconductor laser with an oscillation wavelength of about 660 nm is called a DVD semiconductor laser, and the second semiconductor laser with an oscillation wavelength of about 785 nm is called a CD semiconductor laser.

  Below, using both drawings, recording is performed by using two conventional semiconductor lasers with different oscillation wavelengths and two beam splitters, using both information on two optical disks with different specifications such as substrate thickness. An optical pickup that can be reproduced will be described in detail.

  FIG. 4 is a schematic configuration diagram of an optical pickup according to an embodiment of the prior art, in which the DVD optical disc 1 and the CD optical disc 2 having different specifications such as substrate thickness are reproduced on the same diagram. It shows.

  The substrate thickness of the DVD optical disk 1 is 0.6 mm. The substrate thickness of the CD-based optical disk 2 is 1.2 mm. Actually, there are many other types of specifications for each optical disc, but for the sake of simplicity of explanation, a single-plate disc having only one recording surface is shown here.

  The oscillation wavelength of the DVD semiconductor laser 3 is approximately 660 nm, and the oscillation wavelength of the CD semiconductor laser 27 is approximately 785 nm. In general, the corresponding wavelength of the DVD optical disk 1 is the 650 nm band and the corresponding wavelength of the CD optical disk 2 is the 780 nm band. However, since the actual oscillation wavelength of the semiconductor laser varies, the design wavelength is set to the actual semiconductor. The actual condition is to match the center wavelength of the laser.

  First, the case of reproducing the DVD optical disk 1 will be described. The light beam emitted from the light emitting point 3a of the DVD semiconductor laser 3 is incident on the diffraction grating 50 and separated into a main light beam 51 and two sub light beams (not shown). The secondary light beam is used for tracking detection of the optical disk by the three-beam method or the differential push-pull method. In the drawing, for the sake of simplicity, only the ray path of the main light beam 51 is shown, and the ray path of the sub-light beam is omitted.

  In the conventional example, the semiconductor laser 3 is fixed to the optical pickup case 52 without adjustment. The diffraction grating 50 is a one-dimensional adjustment in the direction around the optical axis.

  After the light beam 51 is reflected by the dichroic half mirror film surface 53a of the dichroic half mirror 53 that is the second beam splitter, the light beam 51 passes through the dichroic half prism 54 that is the first beam splitter and the rising mirror 14 that is the reflection mirror. Then, the light is converted into a substantially parallel light beam 55 by the coupling lens 15 and reaches the objective lens 19.

  The dichroic half mirror film surface 54a also has spectral characteristics with a transmittance of about 100% and a reflectance of about 0% with respect to a light beam having a wavelength of about 660 nm of a DVD semiconductor laser. It should be noted that the transmittance and reflectance of the light beam 62 having a wavelength of about 785 nm of the CD semiconductor laser 2 have a spectral characteristic of about 50%.

  The objective lens 19 is integrally held by an actuator (not shown). By energizing a drive coil (not shown), a light beam can be focused on the information recording surface 1a of the DVD optical disk 1 to form a light spot. Is possible.

  The light beam 56 reflected from the DVD optical disk 1 follows the same optical path as that of the forward light, and passes through the objective lens 19, the coupling lens 15, and the rising mirror 14, and then the dichroic half serving as the first beam splitter. The light enters the dichroic half mirror film surface 54 a of the prism 54.

  The dichroic half mirror film surface 54a has a spectral characteristic with a transmittance of approximately 100% with respect to a light beam having a wavelength of approximately 660 nm, and therefore transmits approximately 100%. The light beam 57 transmitted through the dichroic half mirror film surface 54a is transmitted through the dichroic half film surface 53a of the dichroic half mirror 53, which is the second beam splitter, and then guided to the photodetector 24 through the detection lens 58. It has become.

  Therefore, the total light utilization efficiency of the two beam splitters in the DVD outward path is approximately 50%.

  Next, a case where the CD optical disk 2 is reproduced will be described. The light beam 59 emitted from the light emitting point 27a of the CD semiconductor laser 27 that emits light at a wavelength of about 785 nm is incident on the diffraction grating 60a of the auxiliary lens 60 and is separated into a main light beam 61 and two sub light beams (not shown). The The secondary light beam is used for tracking detection of the optical disk by the three-beam method or the differential push-pull method. In the drawing, for the sake of simplicity, only the light path of the main light beam 61 is shown, and the light path of the sub light beam is omitted.

  The light beam 61 passes through the convex spherical lens surface 60 b of the auxiliary lens 60 and becomes a light beam 62. The convex spherical lens surface 60b is formed for the purpose of shortening the optical path length and improving the light utilization efficiency. The auxiliary lens 60 has a diffraction grating 60a and a convex spherical lens surface 60b, and realizes the above two functions with one component.

  The CD semiconductor laser 27 is fixed to the case 52 of the optical pickup with an adhesive after adjusting the position in the direction perpendicular to the optical axis. The auxiliary lens 60 is configured to be fixed with an adhesive after adjusting the rotation in the optical axis direction and around the optical axis.

  The light beam 62 is reflected by the dichroic half mirror film surface 54a of the dichroic half prism 54, which is the first beam splitter, and then converted into a substantially parallel light beam 62 by the coupling lens 15 via the rising mirror 14. The objective lens 19 is reached.

  The objective lens 19 is integrally held by an actuator (not shown). By energizing a drive coil (not shown), a light beam can be focused on the information recording surface 2a of the CD optical disk 2 to form a light spot. Is possible.

  The light beam 63 reflected from the CD optical disk 2 follows the same optical path as that of the outward light, and passes through the objective lens 19, the coupling lens 15, and the rising mirror 14, and then the dichroic half serving as the first beam splitter. The light enters the dichroic half mirror film surface 54 a of the prism 54. Since the dichroic half mirror film surface 54a has a spectral characteristic of approximately 50% in both transmittance and reflectance with respect to the light beam having a wavelength of approximately 785 nm as described above, approximately 50% is reflected and approximately 50% is transmitted. To do. The light beam 64 that has passed through the dichroic half mirror film surface 54a passes through the dichroic half film 53a of the dichroic half mirror 53 that is the second beam splitter, and then is guided to the photodetector 24 through the detection lens 58. ing. The dichroic half mirror 53 is disposed at an angle of 45 ° with respect to the optical axis of the light beam 64. Further, the dichroic half mirror film surface 53a has a spectral characteristic of about 100% transmittance and about 0% reflectance with respect to the light beam 64 having a wavelength of about 785 nm of the semiconductor laser 2 for CD. Is transparent.

  Therefore, the combined light utilization efficiency of the two beam splitters in the CD system is approximately 50%.

  In the conventional example, the detection lens 58 is fixed to the case 52 of the optical pickup with an adhesive after adjusting the position in the optical axis direction.

    The photodetector 24 is fixed to the substrate 65, and is fixed to the case 52 of the optical pickup with an adhesive after adjusting the position in the direction perpendicular to the optical axis.

  As described above, in an optical pickup equipped with two semiconductor lasers having different oscillation wavelengths, a dichroic prism or a dichroic mirror is used as a beam splitter for synthesizing incident light from the two semiconductor lasers. In order to reduce the size of the optical pickup, it is necessary to dispose a beam splitter in the divergent light from the semiconductor laser. In a normal design, the incident angle of the light beam varies by about ± 6 to 7 °. However, since the transmission reflectance of the dichroic film depends on the incident angle, it is not possible to efficiently combine the incident light from the two semiconductor lasers. Further, in a dichroic film design with a small number of layers in order to obtain an inexpensive beam splitter, the transmission reflectance can obtain only a spectral characteristic that is moderate with respect to the wavelength. Usually, since the oscillation wavelength of the semiconductor laser has a variation of about ± 20 nm with respect to the center wavelength, it is impossible to efficiently synthesize incident light from the two semiconductor lasers with the gentle spectral characteristics as described above. Compared to the prism type, the mirror type has the possibility of practical dichroic film design, but in the case of a dichroic mirror, there is a problem that astigmatism occurs when divergent light is transmitted through a parallel plate. . Also, in the prism type, there is a possibility of practical dichroic film design if the incident angle to the dichroic film is smaller than 45 °, but it becomes a complicated prism shape. It becomes expensive compared with a prism.

  If the optical pickup only performs reproduction without recording, the beam splitter is not required to have a very high synthesis efficiency. However, an optical pickup for recording / reproducing requires a very high synthesis efficiency. In particular, it is necessary to improve the output optical power on the optical disk surface in order to achieve an optical disk rotation speed or linear speed higher than the standard speed by using an inexpensive high-power semiconductor laser. Required.

  However, when the incident angle of the light beam varies or the wavelength of the semiconductor laser varies as described above, the conventional beam splitter using the dichroic film efficiently absorbs the incident light from the two semiconductor lasers having different wavelengths. This has been a major obstacle to the practical use of an optical pickup that cannot be synthesized and can perform double speed recording at low cost. That is, in the conventional example, the total efficiency of the two beam splitters of the DVD-system outward path and the CD-system outbound path has been described as approximately 50%, but as described above, the conventional beam splitter using the dichroic film is actually approximately Only a light utilization efficiency of less than 50% can be obtained.

  Further, in an optical pickup that records and reproduces both a DVD optical disk and a CD optical disk, both a semiconductor laser for DVD and a semiconductor laser for CD require a semiconductor laser with high output optical power. However, the maximum optical power of a high-power semiconductor laser that is currently available at a low cost is approximately 150 mW for a CD semiconductor laser, whereas it is as small as approximately 70 mW for a DVD semiconductor laser. This is because the development period of the high-power DVD semiconductor laser is relatively short compared to the development period of the high-power CD semiconductor laser. Therefore, the optical pickup for recording and reproducing both the DVD optical disk and the CD optical disk is more suitable when the short wavelength DVD semiconductor laser is used than when the long wavelength CD semiconductor laser is used. Two beam splitter configurations with higher light utilization efficiency should be required. However, in the conventional optical pickup, consideration is given to a technique for making the light utilization efficiency of the DVD system higher than that of the CD system. There wasn't.

  Also, in the conventional optical pickup configuration, the return light to the semiconductor laser has a component in the polarization direction that matches the polarization direction of the light emitted from the semiconductor laser, which may affect the oscillation mode of the semiconductor laser. . In this case, there may occur a problem that the optical power output is lowered or the optical power output fluctuates with respect to the same current input. Since the optical power output is relatively low at the time of reproduction, the power output can be kept substantially constant without any practical problem by auto power control in which the optical power is monitored and feedback-controlled. However, if the maximum optical power output decreases during recording, the power output cannot be kept stable and constant even if auto power control is used. Furthermore, since an overcurrent exceeding the maximum rated current is input, the semiconductor laser may be deteriorated or destroyed.

  As a means for making the polarization direction of the return light to the semiconductor laser orthogonal to the polarization direction of the light emitted from the semiconductor laser, a technique using a quarter wavelength plate is known. Since it is necessary to use a normal quarter-wave plate that matches the wavelength of each semiconductor laser, it is necessary to arrange the quarter-wave plate in front of the beam splitter that synthesizes the incident light from the two semiconductor lasers. In this case, the light beam that has been circularly polarized by the quarter-wave plate passes through the beam splitter and the rising mirror. The beam splitter and the rising mirror are composed of a dielectric multilayer film. Generally, when a light beam is transmitted or reflected through the dielectric multilayer film, a phase difference of polarization occurs, so that circularly polarized light changes to elliptically polarized light. For this reason, the polarization direction of the return light to the semiconductor laser cannot be made completely orthogonal to the polarization direction of the outgoing light from the semiconductor laser. Therefore, the return light to the semiconductor laser generates a component in the polarization direction that matches the polarization direction of the light emitted from the semiconductor laser, and the problem of return light as described above occurs.

  Also, polycarbonate (PC) is used as the substrate material for the optical disk. Although this material is excellent in environmental resistance, it is a material having relatively large birefringence, that is, a phase difference of polarized light. Thus, when the birefringence of the optical disk is large, the reflected light from the optical disk changes from the original polarized light to the elliptically polarized light even when the incident light to the optical disk is linearly polarized light or circularly polarized light. In general, the transmission reflectance of a beam splitter differs between P-polarized light and S-polarized light. The P-polarized light transmittance is larger than the S-polarized light transmittance, and the S-polarized light transmittance is larger than the P-polarized light reflectance. For example, in an optical pickup designed so that the polarization component incident on the photodetector after passing through the beam splitter is only P-polarized light, if the birefringence of the optical disk is large, the P-polarized component decreases and the S-polarized component increases. Therefore, the transmittance decreases as a whole. On the other hand, in an optical pickup designed so that the polarization component incident on the photodetector after passing through the beam splitter is only S-polarized light, if the birefringence of the optical disk is large, the S-polarized component decreases and the P-polarized component is reduced. As a result, the transmittance increases as a whole. In either case, the transmittance varies according to the birefringence phase difference of the optical disc. Here, since the phase difference of birefringence is proportional to the substrate thickness of the optical disk, the phase difference of birefringence is twice as large for a CD with a thickness of 1.2 mm as compared with a DVD with a thickness of 0.6 mm. large.

  In a CD-type optical disk having a large birefringence, the P-polarized component and the S-polarized component incident on the beam splitter largely fluctuate as described above, so that the fluctuation of the optical power incident on the photodetector via the beam splitter varies. However, in the conventional optical pickup, no consideration has been given to the technology for mitigating this power fluctuation.

  Further, in the configuration including the front light monitor detector used for auto power control of the first semiconductor laser and the second semiconductor laser, it is necessary to use two front light monitor photodetectors corresponding to the two conventional semiconductor lasers. was there. In addition, in order to guide the light beam to the front light monitor photodetector, it is transmitted or reflected through the beam splitter with varying light utilization efficiency, so that stable auto power control cannot be obtained.

  Accordingly, an object of the present invention is to synthesize two light beams from two semiconductor lasers more efficiently even when the incident angle of the light beam to the beam splitter varies or the oscillation wavelength of the semiconductor laser varies. To provide an optical pickup and an optical disc apparatus having a beam splitter configuration.

  Another object of the present invention is to provide two beam splitter configurations with higher light utilization efficiency when a short wavelength DVD semiconductor laser is used than when a long wavelength CD semiconductor laser is used. An optical pickup and an optical disc apparatus are provided.

  The object of the present invention is that the polarization direction of the return light to the semiconductor laser is either in the case of using a long wavelength CD semiconductor laser or in the case of using a short wavelength DVD semiconductor laser. An object of the present invention is to provide an optical pickup and an optical disc apparatus configured to be orthogonal to the polarization direction of light emitted from a semiconductor laser.

  In addition, the object of the present invention is that the light incident on the photodetector by the birefringence of the optical disk substrate is longer when the long wavelength CD semiconductor laser is used than when the short wavelength DVD semiconductor laser is used. It is an object to provide an optical pickup and an optical disc apparatus with less power fluctuation.

  Another object of the present invention is to provide a stable auto power with one front light monitor photodetector in a configuration including a front light monitor photodetector used for auto power control of the first semiconductor laser and the second semiconductor laser. It is an object to provide an optical pickup and an optical disc apparatus capable of obtaining control.

The above object can be achieved, for example, by the invention described in the claims.

According to the present invention, it is possible to efficiently synthesize light beams from a plurality of semiconductor lasers.

  Hereinafter, the configuration and operation of an optical pickup as a first embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of an optical pickup according to an embodiment of the present invention, and shows a state in which a DVD-type optical disc 1 and a CD-type optical disc 2 which are optical discs having different specifications are recorded and reproduced. It is shown repeatedly.

  The substrate thickness of the DVD optical disk 1 is 0.6 mm. The substrate thickness of the CD-based optical disk 2 is 1.2 mm. Actually, there are many other types of specifications for each optical disc, but for the sake of simplicity of explanation, a single-plate disc having only one recording surface is shown here.

  The corresponding wavelength of the DVD semiconductor laser 3 is approximately 660 nm, whereas the corresponding wavelength of the CD semiconductor laser 27 is approximately 785 nm. In general, the corresponding wavelength of the DVD optical disk 1 is the 650 nm band and the corresponding wavelength of the CD optical disk 2 is the 780 nm band. However, since the actual semiconductor laser wavelength varies, the design wavelength is set to the actual semiconductor laser. The actual condition is to match the center wavelength.

  First, the case where the DVD optical disk 1 is recorded and reproduced will be described. The horizontally polarized light beam 4 emitted from the light emitting point 3a of the DVD semiconductor laser 3 that emits light at a wavelength of about 660 nm passes through the auxiliary lens 5 and is a composite optical system having a half-wave plate function and a diffraction grating function. Incident on the element 6.

  The convex spherical lens surface 5a of the auxiliary lens 5 is formed for the purpose of shortening the optical path length and improving the light utilization efficiency.

  The composite optical element 6 has a configuration in which a half-wave plate 6a is sandwiched and bonded between a glass substrate 6b and a diffraction grating 6c. The horizontally polarized light beam 4 emits a vertically polarized light beam 7 by the action of the half-wave plate 6a. Further, due to the action of the diffraction grating 6c, the main light beam 7 and two sub light beams (not shown) are separated. The secondary light beam is used for tracking detection of the optical disk by the three-beam method or the differential push-pull method. In the figure, for the sake of simplicity, only the path of the light beam of the main light beam 7 is shown, and the path of the light beam of the sub light beam is omitted.

  The composite optical element 6 including the half-wave plate 6a and the diffraction grating 6c is integrated with the auxiliary lens 5 that can be rotationally adjusted. Thereby, the optical axis angle of the half-wave plate 6a can be accurately set by adjusting the grating angle of the diffraction grating 6c that generates the three beams used for tracking detection by adjusting the rotation of the auxiliary lens 5. It becomes possible. As a result, the horizontally polarized light beam 4 can be accurately converted into a vertically polarized light beam 7.

  The adjustment of the auxiliary lens 5 is only rotational adjustment, not the optical axis direction adjustment. Instead, the optical axis direction adjustment is performed by front-rear adjustment of the semiconductor laser 3 for DVD. Accordingly, it is not necessary to provide a large adjustment margin for adjusting the auxiliary lens 5, an assembly configuration that restricts the movement in the front-rear direction is possible, and there is an effect that the displacement of components due to a change with time does not occur.

  Further, the adjustment of the DVD semiconductor laser 3 is performed only in the front-rear direction, and is not adjusted in the direction orthogonal to the optical axis. As a result, it is not necessary to provide a large adjustment margin for adjusting the semiconductor laser 3 for DVD, and an assembly configuration that restricts the movement in the direction orthogonal to the optical axis is possible. There is.

  Further, the DVD semiconductor laser 3 is attached to a metal holder 8 with good heat conduction for covering in the horizontal direction, and the intensity center of the light beam 4 with respect to the metal case 9 with good heat conduction of the optical pickup. After adjusting the tilt so that is aligned with the optical axis, the adhesive is fixed. The holder 8 is only for one-dimensional adjustment only in the horizontal direction. Accordingly, it is not necessary to provide a large adjustment margin for adjusting the holder 8, and an assembly configuration that restricts movements other than the horizontal tilt is possible, and there is an effect that there is no occurrence of component displacement due to changes over time.

  In the conventional adjustment, the semiconductor laser is two-dimensionally adjusted in the direction orthogonal to the optical axis, and the auxiliary lens is two-dimensionally adjusted in the optical axis direction and the rotational direction. For this reason, it is necessary to provide a large adjustment margin for adjusting each of the two adjustment points, and there is a problem that the relative position between the semiconductor laser and the auxiliary lens cannot be set precisely. Since each adjustment is limited to only one dimension, there is an effect that there is no problem as described above.

  In this embodiment, the heat generated by the DVD semiconductor laser 3 is efficiently radiated to the case 9 of the metal optical pickup having good heat conduction through the metal holder 8 having good heat conduction. The temperature rise of the DVD semiconductor laser 3 can be prevented.

  Next, the vertically polarized light beam 7 is reflected by the polarization beam splitter film surface 10a of the polarization beam splitter prism 10 which is the first beam splitter to become a vertically polarized light beam 11. A polarization beam splitter, also called PBS, is an optical element that efficiently reflects S-polarized light and efficiently transmits P-polarized light. Since the vertically polarized light beam 7 is S-polarized with respect to the polarizing beam splitter film surface 10a, the light use efficiency of the light beam 11 which is reflected light can be made very high.

  In this embodiment, the polarization beam splitter film surface 10a has a dichroic film characteristic that efficiently reflects short-wavelength light and efficiently transmits long-wavelength light. FIG. 2 shows the spectral transmittance characteristics of the polarizing beam splitter film surface 10a. The spectral reflectance characteristic is a characteristic obtained by subtracting the spectral transmittance characteristic from 100%. Since the light beam 7 is short wavelength light emitted from the semiconductor laser 3 for DVD, the light utilization efficiency of the light beam 11 which is reflected light can be made very high. The polarizing beam splitter film surface 10a having both dichroic film characteristics and PBS film characteristics was able to reflect light more efficiently even when the incident angle of the light beam varied or the oscillation wavelength of the DVD semiconductor laser 3 varied.

  In the present embodiment, the half-wave plate 6a is disposed in the optical path from the DVD semiconductor laser 3 as the first semiconductor laser to the polarizing beam splitter prism 10 as the first beam splitter. The horizontally polarized light beam emitted from the first semiconductor laser can be converted into the vertically polarized light and incident on the first beam splitter, and the light utilization efficiency of the light beam 11 that is reflected light is very high. It was possible to produce a higher effect.

  The vertically polarized light beam 11 is incident on a beam splitter mirror 12 which is a second beam splitter. The light is reflected by the beam splitter film surface 12 a on the surface of the beam splitter mirror 12 to become a vertically polarized light beam 13.

  The beam splitter mirror 12 was disposed at an angle of 30 ° with respect to the optical axis of the light beam 11. Thus, by arranging at an angle of 30 ° smaller than 45 °, it is possible to design a spectral characteristic that brings the P-polarized light transmittance and S-polarized light transmittance of the beam splitter mirror 12 closer as described below.

  Now, the film design of the beam splitter film surface 12a will be described in detail. FIG. 3 shows the spectral transmittance characteristics of the beam splitter film surface 12a. The spectral reflectance characteristic is a characteristic obtained by subtracting the spectral transmittance characteristic from 100%. The P-polarized light transmittance of the beam splitter film surface 12a was designed to be about 10% with respect to the wavelength of about 660 nm of the DVD semiconductor laser 3. In general, the S-polarized light transmittance is smaller than the P-polarized light transmittance, but the film design is devised so that the decrease in the S-polarized light transmittance is minimized. However, the film was designed with a dielectric multilayer film with little light absorption. According to the absorption film and the metal film, it is possible to make the P-polarized light transmittance and the S-polarized light transmittance closer, but there is a problem that the light use efficiency is lowered because the absorption film is accompanied by light absorption. Neither was adopted due to problems in environmental resistance such as corrosion. As a result of this film design, the S-polarized light transmittance of the beam splitter film surface 12a was about 5% lower than the P-polarized light transmittance by about 5%. Accordingly, the S-polarized reflectance of the beam splitter film surface 12a was approximately 95%, and the P-polarized reflectance was approximately 90%.

  Since the vertically polarized light beam 11 is S-polarized with respect to the beam splitter film surface 12a, the reflected vertically polarized light beam 13 has a light utilization efficiency of approximately 95%. The light utilization efficiency of reflection of the polarizing beam splitter prism 10 as the first beam splitter is approximately 100%, and the light utilization efficiency of reflection of the beam splitter mirror 12 as the second beam splitter is approximately 95%. The light utilization efficiency of the DVD forward path by the beam splitter obtained by combining the beam splitter and the second beam splitter is approximately 95%, and a very high light utilization efficiency required for an optical pickup for recording and reproduction can be obtained. As a result, the output optical power on the optical disk surface can be improved, and an inexpensive high-power semiconductor laser can be used to achieve a double speed that is higher than the standard speed of the rotation speed or linear speed of the optical disk.

  The light beam 13 is converted into a substantially parallel light beam 16 by a coupling lens 15 via a rising mirror 14 that is a reflection mirror, and is incident on a broadband quarter-wave plate 17. The broadband quarter-wave plate 17 is disposed between the beam splitter mirror 12, which is the second beam splitter, and the DVD optical disc 1 or the CD optical disc 2, and has a wavelength of about 660 nm and a wavelength of about 785 nm. It is devised so as to act as a quarter-wave plate for light of any wavelength in any wavelength. The vertically polarized light beam 16 becomes a clockwise circularly polarized light beam 18 by the polarization action of the broadband quarter-wave plate 17.

  The light beam 18 reaches the DVD optical disk 1 through the objective lens 19.

  For simplicity of explanation, the lower part shows a top view and the upper part shows a front view with a two-dot chain line 14a of the rising mirror 14 as a boundary.

  The objective lens 19 is integrally held by an actuator (not shown). By energizing a drive coil (not shown), a light beam can be focused on the information recording surface 1a of the DVD optical disk 1 to form a light spot. Is possible.

  The clockwise circularly polarized light beam 18 reflects from the DVD optical disk 1 and becomes a counterclockwise circularly polarized light beam 20 this time. The counterclockwise circularly polarized light beam 20 travels in the reverse optical path similar to the forward light and enters the broadband quarter-wave plate 17 through the objective lens 19. The counterclockwise circularly polarized light beam 20 is now a horizontally polarized light beam 21 due to the polarization action of the broadband quarter-wave plate 17.

  The light beam 21 is incident on the beam splitter film surface 12 a on the surface of the beam splitter mirror 12, which is the first beam splitter, via the coupling lens 15 and the rising mirror 14. As described above, the beam splitter film surface 12a has a P-polarized light transmittance of about 10%, an S-polarized light transmittance of about 5%, a P-polarized light reflectance of about 90%, and an S-polarized light with respect to a light beam having a wavelength of about 660 nm. It has a spectral characteristic with a reflectance of approximately 95%. Since the horizontally polarized light beam 21 is P-polarized with respect to the beam splitter film surface 12a, approximately 10% is transmitted and approximately 90% is reflected.

  The horizontally polarized light beam 22 transmitted through the beam splitter film surface 12a is guided to the photodetector 24 through the detection lens 23.

  In this embodiment, the detection lens 23 is fixed to the optical pickup case 9 without adjustment. This makes it possible to precisely set the relative position and angle between the detection lens 23 and the case 9, and it is not necessary to provide a large adjustment margin for adjusting the case 9 and the detection lens 23. There is an effect that the parts do not shift due to.

  Further, the photodetector 24 is fixed to the substrate 25, and the position of the photodetector 24 is adjusted with respect to the case 9 of the optical pickup, and then the optical detector 24 is bonded and fixed. The substrate 25 performs a total three-dimensional adjustment in the two-dimensional direction that is perpendicular to the optical axis and the optical axis direction by using a three-dimensional adjustment jig (not shown) so that the adhesive 26 is solidified after the adjustment is completed. did. In the conventional adjustment, the detection lens is one-dimensional adjustment in the optical axis direction, and the photodetector is two-dimensional adjustment in the direction perpendicular to the optical axis. For this reason, there has been an advantage in the prior art that adjustment is possible with a relatively simple adjustment means without the need for a three-dimensional adjustment jig. However, since there are two adjustment points, a large adjustment margin is required for each adjustment. There is a problem that the absolute position of the detection lens cannot be set precisely. In the present embodiment, although a three-dimensional adjustment jig is required, there is an effect that there is no problem as described above. Conventionally, the components to be adjusted are two points, that is, the detection lens and the photodetector, but in this embodiment, the component to be adjusted is one point on the substrate 25, and the number of components to be adjusted is reduced by one point. I was able to.

  Next, a case where the CD-type optical disc 2 is recorded and reproduced will be described. The horizontally polarized light beam 28 emitted from the light emitting point 27 a of the CD semiconductor laser 27 that emits light at a wavelength of about 785 nm passes through the auxiliary lens 29 and enters the diffraction grating 30.

  The convex spherical lens surface 29a of the auxiliary lens 29 is formed for the purpose of shortening the optical path length and improving the light utilization efficiency.

  The horizontally polarized light beam 28 is separated into a main light beam 31 and two sub light beams (not shown) by the action of the diffraction grating 30. The secondary light beam is used for tracking detection of an optical disk by a three-beam method or a differential push-pull method. In the figure, for the sake of simplicity of explanation, only the light beam path of the main light beam 31 is shown, and the light beam path of the sub light beam is omitted.

  The diffraction grating 30 has a structure in which it is integrated with an auxiliary lens 29 that can be adjusted in the optical axis direction by bonding.

  The adjustment of the auxiliary lens 29 is only the adjustment in the longitudinal direction of the optical axis, and the rotation is not adjusted. Accordingly, it is not necessary to provide a large adjustment margin for adjusting the auxiliary lens 29, and an assembly configuration that restricts the movement in the rotational direction is possible, and there is an effect that no component deviation due to a change with time occurs.

  Further, the CD semiconductor laser 27, the metal holder 32 having good heat conductivity for heating the CD semiconductor laser 27, and the auxiliary lens 29 are integrally attached to the metal holder 33 having good heat conductivity. . The holder 33 performs two-dimensional adjustment in the direction orthogonal to the optical axis and three-dimensional adjustment of rotation adjustment on the metal case 9 with good heat conduction of the optical pickup using an adjustment jig (not shown). The holder 33 is not adjusted in the optical axis direction. Instead, the CD semiconductor laser 27 is adjusted with respect to the holder 32 in the optical axis direction.

  Further, in this embodiment, the heat generated by the CD semiconductor laser 27 passes through the metal holder 32 with good heat conduction and the metal holder 33 with good heat conduction. Therefore, the temperature rise of the CD semiconductor laser 27 can be prevented.

  Next, the horizontally polarized light beam 31 passes through the polarization beam splitter film surface 10a of the polarization beam splitter prism 10 which is the first beam splitter, and becomes a horizontally polarized light beam 34. As described above, the polarization beam splitter is also called PBS, and is an optical element that efficiently reflects S-polarized light and efficiently transmits P-polarized light. Since the light beam 31 in the horizontal direction is P-polarized with respect to the polarizing beam splitter film surface 10a, the light use efficiency of the light beam 34 that is transmitted light can be made very high.

  Further, in this embodiment, as described above, the polarization beam splitter film surface 10a has a dichroic film characteristic that reflects short wavelength light and transmits long wavelength light. Since the light beam 31 is long-wavelength light emitted from the CD semiconductor laser 27, the light utilization efficiency of the light beam 34, which is transmitted light, can be greatly increased. The polarizing beam splitter film surface 10a having both the dichroic film characteristics and the polarizing beam splitter film characteristics was able to transmit light more efficiently even when the incident angle of the light beam varied or the wavelength of the semiconductor laser varied.

  The horizontally polarized light beam 34 enters the beam splitter mirror 12 which is the second beam splitter. The light is reflected by the beam splitter film surface 12 a on the surface of the beam splitter mirror 12 to become a horizontally polarized light beam 35.

  The beam splitter mirror 12 was disposed at an angle of 30 ° with respect to the optical axis of the light beam 34. Thus, by arranging at an angle of 30 ° smaller than 45 °, it is possible to design a spectral characteristic that brings the P-polarized light transmittance and S-polarized light transmittance of the beam splitter mirror 12 closer as described below.

  Now, the film design of the beam splitter film surface 12a will be described in detail. The S-polarized light transmittance of the beam splitter film surface 12a is designed to be about 10% with respect to the wavelength of about 785 nm of the CD semiconductor laser 27. In general, the P-polarized light transmittance is larger than the S-polarized light transmittance, but the increase in the P-polarized light transmittance is minimized by devising the film design. However, the film was designed with a dielectric multilayer film with little light absorption. According to the absorption film or the metal film, it is possible to make the S-polarized light transmittance and the P-polarized light transmittance closer to each other, but there is a problem that the light use efficiency is lowered because the absorption film involves light absorption. Neither was adopted due to problems in environmental resistance such as corrosion. As a result of this film design, the P-polarized light transmittance of the beam splitter film surface 12a was approximately 18%, which is approximately 8% higher than the S-polarized light transmittance. Therefore, the P-polarized reflectance of the beam splitter film surface 12a was approximately 82%, and the S-polarized reflectance was approximately 90%.

  Since the horizontally polarized light beam 34 is P-polarized with respect to the beam splitter film surface 12a, the reflected horizontally polarized light beam 35 has a light utilization efficiency of approximately 82%. The light utilization efficiency of reflection of the polarizing beam splitter prism 10 as the first beam splitter is about 100%, and the light utilization efficiency of reflection of the beam splitter mirror 12 as the second beam splitter is about 82%. The light utilization efficiency of the CD forward path by the beam splitter in which the beam splitter and the second beam splitter are combined is approximately 82%, so that a very high light utilization efficiency required for an optical pickup for recording and reproduction can be obtained. As a result, the output optical power on the optical disk surface can be improved, and an inexpensive high-power semiconductor laser can be used to achieve a double speed that is higher than the standard speed of the rotation speed or linear speed of the optical disk.

  The light beam 35 is converted into a substantially parallel light beam 36 by the coupling lens 15 via the rising mirror 14 and is incident on the broadband quarter-wave plate 17. The broadband quarter-wave plate 17 is devised so as to act as a quarter-wave plate for light having a wavelength of approximately 660 nm and light having a wavelength of approximately 785 nm at any wavelength. It has been done. The horizontally polarized light beam 36 becomes a counterclockwise circularly polarized light beam 37 by the polarization action of the broadband quarter-wave plate 17.

  The light beam 37 reaches the CD optical disk 2 through the objective lens 19.

  The objective lens 19 is integrally held by an actuator (not shown). By energizing a drive coil (not shown), a light beam can be focused on the information recording surface 2a of the CD optical disk 2 to form a light spot. Is possible.

  The counterclockwise circularly polarized light beam 37 is reflected from the CD optical disk 2 and becomes a clockwise circularly polarized light beam 38 this time. The clockwise circularly polarized light beam 38 follows the same optical path as the outward light and enters the broadband quarter-wave plate 17 through the objective lens 19. The clockwise circularly polarized light beam 38 is now a vertically polarized light beam 39 due to the polarization action of the broadband quarter wave plate 17.

  The light beam 39 is incident on the beam splitter film surface 12a on the surface of the beam splitter mirror 12, which is the first beam splitter, via the coupling lens 15 and the rising mirror. As described above, the beam splitter film surface 12a has an S-polarized light transmittance of about 10%, a P-polarized light transmittance of about 18%, an S-polarized light reflectance of about 90%, and a P-polarized light with respect to a light beam having a wavelength of about 785 nm. It has spectral characteristics with a reflectance of approximately 82%. Since the vertically polarized light beam 39 is S-polarized with respect to the beam splitter film surface 12a, approximately 10% is transmitted and approximately 90% is reflected.

  The vertically polarized light beam 40 transmitted through the beam splitter film surface 12 a is guided to the photodetector 24 through the detection lens 23.

  As described above, in the present embodiment, the polarization beam splitter prism 10 is used as the first beam splitter in the optical pickup using the DVD semiconductor laser 3 and the CD semiconductor laser 27 which are two semiconductor lasers having different wavelengths. Therefore, even when the incident angle of the light beam of the polarization beam splitter prism 10 varies or the wavelength of the semiconductor laser varies, the incident light from the two semiconductor lasers can be combined more efficiently.

  In this embodiment, the oscillation wavelength of the first semiconductor laser is shorter than that of the second semiconductor laser, and the first beam splitter efficiently reflects short wavelength light and efficiently transmits long wavelength light. Although the dichroic film characteristics have been awaited, it is not limited to this.

  For example, as another example, the oscillation wavelength of the first semiconductor laser is longer than the oscillation wavelength of the second semiconductor laser, and the first beam splitter efficiently reflects the long wavelength light and reflects the short wavelength light. It is also possible to provide dichroic film characteristics that allow efficient transmission. Also in this embodiment, since the first beam splitter has both the dichroic film characteristic and the polarization beam splitter film characteristic, two semiconductors can be used even when the incident angle of the light beam varies or the wavelength of the semiconductor laser varies. The light beams from the laser can be synthesized more efficiently.

  Further, in this embodiment, by using a broadband quarter-wave plate 17, a case where a DVD semiconductor laser 3 which is a short wavelength semiconductor laser is used, and a case where a CD semiconductor laser which is a long wavelength semiconductor laser is used. In any case where 27 is used, the polarization direction of the return light to the semiconductor laser returns orthogonal to the polarization direction of the outgoing light from the semiconductor laser. The polarization direction of the return light to the semiconductor laser has no component with the same polarization direction as the polarization direction of the outgoing light from the semiconductor laser, so there is no effect on the oscillation mode of the semiconductor laser, and no light is applied to the same current input. There are no problems such as a decrease in power output or fluctuation in optical power output. In both cases of reproduction and recording, auto power control can be used to keep the power output stable and constant. Therefore, an overcurrent exceeding the maximum rated current is input, and the semiconductor laser does not deteriorate or break down.

  In this embodiment, the polarization direction of the light beam 11 from the short wavelength DVD semiconductor laser is S-polarized, and the long wavelength CD semiconductor is used. The light beam 34 from the laser 27 was P-polarized light. As a result, the light utilization efficiency of the beam splitter in the DVD outward path is approximately 95%, and the light utilization efficiency of the beam splitter in the CD outbound path is approximately 85%. In this way, the light utilization efficiency of the beam splitter in the DVD outbound path could be set to be greater than the light utilization efficiency of the beam splitter in the CD outbound path. The maximum optical power of the CD semiconductor laser 27 available at a low cost is about 150 W, whereas the maximum optical power of the DVD semiconductor laser 3 available at a low price is still as low as about 70 W. In this embodiment, the efficiency of the beam splitter in the DVD outbound path can be set larger than that of the beam splitter in the CD outbound path, so that the standard speed can be achieved even when the DVD semiconductor laser 3 having a maximum optical power as small as about 70 W is used. On the other hand, a recording performance of approximately double speed could be obtained.

  In this embodiment, the polarization direction of the light beam 21 from the short-wavelength DVD semiconductor laser is P-polarized, and the long-wavelength CD semiconductor is incident on the beam splitter mirror 12 as the second beam splitter in the return path. The light beam 39 from the laser 27 is S-polarized light. As a result, the light utilization efficiency of the beam splitter in the DVD return path is approximately 10% for P-polarized light and approximately 5% for S-polarized light.

  When the DVD optical disc 1 has no birefringence, only the P-polarized component is present. However, when birefringence is present, the P-polarized component is decreased and the S-polarized component is increased. Therefore, if the DVD optical disk 1 has birefringence, the light use efficiency varies from approximately 10% to approximately 5%. That is, the variation ratio of the light utilization efficiency is about twice as much as the maximum.

  When the CD optical disk 2 has no birefringence, only the S-polarized component is present. However, when birefringence is present, the S-polarized component decreases and the P-polarized component increases. Therefore, if the CD optical disk 2 has birefringence, the light use efficiency varies from approximately 10% to approximately 18%. That is, the variation ratio of the light utilization efficiency is about 1.8 times at maximum.

  Thus, the variation ratio of the light utilization efficiency of the CD outbound path can be made smaller than the variation ratio of the light utilization efficiency of the DVD outbound path. Since the optical disc substrate has a birefringence larger than that of the DVD optical disc 1, the optical disc substrate 2 has a larger variation ratio of the light utilization efficiency of the CD outward path, thereby reducing the photodetector by the birefringence of the CD optical disc substrate. The fluctuation of the optical power incident on the can was reduced.

  Next, a configuration including the front light monitor photodetector 41 used for auto power control of the first semiconductor laser and the second semiconductor laser will be described. In this embodiment, the light beams 11 and 34 emitted from the polarization beam splitter prism 10 serving as the first beam splitter pass through the sky without passing through the beam splitter mirror 12 serving as the second beam splitter. The light beams 42 and 43 are incident on the front light monitor light detector 41.

  Thus, since the light beam after combining the light beams from the two semiconductor lasers with the first beam splitter is used for the front light monitor, only one front light monitor photodetector is required. Further, since light does not pass through the beam splitter mirror 12 as the second beam splitter, there is no decrease in light utilization efficiency due to transmission. Further, even when the light utilization efficiency of the second beam splitter varies or the light utilization efficiency changes with time due to wavelength change or temperature change, the optical power of the light beams 42 and 43 to the front light monitor photodetector varies. There is nothing to do. Therefore, stable auto power control can be obtained. Further, there is an advantage that no additional parts such as a reflection mirror are required to guide the light beam to the front light monitor photodetector. In order to make the light beams 42 and 43 passing over the beam splitter mirror 12 enter the front light monitor light detector 41, the installation position of the front light monitor light detector 41 is biased upward. Since a sufficient space can be secured between the pickup and the optical disk, the height of the optical pickup is not increased. In general, the intensity distribution of the light beam of a semiconductor laser is wide in the vertical direction and narrow in the horizontal direction. In the present embodiment, since the upward direction with a wide intensity distribution is selected, it is possible to sufficiently secure the optical power to the front light monitor photodetector.

  As described above, according to the embodiment of the present invention, the first semiconductor laser and the second semiconductor laser having different oscillation wavelengths and the first light beam emitted from the first semiconductor laser are reflected. A first beam splitter that combines the optical paths of the first light beam and the second light beam by transmitting the second light beam emitted from the second semiconductor laser; the first light beam; and the second light beam; An objective lens that irradiates an optical disk with a light beam, a photodetector that detects a first light beam and a second light beam reflected from the optical disk, and a first semiconductor laser and a second semiconductor laser that are emitted from the first semiconductor laser. And a second beam beam for guiding the first light beam and the second light beam reflected from the optical disc to the photodetector, The first beam splitter includes at least a first beam splitter, wherein the information of both the first optical disc and the second optical disc having different substrate thicknesses can be recorded and reproduced. A polarization beam splitter having a characteristic of efficiently transmitting P-polarized light and efficiently reflecting S-polarized light with respect to the oscillation wavelength of the semiconductor laser and the oscillation wavelength of the second semiconductor laser, and emitting the first semiconductor laser. The polarization state of one light beam is incident on the first beam splitter with S polarization and reflected, and the polarization state of the second light beam emitted from the second semiconductor laser is incident on the first beam splitter with P polarization. And configured to transmit. As a result, even when the incident angle of the light beam to the first beam splitter varies or the oscillation wavelength of the semiconductor laser varies, the light beams from the two semiconductor lasers can be combined more efficiently. is there.

  Further, the oscillation wavelength of the first semiconductor laser is shorter than the oscillation wavelength of the second semiconductor laser, and the first beam splitter efficiently reflects light having a short wavelength that is the oscillation wavelength of the first semiconductor laser. A dichroic film characteristic that efficiently transmits long-wavelength light, which is the oscillation wavelength of the second semiconductor laser, was provided. As a result, even when the incident angle of the light beam to the first beam splitter varies or the oscillation wavelength of the semiconductor laser varies, the light beams from the two semiconductor lasers can be combined more efficiently. is there.

  Further, the oscillation wavelength of the first semiconductor laser is longer than the oscillation wavelength of the second semiconductor laser, and the first beam splitter efficiently reflects the long wavelength light that is the oscillation wavelength of the first semiconductor laser. A dichroic film characteristic that efficiently transmits light having a short wavelength, which is the oscillation wavelength of the second semiconductor laser, was provided. As a result, even when the incident angle of the light beam to the first beam splitter varies or the oscillation wavelength of the semiconductor laser varies, the light beams from the two semiconductor lasers can be combined more efficiently. is there.

  In addition, the polarization state of the first light beam emitted from the first semiconductor laser is reflected by being incident on the second beam splitter as S-polarized light, and the polarization state of the second light beam emitted from the second semiconductor laser. Is incident on the second beam splitter with P-polarized light and reflected, and functions as a quarter-wave plate for both the oscillation wavelength of the first semiconductor laser and the oscillation wavelength of the second semiconductor laser. A broadband quarter wave plate was placed between the second beam splitter and the optical disc. As a result, in either case of using the DVD semiconductor laser 1 which is a short wavelength semiconductor laser or the CD semiconductor laser 2 which is a long wavelength semiconductor laser, the return to the semiconductor laser is performed. The polarization direction of the light returns orthogonal to the polarization direction of the light emitted from the semiconductor laser. The polarization direction of the return light to the semiconductor laser has no component with the same polarization direction as the polarization direction of the outgoing light from the semiconductor laser, so there is no effect on the oscillation mode of the semiconductor laser, and no light is applied to the same current input. There are no problems such as a decrease in power output or fluctuation in optical power output. In both cases of reproduction and recording, auto power control can be used to keep the power output stable and constant. Therefore, there is no case where an overcurrent exceeding the maximum rated current is input and the semiconductor laser is not deteriorated or destroyed.

  In addition, the polarization direction to be incident on the beam splitter mirror, which is the second beam splitter in the forward path, is set so that the light beam from the short wavelength DVD semiconductor laser is S-polarized, and the light beam from the long wavelength CD semiconductor laser is P. Polarized light was used. As a result, the light utilization efficiency of the DVD forward beam splitter was set to be larger than the light utilization efficiency of the CD forward beam splitter, and a DVD semiconductor laser with a small maximum optical power could be used.

  In addition, the direction of polarization incident on the beam splitter mirror, which is the second beam splitter, in the return path is P-polarized light from the short wavelength DVD semiconductor laser, and S light is emitted from the long wavelength CD semiconductor laser. Polarized light was used. As a result, the variation ratio of the light utilization efficiency of the CD outbound path can be made smaller than the variation ratio of the light utilization efficiency of the DVD outbound path, and the variation of the optical power incident on the photodetector due to the birefringence of the CD optical disk substrate can be reduced. I was able to.

  A front light monitor photodetector used for auto power control of the first semiconductor laser and the second semiconductor laser includes a first light beam emitted from the first beam splitter and a second light beam. The first light beam and the second light beam that pass through the sky without passing through the two beam splitters are disposed. Thus, only one front light monitor photodetector is required. Further, there is no decrease in light utilization efficiency due to transmission through the second beam splitter. Even when the light utilization efficiency of the second beam splitter varies or the light utilization efficiency changes with time due to wavelength change or temperature change, the optical power of the light beam to the front light monitor photodetector may fluctuate. And stable auto power control can be obtained. Further, no additional components such as a reflecting mirror are required to guide the light beam to the front light monitor photodetector. In addition, since the upward direction in which the intensity distribution of the light beam of the semiconductor laser is wide is selected, there is an effect that sufficient optical power to the front light monitor photodetector can be ensured.

It is a schematic block diagram of the optical pick-up of a present Example. This is a spectral transmittance characteristic of the polarizing beam splitter film surface 10a of the optical pickup of the present embodiment. This is a spectral transmittance characteristic of the beam splitter film surface 12a of the optical pickup of the present embodiment. It is a schematic block diagram of the conventional optical pick-up.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... DVD-type optical disk, 1a ... Information recording surface, 2 ... CD-type optical disk, 2a ... Information recording surface, 3 ... Semiconductor laser for DVD, 3a ... Light emission point, 4 ... Light beam, 5 ... Auxiliary lens, 5a ... Convex spherical surface Lens surface, 6 ... Composite optical element, 6a ... 1/2 wavelength plate, 6b ... Glass substrate, 6c ... Diffraction grating, 7 ... Light beam, 8 ... Holder, 9 ... Case, 10 ... Polarizing beam splitter prism, 10a ... Polarization beam splitter film surface, 11... Light beam, 12... Beam splitter mirror, 12 a. Beam: 17 ... Broadband quarter wave plate, 18 ... Light beam, 19 ... Objective lens, 20 ... Light beam, 21 ... Light beam, 22 ... Light beam, 23 ... Detection lens, 24 ... Optical detection 25 ... substrate 26 ... adhesive 26b ... secondary light beam 27 ... semiconductor laser for CD 27a ... light emitting point 28 ... light beam 29 ... auxiliary lens 29a ... convex spherical lens surface 30 ... diffraction grating 31 ... light beam, 32 ... holder, 33 ... holder, 34 ... light beam, 35 ... light beam, 36 ... light beam, 37 ... light beam, 38 ... light beam, 39 ... light beam, 40 ... light beam, 41 ... Front light monitor light detector, 42 ... Light beam, 43 ... Light beam, 50 ... Auxiliary lens, 50a ... Diffraction grating, 51a ... Main light beam, 51b ... Sub main beam, 51c ... Sub main beam, 52 ... Light beam 53 ... light spot, 54 ... light beam, 55 ... light beam, 56 ... light beam, 57 ... light beam, 58 ... detection lens, 59 ... light beam, 60 ... auxiliary lens, 60a ... diffraction grating, 61b ... convex spherical surface Len Surface, 61 ... light beam, 62 ... light beam, 63 ... light beam, 64 ... light beam, 65 ... substrate.

Claims (2)

An optical pickup that irradiates an optical disk with a light beam and receives light reflected by the optical disk,
A first semiconductor laser;
A second semiconductor laser having an oscillation wavelength different from that of the first semiconductor laser;
A wave plate for converting a P-polarized light beam emitted from the first semiconductor laser into an S-polarized light beam;
A first light beam of the divergent light beam emitted from the first semiconductor laser, polarized to S-polarized light by the wave plate is reflected, and a second of the P-polarized divergent light beam emitted from the second semiconductor laser is reflected. A first beam splitter having a function of transmitting a light beam, and synthesizing optical paths of the first light beam and the second light beam;
A photodetector for detecting the first light beam and the second light beam reflected by the optical disc;
A ratio of the S-polarized light transmittance to the P-polarized light transmittance of the first light beam is smaller than a ratio of the S-polarized light transmittance to the P-polarized light transmittance of the second light beam; It is disposed on the optical axis of the light beam emitted from the beam splitter, reflects the first light beam and the second light beam emitted from the first beam splitter toward the optical disc, and reflects them on the optical disc. A second beam splitter that transmits the first light beam and the second light beam and guides them to the photodetector;
The first of said first light beam and second light beam of the divergent light beam emitted from the beam splitter, the second the passing through the external beam splitter of the first light beam and second light beam And a front monitor photodetector for receiving light,
The front monitor light detector of the first light beam and second light beam of the divergent light flux emitted from the first beam splitter, positioned to receive the broad direction of the light beam of the light intensity distribution An optical pickup that has been.   The optical pickup according to claim 1, wherein the front monitor light detector feedback-controls the optical power of the first semiconductor laser and the second semiconductor laser.

Images