JP2007287278A - Optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup device quipped with semiconductor laser of which the position of light emitting points are different from each other, the optical pickup device enabling a single hologram to generate a beam for generating focus and tracking error detection signals, thereby reducing the assembling and adjusting man-hour and the manufacturing cost thereof. <P>SOLUTION: The optical pickup device is provided with a first laser emitting a light beam of first wavelength, a second laser emitting a light beam of second wavelength, a hologram 14 diffracting reflected return light from an optical recording medium, and a photodetector 16 receiving the diffracted light beam and detecting a focus error signal and a tracking error signal. For the light beam of the first wavelength, the focus error signal is detected using the light beam diffracted in a first area 14a of the hologram, and for the light beam of the second wavelength, the focus error signal is detected using the light beam diffracted in a second area 14b of the hologram. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical pickup device for reproducing and recording information on an optical recording medium.

  Optical disks are being used in many fields such as audio, video, and computers because they can record a large amount of information signals at high density. In particular, optical discs of various different standards such as CD (Compact Disk), DVD (Digital Versatile Video Disk), HD-DVD (High Definition DVD), and BD (Blu-ray Disk) have been developed. There is an increasing demand for compatibility in which disks of different standards can be recorded or reproduced with a single optical pickup.

  Here, in CD and CD-R, the characteristics of the substrate and the recording medium are optimized with respect to an infrared light beam having a wavelength of 780 nm. In the DVD, the above characteristics are optimized for a red light beam having a wavelength of around 650 nm. In the HD-DVD, BD, etc., the above characteristics for a blue light beam having a wavelength of around 400 nm are optimized.

  As an optical pickup compatible with such optical discs recorded or reproduced at different wavelengths, for example, in Patent Document 1 (Japanese Patent Laid-Open No. 2002-92933), as shown in FIGS. An optical pickup device having a structure has been proposed.

  FIG. 10 is a cross-sectional view showing the structure of a conventional integrated optical pickup device, and FIG. 11 is a schematic diagram showing the optical system of the conventional optical pickup device.

  This optical pickup device includes a first semiconductor laser 1, a second semiconductor laser 2, a three-beam diffraction grating 3, a first hologram 6, a second hologram 7, a collimator lens 10, an objective, A lens 11 and a light receiving element 8 are provided.

  The first semiconductor laser 1 oscillates in the 635 nm band, and the second semiconductor laser 2 oscillates in the 780 nm band. The three-beam diffraction grating 3 generates three beams for tracking control from the light beam of each light source. The hologram 6 diffracts the reflected light from the optical disk 12 and guides it to the light receiving element 8.

  The laser unit 9 includes a first semiconductor laser 1, a second semiconductor laser 2, a three-beam diffraction grating 3, a first hologram 6, a second hologram 7, transparent substrates 4 and 5, And a photodetector 8.

  The first semiconductor laser 1 that oscillates in the 650 nm band and the second semiconductor laser 2 that oscillates in the 780 nm band are arranged close to each other. The three-beam diffraction grating 3 generates three beams for tracking control. The first hologram 6 diffracts the light beams of the first semiconductor laser 1 and the second semiconductor laser 2.

  The second hologram 7 diffracts only the light beam of the second semiconductor laser 2 out of the light diffracted by the first hologram 6 and guides it to the light receiving element 8. The first hologram 6 is formed on the upper surface side of the transparent substrate 5, and the second hologram 7 and the diffraction grating 3 are formed on the lower surface side of the transparent substrate 4.

  Next, a method for reproducing the optical disk 12 will be described. For example, when reproducing a DVD, the light beam K emitted from the first semiconductor laser 1 in the 650 nm band passes through the diffraction grating 3 and enters the first hologram 6 and is diffracted. Among them, the 0th-order light is condensed on the optical disk 12 by the collimator lens 10 and the objective lens 11.

  Then, the return light reflected by the optical disk 12 is diffracted by the first hologram 6, passes through the second hologram 7, and is condensed on the photodetector 8.

  When reproducing a CD, the light beam J emitted from the second semiconductor laser 2 in the 780 nm band is divided into three beams by the diffraction grating 3 and incident on the first hologram element 6 to be diffracted again. The Among them, the 0th-order light is condensed on the optical disk 12 having a substrate thickness of 1.2 mm by the collimator lens 10 and the objective lens 11.

  Then, the return light reflected by the optical disk 12 is diffracted by the first hologram 6, then diffracted by the second hologram 7 and condensed on the photodetector 8.

  The first hologram 6 is set to a groove depth that diffracts both the light of the wavelength of the first semiconductor laser 1 and the light of the wavelength of the second semiconductor laser 2. Since the respective wavelengths are different, the diffraction angles for light of both wavelengths are different. The first hologram 6 is designed so as to be ideally focused on the photodetector 8 as shown in FIG. 12 with respect to the light of the first semiconductor laser 1.

  At this time, the diffracted light of the second semiconductor laser 2 has a larger diffraction angle than the diffracted light of the first semiconductor laser 1, and when there is no second hologram 7, the ideal light detector 8 starts from above. The light is condensed on the shifted optical path 13.

  In order to use the photodetector 8 in common, it is necessary to collect light on the photodetector 8. Therefore, as shown in FIG. 13, a second hologram 7 is provided to diffract the diffracted light again so as to be condensed on the photodetector 8.

  Even if the second hologram 7 is provided, the light of the first semiconductor laser 1 is not affected because the 0th-order diffracted light (transmitted light) of the second hologram 7 is used. The second hologram 7 may be a wavelength selective hologram that does not diffract the light of the first semiconductor laser 1.

  Next, the structure of the first hologram 6 and the photodetector 8 and the servo signal detection method will be described. FIG. 12 shows the light receiving element shapes of the first hologram 6 and the photodetector 8. The hologram 6 is divided into three regions 6a to 6c by a dividing line 6d in the x direction corresponding to the radial direction of the optical disc 12 and a dividing line 6e in the y direction corresponding to the track direction.

  The light receiving element 8 includes a two-divided light receiving element divided into a light receiving region 8a and a light receiving region 8b, and eight light receiving regions 8c to 8j. Here, outputs from the light receiving regions 8a to 8j are Sa to Sj, respectively.

  For example, when reproducing a DVD, the return light from the optical disk 12 of the light emitted from the first semiconductor laser 1 enters the first hologram 6. When the focused beam by the objective lens 11 is focused on the information recording surface of the optical disc 12, the light diffracted in the region 6a of the first hologram 6 out of the incident beam is divided into two divided light receiving regions 8a, Condensed on the dividing line 8b. The light diffracted by the region 6b of the first hologram 6 is condensed on the light receiving region 8d, and the light diffracted by the region 6c of the first hologram 6 is condensed on the light receiving region 8c.

  As the servo signal, the focus error signal (FES) by the single knife edge method can be detected by FES = Sa−Sb using Sa and Sb.

  Further, when the optical disc 12 on which pit information is recorded is reproduced, a change in the phase difference between the Sc and Sd signals can be detected to detect the tracking error signal 1 (TES1) by the phase difference (DPD) method. In the case of the optical disk 12 having grooves, the tracking error signal 2 (TES2) by the push-pull method can be detected by TES2 = Sc-Sd.

  Furthermore, the recorded information signal (RF signal) can be reproduced by RF = Sa + Sb + Sc + Sd.

  Next, a case where a CD is reproduced will be described. When the return light from the optical disk 12 of the light emitted from the second semiconductor laser 2 is diffracted by the first hologram 6 and travels as it is, the beam enters the optical path 13 in FIG.

  Therefore, as shown in FIG. 13, the second hologram 7 is divided into four by dividing lines 7e and 7f in the x direction and dividing line 7g in the y direction. Diffracted light from the region 6a of the first hologram 6 enters the region 7a and is diffracted so as to be condensed on the dividing lines of the light receiving regions 8a and 8b. The diffracted light from the region 6b of the hologram 6 enters the region 7b and is diffracted so as to be collected in the light receiving region 8d.

  The diffracted light from the region 6c of the first hologram 6 is incident on the regions 7c and 7d, the diffracted light from the region 7c is collected on the light receiving region 8c, and the diffracted light from the region 7d is collected on the light receiving region 8d. Form. Here, the reason why the dividing line 7g for dividing the regions 7c and 7d is provided will be described.

  The emission points of the first semiconductor laser 1 and the second semiconductor laser 2 are shifted in the x direction. Thereby, when the dividing line 6e of the first hologram 6 is formed so as to divide the light beam from the semiconductor laser 1 at the intensity center, the intensity center of the light beam of the second wavelength is a region that is larger than the dividing line 6e. It shifts to the 6c side.

  Therefore, the dividing line 7g of the hologram 7 is such that when the diffracted light from the region 7d enters the light receiving region 8d, the amount of the direct current component of the light beam incident on the light receiving region 8c and the light beam incident on the light receiving region 8d. It is formed at a position where the amount of direct current component is equal.

  By providing such a hologram 7, the light beam of the second wavelength is made incident on the light receiving element of the photodetector 8. The light from the second semiconductor laser 2 is divided into a main beam and two sub beams by the three-beam diffraction grating 3. Therefore, the two sub beams diffracted in the region 6a are condensed on the light receiving region 8f and the light receiving region 8e, respectively, and the two sub beams diffracted in the region 6b of the first hologram 6 are respectively collected in the light receiving region 8j and the light receiving region 8i. And the two sub beams diffracted by the region 6c of the first hologram 6 are condensed on the light receiving region 8h and the light receiving region 8g, respectively.

  The focus error signal (FES) can be detected by FES = Sa−Sb as in the DVD side.

  The tracking error signal 6 (TES6) can be detected by TES6 = (Sf + Sh + Sj) − (Se + Sg + Si) by the three beam method.

  Further, the tracking error signal 7 (TES7) by the differential push-pull (DPP) method can also be detected by TES7 = (Sd−Sc) −k · ((Sj−Sh) + (Si−Sg)).

  Here, the coefficient k is for correcting the difference in light intensity between the main beam and the sub beam. If the intensity ratio is main beam: sub beam: sub beam = a: b: b, the coefficient k = a / (2b). is there.

Furthermore, the recorded information signal (RF signal) can be reproduced by RF = Sa + Sb + Sc + Sd.
JP 2002-92933 A

  According to the above-described optical pickup device, the first and second light beams are condensed on the same photodetector 8 and incident on the same light receiving regions 8a to 8j. Two holograms 6 and 7 are indispensable, and two transparent substrates 4 and 5 are required. Therefore, the position of each of the transparent substrates 4 and 5 must be adjusted at the time of assembly adjustment, and the assembly process becomes complicated.

  Further, as shown in FIG. 13, when the second hologram 7 is provided with a dividing line 7e in the y direction, the regions 7c and 7d are caused in the semiconductor laser 2 due to a change in emission wavelength caused by a temperature change or a change in light output. The incident light beam fluctuates in the x direction, and a tracking offset occurs.

  The present invention has been made in order to solve the above-mentioned problems, and a first object of the present invention is to provide a focus error with one hologram in an optical pickup device including semiconductor lasers having different light emitting points. It is an object of the present invention to provide an optical pickup device that can generate a beam for generating a signal and a tracking error detection signal, and can reduce assembly adjustment man-hours and manufacturing costs. A second object of the present invention is to provide an optical pickup apparatus that operates stably without generating a tracking offset due to wavelength fluctuation.

  According to the optical pickup device based on the present invention, the first semiconductor laser that emits the light beam of the first wavelength, the second semiconductor laser that emits the light beam of the second wavelength, and the first semiconductor laser described above. Means for condensing the light beam emitted from the semiconductor laser and the second semiconductor laser onto the optical recording medium, a hologram for diffracting the reflected return light from the optical recording medium in a predetermined direction, and the diffracted light A photodetector that receives the light beam and detects a focus error signal and a tracking error signal. The hologram is divided into a first area and a second area at least by a dividing line extending in a direction corresponding to a direction in which the first semiconductor laser and the second semiconductor laser are arranged. In the detection of one or both of the error signal and the tracking error signal, the error signal is obtained by using the light beam diffracted in the first region of the hologram for the light beam having the first wavelength. And detecting the error signal by using the light beam diffracted in the second region of the hologram for the light beam having the second wavelength.

  In the optical pickup device, for the light beam having the first wavelength, a focus error signal is detected using the light beam diffracted in the first region of the hologram, and the light having the second wavelength is detected. For the beam, the focus error signal may be detected using a light beam diffracted in the second region of the hologram.

  In the optical pickup device, the photodetector includes at least one two-divided photodetector, the first wavelength light beam diffracted by the first region of the hologram, and the first of the hologram. The hologram may be configured such that the light beam having the second wavelength diffracted in the second region is incident on a dividing line of the same two-divided photodetector.

  Further, in the optical pickup device, the first region of the hologram corresponds to a direction in which the first semiconductor laser and the second semiconductor laser are aligned through the intensity center of the light beam having the first wavelength. And the second region of the hologram passes through the intensity center of the light beam having the second wavelength, and the first semiconductor laser and the second semiconductor. You may further divide | segment by the dividing line extended in the direction orthogonal to the direction corresponding to the direction where a laser is located in a line. In this configuration, with respect to the light beam having the first wavelength, a tracking error signal is detected using the light beam having the first wavelength divided into two in the first region of the hologram, and the second light beam is detected. The tracking error signal may be detected using a light beam having a second wavelength divided into two in the second region of the hologram.

  Further, a correction hologram that diffracts the light beam having the second wavelength divided by the hologram is provided between the hologram and the photodetector, and the correction hologram is the first hologram divided by the hologram. The light beams having the two wavelengths may be incident on the same region as the region of the photodetector on which the light beams having the first wavelength divided by the hologram are incident.

  According to the optical pickup device of the present invention, it is possible to generate a focus error signal and a tracking error detection signal generation beam with one hologram in an optical pickup device including semiconductor lasers having different light emitting points. Thus, it is possible to provide an optical pickup device that can reduce assembly adjustment man-hours and manufacturing costs. Further, according to the optical pickup device of the present invention, it is possible to provide an optical pickup device that operates stably without generating a tracking offset due to wavelength variation.

Embodiments according to the present invention will be described in detail with reference to the drawings.
(Embodiment 1)
Hereinafter, an embodiment according to the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional view showing the structure of the integrated optical pickup device according to the present embodiment. The integrated optical pickup device shown in FIG. 1 includes a first semiconductor laser 1, a second semiconductor laser 2, a three-beam diffraction grating 3, and a hologram 14.

  Comparing the optical pickup device of the present embodiment shown in FIG. 1 with the conventional optical pickup device shown in FIG. 10, the optical pickup device of the present embodiment has only one transparent substrate 15. In addition, the hologram 14 is formed on the surface of the transparent substrate 15 on the optical disk side, the hologram is not formed on the surface of the photodetector 16 side, and the structure of the hologram 14 and the structure of the photodetector 16 are different.

  The first wavelength of the light beam emitted from the semiconductor laser 1 is arranged to be shorter than the second wavelength of the light beam emitted from the semiconductor laser 2. For example, when the emission wavelength of the semiconductor laser 1 is in the 400 nm band, the emission wavelength of the semiconductor laser 2 is set to the 635 nm band or the 780 nm band, and when the emission wavelength of the semiconductor laser 1 is in the 635 nm band, the emission wavelength of the semiconductor laser 2 is set to 780 nm. The semiconductor lasers 1 and 2 are arranged so as to form a band.

  FIG. 2 is a diagram showing the structure of the hologram and the photodetector of the present embodiment. As shown in FIG. 2, the hologram 14 provided in the laser unit includes two regions 14a and 14b divided by a dividing line 14c in the x direction. The photodetector 16 includes a two-divided light receiving element divided into regions 16a and 16b by a dividing line 16g in the x direction, and regions of the light receiving regions 16c to 16e. Here, outputs from the light receiving regions 16a to 16e are Sa to Se, respectively.

  Here, the region 14a of the hologram 14 is formed so as to be condensed on the dividing line of the light receiving regions 16a and 16b when the light beam having the first wavelength passes. The region 14b of the hologram 14 is formed so as to be condensed on the dividing line 16g of the light receiving regions 16a and 16b when the light beam having the second wavelength passes.

  Next, a signal detection method will be described. FIG. 3 is a diagram illustrating a signal detection method in the optical pickup device of the present embodiment. Reflected light from the optical disk of the light beam emitted from the semiconductor laser 1 enters the hologram 14. As shown in FIG. 3, the light beam that has passed through the region 14a of the hologram 14 is collected on the dividing line 16g of the light receiving regions 16a and 16b.

  In the region 14b, a hologram pattern is formed so as to be condensed on the dividing line 16g of the light receiving regions 16a and 16b when the light beam of the second wavelength passes. The emission wavelength of the first semiconductor laser is shorter than the emission wavelength of the second semiconductor laser, and the diffraction angle by the hologram 14 becomes small.

  Therefore, the light beam having the first wavelength diffracted in the region 14b is incident on the light receiving region 16e on the hologram side with respect to the regions 16a and 16b. The two sub beams generated by the three-beam diffraction grating 3 in FIG. 1 are incident on the light receiving regions 16c and 16d, respectively.

  The focus error signal (FES) can be detected by FES = Sa−Sb using the knife edge method.

  The tracking error signal (TES) can be detected by TES = Sc−Sd using the three-beam method.

The information signal (RF) is obtained by RF = Sa + Sb + Se.
As for the reflected light from the optical disk of the light beam emitted from the semiconductor laser 2, the light beam diffracted in the region 14b of the hologram 14 is condensed on the dividing line 16g of the light receiving regions 16a and 16b. In the area 14a, a hologram pattern is formed so that the light beam having the first wavelength is condensed on the dividing line of the light receiving areas 16a and 16b. Since the second wavelength is longer than the first wavelength, the diffraction angle at the hologram 14 is larger for the light beam having the second wavelength. Therefore, the second wavelength light beam diffracted in the region 14a enters the light receiving region 16f.

  The focus error signal (FES) can be detected by FES = Sa−Sb by using the knife edge method, similarly to the light beam having the first wavelength.

  The tracking error signal (TES) can also be detected by the arithmetic expression TES = Sc−Sd using the three-beam method, like the light beam of the first wavelength.

  The information signal (RF) is obtained by RF = Sa + Sb + Sf, which has a different calculation formula from that of the light beam having the first wavelength.

  In this embodiment, since the knife edge method is used to detect the focus error signal, the hologram 14 is formed so that the beam incident on the dividing line 16g of the two-divided light receiving regions 16a and 16b is condensed. However, when another focus error signal detection method is used, for example, when an astigmatism method or a spot size method is used, the hologram 14 is formed so as to have a beam shape corresponding to the focus error signal detection method. Good.

(Embodiment 2)
A second embodiment according to the present invention will be described with reference to FIGS. The basic structure of the optical pickup device of the second embodiment is the same as that of the first embodiment, but the structure of the hologram and the structure of the photodetector are different. Hereinafter, this part will be mainly described.

  FIG. 4 is a cross-sectional view showing the structure of the integrated optical pickup device according to the present embodiment. FIG. 5 is a diagram showing the structure of the hologram and the photodetector of this embodiment. FIG. 5A shows the structure of the hologram 17 formed on the optical disc side surface of the transparent substrate 15 shown in FIG.

  The hologram 17 is divided into four regions 17a to 17d by a dividing line 17e in the x direction (radial direction) and dividing lines 17f and 17g in the y direction (tangential direction). The position in the x direction of the dividing line 17f is formed so as to coincide with the position in the x direction of the intensity center of the light beam emitted from the semiconductor laser 1. Further, the position of the dividing line 17g in the x direction is formed so as to coincide with the position of the intensity center of the light beam emitted from the semiconductor laser 2 in the x direction.

  The photodetector 18 will be described. As shown in FIG. 5B, the photodetector 18 is divided into two divided light receiving areas 18a and 18b divided into two by a dividing line 18m, two divided light receiving areas 18c and 18d divided into two by a dividing line 18n, It has area | regions 18e-18l. Here, outputs from the light receiving regions 18a to 18l are Sa to Sl.

  The region 17a of the hologram 17 is formed so as to be condensed on the dividing line 18m with respect to the light beam having the first wavelength, and the region 17b is collected on the dividing line 18n with respect to the light beam having the first wavelength. It is formed to shine. The region 17c is formed so as to be condensed on the dividing line 18n with respect to the light beam having the second wavelength, and the region 17d is condensed on the dividing line 18m with respect to the light beam having the second wavelength. It is formed to do.

  Next, a signal detection method will be described. FIG. 6 is a diagram illustrating a signal detection method in the optical pickup device of the present embodiment. The light beam of the first wavelength emitted from the first semiconductor laser 1 and reflected by the optical disk is incident on the hologram 17 shown in FIG.

  The light beam incident on the region 17a is diffracted and condensed on the dividing line 18m of the light receiving regions 18a and 18b. The light beam incident on the region 17b is diffracted and condensed on the dividing line 18n of the light receiving regions 18c and 18d. In the regions 17c and 17d, a hologram pattern is formed so that the light beam of the second wavelength is condensed on the dividing lines 18n and 18m, respectively. Therefore, when the first wavelength enters the hologram 17, the diffracted light from the region 17c enters the light receiving region 18k, and the diffracted light from the region 17d enters the light receiving region 18i.

  Error signals and information signals are detected using the light beams incident on these light receiving areas.

  The focus error signal (FES) can be detected by FES = (Sa + Sc) − (Sb + Sd) using the knife edge method. The tracking error signal can be detected using a three-beam method (TES1), a differential push-pull method (TES2), or a DPD method (TES3).

  TES1 = (18e + 18g) − (18f + 18h), TES2 = (18a + 18b) − (18c + 18d) −k ((18e + 18f) − (18g + 18h)), TES3 = ph ((18a + 18b) − (18c + 18d)) .

  Note that k is for correcting the difference in light intensity between the main beam and the sub beam, and if the intensity ratio is main beam: sub beam: sub beam = a: b: b, the coefficient k = a / (2b). Further, ph () indicates the calculation of the phase component of each signal in parentheses.

  The information signal (RF) can be detected by signal calculation of RF = 18a + 18b + 18c + 18d + 18i + 18k.

  Next, a method for performing signal detection with a light beam of the second wavelength emitted from the second semiconductor laser will be described. The light beam having the second wavelength reflected from the optical disk enters the hologram 17 as shown in FIG. The light beams incident on the regions 17c and 17d of the hologram 17 are diffracted by the hologram 17 and condensed on the dividing lines 18n and 18m of the light receiving element 18, respectively.

  In the regions 17a and 17b, hologram patterns are formed so as to be condensed on the dividing lines 18m and 18n, respectively, when the light beam having the first wavelength is diffracted. Therefore, when a light beam having a second wavelength longer than the first wavelength is incident, the diffracted light from the region 17a is incident on the light receiving region 18l, and the diffracted light from the region 17b is incident on the light receiving region 18j. .

  By receiving these light beams in each light receiving region, an error signal and an information signal are detected.

  The focus error signal (FES) can be detected by FES = (Sa + Sc) − (Sb + Sd) using the knife edge method. The tracking error signal can be detected using a three-beam method (TES1), a differential push-pull method (TES2), or a DPD method (TES3).

  TES1 = (Se + Sg) − (Sf + Sh), TES2 = (Sa + Sb) − (Sc + Sd) −k ((Se + Sf) − (Sg + Sh)), TES3 = ph ((Sa + Sb) − (Sc + Sd)) .

  Note that k is for correcting the difference in light intensity between the main beam and the sub beam, and if the intensity ratio is main beam: sub beam: sub beam = a: b: b, the coefficient k = a / (2b). Further, ph () indicates the calculation of the phase component of each signal in parentheses.

  Further, the information signal (RF) can be detected by RF = Sa + Sb + Sc + Sd + Sj + Sl.

  In the present embodiment, a three-beam method, a differential push-pull method, and a DPD method can be used as a tracking error detection method, and the tracking error detection method is limited to the three-beam method as compared with the first embodiment. Thus, it is advantageous to be able to cope with many kinds of optical disks having different structures.

  In this embodiment, since the knife edge method is used to detect the focus error signal, the hologram 17 is formed so that the light beam incident on the dividing lines 18m and 18n of the two-divided light receiving element is condensed. When another focus error signal detection method is used, for example, when an astigmatism method or a spot size method is used, the hologram 17 may be formed so as to have a beam shape corresponding to the focus error signal detection method. .

(Embodiment 3)
A third embodiment according to the present invention will be described with reference to FIGS. The optical pickup device of the third embodiment is common to the optical pickup device of the above embodiment in its basic configuration. The same constituent elements as those in FIG.

  FIG. 7 is a cross-sectional view showing the structure of the integrated optical pickup device of the present embodiment. In the optical pickup device of the present embodiment, as shown in FIG. 7, the correction hologram 20 is formed on the surface of the transparent substrate 15 on the photodetector side. The structures of the hologram 19 and the photodetector 21 are different from those in the above embodiment.

  FIG. 8 is a diagram showing the structure of the hologram and the photodetector of the optical pickup device of the present embodiment. As shown in FIG. 8A, the hologram 19 is divided into four regions 19a to 19d by dividing lines 19e in the x direction (radial direction) and dividing lines 19f and 19g in the y direction (tangential direction). The position of the dividing line 19f in the x direction is formed to coincide with the position in the x direction of the intensity center of the light beam emitted from the semiconductor laser 1. Further, the position of the dividing line 19g in the x direction is formed so as to coincide with the position of the intensity center of the light beam emitted from the semiconductor laser 2 in the x direction.

  As shown in FIG. 8B, the correction hologram 20 is divided into four by a dividing line 20 e in the x direction and a dividing line 20 f in the y direction, and the second semiconductor laser 2 out of the light diffracted by the hologram 19. Only the light beam is diffracted and guided to the photodetector 21. The light of the first semiconductor laser 1 is not affected because the 0th-order diffracted light (transmitted light) of the correction hologram 20 is used. The correction hologram 20 may be a wavelength selective hologram that does not diffract the light of the first semiconductor laser 1.

  The photodetector 21 shown in FIG. 8C includes a two-divided light receiving area 21a, 21b divided into two by a dividing line 21k, a two-divided light receiving area 21c, 21d divided into two by a dividing line 21l, and a light receiving area 21e. To 21j. Here, the outputs of the light receiving regions 21a to 21j are Sa to Sj.

  Further, the hologram pattern is formed in the region 19a of the hologram 19 so that the light beam having the first wavelength is condensed on the dividing line 21k of the light receiving regions 21a and 21b. In the region 19b, a hologram pattern is formed so that the light beam having the first wavelength is condensed on the dividing line 21l of the light receiving regions 21c and 21d. In the region 19c, a hologram pattern is formed so as to focus the light beam having the first wavelength on the light receiving region 21i. In the region 19d, a hologram pattern is formed so as to focus the light beam having the first wavelength on the light receiving region 21j.

  Next, a signal detection method will be described. FIG. 9 is a diagram illustrating a signal detection method in the optical pickup device of the present embodiment. First, a method for detecting the light of the first semiconductor laser 1 will be described.

  The light beam having the first wavelength reflected from the optical disk is incident on the hologram 19 as shown in FIG. The light beams diffracted by the regions 19a and 19b of the hologram 19 are condensed on the dividing lines 21k and 21l of the photodetector 21, respectively. The light beams diffracted in the areas 19c and 19d are condensed on the light receiving areas 21i and 21j, respectively.

  The focus error signal (FES) can be detected by FES = (21a + 21c) − (21b + 21d). The tracking error signal can be detected by using the 3-beam method (TES1), the differential push-pull method (TES2), and the DPD method (TES3). , TES2 = ((Sa + Sb) − (Sc + Sd)) − k ((Se + Sk) − (Sf + Sh)), TES3 = ph ((Sa + Sb) − (Sc + Sd)).

  The information signal (RF) can be detected by RF = 21a + 21b + 21c + 21d + 21i + 21j.

  Next, a method for detecting the light beam of the second semiconductor laser 2 will be described. The light beam of the second wavelength reflected by the optical disk is incident on the hologram 19 as shown in FIG. 9B, and is divided into four light beams. The light beams diffracted by the regions 19a, 19b, 19c, and 19d of the hologram 19 are incident on the regions 20a, 20b, 20c, and 20d of the correction hologram 20, respectively.

  The light beam incident on the correction hologram region 20c is diffracted and condensed on the dividing line 21k of the light receiving regions 21a and 21b. The light beam incident on the region 20d is diffracted and condensed on the dividing line 21l of the light receiving regions 21c and 21d. The light beams incident on the regions 20a and 20b are diffracted and condensed on the light receiving regions 21i and 21j, respectively.

  The focus error signal (FES) can be detected by FES = (Sa + Sc) − (Sb + Sd) from the light amount of the light beam incident on each light receiving area, similarly to the signal calculation at the first wavelength.

  The tracking error signal can be detected by using the 3-beam method (TES1), the differential push-pull method (TES2), and the DPD method (TES3). ), TES2 = ((Sa + Sb) − (Sc + Sd)) − k ((Se + Sk) − (Sf + Sh)), TES3 = ph ((Sa + Sb) − (Sc + Sd)).

  The information signal (RF) can be detected by RF = 21a + 21b + 21c + 21d + 21i + 21j.

  In the present embodiment, the number of light receiving regions can be reduced as compared with the second embodiment, and light beams of all the first and second wavelengths are condensed on the photodetector, so that light is received. The total area of the element can be reduced, and there is an advantage that a small and low-cost photodetector can be configured.

  In this embodiment, since the knife edge method is used to detect the focus error signal, the hologram 19 and the correction hologram 20 are arranged so that the light beam incident on the dividing lines 21k and 21l of the two-divided light receiving element is condensed. Forming. When other focus error signal detection methods are used, for example, when an astigmatism method or a spot size method is used, the hologram 19 and the correction hologram 20 are arranged so as to have a beam shape corresponding to the focus error signal detection method. What is necessary is just to form.

  According to the optical pickup device according to the first and second embodiments, in an optical pickup including two light sources having different emission wavelengths and emission points, a single hologram is used and a common light receiving element is used for light beams of two wavelengths. Since the error signal can be detected, the number of assembling steps and member costs can be reduced, and the cost of the optical pickup can be reduced.

  Further, according to the optical pickup device according to the third embodiment, unlike the conventional optical pickup device, a tracking offset does not occur even if the wavelength of the light source fluctuates, and is stable against temperature change and light output fluctuation. Operation can be realized.

  In addition, the said embodiment disclosed this time is an illustration in all the points, Comprising: It does not become the basis of limited interpretation. Therefore, the technical scope of the present invention is not interpreted only by the above-described embodiments, but is defined based on the description of the claims. Moreover, all the changes within the meaning and range equivalent to a claim are included.

It is sectional drawing which shows the structure of the integrated optical pick-up apparatus in Embodiment 1 based on this invention. It is a figure which shows the structure of the hologram in Embodiment 1 based on this invention, and a photodetector. It is a figure which shows the signal detection method of the optical pick-up apparatus in Embodiment 1 based on this invention. It is sectional drawing which shows the structure of the integrated optical pick-up apparatus in Embodiment 2 based on this invention. It is a figure which shows the structure of the hologram in Embodiment 2 based on this invention, and a photodetector. It is a figure which shows the signal detection method of the optical pick-up apparatus in Embodiment 2 based on this invention. It is sectional drawing which shows the structure of the integrated optical pick-up apparatus in Embodiment 3 based on this invention. It is a figure which shows the structure of the hologram in Embodiment 3 based on this invention, and a photodetector. It is a figure which shows the signal detection method of the optical pick-up apparatus in Embodiment 3 based on this invention. It is sectional drawing which shows the structure of the conventional integrated optical pick-up apparatus. It is the schematic which shows the optical system of the conventional optical pick-up apparatus. It is a figure which shows the hologram and photodetector of the conventional optical pick-up apparatus. It is a figure which shows the hologram and photodetector of the conventional optical pick-up apparatus.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 1st semiconductor laser, 2nd 2nd semiconductor laser, 3 beam diffraction grating, 9 Laser unit, 10 Collimator lens, 11 Objective lens, 12 Optical disk, 13 Optical path, 14, 17, 19 Hologram, 16, 18, 21 Photodetector, 20 correction hologram.

Claims (6)

A first semiconductor laser that emits a light beam of a first wavelength;
A second semiconductor laser that emits a light beam of a second wavelength;
Means for condensing the light beam emitted from the first semiconductor laser and the second semiconductor laser on an optical recording medium;
A hologram for diffracting reflected return light from the optical recording medium in a predetermined direction;
An optical pickup device including a photodetector that receives the diffracted light beam and detects a focus error signal and a tracking error signal;
The hologram is divided into a first region and a second region at least by a dividing line extending in a direction corresponding to a direction in which the first semiconductor laser and the second semiconductor laser are arranged.
In the detection of one or both of the focus error signal and the tracking error signal, the light beam having the first wavelength is obtained by using the light beam diffracted in the first region of the hologram. An optical pickup device that detects an error signal and detects the error signal by using a light beam diffracted in the second region of the hologram for the light beam of the second wavelength. For the light beam of the first wavelength, a focus error signal is detected using the light beam diffracted in the first region of the hologram,
2. The optical pickup device according to claim 1, wherein a focus error signal is detected using a light beam diffracted in the second region of the hologram for the light beam having the second wavelength. The photodetector includes at least one two-part photodetector.
The light beam having the first wavelength diffracted by the first region of the hologram and the light beam having the second wavelength diffracted by the second region of the hologram are divided into the same two parts. The optical pickup device according to claim 1, wherein the hologram is configured to be incident on a dividing line of a photodetector. A first region of the hologram is a division extending in a direction orthogonal to a direction corresponding to a direction in which the first semiconductor laser and the second semiconductor laser are aligned, passing through the intensity center of the light beam having the first wavelength. Are further divided by lines,
A second region of the hologram passes through the intensity center of the light beam having the second wavelength, and extends in a direction orthogonal to a direction corresponding to a direction in which the first semiconductor laser and the second semiconductor laser are aligned. The optical pickup device according to claim 1, further divided by a line. For the light beam of the first wavelength, a tracking error signal is detected using the light beam of the first wavelength divided in two in the first region of the hologram,
5. The light according to claim 4, wherein a tracking error signal is detected using a light beam having a second wavelength divided into two in the second region of the hologram with respect to the light beam having the second wavelength. Pickup device. Between the hologram and the photodetector is provided a correction hologram that diffracts the light beam of the second wavelength divided by the hologram,
The correction hologram causes each light beam having the second wavelength divided by the hologram to be in the same region as the region of the photodetector on which each light beam having the first wavelength divided by the hologram is incident. 6. The optical pickup device according to claim 1, wherein the optical pickup device is made incident.

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