JP2007220215A - Optical pickup device and optical disk device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup device and an optical disk device, which execute sure operations with respect to several types of optical disks with simple configurations. <P>SOLUTION: In a diffraction grating 14 for generating a diffracted light from an optical beam reflected on an optical recording medium, a grating pattern of the diffraction grating 14 is selected so as to generate ± secondary diffracted lights for the optical beam of a first wavelength, and ± primary diffracted lights for the optical beam of a second wavelength roughly double of the first wavelength. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention is suitable for application to an optical pickup device used in an optical disc apparatus compatible with a plurality of types of optical discs.

  Conventionally, as a focus control method in an optical pickup of an optical disk device, a + 1st order diffracted light and a −1st order diffracted light are generated by passing a reflected light beam reflected by an optical disk through a diffraction grating, and the + 1st order diffracted light and −1st order diffracted light are generated. An SSD (Spot Size Detection) method for generating a focus error signal based on a difference in spot size is widely used.

  On the other hand, in recent years, various types of optical disks such as CD (Compact-Disc) and DVD (Digital Versatile Disc) have been manufactured, and along with this, optical disk devices corresponding to a plurality of types of optical disks have been commercialized.

  Here, when the SSD method is applied to a DVD and CD compatible optical disc apparatus, the wavelength is different between the DVD laser beam (wavelength 660 [nm]) and the CD laser beam (wavelength 780 [nm]). The diffraction angle when passing through the diffraction grating is also different, and thereby the spot of ± 1st order diffracted light of DVD and the spot of ± 1st order diffracted light of CD are irradiated to different positions on the light receiving element. For this reason, it is necessary to separately provide a photodetector for receiving the ± 1st order diffracted light of the DVD and a photodetector for receiving the ± 1st order diffracted light of the CD, which complicates the configuration of the optical pickup. There was a problem of becoming.

In order to solve this problem, the diffraction grating is divided into a DVD diffraction region and a CD diffraction region, the diffraction angle of the DVD laser light passing through the DVD diffraction region, and the CD light passing through the CD diffraction region. By setting the grating pitch of the diffraction region for DVD and the grating pitch of the diffraction region for CD so that the diffraction angles of the laser light coincide with each other, the ± 1st order diffracted light of DVD and the ± 1st order diffracted light of CD are shared. An optical pickup that receives light with a photodetector has been proposed (see, for example, Patent Document 1).
JP 2001-84609 A (FIG. 1)

  However, in the optical pickup having the above-described configuration, the ± first-order diffracted light of the CD laser light that has passed through the DVD diffraction region and the ± first-order diffracted light of the DVD laser light that has passed through the CD diffraction region are both photodetectors. Is not received. For this reason, in the optical pickup having the above-described configuration, the utilization efficiency of the reflected light beam is low, the signal level of the output of the photodetector is low, and it is easily affected by noise, thereby uncertain servo control such as focus control. There is a problem of becoming.

  Further, in the optical pickup having the above-described configuration, ± 1st order diffracted light of CD laser light that has passed through the DVD diffraction region and ± 1st order diffracted light of DVD laser light that has passed through the CD diffraction region can be obtained by another photodetector. It is also possible to generate a reproduction signal or tracking error signal by receiving light, but in this case, the number of light beams reaching the photodetector increases, and stray light from the unfocused recording layer when using a multilayer disk is used. When the light enters the photodetector, an error occurs in the focus error signal or the like, which causes a problem that servo control such as focus control becomes uncertain.

  In recent years, next-generation optical discs such as Blu-ray Disk (hereinafter referred to as BD) using a laser beam having a wavelength of 405 [nm] in the blue wavelength region have also appeared, and three types of discs, CD, DVD and BD. Although an optical pickup compatible with the above has been developed, in such an optical pickup, when the diffraction grating is divided into three diffraction regions for DVD, CD and BD, the utilization efficiency of the reflected light beam is further reduced. There was a problem of doing. In addition, there is a problem in that it is difficult to realize an appropriate focus pull-in range for each of DVD, CD, and BD with such an optical pickup that supports three types of optical disks.

  The present invention has been made in consideration of the above points, and an object of the present invention is to propose an optical pickup apparatus and an optical disk apparatus that can perform reliable operations on a plurality of types of optical disks with a simple configuration.

  In order to solve such a problem, in the present invention, in an optical pickup device corresponding to a plurality of types of optical recording media that read out information using light beams of different wavelengths, the light that receives the light beams reflected by the optical recording media. Provided between the detector, the optical recording medium, and the photodetector, ± 2nd order diffracted light is generated for the light beam of the first wavelength and is incident on the photodetector, and the abbreviated first wavelength. A diffraction grating that generates ± first-order diffracted light and makes it incident on the photodetector is provided for the light beam having the second wavelength that is doubled.

  The grating pattern of the diffraction grating is generated so that ± 2nd order diffracted light is generated for the light beam of the first wavelength and ± 1st order diffracted light is generated for the light beam of the second wavelength that is twice that of the light beam. By selecting, by making the diffraction angles of the ± 2nd order diffracted light of the first wavelength light beam and the ± 1st order diffracted light of the second wavelength light beam substantially coincide, The ± first-order diffracted light of the second-order diffracted light and the light beam of the second wavelength can be made incident on the common photodetector.

  According to the present invention, ± 2nd order diffracted light is generated for the light beam of the first wavelength, and ± 1st order diffracted light is generated for the light beam of the second wavelength that is twice that of the light beam. By selecting the grating pattern of the diffraction grating, the diffraction angles of the ± 2nd order diffracted light of the light beam of the first wavelength and the ± 1st order diffracted light of the light beam of the second wavelength are made to substantially coincide with each other. The optical pickup device can make the ± 2nd order diffracted light of the light beam of the wavelength and the ± 1st order diffracted light of the light beam of the second wavelength incident on the common photodetector, thereby minimizing the number of the photodetectors. Can be miniaturized. In addition, the influence of stray light when using a multi-layer disc can be reduced, and diffracted light can be generated using the entire part of the light beam of the light beam, so the light beam output efficiency is improved and the output signal of the photodetector is improved. Since the level can be increased, it is possible to improve the accuracy of the signal and realize an optical pickup device capable of performing reliable operation on a plurality of types of optical disks.

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

(1) Overall Configuration of Optical Disc Device In FIG. 1, reference numeral 1 denotes an optical disc device to which the present invention is applied as a whole, and the control unit 2 executes the program according to a basic program or application program stored in a nonvolatile memory (not shown). Each part of the optical disk apparatus 1 is controlled.

  That is, the control unit 2 rotates the spindle motor 4 via the servo circuit 3 and rotationally drives the optical disc 8 placed on a turntable (not shown). Further, the control unit 2 rotates the feed motor 5 via the servo circuit 3 to move the optical pickup 7 in the radial direction of the optical disk 8. Further, the control unit 2 controls the signal processing unit 6 to execute reading and writing of data with respect to the optical disc 8.

  Further, the control unit 2 controls a lens driving device (not shown) of the optical pickup 7, drives the objective lens of the optical pickup 7 in the tracking direction and the focusing direction, and focuses the laser beam on the recording surface of the optical disk 8. Let

  The optical disc apparatus 1 is compatible with three types of optical discs of DVD, CD, and BD, and stores various control parameters such as an optimum light beam output corresponding to the disc type in a nonvolatile memory (not shown). The control unit 2 recognizes the type of the mounted optical disk 8 based on a reproduction signal from the optical pickup 7 and the like, and uses a control parameter corresponding to the recognized type to output a laser output, a light emission pattern, a spindle rotation speed, and the like. To control.

(2) Configuration of Optical Pickup FIG. 2 shows the configuration of the optical pickup 7 for red laser light (wavelength 660 [nm]) corresponding to DVD, infrared laser light (780 [nm]) corresponding to CD, and BD. From the laser diode 9 corresponding to the three wavelengths of the corresponding blue laser light (wavelength 405 [nm]), a laser light having a wavelength corresponding to the type of the optical disk 8 to be used is emitted as an outgoing light beam and incident on the polarization beam splitter 10. Let

  The polarization beam splitter 10 transmits the outgoing light beam according to its polarization plane, converts it into parallel light by the collimator lens 11, and enters the quarter-wave plate 12. The quarter-wave plate 12 converts the outgoing light beam from P-polarized light to circularly-polarized light and enters the objective lens 12. The objective lens 12 condenses the emitted light beam and irradiates the optical disk 8.

  Furthermore, the objective lens 12 condenses the reflected light beam formed by irradiating the optical disk 8 with the emitted light beam, and converts the circularly polarized light into S-polarized light by the quarter wavelength plate 12 so as to enter the collimator lens 11. The collimator lens 11 converts the reflected light beam from parallel light into convergent light and makes it incident on the polarization beam splitter 10.

  The polarization beam splitter 10 causes the reflected light beam to be substantially totally reflected in accordance with the polarization direction and enter the diffraction grating 14. The diffraction grating 14 generates + n-order and −n-order (n = 1, 2, 3,...) Diffracted light with a diffraction angle corresponding to the wavelength of the reflected light beam, and irradiates the light receiving element 15. Here, the + n-order diffracted light and the −n-order diffracted light are the front focal point and the back focal point, respectively, and the light receiving element generates a focus error signal using the SSD method based on the received light amounts of the + n-order diffracted light and the −n-order diffracted light. At the same time, a reproduction signal is generated based on the light amounts of the + n-order diffracted light and the −n-order diffracted light, and is supplied to the signal processing unit 6 (FIG. 1).

(3) Structure of diffraction grating Next, the structure of the diffraction grating 14 according to the present invention will be described in detail. 3C shows the cross-sectional shape of the grating pattern of the diffraction grating 14, and FIG. 4C shows the planar shape of the grating pattern. The diffraction grating 14 is a first grating pattern 14A having a grating period L / 2 and a grating depth D1 mainly acting on light having a wavelength of 405 [nm] (FIGS. 3A and 4A). The second grating pattern 14B having a grating period L and a grating depth D2 mainly acting on light having a wavelength of 660 [nm] and a wavelength of 780 [nm] (FIGS. 3B and 4B) Are combined patterns (FIGS. 3C and 4C). As shown in FIG. 4C, the grating pattern of the diffraction grating 14 is an array of quadratic curves, whereby the diffraction grating 14 exhibits the action of a cylindrical lens.

  The grating pattern of the diffraction grating 14 in which the first grating pattern 14A and the second grating pattern 14B are overlapped is L / 4, L / 8, L / 8, L / 4, L / 8, L / 8. At intervals, the lattice depth changes as D1 + D2, D2, 0, D1, 0, D2.

  Note that as the grating pattern of the diffraction grating 14, a pattern (FIG. 3D) in which peaks and valleys of the grating pattern shown in FIG. The lattice pattern in this case is L / 8, L / 4, L / 8, L / 8, L / 4, L / 8, and the lattice depths are D1 + D2, D2, D1 + D2, D1, 0, D1. It has changed.

  The grating depths D1 and D2 are D1 = 1.6 × λ / (n−1) and D2 = 0.92 with respect to a wavelength λ of 405 [nm], where n is the refractive index of the diffraction grating 14. Xλ / (n-1) In this embodiment, the refractive index of the diffraction grating 14 is 1.5. In this case, the grating depth D1 is 1.3 [μm], and the grating depth D2 is 0.75 [μm].

  FIG. 5 shows the relationship of the diffraction efficiency to the grating depth in a diffraction grating having a grating interval L. When the grating depth is D1 = 1.3 [μm], it is mainly ± 1 for light with a wavelength of 405 [nm]. Next-order diffracted light is generated, and 0th-order diffracted light is mainly generated for light having wavelengths of 660 [nm] and 780 [nm]. Since the first grating pattern 14A has a grating period of L / 2 and a grating depth of D1, the first grating pattern 14A generates ± second-order diffracted light with respect to light having a wavelength of 405 [nm]. This transmits light of 660 [nm] and 780 [nm].

  In addition, when the grating depth is D2 = 0.75 [μm], ± 1st order diffracted light is mainly generated for light of wavelengths 660 [nm] and 780 [nm], and for light of wavelength 405 [nm]. Mainly generate 0th-order diffracted light. Since the second grating pattern 14B has a grating period of L and a grating depth of D2, the second grating pattern 14B generates ± first-order diffracted light with respect to light having wavelengths of 660 [nm] and 780 [nm]. In addition, light having a wavelength of 405 [nm] is transmitted.

  The diffraction grating 14 formed by superimposing the first grating pattern 14A and the second grating pattern 14B has a pattern with a grating period L / 2 and a grating depth D1 for light having a wavelength of 405 [nm]. It acts to generate ± 2nd order diffracted light, and a pattern having a grating period L and a grating depth D2 acts on light of wavelengths 660 [nm] and 780 [nm] to generate ± 1st order diffracted light.

  FIGS. 6A to 6C show the diffraction efficiency from the 0th order to the ± 7th order by the diffraction grating 14 for each wavelength, and the light of wavelength 405 [nm] is shown in FIG. ), The ± 2nd order diffracted light is dominant, and the light of wavelengths 660 [nm] and 780 [nm] is ± 1st order diffracted light as shown in FIG. 6 (B) and FIG. 6 (C). It turns out that it is dominant.

  Here, since the diffraction angle by the diffraction grating is proportional to the wavelength, the diffraction angles of the ± 2nd order diffracted light having the wavelength of 405 [nm] and the ± 1st order diffracted light having the wavelength of 780 [nm] are substantially the same. Also, the ± 1st order diffracted light of wavelength 660 [nm] and the ± 1st order diffracted light of wavelength 780 [nm] have close diffraction angles. Therefore, ± 2nd order diffracted light having a wavelength of 405 [nm], ± 1st order diffracted light having a wavelength of 780 [nm], and ± 1st order diffracted light having a wavelength of 660 [nm] can be received by a common photodetector. .

  FIG. 7A shows the irradiation state of ± 2nd order diffracted light of each wavelength with respect to the photodetectors 15A and 15B of the light receiving element 15, and ± 2 next time with a wavelength of 405 [nm] to the photodetectors 15A and 15B. Only Origami has arrived. On the other hand, FIG. 7B shows the irradiation state of ± 1st order diffracted light of each wavelength with respect to the photodetectors 15A and 15B, and the wavelengths of 660 [nm] and 780 [nm] with respect to the photodetectors 15A and 15B. Only ± first-order diffracted light has reached.

  That is, when using a BD using a laser beam having a wavelength of 405 [nm], only the ± 2nd-order diffracted light is irradiated to the photodetectors 15A and 15B, and diffracted light of other orders affects the photodetectors 15A and 15B. Does not reach. Further, when using a DVD using a laser beam having a wavelength of 660 [nm] and using a CD using a laser beam having a wavelength of 780 [nm], only the ± first-order diffracted light is applied to the photodetectors 15A and 15B, and the other orders. Diffracted light does not affect the photodetectors 15A and 15B.

  The light-receiving surface of the photodetector 15A is divided into light-receiving surfaces A, E, and B in a strip shape. Similarly, the light-receiving surface of the photodetector 15B is divided into light-receiving surfaces C, F, and D. The light receiving element 15 performs current / voltage conversion on the output signals of the light receiving surfaces A to F to generate detection signals A to F, and further, a focus error signal using an arithmetic expression FE = (A + B + F) − (C + D + E) of the SSD method. An FE is generated and supplied to the signal processing unit 6 (FIG. 1).

  Further, since the diffraction angle by the diffraction grating is proportional to the wavelength, the lens power of the diffraction grating is also proportional to the wavelength. Since this optical pickup 7 uses ± 2nd order diffracted light for wavelength 405 [nm] and ± 1st order diffracted light for wavelengths 660 [nm] and 780 [nm], these lens powers are almost equal. It becomes. As a result, the optical pickup 7 can set an optimum focus pull-in range for each of DVD, CD, and BD.

8A to 8C show the focal positions of ± 2nd order diffracted light having a wavelength of 405 [nm], ± 1st order diffracted light having a wavelength of 660 [nm], and ± 1st order diffracted light having a wavelength of 780 [nm]. Each of them focuses on a position defocused by y _BD , y _DVD , and y _CD from the light receiving surface of the photodetector.

Here, for example, the focus pull-in range X in BD is obtained by X = y _BD / β ^{2 where} β is the lateral magnification (ratio of the objective lens focal length to the collimator lens focal length). Normally, a focus pull-in range X in BD is 3 [μm], and a lateral magnification β is 12, which sets y _BD .

The relationship between the defocus positions y _BD , y _DVD , and y _CD in the optical pickup 7 of the present invention is as follows: y _DVD = 660 [nm] / (405 [nm] × 2) × y _BD , y _CD = 780 [nm] / (405 [nm] × 2) × y _BD . In general, it is appropriate that the lateral magnifications of DVD and CD are 6 and 4.5, respectively. As a result, the focus pull-in range X in the optical pickup 7 of the present invention is 3 [μm] for BD, 10 [μm] for DVD, and 21 [CD] for CD, as shown in FIG. μm] and an appropriate value as an optical pickup can be obtained.

  Further, in the case of an optical pickup using a general DVD / CD compatible objective lens, the lateral magnification of the CD is 6, which is the same as that of the DVD, but even in this case, as shown in FIG. The range X is 12 [μm], and a practical focus pull-in range can be realized.

(4) Operation and Effect In the above configuration, the optical pickup 7 generates ± second-order diffracted light with respect to the light beam having a wavelength of 405 [nm] and light having a wavelength of 660 [nm] and a wavelength of 780 [nm]. The grating pattern of the diffraction grating 14 was set so that ± 1st order diffracted light was generated for the beam.

  For this reason, in this optical pickup 7, the diffraction angle of ± 2nd order diffracted light with a wavelength of 405 [nm] is close to the diffraction angle of ± 1st order diffracted light with a wavelength of 660 [nm] and a wavelength of 780 [nm], It is possible to irradiate a close range on the light receiving element 15, and these can be received by the common photodetectors 15A and 15B.

  As a result, in this optical pickup 7, the number of photodetectors provided on the light receiving element 15 can be minimized, and further, the number of amplifiers on the light receiving element 15 for current / voltage conversion of the output of the photodetector can be increased. Thus, the light receiving element 15 can be reduced in size and power consumption, and the optical pickup 7 and the optical disc apparatus 1 can be reduced in size and power consumption. Since ± 2nd order diffracted light with a wavelength of 405 [nm] and ± 1st order diffracted light with a wavelength of 660 [nm] and a wavelength of 780 [nm] are irradiated in a close range, the photodetectors 15A and 15B that receive them are received. Light receiving area can be reduced, and the parasitic capacitances of the photodetectors 15A and 15B can be reduced, thereby improving the frequency characteristics of the photodetectors 15A and 15B and generating more accurate signals. .

  Further, in this optical pickup 7, an L / 2 period grating pattern for generating ± 2nd order diffracted light having a wavelength of 405 [nm] and an L period for generating ± 1st order diffracted light having a wavelength of 660 [nm] and a wavelength of 780 [nm]. When the grating pattern of the diffraction grating 14 is formed by superimposing the grating pattern, the diffracted light can be generated using the entire portion of the reflected light beam incident on the diffraction grating 14. For this reason, this optical pickup 7 has high utilization efficiency of the reflected light beam, and can increase the amount of diffracted light incident on the photodetectors 15A and 15B, thereby increasing the signal level of the output of the photodetector, It is possible to reduce the influence of noise and generate a more accurate signal.

  Further, in this optical pickup 7, since the number of photodetectors provided on the light receiving element 15 can be minimized, the influence of stray light from the unfocused recording layer entering the photodetector when using a multilayer disk is minimized. In the limit, a signal with higher accuracy can be generated.

  Furthermore, with this optical pickup 7, it is possible to set an appropriate focus pull-in range for each of BD, DVD, and CD, whereby the servo characteristics are stabilized and the reproduction signal characteristics are also improved. Also, resistance to disturbances such as device collisions is improved. In addition, the fact that the focus pull-in range can be optimally set also means that the lateral magnification of each of BD, DVD and CD can be optimally set, thereby optimizing the light utilization efficiency. Therefore, the power consumption of the laser diode can be reduced and the reliability can be improved.

(5) Other Embodiments In the above-described embodiment, the present invention is applied to the optical pickup 7 in which each optical element such as the laser diode 9 and the polarization beam splitter 10 is individually mounted on the chassis. However, the present invention is not limited to this, and the present invention can also be applied to an optical pickup 7 using an optical integrated element in which various optical elements are integrated.

  FIG. 10, in which parts corresponding to those in FIG. 2 are given common reference numerals, shows the optical pickup 20 having such a configuration, and includes an optical integrated element 21, a collimator lens 11, a quarter-wave plate 12, and an objective lens 13. For example, it is mounted on an optical pickup base (not shown) made of an aluminum die cast product.

  The optical integrated element 21 is configured by assembling various components to a package 22 in which a laser diode 9 or the like is embedded and sealed. That is, a light receiving element 15 for obtaining a reproduction signal and a focus error signal from the reflected laser light reflected by the optical disk 8 is attached to the upper surface of the package 22, and a mold composite element 23 having a diffraction grating 14 and a hologram 23B. Is attached via a spacer 24. Furthermore, a laminated prism 25 configured by combining a plurality of prisms is attached to the upper surface of the mold composite element 23.

  The package 22 has a box shape formed of ceramics, for example, and a laser diode 9, a prism 32, and a second light receiving element 33 are disposed therein. A reflective lid 21A that covers the entire opening of the package 22 is attached to the lower end of the peripheral surface portion of the package 21. The laser diode 9, the prism 32, and the second light receiving element 33 are sealed inside the package 22. Is done.

  The prism 32 functions as an optical path changing body that changes the optical path of the laser light emitted from the laser diode 9. That is, in the incident direction of the laser beam in the prism 32, a reflecting surface 32A inclined upward by 45 ° with respect to the optical path of the laser beam is provided, and the reflecting surface 32A emits about 80% of the laser beam. Reflects upward as a beam and transmits the remaining 20% as a monitor light beam.

  The monitor light beam transmitted through the reflecting surface 32A of the prism 32 is refracted downward by the prism 32 and guided to the upper surface of the reflecting lid 21A. A reflective surface is formed on the upper surface of the reflective lid 21A, and the reflective lid 21A reflects the monitor light beam from the prism 32 on the reflective surface, and a monitor light detector (not shown) of the second light receiving element 33. ). The light amount of the monitor light beam is proportional to the light emission power of the laser diode 9, and the monitor light detector generates a detection current proportional to the light emission power of the laser diode 9 according to the incident light amount of the monitor light beam.

  On the other hand, the outgoing light beam reflected by the reflecting surface 32 </ b> A of the prism 32 passes through the outgoing hole opened in the package 22 and enters the polarizing beam splitter 10 of the laminated prism 24.

  The polarization beam splitter 10 transmits the outgoing light beam according to its polarization plane, converts it into parallel light by the collimator lens 11, and enters the quarter-wave plate 12. The quarter-wave plate 12 converts the outgoing light beam from P-polarized light to circularly-polarized light and enters the objective lens 12. The objective lens 12 condenses the emitted light beam and irradiates the optical disk 8.

  Furthermore, the objective lens 12 condenses the reflected light beam formed by irradiating the optical disk 8 with the emitted light beam, and converts the circularly polarized light into S-polarized light by the quarter wavelength plate 12 so as to enter the collimator lens 11. The collimator lens 11 converts the reflected light beam from parallel light into convergent light and makes it incident on the polarization beam splitter 10.

  The polarization beam splitter 10 causes the reflected light beam to be substantially totally reflected in accordance with the polarization direction and enter the half mirror 24B. The half mirror 24 </ b> B reflects a part of the reflected light beam by 90 degrees and enters the diffraction grating 14 of the mold composite element 23, and the + and − diffracted lights diffracted by the diffraction grating 14 are focused on the light receiving element 15. The light is incident on an error signal generating photodetector (not shown). The half mirror 24B transmits the remainder of the reflected laser light and makes it incident on a reproduction signal generating photodetector (not shown) of the light receiving element 12 through the total reflection mirror 24C.

  Also in the optical pickup 20 using such an optical integrated element 21, by using the diffraction grating 14 having the above-described diffraction characteristics, the number of photodetectors and amplifiers can be minimized, and the light receiving element 15 can be reduced in size and size. It is possible to obtain effects such as power consumption, improvement of frequency characteristics and use efficiency of reflected light beam, reduction of influence of stray light when using a multilayer disk, and optimization of a focus pull-in range.

  Further, in the above-described embodiment, the case where the present invention is applied to the optical disk apparatus corresponding to the three types of optical disks of BD, DVD, and CD has been described. However, the present invention is not limited to this, and the grating pattern of the diffraction grating 14 By appropriately setting the above, the present invention can be applied to an optical disc apparatus corresponding to various other types of optical discs.

  The present invention can be applied to an optical disc apparatus corresponding to a plurality of types of optical discs.

It is a block diagram which shows the whole structure of an optical disk device. It is a basic diagram which shows the structure of an optical pick-up. It is a basic diagram which shows the cross-sectional shape of the diffraction grating by this invention. It is a basic diagram which shows the grating pattern of the diffraction grating by this invention. It is a graph which shows the relationship between a grating depth and diffraction efficiency. It is a graph which shows the relationship between a diffraction order and diffraction efficiency. It is a basic diagram which shows the irradiation state of the diffracted light with respect to a photodetector. It is a basic diagram with which it uses for description of the defocus position about each wavelength. It is a table | surface which shows the focus drawing-in range about each wavelength. It is a basic diagram which shows the structure of the optical pick-up of other embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Optical disk apparatus, 2 ... Control part, 3 ... Servo circuit, 4 ... Spindle motor, 5 ... Feed motor, 6 ... Signal processing part, 7 ... Optical pick-up, 8 ... Optical disk, 9 ... DESCRIPTION OF SYMBOLS Laser diode, 10 ... Polarizing beam splitter, 11 ... Collimator lens, 12 ... 1/4 wavelength plate, 13 ... Objective lens, 14 ... Diffraction grating, 15 ... Light receiving element.

Claims (9)

An optical pickup device corresponding to a plurality of types of optical recording media for reading information using light beams of different wavelengths,
A photodetector for receiving the light beam reflected by the optical recording medium;
Provided between the optical recording medium and the optical detector, ± 2nd order diffracted light is generated and incident on the optical detector with respect to the optical beam of the first wavelength, and the first wavelength is approximately An optical pickup device comprising: a diffraction grating that generates ± first-order diffracted light and makes it incident on the photodetector for a light beam having a second wavelength that is twice the wavelength. The optical pickup device according to claim 1, wherein the first wavelength is approximately 405 [nm], and the second wavelength is approximately 660 [nm] or approximately 780 [nm]. The diffraction grating has a first grating pattern that generates ± 2nd order diffracted light with respect to the light beam with the first wavelength, and a second that generates ± 1st order diffracted light with respect to the light beam with the second wavelength. The optical pickup device according to claim 2, wherein the optical pickup device has a composite lattice pattern in which the lattice pattern is superimposed. The first grating pattern has a grating period L / 2 and a grating depth D1, the second grating pattern has a grating period L and a grating depth D2, and the synthesized grating pattern has approximately L / 4, L The lattice depth is substantially D1 + D2, D2, 0, D1, 0, D2 at intervals of / 8, L / 8, L / 4, L / 8, and L / 8. Optical pickup device. When the refractive index of the diffraction grating is n and the wavelength λ is 405 [nm], the grating depth D1 is approximately 1.6 × λ / (n−1), and the grating depth D2 is approximately 0.92. The optical pickup device according to claim 4, wherein xλ / (n−1). The first grating pattern has a grating period L / 2 and a grating depth D1, the second grating pattern has a grating period L and a grating depth D2, and the synthesized grating pattern has approximately L / 8, L The lattice depth is substantially D1 + D2, D2, D1 + D2, D1, 0, D1 at intervals of / 4, L / 8, L / 8, L / 4, and L / 8. Optical pickup device. When the refractive index of the diffraction grating is n and the wavelength λ is 405 [nm], the grating depth D1 is approximately 1.6 × λ / (n−1), and the grating depth D2 is approximately 0.92. The optical pickup device according to claim 6, wherein xλ / (n−1). A focus error signal is generated based on the detection result of detecting the spot size of the ± 2nd order diffracted light of the light beam of the first wavelength or the ± 1st order diffracted light of the light beam of the second wavelength by the photodetector. The optical pickup device according to claim 1. An optical disc apparatus corresponding to a plurality of types of optical recording media for reading information using light beams of different wavelengths,
A photodetector for receiving the light beam reflected by the optical recording medium;
Provided between the optical recording medium and the optical detector, ± 2nd order diffracted light is generated and incident on the optical detector with respect to the optical beam of the first wavelength, and the first wavelength is approximately An optical disc apparatus comprising: a diffraction grating that generates ± first-order diffracted light and makes it incident on the photodetector for a light beam having a second wavelength that is twice the wavelength.

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