JP2009009676A - Optical head and optical disk system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a recording and reproducing optical head and optical disk system compatible with BD/HDDVD/DVD/CD. <P>SOLUTION: The optical head and the optical disk system include semiconductor laser devices 2a, 2c with wavelengths of 455 nm, 655 nm, and 785 nm; a polarized-light switching component 5 for luminous fluxes with the wavelength of 455 nm and a polarizing beam splitter 6, and also, has a first collimator lens 8a for converting light fluxes having passed through the polarizing beam splitter 6 to almost parallel light fluxes; a first quarter-wavelength plate 9a; an object lens for BD 11a; and a first photodetector 14a; and furthermore, has a composite prism 7 for transmitting most of light fluxes from the semiconductor laser 2c with the wavelengths of 655 nm and 785 nm while reflecting light fluxes reflected by the polarizing beam splitter 6; a second collimator lens 8b for converting light fluxes emitted from the composite prism 7 to almost parallel light fluxes; a second quarter-wavelength plate 9b; a HDDVD/DVD/CD-compatible object lens 11b; and a second photodetector 14b. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical head and an optical disc apparatus.

  Optical disc devices such as Digital Versatile Disc (hereinafter referred to as DVD) and Compact Disc (hereinafter referred to as CD) are widely used as information recording / reproducing devices characterized by non-contact, large capacity, high-speed access and low-cost media. ing. In recent years, in order to record and store a larger amount of information, Blu-ray Disc (hereinafter referred to as BD) and High-Definition DVD (hereinafter referred to as HD DVD) using a laser with a wavetable of about 405 nm band. High-density optical disk devices with different standards have been developed.

  Under such circumstances, there is a strong demand in the market for compatible optical heads compatible with both BD and HD DVD standards as well as DVD and CD.

  Therefore, in Japanese Patent Application Laid-Open No. 2006-268899, a BD / HD DVD / DVD / CD compatible optical head is achieved by using a three-wavelength laser in which three lasers are housed in one package and using a polarization state changing means. is doing. Japanese Patent Laid-Open No. 2006-24351 similarly achieves a BD / HD DVD / DVD / CD compatible optical head by switching the optical path using a Bragg grating.

JP 2006-268899 A JP 2006-24351 A

  In Example 1 (FIG. 1) in Japanese Patent Laid-Open No. 2006-268899, a three-wavelength laser is used, but a blue laser uses a GaN substrate, while a red / infrared laser uses a GaAs substrate. Therefore, a monolithic type three-wavelength laser in which three lasers are arranged on the same substrate cannot be manufactured. For this reason, when it is considered that the blue laser and the monolithic two-wavelength (red / infrared) laser are arranged on a straight line, the emission point of the blue laser is far away from the emission point of the two-wavelength laser, and the compatible objective There arises a problem that large aberration occurs due to the image height characteristics of the lens. Further, since different substrates are bonded together, the emission point variation between the blue laser and the two-wavelength laser is very large compared to the emission point variation in the monolithic two-wavelength laser, and the light receiving surface provided in the photodetector. There arises a problem that the light spot cannot be incident on the center of the screen. In addition, the three-wavelength laser has a problem that the price is high due to low yield.

  On the other hand, it is possible to arrange the blue laser emission point on the upper side or the lower side of the two-wavelength laser emission point, but in this case, due to restrictions on the arrangement of the light receiving surface in the photodetector, TES The DPP method cannot be used for detection. In the configuration in which three wavelengths are put in one photodetector, the reflected light from the optical disk can be divided into multiple parts to have the same effect as the DPP method, as in the BD system of Example 1 described below. Can not. In consideration of the eccentricity of the optical disk and the spindle motor, the normal push-pull method is not practical, and therefore, the differential phase detection method (hereinafter referred to as the DPD method) must be used as the TES detection. In that case, due to the principle of the DPD method, it is not possible to cope with signal recording on an optical disc and reproduction of an optical disc having an unrecorded portion. Therefore, when a three-wavelength laser is used, even when three light emitting points are two-dimensionally arranged, there are problems that recording is not supported, light emitting point variation is large, and cost is high.

  As described above, the problem is that the optical head disclosed in JP-A-2006-268899 using a three-wavelength laser cannot cope with recording.

  In Japanese Patent Application Laid-Open No. 2006-24351, two objective lenses are arranged in the radial direction of the optical disk, and a light beam from a blue laser is similarly incident from the radial direction. Then, using the Bragg grating, the optical path is switched so that the light beam is incident on the BD objective lens and the HD DVD objective lens. The reflected light from the optical disk is received by the same photodetector for both BD and HD DVD.

  Since BD and HD DVD record signals at high density, the various margins allowed for the optical head are smaller than that of CD or DVD, that is, it is more difficult to ensure performance. Therefore, when producing a BD / HD DVD / DVD / CD compatible optical head, it is most important to ensure the characteristics of BD and HD DVD. However, in the configuration of Japanese Patent Application Laid-Open No. 2006-24351, 1) both the BD and HD DVD use the same collimator lens and detection lens, so that the optimal forward magnification and detection system magnification cannot be given to each. 2) Since the BD and the HD DVD have the same optical system except for the mirror and the objective lens, when the assembly adjustment of one of the BD or HD DVD is finished, the other optical System adjustment cannot be performed.

  Taking the case where the BD optical system is adjusted first as an example, ideally, when the BD optical system has been adjusted, the HD DVD is in the best condition by simply switching the optical path using the Bragg grating. Become. However, in an actual machine, there are deviations from ideal conditions due to errors in parts dimensions, refractive index, etc., assembly errors, and the like. Therefore, even if the diffraction grating is adjusted so that the three-spot interval on the optical disc is optimal in the BD, the interval is shifted in the HD DVD, or the light spot is incident on the ideal position of the photodetector in the BD. Even with such adjustment, a phenomenon occurs in which a light spot is incident on a position shifted from the ideal position of the photodetector in HD DVD. As described above, in a configuration in which BD and HD DVD have the same optical path as disclosed in JP-A-2006-24351, it is difficult to ensure the characteristics of BD and HD DVD.

  An object of the present invention is to provide an optical head and an optical disk apparatus compatible with BD / HD DVD / DVD / CD compatible recording and reproduction.

  The above object can be achieved by devising the configuration and arrangement of the laser and the photodetector as an example.

  According to the present invention, it is possible to provide a BD / HD DVD / DVD / CD compatible recording / reproducing optical head and optical disc apparatus.

  A specific configuration for carrying out the present invention will be described below using Example 1.

  Hereinafter, embodiments according to the present invention will be described in detail with reference to the drawings. Here, as an example of the embodiment, a BD / HD DVD / DVD / CD compatible optical head and an optical disk apparatus equipped with the same will be described.

  First, a BD optical system will be described with reference to FIGS. 1 to 3. FIG. 1 shows the configuration of an optical head according to the present invention, in which the horizontal direction is the radial direction (= tracking direction) 17 of the optical disk, the vertical direction is the tangential direction 18 of the optical disk, and the direction perpendicular to the paper surface is the focusing direction 19. is there.

  The divergent light emitted from the semiconductor laser 2a and having a wavelength of about 405 nm and whose polarization direction is substantially parallel to the paper surface enters the liquid crystal element 5. The liquid crystal element 5 has an action of converting the polarization direction of the incident light beam from a direction substantially parallel to the paper surface to a direction substantially perpendicular to the paper surface when the drive voltage is applied, but does not apply the drive voltage. In some cases, the incident light beam is transmitted as it is without changing the polarization direction. In the BD system of the optical head of the present invention, since no voltage is applied to the liquid crystal element 5, the light beam incident on the liquid crystal element 5 exits the liquid crystal element 5 with its polarization direction being substantially parallel to the paper surface. The light beam emitted from the liquid crystal element 5 enters a polarizing beam splitter (hereinafter referred to as PBS) 6, but the P-polarized component occupying most of the incident light beam passes through PBS 6, and the remaining S-direction component is PBS 6. To reflect. The PBS 6 has Tp = 98%, Rs = 98%, and has a characteristic of transmitting almost 100% of the P-polarized component of the incident light beam and reflecting almost 100% of the S-direction component.

  The light beam reflected from the PBS 6 is divided into three light beams by the diffraction grating 3b, and the light beam incident on the composite prism 7 is reflected, whereas the light beam passing above the composite prism 7 goes straight as it is. The unit enters the front monitor 16. The front monitor 16 is provided to detect a change in the intensity of the laser beam emitted from the semiconductor laser 2a. By feeding back the output of the front monitor 16 to the laser control circuit in the optical disc apparatus, the front monitor 16 The intensity of the emitted light is made constant.

  On the other hand, a light beam having a polarization direction transmitted through PBS 6 and parallel to the paper surface is converted into a substantially parallel light beam by the collimator lens 8a. The collimating lens 8a is attached to a drive mechanism (not shown), and the collimating lens 8a is moved in the optical axis direction 18 to change the emitted light beam from substantially parallel light to weakly convergent light or weakly divergent light. It can be changed to. Thus, it is possible to correct the spherical aberration caused by the substrate thickness error of the optical disk by changing the amount of spherical aberration of the light spot focused on the optical disk.

  The light beam emitted from the collimating lens 8a enters the polarizing diffraction grating 4a. This polarizing diffraction grating 4a acts as a diffraction grating when a light beam having a polarization direction perpendicular to the paper surface is incident, and as a diffraction grating when a light beam having a polarization direction parallel to the paper surface is incident. The light beam is transmitted as it is. Here, since a light beam having polarized light in a direction parallel to the paper surface is incident, the light beam is transmitted without being diffracted.

  The light beam emitted from the polarizing diffraction grating 4a enters the quarter-wave plate 9a, is converted into circularly polarized light, is bent in a focusing direction 19 by a rising mirror (not shown), and is mounted on the actuator 10 Light is focused on the signal recording surface of the BD by the objective lens 11a. The objective lens 11a is a BD-only lens with NA = 0.85 and one glass (single lens).

  The light beam reflected from the optical disk is converted into a substantially parallel light beam by the objective lens 11a, is reflected by a rising mirror (not shown), and is incident on the quarter-wave plate 9a again, and the polarization direction thereof is perpendicular to the paper surface. Is converted. The light beam emitted from the quarter-wave plate 9a enters the polarizing diffraction grating 4a and is divided into a plurality of light beams. The plurality of light beams emitted from the polarizing diffraction grating 4a are converted into convergent light by the collimating lens 8a, reflected by the PBS 6, and then incident on the photodetector 14a.

  FIG. 2 shows a pattern of the grating formed on the polarizing diffraction grating 4a. The polarizing diffraction grating 4a is composed of 12 deflecting grating surfaces (a to l), and a dotted line 31 indicates the diameter of a light beam incident on the polarizing diffraction grating 4a. A region 32 surrounded by a two-dot chain line portion and a dotted line 31 (hatched) is a push-pull region where the diffracted 0th-order light and ± first-order light are reflected by the BD track. ing.

  A light beam whose polarization direction is the focusing direction that is incident on the polarizing diffraction grating 4a is divided into ± first-order light on each of the 12 deflecting grating surfaces (a to l), so that a total of 24 light beams are generated. Emitted. Here, the intensity ratio between the + 1st order light and the −1st order light is set to 1: 5. Further, the 0th order light is not generated.

  FIG. 3 shows a light receiving surface pattern in the photodetector 14a. The photodetector includes 18 light receiving surfaces, −1st order light diffracted by the polarizing diffraction grating 4a is incident on the light receiving surfaces A to J, and + 1st order is applied to the light receiving surfaces M to T. It is configured so that light enters. The circles (◯) shown in FIG. 3 indicate the light beams irradiated to the respective light receiving surfaces at the time of focusing, and the signs a to l are light beams diffracted on the deflectable grating surface with the same signs in FIG. It is shown that.

In the BD system in the optical head of the present invention, a knife edge method is used for detecting a focus error signal (hereinafter referred to as FES), and a modified DPP method and a DPD method are used for detecting a TES. Each arithmetic expression is as follows.
FES = (O + N)-(M + P)
TES = {(A + B + E + F)-(C + D + H + G)}-Gain × {(Q + R)-(T + S)}
DPD = {ph (A + C + E + G) -ph (B + D + F + H)}: phase comparison RF = A + B + C + D + E + F + G + H + I + J
Note that {(A + B + E + F)-(C + D + H + G)} in the TES substantially corresponds to the main push-pull signal. On the other hand, the sub push-pull signal has both the push-pull amplitude and the DC offset component accompanying the lens shift, whereas {(Q + R)-(T + S)} As shown in FIG. 4, since signals other than the push-pull region are incident, there is no push-pull amplitude, and only a DC offset component accompanying the lens shift. Therefore, in the above TES, even if Gain × {(Q + R) − (T + S)} is subtracted, the push-pull amplitude does not increase, but by setting Gain appropriately. It is possible to cancel the DC offset accompanying the lens shift.

  As described above, the TES in the BD system of the optical head of the present invention has the same effect as the normal DPP method despite the fact that there is one spot on the optical disk. For this reason, it is possible to record a signal on an unrecorded optical disk.

  Next, the optical system of HD DVD will be described with reference to FIGS.

  The divergent light emitted from the semiconductor laser 2a and whose polarization direction is substantially parallel to the paper surface is converted by the liquid crystal element 5 to which the drive voltage is applied into the polarization direction that is substantially perpendicular to the paper surface. The light beam emitted from the liquid crystal element 5 enters the PBS 6, and the S-polarized component that occupies most of the light beam is reflected, and then incident on the diffraction grating 3 b, in order to perform TES detection using the DPP method. And is divided into three luminous fluxes of ± primary light. Among the light beams emitted from the diffraction grating 3b, most of the light beams enter the combining prism 7, and almost 100% of the incident light beams are reflected. The synthetic prism 7 has characteristics of Tp = 98% and Rs = 98% with respect to a light beam having a wavelength of about 405 nm. Further, as will be described later, the light flux having a wavelength of about 655 nm and a wavelength of about 785 nm has characteristics of Tp = 98% and Ts = 98%. On the other hand, the light beam passing through the upper side of the combining prism 7 goes straight as it is, and part of the light enters the front monitor 16.

  A light beam having a polarization direction reflected by the combining prism 7 and perpendicular to the paper surface is converted into a substantially parallel light beam by the collimator lens 8b, and then converted into circularly polarized light by the quarter-wave plate 9b. The quarter-wave plate 9b is not only a light beam having a wave table of about 405 nm, but also a wide-band quarter wave that acts as a quarter-wave plate for a light beam having a wavelength of about 655 nm and a wavelength of about 785 nm, as will be described later. It is a wave plate.

  The light beam emitted from the quarter-wave plate 9b is bent in the focusing direction 19 by a rising mirror (not shown), and then the light is focused on the signal recording surface of the HD DVD by the objective lens 11b mounted on the actuator 10 It is. This objective lens 11b is a single plastic (single) HD DVD / DVD / CD compatible objective lens, and NA = 0.65 for HD DVD luminous flux. The objective lens 11b is a three-wavelength infinite lens designed to obtain predetermined characteristics when a parallel light beam is incident on any of the HD DVD light beam, DVD light beam, and CD light beam. . As a result, it is possible to receive light beams of HD DVD, DVD, and CD by one photodetector 14b.

  The light beam reflected from the optical disk is converted into a substantially parallel light beam by the objective lens 11b, is reflected by a rising mirror (not shown), and is incident on the quarter-wave plate 9b again, and its polarization direction is parallel to the paper surface. Is converted. The light beam emitted from the quarter-wave plate 9b is converted into convergent light by the collimator lens 8b, then passes through the combining prism 7 and the broadband PBS 12, and is guided to the photodetector 14b by the detection lens 13b.

  FIG. 5 shows a light receiving surface pattern in the photodetector 14b. The light receiving surface has a configuration in which three commonly used quadrant detectors 34, 35, and 36 are arranged. However, as will be described later, in the optical head of the present invention, since a two-wavelength laser is used in the DVD / CD system, three quadrant detectors 37, 38, and 39 are further arranged. The HD DVD luminous flux and the DVD luminous flux enter the quadrant detectors 34, 35, and 36, and the CD luminous flux enters the quadrant detectors 37, 38, and 39.

In the HD DVD system in the optical head of the present invention, the astigmatism method is used for FES detection, and the DPP method and DPD method are used for TES detection. Each arithmetic expression is as follows.
FES = (A + C)-(B + D)
TES = {(A + D)-(B + C)}-Gain × {(E1 + E4 + F1 + F4)-(E2 + E3 + F2 + F3)}
DPD = {ph (A + C) −ph (B + D)}: phase comparison RF = A + B + C + D
As described above, since the DPP method is used for TES detection in the HD DVD system of the optical head of the present invention, it is possible to record a signal on an unrecorded optical disk.
Further, in the optical system of the optical head according to the present invention, the collimating lens is different between the BD 8a and the HD DVD 8b, so that an optimum optical magnification can be given to each. Also, since the diffraction grating is different for the BD 4a and the HD DVD 3b, it is possible to adjust the diffraction grating 4a, 3b to the best position / angle for each in the optical head assembly stage. It is. Furthermore, since the photodetectors are different for the BD 14a and the HD DVD 14b, the photodetectors 14a and 14b can be adjusted to the best positions for each in the optical head assembly stage. Is possible. And since it is the structure which can respond to both BD and HD DVD with one blue laser, it becomes small and cheap.

  As described above, in the optical head of the present invention, high recording / reproduction quality can be obtained for both the BD system and the HD DVD system.

  In the optical head of the present invention, a light beam that passes through the PBS 6 is used in the BD system, and the reflectance and transmittance characteristics of the composite prism 7 are set as described above. It becomes possible to delete the broadband half-wave plate (HWP2) in Example 1 (FIG. 1) of the publication. In the optical head of the present invention, the light utilization efficiency in the HD DVD system is maximized by setting the reflectivity of the combining prism 7 with respect to the HD DVD light flux to approximately 100%.

  Next, the DVD and CD optical system will be described below with reference to FIG. In the optical head of the present invention, in order to reduce the number of components and reduce the size, a monolithic type two-wavelength laser 2c in which a semiconductor laser oscillating at a wavelength of about 655 nm and a semiconductor laser oscillating at a wavelength of about 785 nm are integrated on the same substrate. It is equipped with.

  The divergent light emitted from the two-wavelength laser 2c and having a wavelength of about 655 nm and whose polarization direction is substantially parallel to the paper surface is incident on a half-wave plate (not shown) and converted to a direction whose polarization direction is substantially perpendicular to the paper surface. Is done. The half-wave plate is a broadband half-wave plate that acts as a half-wave plate for both light fluxes having a wavelength of about 655 nm and a wavelength of about 785 nm.

  A light beam emitted from a half-wave plate (not shown) enters the wavelength selective diffraction grating 3c. The wavelength selective diffraction grating 3c splits an incident light beam having a wavelength of about 655 nm into zero-order light and ± first-order light having a diffraction angle θ1 with respect to the zero-order light, whereas a light beam having a wavelength of about 785 nm. Is incident on the zero-order light and the ± first-order light having an angle θ2 different from the diffraction angle θ1 with respect to the zero-order light. By appropriately designing θ1 and θ2, the distance between the main spot and the sub spot on the optical disc can be optimized in each of the DVD system and the CD system. By using this wavelength selective diffraction grating 3c to divide the light beam into three, TES detection using the DPP method can be performed, and both DVD and CD systems can handle recording.

  Nearly 100% of the light beam emitted from the wavelength selective diffraction grating 3c is reflected by the broadband PBS 12. The broadband PBS 12 has characteristics of Tp = 98% and Rs = 98% with respect to any light flux having a wavelength of about 405 nm, a wavelength of about 665 nm, and a wavelength of about 785 nm. Note that Rs having a wavelength of about 405 nm may be any amount due to the configuration of the optical head of the present invention.

  The light beam emitted from the broadband PBS 12 is substantially 100% transmitted through the combining prism 7, and then converted into a substantially parallel light beam by the collimating lens 8b. Further, the light beam passing through the upper side of the combining prism 7 is reflected by the reflecting mirror 15, and then a part thereof enters the front monitor 16.

  The light beam emitted from the collimating lens 8b is converted into circularly polarized light by the quarter wavelength plate 9b, bent in a focusing direction 19 by a rising mirror (not shown), and then DVD by the objective lens 11b mounted on the actuator 10 The light is focused on the signal recording surface. The NA of the objective lens 11b with respect to the DVD light flux is 0.63.

  The light beam reflected from the optical disk is converted into a substantially parallel light beam by the objective lens 11b, is reflected by a rising mirror (not shown), and is incident on the quarter-wave plate 9b again, and its polarization direction is parallel to the paper surface. Is converted. The light beam emitted from the quarter-wave plate 9b is converted into convergent light by the collimator lens 8b, then passes through the combining prism 7 and the broadband PBS 12, and is guided to the photodetector 14b by the detection lens 13b.

  In the optical head of the present invention, the DVD light beam is incident on the light receiving surfaces 34, 35, and 36 of FIG. 5 in the same manner as the HD DVD light beam, and the astigmatism method and the differential astigmatism method are used for FES detection. The DPP method and the DPD method are used for detection.

  The CD light beam also follows the same optical path as the DVD light beam, and is guided to the photodetector 14b. The NA of the objective lens 11b with respect to the CD light beam is 0.51. In the optical head of the present invention, a CD-type light beam is incident on the light receiving surfaces 37, 38, and 39 of FIG. 5, and the astigmatism method is used for FES detection, and the DPP method and the DPD method are used for TES detection.

  As described above, in the optical head of the present invention, both the DVD system and the CD system use the DPP method for TES detection and can cope with recording.

  FIG. 7 shows an outline of an optical system arrangement in a thin optical head (hereinafter referred to as slim optical head) mounted on a notebook personal computer.

  Since BD and HD DVD have the same laser wavelength, when BD and HD DVD are compatible with one objective lens, the light utilization efficiency of BD and / or HD DVD is reduced, and at least one of them is used. Cannot be used for recording. Therefore, in order to support recording in both BD and HD DVD, the BD objective lens and the HD DVD objective lens must be mounted on the optical head. In addition to recording on DVD and CD in addition to BD and HD DVD, 1) 3 objective lens system for adding a DVD / CD compatible objective lens, and 2) the above objective lens for BD, and / or Two objective lens systems that add compatibility to the HD DVD objective lens are conceivable. As for 1), the volume and weight of the actuator increase, it is difficult to ensure acceleration and vibration characteristics, and it is difficult to mount on the slim optical head. Therefore, in the optical head of the present invention, 2) the 2 objective lens system is used.

  In the case of the two-objective system, the combinations of possible objective lenses and corresponding media are the four types shown in Table 1.

ＢＤは、ＮＡが０．８５と大きく、また、温度特性（温度変化に伴う収差の増加）も問題となることから、プラスチック１枚（単玉）ではＢＤ用レンズを作成することが困難である。そこで、プラスチックの２枚組レンズ、或いは、ガラス１枚（単玉）とせざるを得ない。ガラス１枚（単玉）レンズの場合、ガラスに回折格子を切ることにより他の媒体との互換性を持たせることは、技術的には可能であるが、回折格子付きのガラスレンズは、量産性が悪く、非常に価格が高くなってしまう。したがって、表１のb、c、dのようにＢＤ用対物レンズに互換作用を持たせる場合には、プラスチックの２枚組レンズ（プラスチックレンズに互換用の回折格子を作成）、或いは、ガラス１枚（単玉）レンズに別体の回折格子を組み合わせた組レンズとするしかなく、いずれの場合でも２枚組となるため対物レンズの厚さが大きくなり、スリム用光ヘッドでは実装困難である。
それに対し、ＨＤ ＤＶＤ用対物レンズは、ＮＡが０．６５であり、プラスチック１枚（単玉）で構成可能なことから、対物レンズの表面に互換用の回折格子を作成し、ＤＶＤおよびＣＤの互換性を持たせることが可能である。以上の理由から、本発明光ヘッドでは、表１のaの構成を採用し、ガラス１枚（単玉）のＢＤ専用対物レンズと、プラスチック１枚（単玉）のＨＤ ＤＶＤ／ＤＶＤ／ＣＤ互換対物レンズを用いている。

BD has a large NA of 0.85, and temperature characteristics (increased aberration due to temperature change) are also a problem, so it is difficult to make a lens for BD with a single plastic (single ball). . Therefore, it is unavoidable to use a plastic double-lens lens or a single glass (single ball). In the case of a single glass lens, it is technically possible to make glass compatible with other media by cutting the diffraction grating, but glass lenses with a diffraction grating are mass-produced. It ’s not good and the price is very high. Therefore, in order to make the BD objective lens compatible as shown in Table 1, b, c, d, a plastic double lens (create a compatible diffraction grating for the plastic lens) or glass 1 There is no choice but to use a single lens unit as a combination lens with a separate diffraction grating. In either case, the double lens set makes the objective lens thick and difficult to mount with a slim optical head. .
On the other hand, since the objective lens for HD DVD has an NA of 0.65 and can be composed of one piece of plastic (single ball), a compatible diffraction grating is created on the surface of the objective lens, and DVD and CD It is possible to have compatibility. For the above reasons, the optical head of the present invention adopts the configuration of a in Table 1 and is compatible with a single glass (single) BD objective lens and one plastic (single) HD DVD / DVD / CD. An objective lens is used.

  Next, the arrangement of the objective lens and the optical unit will be described. The BD objective lens and the HD DVD / DVD / CD compatible objective lens are arranged in the slim optical head as follows: 1) Two are arranged in the radial direction 17 of the optical disk, 2) Two are tangential directions of the optical disk There are two possible arrangements: As shown in FIGS. 7A to 7C, in the case of 1), both objective lenses 11a and 11b can be disposed on the axis 20 extending from the center of the optical disk in the driving direction of the optical head. In all of BD / HD DVD / DVD / CD, it is possible to use a normal DPP method using three spots. On the other hand, as shown in FIGS. 7D to 7F, in the case of 2), since at least one objective lens cannot be arranged on the shaft 20, when the normal DPP method is used, the off-center side is used. Then, the angle of the track with respect to the three spots changes between the inner periphery and the outer periphery of the optical disc. For this reason, the normal DPP method cannot be used. It should be noted that arrangements other than 1) and 2), that is, two lenses may be arranged obliquely instead of the radial direction 17 and the tangential direction 18, but such an arrangement is similar to the case of 2). At least one objective lens is off-centered and the DPP method cannot be used.

  In the slim optical head, the actuator movable portion 10, the actuator fixing portion 23, and the bar suspension 22 connecting both of them use a space nearly half of the optical head. Therefore, the optical system must be miniaturized so that it can be mounted in the remaining space.

  In the case of the two-lens method, the light beam is incident from the tangential direction 18 as in (a) and (d), and the light beam is incident from the tangential direction 18 and the radial direction 17 as in (b) and (e). A method of entering a light beam from the radial direction 17 as shown in (c) and (f) is conceivable. Of these, (c) and (f) require that the mounting space for the optical units 21d and 21h is not available, and that the shape of the actuator be special so that the bar suspension 22 does not block the light beam incident from the radial direction 17. This is unsuitable for slim optical heads. In addition, (b) and (e) can secure mounting space, but the shape of the actuator must be special like (c) and (f), and the optical units 21b, 21c, 21f, and 21g Is divided into two, it becomes difficult to support BD and HD DVD with one blue laser, and there is a problem that two expensive blue lasers must be mounted.

  On the other hand, (a) and (d) are excellent in that the mounting space is easy to secure, the performance of the actuator is easy to secure, and that one blue laser can handle BD and HD DVD. ing.

  However, in (d), as in JP-A-2006-24351, BD and HD DVD have the same optical path, so it is difficult to ensure the characteristics of BD and HD DVD. On the other hand, in the configuration (a), since the BD and the HD DVD can be designed and adjusted independently, the characteristics of the BD and the HD DVD can be ensured.

  As described above, in the optical head of the present invention, the BD-dedicated lens 11a and the HD DVD / DVD / CD compatible objective lens 11b are arranged in the radial direction 17 so that the light beam is incident from the tangential direction. And an inexpensive slim optical head.

  Next, the optical disk apparatus of the present invention will be described.

  FIG. 8 is a schematic view showing the configuration of the optical disk apparatus of the present invention (for the sake of simplicity, the figure is shown in two dimensions and the optical head components are omitted). In the optical disk apparatus of the present invention, the above-described optical head 1 of the present invention is mounted. Here, the description of the optical head is simplified to avoid duplication, and the BD system in the optical disk apparatus of the present invention is described.

  The optical head 1 of the present invention is a BD / HD DVD / DVD / CD compatible optical head, and includes one semiconductor laser 2a having a wavelength of about 405 nm, one semiconductor laser having a wavelength of about 655 nm, and one semiconductor laser having a wavelength of about 785 nm. One dual-wavelength laser 2c housed in one package is mounted. In addition, two objective lenses, a BD dedicated lens 11a and an HD DVD / DVD / CD compatible objective lens 11b, are arranged on the actuator 10 in the radial direction 17 of the optical disk. The actuator 10 is a tilt actuator that can move in the focusing direction 19, move in the tracking direction 17, and tilt in the radial direction 17 of the optical disc. In addition, two BDs 14a and 14b for HD DVD / DVD / CD are mounted as photodetectors, and one for BD / HD DVD / DVD / CD is mounted as the front monitor 16. A liquid crystal element 5 for switching the optical path between the BD system and the HD DVD system, and a stepping motor 26 for driving the collimator lens 8a in the optical axis direction for correcting spherical aberration in the BD are mounted.

  The light beam emitted from the semiconductor laser 2a passes through the liquid crystal element 5 and the PBS 6, is converted into a substantially parallel light beam by the collimator lens 8a, and then is narrowed down to the signal recording surface of the BD 25 by the objective lens 11a. The reflected light from the optical disk 25 passes through the objective lens 11a and the collimating lens 8a, reflects the PBS 6, and then enters the photodetector 14a. After the light beam incident on the photodetector 14a is converted into an electrical signal, the signal processing circuit 40 detects a servo signal, an RF signal, and the like.

  The FES generated in the signal processing circuit 40 is supplied to the focus control circuit 43. The focus control circuit 43 generates and outputs a drive signal for the actuator 10, whereby the objective lens 11a is controlled in the focusing direction 19 to achieve feedback loop focus control, and always to the recording layer of the optical disc 25. And stay in focus.

  On the other hand, the TES generated in the signal processing circuit 40 is supplied to the tracking control circuit 44. In this tracking control circuit 44, the drive signal of the actuator 10 is generated and output, whereby the objective lens 11a is controlled in the tracking direction 17 to realize the tracking control of the feedback loop, and the track in the recording layer of the optical disc 25 is always maintained. Stay on top.

  The drive signal output from the tracking control circuit 44 is also supplied to a thread control circuit (not shown). Then, in the thread control circuit, a drive signal for controlling a thread motor (not shown) is generated according to the shift amount of the objective lens 11a in the tracking direction, and is output to the thread motor. As a result, the thread motor is moved, and the entire optical head is moved in the radial direction 17 of the optical disk 25.

Further, the signal processing circuit 40 supplies the rotation cycle information read from the optical disc 25 to the spindle control circuit 47. Then, the spindle control circuit 47 generates a signal for driving the spindle motor 48 based on the rotation period information and outputs it to the spindle motor 48.
Further, by feeding back the output of the front monitor 16 to the laser control circuit 42, the intensity of light emitted from the semiconductor laser 2a is made constant.

  A microcomputer (hereinafter referred to as a microcomputer) 46 initializes the circuit, etc., and instructs the laser control circuit 42 to turn on / off the laser and to instruct laser power. In addition, a drive signal generation / non-generation instruction to the drive circuit 41 of the collimating lens driving stepping motor 26, a focus servo loop open / close instruction to the focus control circuit 43, and a tracking control circuit 44 In response, the tracking servo loop is opened / closed, the spindle control circuit 47 is instructed to rotate / stop the spindle, and the rotation speed.

In addition, by instructing the actuator tilt control circuit 45 to output voltage, the actuator tilt control circuit 45 outputs the drive voltage to the actuator.
Further, in order to switch between BD and HD DVD, the liquid crystal element control circuit 49 is instructed to apply the drive voltage to the liquid crystal element 5 or to cancel the application of the drive voltage. In the optical disk device of the present invention, the liquid crystal element 5 is not driven when recording / reproducing BD, and the liquid crystal element 5 is driven when recording / reproducing HD DVD. The liquid crystal element 5 is not driven when recording / reproducing a DVD or CD.

  When recording / reproducing BD, the BD photodetector 14a is set in an active state and the HD DVD / DVD / CD photodetector 14b is set in a sleep state to record an HD DVD, DVD, or CD. / To perform reproduction, the photodetector 14a is set to the sleep state and the photodetector 14b is set to the active state. Then, the gains of the photodetectors 14a and 14b and the front monitor 16 are switched in accordance with the type of the optical disc and recording or reproduction.

  As described above, by mounting the optical head of the present invention and switching the driving voltage of the liquid crystal element 5, it is possible to realize a small and inexpensive optical disc apparatus having good recording / reproduction quality for both BD and HD DVD. Can do.

  Next, an embodiment different from the first example will be described. FIG. 9 shows an optical system configuration of an optical head according to another embodiment of the present invention. Since the present embodiment is different from the optical system shown in FIG. 1 only in the portion of the BD system, the BD system will be briefly described.

  The divergent light emitted from the semiconductor laser 2a and having a wavelength of about 405 nm and whose polarization direction is substantially parallel to the paper surface enters the liquid crystal element 5. The liquid crystal element 5 has an action of converting the polarization direction of the incident light beam from a direction substantially parallel to the paper surface to a direction substantially perpendicular to the paper surface when the drive voltage is applied, but does not apply the drive voltage. In some cases, the incident light beam is transmitted as it is without changing the polarization direction.

  In the BD system of the optical head of the present invention, since no voltage is applied to the liquid crystal element 5, the light beam incident on the liquid crystal element 5 exits the liquid crystal element 5 with its polarization direction being substantially parallel to the plane of the paper. Incident on the diffraction grating 4. This polarizing diffraction grating 4 acts as a diffraction grating when a light beam having a polarization direction parallel to the paper surface is incident, and the incident light beam is divided into at least three light beams of zero-order light and ± first-order light. On the other hand, when a light beam having a polarization direction perpendicular to the paper surface is incident, it does not act as a diffraction grating and transmits the incident light beam as it is. In the BD system, a light beam having polarized light in a direction substantially parallel to the paper surface enters, so that the light beam is divided into at least three parts and enters PBS 6. The P-polarized component occupying most of the incident light beam is transmitted through PBS 6, and the remaining S-direction component is reflected from PBS 6.

  In the case of the HD DVD system, a voltage is applied to the liquid crystal element 5 to change the polarization direction into a direction substantially perpendicular to the paper surface, so that the light beam incident on the polarizing diffraction grating 4 is transmitted therethrough and reflected from the PBS 6. Thereafter, the diffraction grating 3b is divided into at least three light beams of zero-order light and ± first-order light. That is, the polarizing diffraction grating 4 functions as a BD dedicated diffraction grating, and the diffraction grating 3b functions as an HD DVD dedicated diffraction grating, so that each can be adjusted independently. As described above, in the optical head of the present invention, the two objective lenses 11a and 11b are arranged in the radial direction 17 of the optical disc, and the centers of the objective lenses 11a and 11b are on the axis extending from the center of the optical disc in the driving direction of the optical head. Therefore, the DPP method can be used for TES detection in all BD / HD DVD / DVD / CD.

  The light flux whose polarization direction is transmitted through the PBS 6 and parallel to the paper surface is converted into a substantially parallel light flux by the collimator lens 8a. The collimating lens 8a is attached to a drive mechanism (not shown). The light beam emitted from the collimating lens 8a enters the polarizing diffraction grating 4a. The light beam emitted from the polarizing diffraction grating 4a enters the quarter-wave plate 9a, is converted into circularly polarized light, is bent in a focusing direction 19 by a rising mirror (not shown), and is mounted on the actuator 10 Light is focused on the signal recording surface of the BD by the objective lens 11a. The light beam reflected from the optical disk is converted into a substantially parallel light beam by the objective lens 11a, is reflected by a rising mirror (not shown), and is incident on the quarter-wave plate 9a again, and the polarization direction thereof is perpendicular to the paper surface. Is converted. The light beam emitted from the quarter-wave plate 9a is converted into convergent light by the collimator lens 8a, reflected by the PBS 6, and then guided to the photodetector 14a by the detection lens 13a.

  The light receiving surface pattern of the photodetector 14a is shown in FIG. The light receiving surface in the BD system of the optical head of the present invention has a configuration in which three commonly used quadrant detectors 27, 28, 29 are arranged. Astigmatism is used for FES detection, DPP is used for TES detection. Method and DPD method are used.

  As described above, the optical head according to the present invention can use the DPP method for all of the BD / HD DVD / DVD / CD, and therefore can support recording on all media. In addition, in BD and HD DVD, a recording / reproducing signal quality is high, and a small and inexpensive optical head is realized. In addition, the optical disk apparatus equipped with the optical head of the present invention can cope with recording in all of BD / HD DVD / DVD / CD, has excellent recording / reproducing characteristics in BD and HD DVD, and A small and inexpensive optical disc apparatus is realized.

  In the embodiment described above, a liquid crystal element is used for switching the polarization direction. However, instead of the liquid crystal element, for example, a mechanism for rotating a half-wave plate or a half-wave plate in the optical path. A mechanism for taking in and out may be mounted. Further, in FIG. 1, instead of arranging the polarizing diffraction grating 4a between the quarter-wave plate 9a and the PBS 6, a non-polarizing diffraction grating may be arranged between the PBS 6 and the photodetector 14a. . However, in this case, since the effective diameter of the light beam incident on the diffraction grating is reduced, the grating pattern is the same as in FIG. 2, but is also reduced by the smaller effective diameter. Further, instead of using the two-wavelength laser 2c in the DVD / CD system, a DVD laser and a CD laser may be mounted separately. Needless to say, an optical element such as a mirror for bending the optical path or a liquid crystal aberration correction element may be appropriately added to the optical system of the present invention.

It is the schematic plan view which showed the optical system structure and BD optical path in this invention optical head. It is the top view which showed the pattern of the polarizing diffraction grating mounted in BD system of the optical head of this invention. It is the top view which showed the light-receiving surface pattern of the photodetector for BD of this invention optical head. It is the schematic plan view which showed the optical system structure and HD DVD optical path in this invention optical head. It is the top view which showed the light-receiving surface pattern of the photodetector for HD DVD / DVD / CD of the optical head of this invention. It is the schematic plan view which showed the optical system structure and DVD / CD optical path in this invention optical head. It is the schematic plan view which showed the incident method of each light beam in the optical head for slim. It is the schematic plan view which showed another Example in the optical head of this invention. 1 is a schematic plan view showing a configuration of an optical disk device of the present invention. It is the top view which showed the light-receiving surface pattern of the photodetector for BD of this invention optical head.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Optical head, 2 ... Semiconductor laser, 3 ... Diffraction grating, 4 ... Polarization diffraction grating, 5 ... Liquid crystal element, 6 ... PBS, 7 ... Synthetic prism, 8 ... Collimating lens, 9 ... 1/4 wavelength plate, 10 ... Actuator, 11 ... Objective lens, 12 ... Broadband PBS, 13 ... Detection lens, 14 ... Optical detector, 15 ... Reflection mirror, 16 ... Front monitor, 17 ... Radial direction of optical disc (tracking direction), 18 ... Tangent of optical disc Direction, 19 ... focusing direction, 20 ... axis extending from the center of the optical disk in the driving direction of the optical head, 21 ... optical unit, 22 ... bar suspension, 23 ... actuator fixing part, 25 ... optical disk, 26 ... stepping motor, 40 ... signal Processing circuit 41 ... Stepping motor drive circuit 42 ... Laser control circuit 43 ... Focus control circuit 44 ... Tracking control circuit 45 ... Actuator tilt control circuit 46 ... Microcomputer 47 ... Spindle control circuit, 48 ... Spindle motor, 49 ... Liquid crystal element control circuit

Claims (14)

An optical head compatible with CD, DVD, BD and HD DVD,
A laser package equipped with a laser light source for CD and a laser light source for DVD;
A blue laser light source for BD and HD DVD;
A first photodetector for receiving light emitted from the blue laser light source and reflected by a BD;
A second photodetector for receiving light emitted from the laser package and reflected by the CD and DVD, and light emitted from the blue laser light source and reflected by the HD DVD;
Having
Light head. The optical head according to claim 1,
Polarization direction changing means for changing the polarization of light emitted from the blue laser light source;
A beam splitter that transmits the light that has passed through the polarization direction changing means and reflects the reflected light from the BD; and
A synthetic prism that reflects the light that has passed through the polarization direction changing means and transmits the reflected light from the HD DVD;
Having
Light head. The optical head according to claim 2,
A first objective lens for condensing light emitted from the blue laser light source on a BD;
A second objective lens for condensing the light emitted from the laser package on a CD and a DVD and condensing the light emitted from the blue laser light source on an HD DVD;
Have
The first objective lens and the second objective lens are arranged in a radial direction with respect to the disc;
Light head. A first semiconductor laser that emits light having a first wavelength;
A second semiconductor laser that emits light having a second wavelength;
A third semiconductor laser that emits light having a third wavelength;
A polarizing beam splitter that transmits most of the incident light beam when the polarization direction of the light beam emitted from the first semiconductor laser is P-polarized light, and reflects most of the incident light beam when it is S-polarized light; ,
Between the first semiconductor laser and the polarizing beam splitter, there is a polarization switching element capable of switching the polarization direction of the light beam incident on the polarizing beam splitter to at least two states of approximately P-polarized light and approximately S-polarized light. And
A first collimating lens for converting a light beam transmitted through the polarizing beam splitter into a substantially parallel light beam; a first quarter-wave plate for converting the polarization direction of the incident light beam into a substantially circularly polarized light; and a first optical disk A first objective lens that narrows the substantially parallel light flux on the signal recording surface, and a first photodetector that receives reflected light from the first optical disc,
A synthesizing prism that reflects most of the light beam reflected by the polarizing beam splitter and transmits most of the light beam emitted from the second semiconductor laser and the third semiconductor laser; and the synthesizing prism; A second collimating lens that converts the emitted light beam into a substantially parallel light beam, a second quarter-wave plate that converts the polarization direction of the incident light beam into substantially circularly polarized light, and a second light beam having the first wavelength. A second objective lens for narrowing the light beam having the second wavelength on the signal recording surface of the third optical disk and the light beam having the third wavelength on the signal recording surface of the fourth optical disk An optical head comprising a second photodetector for receiving reflected light from the second, third, and fourth optical disks.   The light according to claim 4, wherein the first objective lens and the second objective lens are held by one actuator, and the two objective lenses are arranged in a substantially radial direction of the optical disc. head.   6. A diffraction grating having an action of dividing a light beam having the first wavelength into at least three light beams is disposed between the polarizing beam splitter and the combining prism. Light head.   A polarizing diffraction grating is disposed between the first quarter-wave plate and the polarizing beam splitter, and the polarizing diffraction grating has a light beam that becomes S-polarized light incident on the polarizing beam splitter. 7. The light according to claim 4, wherein the light acts as a diffraction grating that divides the light beam, and has no effect as a diffraction grating when a light beam that becomes P-polarized light is incident. head.   A polarizing diffraction grating is disposed between the polarization switching element and the polarizing beam splitter, and the polarizing diffraction grating has a light beam when a P-polarized light beam is incident on the polarizing beam splitter. The light according to any one of claims 4 to 6, which acts as a diffraction grating that divides the light into at least three, and does not have a function as a diffraction grating when a light beam that becomes S-polarized light is incident. head.   The synthetic prism has a reflectivity of approximately 100% when an S-polarized light beam having a first wavelength is incident, and is approximately when a P-polarized light beam having a first wavelength is incident. 9. A light beam having a transmittance of 100% and having a second and third wavelengths has a transmittance of approximately 100% for both P-polarized light and S-polarized light. The optical head according to any one of the above.   Between the synthetic prism and the second photodetector, P-polarized light is transmitted approximately 100% and S-polarized light is reflected approximately 100% for any of the first, second, and third wavelengths. An optical head according to claim 4, wherein a broadband polarizing beam splitter having the above is disposed.   11. The polarization switching element includes a liquid crystal element, and changes a polarization state of a light beam incident on the polarizing beam splitter by driving the liquid crystal element. The optical head described.   12. The optical head according to claim 4, wherein the second semiconductor laser and the third semiconductor laser are two-wavelength lasers housed in the same package.   The first wavelength is a 405 nm band, the second wavelength is a 655 nm band, and the third wavelength is a 785 nm band. The first optical disk has a protective layer thickness of 0.1 mm, and the second optical disk has a protective layer thickness. The thickness of the protective layer of the third optical disk is 0.6 mm, and the thickness of the protective layer of the fourth optical disk is 1.2 mm. The optical head as described in.   14. An optical disc apparatus comprising the optical head according to claim 4 mounted thereon.

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