JP2005115279A - Hologram element, hologram laser, and optical pickup device using them - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hologram element with which the lowering of the intensity of light which is used in the recording/reproduction of information can be suppressed as much as possible and also the stabilizing of the output of light which is emitted from a light source can be realized. <P>SOLUTION: A hologram element 30 is constituted so that it has a first region 34 which is demarcated so as to involve an optical axis 32 and a second region 35 which is demarcated so as to enclose the first region 34 along the periphery of the first region 34 in a virtual flat surface 33 orthogonal to the optical axis 32 at the time light passes through the virtual flat surface 33 and the first region 34 has a polarizing property which diffracts an extraordinary light beam and does not diffracts an ordinary light beam and the second region does not have a polarizing property. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a hologram element, a hologram laser, and an optical pickup device using the same.

  There is a compact disk (abbreviated as CD) family as a typical optical recording medium (hereinafter sometimes referred to as a disk) on which information is recorded or reproduced using light. A semiconductor laser that emits an infrared laser beam having an oscillation wavelength of 780 nm is used for reading, reproducing, or recording information on the CD.

  In recent years, in accordance with a demand for an increase in recording capacity, which is the amount of information recorded on an optical recording medium, an optical recording medium called a digital versatile disk (abbreviated as DVD) family, which has a larger recording capacity than the CD family, is used in large quantities. It has become. When reproducing or recording information on the DVD family, a semiconductor laser that emits a laser beam having a red wavelength with an oscillation wavelength of 630 nm to 690 nm is used.

  Accordingly, there is a need for an optical pickup device that includes a plurality of semiconductor lasers that respectively oscillate laser beams having different wavelengths and that can reproduce and record information on both optical recording media of the CD family and the DVD family. ing.

  Although development of optical pickup devices having various configurations is underway, one of them is a hologram laser system. In the hologram laser system, a semiconductor laser element, which is a light source that emits laser light, and a light receiving element are housed in one package, and the hologram element is mounted on the top of the package. In this hologram laser system, light emitted from a semiconductor laser is irradiated onto an optical recording medium via an optical pickup optical system, and reflected light from the optical recording medium is condensed on a light receiving element in a package by the hologram element. . By processing the light received by the light receiving element, reproduction information of the optical recording medium can be acquired. This hologram laser method is widely used because the semiconductor laser as the light emitter and the light receiving element as the light receiver are present in the same package, so that the apparatus can be made compact and has high optical reliability. ing.

  FIG. 12 is a diagram showing a simplified configuration of a conventional optical pickup device 1 having a hologram laser system. In the hologram laser 2 provided in the optical pickup device 1, the light 4 emitted from the semiconductor laser 3 is diffracted by the diffraction grating 6 formed in the hologram element 5 to become zero-order light 4 a and ± first-order lights 4 b and 4 c. The ± primary lights 4 b and 4 c are emitted radially outward of the collimating lens 7 and do not enter the collimating lens 7. Only the 0th-order light 4a is incident on the collimating lens 7. The 0th-order light 4 a incident on the collimating lens 7 passes through the objective lens 8 and is condensed on the disk 9. On the contrary, the reflected light 10 from the disk 9 passes through the objective lens 8 and the collimating lens 7 and enters the hologram element 5, and is diffracted by the diffraction grating 6 into 0th-order light 10a and ± first-order light 10b and 10c. Only the secondary light 10 b is guided to the light receiving element 11.

  In such a hologram laser type optical pickup device 1, the light 4 emitted from the semiconductor laser 3 is diffracted by the diffraction grating 6 of the hologram element 5, so that the ± first-order lights 4 b and 4 c are recorded on the disk 9. The zero-order light 4a only reaches the information recording surface of the disk 9 without reaching the surface. Therefore, there is a drawback that the laser intensity on the information recording surface of the disk 9 is low. In particular, in writing (information recording) of CDs and DVDs, since a high laser intensity is required on the information recording surface, the optical pickup device is required to reduce the above-described light loss as much as possible.

  In the conventional optical pickup device 1 shown in FIG. 12, the + first-order light 4b radiated outwardly in the radial direction of the collimating lens 7 is received and detected by the photodiode 12 provided on the side of the collimating lens 7. Since the detection output is fed back to the semiconductor laser 3 to control the optical output, there is an advantage that stable output control is possible.

  In a hologram laser type optical pickup device, it has been proposed to use a hologram element having polarization characteristics as a method of suppressing optical loss (see, for example, Patent Document 1).

  FIG. 13 is a diagram showing a simplified configuration of a conventional optical pickup device 15 that uses a hologram element having polarization characteristics. Since the optical pickup device 15 is similar to the optical pickup device 1 described above, the corresponding parts are denoted by the same reference numerals and description thereof is omitted.

  The polarization hologram element 16 having polarization characteristics is made of materials having different refractive indexes between ordinary light and extraordinary light. A diffraction grating 17 is formed on a surface facing the collimator lens 7 and the diffraction grating is buried with an isotropic adhesive. Configured. The polarization characteristic of the polarization hologram element 16 is not diffracted to the ordinary light of the laser light, but is diffracted only to the abnormal light.

  In the optical pickup device 15 using the polarization hologram element 16 having such polarization characteristics, the light 18 (ordinary light) emitted from the semiconductor laser 3 is transmitted without being diffracted by the diffraction grating 17 of the polarization hologram element 16. The light enters the collimating lens 7. The light transmitted through the collimating lens 7 becomes circularly polarized light by the quarter (1/4) wave plate 19, passes through the objective lens 8, and is condensed on the disk 9. The reflected light 20 from the disk 9 conversely passes through the objective lens 8, becomes linearly polarized light (abnormal light) by the quarter wavelength plate 19, passes through the collimator lens 7, and enters the polarization hologram element 16. The reflected light 20 incident on the polarization hologram element 16 is diffracted by the diffraction grating 17 of the polarization hologram element 16 into 0th-order light 20a and ± 1st-order lights 20b and 20c, and only the + 1st-order light 20b is provided in the hologram laser 21. It is guided to the light receiving element 11.

  In the optical pickup device 15 including such a polarization hologram element 16, the light 18 emitted from the semiconductor laser 3 is not diffracted by the polarization hologram element 16, that is, ± first-order light is not generated. Reduction in the amount of light reaching the information recording surface is suppressed, and the amount of light received by the light receiving element 11 is large, enabling high-speed writing and high-speed reading.

  However, the optical pickup device 15 including the polarization hologram element 16 also has the following problem. Since the pickup device 15 does not generate ± first-order light in the polarization hologram element 16, the laser light emitted from the semiconductor laser 3 and diffused in the vicinity of the collimator lens 7 is received and detected by the photodiode 12, and its detection output Is fed back to the semiconductor laser 3 to control the optical output of the semiconductor laser 3. The light diffused in the vicinity of the collimator lens 7 has a very small amount of light compared to the + 1st order light 4b in the optical pickup device 1 described above, and it is difficult to stably control the output of the semiconductor laser 3.

  One conventional technique for solving such a problem is an optical pickup device 25 including a half mirror 26 on an optical path. FIG. 14 is a diagram showing a simplified configuration of the optical pickup device 25 including the half mirror 26 on the optical path. The optical pickup device 25 is provided with a half mirror 26 that reflects ordinary light with a predetermined reflectance on the optical path between the collimating lens 7 and the quarter-wave plate 19. The half mirror 26 reflects a part of the light emitted from the semiconductor laser 3 and transmitted through the polarization hologram element 16 and the collimating lens 7 so as to enter the photodiode 12. A signal received and detected by the photodiode 12 is fed back to the semiconductor laser 3, and output control of the semiconductor laser 3 is performed.

  In such an optical pickup device 25, although the optical output of the semiconductor laser 3 can be stabilized, an optical member called a half mirror 26 must be added, and an additional assembly adjustment work is required. There is a problem of increased costs. Furthermore, since a part of the light 18 emitted from the semiconductor laser 3 is reflected by the half mirror 26, the problem that the amount of light reaching the information recording surface of the disk 9 is not solved.

JP-A-9-128794

  An object of the present invention is to provide a hologram element and a hologram laser that can suppress a decrease in the intensity of light used for recording / reproducing information as much as possible and can stabilize the output of light emitted from a light source. is there.

The present invention is a hologram element having a plurality of regions defined in a virtual plane perpendicular to the optical axis when light is transmitted,
The hologram element is characterized in that at least one region selected from the plurality of regions has polarization characteristics.

According to the present invention, a plurality of areas are defined such that a first area is defined so as to contain the optical axis in the virtual plane, and a second area is defined so as to surround the first area along the outer periphery of the first area. Area and
The first region has a polarization property, and the second region has no polarization property.

  In addition, the present invention is characterized in that the polarization characteristics of the first region diffract extraordinary light and not ordinary light.

  In addition, the present invention is characterized in that the polarization characteristic of the first region diffracts ordinary light and does not diffract extraordinary light.

According to the present invention, a plurality of areas are defined such that a first area is defined so as to contain the optical axis in the virtual plane, and a second area is defined so as to surround the first area along the outer periphery of the first area. Area and
The polarization characteristic of the first region is different from the polarization property of the second region.

  Further, the present invention is characterized in that a diffraction grating is provided in the second region, and no diffraction grating is provided in the first region.

The present invention also includes any one of the hologram elements described above,
A light source that emits laser light;
A hologram laser comprising: a light receiving element that receives laser light.

The present invention also relates to an optical pickup apparatus that records, reproduces, or erases information by irradiating light onto an optical recording medium.
A light source that emits laser light;
An objective lens for condensing the laser light emitted from the light source onto the information recording surface of the optical recording medium;
A hologram element provided between the light source and the objective lens, the polarization characteristic of the first region diffracts extraordinary light and does not diffract ordinary light, and the hologram element whose polarization characteristic possessed by the first region diffracts ordinary light and does not diffract extraordinary light At least one of a hologram element having a polarization characteristic different from that of the first area and a polarization characteristic of the second area, and a hologram element provided with a diffraction grating in the second area and no diffraction grating in the first area. Two or more hologram elements including one;
An optical pickup device comprising: a light receiving element that receives light reflected by the optical recording medium.

  According to the present invention, the hologram element has a plurality of regions defined in a virtual plane orthogonal to the optical axis when light is transmitted, and at least one region selected from the plurality of regions has polarization characteristics. It is comprised so that it may have. Preferably, a plurality of areas are defined in such a way that a first area is defined so as to contain the optical axis in the virtual plane, and a second area is defined so as to surround the first area along the outer periphery of the first area. In particular, the polarization characteristics of the first region are configured to diffract extraordinary light and not diffract ordinary light so that the first region has polarization characteristics and the second region does not have polarization characteristics.

  In this hologram element, all of the light transmitted through the first region can be used for recording / reproducing information. In addition, since the second region does not have polarization characteristics, the light transmitted through the second region is diffracted by the diffraction grating. However, the diffracted zeroth order light is used for recording / reproducing information, and the first order light. Can be received by the light receiving element for output control and used for output control of the light source.

  As described above, since all of the light transmitted through the first region and the 0th-order light diffracted in the second region can be used for recording / reproducing information, the light use efficiency is improved and optical recording is performed. It is possible to remarkably suppress a decrease in the intensity of light reaching the information recording surface of the medium and obtain a signal with good quality. Further, since the primary light diffracted in the second region has a sufficient amount of light for output control of the light source, stable output control is realized.

  Further, according to the present invention, the polarization characteristic of the first region of the hologram element is configured to diffract ordinary light and not diffract extraordinary light. For example, a quarter-wave plate is provided on the optical path of the optical pickup device, and the reflected light is abnormally transmitted by reciprocating the quarter-wave plate with the light emitted from the light source and the light reflected by the optical recording medium. The reflected light that has become abnormal light is not diffracted when passing through the first region. On the other hand, since the reflected light transmitted through the second region is diffracted, the reflected light diffracted at the second region is incident on the light receiving element, and the non-diffracted reflected light transmitted through the first region is not incident on the light receiving element. can do.

  By using such a hologram element, in an optical recording medium having a multilayer information recording surface, it is possible to prevent light reflected from an information recording surface other than the information recording surface to be reproduced from entering the light receiving element. For example, it is possible to reduce the noise of the tracking error signal and improve the position control accuracy of the objective lens.

  Further, according to the present invention, the hologram element has, for example, a polarization characteristic in which the first region diffracts ordinary light and does not diffract extraordinary light so that the polarization property of the first region and the polarization property of the second region are different. The second region may be configured to have a polarization characteristic that diffracts extraordinary light and does not diffract ordinary light, and a diffraction grating is provided in the second region and no diffraction grating is provided in the first region. It may be configured. In any hologram element, similarly to the hologram element described above, the reflected light diffracted in the second region is incident on the light receiving element, and the undiffracted reflected light transmitted through the first region is not incident on the light receiving element. Therefore, in an optical recording medium having a multilayer information recording surface, reflected light from an information recording surface other than the information recording surface to be reproduced can be prevented from entering the light receiving element.

  According to the invention, in the optical pickup device, two or more hologram elements are provided between the light source and the objective lens, and at least one of the two or more hologram elements provided is polarized light in the first region. Hologram element that diffracts extraordinary light and does not diffract ordinary light, polarization characteristic possessed by first region, hologram element that diffracts ordinary light and does not diffract extraordinary light, polarization property possessed by first region and polarization possessed by second region The characteristic is any of a different hologram element and a hologram element provided with a diffraction grating in the second region and no diffraction grating in the first region.

  In such an optical pickup device, it is possible to obtain a high amount of light for signal detection when recording / reproducing information on a plurality of types of optical recording media using laser beams of different wavelengths. Stable laser output control can be realized.

  FIG. 1 is a diagram showing a simplified configuration of a hologram element 30 according to an embodiment of the present invention, and FIG. 2 is a diagram showing a configuration of an optical pickup device 51 including the hologram element 30 shown in FIG.

  The hologram element 30 has two regions defined in a virtual plane 33 orthogonal to the optical axis 32 when the light 31 emitted from the semiconductor laser 52 that is a light source provided in the optical pickup device 51 is transmitted, that is, in the virtual plane 33. A first region 34 defined to include the optical axis 32, a second region 35 defined to surround the first region 34 along the outer periphery of the first region 34, and the first and second regions 34 and 35, and a diffraction grating 36 formed on the surface opposite to the side facing the semiconductor laser 52 so that the first region 34 has a polarization characteristic and the second region 35 does not have a polarization property. Composed. In the hologram element 30 of the present embodiment, the polarization characteristics of the first region 34 are configured to diffract abnormal light and not diffract ordinary light.

  The hologram element 30 is provided with the first and second regions 34 and 35 and the diffraction grating 36 on the side opposite to the side facing the semiconductor laser 52 of the substrate 38 such as transparent glass. The first and second regions 34 and 35 of the hologram element 30 are made of materials having different refractive indexes between ordinary light and extraordinary light. The above-described diffraction grating 36 is formed on the surface, and the diffraction grating 36 is isotropic. Filled with adhesive. The first and second regions 34 and 35 and the diffraction grating 36 constitute a hologram diffraction pattern 37.

  The diffraction grating 36 of the present embodiment is divided into three on the plan view. With the hologram element 30 mounted on the optical pickup device 51, the hologram element 30 is divided into two parts by a first dividing line 39 parallel to the radial direction of the optical recording medium 53 into a first dividing part 41 and a remaining dividing part 44. The dividing unit 44 is further divided into a second dividing unit 42 and a third dividing unit 43 by a second dividing line 40 orthogonal to the first dividing line 39.

  Such division parts 41, 42, 43 of the diffraction grating 36 are signals for controlling the separation position of the objective lens 54 with respect to the optical recording medium 53 and the relative position of the objective lens 54 with respect to the optical recording medium 53 in the radial direction, that is, It is provided to divide the light 31 emitted from the semiconductor laser so that a focus error signal (FES) and a tracking error signal (TES) can be obtained.

  The optical pickup device 51 provided with the hologram element 30 is generally configured as follows. A semiconductor laser 52, which is a light source that emits laser light, an objective lens 54 that focuses the laser light emitted from the semiconductor laser 52 on the information recording surface of the optical recording medium 53, and between the semiconductor laser 52 and the objective lens 54. In addition, the hologram element 30, the collimating lens 55, the quarter wavelength plate 56, the light receiving element 57 that receives and detects the reflected light from the optical recording medium 53, and the collimating lens 55 are arranged in order from the semiconductor laser toward the objective lens. And a photodiode 58 that is provided in the vicinity and receives and detects light used for light output control of the semiconductor laser 52. The optical pickup device 51 is used to perform at least one of recording, reproducing, and erasing information by irradiating the optical recording medium 53 with light.

  The light receiving element 57 is configured by, for example, a photodiode, and is a photoelectric conversion element that converts irradiated light into an electric signal. The light receiving element 57 is mounted in the same manner as the semiconductor laser 52 in the vicinity of the semiconductor laser 52 mounted on the stem 60 provided with the electrode pins 59. The semiconductor laser 52 and the light receiving element 57 are covered with a cap 61 and packaged as an integral member. The hologram element 30, the semiconductor laser 52 and the light receiving element 57, and the cap 61 covering the semiconductor laser 52 and the light receiving element 57 constitute a hologram laser 62.

  The operation of the optical pickup device 51 will be described below. The light 31 emitted from the semiconductor laser 52 passes through the hologram diffraction pattern 37 of the hologram element 30. Since the laser beam 31 is emitted with a spread angle larger than the effective numerical aperture (NA) of the collimating lens 55, the beam 63 on the hologram element 30 includes the second region 35 as shown in FIG. To have an area.

  In the first region 34 having a polarization characteristic in the hologram diffraction pattern 37, the light 64 that has passed through the laser light 31, which is ordinary light, incident on the first region 34 without being diffracted is guided to the collimator lens 55. On the other hand, in the second region 35 having no polarization characteristic, the light incident on the second region 35 of the laser light 31 is diffracted to become zero-order light 65a and ± first-order light 65b and 65c. The zero-order light 65a is guided to the collimating lens 55. Although the ± first-order light 65b and 65c are radiated outward in the radial direction of the collimating lens 55, the + first-order light 65b is received by the photodiode 58 provided in the vicinity of the collimating lens 55. The output control of the semiconductor laser 52 is performed using the received light amount of the + first-order light 65b by the photodiode 58.

  The light 64 that has passed through the first region 34 and the 0th-order diffracted light 65a by the second region 35 are made into substantially parallel light by the collimator lens 55, and become circularly polarized light by passing through the quarter-wave plate 56, and the objective lens 54 is condensed on the information recording surface of the optical recording medium 53.

  Thus, in the hologram element 30, not all of the light incident on the hologram diffraction pattern 37 is diffracted, but only the light incident on the second region 35 having no polarization characteristic is diffracted. Therefore, the light quantity reduction of the light guided to the collimating lens 55 with respect to the light 31 emitted from the semiconductor laser 52 is caused by the ± first-order lights 65b and 65c diffracted by the second region 35 if the attenuation by the hologram element 30 is ignored. Since the amount of light can be reduced, the light utilization efficiency can be kept high. Further, since the + 1st order light 65b diffracted by the second region 35, not the diffused light, is used for the output control of the semiconductor laser 52, stable output control is possible.

  The reflected light 66 reflected by the optical recording medium 53 passes through the objective lens 54 and passes through the quarter wavelength plate 56 again to become linearly polarized light that is abnormal light. The reflected light 66 further passes through the collimator lens 55 and enters the hologram diffraction pattern 37 of the hologram element 30.

  The first region 34 of the hologram diffraction pattern 37 has a polarization characteristic that diffracts extraordinary light, and the second region 35 does not have a polarization characteristic. Therefore, the reflected light 66 that is extraordinary light is diffracted by the hologram diffraction pattern 37, The zero-order light 67a and the ± first-order lights 67b and 67c are obtained. The + 1st order light 67 b is guided to and incident on the light receiving element 57. The light receiving element 57 can acquire information from the optical recording medium 53 by performing signal processing on the received + first-order light 67b.

  FIG. 3 is a plan view showing a simplified configuration of the hologram element 70 according to the second embodiment of the present invention, and FIG. 4 is a diagram of the light in the forward path in the optical pickup device 75 including the hologram element 70 shown in FIG. FIG. 5 is a diagram showing the behavior of light in the return path in the optical pickup device 75 including the hologram element 70 shown in FIG. The hologram element 70 of the present embodiment and the optical pickup device 75 including the same are similar to the hologram element 30 of the first embodiment and the optical pickup device 51 including the same, and corresponding portions are denoted by the same reference numerals. A description thereof will be omitted.

  The hologram element 70 of the present embodiment has a configuration similar to that of the hologram element 30 described above, and has first and second regions 71 and 72. However, the first region 71 of the hologram element 70 has a polarization characteristic that diffracts ordinary light and does not diffract extraordinary light, and the second region 72 has no polarization property.

  The operation of the optical pickup device 75 including such a hologram element 70 will be described below.

  The laser beam 76 that is ordinary light emitted from the semiconductor laser 52 is diffracted in the first region 71 of the hologram diffraction pattern 73 to become zero-order light 77a and ± first-order light 77b and 77c. Even in the second region 72 having no polarization characteristics, the laser beam 76 is diffracted into zero-order light 78a and ± first-order light 78b and 78c. The 0th-order lights 77a and 78a in the first and second regions 71 and 72 are transmitted through the collimator lens 55, become circularly polarized light by the quarter-wave plate 56, and the information recording surface is light having a multilayer structure by the objective lens 54. The light is condensed on the information recording surface 79 a of the recording medium 79. Although not shown, ± first-order light from the first and second regions 71 and 72 can be used for output control of the semiconductor laser 52.

  The reflected light 80 from the information recording surface 79 a of the optical recording medium 79 passes through the objective lens 54, passes through the quarter wavelength plate 56, becomes linearly polarized light that is abnormal light, and further passes through the collimating lens 55. Then, it enters the hologram diffraction pattern 73 of the hologram element 70. Since the first region 71 has a polarization characteristic that does not diffract extraordinary light, the reflected light 80 is allowed to pass as light 81 without being diffracted. On the other hand, in the second region 72 having no polarization characteristic, the reflected light 80 is diffracted to become zero-order light 82a and ± first-order light 82b and 82c. Of the diffracted light in the second region 72, the + 1st order light 82 b is guided to the light receiving element 57. The light receiving element 57 can acquire information from the optical recording medium 79 by performing signal processing on the received first-order light 82b.

  Since the optical recording medium 79 attached to the optical pickup device 75 in this embodiment has an information recording surface having a multilayer structure, the zero-order light 77a and 78a emitted from the semiconductor laser 52 and diffracted by the hologram diffraction pattern 73 is obtained. Is reflected not only by the focused information recording surface 79a but also by, for example, the information recording surface 79b other than the information recording surface 79a. The reflected light from the information recording surface 79 b is also incident on the first region 71 of the hologram diffraction pattern 73 through the objective lens 54, the quarter wavelength plate 56, and the collimator lens 55. However, as described above, the first region 71 has a polarization characteristic that does not diffract extraordinary light. Therefore, the first region 71 does not diffract reflected light from the information recording surface 79b, that is, is guided to the light receiving element 57 from the reflected light from the information recording surface 79b. Does not generate light.

  As described above, since it is possible to prevent the reflected light from the information recording surface other than the information recording surface 79a that is the information reproduction target from being guided to the light receiving element 57, even in the optical recording medium 79 having a multilayer information recording surface. Therefore, it is possible to obtain a high-quality signal with less noise, and the position of the objective lens 54 can be controlled with high accuracy.

  FIG. 6 is a plan view showing a simplified configuration of a hologram element 90 according to the third embodiment of the present invention, and FIG. 7 is a diagram of the light in the forward path in the optical pickup device 95 including the hologram element 90 shown in FIG. It is a figure which shows a behavior. The hologram element 90 of the present embodiment and the optical pickup device 95 including the same are similar to the hologram element 70 of the second embodiment and the optical pickup device 75 including the same, and corresponding parts are denoted by the same reference numerals. A description thereof will be omitted.

  Hologram element 90 of the present embodiment has a configuration similar to that of hologram element 70 described above, and has first and second regions 91 and 92. However, the polarization characteristic of the first region 91 of the hologram element 90 and the polarization characteristic of the second region 92 are different, and the first region 91 has a polarization characteristic that diffracts ordinary light but not abnormal light. And the second region 92 has a polarization characteristic that diffracts extraordinary light and does not diffract ordinary light.

  The operation of the optical pickup device 95 including such a hologram element 90 will be described below.

  The laser light 96 that is ordinary light emitted from the semiconductor laser 52 is diffracted in the first region 91 of the hologram diffraction pattern 93 to become zero-order light 97a and ± first-order light 97b and 97c. In the second region 92 having a polarization characteristic that does not diffract ordinary light, the laser 96 that is ordinary light is transmitted without being diffracted and becomes transmitted light 98.

  The 0th-order light 97a in the first area 91 and the transmitted light 98 in the second area 92 are transmitted through the collimator lens 55 and become circularly polarized light by the quarter-wave plate 56. The light is condensed on the information recording surface 79a of the optical recording medium 79. Although not shown, the ± first-order light 97b and 97c from the first region 91 can be used for output control of the semiconductor laser 52.

  Although the polarization characteristic of the second region 92 of the hologram element 90 is different from the point that the extraordinary light is diffracted and the ordinary light is not diffracted, the second region 72 of the hologram element 70 of the second embodiment has no polarization characteristic. Since the behavior with respect to the extraordinary light that is reflected light from the optical recording medium 79 is the same between the hologram element 90 and the hologram element 70 of the second embodiment, description of the return path is omitted. The optical pickup device 95 including the hologram element 90 according to the present embodiment can also achieve the same effects as the optical pickup device 75 including the hologram element 70 according to the second embodiment.

  FIG. 8 is a plan view showing a simplified configuration of a hologram element 100 according to the fourth embodiment of the present invention, and FIG. 9 is a diagram of the light in the forward path in the optical pickup device 111 including the hologram element 100 shown in FIG. It is a figure which shows a behavior. The hologram element 100 of the present embodiment and the optical pickup device 111 including the same are similar to the hologram element 70 of the second embodiment and the optical pickup device 75 including the same, and corresponding portions are denoted by the same reference numerals. A description thereof will be omitted.

  Hologram element 100 of the present embodiment has a configuration similar to that of hologram element 70 described above, and has first and second regions 91 and 92. However, the diffraction grating 107 is not formed in the first region 101 of the hologram element 100, but the diffraction grating 107 is formed only in the second region 102. That is, the entire planar shape of the diffraction grating 107 is formed in an annular shape in which a portion corresponding to the first region 101 is empty, and the shapes of the first to third divided portions 104, 105, 106 are formed in a sector shape. . Therefore, the first region 101 is not diffracted regardless of ordinary light and extraordinary light, and the second region 102 has a polarization characteristic that diffracts extraordinary light and does not diffract ordinary light.

  The operation of the optical pickup device 111 including such a hologram element 100 will be described below.

  The laser beam 112, which is ordinary light emitted from the semiconductor laser 52, is transmitted without being diffracted in any of the first and second regions 102 and 103 of the hologram diffraction pattern 103 and becomes transmitted light 113 and 114. The transmitted lights 113 and 114 are transmitted through the collimator lens 55, become circularly polarized light by the quarter wavelength plate 56, and are condensed by the objective lens 54 onto the information recording surface 79a of the optical recording medium 79 having a multilayer structure. Is done.

  The diffraction grating is not formed in the portion corresponding to the first region 101 of the hologram element 100, and the first region 71 in the hologram element 70 of the second embodiment has a polarization characteristic that diffracts extraordinary light and does not open ordinary light. However, since the behavior with respect to extraordinary light that is reflected light from the optical recording medium 79 is the same between the hologram element 100 and the hologram element 70 of the second embodiment, the description of the return path is omitted.

  The optical pickup device 111 including the hologram element 100 according to the present embodiment can also achieve the same effects as the optical pickup device 75 including the hologram element 70 according to the second embodiment.

  10 and 11 are diagrams showing a simplified configuration of an optical pickup device 121 according to another embodiment of the present invention. The optical pickup device 121 is a device that can handle two types of optical recording media, such as CD and DVD, which use laser beams of different wavelengths for recording / reproducing information. Therefore, the optical pickup device 121 includes two first and second semiconductor lasers 122 and 123 that can oscillate laser beams having different wavelengths, and two first and second hologram elements 30 and 124, respectively.

  The first semiconductor laser 122 that emits laser light with an infrared wavelength of 780 nm used for CD, for example, is used. The second semiconductor laser 123 is a red wavelength with a wavelength of 630 to 690 nm used for DVD, for example. The one that emits the laser beam is used. These two semiconductor lasers 122 and 123 are mounted in the same package, and the light receiving element 57 may be provided for each wavelength emitted from each of the semiconductor lasers 122 and 123. Is provided.

  The two hologram elements 30 and 124 are disposed so as to be laminated between the semiconductor lasers 122 and 123 and the collimating lens 55, the second hologram element 124 is disposed near the semiconductor lasers 122 and 123, and the two collimating lenses 55 are disposed. The first hologram element 30 is disposed at the center. As described above, the first hologram element 30 includes the first and second regions 34 and 35. The first region 34 has a polarization characteristic that diffracts extraordinary light and does not diffract ordinary light, and the second region 35 is polarized. It is configured to have no characteristics and is provided for DVD. The second hologram element 124 has no polarization characteristics, that is, is configured to diffract regardless of ordinary light and extraordinary light, and is provided for a CD.

  FIG. 10 shows the operation of the optical pickup device 121 when the optical recording medium is a CD 53a. Infrared light 125 (ordinary light) having a wavelength of 780 nm for CD53a emitted from the first semiconductor laser 122 is diffracted by the second hologram element 124 for CD, and becomes zero-order light 126a and ± first-order lights 126b and 126c. . Only the 0th-order light 126a is guided to the first hologram element 30 for DVD. In the first hologram element 30 for DVD, although the first region 34 has a polarization characteristic, it does not diffract ordinary light, and thus the above-described zeroth-order light 126a is transmitted without being diffracted. Since the second region 35 does not have polarization characteristics, the 0th-order light 126a is diffracted to become 0th-order light and ± first-order light (not shown) (only + 1st-order light is shown as 127b).

  The transmitted light transmitted through the first region 34 of the hologram element 30 and the 0th-order light diffracted by the second region 35 are transmitted through the collimator lens 55 to become substantially parallel light. The light is condensed on the information recording surface of the CD 53 a through the lens 54. Since the quarter wavelength plate 56 is a quarter wavelength plate for red light for DVD, infrared light is elliptically polarized on the information recording surface of the CD 53a.

  The + 1st order light 127 b diffracted by the second region 35 of the hologram element 30 is received and detected by a photodiode 58 disposed in the vicinity of the collimating lens 55 and used for output control of the first semiconductor laser 122.

  The reflected light 128 from the CD 53a passes through the objective lens 54, the quarter-wave plate 56, and the collimator lens 56, and enters the first hologram element 30 for DVD as elliptical light. Since the first and second regions 34 and 35 of the first hologram element 30 diffract extraordinary light, only the extraordinary light component of the reflected light 128 is diffracted into ± first-order lights 129b and 129c. Other light is guided to 124 by the second hologram element for CD. The second hologram element 124 is diffracted into zero-order light 130 a and ± first-order light 130 b and 130 c, and the + 1st-order light 130 b is guided to the light receiving element 57.

  FIG. 11 shows the operation of the optical pickup device 121 when the optical recording medium is a DVD 53b. The red light 131 (ordinary light) having a wavelength of 650 nm for the DVD 53b emitted from the second semiconductor laser 123 is diffracted by the second hologram element 124 for CD, and becomes zero-order light 132a and ± first-order lights 132b and 132c. Only the 0th-order light 132a is guided to the first hologram element 30 for DVD. In the first hologram element 30 for DVD, the first region 34 transmits the 0th-order light 132a without diffracting, as described above. In the second region 35, the 0th order light 132a is diffracted to become 0th order light and ± 1st order light (not shown) (only + 1st order light is shown as 133b).

  The transmitted light that has passed through the first region 34 of the hologram element 30 and the 0th-order light that has been diffracted by the second region 35 are transmitted through the collimator lens 55 to become substantially parallel light and pass through the quarter-wave plate 56. By doing so, it becomes circularly polarized light and is condensed on the information recording surface of the CD 53a through the objective lens 54.

  The + 1st order light 133 b diffracted by the second region 35 of the hologram element 30 is received and detected by a photodiode 58 disposed in the vicinity of the collimating lens 55 and used for output control of the second semiconductor laser 123.

  The reflected light 134 from the DVD 53b passes through the objective lens 54, passes through the quarter-wave plate 56, becomes linearly polarized light that is abnormal light, passes through the collimator lens 56, and passes to the first hologram element 30 for DVD. Incident. Since the first and second regions 34 and 35 of the first hologram element 30 diffract abnormal light, the reflected light 134 is diffracted into zero-order light 135a and ± first-order light 135b and 135c, and + 1st-order light 135b is It is guided to the light receiving element 57.

  As described above, the optical pickup device 121 suppresses a decrease in the intensity of the laser beam used for recording / reproducing information, regardless of whether the information is recorded / reproduced on either the CD 53a or the DVD 53b. Output control can be realized.

It is a figure which simplifies and shows the structure of the hologram element 30 which is one Embodiment of this invention. It is a figure which shows the structure of the optical pick-up apparatus 51 provided with the hologram element 30 shown in FIG. It is a top view which simplifies and shows the structure of the hologram element 70 which is the 2nd Embodiment of this invention. It is a figure which shows the behavior of the light of the going path in the optical pick-up apparatus 75 provided with the hologram element 70 shown in FIG. It is a figure which shows the behavior of the light of a return path in the optical pick-up apparatus 75 provided with the hologram element 70 shown in FIG. It is a top view which simplifies and shows the structure of the hologram element 90 which is the 3rd Embodiment of this invention. It is a figure which shows the behavior of the light of an outward path in the optical pick-up apparatus 95 provided with the hologram element 90 shown in FIG. It is a top view which simplifies and shows the structure of the hologram element 100 which is the 4th Embodiment of this invention. It is a figure which shows the behavior of the light of the going path in the optical pick-up apparatus 111 provided with the hologram element 100 shown in FIG. It is a figure which simplifies and shows the structure of the optical pick-up apparatus 121 which is another form of implementation of this invention. It is a figure which simplifies and shows the structure of the optical pick-up apparatus 121 which is another form of implementation of this invention. It is a figure which simplifies and shows the structure of the conventional optical pick-up apparatus 1 provided with a hologram laser system. It is a figure which simplifies and shows the structure of the conventional optical pick-up apparatus 15 using the hologram element which has a polarization characteristic. It is a figure which simplifies and shows the structure of the optical pick-up apparatus 25 provided with the half mirror 26 on an optical path.

Explanation of symbols

30, 70, 90, 100, 124 Hologram element 34, 71, 91, 101 First region 35, 72, 92, 102 Second region 36, 107 Diffraction grating 37, 73, 93, 103 Hologram diffraction pattern 51, 75, 95, 111, 121 Optical pickup device 52, 122, 123 Semiconductor laser 53 Optical recording medium 54 Objective lens 55 Collimator lens 56 1/4 wavelength plate 57 Light receiving element 58 Photo diode 62 Hologram laser

Claims (8)

A hologram element having a plurality of regions defined in a virtual plane perpendicular to the optical axis when light is transmitted,
A hologram element, wherein at least one region selected from a plurality of regions has polarization characteristics. The plurality of regions include a first region defined to include the optical axis in the virtual plane, and a second region defined to surround the first region along the outer periphery of the first region,
2. The hologram element according to claim 1, wherein the first region has polarization characteristics and the second region does not have polarization characteristics. The polarization characteristic of the first region is
The hologram element according to claim 2, wherein the hologram element diffracts extraordinary light and does not diffract ordinary light. The polarization characteristic of the first region is
3. The hologram element according to claim 2, wherein the hologram element diffracts ordinary light and does not diffract extraordinary light. The plurality of regions include a first region defined to include the optical axis in the virtual plane, and a second region defined to surround the first region along the outer periphery of the first region,
2. The hologram element according to claim 1, wherein the polarization characteristics of the first region are different from the polarization properties of the second region.   The hologram element according to claim 2, wherein a diffraction grating is provided in the second region, and no diffraction grating is provided in the first region. The hologram element according to any one of claims 1 to 6,
A light source that emits laser light;
A hologram laser comprising: a light receiving element that receives laser light. In an optical pickup device that records, reproduces, or erases information by irradiating light onto an optical recording medium,
A light source that emits laser light;
An objective lens for condensing the laser light emitted from the light source onto the information recording surface of the optical recording medium;
Two or more hologram elements provided between a light source and an objective lens, including at least one hologram element according to any one of claims 3 to 6;
An optical pickup device comprising: a light receiving element that receives light reflected by the optical recording medium.

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