JP2011134408A - Optical pickup device - Google Patents

Abstract

In an optical pickup device that uses light of a plurality of wavelengths, it is possible to reduce the thickness and size while sending circularly polarized light to an objective lens.
A CD / DVD laser diode, a BD laser diode, a CD / DVD objective lens for condensing light of CD / DVD wavelength, a BD objective lens for condensing light of BD wavelength, A wave plate integrated reflector 3 that reflects light of CD / DVD wavelength and transmits light of BD wavelength, and a BD laser reflector 4 that reflects light of BD wavelength are provided. Further, a phase difference of 1/8 wavelength is given to the light of the CD / DVD wavelength on the surface to which the light of the wave plate integrated reflector 3 is irradiated, and the wavelength of 1/4 wavelength is given to the light of the BD wavelength. A wave plate that provides a phase difference is provided. In addition, the wavelength plate integrated reflection plate 3 is provided with a reflection film for reflecting the light of the CD / DVD wavelength so that the light of the CD / DVD wavelength transmitted through the wavelength plate is transmitted through the wavelength plate again.
[Selection] Figure 1

Description

  The present invention relates to an optical pickup device used for recording / reproducing both an optical disc such as a compact disc (CD) and a digital versatile disc (DVD) and a Blu-ray disc (BD).

  2. Description of the Related Art Conventionally, in an optical pickup device that records and reproduces an optical disk, a laser diode that emits an infrared laser for CD having a central wavelength of 800 nm, a red laser for DVD having a central wavelength of 650 nm, and the like has been used. In recent years, an optical pickup apparatus that performs high-density recording using a BD laser having a central wavelength of 405 nm has been put into practical use. In addition, the market for optical disc devices equipped with a BD optical pickup device is expanding.

  However, at the stage where BD, CD, and DVD coexist, it is required that a plurality of types of optical discs having different wavelengths can be recorded and reproduced by the same optical disc apparatus.

  The CD and DVD lasers and the BD lasers have different diameters of spots that are focused on the recording surface of the optical disk. Further, since the refractive index of an optical member such as an objective lens differs depending on the wavelength, the same optical system cannot be shared as it is. Therefore, recording / reproduction with respect to a plurality of types of optical disks is realized by setting different optical systems according to wavelengths.

  However, in the case of an optical disk device incorporated in an electronic device such as a notebook computer that is further required to be smaller, lighter, and thinner, in a space similar to that of a conventional optical disk device for CD and DVD, There is a strict requirement that an additional BD recording / reproducing mechanism must be accommodated. However, it is difficult to provide an optical system for recording / reproducing BD in a narrow space separately from the conventional mechanism.

  Therefore, it has been proposed to save space by sharing a part of the optical system.

  FIG. 4 is a schematic diagram showing a basic configuration of an optical system of a conventional optical pickup device. As shown in FIG. 4, in the conventional optical pickup device, when recording or reproducing a CD or DVD, a two-wavelength laser for recording / reproducing CD / DVD from a CD / DVD laser diode 401 is used. Is emitted. Next, the outward light of the two-wavelength laser for CD / DVD passes through the optical member 402. Further, the forward light transmitted through the beam splitter 405 is reflected by the CD / DVD reflection plate 406, transmitted through the optical component 407, and sent to the CD / DVD objective lens 408.

  Here, the optical component 407 has an aperture filter for realizing a necessary numerical aperture so as to be compatible with DVD and CD, a polarization hologram that reacts to DVD light, and 1 for outgoing light. And a quarter-wave plate for generating a quarter-wave phase difference. Outgoing light polarized by the optical component 407 into circularly polarized light and condensed by the CD / DVD objective lens 408 is irradiated onto the optical disk 409. The return light for CD / DVD reflected from the optical disk 409 follows the same path as the forward path, and is returned to linearly polarized light by the optical component 407. Further, the return light passes through the beam splitter 405, is reflected by the optical member 402, and is received by the light receiving detection element 413.

  On the other hand, when recording / reproducing BD, a BD laser is emitted from the BD laser diode 403. Next, the forward light of the BD laser passes through the optical member 404. Further, the outward light is reflected by the reflecting surface of the beam splitter 405. Next, the outward light transmitted through the CD / DVD reflection plate 406 is reflected by the BD laser reflection plate 410, passes through the optical component 411, and is sent to the BD objective lens 412.

  Here, the optical component 411 has a ¼ wavelength plate that generates a ¼ wavelength phase difference with respect to the BD light. Outgoing light that is polarized into circularly polarized light by the optical component 411 and condensed by the BD objective lens 412 is irradiated onto the optical disk 409. The BD return light reflected from the optical disk 409 follows the same path as the forward path and is returned to linearly polarized light by the optical component 411. Further, the return light is reflected by the reflecting surface of the beam splitter 405, reflected by the optical member 404, and received by the light receiving detection element 413.

  With this configuration, recording / reproduction to / from an optical disc compatible with CD, DVD and BD becomes possible.

  An optical pickup device corresponding to each wavelength of CD, DVD, and BD is disclosed in Patent Document 1, for example.

JP 2009-199672 A

  In the conventional optical pickup device, a quarter-wave plate for sending circularly polarized light to the objective lens is attached in the vicinity of the objective lens. For this reason, there is a problem that the quarter-wave plate becomes a restriction for thinning and miniaturization of the optical pickup device.

  The present invention has been made to solve the above-described problems. For example, in an optical pickup device that uses light of a plurality of wavelengths such as BD and CD, circularly polarized light is sent to an objective lens and is thin. An object of the present invention is to provide an optical pickup device that can be reduced in size and size.

  The optical pickup device of the present invention includes a first light source that irradiates first light that is light having a predetermined wavelength, and a second light source that emits second light that is light having a shorter wavelength than the first light. A first objective lens that condenses the first light, a second objective lens that condenses the second light, and reflects the first light toward the first objective lens and the second A first rising mirror that transmits the first light, and a second rising mirror that reflects the second light transmitted through the first rising mirror toward the second objective lens. Further, a phase difference of 1/8 wavelength is given to the first light on the surface of the first rising mirror irradiated with the first light and the second light, and the second light is A wave plate for providing a quarter-wave phase difference is provided. Further, the first rising mirror is provided with a reflective film for reflecting the first light so that the first light transmitted through the wave plate is transmitted through the wave plate again.

  According to such a configuration, the first light has a phase difference of 1/8 wavelength and is reflected by the reflection film of the first rising mirror. Further, the first light passes through the retardation film again in a state where a phase difference of 1/8 wavelength is given. Therefore, the first light is given a phase difference of ¼ wavelength and becomes circularly polarized light. Further, the circularly polarized first light is sent to the first objective lens. On the other hand, the second light is given a phase difference of ¼ wavelength and becomes circularly polarized light. Further, the circularly polarized second light is sent to the second objective lens by the reflection film of the second rising mirror. Therefore, circularly polarized light can be sent to the objective lens without attaching a quarter-wave plate in the vicinity of the objective lens.

  Therefore, for example, in an optical pickup device that uses light of a plurality of wavelengths, such as BD and CD, an optical pickup device that can be reduced in thickness and size while sending circularly polarized light to the objective lens can be provided.

  The wavelength plate may be formed by applying a photo-alignment resin to a substrate to form a photo-alignment film and applying a liquid crystal resin on the photo-alignment film.

  According to such a configuration, since the film thickness of the wave plate can be made uniform, the transmitted wavefront aberration generated in the wave plate can be reduced.

  The wavelength plate may be formed by applying at least one of a photo-alignment resin or a liquid crystal resin to the substrate by spin coating.

  According to such a configuration, since the film thickness of the wave plate can be made more uniform, the transmitted wavefront aberration can be further reduced.

  According to the present invention, in an optical pickup device that uses light of a plurality of wavelengths, such as BD and CD, for example, an optical pickup device that sends circularly polarized light to an objective lens and can be reduced in thickness and size. Can provide.

Schematic diagram of an optical pickup device in an embodiment The figure explaining the optical path after the collimator lens Schematic diagram explaining why the phase difference occurs Schematic diagram of a conventional optical pickup device

(Embodiment)
[1. Overview of optical pickup device 100]
The optical pickup device 100 according to the present embodiment includes laser diodes of three wavelengths for recording / reproducing on each of the BD, DVD, and CD optical disks. Furthermore, the optical pickup device 100 has an optical path of a polarization optical system including a wave plate that is a retardation film that generates a predetermined phase difference at all three wavelengths.

[2. Configuration of Optical Pickup Device 100]
As shown in FIG. 1, the optical pickup device 100 includes a CD / DVD laser diode 2 as a first light source and a BD laser diode 1 as a second light source. Furthermore, a wave plate integrated reflection plate 3 as a first rising mirror including a wave plate and a BD laser reflection plate 4 as a second rising mirror are provided. Further, a CD / DVD objective lens 6 as a first objective lens and a BD objective lens 7 as a second objective lens are provided.

[3. Configuration of wave plate integrated reflector 3]
The present invention is characterized by the structure of the wave plate integrated reflector 3. As shown in FIG. 2, the wave plate integrated reflector 3 has a function of giving a phase difference of 1/8 wavelength to light of CD / DVD wavelength on one surface of a substrate 300 made of a quartz glass plate or the like. A wave plate 302 and a non-reflective coating (not shown) are formed. Further, the wave plate 302 has a function of giving a quarter-wave phase difference to light having a BD wavelength. A dichroic film coat 304 that is a reflective film is formed on the surface of the substrate 300 opposite to the surface on which the wave plate 302 is formed. The dichroic film coat 304 totally reflects light of CD / DVD wavelength incident from the substrate 300 side at an incident angle of about 45 °. Further, the light of the BD wavelength incident on the dichroic film coat 304 from the substrate 300 side at an incident angle of about 45 ° is totally transmitted.

[4. Operation of Optical Pickup Device 100]
As shown in FIGS. 1 and 2, the linearly polarized CD / DVD forward light that is the first light having the center wavelength of 800 nm or the center wavelength of 650 nm emitted from the CD / DVD laser diode 2 passes through the grating element 8. Reflected in the direction of the beam splitter 12 by the plate beam splitter 9. Further, the linearly polarized light passes through the beam splitter 12 and is converted into parallel light by the collimator lens 5.

  On the other hand, the linearly polarized BD forward light, which is the second light having a central wavelength of 405 nm, emitted from the BD laser diode 1 is reflected by the beam splitter 12 and converted into parallel light by the collimator lens 5.

  As described above, the CD / DVD forward light polarized into the circularly polarized light by the wave plate-integrated reflector 3 is condensed by the CD / DVD objective lens 6 and applied to the optical disk 13. Subsequently, the CD / DVD outbound light is reflected according to the pit state formed on the optical disc 13 and becomes CD / DVD backward light.

  On the other hand, the BD forward light polarized in the circularly polarized light by the wave plate integrated reflector 3 is reflected by the BD laser reflector 4. Further, the BD forward light is condensed by the BD objective lens 7 and irradiated onto the optical disc 13. The BD forward light irradiated on the optical disc 13 is reflected according to the pit state formed on the optical disc 13 and becomes BD return light.

  Next, the CD / DVD return light is converted into parallel light by the CD / DVD objective lens 6. Further, the CD / DVD return light is reflected again by the wave plate integrated reflector 3. At that time, the circularly polarized CD / DVD return light passes through the wave plate 302 twice in the same way as the forward path, and is thus polarized into linearly polarized light whose polarization direction is 90 ° different from that of the forward path. For example, when the CD / DVD forward light is linearly polarized light in the vertical direction on the paper surface, the CD / DVD backward light is linearly polarized light in the direction perpendicular to the paper surface.

  On the other hand, the BD return light is converted into parallel light by the BD objective lens 7. Furthermore, the BD return light is reflected by the BD laser reflection plate 4 and sent to the wave plate integrated reflection plate 3. By passing through the wave plate-integrated reflection plate 3, the circularly polarized BD return light becomes linearly polarized light having a polarization direction different by 90 ° from the forward path. For example, when the BD forward light is linearly polarized light in a direction perpendicular to the paper surface, the BD backward light is linearly polarized light in the vertical direction on the paper surface.

  The CD / DVD return light and the BD return light polarized in this way are transmitted through the beam splitter 12 and the plate beam splitter 9. Then, the CD / DVD return light and the BD return light are converted into servo signal diffracted light by the hologram element 10. Further, the light receiving detection element 11 detects an output signal that is the intensity of the CD / DVD return light and the BD return light and a servo signal included in the CD / DVD return light and the BD return light.

[5. Action of wave plate integrated reflector 3]
As shown in FIG. 2, the CD / DVD outward light passes through the wave plate 302 formed on one surface of the substrate 300 once. Further, the CD / DVD outward light passes through the substrate 300. Further, the CD / DVD forward light is reflected by the dichroic film coat 304 and passes through the wave plate 302 again.

  Here, as shown in FIG. 3, the 1/8 wavelength plate with respect to the CD wavelength (800 nm) is a wave plate whose birefringence is 1/8 of the CD wavelength. The 1/8 wavelength plate of the CD wavelength has a function as a 1/4 wavelength plate that gives a phase difference of 1/4 wavelength by passing light of the CD wavelength twice.

  Further, since the BD wavelength (405 nm) is about ½ of the CD wavelength, the ８ wavelength plate at the CD wavelength functions as a ¼ wavelength plate at the BD wavelength. In addition, since the DVD wavelength (650 nm) is close to the CD wavelength, a phase shift slightly occurs compared to the quarter wavelength.

  Thus, the linearly polarized light of the CD / DVD wavelength is polarized into circularly polarized light by passing through the wave plate 302 twice. On the other hand, linearly polarized light having a BD wavelength is polarized into circularly polarized light by passing through the wave plate 302 once.

[6. Manufacturing method of wave plate integrated reflector 3]
First, a dichroic film coat 304 is formed on one surface of the substrate 300 by sputtering or the like. For the dichroic film coat 304, for example, a laminate of several types of optical thin films is used.

  Next, the wave plate 302 is formed on the surface of the substrate 300 opposite to the surface on which the dichroic film coat 304 is formed. For example, the wave plate 302 is formed by the following steps. First, in the first step, a photo-alignment resin is applied to the substrate 300. Next, in the second step, the photo-alignment resin is thermally cured by a hot plate or the like. In this way, a photo-alignment film is formed. At this stage, the alignment of the photo-alignment film is not uniform. Next, in the third step, the photo-alignment film is irradiated with ultraviolet light polarized in a specific direction by an ultraviolet polarized light exposure apparatus or the like. In this way, a photo-alignment film oriented in a certain direction is formed. Next, in a fourth step, a photocurable liquid crystal resin, which is one of liquid crystal resins, is applied on the photo-alignment film. Next, in the fifth step, the photocurable liquid crystal resin is dried by a hot plate or the like. Next, in a sixth step, the photocurable liquid crystal resin is irradiated with ultraviolet rays by an ultraviolet irradiation device or the like. In this way, the photocurable liquid crystal resin is cured, and the wave plate 302 is formed.

  Next, a non-reflective coating that suppresses reflection in each wavelength band of CD, DVD, and BD at an incident angle of 45 ° is formed on the surface of the wave plate 302.

  Finally, the wave plate integrated reflector 3 is completed by being cut into a prescribed size in a direction rotated by 45 ° from the optical axis direction of the wave plate 302.

  The thickness control of the wave plate 302 of the wave plate integrated reflector 3 manufactured in this way is easy, and transmitted wavefront aberration generated in the wave plate 302 is reduced.

  Furthermore, it is preferable to form the wavelength plate 302 by applying at least one of a photo-alignment resin or a liquid crystal resin to the substrate 300 by spin coating.

  In this case, it is easier to control the film thickness of the wave plate 302, and the transmitted wavefront aberration generated in the wave plate 302 is further reduced.

[7. Example of Wave Plate 302]
In the present embodiment, the birefringence of the wavelength plate 302 = 93 nm was obtained by setting the film thickness of the liquid crystal of the wavelength plate 302 to about 1000 nm.

  At this time, the phase difference between CD and DVD is

It is calculated using. On the other hand, the phase difference of BD is

It is calculated using. As a result, the CD phase difference is 84 °, and the DVD phase difference is 103 °. On the other hand, the phase difference of BD is 84 °. Thus, the wave plate 302 gives a phase difference of ¼ wavelength to each wavelength of CD / DVD and BD.

  The value of the phase difference can be managed by controlling the film thickness of the liquid crystal in the wave plate 302.

[8. Summary]
The optical pickup device 100 according to the present embodiment condenses light of CD / DVD wavelength, CD / DVD laser diode 2 that emits light of CD / DVD wavelength, BD laser diode 1 that emits light of BD wavelength, and light of CD / DVD wavelength. A CD / DVD objective lens 6 for focusing, a BD objective lens 7 for condensing light of BD wavelength, a wavelength for reflecting light of CD / DVD wavelength toward the CD / DVD objective lens 6 and transmitting light of BD wavelength A plate-integrated reflection plate 3 and a BD laser reflection plate 4 that reflects light having a BD wavelength transmitted through the wavelength plate-integrated reflection plate 3 toward the BD objective lens 7 are provided. Further, the surface of the wave plate-integrated reflector 3 irradiated with the light of CD / DVD wavelength and the light of BD wavelength gives a phase difference of 1/8 wavelength to the light of CD / DVD wavelength and the BD wavelength. A wave plate 302 is provided that gives a phase difference of ¼ wavelength to the light. Further, a dichroic film coat 304 for reflecting the light of the CD / DVD wavelength is provided on the wavelength plate integrated reflection plate 3 so that the light of the CD / DVD wavelength transmitted through the wavelength plate 302 is transmitted through the wavelength plate 302 again.

  According to such a configuration, the CD / DVD wavelength light is given a phase difference of 1/8 wavelength and is reflected by the dichroic film coat 304. Further, the light of the CD / DVD wavelength is transmitted through the wave plate 302 again in a state where a phase difference of 1/8 wavelength is given. Accordingly, the light of CD / DVD wavelength is given a phase difference of ¼ wavelength and becomes circularly polarized light. Further, the circularly polarized light of CD / DVD wavelength is sent to the CD / DVD objective lens 6. On the other hand, light of BD wavelength is given a phase difference of ¼ wavelength and becomes circularly polarized light. Further, the circularly polarized light having the BD wavelength is sent to the BD objective lens 7 by the BD laser reflection plate 4. Therefore, circularly polarized light can be sent to the objective lens without attaching a quarter-wave plate in the vicinity of the objective lens.

  Therefore, for example, in an optical pickup device 100 that uses light of a plurality of wavelengths such as BD and CD, it is possible to provide an optical pickup device 100 that can be reduced in thickness and size while sending circularly polarized light to the objective lens. .

[9. Other Embodiments]
As described above, the embodiment of the present invention has been illustrated. However, the present invention is not limited to this. Therefore, other embodiments of the present invention will be collectively described below. The present invention is not limited to these. That is, the present invention can be applied to other embodiments that are appropriately modified.

  In the embodiment, an example in which the dichroic film coat 304 is formed on the surface of the substrate 300 opposite to the surface on which the wave plate 302 is formed is shown. However, the present invention is not limited to this. In short, it is only necessary to arrange the outgoing light after it first enters the wave plate 302. For example, the dichroic film coat 304 may be formed between the wave plate 302 and the substrate 300. Further, the dichroic film coat 304 may be formed inside the substrate 300. In this case, for example, the wave plate integrated reflector 3 is formed by bonding the first substrate on which the wave plate 302 is formed and the second substrate on which the dichroic film coat 304 is formed. . Even in such a configuration, the object of the present invention can be achieved.

  In the embodiment, the wave plate 302 formed by applying the photo-alignment resin and the liquid crystal resin is exemplified. However, the present invention is not limited to this. For example, it may be formed by laminating a thin crystal plate. Even in such a configuration, the object of the present invention can be achieved.

  In the embodiment, the light of CD / DVD wavelength is exemplified as the first light. However, the object of the present invention can be achieved only by the light of CD wavelength.

  According to the present invention, for example, in an optical pickup device that uses light of a plurality of wavelengths, such as BD and CD, it is possible to reduce the thickness and size while sending circularly polarized light to an objective lens. Therefore, the present invention is widely useful for an optical disk device used for a notebook personal computer or the like.

1,403 BD laser diode 2,401 CD / DVD laser diode 3 Wave plate integrated reflector 4,410 BD laser reflector 5 Collimator lens 6,408 CD / DVD objective lens 7,412 BD objective lens 8 Grating element 9 Plate Type Beam Splitter 10 Hologram Element 11,413 Light Receiving Detection Element 12,405 Beam Splitter 13,409 Optical Disk 100 Optical Pickup Device 300 Substrate 302 Wavelength Plate 304 Dichroic Film Coat 402,404 Optical Member 406 CD / DVD Reflector 407,411 Optical Parts

Claims (3)

A first light source that emits first light that is light of a predetermined wavelength; a second light source that emits second light that is light of a shorter wavelength than the first light; and the first light. A first objective lens that collects light;
A second objective lens that condenses the second light; a first rising mirror that reflects the first light toward the first objective lens and transmits the second light; An optical pickup device comprising: a second rising mirror that reflects the second light transmitted through the first rising mirror toward the second objective lens;
A phase difference of ８ wavelength is given to the first light on the surface of the first rising mirror that is irradiated with the first light and the second light, and the second light. A wave plate that gives a phase difference of ¼ wavelength with respect to
An optical pickup device comprising a reflective film that reflects the first light on the first rising mirror so that the first light transmitted through the wave plate transmits through the wave plate again. 2. The optical pickup device according to claim 1, wherein the wavelength plate is formed by applying a photo-alignment resin to a substrate to form a photo-alignment film, and applying a liquid crystal resin on the photo-alignment film. . 3. The optical pickup device according to claim 2, wherein the wave plate is formed by applying at least one of a photo-alignment resin or a liquid crystal resin to a substrate by spin coating.

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