JP5767858B2 - Optical diffraction element, optical pickup, and method of manufacturing optical diffraction element - Google Patents

Description

  The present invention relates to an optical diffraction element, an optical pickup, and a method for manufacturing the optical diffraction element.

  There are optical diffraction elements for optical pickups that read data from optical storage media such as CDs, DVDs, and Blu-rays.

Patent Document 1 discloses a diffraction grating. This diffraction grating has a substrate on which concave portions are periodically formed on one surface by etching. In this diffraction grating, the laser light is diffracted by the region where the recess is formed and the other region.
[Prior art documents]
[Patent Literature]
[Patent Document 1] JP 2008-21368 A

  However, the substrate of the above-described diffraction grating has a low strength because the region where the recess is formed is thin. As a result, the substrate of the diffraction grating has a problem in that the thickness of the entire diffraction grating must be increased in order to maintain the strength of the region where the recess is formed.

  In order to solve the above-described problem, a first aspect of the present invention is a transparent substrate and two regions formed on one surface of the substrate and having different orientation directions and arranged periodically. And an optical alignment film.

  In order to solve the above-described problem, a second aspect of the present invention provides the above-described light diffractive element, a laser that inputs polarized light to the light diffractive element, diffracted light from the light diffractive element, and the light An optical pickup includes a beam splitter that separates polarized light from a diffraction element and reflected light from an object, and a light receiving element that receives the reflected light separated by the beam splitter.

  In order to solve the above-mentioned problem, the third aspect of the present invention is to apply a photo-alignment film on one surface of a transparent substrate, and to irradiate the photo-alignment film with polarized light having different polarization directions. By doing so, there is provided an optical diffraction element manufacturing method comprising an alignment forming step of forming two regions having different alignment directions and being arranged side by side periodically.

  It should be noted that the above summary of the invention does not enumerate all the necessary features of the present invention. In addition, a sub-combination of these feature groups can also be an invention.

1 is an overall configuration diagram of an optical pickup according to an embodiment. It is a disassembled perspective view of an optical diffraction element. It is sectional drawing parallel to YZ plane of an optical diffraction element. It is a figure explaining the manufacturing process of an optical diffraction element. It is a figure explaining the manufacturing process of an optical diffraction element. It is a figure explaining the manufacturing process of an optical diffraction element. It is a figure explaining the manufacturing process of an optical diffraction element. It is a figure explaining the manufacturing process of an optical diffraction element. It is sectional drawing parallel to the YZ plane of the optical diffraction element by changed embodiment. It is sectional drawing parallel to the YZ plane of the optical diffraction element by changed embodiment. It is a graph which shows the change of the diffraction efficiency of 0th-order light and ± 1st-order light at the time of changing a retardation ratio. It is a graph which shows the change of the diffraction efficiency ratio of +/- 1st-order light with respect to 0th-order light at the time of changing retardation ratio. It is a graph which shows the change of the diffraction efficiency of 0th-order light and ± 1st-order light when width ratio WR is changed. It is a graph which shows the change of the diffraction efficiency ratio of +/- 1st order light with respect to 0th order light when width ratio WR is changed. It is a disassembled perspective view of the optical diffraction element by changed embodiment. It is a graph which shows the relationship between the crossing angle (theta) of the slow axis of the area | region 23, and the slow axis of the area | region 24, and the diffraction efficiency of 0th order light and 1st order light. It is a graph which shows the relationship between the crossing angle (theta) of the slow axis of the area | region 23, and the slow axis of the area | region 24, and the ellipticity of 0th-order light and 1st-order light.

  Hereinafter, the present invention will be described through embodiments of the invention, but the following embodiments do not limit the invention according to the claims. In addition, not all the combinations of features described in the embodiments are essential for the solving means of the invention.

  FIG. 1 is an overall configuration diagram of an optical pickup according to an embodiment. XYZ indicated by an arrow in FIG. 1 is defined as an XYZ direction.

  As shown in FIG. 1, the optical pickup 1 according to the embodiment irradiates light on an optical storage medium 90 such as a CD, DVD, or Blu-ray that is an example of an object, and stores information stored in the optical storage medium 90. read. The optical pickup 1 includes a laser 2, a polarizing filter 3, an optical diffraction element 4, a polarizing beam splitter 5, a collimating lens 6, a quarter wavelength plate 7, an objective lens 8, a condensing unit 9, And a light receiving element 10. The forward path indicates the path of the light 91 from the laser 2 to the optical storage medium 90, and the return path indicates the path from the optical storage medium 90 to the light receiving element 10.

  The laser 2 is disposed on the most upstream side of the forward path. The laser 2 emits light 91 that is laser light to be input to the optical diffraction element 4 or the like in the −Z direction. The laser light emitted from the laser 2 is linearly polarized light with the Y direction as the polarization direction. The wavelength of the laser light is not particularly limited. For example, when the optical storage medium 90 is a CD, the wavelength is 787 nm. When the optical storage medium 90 is a DVD, the wavelength is 655 nm. In this case, the wavelength is 405 nm.

  The polarizing filter 3 is disposed between the laser 2 and the light diffraction element 4. The polarizing filter 3 transmits light whose polarization direction is the Y direction and blocks light whose polarization direction is the X direction. That is, the polarizing filter 3 transmits the light 91 emitted from the laser 2. On the other hand, the light reflected by the optical storage medium 90 and returning to the polarization filter 3 is blocked by the polarization filter 3 because the X direction is the polarization direction. The polarizing filter 3 may not be provided.

  The light diffraction element 4 is disposed between the polarization filter 3 and the polarization beam splitter 5. The light diffraction element 4 is formed in a square plate shape parallel to the XY plane. Here, the shape of the light diffraction element 4 can be a square, a rectangle, or a parallelogram. In particular, by making the shape of the light diffraction element 4 rectangular or parallelogram, it is possible to easily recognize the direction of the optical axis during assembly and assemble in the correct direction. The optical diffraction element 4 diffracts the light 91 emitted from the laser 2 to generate diffracted light. The light diffraction element 4 rotates the polarization direction of the light 91 having the Y direction emitted from the laser 2 as the polarization direction by 90 ° and converts the light 91 into the light 91 having the X direction as the polarization direction. Details of the light diffraction element 4 will be described later.

  The polarization beam splitter 5 is disposed between the light diffraction element 4 and the collimating lens 6. The polarization beam splitter 5 is an example of a beam splitter, and transmits light whose polarization direction is the X direction and reflects light whose polarization direction is the Y direction. Here, the polarization direction of the forward light 91 transmitted through the light diffraction element 4 and traveling in the −Z direction is the X direction. Accordingly, the polarization beam splitter 5 transmits the forward light 91. On the other hand, the polarization direction of the return light 91 that is reflected by the optical storage medium 90 and travels in the + Z direction is rotated by 90 ° by a quarter-wave plate 7 to be described later to become the Y direction. Therefore, the polarization beam splitter 5 reflects the light 91 on the return path in the + Y direction. Thereby, the polarization beam splitter 5 separates the light 91 that is the polarized light emitted from the laser 2 and the light 91 that is the reflected light reflected by the optical storage medium 90.

  The collimating lens 6 is disposed between the polarizing beam splitter 5 and the quarter wavelength plate 7. The collimating lens 6 converts the light traveling in the −Z direction into parallel light and collects the parallel light traveling in the + Z direction.

  The quarter wavelength plate 7 is disposed between the collimating lens 6 and the objective lens 8. The quarter wavelength plate 7 converts linearly polarized light into circularly polarized light and converts circularly polarized light into linearly polarized light. Therefore, the quarter wavelength plate 7 converts the forward light 91 that is linearly polarized light into circularly polarized light. The quarter-wave plate 7 converts the return light 91 that is circularly polarized light reflected by the optical storage medium 90 into linearly polarized light. Here, since the optical storage medium 90 is a fixed end, the rotation direction of the circularly polarized light before reaching the optical storage medium 90 and the rotation direction of the circularly polarized light after being reflected by the optical storage medium 90 are opposite. Therefore, the polarization direction of the return light 91 transmitted through the quarter wavelength plate 7 is the Y direction rotated by 90 ° from the polarization direction of the linearly polarized light before reaching the quarter wavelength plate 7.

  The objective lens 8 is disposed between the quarter wavelength plate 7 and the optical storage medium 90. The objective lens 8 condenses the substantially parallel light 91 on the optical storage medium 90 in the forward path.

  The condensing unit 9 is disposed between the polarization beam splitter 5 and the light receiving element 10. The condensing part 9 can be comprised by single or several lenses, such as a cylindrical lens and a concave lens, for example. The condensing unit 9 condenses the light 91 reflected by the polarizing beam splitter 5 in the + Y direction onto the light receiving element 10 after being reflected by the optical storage medium 90.

  The light receiving element 10 is arranged on the + Y direction side of the light collecting unit 9 and on the most downstream side of the return path. The light receiving element 10 receives the return light 91 that is reflected by the optical storage medium 90 and separated by the polarization beam splitter 5. The light receiving element 10 converts the received light 91 into an electrical signal and then outputs the electrical signal.

  FIG. 2 is an exploded perspective view of the optical diffraction element. FIG. 3 is a cross-sectional view of the optical diffraction element parallel to the YZ plane.

  2 and 3, the optical diffraction element 4 includes a substrate 11, a light orientation film 12 and a liquid crystal layer 13 for changing the polarization direction, a light orientation film 14 and a liquid crystal layer 15 for light diffraction, and a reflection. And a prevention film 16. The substrate 11 is disposed on the optical storage medium 90 side, and the antireflection film 16 is disposed on the laser 2 side.

  The substrate 11 has a substantially uniform thickness over the entire surface, and is formed in a square shape of 2 mm to 5 mm × 2 mm to 5 mm. The substrate 11 is made of a transparent glass plate having a high transmittance at the wavelength of the laser beam. The substrate 11 may be made of a transparent material such as a resin plate, a resin film, or a resin material containing glass fibers. In particular, when the substrate 11 is made of a material containing glass fiber, the strength and workability can be improved. The substrate 11 holds the photo-alignment film 12, the liquid crystal layer 13, the photo-alignment film 14, the liquid crystal layer 15, and the antireflection film 16.

  The photo-alignment film 12 is an example of a second photo-alignment film. The photo-alignment film 12 is an ultraviolet curable resin and is made of a photo-alignment compound such as a photodecomposition type, a photo-quantization type, or a photo-isomerization type. The photo-alignment film 12 has a thickness of about 0.01 μm to 1 μm. The photo-alignment film 12 is formed on the + Z plane of the substrate 11. In other words, the photo-alignment film 12 is disposed between the substrate 11, the liquid crystal layer 13, and the photo-alignment film 14. The photo-alignment film 12 has a uniform alignment direction that is inclined with respect to the alignment direction of the photo-alignment film 14 described later. This means that the alignment direction of the photo-alignment film 12 is skewed with respect to the polarization direction of the light 91 from the laser 2 incident on the photo-alignment film 12. As an example, the alignment direction of the photo-alignment film 12 is a direction inclined by 45 ° from the alignment direction of the photo-alignment film 14. The photo-alignment film 12 aligns the optical axis of the liquid crystal layer 13 according to this alignment direction. The optical axis here is a slow axis. Another example of the optical axis is a fast axis.

  The liquid crystal layer 13 is an example of a second liquid crystal layer and has a half-wave plate configuration. The liquid crystal layer 13 is formed on the photo-alignment film 12 between the substrate 11 and the photo-alignment film 14. The liquid crystal layer 13 is made of an organic film such as a polymerizable liquid crystal having birefringence. The liquid crystal layer 13 has a thickness of about 0.5 μm to 10 μm. The liquid crystal layer 13 has an optical axis aligned in parallel based on the uniform alignment direction of the photo-alignment film 12. In the example shown in FIG. 2, the optical axis of the liquid crystal layer 13 is a direction inclined by 45 ° from the alignment direction of the photo-alignment film 14. Therefore, the liquid crystal layer 13 rotates the polarization direction of the light 91 having the Y direction emitted from the laser 2 as the polarization direction by 90 ° and converts the light 91 to the light 91 having the X direction as the polarization direction. Further, the liquid crystal layer 13 rotates the polarization direction of the return light 91 transmitted through the polarization beam splitter 5 and having the Y direction as the polarization direction by 90 ° to convert the light 91 into the light 91 having the X direction as the polarization direction.

  The photo-alignment film 14 is an ultraviolet curable resin and is made of a photo-alignment compound such as a photodecomposition type, a photo-quantization type, or a photo-isomerization type. The photo-alignment film 14 has a thickness of about 0.01 μm to 1 μm. The photo-alignment film 14 is formed on the liquid crystal layer 13. In other words, the photo-alignment film 14 is indirectly formed on the + Z side surface of the substrate 11. The photo-alignment film 14 has two rectangular regions 21 and 22 having a width in the Y direction of 100 μm or less and extending in the X direction. The region 21 and the region 22 are formed in substantially the same shape. In the Y direction, the regions 21 and 22 are arranged alternately and periodically. The region 21 has an alignment direction in the X direction. Therefore, the orientation direction of the region 21 is parallel to the X direction that is the polarization direction of the light 91 emitted from the laser 2. The region 22 has an alignment direction in the Y direction. That is, the photo-alignment film 14 has two regions 21 and 22 whose alignment directions are orthogonal to each other. The photo-alignment film 14 aligns the optical axis of the liquid crystal layer 15 according to these alignment directions.

The liquid crystal layer 15 is formed on the photo-alignment film 14. The liquid crystal layer 15 is made of an organic film such as a polymerizable liquid crystal having birefringence. The liquid crystal layer 15 has a thickness of about 0.5 μm to 10 μm. The liquid crystal layer 15 has two rectangular regions 23 and 24 extending in the X direction. The region 23 has an optical axis aligned in parallel based on the alignment direction of the region 21 of the photo-alignment film 14, and the region 24 is an optical axis aligned in parallel based on the alignment direction of the region 22 of the photo-alignment film 14. Have The region 23 has substantially the same shape as the region 21 of the photo-alignment film 14 and is disposed on the region 21. The region 24 has substantially the same shape as the region 22 of the photo-alignment film 14 and is disposed on the region 22. Therefore, in the Y direction, the regions 23 and 24 are arranged alternately and periodically. The optical axis of the region 23 is parallel to the X direction that is the polarization direction of the light 91 emitted from the laser 2. The optical axis of the region 24 is parallel to the Y direction. Accordingly, the region 23 delays the phase of the polarization component in the Y direction, and the region 24 delays the phase of the polarization component in the X direction. As a result, the liquid crystal layer 15 has the polarization direction in the X direction, diffracts the forward light 91 traveling in the Z direction, and is tilted in the Y direction from the Z direction to the 0th order light 91 ₀ substantially parallel to the Z direction The generated primary light 91 ₁ , secondary light (not shown) further inclined from the Z direction, and the like are generated.

  The antireflection film 16 is formed on the liquid crystal layer 15. In other words, the antireflection film 16 is disposed outside the photo-alignment film 12, the liquid crystal layer 13, the photo-alignment film 14, and the liquid crystal layer 15 when viewed from the substrate 11. The antireflection film 16 suppresses reflection of light 91 emitted from the laser 2 and incident on the light diffraction element 4. Thereby, the anti-reflective film 16 improves the efficiency of the light used among the arrived light 91. Further, since the antireflection film 16 also suppresses light that is reflected and scattered, noise that reduces reading of signals from the optical storage medium 90 can be reduced.

  Next, the operation of the optical pickup 1 having the optical diffraction element 4 of the above-described embodiment will be described.

  First, light 91 which is laser light is emitted from the laser 2. The light 91 has a polarization direction in the Y direction and travels in the −Z direction. This light 91 reaches the polarizing filter 3. Here, the light 91 is linearly polarized light whose polarization direction is the Y direction. Therefore, most of the light 91 passes through the polarizing filter 3 and reaches the light diffraction element 4.

Since the anti-reflection film 16 is provided on the + Z side of the light diffraction element 4, the light 91 reaching the light diffraction element 4 is incident on the anti-reflection film 16 with almost no reflection. The light 91 that has passed through the antireflection film 16 enters the liquid crystal layer 15. Since the liquid crystal layer 15 has two regions 23 and 24 whose optical axes are orthogonal to each other, the light 91 diffracts the liquid crystal layer 15. As a result, the light 91 becomes zero-order light 91 ₀ , primary light 91 ₁ ,. The diffracted light 91 passes through the photo-alignment film 14 and then reaches the liquid crystal layer 13. Since the liquid crystal layer 13 has a half-wave plate configuration, linearly polarized light 91 having the Y direction as the polarization direction is converted by the liquid crystal layer 13 into linearly polarized light 91 having the X direction as the polarization direction. Thereafter, the light 91 passes through the photo-alignment film 12 and the substrate 11 and is emitted from the light diffraction element 4.

  Thereafter, the light 91 reaches the polarization beam splitter 5. Here, since the light 91 has the polarization direction of the X direction, it passes through the polarization beam splitter 5 and reaches the collimating lens 6. Thereafter, the light 91 is converted into parallel light by the collimating lens 6 and then reaches the quarter-wave plate 7.

Next, the linearly polarized light 91 is converted into circularly polarized light by the quarter wavelength plate 7 and then reaches the objective lens 8. The light 91 is collected by the objective lens 8 and reaches the optical storage medium 90. Thereafter, of the light 91 that has reached the optical storage medium 90, either the 0th-order light 91 ₀ , the primary light 91 ₁ , or other multi-order light is reflected in the + Z direction by the optical storage medium 90. The Thereafter, the reflected light 91 is converted into parallel light by the objective lens 8 and then reaches the quarter-wave plate 7. The circularly polarized light 91 is converted into linearly polarized light by the quarter wavelength plate 7. Here, the rotation direction of the circularly polarized light 91 on the return path is reversed from the rotation direction of the outbound path by reflection of the optical storage medium 90 that is a fixed end. Therefore, the polarization direction of the linearly polarized light 91 transmitted through the quarter wavelength plate 7 in the return path is rotated by 90 ° from the polarization direction of the linearly polarized light 91 that has reached the quarter wavelength plate 7 in the forward path, and the Y direction. It has become.

  Next, the light 91 that is parallel light is collected by the collimating lens 6 and reaches the polarization beam splitter 5. Here, the polarization beam splitter 5 reflects light whose polarization direction is the Y direction. Accordingly, the return light 91 that is linearly polarized light with the Y direction as the polarization direction is reflected by the polarizing beam splitter 5 in the + Y direction. A part of the light 91 in the return path passes through the polarization beam splitter 5, but most of the transmitted light 91 is polarized light whose polarization direction is the Y direction. Then, the polarization direction of the transmitted light 91 is rotated by 90 ° by the liquid crystal layer 13 of the light diffraction element 4 and becomes the X direction. Thereby, the light 91 transmitted through the polarization beam splitter 5 is blocked by the polarization filter 3 and does not reach the laser 2.

Thereafter, the light 91 reflected in the + Y direction by the polarization beam splitter 5 is collected by the light collecting unit 9 onto the light receiving element 10. The light 91 received by the light receiving element 10 is converted into an electrical signal and output. Here, in the initial setting of the optical pickup 1, the three-beam tracking method is executed. That is, among the light 91 which is diffracted by the light diffraction element 4, as the primary light 91 ₁ and the like is received by the light receiving element 10 is reflected, 0 order light 91 ₀ is received by the light receiving element 10, The optical pickup 1 is adjusted.

  Next, a method for manufacturing the optical diffraction element 4 according to the above-described embodiment will be described. 4-8 is a figure explaining the manufacturing process of an optical diffraction element. 4, 6, and 7, a large arrow indicates a light irradiation direction, and a small arrow on the side indicates a light polarization direction.

  First, as shown in FIG. 4, in the second application step, a photo-alignment film 12 made of, for example, an ultraviolet curable resin is applied to the entire + Z surface of the transparent substrate 11. Thereafter, in the second alignment formation step, the photo-alignment film 12 is aligned by irradiating the photo-alignment film 12 with linearly polarized light that is ultraviolet rays and has a polarization direction oblique to the alignment direction of the photo-alignment film 14. Let As a result, the photo-alignment film 12 having a uniform alignment direction oblique to the alignment direction of the photo-alignment film 14 is formed.

  Next, as shown in FIG. 5, in the second liquid crystal forming step, liquid crystal is applied on the photo-alignment film 12. Thereafter, the liquid crystal is dried and then cured by irradiating with ultraviolet rays, whereby the liquid crystal layer 13 is formed. The liquid crystal layer 13 may be cured by heating. Here, the optical axis of the liquid crystal layer 13 is aligned in parallel based on the alignment direction of the lower optical alignment film 12. As a result, a liquid crystal layer 13 having an optical axis parallel to the uniform alignment direction of the photo-alignment film 12 is formed.

  Next, as shown in FIG. 6, the photo-alignment film 14 is applied to the entire + Z plane of the liquid crystal layer 13. In other words, in the coating process, the photo-alignment film 14 is indirectly coated on the + Z surface of the transparent substrate 11. In this state, a mask 31 is arranged in the + Z direction of the photo-alignment film 14 with a predetermined interval. An opening 32 having the same shape as the region 21 is formed in the mask 31. The opening 32 of the mask 31 is disposed above a region where the region 21 is formed. Next, in the alignment forming process, the linearly polarized light whose polarization direction is the X direction is irradiated to the photo alignment film 14 through the opening 32 of the mask 31. Thereby, the orientation direction of the region 21 is oriented in the X direction.

  Next, as shown in FIG. 7, the mask 31 is moved in the Y direction so that the opening 32 is located above the region 22. In this state, the photo-alignment film 14 is irradiated through the mask 31 with linearly polarized light whose polarization direction is the Y direction. Thereby, the orientation direction of the region 22 is oriented in the Y direction. As a result, the photo-alignment film 14 is irradiated with linearly polarized light orthogonal to each other, and the alignment directions for forming the two regions 21 and 22 in the photo-alignment film 14 that are perpendicular to each other and periodically arranged side by side. The forming process ends.

  Next, as shown in FIG. 8, a liquid crystal is applied on the photo-alignment film 14. Thereafter, the liquid crystal is dried and then cured by irradiating with ultraviolet rays, whereby the liquid crystal layer 15 is formed. The liquid crystal layer 15 may be cured by heating. Here, the optical axis of the liquid crystal layer 15 is aligned in parallel based on the alignment direction of the lower optical alignment film 14. Therefore, the optical axis of the region 23 of the liquid crystal layer 15 formed on the region 21 of the photo-alignment film 14 is in the X direction. On the other hand, the optical axis of the region 24 of the liquid crystal layer 15 formed on the region 22 of the photo-alignment film 14 is the Y direction. Thereby, the liquid crystal layer 15 is formed in which the two regions 23 and 24 having the optical axes aligned in parallel based on the alignment directions of the two regions 21 and 22 of the photo-alignment film 14 are periodically arranged. To complete the liquid crystal forming process.

  Next, the antireflection film 16 is formed on the entire + Z plane of the liquid crystal layer 15. Thereby, the optical diffraction element 4 shown in FIG. 3 is completed.

  Next, the effect of the optical diffraction element 4 according to the above-described embodiment will be described.

  According to the above embodiment, in the light diffraction element 4, the liquid crystal layer 15 diffracts light by the region 23 and the region 24 whose optical axes are orthogonal to each other and periodically arranged side by side. I am letting. Thereby, the optical diffraction element 4 can make the board | substrate 11 into substantially uniform thickness over the whole surface, and can be set as the intensity | strength substantially equal over the whole surface. As a result, the thickness of the optical diffraction element 4 can be reduced and the size can be reduced.

  Since the optical diffraction element 4 does not need to form irregularities on the substrate 11, the flatness can be improved. As a result, the light diffraction element 4 can obtain a sufficient transmitted wavefront aberration without providing a cover glass or the like. In addition, since it is not necessary to form irregularities on the substrate 11, it is possible to suppress dust and the like from accumulating on the substrate 11. As a result, the light diffractive element 4 is easy to handle, improves workability, and can suppress deterioration of optical performance due to dust or the like.

  In the optical diffraction element 4, the liquid crystal layer 13 that functions as a half-wave plate and the liquid crystal layer 15 that functions as a diffraction grating are sequentially applied on the same substrate 11. Here, when the half-wave plate and the diffraction grating are manufactured as separate parts and then assembled, each part before assembly requires a certain thickness in order to maintain strength. For this reason, the thickness of the optical diffraction element is increased. On the other hand, in the case of the optical diffraction element 4 according to the embodiment, if the substrate 11 has a predetermined strength, the thickness of the liquid crystal layer 13 and the liquid crystal layer 15 formed by coating can be reduced. Thereby, the optical diffraction element 4 can be reduced in thickness. In addition, the assembly process and the alignment process of the liquid crystal layer 13 and the liquid crystal layer 15 are not necessary, so that the manufacturing process can be simplified.

  In the optical diffraction element 4, the antireflection film 16 is formed on the surface on which the light 91 from the laser 2 is incident. Thereby, the optical diffraction element 4 can reduce the reflection of the light 91 that has arrived, and can improve the efficiency of the light used by the antireflection film 16. The light diffraction element 4 can also suppress light scattered by reflection by the antireflection film 16. Thereby, noise that reduces reading of signals from the optical storage medium 90 can be reduced. Furthermore, the liquid crystal layer 15 can be prevented from being exposed to the atmosphere by the antireflection film 16. As a result, the liquid crystal layer 15 can be prevented from being deteriorated due to oxidation or the like.

  Next, an embodiment in which the optical diffraction element of the above-described embodiment is changed will be described. In addition, the same code | symbol is attached | subjected to the structure similar to embodiment mentioned above, and description is abbreviate | omitted. FIG. 9 is a cross-sectional view parallel to the YZ plane of the optical diffraction element according to the modified embodiment.

  As shown in FIG. 9, in the optical diffraction element 4 according to this embodiment, the photo-alignment film 14, the liquid crystal layer 15, the photo-alignment film 12, the liquid crystal layer 13, and the antireflection film 16 are arranged on the + Z plane of the substrate 11 in this order. Has been. In other words, the photo-alignment film 12 is disposed on the opposite side of the photo-alignment film 14 from the substrate 11 and has a uniform alignment direction that is inclined with respect to the alignment direction of the photo-alignment film 14. The liquid crystal layer 13 is formed on the photo-alignment film 12 and has an optical axis aligned in parallel based on the uniform alignment direction of the photo-alignment film 12.

  In the method for manufacturing the optical diffraction element 4 according to this embodiment, first, a coating process, an alignment forming process, and a liquid crystal forming process are performed.

  Next, in the second coating step, the photo-alignment film 12 is applied on the opposite side of the photo-alignment film 14 from the substrate 11.

  Next, in the second alignment formation step, the photo-alignment film 12 is irradiated with polarized light having a polarization direction oblique to the alignment direction of the photo-alignment film 14. As a result, the photo-alignment film 12 having a uniform alignment direction oblique to the alignment direction of the photo-alignment film 14 is formed.

  Next, a liquid crystal is applied on the photo-alignment film 12 in the second liquid crystal forming step. Thereafter, the liquid crystal is dried and cured to form the liquid crystal layer 13 having the optical axis aligned in parallel based on the uniform alignment direction of the photo-alignment film 12.

  Thereafter, an antireflection film 16 is formed on the liquid crystal layer 13 to complete the optical diffraction element 4 shown in FIG.

  Next, an embodiment in which the above-described optical diffraction element is changed will be described. In addition, the same code | symbol is attached | subjected to the structure similar to embodiment mentioned above, and description is abbreviate | omitted. FIG. 10 is a cross-sectional view parallel to the YZ plane of the optical diffraction element according to the modified embodiment.

  As shown in FIG. 10, in the optical diffraction element 4 according to this embodiment, the photo-alignment film 14, the liquid crystal layer 15, and the antireflection film 16 are arranged in this order on the + Z plane of the substrate 11, and the photo-alignment film 12, The liquid crystal layer 13 is arranged on the −Z plane of the substrate 11 in this order. In other words, the photo-alignment film 12 is disposed on the surface of the substrate 11 opposite to the photo-alignment film 14 and has a uniform alignment direction that is inclined with respect to the alignment direction of the photo-alignment film 14. The liquid crystal layer 13 is formed on the photo-alignment film 12 and has an optical axis aligned in parallel based on the uniform alignment direction of the photo-alignment film 12.

  In an example of the manufacturing method of the optical diffraction element 4 according to this embodiment, first, a coating process, an alignment forming process, and a liquid crystal forming process are performed. Thereafter, an antireflection film 16 is formed on the liquid crystal layer 13.

  Next, in the second application step, the photo-alignment film 12 is applied to the surface of the substrate 11 opposite to the photo-alignment film 14.

  Next, in the second alignment formation step, the photo-alignment film 12 is irradiated with polarized light having a polarization direction oblique to the alignment direction of the photo-alignment film 14. As a result, the photo-alignment film 12 having a uniform alignment direction oblique to the alignment direction of the photo-alignment film 14 is formed.

  Next, a liquid crystal is applied on the photo-alignment film 12 in the second liquid crystal forming step. Thereafter, the liquid crystal is dried and cured to form the liquid crystal layer 13 having the optical axis aligned in parallel based on the uniform alignment direction.

  Thereby, the optical diffraction element 4 shown in FIG. 10 is completed.

  In the method for manufacturing the optical diffraction element 4 according to this embodiment, the coating process, the alignment forming process, and the liquid crystal forming process may be performed after the second liquid crystal forming process.

  In the embodiment of FIGS. 1 to 10 described above, one set of the photo-alignment film 12 and the liquid crystal layer 13 functioning as a half-wave plate is provided, but the configuration of the half-wave plate is not limited thereto. As another example, a half-wave plate may be configured by stacking a plurality of sets of the photo-alignment film 12 and the liquid crystal layer 13 so that the optical axes have a predetermined relationship. Accordingly, a phase difference of ½ wavelength can be given to laser beams having different wavelengths, and a plurality of types of optical storage media can be handled.

  As another embodiment that is partially changed, the polarization direction of the light emitted from the laser may be tilted from the optical axis of the liquid crystal layer that diffracts the light.

  As another embodiment that is partially changed, the areas of the two regions of the liquid crystal layer that diffract light may be different. Thereby, the intensity | strength and direction of 0th order light, primary light, or multi-order light can be changed.

  Further, as another embodiment that is partially changed, the photo-alignment film 14 may be thickened and the liquid crystal layer 15 may be omitted. In this case, the thickness of the photo-alignment film 14 is preferably set in accordance with the wavelength of the light 91 to be diffracted. For example, when the wavelength of the light 91 to be diffracted is 405 nm to 787 nm, the thickness of the photo-alignment film 14 is preferably about 0.5 μm to 10 μm. In the manufacturing method of this embodiment, the material which comprises the photo-alignment film | membrane 14 is apply | coated corresponding to the above-mentioned thickness. Thereafter, the applied material is cured by irradiating with linearly polarized ultraviolet rays having a desired polarization direction through the mask 31, whereby the thick photo-alignment film 14 can be formed. Similarly, the photo-alignment film 12 may be thickened and the liquid crystal layer 13 may be omitted.

  As another embodiment that is partially changed, the optical axis of the liquid crystal layer 15 may be set in a direction other than parallel to the alignment direction of the photo-alignment film 14. For example, the optical axis of the liquid crystal layer 15 may be rotated by 90 ° from the alignment direction of the photo-alignment film 14. Similarly, the optical axis of the liquid crystal layer 13 may be set in a direction other than parallel to the alignment direction of the photo-alignment film 12. The optical axis of the liquid crystal layer 13 may be rotated by 90 ° from the alignment direction of the photo-alignment film 12.

Next, the relationship between the retardation Re, the diffraction efficiency, and the diffraction efficiency ratio of the region 23 and the region 24 investigated by simulation will be described. This simulation was performed in a configuration in which the photo-alignment film 12 and the liquid crystal layer 13 were omitted from the configuration in FIG. The retardation Re is defined by the following equation.
Re = (ne−no) · d
Here, ne is the extraordinary refractive index of the material of the regions 23 and 24. no is the ordinary refractive index of the material of the regions 23 and 24. d is the thickness of the region 23 and the region 24.
The wavelength of incident light is λ, and (Re / λ) is called a retardation ratio. FIG. 11 is a graph showing changes in diffraction efficiency of 0th-order light and ± 1st-order light when the retardation ratio is changed. FIG. 12 is a graph showing changes in the diffraction efficiency ratio of ± 1st order light with respect to 0th order light when the retardation ratio is changed. The diffraction efficiency ratio is (± first-order light diffraction efficiency) / (zero-order light diffraction efficiency). Note that [-] in the figure indicates that the unit is dimensionless.

  The conditions for this simulation will be described. The shape of the region 23 and the region 24 is the same. The direction of the slow axis of the region 23 and the direction of the slow axis of the region 24 are orthogonal. The incident light is linearly polarized light having a polarization direction orthogonal to the longitudinal direction of the regions 23 and 24. In other words, the polarization direction of the incident light is parallel to the slow axis of the region 23.

  As shown in FIG. 11, it can be seen that as the retardation ratio increases, the diffraction efficiency of the zero-order light decreases and the diffraction efficiency of the first-order light increases. The retardation ratio at the inflection point of the diffraction efficiency of the 0th-order light is about 0.25. On the other hand, the retardation ratio at the inflection point of the diffraction efficiency of the primary light is about 0.25. As shown in FIG. 12, it can be seen that the diffraction efficiency ratio increases exponentially as the retardation ratio increases. Thereby, the diffraction efficiency ratio can be controlled by changing the retardation ratio. For example, in the optical pickup, when the desired diffraction efficiency ratio is 0.1, the retardation ratio may be set to 0.15.

  Next, the relationship between the width ratio of the region 23 and the region 24, the diffraction efficiency, and the diffraction efficiency ratio by simulation will be described. This simulation was performed in a configuration in which the photo-alignment film 12 and the liquid crystal layer 13 were omitted from the configuration in FIG. The width is the length of the regions 23 and 24 in the direction orthogonal to the longitudinal direction. In the following description, the ratio of the width of the region 23 to the width of the region 24 is referred to as a width ratio WR. FIG. 13 is a graph showing changes in diffraction efficiency of 0th-order light and ± 1st-order light when the width ratio WR is changed. FIG. 14 is a graph showing a change in the diffraction efficiency ratio of ± first-order light with respect to zero-order light when the width ratio WR is changed.

  The conditions for this simulation will be described. The ratio of the retardation to the wavelength of the region 23 and the region 24 is 0.25. The direction of the slow axis of the region 23 and the direction of the slow axis of the region 24 are orthogonal. The incident light is linearly polarized light having a polarization direction orthogonal to the longitudinal direction of the regions 23 and 24. In other words, the polarization direction of the incident light is parallel to the slow axis of the region 23.

  As shown in FIG. 13, it can be seen that as the width ratio WR increases, the diffraction efficiency of the 0th-order light decreases and the diffraction efficiency of the 1st-order light increases. Accordingly, as shown in FIG. 14, it can be seen that the diffraction efficiency ratio increases as the width ratio WR increases. However, it can be seen that the diffraction efficiency ratio hardly changes when the width ratio WR exceeds a certain value. The inflection point of the primary light has a width ratio WR of about 0.25. The inflection point of the diffraction efficiency ratio has a width ratio WR of about 0.25. Accordingly, it can be seen that the inflection point of the primary light and the inflection point of the diffraction efficiency ratio are generated at substantially the same width ratio WR. In the optical pickup having a retardation ratio of 0.25, when the desired diffraction efficiency ratio is 0.1, the width ratio WR may be set to 0.25.

  FIG. 15 is an exploded perspective view of an optical diffraction element according to a modified embodiment. As shown in FIG. 15, in the optical diffraction element 104 of the present embodiment, the alignment direction of the region 21 and the alignment direction of the region 22 of the photo-alignment film 14 are different from each other. An intersection angle between the alignment direction of the region 21 and the alignment direction of the region 22 is defined as “θ”. The crossing angle θ may be appropriately changed between 0 ° <θ ≦ 90 °. The optical axis of the region 23 of the liquid crystal layer 15 and the optical axis of the region 24 are different from each other along the alignment direction of the regions 21 and 22. The optical axis of the region 23 of the liquid crystal layer 15 and the optical axis of the region 24 intersect at an intersection angle θ. Such a configuration can be manufactured by irradiating polarized light having different polarization directions when the regions 21 and 22 of the photo-alignment film 14 are formed.

  By controlling the crossing angle θ, it is possible to set the diffraction efficiencies of the zero-order light and the first-order light. Further, by controlling the crossing angle θ, the zero-order light can be made into elliptically polarized light, and its ellipticity can be set. Thereby, for example, when the light diffraction element 104 is applied to a laser light source projector, the emitted zero-order light can be made into elliptically polarized light having a desired ellipticity. As a result, it is possible to suppress deterioration in image quality due to speckles and color unevenness due to the high coherency of the light emitted from the laser light source.

  Next, the relationship between the crossing angle θ of the slow axes of the regions 23 and 24 of the optical diffraction element 104 in FIG. 15, the diffraction efficiency, and the ellipticity investigated by simulation will be described. This simulation was performed in a configuration in which the photo-alignment film 12 and the liquid crystal layer 13 were omitted from the configuration in FIG. The conditions for this simulation will be described. The ratio of retardation to wavelength in the regions 23 and 24 is 0.15. The shape of the region 23 and the region 24 is the same. The slow axis of the region 23 is fixed in a state orthogonal to the longitudinal direction of the regions 23 and 24. Then, the crossing angle θ between the slow axis of the region 23 and the slow axis of the region 24 is changed between 0 ° and 90 °. The incident light is linearly polarized light having a polarization direction orthogonal to the longitudinal direction of the regions 23 and 24. In other words, the polarization direction of the incident light is parallel to the slow axis of the region 23.

  FIG. 16 is a graph showing the relationship between the crossing angle θ between the slow axis of the region 23 and the slow axis of the region 24 and the diffraction efficiency of the 0th order light and the 1st order light. As shown in FIG. 16, as the crossing angle θ increases, the diffraction efficiency of the zero-order light decreases and the diffraction efficiency of the first-order light increases.

  FIG. 17 is a graph showing the relationship between the crossing angle θ between the slow axis of the region 23 and the slow axis of the region 24 and the ellipticity of the 0th order light and the 1st order light. The ellipticity is the ratio of the minor axis to the major axis. That is, “ellipticity = minor axis / major axis”. As shown in FIG. 17, when the crossing angle θ is 47 ° to 50 °, the ellipticity of the 0th-order light has a maximum value of 0.24. It can also be seen that when the crossing angle θ is 0 ° or 90 °, the 0th-order light is emitted as linearly polarized light. On the other hand, it can be seen that the ellipticity of the primary light is substantially 0 regardless of the change in the crossing angle θ. Thereby, it is understood that the primary light is emitted as linearly polarized light regardless of the crossing angle θ.

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. It will be apparent to those skilled in the art that various modifications or improvements can be added to the above-described embodiment. It is apparent from the scope of the claims that the embodiments added with such changes or improvements can be included in the technical scope of the present invention.

  The order of execution of each process such as operations, procedures, steps, and stages in the apparatus, system, program, and method shown in the claims, the description, and the drawings is particularly “before” or “prior to”. It should be noted that the output can be realized in any order unless the output of the previous process is used in the subsequent process. Regarding the operation flow in the claims, the description, and the drawings, even if it is described using “first”, “next”, etc. for convenience, it means that it is essential to carry out in this order. It is not a thing.

DESCRIPTION OF SYMBOLS 1 Optical pick-up 2 Laser 3 Polarizing filter 4 Optical diffractive element 5 Polarizing beam splitter 6 Collimating lens 7 1/4 wavelength plate 8 Objective lens 9 Condensing part 10 Light receiving element 11 Substrate 12 Photo-alignment film 13 Liquid crystal layer 14 Photo-alignment film 15 Liquid crystal Layer 16 Antireflection film 21 Region 22 Region 23 Region 24 Region 31 Mask 32 Opening 90 Optical storage medium 91 Light 91 ₀ 0th order light 91 ₁ 1st order light 104 Optical diffraction element

Claims (6)

A second coating step of coating the second photo-alignment film on one surface of the transparent substrate ;
A second alignment forming step of aligning the second photo-alignment film having a uniform alignment direction by irradiating the second photo-alignment film with polarized light;
A coating step of directly coating the photo-alignment film on the opposite side of the second photo-alignment film from the substrate ;
It said optical alignment layer, by irradiating a polarized light polarization directions different from each other, a different direction alignment direction from each other, Bei example an alignment formation step of forming two regions arranged side by side periodically,
In the second alignment formation step, by irradiating the second photo-alignment film with polarized light having a polarization direction oblique to the alignment direction of the photo-alignment film, the alignment direction of the photo-alignment film A method of manufacturing an optical diffraction element, wherein the second optical alignment film having a uniform alignment direction that is skewed is aligned . An application step of applying a photo-alignment film on one surface of a transparent substrate;
An alignment forming step of irradiating the optical alignment film with polarized light having different polarization directions from each other, thereby forming two regions in which the alignment directions are different from each other and periodically arranged,
A second coating step of directly coating the second photo-alignment film on the opposite side of the photo-alignment film from the substrate;
Uniform orientation direction oblique to the alignment direction of the photo-alignment film by irradiating the second photo-alignment film with polarized light having a polarization direction oblique to the alignment direction of the photo-alignment film A second alignment forming step of aligning a second photo-alignment film having
The manufacturing method of an optical diffraction element provided with . A second coating step of coating the second photo-alignment film on one surface of the transparent substrate;
A second alignment forming step of aligning the second photo-alignment film having a uniform alignment direction by irradiating the second photo-alignment film with polarized light;
A second liquid crystal forming step of forming a second liquid crystal layer having an optical axis oriented based on the uniform orientation direction by applying and curing a liquid crystal on the second photo-alignment film;
A coating step of directly coating the photo-alignment film on the side opposite to the second photo-alignment film in the second liquid crystal layer;
An alignment forming step of irradiating the photo-alignment film with polarized light having different polarization directions, thereby forming two regions having different alignment directions and periodically arranged side by side;
With
In the second alignment formation step, by irradiating the second photo-alignment film with polarized light having a polarization direction oblique to the alignment direction of the photo-alignment film, the alignment direction of the photo-alignment film A method of manufacturing an optical diffraction element, wherein the second optical alignment film having a uniform alignment direction that is skewed is aligned. A liquid crystal forming step of forming a liquid crystal layer in which two regions having optical axes aligned based on the alignment direction of the two regions are periodically arranged by applying a liquid crystal on the photo-alignment film; The manufacturing method of the optical diffraction element of Claim 3 further provided. An application step of applying a photo-alignment film on one surface of a transparent substrate;
An alignment forming step of irradiating the optical alignment film with polarized light having different polarization directions from each other, thereby forming two regions in which the alignment directions are different from each other and periodically arranged,
Liquid crystal that forms a liquid crystal layer in which two regions having optical axes aligned based on the alignment direction of the two regions are periodically arranged by applying and curing a liquid crystal on the photo-alignment film Forming process;
A second coating step of directly coating the second photo-alignment film on the opposite side of the liquid crystal layer from the alignment film;
Uniform orientation direction oblique to the alignment direction of the photo-alignment film by irradiating the second photo-alignment film with polarized light having a polarization direction oblique to the alignment direction of the photo-alignment film A second alignment forming step of aligning the second photo-alignment film having
The manufacturing method of an optical diffraction element provided with. After the second alignment formation step,
By applying the liquid crystal onto the second optical alignment layer, to claim 5, further comprising a second liquid crystal forming step of forming a second liquid crystal layer having an optical axis oriented in accordance with the uniform alignment direction The manufacturing method of the optical diffraction element of description.

Images