JP2006106726A - Polarized light diffracting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarized light diffracting element which can be manufactured inexpensively. <P>SOLUTION: A polarized light diffracting element 1 is provided with a polarized light diffracting body 11 of which the diffraction efficiency with respect to various order of diffraction light is different in accordance with the vibration direction of incident polarized light. The polarized light diffracting body 11 has a plurality of structural birefringence sections 111 in which structural birefringence is generated by the projecting and recessing parts being formed on the surface of the polarized light diffracting body 11. The structural birefringence sections 111 are spaced apart from each other so as to function as diffraction gratings. An in-between structural birefringence section 113 has a medium which is different from a medium that constitutes the structural birefringence section. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a polarization diffraction element and an optical head device using the polarization diffraction element.

  Polarization diffraction elements have many uses, and are used as hologram polarization optical elements for recording and reproducing optical information on optical recording media such as optical disks such as CD (Compact Disk) and DVD (Digital Versataile Disk). It is also used as an analyzer for magneto-optical disk heads.

  Conventional polarization diffraction elements use birefringent materials such as liquid crystal. (For example, refer to the column of prior art in Patent Document 1)

  An example of the configuration of a conventional polarization diffraction element is shown in FIG. 4 taking a polarization beam splitter of an optical disk as an example. The polarization diffraction element 1 passes light from a light source (not shown) such as a laser and irradiates the optical recording medium 2, but functions as a diffraction grating for reflected light from the optical recording medium 2. In order to realize such a function, the polarization diffraction element 1 is provided with a quarter-wave plate 12 on the optical recording medium 2 side of the white plate glass 42, and a long birefringent material 411 is arranged on the opposite side at regular intervals. The filling resin 41 is filled so as to cover the birefringent material 411.

  As the birefringent material 411, for example, liquid crystal, polycarbonate, calcite, crystal, sapphire, mica, or LN (lithium niobate) is used. Here, the refractive index of the birefringent material with respect to the polarized light having the vibration direction in the longitudinal direction of the birefringent material 411 is n2, and the refraction of the birefringent material with respect to the polarized light having the vibration direction perpendicular to the longitudinal direction of the birefringent material 411. If the rate is n1, the refractive index of the filling resin 41 is set to n1 which is the same as the refractive index n1 of the birefringent material for polarized light having a vibration direction perpendicular to the longitudinal direction of the birefringent material 411.

Therefore, when the light from the light source is polarized light having a vibration direction perpendicular to the longitudinal direction of the birefringent material 411, the birefringent material 411 and the filling resin 41 have the same refractive index, and thus function as a diffraction grating. No diffracted light is generated. On the other hand, the reflected light converted from the polarized light having the vibration direction perpendicular to the long direction of the birefringent material 411 to the polarized light having the long vibration direction of the birefringent material 411 by the quarter wavelength plate 12. On the other hand, since the birefringent material 411 and the filling resin 41 have different refractive indexes, it functions as a diffraction grating and generates diffracted light.
JP 2000-249831 A

  Since the conventional polarization diffraction element uses a birefringent material such as liquid crystal, the manufacturing cost has been increased.

  An object of the present invention is to provide a polarization diffraction element and an optical head device that can be manufactured at low cost. It is another object of the present invention to provide a polarization diffraction element and an optical head device having high optical characteristics.

  The polarization diffraction element according to the present invention has a plurality of structural birefringent portions having different refractive indices depending on the vibration direction of polarized light having irregularities with a pitch of λ or less of incident polarized light, and the structural birefringent portions are mutually connected. A polarization diffractive element that is provided apart and has a pitch between adjacent structural birefringent portions larger than the wavelength λ, and a refractive index adjusting unit between the structural birefringent portion and the adjacent structural birefringent portion The refractive index adjustment unit includes a refractive index adjustment unit having a refractive index different from that of the medium constituting the structural birefringence unit. According to such a configuration, it is not necessary to use a birefringent material such as a liquid crystal in a portion that generates birefringence, and thus the manufacturing cost can be reduced. Furthermore, since the diffraction efficiency can be easily adjusted by changing the material of the refractive index adjusting unit, high optical characteristics can be easily realized.

  Here, the polarization diffraction element transmits polarized light parallel to the fine groove formed by the unevenness provided in the structural birefringence portion, and functions as a diffraction grating for polarized light perpendicular to the fine groove. Is preferred.

  The refractive index of the refractive index adjusting unit is preferably higher than the minimum refractive index of the medium constituting the structural birefringent unit.

  More specifically, the refractive index of the refractive index adjusting portion is determined by the refractive index of the structural birefringent portion with respect to polarized light parallel to the microgroove formed by the unevenness provided in the structural birefringent portion or the fine groove. It is preferable that the refractive index of the birefringence portion is substantially the same with respect to the polarized light perpendicular to. Further, the refractive index of the refractive index adjusting unit is such that the refractive index of the structural birefringent portion with respect to the polarized light parallel to the fine groove formed by the unevenness provided in the structural birefringent portion and the polarized light perpendicular to the fine groove. It is also possible to make it different from both of the refractive indexes of the birefringence portion.

The refractive index adjusting unit in a preferred embodiment is formed of a resin having a refractive index different from that of the medium constituting the structural birefringent unit. In particular, the refractive index adjusting unit can be easily manufactured by being formed of a photocurable resin.
In an optical head using a polarization diffraction element, it is desirable to include the polarization diffraction element having the above configuration.

  According to the present invention, it is possible to provide a polarization diffraction element and an optical head device that can be manufactured at low cost. Furthermore, according to the present invention, a polarization diffraction element and an optical head device having high optical characteristics can be provided.

Embodiment 1 of the Invention
FIG. 1 shows a schematic sectional view of a polarization diffraction element according to Embodiment 1 of the present invention. 1A is an overall schematic diagram, FIG. 1B is a diagram for explaining incident light from a light source, and FIG. 1C is a diagram for explaining light reflected by an optical recording medium 2. .

  The polarization diffraction element 1 includes a polarization diffraction body 11 and a quarter wavelength plate 12. As shown in FIG. 1A, the polarization diffractive body 11 is provided on the light source side, and the quarter wavelength plate 12 is provided on the optical recording medium 2 side. The polarization diffractive body 11 and the quarter-wave plate 12 are preferably integrated as shown in FIG. 1A from the viewpoint of handling of parts and the number of parts, but they may be separated. .

  The polarization diffractive body 11 is formed of a transparent plastic resin such as an acrylic resin or a cycloolefin polymer resin.

  A plurality of structural birefringent portions 111 having a plurality of projections and depressions are present on the light source side surface of the polarization diffractive body 11. The uneven pitch W3 in the structural birefringent portion 111 is set to be smaller than the wavelength of light passing therethrough. As a result, the refractive index for TM polarized light and the refractive index for TE polarized light have different values and the same properties as the birefringent material. The concave portion 112 of the structural birefringent portion 111 in the first embodiment is not filled with resin or the like and air is present. The respective structural birefringent portions 111 have the same width W1 and are arranged at the same interval W2. The pitch between adjacent structural birefringent portions (W1 + W2 in FIG. 1) is larger than the wavelength of incident light.

  The unevenness in the structural birefringent portion 111 extends in a direction perpendicular to the paper surface of FIG. 1A as a plurality of parallel grooves. That is, the structural birefringent portion 111 has a structure in which a plurality of rectangular concave grooves that are long in the direction perpendicular to the paper surface are formed and the directionality is anisotropic. In this example, air is located in the concave / convex concave portion, but the concave portion may be filled with a substance or medium having a refractive index different from that of the polarizing diffraction body 11.

  A refractive index adjustment unit 113 is provided between the structural birefringence units 111. The refractive index adjusting unit 113 has a refractive index different from the refractive index of the medium constituting the structural birefringent unit 111, that is, the resin serving as the convex medium of the structural birefringent unit and the air located in the concaved portion. The refractive index adjusting unit 113 is formed of a thermosetting polymer resin, a photocurable polymer resin such as a UV curable resin, or the like.

  The refractive index of the structural birefringent portion 111 is n2 for TM polarized light and n1 for TE polarized light (n1 and n2 are not equal). Further, the refractive index of the refractive index adjusting unit 113 is n1 which is the same as the refractive index of the structural birefringent unit 111 with respect to the TE polarized light. In addition, it is also possible to easily adjust the diffraction efficiency for each order diffracted light with respect to each polarized light by changing the refractive index by changing the material used in the refractive index adjusting unit 113.

  The quarter wave plate 12 converts the linearly polarized light that has passed through the polarization diffractor from the light source to circularly polarized light and irradiates the optical recording medium 2, or converts the circularly polarized light reflected by the optical recording medium 2 into linearly polarized light. And has a function of making it incident on the polarization diffractive body 11. Note that a 5/4 wavelength plate may be provided instead of the 1/4 wavelength plate 12.

  Next, the behavior of light will be described with reference to FIGS. In this example, since the light from the light source is laser light, it is already linearly polarized light. The position is adjusted so that the linearly polarized light becomes TE polarized light. As shown in FIG. 1B, when the TE polarized light L1 is incident on the polarization diffractive body 11, the structural birefringence unit 111 has the same refractive index n1 as that of the refractive index adjustment unit 113. For this reason, the TE polarized light L1 passes through as it is and enters the quarter-wave plate 12. Therefore, the polarization diffractive body 11 in this state has high zero-order transmission efficiency. The TE polarized light L1 incident on the quarter-wave plate 12 is converted into circularly polarized light L2 and emitted to the optical recording medium 2.

  The reflected light L3 reflected from the optical recording medium 2 is circularly polarized light. The reflected light L3 is incident on the quarter wavelength plate 12 again. As shown in FIG. 1C, the reflected light L <b> 3 is converted into TM polarized light L <b> 4 that is linearly polarized light in the quarter wavelength plate 12 and is incident on the polarization diffracting body 11.

  Since the structural birefringence part 111 of the polarization diffractive body 11 has a refractive index different from that of the refractive index adjustment part 113 for the TM polarized light L4, it functions as a diffraction grating.

  Next, an example of a method for manufacturing the polarization diffraction element according to the first embodiment of the present invention will be described with reference to FIGS. First, a patterning process is performed (S101). In this patterning step, first, a resist is applied to the silicon substrate, and pattern exposure is performed by a KrF stepper device. Next, an etching process is performed (S102). In this example, etching is performed by D-RIE (Deep Reactive Ion Etching). Thereafter, a conductive film is formed on the resist by sputtering or the like, and then a die, that is, a plating stamper is formed by electrolytic plating (S103). The stamper is a so-called inversion type, and a shape for forming the polarization diffractive body 11 is formed on one surface thereof. In a preferred embodiment, one stamper is formed with a shape corresponding to the plurality of polarization diffraction bodies 11. The stamper is made of, for example, Ni, Cu, or Au.

  Resin molding is performed using the stamper thus manufactured (S104). At this time, the resin may be processed into a predetermined shape by the 2P method or nanoprinting. FIG. 3A shows a cross-sectional view of the polarization diffractive body 11 formed by resin molding. On the upper surface of the polarization diffractive body 11 at this stage, concaves and convexes to be the structural birefringent part 111 and concave parts in which the refractive index adjusting part 113 is formed are formed, but nothing is filled therein.

  Next, resin coating is performed (S105). FIG. 3B shows a state after the resin is applied. In this example, a UV curable resin 115 is applied as a resin. Then, an exposure / development process is performed (S106). The exposure is performed by irradiating with ultraviolet light in a state where the structural birefringent portion 111 is shielded from light and the mask for exposing the refractive index adjusting portion 113 is disposed (FIG. 3C). Thereby, the UV curable resin 115 in the refractive index adjusting unit 113 is cured, and further, the uncured UV curable resin 115 filled in the concave portion of the structural birefringent unit 111 is removed by development.

  Then, it isolate | separates into the several polarization | polarized-light diffraction body 11 by a dicing process (S107).

  As described above, since the polarization diffraction element according to the first embodiment of the present invention is formed without using an expensive birefringent material such as liquid crystal, it can be manufactured at a very low cost.

Other embodiments.
In the above example, the quarter-wave plate is used. However, the present invention is not limited to this, and a concave and convex fine groove having a pitch smaller than the wavelength of light passing through the surface on the optical recording medium side of the diffraction grating element is provided. You may make it achieve a function.

  The polarization diffraction element according to this example has the structure shown in FIG. The polarization diffractive body 11 was manufactured using an acrylic resin for optical waveguide, which is an ultraviolet curable resin manufactured by NTT-AT having a refractive index of 1.60. The refractive index adjusting unit 113 is made of a fluorine-based resin (Opstar manufactured by JSR Corporation), which is an ultraviolet curable resin having a refractive index of 1.38. Since the concave portion 112 of the structural birefringent portion 111 is not filled with anything, the refractive index is 1 for air.

  The width of the concave portion 112 of the structural birefringent portion 111 is 195 nm, the depth of the concave portion 112 and the depth of the refractive index adjusting portion 113 are 2794 nm. The uneven pitch W3 in the structural birefringent portion 111 is 390 nm, which is shorter than the wavelength 780 nm of incident light and has a half length. The width of the convex portion of the structural birefringent portion 111 is 195 nm. In this case, the refractive index of the structural birefringent portion 111 is 1.38 for TE polarized light and 1.24 for TM polarized light.

  In such a configuration, diffraction does not occur with respect to TE polarized light, and almost all light can be diffracted with respect to TM polarized light. According to the result calculated using the scalar diffraction theory using the thin film approximation, the 0th-order diffracted light that is transmitted without being diffracted is 99% or more for TE polarized light and 0 for TM polarized light. It was derived to have a diffraction efficiency of less than 1%. Further, regarding the + 1st order diffracted light, it was derived that it has a diffraction efficiency of less than 0.1% for TE polarized light and about 40% for TM polarized light.

It is sectional drawing of the polarization | polarized-light diffraction element concerning this invention. It is a flowchart which shows the manufacture flow of the polarization | polarized-light diffraction element concerning this invention. It is sectional drawing which shows the manufacture flow of the polarization | polarized-light diffraction element concerning this invention. It is sectional drawing of the conventional polarization | polarized-light diffraction element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Polarization diffraction element 2 Optical recording medium 11 Polarization diffractive body 12 1/4 wavelength plate 41 Filling resin 42 White plate glass 111 Structural birefringence part 112 Recession 113 Refractive index adjustment part 115 Curable resin 411 Birefringence material

Claims (8)

There are a plurality of structural birefringent portions having different refractive indexes depending on the vibration direction of polarized light having irregularities with a pitch of λ or less of incident polarized light, and the structural birefringent portions are provided apart from each other and adjacent structures A polarization diffraction element in which the pitch between the characteristic birefringence portions is larger than the wavelength λ,
Between the structural birefringent part and the adjacent structural birefringent part is defined as a refractive index adjusting part, and the refractive index adjusting part has a refractive index different from that of the medium constituting the structural birefringent part. A polarization diffraction element characterized by having.   2. The polarization diffraction element according to claim 1, wherein a refractive index of the refractive index adjusting unit is higher than a minimum refractive index of a medium constituting the structural birefringent unit.   The refractive index of the refractive index adjusting part is substantially the same as the refractive index of the structural birefringent part for polarized light in either the parallel or vertical direction with respect to the fine groove provided in the structural birefringent part. The polarization diffraction element according to claim 1 or 2.   The refractive index of the refractive index adjusting unit is different from the refractive index of the structural birefringent unit with respect to polarized light in parallel or perpendicular direction with respect to the fine groove provided in the structural birefringent unit. Item 3. The polarization diffraction element according to Item 1 or 2.   The polarization diffraction element according to claim 1, wherein the refractive index adjusting unit is formed of a resin.   The polarizing diffraction element according to claim 5, wherein the refractive index adjusting unit is made of a photocurable resin.   The polarization diffraction element according to any one of claims 1 to 6, wherein the polarization diffraction element further includes a quarter or 5/4 wavelength plate.   An optical head device comprising the polarization diffraction element according to claim 1.

Images