JP2006134504A - Polarized beam splitting element and its manufacturing method, optical head unit, and optical disk drive - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a polarized beam splitting element which can obtain a large diffraction angle even for short-wavelength light, has large diffraction efficiency and superior polarized beam selectivity, has good temperature characteristics of diffraction efficiency and small incidence angle dependency, and also has high efficiency against divergent light and temperature variation. <P>SOLUTION: The polarized beam splitting element 1 which has a cyclic structure comprising an optical anisotropic (birefringent) area 4 and an optical isotropic area 5 and is a refractive index modulation type to diffract incident light is characterized in that f(d)≤¾Δn<SB>H</SB>¾≤1.3×f(d) and f(d)=(λ/d)√(-cos2ϕ), where (d) is the film thickness of the cyclic structure, ϕ is the tilt of a grating in the element, and Δn<SB>H</SB>is a refractive index modulation quantity generated with the refractive index of the optical anisotropic (birefringent) area 4 to incident light having a specified polarizing direction and the refractive index of the optical istropic area 5. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a polarization separation element having a function of transmitting or diffracting an element depending on the polarization direction of incident light, and in particular, a polarization-selective polarization separation element (polarization diffraction element, polarization hologram) used in an optical head device (optical pickup device) or the like. And an optical head device using the polarization splitting device, and an optical disk drive device mounted with the optical head device.

Conventionally, as a polarization-selective polarization separation element (polarization diffraction element, polarization hologram element, etc.) used for an optical head device (sometimes referred to as an optical pickup device), there are the following conventional techniques.
(1) In Patent Document 1 (Japanese Patent No. 3299384 (Japanese Patent Laid-Open No. 7-287117)), a diffraction grating shape is formed on an optically anisotropic substrate, and a refractive index is defined in a groove portion of this diffraction grating shape. A polarizing beam splitter filled with the prepared material is disclosed.
(2) In Patent Document 2 (Japanese Patent No. 550905 (Japanese Patent Laid-Open No. 10-92004)), a diffraction grating shape is formed on an isotropic substrate, and an optical anisotropy is formed in the groove of the diffraction grating shape. An optically anisotropic diffraction element filled with a material is disclosed.
(3) Patent Document 3 (Japanese Patent Laid-Open No. 10-74333) uses a liquid crystal cell in which a photopolymerizable liquid crystal is sandwiched by a translucent substrate having a periodic transparent electrode pattern, and a voltage is applied to the transparent electrode pattern. The liquid crystal is periodically vertically aligned to apply photopolymerization, and the non-voltage application unit is photopolymerized in a horizontal alignment state, thereby forming an optical structure having a periodic structure of horizontal alignment regions and vertical alignment regions. An isotropic diffractive element is disclosed.
(4) In Patent Document 4 (Japanese Patent Application Laid-Open No. 11-271536), the photopolymerizable liquid crystal as described above is used, and exposure is performed by a method such as interference exposure in a horizontally aligned state. There is disclosed a hologram element that is periodically solidified by polymerization and then solidified by reaction in a state in which an external field is applied to an unexposed portion and vertically aligned.
(5) In Patent Document 5 (Japanese Patent Application Laid-Open No. 2000-221465), two-beam interference exposure is performed by controlling an optical medium including liquid crystal and polymer within a specific temperature range corresponding to the NI point of the liquid crystal. Thus, a diffractive optical element having a structure in which liquid crystal is aligned in a uniform direction with respect to a fine periodic structure is disclosed.
(6) In Patent Document 6 (Japanese Patent Laid-Open No. 2003-270419), the element temperature at which the diffraction efficiency takes a minimum value is in the range of 25 ° C. to 70 ° C., and the element has a refractive index anisotropy and a refractive index. A diffractive optical element having a structure in which regions having different temperature dependencies are alternately arranged is disclosed.

Japanese Patent No. 3299384 (Japanese Patent Laid-Open No. 7-287117) Japanese Patent No. 550905 (JP-A-10-92004) JP 10-74333 A Japanese Patent Laid-Open No. 11-271536 JP 2000-212465 A JP 2003-270419 A BellSyst. Tech. J., 48, 1969, P2909-2947

  In recent years, in order to reduce the size of an optical head device (optical pickup device) mounted on an optical disk drive device or the like, a laser diode (LD) as a light source and a photodetector (photodetector) are arranged close to each other to separate the polarization. Light emitted from the light source using an element (for example, a polarization selective hologram element) is efficiently condensed on the disk surface without being diffracted, and is reflected by the disk surface and then returned after the polarization plane has been rotated 90 degrees. A method has been proposed in which only the light is diffracted and efficiently guided into the light receiving element of the photodetector. In addition, in the optical disk drive device, the wavelength of the light source has been shortened to increase the density. When the hologram element described above is used, the diffraction angle depends on the wavelength. Therefore, in order to obtain a diffraction angle necessary for realizing a small layout, a diffraction grating having a shorter pitch is required. On the other hand, as the wavelength of the light source is shortened, the sensitivity of the light receiving element of the photodetector is lowered, so that the efficiency of the optical system must be increased. In addition, there is a need to improve the efficiency of the optical system in order to improve the writing and reading speed, and it is important to maintain the high efficiency of the characteristics of such an optical system even when the temperature in the device and the surrounding environment change. It is said that. That is, there is a demand for a polarization selective hologram element that has a high diffraction efficiency, a good polarization selectivity, and a low temperature dependency at a short pitch.

  On the other hand, in the conventional examples described in Patent Document 1 and Patent Document 2, it is necessary to form a diffraction grating shape by a method such as dry etching. In such a structure, in order to obtain high diffraction efficiency, it is necessary to increase the depth of the groove shape, which is accompanied by processing difficulties. There is also a problem that it is difficult to uniformly fill the deep groove shape with the material. In the conventional example described in Patent Document 3, the pitch of the grating is determined by the pitch of the transparent electrode. However, along with restrictions on miniaturization of the electrode, if the film is thickened to increase the diffraction efficiency, the film thickness becomes thicker than the pitch of the electrode. Therefore, there is a problem that a desired electric field cannot be applied to the liquid crystal layer due to the influence of the adjacent electrode. Further, when the pitch is short, there is a problem that the alignment of the vertical alignment region affects the adjacent horizontal alignment region, and a desired alignment distribution cannot be obtained. Further, in the conventional example described in Patent Document 4, it is possible to reduce the exposure pitch, but there is a problem that it is difficult to form a short pitch as exposed due to thermal diffusion of the reactive species. is there. Furthermore, in the conventional example described in Patent Document 5, a periodic structure with a short pitch can be formed relatively easily by utilizing the phase separation between the polymer and the liquid crystal, but it is difficult to fully utilize the birefringence of the liquid crystal phase portion. It is difficult to obtain good polarization selectivity and good transmittance at a short wavelength.

  Next, regarding the temperature dependence, in the conventional examples described in Patent Documents 1, 3, and 4, since a polymer film or a photocurable liquid crystal is used as the optical anisotropy region of the lattice, the element characteristics are relatively Although the temperature dependency is small, as described above, the birefringence is small and there is a problem of increasing the film thickness. On the other hand, in the conventional examples described in Patent Document 2 and Patent Document 5 having relatively large birefringence, the temperature dependence is large because non-curable liquid crystal is used, and the temperature change of the optical pickup device or the projector is large. When incorporated in an apparatus, it is difficult to maintain high diffraction efficiency depending on the use conditions. Therefore, as in the conventional example described in Patent Document 6, it has been proposed to form a lattice region having different temperature dependence by using materials having different temperature dependence and to reduce the temperature dependence as the element characteristics. However, in the lattice area with a short pitch inside the element, the temperature dependence of the selected material alone may be slightly different and it is difficult to achieve matching. In addition, it is difficult to realize a material selection that achieves both birefringence and temperature dependency because there are many restrictions.

  The present invention has been made in view of the above circumstances, and can obtain a large diffraction angle even in short-wavelength light such as blue, has a large diffraction efficiency and excellent polarization selectivity, has a good temperature characteristic of the diffraction efficiency, and is incident. An object of the present invention is to provide a polarization separation element (polarization selective hologram element) that has a small angle dependency and is highly efficient against diverging light and temperature changes. Moreover, an object of this invention is to provide the manufacturing method of the polarization splitting element. Another object of the present invention is to provide a small optical head device (optical pickup device) for an optical disk (or a magneto-optical disk) using the polarization separation element. A further object of the present invention is to provide an optical disk drive device equipped with the optical head device.

In order to achieve the above object, the present invention employs the following technical means.
The first means of the present invention has a periodic structure (hereinafter referred to as a periodic structure) composed of a region exhibiting optical anisotropy or birefringence and a region exhibiting optical isotropy, and incident light. In the refractive index modulation type polarization separation element that diffracts λ, the incident wavelength is λ, the film thickness of the periodic structure is d, the inclination of the grating inside the element is φ (where φ is a vector perpendicular to the grating periodic structure, The optical anisotropy or birefringence with respect to incident light in a specific polarization direction is shown when the periodic structure arrangement surface is set as a reference (0 °) and 45 ° <φ <135 °. The refractive index modulation amount Δn _H generated by the refractive index of the region and the refractive index of the region exhibiting optical isotropy is expressed as follows:
f (d) ≦ | Δn _H | ≦ 1.3 · f (d)
f (d) = (λ / d) √ (−cos2φ)
(Claim 1).

According to a second means of the present invention, in the polarization separation element of the first means, the region showing the optical anisotropy or birefringence with respect to incident light in a polarization direction orthogonal to the specific polarization direction, and the optical The refractive index modulation amount Δn _H generated by the isotropic region is
| Δn _H | ≦ 0.065 · f (d)
(Claim 2).

According to a third means of the present invention, in the polarization separation element of the first or second means, at least one region of the optical anisotropy or birefringence region and the optically isotropic region is provided. And a non-polymerizable liquid crystal or a polymerizable liquid crystal.
According to a fourth means of the present invention, in the polarization separation element of any one of the first to third means, the specific polarization direction has the region exhibiting the optical anisotropy or birefringence, and the It is orthogonal to the boundary of the optically isotropic region (claim 4).

  A fifth means of the present invention is a method of manufacturing a polarization separation element for producing the polarization separation element according to any one of the first to fourth means, comprising a non-polymerizable liquid crystal, a polymerizable monomer or a prepolymer, A layer mainly composed of a polymer by injecting a composition comprising a photopolymerization initiator between a pair of transparent substrates, the distance between which is controlled by a spacer member, and two-beam interference exposure of the composition. And a step of forming a periodic phase separation structure with a layer mainly composed of non-polymerizable liquid crystal (claim 5).

According to a sixth means of the present invention, in the method for producing a polarized light separating element according to the fifth means, the non-polymerizable liquid crystal material in the composition is based on the total amount of the polymerizable monomer or prepolymer: 100 parts by weight. And used at a ratio of 15 parts by weight to 500 parts by weight (claim 6).
The seventh means of the present invention is characterized in that, in the method for producing a polarization separation element of the fifth or sixth means, the polymerizable monomer or prepolymer is one having a large curing shrinkage due to polymerization. (Claim 7).
Further, according to an eighth means of the present invention, in the method for manufacturing a polarization separation element according to any one of the fifth to seventh means, the amount of the photopolymerization initiator added is the total amount of the polymerizable monomer or prepolymer. On the other hand, it is 0.1 to 10% by weight (claim 8).

According to a ninth means of the present invention, in the method for manufacturing a polarization separating element according to any one of the fifth to eighth means, the film thickness of the composition is set to a height of a spacer member interposed between the pair of substrates. The height of the spacer member is set so that the film thickness of the composition becomes a predetermined thickness according to the wavelength of diffracted light and the refractive index difference between the polymer part and the liquid crystal part of the periodic structure. (Claim 9).
According to a tenth means of the present invention, in the method for manufacturing a polarization separation element according to any one of the fifth to ninth means, the substrate holding the composition in the two-beam interference exposure and the phase separation process. Is kept heated to a temperature in the range of 40 ° C. to 100 ° C. (Claim 10).

The eleventh means of the present invention is the method of manufacturing a polarization beam splitting element according to any one of the fifth to tenth means, wherein the wavelength of the light source used for the two-beam interference exposure is a short wavelength (for example, 514 nm or less). (Claim 11).
According to a twelfth means of the present invention, in the method of manufacturing a polarization separation element according to any one of the fifth to eleventh means, the exposure amount during the ^two- beam interference exposure is 0.5 J / cm ^{2 to} 30 J. It is set in the range of / cm ² (claim 12).

The thirteenth means of the present invention is an optical head for condensing light from a light source on a recording medium and detecting reflected light from the recording medium with a photodetector to record or reproduce information, or record and reproduce information. In the apparatus, an optical element that deflects reflected light from the recording medium toward the photodetector is provided in an optical path from the recording medium to the photodetector, and the optical element is any one of the first to fourth optical elements. It is a polarization separation element according to one means (claim 13).
According to a fourteenth means of the present invention, in the optical head device of the thirteenth means, the light source and the photodetector are housed in one case, and the polarization separation element is provided at the light output / incident part of the case. Are integrated (claim 14).

  According to a fifteenth means of the present invention, in an optical disc drive apparatus for recording or reproducing information or recording and reproducing information on a recording medium using an optical head device, the thirteenth or fourteenth means is used as the optical head device. This optical head device is mounted (claim 15).

In the polarization separation element of the first means, the range of change of the refractive index modulation amount in the allowable diffraction efficiency can be widened by setting the refractive index modulation amount Δn _H to the range of the above equation. Therefore, a change in the refractive index modulation amount due to temperature, that is, a decrease in diffraction efficiency due to temperature can be suppressed, and a polarization separation element with good temperature characteristics of diffraction efficiency can be obtained.

In the polarization separation element of the second means, by setting the refractive index modulation amount Δn _H of the polarization separation element in the range of the above formula for the incident light in the polarization direction orthogonal to the specific polarization direction, The resulting diffraction efficiency is 1% or less. Therefore, good polarization selectivity can be obtained.
Further, the polarization separation element of the third means includes a liquid crystal generally used for a display device or the like in a region showing optical anisotropy or birefringence or a region showing optical isotropy. Therefore, in terms of manufacturing, mass production is good at low cost. Further, since the optical anisotropy (or birefringence) of the liquid crystal is large, the diffraction efficiency can be improved relatively easily.
Furthermore, in the polarization separation element of the fourth means, the specific polarization direction is orthogonal to the boundary between the optically anisotropic (or birefringent) region and the optically isotropic region, The birefringence of the polarization separation element can be utilized to the maximum. Therefore, by optimizing the film thickness and the refractive index modulation amount, a polarization separation element with high diffraction efficiency and good polarization selectivity can be obtained.

  According to the manufacturing methods of the fifth to twelfth means of the present invention, it is possible to produce a polarization separation element having high diffraction efficiency and good polarization selectivity of the first to fourth means.

According to the thirteenth means of the present invention, as an optical element for deflecting the reflected light from the recording medium toward the photodetector, the polarization selectivity is high with high diffraction efficiency by any one of the first to sixth means. Since a good polarization separation element is used, the light emitted from the light source concentrates on the recording medium efficiently without being diffracted, and has a large diffraction efficiency on the return path of the reflected light from the recording medium (the polarization plane is rotated by 90 °). Can diffract the information into a photodetector. Therefore, it is possible to realize a small-sized optical head device with high light utilization efficiency.
According to the fourteenth means of the present invention, the light source and the photodetector are housed in one case, and the polarization separating element is integrated with the light output / incident part of the case. An optical head device that can be easily attached and adjusted can be realized.

  According to the fifteenth means of the present invention, since the optical head device having the small and high light utilization efficiency of the thirteenth or fourteenth means is mounted, a compact optical disk drive device with high light utilization efficiency is realized. be able to.

Hereinafter, the configuration, operation, and action of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram showing an outline of a cross-sectional configuration of a polarization beam splitting element according to the present invention. This polarization separation element 1 has a periodic structure (periodic structure) composed of a region 4 exhibiting optical anisotropy (birefringence) and a region 5 exhibiting optical isotropy. By mainly holding a composition comprising a non-polymerizable liquid crystal, a polymerizable monomer or prepolymer, and a photopolymerization initiator between a pair of transparent substrates 2 and 3 and subjecting the composition to two-beam interference exposure, Polymer in which a periodic phase separation structure of a layer (optically isotropic region) 5 made of a polymer and a layer (optically anisotropic (birefringent) region) 4 mainly made of a non-polymerizable liquid crystal is formed It is a dispersion liquid crystal type polarization separation element. As a functional operation of the polarization separation element 1, for example, as shown in FIG. 2 (a), the polarization direction incident on the polarization separation element 1 is S-polarized light (here, the lattice ridge direction which is the direction perpendicular to the paper surface). When the refractive index n of the optically isotropic region 5 and one refractive index no of the optically anisotropic (birefringent) region 4 are n = no, the light is transmitted as it is. Further, as shown in FIG. 2B, the incident polarization direction is P-polarized light (here, the grating array direction which is the left-right direction on the paper surface), and the refractive index n of the optically isotropic region 5 and the optical When the other refractive index ne of the anisotropic (birefringent) region 4 is n ≠ ne, the light is diffracted. In this manner, transmission and diffraction are selected depending on the polarization direction of incident light.

Here, there are generally various types of polarization separation elements (polarization diffraction elements) using diffraction, for example, amplitude modulation type and phase modulation type elements. The phase modulation type is superior in terms of diffraction efficiency, and the phase modulation type includes a surface relief type and a refractive index modulation type. Polarization diffraction elements are classified into thick and thin elements, and are generally defined by the following equations.
Q = (2πλd) / (nΛ ² )
(Where λ: wavelength, d: thickness, n: refractive index of recording material, Λ: pitch of periodic structure)
(1) Thin → Q ≒ 0
(2) Thick → Q >> 1

Here, for example, the diffraction efficiency of a polarization diffraction element whose period is sufficiently large and thin compared to the wavelength can be applied to the Fraunhofer diffraction theory and the scalar diffraction theory. The vector diffraction theory that is analysis can be applied. Further, the diffraction efficiency of a refractive index modulation element (thick hologram) that can be regarded as being thick can be adapted to Kogelnik's coupled wave theory (see Non-Patent Document 1 (BellSyst. Tech. J., 48, 1969, P2909-2947)). This is because when light of a certain wavelength is incident on each region forming a periodic structure, the light scattered in each region has a stronger scattering component in a specific direction corresponding to the wavelength, the incident angle, and the periodic structure pitch of each region. It meets the diffraction conditions of the matching black. Here, the polarization separation element 1 having the configuration shown in FIG. 1 corresponds to this refractive index modulation type. Generally the diffraction efficiency depends on the refractive index modulation [Delta] n _H and the thickness d of a hologram, the refractive index modulation [Delta] n _H _max the diffraction efficiency is maximized (100%) is expressed by the following equation.
f (d) = Δn _H _max = (λ / d) √ (−cos 2φ)

That is, when the refractive index modulation amount Δn _{H of the} region 4 exhibiting optical anisotropy in a specific polarization direction and the region 5 exhibiting optical isotropy is constant, the thickness d ( Hereinafter, a high diffraction efficiency can be set by setting (sometimes referred to as a film thickness). Here, φ is a vector perpendicular to the lattice periodic structure as shown in FIG. 1, and is in a relationship of 45 ° <φ <135 ° with the periodic structure arrangement surface as a reference (0 °). In general, the refractive index of a substance existing in a birefringent region or an isotropic region has temperature dependence, and it is difficult to always maintain a constant refractive index. This change in refractive index due to temperature greatly affects the characteristics of the functional operation described above, leading to fluctuations in diffraction efficiency and a decrease in polarization selectivity, which is a serious problem in practice. The polarization selectivity is defined as S-polarization diffraction efficiency / P-polarization diffraction efficiency.

FIG. 3 shows the relationship between the refractive index modulation amount Δn _H and the diffraction efficiency of the refractive index modulation type polarization beam splitter. The refractive index modulation amount Δn _H shown here is the difference in the refractive index distribution inside the polarization splitting element shown in FIG. 1, but for the sake of brevity, Δn _H is | no−n | or | ne. Equivalent to −n | FIG. 4 shows the temperature dependence of the general refractive index of the isotropic region n and the birefringent regions no and ne. As the temperature rises as shown in FIG. 4, the absolute values of the refractive indices n, no, ne change, and | no-n | and | ne-n | change relatively. As described above, along with the change in the refractive index due to the temperature rise, the diffraction efficiency of the polarization separation element varies greatly depending on the temperature. That is, when the maximum diffraction efficiency is set, Δn _H decreases with increasing temperature and the diffraction efficiency tends to decrease (arrow in FIG. 3). Here, in order to generally obtain high diffraction efficiency, Δn _H must be large to some extent. Therefore, when obtaining high diffraction efficiency, it is preferable to set | ne−n | as Δn _H.

To show the refractive index modulation [Delta] n _H in FIG. 3 the relation of the diffraction efficiency in detail, to those normalized modified refractive index modulation [Delta] n _H _max that any refractive index modulation [Delta] n _H is the maximum diffraction efficiency is obtained The relationship of diffraction efficiency is shown in FIG. Here, conventionally, for example, in an element that ideally obtains a maximum efficiency of 100%, when the allowable diffraction efficiency is 80% or more, the amount of change in Δn _H / Δn _{H —} max is 0.3 (FIG. 5). = | 1-0.7 |) is acceptable. On the other hand, in the present invention, the refractive index modulation amount Δn _H is expressed by the following equation:
f (d) ≦ | Δn _H | ≦ 1.3 · f (d)
f (d) = (λ / d) √ (−cos2φ)
Therefore, the change amount of Δn _H / Δn _H — max can accept a change of 0.6 (= | 1.3−0.7 |), and the change amount of Δn _H is the maximum. A range twice that of the prior art can be tolerated. That is, since the variation range of Δn _H with temperature can be widened, a polarization separation element with good temperature characteristics of diffraction efficiency can be obtained.

Furthermore, as described above, the refractive index modulation amount that realizes good temperature characteristics with high diffraction efficiency is for a specific polarization direction, and the refractive index modulation amount Δn _H in the polarization direction orthogonal to the polarization direction is ,
| Δn _H | ≦ 0.065 · f (d)
By setting in this range, the diffraction efficiency becomes 1% or less as shown in FIG. The relationship between the refractive index modulation amount and the diffraction efficiency in FIG. 6 is the same as described above. Therefore, high diffraction efficiency can be obtained in a specific polarization direction, and very low diffraction efficiency can be obtained in a polarization direction orthogonal to the specific polarization direction, so that good polarization selectivity can be obtained.

  Here, a method for producing the polarization separation element of the present invention will be described in detail. FIG. 7 shows an outline of a cross-sectional configuration of the element before phase separation. Here, in order to increase the birefringence, the non-polymerizable liquid crystal molecule 6 and the polymerizable monomer (in order to include liquid crystal in at least one of the region exhibiting optical anisotropy and the region exhibiting optical isotropy) Alternatively, a composition 8 in which a prepolymer) 7 and a photopolymerization initiator (not shown) are uniformly mixed is sandwiched between two transparent substrates 2 and 3. The thickness of the composition 8 can be controlled by a spacer member (not shown) for controlling the substrate interval. In addition, since this composition 8 has photosensitivity, it is preferable to handle it in an environment where light in a wavelength region having sensitivity is blocked in the device manufacturing process.

  As the non-polymerizable liquid crystal 6, a general liquid crystal having refractive index anisotropy can be used. When selecting a liquid crystal material, it is possible to select a liquid crystal material having a refractive index substantially equal to the refractive index of the cured layer of the polymerizable monomer or prepolymer in an orientation state of a certain order parameter. Then, the polymerizable monomer or the prepolymer may be selected so that the refractive index of the liquid crystal is almost equal to the refractive index in an orientation state with a certain order parameter. The composition of the non-polymerizable liquid crystal may be any of nematic, cholesteric, and smectic types, and conventionally known biphenyl, terphenyl, phenylcyclohexane, biphenylcyclohexane, benzoic acid phenyl ester, cyclohexanecarboxylic acid phenyl ester, phenylpyrimidine, phenyl Dioxane, Tran, 1-phenyl-2-cyclohexylethane, 1-phenyl-2-biphenylethane, 1-cyclohexyl-2-biphenylethane, biphenylcarboxylic acid phenyl ester, 4-cyclohexylbenzoic acid phenyl ester, etc. A liquid crystal having a cyano group, a halogen group, or the like as a substituent, such as a group, an alkoxy group, or a polar group for imparting dielectric anisotropy can be used. The non-polymerizable liquid crystal material is preferably used in a proportion of 15 parts by weight to 500 parts by weight with respect to 100 parts by weight of the total amount of polymerizable monomers or prepolymers.

  As the polymerizable monomer (or its prepolymer) 7, it is preferable to use a monomer that has a large cure shrinkage due to polymerization. As such a polymerizable monomer, a photopolymerizable compound having an ethylenically unsaturated bond, a photopolymerization having at least one ethylenically unsaturated double bond in one molecule, a photocrosslinkable monomer, Examples of monomers and copolymers thereof include unsaturated carboxylic acids and salts thereof, esters of unsaturated carboxylic acids and aliphatic polyhydric alcohol compounds, unsaturated carboxylic acids and Examples thereof include amides with aliphatic polyvalent amine compounds. Particularly, bifunctional or higher polyfunctional monomers have large curing shrinkage and can be suitably used. Examples of unsaturated carboxylic acid monomers include acrylic acid, methacrylic acid, itaconic acid, crotonic acid, isocrotonic acid, maleic acid, and halogen-substituted unsaturated carboxylic acids such as chlorinated unsaturated carboxylic acids and brominated unsaturated carboxylic acids. And fluorinated unsaturated carboxylic acid. Examples of unsaturated carboxylic acid salts include sodium and potassium salts of the aforementioned acids. Moreover, polyfunctional acrylates and methacrylates such as urethane acrylates, polyester acrylates, epoxy resins and (meth) acrylic acid can be mentioned. In addition to the above, a thermal polymerization inhibitor, a plasticizer, and the like may be added.

  As the photopolymerization initiator, known materials can be used, for example, biacetyl, acetophenone, benzophenone, Michler ketone, benzyl, benzoin alkyl ether, benzyl dimethyl ketal, 1-hydroxy-2-methyl-1-phenylpropane-1- ON, 2-chlorothioxanthone, methylbenzoyl formate, 1- (4-isopropylphenyl) -2-hydroxy-2-methylpropan-1-one, diethoxyacetophenone, 1-hydroxycyclohexyl phenyl ketone, 2,2-dimethoxy Examples include -1,2-diphenylethane-1-one, α-aminoalkylphenone, bisacylphosphine oxide, and metallocene. The addition amount of the photopolymerization initiator varies depending on the absorbance of each material with respect to the wavelength of the irradiated light, but is preferably 0.1% by weight or more and 10% by weight or less based on the total amount of the monomer or prepolymer. More preferably, the content is 5% by weight or more and 3% by weight or less. When the amount of the photopolymerization initiator added is too small, phase separation between the polymer and the liquid crystal hardly occurs, and the necessary exposure time becomes long. On the other hand, if there are too many photopolymerization initiators, the polymer and liquid crystal are cured with insufficient phase separation, so that many liquid crystal molecules are taken into the polymer and the polarization selectivity is reduced. There is.

  As the spacer member, a spherical spacer, a fiber spacer, a film or the like used in a liquid crystal display device can be used. Further, the protrusion shape may be processed on the substrate surface by photolithography and etching or molding technique. The spacer member is preferably formed outside the effective area of the hologram. The height of the spacer member is preferably in the range of several μm to several tens of μm, and is appropriately set to have a desired periodic structure layer (hologram layer) thickness according to the wavelength of the diffracted light and the refractive index difference between the polymer part and the liquid crystal part. Is set. As the transparent substrates 2 and 3, glass, plastic, or the like used in a liquid crystal display device can be used.

  Next, a process of forming a periodic structure (hologram) by phase separation (periodic structure formation of an optically anisotropic region and an optically isotropic region) will be described with reference to FIG. Here, a composition 8 injected between a pair of substrates 2 and 3 as shown in FIG. 7 is subjected to two-beam interference exposure, whereby a layer mainly composed of a polymer and a layer mainly composed of a non-polymerizable liquid crystal are formed. The step of forming the periodic phase separation structure will be described. FIG. 9 shows a basic configuration of the two-beam interference exposure apparatus. This two-beam interference exposure apparatus includes an exposure laser apparatus (light source having coherence) 51, a spatial filter including an objective lens 52 and an aperture 53, a collimator lens 54, a half mirror 55, and mirrors 56a and 56b. 7 is a recording material made of the composition 8 injected between a pair of substrates 2 and 3 as shown in FIG. 7, and 58 is a temperature control stage for heating the recording material. The exposure laser device 51 uses a short wavelength light source such as krypton ion laser (oscillation wavelength 407 nm), helium cadmium laser (oscillation wavelength 442 nm), argon laser (oscillation wavelength 488 nm or 514 nm). Any light source may be used. When a laser that oscillates in a single longitudinal mode is used as the exposure laser device 51, a coherence length is increased, and a diffraction grating with less noise can be manufactured. A spatial filter including the objective lens 52 and the aperture 53 is not always necessary, but noise may be added to the laser beam by an optical element up to the half mirror 55, and is useful for improving the beam quality. . When the laser beam is divided into two by the half mirror 55, the beams are superposed at a predetermined angle by the mirrors 56a and 56b to generate interference fringes, and the recording material (exposed sample) 57 is arranged at the position where the interference fringes are generated. A diffraction grating corresponding to the interference fringe pitch can be produced. Here, the spatial filter (the objective lens 52 and the aperture 53) and the collimating lens 54 are disposed in front of the half mirror 55, but may be disposed after each of the mirrors 56a and 56b. Furthermore, by arranging a converging lens (not shown) after the collimating lens 54, interference exposure using convergent light becomes possible. When interference exposure using convergent light is used, the convergence position when reproducing can be set.

  In FIG. 8, when exposure is performed in the composition 8 as a recording material using a two-beam interference exposure apparatus with a laser light source having a desired wavelength configured as shown in FIG. 9, polymerization occurs in the bright part of the interference fringes. Photopolymerization reaction of the polymerizable monomer (or prepolymer) 7 starts. At this time, curing shrinkage occurs to cause a density difference, the adjacent polymerizable monomer (or prepolymer) 7 moves to the bright part, and further polymerization proceeds. At the same time, the non-polymerizable liquid crystal 6 present in the bright part is driven out toward the dark part to cause phase separation. At this time, it is considered that when the liquid crystal molecules move, a force to align the major axis of the liquid crystal molecules in the moving direction by the interaction with the monomer or polymer chain is considered to work. That is, it is considered that a force for orienting liquid crystal molecules in the direction of the interference fringe acts in the phase separation process. Finally, as shown in the lower diagram of FIG. 8, the polymer layer 7 (optical isotropic region 5) and the non-polymerizable liquid crystal layer 6 (optical anisotropy (compounds)) correspond to the bright and dark pitches of the interference fringes. It is considered that a state in which the periodic structure of the (refractive) region 4) is formed and the orientation vector of the liquid crystal layer portion is oriented in the interval direction of the interference fringes is obtained. In this interference exposure and phase separation process, it is preferable to keep the sample heated to an appropriate temperature. It is considered that the phase separation speed changes depending on the temperature and affects the orientation of the liquid crystal molecules. The optimum heating temperature varies depending on the material used, but is preferably about 40 ° C to 100 ° C.

  In the periodic structure of the polymer layer 7 (optically isotropic region 5) and the nonpolymerizable liquid crystal layer 6 (optically anisotropic (birefringent) region 4) by phase separation, strictly speaking, the polymer and the nonpolymerizable liquid crystal However, it is difficult to completely separate periodically, and the polymer layer referred to here is a region having a large amount of polymer components and may contain liquid crystal molecules. The non-polymerizable liquid crystal layer is a region having a large amount of non-polymerizable liquid crystal components and may contain a polymer component. Actually, the interface between the polymer layer and the liquid crystal layer is assumed to be uneven rather than an ideal plane, so the variation in the major axis direction of the liquid crystal molecules at the interface is large as shown in FIG. Order parameters are relatively small. Accordingly, the birefringence of the liquid crystal layer is relatively smaller than the birefringence of the material alone.

The pitch of the periodic structure to be produced varies depending on the desired diffraction angle and wavelength, but is generally in the range of 0.2 μm to 10 μm. For example, in order to obtain a diffraction angle of 20 ° with respect to incident light with a wavelength of 405 nm, a pitch of approximately 1.1 μm is required, and with respect to incident light with a wavelength of 650 nm, a pitch of approximately 2.3 μm is required. The inclination angle of the boundary surface between the polymer layer and the liquid crystal layer is preferably about 0 ° to ± 20 °, with 0 ° when the boundary surface is perpendicular to the substrate surface. The exposure amount at the time of two-beam interference exposure varies depending on the addition concentration of the photopolymerization initiator and the temperature at the time of exposure, but is preferably 0.5 J / cm ² to 30 J / cm ² , and 1 J / cm ² to 15 J / cm ^2. Is more preferable. Here, the explanation is based on the two-beam interference exposure system that can realize a narrower pitch. However, if the desired pitch can be realized, the phase separation process is promoted in stepper exposure, mask exposure, etc., and a polarization separation element is manufactured. May be.

  As described above, the liquid crystal material included in the periodic structure of the optically anisotropic region and the optically isotropic region of the polarization separation element is widely used for display devices and the like. Further, since the birefringence (refractive index anisotropy) when used as a polarization separation element is larger than that of a conventional stretched polymer film, there is an advantage that the diffraction efficiency can be improved relatively easily. Further, the magnitude of the birefringence of the polarization separation element can be set to some extent under exposure conditions such as temperature and exposure amount. Although the non-polymerizable liquid crystal has been described above, the same effect can be obtained to some extent even when the polymerizable liquid crystal is used. When a polymerizable liquid crystal is used, birefringence is reduced, but reliability such as thermal stability is improved.

  Here, in the polarization separation element generated by the phase separation as described above, the polarization direction in the case of diffracting is an apparent liquid crystal in order to make the best use of the birefringence generated by the polymer or liquid crystal. It is preferable to be parallel to the orientation direction. As described above, the orientation vector of the liquid crystal is considered to be directed to the array direction of the periodic structure of the optically anisotropic region and the optically isotropic region, that is, the polarization direction of the incident light when diffracting is desired. Is preferably orthogonal to the boundary between the optically anisotropic region and the optically isotropic region. Thus, by setting the specific polarization direction incident on the element to be orthogonal to the boundary of the periodic structure, the polarization separation function as the element can be utilized to the maximum. Here, the periodic structure of the optically anisotropic region 4 and the optically isotropic region 5 of the polarization beam splitting element 1 shown in FIGS. 1 and 8 is illustrated as being substantially perpendicular to the substrate surface. Not limited to this, even if the boundary surface of the periodic structure of the optically anisotropic region 4 and the optically isotropic region 5 is inclined with respect to the substrate surface as shown in FIGS. The inclination angle can be set in the range of 0 ° to ± 20 °, where 0 ° is the case where the boundary surface is perpendicular to the substrate surface.

  As a method for forming the inclined region, it can be formed by gradation mask exposure, photolithography and etching by electron beam (EB) drawing, cutting processing, molding technique, two-beam interference exposure, or the like. When the inclined region is formed in this way, the diffracted light by the black diffraction is emitted only on one side of the plus direction or the minus direction according to the inclination direction of the periodic structure, and high efficiency can be achieved in one direction. In addition, by optimizing the refractive index modulation amount and the thickness of the periodic structure in the optically anisotropic region and the optically isotropic region with respect to the polarization direction to be diffracted, only positive or negative first-order diffracted light can be highly efficient. It is possible to set so that the second order or higher order diffracted light is almost zero.

  With respect to the polarization separation element according to the present invention described above, for example, a polarization separation element manufactured by two-beam interference exposure can easily form a short pitch of about 1 μm, and therefore an optical head device that requires a large diffraction angle for miniaturization. This is particularly effective when used in a polarization separation element for an (optical pickup device).

  FIG. 11 is a diagram showing a basic configuration example of an optical head device (optical pickup device) using the polarization separation element (polarization selective hologram element) of the present invention. 11, reference numeral 11 is a semiconductor laser (laser diode (LD)), 12 is a polarization separation element (polarization selective hologram element) having the structure described with reference to FIGS. 1 and 2 (or FIG. 10), and 13 is 1 / 4 wavelength plate, 14 is a collimator lens, 15 is an objective lens, 16 is an optical disk as a recording medium, and 17 is a light receiving element (for example, a photodiode) of a photodetector.

  In FIG. 11, the linearly polarized light that is the readout light emitted from the semiconductor laser 11 passes through the polarization separation element 12 and the quarter wavelength plate 13, and is converted into substantially parallel light by the collimator lens 14 and guided to the objective lens 15. The light is condensed on the recording layer of the optical disc 16. The plane of polarization of the light reflected by the optical disk 16 is rotated by 90 ° by the quarter-wave plate 13 placed in a common optical path for input and output. The polarization separation element 12 is placed in a common optical path for input and output near the semiconductor laser. The refractive index modulation amount of the region where the polarized light emitted from the semiconductor laser 11 exhibits optical anisotropy (birefringence) and the region where the polarization isolator 12 exhibits optical isotropy becomes 0 (ideally). If the direction is correct, the light is transmitted with almost no loss and condensed on the recording layer of the optical disc 16. Since the return light from the optical disc 16 is incident on the polarization separation element 12 with the polarization plane rotated by 90 °, the refractive index modulation amount in the region showing optical anisotropy and the region showing optical isotropy is not zero. By setting a film thickness at which an allowable diffraction efficiency is obtained for this refractive index modulation amount, a high diffraction efficiency can be achieved. At this time, if the separation angle of the polarization separation element 12 is 15 ° or more, the polarization separation element 12, the semiconductor laser 11 and the photodiode 17 can be brought close to each other, and the optical path length can be shortened. Here, when the separation angle is 20 ° and the wavelength is 405 nm, the pitch of a desired diffraction grating (hologram) is approximately 1 micron. Since the polarization separation element 12 of the present invention can be configured to have a very short grating interval as described above, high diffraction efficiency can be obtained even with such a short grating interval.

Next, FIG. 12 is a diagram showing another configuration example of an optical head device (optical pickup device) using the polarization separation element (polarization selective hologram element) of the present invention.
In this optical head device, a light source (semiconductor laser) 11 and a photodetector (photodiode) 17 are housed in one case 18, and a polarization separation element 12 is joined to a light output / incident part of the case 8 to be integrated. It has become. Thus, by assembling the light source 11, the photodetector 17, and the polarization separation element 12 to constitute a unit, assembly and adjustment of each element of the optical head device is facilitated.

Next, an example of an optical disk drive device on which the optical head device (optical pickup device) is mounted will be described.
The optical head device (optical pickup device) shown in FIG. 11 uses the polarization-selective polarization separation element (polarization-selective hologram element) of the present invention as the polarization separation element 12, and therefore has high light utilization efficiency and high-speed recording.・ Reliable signals suitable for playback can be obtained. Moreover, if the diffraction efficiency is high, the gain of the optical integrated circuit (OPIC) of the signal detection system can be reduced, which can contribute to the high-speed response of the OPIC. If the diffraction efficiency does not change depending on the incident angle, a signal with a small offset can be obtained. Therefore, it is possible to increase the recording / reproducing speed and stable servo control of the optical disk drive device.

  Furthermore, the optical head device shown in FIG. 12 uses the polarization-selective polarization separation element (polarization-selective hologram element) of the present invention as the polarization separation element 12, and a case 18 containing the semiconductor laser 11 and the photodiode 17. Since it is an integrated configuration, it is possible to reduce the size and thickness of the optical head device. For example, an optical head device (optical pickup device) of an optical disk drive device mounted on a notebook personal computer, a display integrated drive device, or the like. ) Can be suitably used.

  Next, one configuration example of the optical disk drive apparatus is shown in FIG. FIG. 13 is a block diagram showing an example of a schematic configuration of the optical disc drive apparatus. This optical disk drive device 20 includes a spindle motor 22 for rotating the optical disk 16 as a recording medium, an optical head device (optical pickup device) 23, a laser control circuit 24, an encoder 25, a motor driver 27, and a reproduction signal processing circuit 28. , A servo controller 33, a buffer RAM 34, a buffer manager 37, an interface 38, a read only memory (ROM) 39, a central processing unit (CPU) 40, a random access memory (RAM) 41, and the like. Note that the arrows in FIG. 13 indicate the flow of typical signals and information, and do not represent the entire connection relationship of each block. Moreover, the structure of FIG. 13 is an example, and is not limited to this.

  As the optical disc 16 as a recording medium, a CD (compact disc) optical disc (CD, CD-R, CD-RW) or a DVD (digital versatile disc) optical disc (DVD, DVD-R, DVD + R). , DVD-RW, DVD + RW, DVD-RAM, etc.), high-density optical discs using blue semiconductor lasers as light sources, etc., but the optical head device (optical pickup device) 23 has a plurality of light sources having different wavelengths, If the light source is selectively driven according to the type of the optical disc 16, an optical disc drive device capable of recording and reproducing with respect to a plurality of types of optical discs can be configured.

In FIG. 13, an optical head device (optical pickup device) 23 irradiates a recording surface on which a spiral or concentric track of an optical disk 16 is formed with a laser beam and receives reflected light from the recording surface. For example, having a configuration as shown in FIG. 11 or FIG.
The reproduction signal processing circuit 28 converts a current signal that is an output signal of the optical head device (optical pickup device) 23 into a voltage signal, and based on the voltage signal, a wobble signal, an RF signal including reproduction information, and a servo signal (focus). Signal, tracking signal) and the like. Then, the reproduction signal processing circuit 28 extracts address information, a synchronization signal, and the like from the wobble signal. The address information extracted here is output to the CPU 40, and the synchronization signal is output to the encoder 25. Further, the reproduction signal processing circuit 28 performs error correction processing or the like on the RF signal and then stores it in the buffer RAM 34 via the buffer manager 37. The servo signal is output from the reproduction signal processing circuit 28 to the servo controller 33. The servo controller 33 generates a control signal for controlling the optical head device (optical pickup device) 23 based on the servo signal and outputs the control signal to the motor driver 27.

  The buffer manager 37 manages input / output of data to / from the buffer RAM 34, and notifies the CPU 40 when the accumulated data amount reaches a predetermined value. The motor driver 27 controls the optical head device (optical pickup device) 23 and the spindle motor 22 based on a control signal from the servo controller 33 and an instruction from the CPU 40. The encoder 25 takes out the data stored in the buffer RAM 34 through the buffer manager 37 based on an instruction from the CPU 40, adds an error correction code, etc., creates data to be written to the optical disc 16, and reproduces it. Write data is output to the laser control circuit 24 in synchronization with the synchronization signal from the signal processing circuit 28. The laser control circuit 24 controls the laser light output from the optical head device (optical pickup device) 23 based on the write data from the encoder 25.

The interface 38 is a bidirectional communication interface with a host (for example, a personal computer) and conforms to a standard interface such as ATAPI (AT Attachment Packet Interface) and SCSI (Small Computer System Interface).
The ROM 39 stores a control program written in a code readable by the CPU 40. The CPU 40 controls the operation of each unit according to the program stored in the ROM 39, and temporarily holds data necessary for control in the RAM 41.

As described above, one configuration example of the optical disk drive apparatus has been described. In the present invention, an optical head apparatus (polarization selective hologram element) 12 having a high diffraction efficiency is used as the optical head apparatus (optical pickup apparatus) 23 ( Since the optical pickup device) is mounted, the light use efficiency is high and the polarization selectivity is good, so that a highly reliable signal can be obtained and the recording / reproducing speed can be increased. Further, it is possible to realize a high density optical disc drive apparatus using a blue semiconductor laser as a light source.
Furthermore, in the present invention, a plurality of light sources having different wavelengths are provided in the optical head device (optical pickup device) 23, so that the wavelength used for a CD-type or DVD-type optical disc, a high-density optical disc using a blue semiconductor laser as a light source, or the like. It is possible to realize an optical disc drive apparatus capable of recording or reproducing optical discs of different standards.

  Next, more specific examples and comparative examples of the configuration and manufacturing method of the polarization beam splitter according to the present invention will be described.

Example 1
First, an antireflection film for blue light was formed on one surface of a 0.7 mm thick glass substrate, and two glass substrates were bonded together with an adhesive mixed with a bead spacer having a diameter of about 4 μm to form a cell. The adhesive was applied to two locations on the edge of the substrate on the surface opposite to the antireflection film forming surface.
Next, a composition comprising a mixture of the following materials (1) to (5) is injected into the cell (between the substrates) by the capillary method while heating to about 60 ° C., and a composition layer having a thickness of about 3 to 9 μm is formed. Each was formed. Since this composition is reactive to light having a shorter wavelength than green, it was handled in a dark room using red light.

(1) Nematic liquid crystal (Merck TL216, Δε> 0): 30 parts by weight
(2) Phenyl glycidyl ether acrylate hexamethylene diisocyanate urethane prepolymer (AH600 manufactured by Kyoeisha Chemical Co., Ltd.): 75 parts by weight
(3) Dimethylol tricyclodecane diacrylate (DCP-A manufactured by Kyoeisha Chemical): 10 parts by weight
(4) 2-hydroxyethyl methacrylate (Kyoeisha Chemical HO): 5 parts by weight
(5) Bisacylphosphine oxide photopolymerization initiator (Ciba Geigy's Irgacure 819): 1 part by weight

Next, a two-beam interference exposure apparatus as shown in FIG. 9 was prepared using an exposure laser apparatus 51 using a He—Cd laser having a wavelength of 442 nm and an output of 80 mW as a light source. The laser beam is magnified by the collimating lens 54, divided by the half mirror 55, and one light beam is made into parallel light of about 10 mW / cm ² , reflected by the mirrors 56a and 56b, and the crossing angle of the ^two light beams is set to 26 degrees. Set. At this wavelength and crossing angle, interference fringes with a period of about 1 μm are generated in the crossing region of the two light beams.
The cell substrate (recording material 57) was attached to a heating device 58 for temperature control, and was subjected to two-beam interference exposure for about 1 minute in a state heated to about 60 ° C. to produce a polarization separation element. At this time, the two light beams are set to enter from directions of +26 degrees and 0 degrees with respect to the vertical direction of the substrate surface, and the inclination of the grating formed inside the element is approximately 81.7 with respect to the substrate surface. Degree.

A linearly polarized laser beam having a wavelength of 442 nm was irradiated from the perpendicular direction to the substrate surface of the fabricated element, and the + 1st order diffracted light intensity with respect to the incident light intensity was measured. The incident light intensity was adjusted using an ND filter so that the incident light intensity was about 5 mW, and the incident angle characteristic of the diffraction efficiency was measured in a range of ± 20 ° from the direction perpendicular to the substrate surface of the element using a rotating stage. The refractive index modulation amount Δn _H of the element was obtained from this incident angle characteristic. In addition, a linearly polarizing plate and a half-wave plate are arranged in the incident optical path, and the polarization direction (P-polarized light, S-polarized light) incident on the element can be switched by rotating the optical axis of the half-wave plate by 45 degrees. The polarization selectivity of the + 1st order diffraction efficiency was measured. At this time, the P-polarized light was orthogonal to the interference fringes during interference exposure, and the S-polarized light was the direction of the interference fringes. Various characteristics of the fabricated device are shown below.

In Example 1, in the cell produced as described above, the gap (thickness) of the cell before encapsulating the composition was about 4 μm. In this case, the amount of change in the refractive index at which 100% diffraction efficiency is obtained is expressed by the following equation:
Δn _H _max = (λ / d) √ (−cos2φ)
Therefore, Δn _H — max = 0.108. Δn _H obtained from the incident angle characteristic was 0.133, the + 1st-order diffraction efficiency of P-polarized light was 86%, and the diffraction efficiency of S-polarized light was 0%. That is, the polarization selectivity (S-polarized light / P-polarized light) of the + 1st order diffracted light was 0%.

(Comparative Example 1)
Next, as Comparative Example 1, a polarization separation element was produced in substantially the same manner as in Example 1. Various characteristics of the fabricated device are shown below.
In Comparative Example 1, in the cell produced as described above, the gap (thickness) of the cell before encapsulating the composition was about 3.5 μm. In this case, the amount of change in the refractive index at which 100% diffraction efficiency is obtained is expressed by the following equation:
Δn _H _max = (λ / d) √ (−cos2φ)
Therefore, Δn _{H —} max = 0.123. Δn _H obtained from the incident angle characteristics was 0.091, the + 1st-order diffraction efficiency of P-polarized light was 81%, and the diffraction efficiency of S-polarized light was 0%. That is, the polarization selectivity (S-polarized light / P-polarized light) of the + 1st order diffracted light was 0%.

Here, the temperature characteristics of the + 1st order diffracted light efficiency in the P-polarized light of the cell produced in Example 1 and the cell produced in Comparative Example 1 were measured. FIG. 14 shows temperature characteristics of the diffraction efficiency ratio (vs. room temperature (RT)) normalized by the diffraction efficiency at room temperature. From FIG. 14, it can be seen that in the range of 25 ° C. to 75 ° C., the reduction rate of the diffraction efficiency is lower in Example 1. That is, the refractive index modulation amount Δn _H with respect to a specific polarization direction of the polarization separating element is
f (d) ≦ | Δn _H | ≦ 1.3 · f (d)
f (d) = (λ / d) √ (−cos2φ)
It can be seen that the temperature characteristics are improved by the relationship.

(Example 2)
A polarization separation element was produced in the same manner as in Example 1 except that the temperature during interference exposure was set to 80 ° C. Various characteristics of the fabricated device are shown below.
In Example 2, in the cell produced as described above, the gap (thickness) of the cell before encapsulating the composition was about 4.5 μm, and Δn _H obtained from the incident angle characteristic of P-polarized light was 0.00. is 124, the + 1-order diffraction efficiency 84.6%, [Delta] n _H determined from the incident angle characteristic of the S-polarized light is 0, the + 1-order diffraction efficiency was 0%. That is, the polarization selectivity (S-polarized light / P-polarized light) of the + 1st order diffracted light was 0%.

(Comparative Example 2)
A polarization separation element was produced in the same manner as in Example 1 except that the temperature during interference exposure was set to 100 ° C. Various characteristics of the fabricated device are shown below.
In Comparative Example 2, in the cell produced as described above, the gap (thickness) of the cell before encapsulating the composition was about 4.5 μm, and Δn _H obtained from the incident angle characteristic of P-polarized light was 0.00. is 125, the + 1-order diffraction efficiency 86.4%, [Delta] n _H determined from the incident angle characteristic of the S-polarized light is 0.008, the + 1-order diffraction efficiency was 1.1%. That is, the polarization selectivity (S-polarized light / P-polarized light) of the + 1st order diffracted light was 1.2%.

Here, when the characteristics of Example 2 and Comparative Example 2 are compared, both diffraction efficiencies are 80% or higher, and high efficiency is obtained. However, the polarization selectivity is 0% in Example 2, and 1 in Comparative Example 2. 2%.
In both cells, the wavelength λ = 441.6 nm, the film thickness d = 4.5 μm, and the lattice inclination φ = 81.7 degrees are almost the same, and when 0.065 · f (d) is obtained,
f (d) = (λ / d) √ (−cos 2φ) = 0.096
And
| Δn _H | ≦ 0.006 (= 0.065 · f (d))
It became.
Since Δn _H of S-polarized light in Example 2 and Comparative Example 2 is 0 and 0.008, respectively, Comparative Example 2 does not satisfy the relationship of the above equation, and Example 2 satisfies the relationship of the above equation. It is considered that good polarization selectivity was obtained with the device of Example 2.

(Example 3)
In the cell fabricated in Example 1, the diffraction efficiency when the polarization direction of incident light (provisional P-polarized light) is inclined by 5 ° with respect to the direction of interference fringes during interference exposure is 80%. The diffraction efficiency in the direction of polarization perpendicular to (temporary S-polarized light) was 1%. That is, the polarization selectivity was 1.3%, and the diffraction efficiency and polarization selectivity were deteriorated as compared with the characteristics in Example 1. This is presumably because the polarization direction of the incident light was not parallel or perpendicular to the direction of the interference fringes during interference exposure. In other words, in order to obtain good polarization selectivity, the polarization direction of incident light must be parallel or perpendicular to the direction of interference fringes during interference exposure. This is equivalent to the incident polarization direction being orthogonal or parallel to the boundary of the element internal periodic structure formed by interference fringes.

Example 4
A polarization separation element was produced in the same manner as in Example 1. When this element is used in an optical head device (optical pickup device) configured as shown in FIG. 11, the substrate surface of the polarization separation element 12 is perpendicular to the optical axis from the light source (semiconductor laser) 11 to the optical disk 16 surface. Can be arranged. In addition, when the distance between the semiconductor laser 11 and the photodiode 17 in FIG. 11 is constant, the diffraction angle is as large as 26 degrees, so the distance between the formation surface of the semiconductor laser 11 and the photodiode 17 and the polarization separation element 12 is large. Can be shortened. Therefore, the overall thickness of the optical head device (optical pickup device) can be reduced.
Further, since the distance between the formation surface of the semiconductor laser 11 and the photodiode 17 and the polarization separation element 12 can be shortened, for example, the semiconductor laser (LD) 11 and the photodiode (PD) 17 are accommodated as shown in FIG. A polarization separation element (HO) 12 can be attached to the light incident / exit section of the case 18 and unitized. By using such an integrated unit of LD / PD / HO, assembly / adjustment of the optical head device is possible. Becomes easier. Furthermore, by using this optical head device (optical pickup device), it is possible to realize a thin and compact optical disc drive device with high light utilization efficiency.

  As described above, according to the present invention, a large diffraction angle can be obtained even for short-wavelength light such as blue, it has high diffraction efficiency, excellent polarization selectivity, good temperature characteristics of diffraction efficiency, and an incident angle. It is possible to realize a polarization separation element (polarization selective hologram element) that is small in dependence and highly efficient against diverging light and temperature change. By using this polarization separation element, it is possible to easily realize a compact optical head device (optical pickup device) compatible with a high-density optical disc, and further, a compact and compact device equipped with the optical head device. An optical disk drive device can be realized. Such a small and compact optical disk drive device can be suitably used as an optical disk drive device mounted on a desktop or notebook personal computer, and also suitably used for a portable display-integrated optical disk drive device or the like. be able to.

Furthermore, the polarization separation element of the present invention can be used as a polarization selective hologram element for downsizing an optical head device used for recording and reproduction of a magneto-optical disk or the like in addition to an optical disk.
The polarization separation element of the present invention can also be used as a polarization separation element for improving the light use efficiency of illumination light in an illumination optical system used in a projection display device or the like.
Furthermore, the polarization separation element of the present invention can also be applied to an optical switch for switching the optical path according to the polarization plane.

It is a figure which shows the outline of a cross-sectional structure of the polarization splitting element which concerns on this invention. It is explanatory drawing of operation | movement of the polarization separation element of a structure shown in FIG. It is a graph showing the relationship of the refractive index modulation [Delta] n _H and the diffraction efficiency of the polarization separating element of the refractive index modulation type. It is a figure which shows the temperature dependence of the general refractive index of isotropic area | region n and birefringent area | region no, ne. The refractive index modulation [Delta] n _H is a diagram showing a relationship between normalized as the diffraction efficiency in the refractive index modulation [Delta] n _H _max the resulting maximum diffraction efficiency. The refractive index modulation [Delta] n _H is an enlarged view showing a part of the relationship between the diffraction efficiency obtained by normalizing refractive index modulation [Delta] n _H _max the resulting maximum diffraction efficiency. It is a figure which shows the outline of the cross-sectional structure of the element (cell) before performing phase separation. It is a figure which shows the formation process of the periodic structure by phase separation. It is a figure which shows the basic composition of a two-beam interference exposure apparatus. It is explanatory drawing of operation | movement of the polarization separation element of the structure where the boundary surface of a periodic structure inclines with respect to a substrate surface. It is a figure which shows the basic structural example of the optical head apparatus using the polarization splitting element of this invention. It is a figure which shows another structural example of the optical head apparatus using the polarization splitting element of this invention. 1 is a block diagram showing an example of a schematic configuration of an optical disk drive device equipped with an optical head device of the present invention. It is a figure which shows the temperature characteristic of the diffraction efficiency ratio (vs. room temperature (RT)) normalized by the diffraction efficiency at room temperature.

Explanation of symbols

1: Polarized light separating element 2, 3: Transparent substrate 4: Optically anisotropic (birefringent) region 5: Optically isotropic region 6: Non-polymerizable liquid crystal 7: Polymerizable monomer (or prepolymer)
8: Composition 11: Semiconductor laser 12: Polarization separation element (polarization selective hologram element)
13: 1/4 wavelength plate 14: Collimator lens 15: Objective lens 16: Optical disk (recording medium)
17: Photodiode (light receiving element)
18: Case 23: Optical head device (optical pickup device)

Claims (15)

Refractive index modulation type polarization having a periodic structure (hereinafter, referred to as a periodic structure) composed of a region exhibiting optical anisotropy or birefringence and a region exhibiting optical isotropy, and diffracting incident light. In the separation element,
The incident wavelength is λ, the thickness of the periodic structure is d, and the inclination of the grating inside the element is φ (where φ is a vector perpendicular to the grating periodic structure, and 45 ° with the periodic structure array plane as the reference (0 °)) <Φ <135 °), the refractive index of the region showing the optical anisotropy or birefringence with respect to incident light in a specific polarization direction and the optical isotropy. The refractive index modulation amount Δn _H generated by the refractive index of the region shown in FIG.
f (d) ≦ | Δn _H | ≦ 1.3 · f (d)
f (d) = (λ / d) √ (−cos2φ)
A polarization separation element characterized by having the following relationship: The polarization separating element according to claim 1,
The refractive index modulation amount Δn _H generated by the region showing the optical anisotropy or birefringence with respect to the incident light in the polarization direction orthogonal to the specific polarization direction and the optical isotropic region,
| Δn _H | ≦ 0.065 · f (d)
A polarization separation element characterized by having the following relationship: The polarization separation element according to claim 1 or 2,
A polarization separation element comprising a non-polymerizable liquid crystal or a polymerizable liquid crystal in at least one of the region exhibiting optical anisotropy or birefringence and the optically isotropic region. The polarization separation element according to any one of claims 1 to 3,
The polarization separation element, wherein the specific polarization direction is orthogonal to a boundary between the optically anisotropic or birefringent region and the optically isotropic region. A method for manufacturing a polarization separation element for producing the polarization separation element according to any one of claims 1 to 4,
A step of injecting a composition comprising a non-polymerizable liquid crystal, a polymerizable monomer or prepolymer, and a photopolymerization initiator between a pair of transparent substrates whose substrate spacing is controlled by a spacer member; A method for producing a polarization separation element, comprising the step of forming a periodic phase separation structure of a layer mainly made of a polymer and a layer mainly made of a non-polymerizable liquid crystal by performing light beam interference exposure . In the manufacturing method of the polarization separation element according to claim 5,
The non-polymerizable liquid crystal material in the composition is used in a ratio of 15 parts by weight to 500 parts by weight with respect to 100 parts by weight of the total amount of the polymerizable monomer or prepolymer. Manufacturing method. In the manufacturing method of the polarization separation element according to claim 5 or 6,
As the polymerizable monomer or prepolymer, a method for producing a polarized light separating element, which has a large curing shrinkage due to polymerization, is used. In the manufacturing method of the polarization separation element according to any one of claims 5 to 7,
The method for producing a polarization separation element, wherein the addition amount of the photopolymerization initiator is 0.1 wt% or more and 10 wt% or less with respect to the total amount of the polymerizable monomer or prepolymer. In the manufacturing method of the polarization splitting device according to any one of claims 5 to 8,
The film thickness of the composition is controlled by the height of the spacer member interposed between the pair of substrates, and the height of the spacer member is determined by the wavelength of the diffracted light, the polymer part of the periodic structure, and the liquid crystal part. A method for manufacturing a polarization separation element, wherein the film thickness of the composition is set to a predetermined thickness according to a difference in refractive index. In the manufacturing method of the polarization separation element according to any one of claims 5 to 9,
In the two-beam interference exposure and phase separation process, the substrate for holding the composition is heated and held at a temperature in the range of 40 ° C to 100 ° C. In the manufacturing method of the polarization splitting device according to any one of claims 5 to 10,
The method of manufacturing a polarization separation element, wherein a wavelength of a light source used for the two-beam interference exposure is a short wavelength. In the manufacturing method of the polarization splitting device according to any one of claims 5 to 11,
The two light exposure amount at the time of beam interference ^exposure, the method of manufacturing the polarization separating element, characterized in that set in the range of ^{0.5J / cm 2 ~30J / cm 2} . In an optical head device for condensing light from a light source on a recording medium and detecting reflected light from the recording medium with a photodetector to record or reproduce information, or record and reproduce,
An optical element for deflecting reflected light from the recording medium toward the photodetector is provided in an optical path from the recording medium to the photodetector, and the optical element is any one of claims 1 to 4. An optical head device comprising the polarization separation element according to claim 1. The optical head device according to claim 13, wherein
An optical head device characterized in that the light source and the photodetector are housed in one case, and the polarization separation element is integrated in a light output / incident part of the case. In an optical disk drive apparatus for recording or reproducing information, or recording and reproducing information using an optical head device for a recording medium,
15. An optical disk drive device, wherein the optical head device according to claim 13 or 14 is mounted as the optical head device.

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