JP4013892B2 - Diffraction element and optical attenuator - Google Patents

Description

  The present invention relates to a diffractive element and an optical attenuator, and in particular, a liquid crystal is used as a part of a diffraction grating, a voltage is applied to the liquid crystal to control a substantial refractive index of the liquid crystal, and incident light is diffracted to 0. The present invention relates to a diffraction element and an optical attenuator for controlling the amount of next diffracted light (transmitted light).

  Conventionally, diffraction using a blue phase of a cholesteric liquid crystal containing a chiral material and having an isotropic refractive index (hereinafter, referred to as a blue phase liquid crystal) whose refractive index changes isotropically according to the magnitude of an applied voltage. An element is disclosed (for example, refer to Patent Document 1). FIG. 10 shows a configuration example of the liquid crystal element 100 such as a diffraction element and a conceptual cross-sectional view of the optical system. In the conventional liquid crystal element 100, the blue phase liquid crystal 2 is sandwiched between two glass substrates 5 and 6 on which transparent electrode films 3 and 4 are formed by patterning, and a seal 7 therebetween.

  A voltage output from the power supply 8 is applied between the opposing transparent electrode films 3 and 4. The amount of 0th-order diffracted light emitted from the light source 14 and traveling straight through the liquid crystal element 100 and reaching the projection screen 15 varies depending on the magnitude of the applied voltage. The liquid crystal element 100 having such a configuration is capable of high-speed switching, and a phase grid (that is, a phase diffraction grating) or the like is obtained using the liquid crystal element 100.

Here, since the isotropic blue phase having an isotropic refractive index appears only within a temperature range of 1 to 5 ° C., the temperature is controlled by forming the heat generating transparent plate 16 as a transparent heat generating element on the glass substrate 5. To maintain the blue phase. However, since the blue phase appears only within a very narrow temperature range as described above, accurate and difficult temperature control is required. Therefore, in order to solve the temperature control problem, the monomer is polymerized by mixing the monomer with the liquid crystal and irradiating ultraviolet rays in the temperature range of the blue phase liquid crystal. A technology has been developed that allows expansion from 5 ° C. to over 60 ° C. Hereinafter, the blue phase liquid crystal whose temperature range is expanded as described above is referred to as a polymer-stabilized blue phase liquid crystal. A high-speed response of 1 msec or less has been confirmed by using a polymer-stabilized blue phase liquid crystal (for example, Non-Patent Document 1). However, a configuration example of a switching element that does not depend on the state of incident polarization using optical isotropy has not been disclosed so far.
US Patent No. 4,767,194 Nature, Material, Vol. 1, September 2002, p. 64 (Nature Materials, Vol. 1, 2002, September, P. 64)

  However, such a conventional diffractive element and optical attenuator require two substrates having electrodes formed by patterning, have a complicated electrode structure, and the positions of the opposing electrodes are shifted. Since a phase diffraction grating having performance such as a desired refractive index according to the applied voltage cannot be obtained, high alignment accuracy is required. In particular, in order to obtain a diffraction grating that efficiently diffracts incident light at a large angle, it is necessary to pattern and align the distance between adjacent electrodes with an accuracy within 10 μm, and it is difficult to obtain a practical optical element. there were.

  In addition, the electric field generated by the opposing electrode pair is also generated in the liquid crystal region where there is no electrode, and the refractive index of the liquid crystal changes accordingly, so that a phase diffraction grating having desired characteristics cannot be obtained, and diffraction is performed. There was a problem that efficiency deteriorated.

  These problems are the same when a polymer-stabilized blue phase liquid crystal having an extended temperature range in which the blue phase liquid crystal is developed is used.

  The present invention has been made to solve such problems, and uses a blue phase liquid crystal or a polymer-stabilized blue phase liquid crystal, and does not depend on incident polarization, and is equivalent to or faster than conventional high-speed optical switching. A diffraction element and an optical attenuator that can stably realize an extinction ratio are provided.

In view of the above points, the invention according to claim 1 is formed using a substrate that transmits light, and an isotropic refractive index solid material having an isotropic refractive index on the substrate, and has a cross-sectional structure. A grating having periodic irregularities, a cholesteric blue phase liquid crystal in which at least a concave portion of the grating having periodic irregularities is filled, a refractive index isotropically changed, and a cholesteric blue phase is expressed; and the cholesteric blue phase liquid crystal An electrode for applying a voltage, a diffraction grating is constituted by the grating and the cholesteric blue phase liquid crystal, and a refractive index of the cholesteric blue phase liquid crystal constituting the diffraction grating is applied via the electrode a diffraction element which is to be changed by the cholesteric blue phase liquid crystal, the cholesteric by the inclusion of predetermined polymer materials A polymer-stabilized cholesteric blue phase liquid crystal in which an expression temperature range of a roux phase is expanded, and the electrodes are provided between the substrate and the lattice, and are arranged in a line along the lattice adjacent to each other Each electrode is connected to each other, and a voltage is applied between the adjacent electrodes via the two electrode sets .

  With this configuration, the cholesteric blue phase liquid crystal is filled in the concave portions of the lattice, and the refractive index of the cholesteric blue phase liquid crystal is controlled by the magnitude of the applied voltage. It is possible to realize a diffraction element that can stably obtain the high-speed optical switching and the extinction ratio.

Also, with this configuration, a polymer-stabilized cholesteric blue phase liquid crystal is used as the cholesteric blue phase liquid crystal, so that a stable high extinction ratio independent of incident polarization can be obtained over a wide temperature range and a diffraction element capable of high-speed optical switching can be realized .

Further, this configuration, since the may be formed by patterning an electrode on only the substrate surface to form a diffraction grating made of isotropic refractive index solid material, the electrode on the substrate surface facing the need to align unnecessary since there can also be realized diffractive element can be simplified than the conventional device operation made steps.

According to a second aspect of the present invention, the diffraction element according to the first aspect and incident high-order diffracted light generated by applying a voltage through the electrode of the diffractive element travel straight through the diffractive element. Separation means for separating the transmitted incident light from the 0th-order diffracted light and extracting the 0th-order diffracted light, and adjusting the amount of the 0th-order diffracted light according to the magnitude of the voltage applied through the electrode. It has the structure made into.

  With this configuration, the diffraction element of the present invention using a blue phase liquid crystal or a polymer-stabilized blue phase liquid crystal and a sorting unit are provided, so that high-speed optical switching and quenching that are equal to or higher than conventional ones are performed without depending on incident polarization. An optical attenuator that can stably obtain the ratio can be realized.

  In the present invention, by using a blue phase liquid crystal or a polymer stabilized blue phase liquid crystal, high-speed optical switching and an extinction ratio equal to or higher than those in the past can be stably obtained without depending on the state of incident polarized light. A diffraction element and an optical attenuator having an effect can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment) (Reference example)
FIG. 1 is a diagram conceptually showing a cross-sectional structure of the diffraction element according to the first embodiment of the present invention. A diffractive element 10 shown in FIG. 1 has transparent electrode films 3 and 4 formed on one side of translucent substrates 5 and 6, respectively, and a substantially rectangular parallelepiped isotropic refractive index solid material between the transparent electrode films 3 and 4. Are arranged in parallel and periodically to form a grating 2A, and a diffraction grating 1 in which a region between each isotropic refractive index solid material forming the grating 2A is occupied by an isotropic refractive index liquid crystal 2B is formed, The isotropic refractive index liquid crystal 2 </ b> B is sealed by the transparent electrode films 3 and 4 and the seal 7.

Here, the isotropic refractive index solid material, regardless of the polarization direction of incident light refractive index n _s is good the constant and birefringence without transparent material, as isotropic refractive index solid material, SiO ₂ Alternatively, an inorganic material such as SiN or SiN may be used, or an organic material such as polyimide or an ultraviolet curable resin may be used. Further, a periodic arrangement pattern (hereinafter referred to as a diffraction grating pattern) of the grating 2A and the isotropic refractive index liquid crystal 2B constituting the diffraction grating 1 is formed to have a desired film thickness d of about 1 μm to 100 μm. An isotropic refractive index solid material is obtained by processing using a fine processing technique such as photolithography or dry etching. When a photosensitive material such as photosensitive polyimide is used as the grating 2A (isotropic refractive index solid material), it can be processed into a grating shape simply by performing exposure and development using a mask corresponding to the diffraction grating pattern. The pattern production process can be simplified, which is preferable.

  Next, the sealing of the isotropic refractive index liquid crystal 2B is performed by printing and applying a seal 7 on one side of the transparent substrate 6 on which the transparent electrode film 4 is formed, as in the conventional liquid crystal element. 5 is formed into a cell by pressure-solidifying the sealing material. Then, an isotropic refractive index liquid crystal 2B in which the refractive index n (V) isotropically changed according to the magnitude of the applied voltage V is injected from an injection port (not shown) provided in a part of the seal. Then, the region between the isotropic refractive index solid materials of the grating 2A is filled with the isotropic refractive index liquid crystal 2B, and the inlet is sealed to complete the diffraction element 10. Here, the thickness d of the isotropic refractive index solid material of the grating 2A in the direction perpendicular to the translucent substrate 5 defines the layer thickness of the isotropic refractive index liquid crystal 2B, and is used in the conventional liquid crystal element. It is not necessary to use a gap control material.

  The liquid crystal used as the isotropic refractive index liquid crystal 2B may be any material as long as the refractive index with respect to incident light changes isotropically according to the magnitude of the applied voltage V. When a blue phase liquid crystal is used as the isotropic refractive index liquid crystal 2B, it is preferable because a high-speed response of 1 msec or less is realized. In addition, when a polymer-stabilized blue phase liquid crystal is used as the isotropic refractive index liquid crystal 2B, the temperature range in which the blue phase appears is expanded, and thus temperature control for keeping the isotropic refractive index liquid crystal 2B in the blue phase. Is more preferable. The materials used for the polymer-stabilized blue phase liquid crystal and the manufacturing method thereof are disclosed in Non-Patent Document 1 and the like, and the description thereof is omitted. In the following, unless otherwise specified, the concave portion of the grating 2A having the irregular periodicity includes a polymer-stabilized cholesteric blue phase liquid crystal in which the refractive index changes isotropically and expresses a cholesteric blue phase. It shall be filled with blue phase liquid crystal.

  The voltage V output from the power supply 8 is applied to the isotropic refractive index liquid crystal 2B through the transparent electrode films 3 and 4, and the refractive index is controlled by controlling the orientation of the isotropic refractive index liquid crystal 2B. Used for.

  Hereinafter, an example of the voltage response of the diffraction element 10 according to the first embodiment of the present invention will be described. FIG. 2 is an explanatory diagram for explaining an example of a voltage response of the diffraction element 10 according to the first embodiment of the present invention. 2A shows the case where the applied voltage V = 0, and FIG. 2B shows the voltage when the voltage Vm at which ± 1st order diffracted light is maximum (that is, 0th order diffracted light (transmitted light) is minimum) is applied. It is explanatory drawing for demonstrating the example of a response. Hereinafter, diffracted light other than the 0th-order diffracted light is also referred to as high-order diffracted light.

As shown in FIG. 1, in the diffraction grating 1 having a structure in which a substantially rectangular parallelepiped grating 2A and an isotropic refractive index liquid crystal 2B are alternately arranged periodically, the width of the grating 2A and the isotropic refractive index liquid crystal 2B When the ratio to the width is 1: 1, the 0th-order diffraction efficiency η ₀ indicating the rate at which incident light of wavelength λ travels straight through the diffractive element 10 is η ₀ = cos ² (π × Δn × d / λ) is approximately described. Here, △ n is the difference between the refractive index _{n s} of the refractive index n (V) and grating 2A isotropic refractive index liquid crystal 2B constituting the diffraction grating 1, ie △ n = n (V) -n s is there.

Therefore, by selecting the n (0) = n _s become as isotropic refractive index solid material and isotropic refractive index liquid crystal 2B grating 2A when no voltage is applied, as shown in FIG. 2 (a) In addition, the 0th-order diffraction efficiency η ₀ is 100%, and the incident light is transmitted in a straight line, so that it is possible to almost eliminate the loss of light amount due to the generation of high-order diffracted light. On the other hand, by increasing the applied voltage V, the difference between the n (V) and n _s ([Delta] n) is increased, the zero-order diffraction efficiency eta ₀ is decreased, △ n × d = λ / 2 become the applied voltage At Vm, as shown in FIG. 2B, the zero-order diffraction efficiency η ₀ can be made substantially zero, and the ± first-order diffracted light can be maximized.

  As a separating means for separating the 0th-order diffracted light that passes straight through the diffraction element and the diffracted light that does not pass straight through (high-order diffracted light) and extracts only the straight-passed transmitted light, there is a light collecting element such as a lens or a condenser mirror. . In an optical system for condensing light emitted from a light source on a light receiving portion of a photodetector using a condensing element such as a lens or a condensing mirror, the diffraction element of the present invention is a condensing point by the light source and the condensing element. By arranging in the optical path between the two, an optical attenuator that can adjust the amount of light condensed at the condensing point according to the voltage value applied between the electrodes in the diffraction element. For example, a light receiving surface of a photodetector is disposed at the condensing point position, and the amount of light signal is detected.

  That is, high-order diffracted light (for example, ± 1st-order diffracted light) generated according to the applied voltage between the electrodes in the diffractive element is not condensed on the light receiving surface of the photodetector by the condensing element. Zero-order diffracted light that is not diffracted by the grating is collected on the light receiving surface of the photodetector. As a result, since the 0th-order diffracted light quantity changes according to the magnitude of the applied voltage between the electrodes, an optical attenuator in which the signal light quantity of the photodetector is variable.

  Here, in order to obtain a high extinction ratio, it is necessary to separate linearly transmitted light (0th-order diffracted light) and high-order diffracted light, and light that has been transmitted through the diffractive element and light source that emits a light beam with a sharp directivity is transmitted. A configuration using a condensing element that condenses light on a minute light receiving surface of the detector is preferable. An optical transmission line such as an optical fiber or an optical waveguide may be interposed between the light source and the diffraction element or between the photodetector and the diffraction element.

  FIG. 3 shows a cross-sectional view of a configuration example in which the condensing element of the convex lens 11 and the aperture stop 12 are used as the sorting means. The linearly transmitted light (0th order diffracted light) of the diffraction element 10 passes through the opening of the aperture stop 12 placed at the condensing point position of the convex lens, and the high order diffracted light is condensed around the opening of the aperture stop 12. Therefore, the intensity-modulated outgoing light can be obtained.

That is, by switching the applied voltage from 0 to Vm or from Vm to 0, a high-speed response optical switch having a high extinction ratio can be realized. Also, by applying a voltage between 0 and Vm, an optical attenuator in which the 0th-order diffraction efficiency η ₀ changes from 100% to 0% can be realized.

  Next, FIG. 4 shows a cross-sectional view of the diffraction element 20 using the diffraction grating 21 having a sawtooth cross section of the isotropic refractive index solid material. Here, d is the film thickness of the thickest portion of the sawtooth of the isotropic refractive index solid material constituting the grating 22A of the diffraction grating 21, and P is the grating pitch. The diffraction element 20 has the same configuration as that of the diffraction element 10 except that the cross-sectional shape of the diffraction grating is different from that of the diffraction element 10. Accordingly, the same elements as those in FIG. 1 are denoted by the same reference numerals.

At this time, the 0th-order diffraction efficiency η ₀ indicating the rate at which incident light of wavelength λ travels straight through the diffractive element 20 is η ₀ = {sin (π × Δn × d / λ) / (π × Δn × d / Λ)} ² approximately. Further, the diffraction efficiency η ₁ of the _first -order diffracted light whose diffraction angle θ is defined by sin θ = λ / P is η ₁ = {sin (π × Δn × d / λ) / (π−π × Δn × d / Λ)} ² approximately. Accordingly, η ₀ = 100% when Δn = 0, and η ₁ = 100% when Δn × d = λ. That is, by switching between the voltage V1 where n (V1) = _ns and the voltage V2 where n (V2) = _ns + λ / d, the traveling direction of the emitted light of the diffraction element 20 is changed with respect to the direction of the incident light. It is possible to switch in a direction inclined by θ.

  For example, as shown in a cross section in FIG. 5, the convex lens 11 is arranged on the light emitting side of the diffraction element 20 to collect the transmitted light of the diffraction element 20, and the condensing point position of the 0th-order diffracted light and the first-order diffracted light The optical transmission path can be switched by disposing the optical transmission parts 13A and 13B of the optical fiber at the condensing point position and switching the applied voltage between the transparent electrode films 3 and 4 between V1 and V2.

  The diffractive element 10 and the diffractive element 20 are configuration examples of a diffractive element that transmits incident light. However, a reflective diffractive element can be formed by forming a light reflecting film on one surface of a translucent substrate constituting the diffractive element.

  FIG. 6 shows a configuration in which a light reflecting film 9 is provided between the light transmitting substrate 5 and the transparent electrode film 3, that is, a light reflecting film 9 is formed on one surface of the light transmitting substrate 5, and further transparent on the light reflecting film 9. A sectional view of a diffraction element 30 having a configuration in which an electrode film 3 is formed is shown. The diffractive element 30 has the same configuration as the diffractive element 10 except that the light reflecting film 9 is formed between the translucent substrate 5 and the transparent electrode film 3, but reflects and diffracts incident light. It is a reflection type diffraction element. That is, the same elements as those in FIG.

  The light reflecting film 9 may be a metal film such as aluminum or gold, or alternatively, a high refractive index dielectric and a low refractive index dielectric are alternately arranged so that the optical film thickness of each film is about ¼ wavelength of incident light. A light reflecting film made of a laminated optical multilayer film may be used. When a metal reflective film is used as the light reflective film 9, the transparent electrode film 3 can be omitted because it functions also as an electrode film for applying a voltage to the isotropic refractive index liquid crystal 2B. When the optical multilayer reflective film is used, the optical multilayer reflective film may be formed as the light reflective film 9 on the transparent electrode film 3 formed on the translucent substrate 5.

In the case of such a reflective diffractive element 30, incident light travels back and forth through the diffraction grating 1, so that ± 1st-order diffracted light becomes maximum as compared with a transmissive diffractive element as shown in FIGS. 1 and 4. Since the refractive index difference Δn necessary for the next diffraction efficiency η _{0 to} be substantially zero is half, the applied voltage Vm is reduced. Alternatively, even if the film thickness d of the grating 2A of the diffraction grating 1 is halved, the voltage dependency of the 0th-order diffraction efficiency η ₀ equivalent to that of the transmission type diffraction element is obtained, so that the manufacturing time of the diffraction grating can be shortened.

  FIG. 7 is a cross-sectional view showing a configuration example of an optical attenuator using the diffraction element 30. In FIG. 7, the light emitted from the optical transmission unit 13 of the optical fiber is arranged so as to be collimated by the convex lens 11 and perpendicularly incident on the diffraction element 30. The reflected light emitted without being diffracted by the diffractive element 30 passes through the convex lens 11 again, is collected by the optical transmission unit 13 of the original optical fiber, and propagates into the optical fiber. On the other hand, the reflected light diffracted by the diffractive element 30 is transmitted through the convex lens 11 again and is not condensed on the optical transmission unit 13 of the original optical fiber, and therefore does not propagate through the optical fiber. Therefore, an optical attenuator that can adjust the amount of light returning to the optical fiber according to the magnitude of the applied voltage can be realized.

  In the diffraction grating of this embodiment, it is preferable to use liquid crystal molecules having positive dielectric anisotropy as the blue layer liquid crystal in order to more effectively eliminate the polarization dependency when a voltage is applied.

  As described above, the diffraction element according to the first embodiment of the present invention fills the concave portion of the grating with the blue phase liquid crystal and controls the refractive index of the blue phase liquid crystal by the applied voltage. High-speed optical switching and extinction ratio equivalent to or higher than those of the prior art can be stably obtained without depending on polarization.

  In addition, by using a polymer-stabilized blue phase liquid crystal as the blue phase liquid crystal, a stable high extinction ratio that does not depend on incident polarized light can be obtained in a wide temperature range and high-speed optical switching can be performed.

  In addition, since the electrodes are provided on the opposite surfaces of the isotropic refractive index liquid crystal, it is not necessary to pattern the electrodes according to the lattice shape or to align the patterns.

  In addition, the optical attenuator according to the first embodiment of the present invention is provided with the diffraction element of the present invention using a blue phase liquid crystal including a polymer-stabilized blue layer liquid crystal and a sorting unit, and therefore depends on incident polarization. Therefore, it is possible to realize an optical attenuator that can stably obtain a high-speed optical switching and an extinction ratio equivalent to or higher than those of the prior art.

(Second Embodiment)
FIG. 8 is a cross-sectional view of a diffraction element according to the second embodiment of the present invention, and FIG. 9 is a plan view of this diffraction element. The diffractive element 40 according to the second embodiment of the present invention is a transparent electrode patterned in place of the transparent electrode film 3 except for the transparent electrode film 4 from the diffractive element 10 according to the first embodiment of the present invention. The film 3A, 3B is provided. Here, the transparent electrode films 3A and 3B are formed so as to be sandwiched between the translucent substrate 5 and the grating 2A. Other components are the same as those of the diffraction element 10 according to the first embodiment of the present invention, and the description thereof is omitted. Accordingly, the same elements as those in FIG. 1 are denoted by the same reference numerals.

  As shown in FIG. 8, each of the linear transparent electrodes 3A and 3B formed on the diffraction grating 1 is divided into a pair of two electrodes connected every other. Specifically, every other pair, for example, composed of a transparent electrode film 3A and a group composed of a transparent electrode film 3B are divided, and a voltage is applied between the electrodes forming these groups and adjacent to each other. A voltage is applied between the electrodes. As described above, when a voltage is applied between adjacent electrodes, an electric field in the Y-axis direction is generated in the isotropic refractive index liquid crystal 2B of the diffraction grating 1, so that the refractive index of the liquid crystal 2 varies depending on the magnitude of the voltage V. Isotropic change. As a result, a response equivalent to the voltage response described in the diffraction element according to the first embodiment of the present invention is obtained. In the diffraction grating of the present embodiment, it is preferable to use liquid crystal molecules having negative dielectric anisotropy as the blue layer liquid crystal in order to more effectively eliminate the polarization dependency when a voltage is applied.

  The diffraction element 40 shown in FIG. 8 is an example in which the transparent electrode films 3A and 3B are formed only at a portion where the grating 2A and the translucent substrate 5 are in contact (hereinafter referred to as the bottom surface of the grating 2A). The transparent electrode film may also be formed on the side surface in contact with the isotropic refractive index liquid crystal 2B, and may be electrically connected to the transparent electrode film formed on the bottom surface of the grating 2A. By adopting such an electrode structure, even when the layer thickness d of the grating 2A is large, a uniform electric field in the Y direction can be generated in the thickness direction of the isotropic refractive index liquid crystal 2B, and the grating pitch P is Since the electric field strength generated by shortening can be increased, a large optical path length difference Δn × d (difference between the optical path length of the grating 2A and the optical path length of the isotropic refractive index liquid crystal 2B) can be obtained at a relatively low voltage. A large change in the 0th-order diffracted light that is obtained and transmitted in a straight line can be achieved.

  Further, by forming the transparent electrode films 3A and 3B on the translucent substrate 5 on which the optical multilayer film is formed as a light reflecting film, a reflective diffractive element similar to the diffractive element 30 shown in FIG. 6 is obtained. The voltage response is obtained.

  With the configuration of the diffractive element according to the second embodiment of the present invention, the electrode and the diffraction grating can be processed and formed only on the translucent substrate 5, so that the number of members can be reduced and the manufacturing process can be simplified. . In the diffraction element according to the first and second embodiments of the present invention, a so-called hologram grating pattern that spatially divides the diffraction grating pattern or distributes a spatially bent shape or grating pitch other than a straight line. By doing so, it is possible to generate a plurality of diffracted light and convert the wavefront of the diffracted light, which is effective when the diffracted light is used for signal light detection or the like.

  Further features of the diffraction element and the optical attenuator of the present invention will be specifically described with reference to the following examples.

A sectional view of the diffraction element 10 of this example is shown in FIG. Transparent electrode films 3 and 4 made of ITO are formed on one side of translucent substrates 5 and 6 made of glass. Further, polyimide is spin-coated on the surface of the translucent substrate (glass) 5 on which the transparent electrode film (ITO) 3 is formed. Thereafter, by firing solidified polyimide spin coated, the refractive index _{n s} at a wavelength of 633nm is 1.54, the film thickness d to form an isotropic refractive index layer of 7 [mu] m. A lattice 2A is formed by photolithography and dry etching of a polyimide film formed as an isotropic refractive index layer. The grating 2A is formed such that isotropic solid materials having a substantially rectangular parallelepiped shape are arranged in parallel and periodic irregularities, and is perpendicular to the translucent substrate (glass) 5 (Z direction shown in FIG. 1). Further, the ratio of the width of the isotropic refractive index solid material to the width of the isotropic refractive index liquid crystal 2B in the direction (Y direction shown in FIG. 1) in which the thickness is 7 μm and the period of the arrangement of the substantially rectangular parallelepiped is the shortest is 1: 1. It is formed so that the lattice pitch P, which is the period of the arrangement of substantially rectangular parallelepipeds, is 20 μm.

  Next, a seal 7 is printed and applied to the surface of the translucent substrate (glass) 6 on which the transparent electrode film (ITO) 4 is formed using a sealing material, and then pressed and solidified on the translucent substrate (glass) 5. Convert to cell. When the seal 7 is formed by cell formation, a chiral material, a liquid crystal monomer, and a polymerization initiator are mixed into a nematic liquid crystal having positive dielectric anisotropy from an injection port (not shown) provided in a part of the seal 7. The liquid crystal obtained in this manner is injected and filled into the recesses of the periodic lattice 2A to form an isotropic refractive index liquid crystal 2B.

  In the same manner as the material and the manufacturing method described in Non-Patent Document 1, in a state where the temperature is adjusted so that the liquid crystal phase becomes a blue phase, the cell into which the liquid crystal is injected is irradiated with ultraviolet rays to polymerize the monomer, and the blue A polymer-stabilized blue phase liquid crystal in which the temperature range of the phase is from room temperature to 50 ° C. is formed, which is referred to as isotropic refractive index liquid crystal 2B. Further, the injection port provided in a part of the seal 7 is sealed with an adhesive to form the diffraction element 10.

  As a result of measuring performance using an experimental element composed only of a polymer-stabilized blue phase liquid crystal formed in a cell having a transparent electrode interval of 10 μm, the refractive index n (V) of the polymer-stabilized blue phase liquid crystal is 1 kHz. As the rectangular waveform voltage is applied, n (0) = 1.54 changes to n (150V) = 1.49, the refractive index changes isotropically about 0.05, and the response of the experimental element The speed was about 1 msec. In general, since the refractive index of liquid crystal changes according to the magnitude of the applied electric field, the same refractive index change can be obtained at a lower voltage as the electrode interval is narrower. Further, the response speed is substantially proportional to the square of the electrode interval, and the higher the electrode interval, the higher the response speed.

  That is, the distance between the electrodes constituting the diffraction element 10 of the present embodiment is the thickness of the isotropic refractive index solid material constituting the grating 2A (equal to the thickness of the isotropic refractive index liquid crystal 2B) d (= 7 μm). Therefore, the applied voltage for realizing the refractive index of the experimental element is about 7/10 of that of the experimental element, and the response speed is increased by 1 minsec or less because the distance between the electrodes is reduced. It becomes.

Difference △ n of the refractive index n _s of the refractive index n (V) and grating 2A isotropic refractive index liquid crystal 2B filled in the recess of the grating. 2A, n (0) at the time of non-voltage application = for n _s △ When n = 0, Δn = 0.05 when 105 V is applied, and an optical path length difference Δn × d = 0.35 μm between the optical path length of the grating 2A and the optical path length of the isotropic refractive index liquid crystal 2B is generated. . As a result, when a laser beam having a wavelength of λ = 633 nm is incident on the diffraction element 10, only 0th-order diffracted light that passes straight through is obtained at V = 0, as shown in FIG. Next-order diffracted light is generated and linearly transmitted light is reduced. Finally, at Vm (100 V or less) where Δn × d is λ / 2, as shown in FIG. 2B, the linearly transmitted light becomes almost zero.

  Therefore, as shown in FIG. 3, the aperture 12 of the aperture stop is disposed at the condensing point position of the convex lens 11, and the higher order diffracted light other than the 0th order diffracted light that is transmitted straight through is blocked, thereby increasing the magnitude of the applied voltage. Accordingly, the intensity-modulated outgoing light is obtained. Since both the grating 2A and the isotropic refractive index liquid crystal 2B have an isotropic refractive index that does not depend on the polarization of incident light, a diffractive element that exhibits voltage response independent of the polarization of incident light is obtained. Since the polarization direction of incident light does not change, a diffraction element applied to a wide range of applications can be realized.

In the diffraction element 40 whose sectional view is shown in FIG. 8, the optical film thickness (refractive index × film thickness) is λ / 4 with respect to the wavelength λ = 633 nm on the patterned transparent electrode films 3A and 3B. In addition, 16 layers of SiO ₂ films (as low refractive index dielectrics) and Ta ₂ O ₅ films (as high refractive index dielectrics) are alternately stacked to form a light reflection film (not shown) (hereinafter referred to as a dielectric multilayer reflection film). ) To form a reflective diffraction element. Since incident light reciprocates through the layer in which the grating 2A and the isotropic refractive index liquid crystal 2B are formed, the film thickness d of the grating 2A is set to 3.5 μm, which is half of that in the first embodiment. Further, in order to effectively apply a high electric field to the isotropic refractive index liquid crystal 2B at a low voltage, the lattice pitch P is set to 10 μm, and processing is performed so that the distance between the adjacent transparent electrode films 3A and 3B is 5 μm. Further, as the isotropic refractive index liquid crystal 2B, a chiral material, a monomer, and a polymerization initiator are mixed and used in a nematic liquid crystal having negative dielectric anisotropy. The constituent parts other than the above constituent parts are the same as those described in the diffraction element 40 described in the second embodiment of the present invention and the diffraction element 10 in Example 1.

  In the diffraction element of Example 2 thus formed, the electrode interval d is 5 μm corresponding to half of the experimental element of Example 1, so that the applied voltage can be almost halved and the response speed is also high. 1 msec or less.

Specifically, although the de-energized state is n (0) = refractive index difference for _{n s} △ _n = 0, at the time of 75V is applied △ n = 0.05 next, 2 × △ n × d for reflective = 0.35 μm optical path length difference occurs. As a result, when laser light having a wavelength of λ = 633 nm is incident on the diffraction element, 0th-order diffracted light (hereinafter referred to as regular reflected light, which is reflected by the dielectric multilayer reflective film in accordance with the normal reflection law when V = 0) Is referred to as regular reflection.) However, as the voltage V increases, higher-order diffracted light is generated and regular reflected light decreases. Eventually, Δn × d becomes Vm (about 75 V) at which λ / 4, and the regular reflection light becomes almost zero.

  Therefore, in the configuration shown in FIG. 7, the diffractive element of the second embodiment is used instead of the reflective diffractive element 30, and the light incident / incident end of the optical fiber 13 is arranged at the condensing point position of the convex lens 11. By transmitting only the 0th-order diffracted light normally reflected by the diffraction element of the second embodiment through the optical fiber 13, the reflected light whose intensity is modulated according to the applied voltage returns to the optical fiber 13 and propagates in the optical fiber 13 in a feedback manner. It will be.

As described above, the diffraction element according to the second embodiment of the present invention may be formed by patterning the electrode only on the substrate surface side on which the grating made of the isotropic refractive index solid material is formed. since the substrate surface facing electrode does not need to be an unnecessary and alignment can be simplified than the conventional device operation made steps.

In addition, the optical attenuator according to the second embodiment of the present invention is provided with the diffraction element having the electrode patterned only on the substrate surface side and the separating means, so that it does not depend on the state of incident polarized light and is equivalent to the conventional one. or it is possible to a more high-speed optical switching may be the extinction ratio stable, it can be simplified than the conventional process made device operation.

  The diffractive element and the optical attenuator according to the present invention do not depend on the incident polarized light, and the diffractive element and the optical attenuation are effective in that high-speed optical switching and extinction ratio equivalent to or higher than those of the conventional one can be stably obtained. It can also be used for purposes such as vessels.

The figure which shows notionally the cross-section of the diffraction element which concerns on the 1st Embodiment of this invention Explanatory drawing for demonstrating an example of the voltage response of the diffraction element which concerns on the 1st Embodiment of this invention Sectional drawing which shows notionally the structure using the condensing element of a convex lens and an aperture stop as a classification means The figure which shows notionally the cross-sectional structure of the diffraction element using the diffraction grating whose cross-sectional shape of an isotropic refractive index solid material is a sawtooth wave shape Explanatory drawing for demonstrating an example of operation | movement of the diffraction element shown in FIG. The figure which shows notionally the cross-section of the diffraction element of the structure which provided the light reflection film between the translucent substrate and the transparent electrode film The figure which shows notionally the cross-section of an example of the optical attenuator using the diffraction element shown in FIG. The figure which shows notionally the cross-section of the diffraction element which concerns on the 2nd Embodiment of this invention The figure which shows notionally the planar structure of the diffraction element shown in FIG. A diagram conceptually showing the cross-sectional structure of a conventional diffraction element

Explanation of symbols

1, 21 Diffraction grating 2A, 22A Grating 2B, 22B Isotropic refractive index liquid crystal 3, 3A, 3B, 4 Transparent electrode film 5, 6 Translucent substrate (glass)
DESCRIPTION OF SYMBOLS 7 Seal 8 Power supply 9 Light reflecting film 10, 20, 30, 40 Diffraction element 11 Convex lens 13, 13A, 13B Optical fiber optical transmission part 14 Light source 15 Projection screen 100 Liquid crystal element

Claims (2)

A substrate that transmits light;
A grating formed on the substrate using an isotropic refractive index solid material having an isotropic refractive index, the cross-sectional structure of which has periodic irregularities;
A cholesteric blue phase liquid crystal that fills at least a concave portion of the grating having the periodic irregularities, has a refractive index isotropically changed, and exhibits a cholesteric blue phase;
An electrode for applying a voltage to the cholesteric blue phase liquid crystal,
It consists diffraction grating by said grating and cholesteric blue phase liquid crystal, met diffraction element refractive index of the cholesteric blue phase liquid crystal has to be changed by a voltage applied through the electrodes constituting the diffraction grating And
The cholesteric blue phase liquid crystal is a polymer-stabilized cholesteric blue phase liquid crystal in which an expression temperature range of the cholesteric blue phase is expanded by containing a predetermined polymer material,
The electrode is provided between the substrate and the grid, and consists of a set of two electrodes to which linear electrodes along the grid adjacent to each other are connected,
A diffraction element in which a voltage is applied between adjacent electrodes via a set of the two electrodes. The high-order diffracted light of incident light generated by applying a voltage via the diffraction element according to claim 1 and an electrode of the diffractive element is separated from the 0th-order diffracted light of the incident light passing straight through the diffractive element. And a fractionating means for extracting the 0th-order diffracted light,
An optical attenuator configured to adjust the light amount of the 0th-order diffracted light according to the magnitude of the voltage applied through the electrode.

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