JP4920997B2 - Polarization control element, polarization control method and polarization control device - Google Patents

Description

  The present invention relates to a polarization control element having high efficiency, high heat resistance, and high light resistance that can be applied to a display device, optical measurement technology, optical equipment, measurement equipment, and the like. The present invention also relates to a polarization control element capable of modulating polarization characteristics with an external signal and a polarization control method thereof. Furthermore, the present invention relates to a polarization control device having the polarization control element.

  Conventionally, a polarization control element such as a polarizing plate or a wave plate transmits a single component in the polarization direction of incident light by providing anisotropy in propagation characteristics and absorption characteristics with respect to two orthogonal directions. Is a device that polarizes the polarization state from linearly polarized light to circularly polarized light. Such elements are used, for example, to turn on and off pixels of liquid crystal panels and organic EL (Electro Luminescence) displays, as well as optical measurement technologies such as ellipsometry (polarization analysis), laser interferometers, optical shutters, etc. It is used in various optical instruments and measuring instruments. In particular, there is an increasing demand for image projection devices such as liquid crystal projectors.

  A polarizing plate is an element that extracts a specific polarization component from naturally polarized light or polarized light, and transmits only one of the two orthogonally polarized components of incident light and absorbs (or reflects / scatters) the other. It is a shield. At present, many polarizing plates used in liquid crystal panels, in particular, absorb dichroism by dyeing and adsorbing dichroic materials such as iodine and organic dyes onto a substrate film such as polyvinyl alcohol, and then highly stretching and orienting them. Is expressed.

  On the other hand, a retardation plate (or phase shifter) such as a half-wave plate or a quarter-wave plate is made of a birefringent optical crystal, and the refractive index of ordinary and extraordinary rays depending on the orientation of the crystal. The polarization state is modulated by the difference between the two. A half-wave plate is a half-wave plate where the optical path difference between the ordinary ray and the extraordinary ray is ½ of the wavelength, and a quarter-wave plate is one-quarter. ). As such a material showing birefringence, calcite or quartz is used.

  By the way, a polarization control element using absorption is easily affected by heat, and when irradiated with high-intensity light, there are problems such as a decrease in transparency and scorching, and the amount of irradiation light cannot be increased. In addition, when the operating temperature conditions are severe and the projector is used in a liquid crystal projector or the like, a cold air mechanism is required, which makes it difficult to reduce the size of the device and causes image quality defects due to dust adhesion. .

  In addition, in the polarization control element utilizing the anisotropy of the refractive index, the optical crystal material exhibiting birefringence is limited, and there is a problem that the usable wavelength range is limited. In addition, since the film thickness, that is, the optical path difference is adjusted by bonding the optical crystal material and the polarization state is controlled, the dependence on the optical crystal material is strong and the degree of freedom of polarization controllability is low. In addition, there is a problem that it is difficult to reduce the size and thickness of the polarization control element itself.

Accordingly, the following conventional techniques are known for such problems.
First, a wire grid polarizer in which fine wires of gold or aluminum are formed on a transparent substrate has been proposed as a polarization control element excellent in heat resistance that can be manufactured at low cost with good mass productivity. This polarizing element has been put to practical use as a polarizing element that functions with respect to light having a wavelength longer than 2.5 μm.
Furthermore, a wire grid structure that can be driven at a visible wavelength (400 to 700 nm) as shown in the following prior art 1 has been proposed due to recent advances in microfabrication technology (see, for example, Patent Document 1).

  The problem in prior art 1 is to provide a wire grid polarizer that can provide high transmission and reflection efficiency over the entire visible spectrum. Another object of the present invention is to provide a wire grid polarizer capable of realizing high efficiency over a wide range of incident angles. As shown in FIG. 21, the solution is that the wire grid polarizer has a plurality of elongated elements 1240 supported on a substrate 1210, and a region 1250 having a refractive index lower than the refractive index of the substrate includes the elements and the substrate. The longest wavelength at which resonance occurs is reduced. Such a wire grid polarizer forms a microgrid structure with a visible wavelength by forming an aluminum thin film on one side of a transparent substrate and pattern-etching it. At this time, with respect to the fine line direction of the fine grid, the light whose polarization plane is orthogonal to the light is transmitted, and the light whose polarization plane is parallel is reflected. As a result, the incident angle dependency is relatively small, and a relatively good polarization separation function can be provided for the conical ray group.

  Further, as a method for realizing a wave plate or phase plate for controlling the polarization state by the interaction of light on a two-dimensional surface, a minute metal pattern is formed on a support substrate as shown in the following prior arts 2 and 3. Thus, a technique for controlling the polarization state has been proposed (see Non-Patent Document 1 and Patent Document 2).

  In Prior Art 2 (Non-Patent Document 1), as shown in FIG. 22, asymmetric nano-particles having a gold L-shaped structure with a pitch equal to or less than a wavelength are produced on a substrate using an electron beam lithography technique. . When such a structure is irradiated with light, as shown in the graph on the right side of FIG. 22, the transmitted light exhibits a different absorption spectrum depending on the direction of the polarization plane of the incident light. A polarized light selection element is realized. Second harmonic generation has also been observed due to symmetry disturbances.

  Prior Art 3 (Patent Document 2) relates to an optical device 210 having a saddle-shaped or C-shaped or mirror-symmetric metal pattern 214 on a smooth Si substrate 212 as shown in FIG. It is. The pattern size is 700 nm to 4 μm, and has a chirality in which the inclination of the end of the pattern is inclined from a right angle. Depending on the magnitude of this inclination, a phase difference occurs in two components of the polarization direction. Depending on the orientation of the pattern edge, a difference between clockwise and counterclockwise polarization occurs. In addition, an optical element that can control polarization characteristics by providing a piezoelectric layer has been proposed.

Special table 2003-502708 gazette International Publication No. 03/054592 Pamphlet Brian K. Canfield, et.al “Linear and nonlinear optical responses influenced by broken symmetry in an array of gold nanoparticles” Optics Express, vol. 12, No. 22, 5418-5423 (2004)

  The wire grid polarizer shown in the prior art 1 is a polarization separation element that transmits only polarized light components in one direction by reflecting or scattering incident light at a thin metal wire portion. In order to obtain a high extinction ratio, a substrate is used. Therefore, it is necessary to form a metal pattern having a high aspect ratio with respect to the vertical direction. In addition, there is a problem in that sufficient transmittance and extinction ratio cannot be obtained for light having a short wavelength due to manufacturing accuracy. Here, the extinction ratio is a ratio of two orthogonal polarization components in transmitted light. In addition, the wire grid polarizer is simply a polarization separation element, and in order to control the polarization state including the phase, it is necessary to use it in combination with the existing retardation plate, thermal damage of the retardation plate, There was a problem that the device could not be miniaturized.

  The prior art 2 has a function of an optical rotator capable of controlling the plane of polarization by a nano-sized metal pattern. This is because the use of light having a wavelength close to the resonance frequency of the metal makes the difference between absorption and scattering different. This is based on the principle of changing the polarization state by utilizing the directivity, and the light use efficiency with high loss cannot be obtained. Further, as shown in FIG. 22, since it is difficult to accurately produce a uniform asymmetric structure with the current processing technique, there is a problem that variations in shape occur and desired polarization control characteristics cannot be obtained. there were.

  Moreover, although the prior art 3 has the function of the retardation plate which converts linearly polarized light into elliptically polarized light using the chirality of the nano-sized metal pattern, a sufficiently large ellipticity is not obtained. In order to realize a practical half-wave plate or quarter-wave plate, a configuration such as multilayering is required. However, the volume of the metal portion is increased and absorption is increased, so that there is a problem that the light use efficiency is lowered. Further, when the structure becomes complicated like the optical element of the prior art 3, it is difficult to accurately produce a structure having uniform chirality due to a problem of processing accuracy. There was a problem that control characteristics could not be obtained.

  Furthermore, these conventional polarization control elements are passive optical elements having optical response characteristics unique to the elements. The more complex the functions to be realized, the more the number of optical elements increases, making the optical system smaller and lighter. There was a problem that restrictions would occur.

In view of the above-mentioned problems of the prior art, the present inventors have previously proposed as follows.
For example, in prior application 1 (Japanese Patent Application No. 2005-150072), a polarization control element having excellent heat resistance and light resistance, high light transmittance or high reflectance, and a polarization control element having a high degree of design freedom are provided. 24, as shown in FIG. 24, a metal composite structure 6 composed of two or more metal structures 2 arranged in a region below the wavelength of incident light and periodically arranged is formed on a substrate 1. Polarized light with high light transmittance, high phase flexibility, high heat resistance and light resistance, capable of giving a sufficient phase difference due to the structure formed above and interacting with near-field light A control element is proposed.

  In the prior application 2 (Japanese Patent Application No. 2005-150073), a polarization control element that has high light transmittance, can provide a sufficient phase difference, has a high degree of design freedom, and is excellent in heat resistance and light resistance. As an object to provide, as shown in FIG. 25, a metal structure (metal particle) 2 that is smaller than the wavelength of incident light is incident on a flat surface of a transparent substrate (for example, a glass substrate) 1. A two-dimensional arrangement with a distance smaller than the wavelength of light, which has high light transmittance, can provide a sufficient phase difference, has a high degree of design freedom, and has excellent heat resistance and light resistance. An element 10 is proposed.

  Furthermore, in the prior application 3 (Japanese Patent Application No. 2005-150074), as shown in FIG. 26, a glass substrate is realized with the object of providing a polarization control element having excellent heat resistance while realizing a wave plate that generates a phase difference. By continuously forming a pattern of a metal structure (first metal particle 2, second metal particle 3) made of two or more kinds of metals or alloys on a transparent substrate 1 such as A polarization control element 10 that realizes a wave plate that generates a phase difference in the polarization component of reflected light, has excellent heat resistance, and has a high degree of freedom in designing a polarization state is proposed.

  Further, in the prior application 4 (Japanese Patent Application No. 2005-150075), the support substrate on which the metal structures are arranged has a sub-wavelength structure, and a structure in which strong evanescent light is generated on the substrate surface layer is combined, and the near-field light and the evanescent light are combined. Thus, as shown in FIG. 27, the light emission and the light absorption are generated more strongly, and the control performance of the optical characteristics is improved. As shown in FIG. A polarization control element 10 in which a metal composite structure 6 composed of arranged metal structures 2 is formed on a transparent substrate 1 such as a glass substrate has been proposed. The surface has a periodic structure whose height is periodically modulated, and the periodic structure has a period smaller than the wavelength of the incident light.

In the prior applications 1 to 4, the metal structure 2 having a size equal to or smaller than the wavelength of the light to be irradiated is used, and a plurality of metal structures 2 are formed on the substrate 1 so as to be close to the nano size. By performing the control, a limitation due to processing accuracy and a decrease in absorption due to metal are realized. In addition, by selecting the metal material and the wavelength of the light to be irradiated, a large change in the polarization state is realized, and the polarization control characteristics are improved.
However, the above-mentioned prior applications 1 to 4 are a structure in which a metal structure is arranged on the substrate surface or a structure protected by a coating material, and damage caused by contact or fluctuation of the surface shape affects the polarization control characteristics. There are challenges. In addition, since the influence of the interaction between the metal structure and the surface via light is not taken into account, there is a problem that it is difficult to obtain a polarization control characteristic as designed.

The present invention has been made in view of the above circumstances, and has excellent heat resistance and light resistance, is resistant to external damage, has a thin element thickness, and has a light transmittance. Alternatively, it is an object to provide a polarization control element with high reflectivity, and further to provide an element configuration that can be easily manufactured.
The present invention also provides a configuration of a polarization control element with a high degree of freedom in design, a specific material of a metal structure that constitutes the polarization control element, and a unit arrangement pattern that constitutes the polarization control element. To provide a specific spatial arrangement, to provide a specific arrangement method of the composite arrangement pattern constituting the polarization control element, and to provide a specific material of the film constituting the polarization control element To do.
A further object of the present invention is to provide a multifunctional polarization control element having various polarization control functions.
A further object of the present invention is to provide a polarization control method for a polarization control element.
A further object of the present invention is to provide a polarization control device using a polarization control element.

In order to achieve the above object, the present invention employs the following technical means.
The first means of the present invention is a polarization control element, a unit arrangement pattern in which two or more minute metal structures are arranged in a region below the wavelength of incident light, and a single layer supporting the metal structure. It has the above film, and has a composite array pattern in which a plurality of unit array patterns are arranged in the same orientation in a two-dimensional plane inside the film.
The “metal structure” is based on a “metal material capable of exciting surface plasmons or localized surface plasmons” described later, and is “dot-like”, and two or more metal structures are spaced apart from each other at a predetermined interval. Are arranged apart from each other.
Specifically, the “dot shape” can be a “cylindrical shape” or a “hemispherical shape” as described later, but is the same shape.

According to a second means of the present invention, in the polarization control element of the first means, the reflectance of the film including the composite array pattern () made of one or more materials on the end face close to the composite array pattern It has an adjustment film.
According to a third means of the present invention, in the polarization control element of the first or second means, the metal material constituting the metal structure is gold (Au), silver (Ag), platinum (Pt), Any one of aluminum (Al), nickel (Ni), chromium (Cr), copper (Cu), or a combination thereof, or an alloy material / mixed material containing these as a main component It is characterized by.

According to a fourth means of the present invention, in the polarization control element of any one of the first to third means, the unit array pattern is composed of two metal structures with adjusted intervals and orientations. It is characterized by.
According to a fifth means of the present invention, in the polarization control element of any one of the first to third means, the unit arrangement pattern has an interval, an orientation, and an angle between two axes at which the metal structures are arranged. It is comprised by the three metal structures which adjusted these.
Furthermore, the sixth means of the present invention is the polarization control element according to any one of the first to third means, wherein the unit array pattern has four spacing, orientation, and spatial symmetry adjusted, Or it is comprised by the metal structure of more than that number, It is characterized by the above-mentioned.

In a seventh means of the present invention, in the polarization control element of any one of the first to sixth means, the spatial arrangement of the unit arrangement pattern constituting the composite arrangement pattern is a square lattice shape, a rectangular lattice shape, It is one of hexagonal lattice, stripe, concentric circle, and random.
The eighth means of the present invention is the polarization control element of any one of the first to seventh means, wherein the material constituting the film is a dielectric material, a metal material, a semiconductor material, or a birefringent material. The electro-optic crystal material, the electrostrictive material, the magnetic material, or a combination thereof.
Furthermore, a ninth means of the present invention is a multifunctional polarization control element, characterized in that it has a configuration in which a plurality of stages of polarization control elements of any one of the first to eighth means are stacked. .

  A tenth means of the present invention is a polarization control method, wherein the polarization control element of any one of the first to ninth means is used, and the polarization characteristic of the polarization control element is modulated by an external signal. And

  The eleventh means of the present invention is a polarization control device, comprising the polarization control element of any one of the first to ninth means, and means for modulating the polarization characteristic of the polarization control element by an external signal. It is characterized by that.

  The polarization control element of the first means realizes control of polarization characteristics using a metal structure that is an inorganic material, has excellent heat resistance and light resistance, and realizes an extremely thin polarization control element. Can do. In addition, since the metal structure is covered with a film, resistance to external damage can be realized. In addition, it is possible to realize a polarization control element that is very simple in shape, film configuration, and the like, and that can be easily manufactured.

In the polarization control element of the second means, the interaction between the metal structure and the film interface is controlled by the film configuration, and the polarization control characteristic can be modulated, so that the polarization control element has a high degree of design freedom. Can be realized.
Further, in the polarization control element of the third means, a polarization control element capable of adjusting the operating wavelength and the strength of interaction between metal structures by providing a specific metal material used for polarization control. Can be realized.

  In the polarization control elements of the fourth to sixth means, the specific configuration of the polarization control element is provided by providing the number of specific metal structures and the unit arrangement pattern for controlling the polarization state. can do.

In the polarization control element of the seventh means, by providing a specific composite array pattern of unit array patterns, it is possible to provide a configuration of the polarization control element according to the intended use.
Further, in the polarization control element of the eighth means, a passive type and an active type polarization control element can be realized by providing a specific film material constituting the polarization control element.
Further, the polarization control element of the ninth means has a configuration in which the polarization control elements of any one of the first to eighth means are stacked in a plurality of stages, and a plurality of surfaces including the metal structure are provided. Thus, a multifunctional polarization control element having various polarization control functions can be realized.

In the polarization control method of the tenth means, the polarization state of the incident light is obtained by using the polarization control element of any one of the first to ninth means and modulating the polarization characteristics of the polarization control element by an external signal. Can be easily controlled.
Further, in the polarization control device of the eleventh means, the polarization control element of any one of the first to ninth means and means for modulating the polarization characteristics of the polarization control element by an external signal (for example, electrical means, A polarization control device capable of easily controlling the polarization state of the polarization control element.

  Hereinafter, the configuration, operation, and effects of the present invention will be described in detail based on the illustrated embodiments.

[Example 1]
The present embodiment relates to a polarization control element according to the first, third, fourth, fifth, sixth, seventh and eighth means, a polarization control method according to the tenth means, and a polarization control apparatus according to the eleventh means.
The polarization control element, the polarization control method, and the polarization control apparatus of this embodiment will be described with reference to FIGS. FIG. 1 is a conceptual diagram illustrating the function of the polarization control element of this embodiment. The polarization control element 100 modulates the polarization state of the incident light 104 by utilizing a unit array pattern composed of a plurality of metal structures included in the polarization control element 100 and the light interaction, and is desired. The outgoing polarization state is taken out. FIG. 1 shows an example in which linearly polarized light of incident light 104 is converted into circularly polarized outgoing light 105 by the polarization control element 100, and functions equivalent to those of a conventional quarter-wave plate are realized by an in-plane structure. can do. In addition, since the conventional quarter wave plate uses the anisotropy of the crystal and utilizes the phase change according to the propagation distance, the film thickness of several wavelengths is necessary, and the material to be used is The performance was dependent.

  In addition to the example of FIG. 1, the polarization control element of this embodiment includes a half-wave plate that rotates linearly polarized light by 90 degrees, a polarizing plate that extracts linearly polarized light from random polarized light, and natural polarized light. It can be made to function as an element having a function of a circularly polarizing plate for extracting clockwise circularly polarized light or counterclockwise circularly polarized light.

  A configuration example of the polarization control element of this embodiment will be described with reference to FIG. 2A and 2B are a cross-sectional view and a top view showing one configuration example of the polarization control element of this embodiment. The polarization control element 100 of this embodiment includes a unit arrangement pattern 106 in which two or more minute metal structures 103 are arranged in a region below the wavelength of incident light, and one or more films 101 that support the metal structures 103. , 102, and a plurality of unit array patterns 106 are arranged in the same orientation in a two-dimensional plane inside the film. That is, the polarization control element 100 according to the present embodiment is in a two-dimensional plane within one of the two types of transparent films 101 and 102 (for example, the film 101) and separated from the interface between the film 101 and the film 102 by a distance h. A plurality of metal structures 103 are arranged, and two or more minute metal structures 103 are arranged in a region below the wavelength of incident light to form a unit arrangement pattern 106. A plurality of unit arrangement patterns 106 are arranged in the same orientation. It has the structure arranged by.

  In FIG. 2, the films 101 and 102 made of two kinds of materials are shown. However, the films need not be limited to two kinds, and at least one kind, that is, air and film, depends on the method of using the polarization control element 100. From a configuration having an interface of the above to a configuration having a multilayer structure can be used. For example, FIG. 3 is a cross-sectional view of a configuration in which the polarization control element 100 of the present embodiment is used in a reflective type, in which a reflective film 107 in which a metal material or a dielectric material is laminated is provided on the lowermost surface. In this case, the light interacting with the unit array pattern 106 is returned to the incident light side by the reflective film 107, and after interacting with the unit array pattern 106 again, it is emitted to the outside as reflected light 105b.

  As the material used for the film including the metal structure 103, the material described in the eighth means is used. When used as a passive element having an inherent function, a dielectric material, a birefringent material, and a metal material can be used. The dielectric material is used to control the strength of the interaction between the arrangement pattern and the light by the metal structure 103 and the operating wavelength by selecting the refractive index with respect to the wavelength of the incident light. The birefringent material can give anisotropy to the interaction between the unit array pattern 106 and light. Metallic materials are used to control absorption and phase. In addition, when used as an active element that modulates by applying an electric field or magnetic field by an electric field applying means or a magnetic field applying means from the outside, a semiconductor material, an electro-optic crystal material, an electrostrictive material, or a magnetic material can be used. The polarization control element 100 of this embodiment can externally modulate the polarization state by utilizing the fact that the polarization state changes greatly due to minute refractive index changes, displacements, magneto-optical effects, and the like. It is possible to configure a polarization control device that can easily control the above. Further, the above material completely covers the metal structure 103 and also plays a role of protecting the metal structure 103.

The dot-shaped minute metal structures 103 arranged inside the film 101 must have a size equal to or smaller than the diffraction limit (about the wavelength) of incident light, and are constituted by a plurality of metal structures 103. It is preferable that the size of the unit array pattern 106 to be performed is also less than or equal to the diffraction limit. The shape of the metal structure 103 is a cylindrical shape in FIG. 2, but it is sufficient that all the metal structures have the same shape. For ease of processing, the shape of the metal structure 103 is arbitrary such as a hemispherical shape. It doesn't matter. A method for manufacturing the metal structure 103 and the film 101 including the metal structure will be described with reference to FIGS.

  FIG. 4 is a diagram showing step by step the manufacturing procedure of the polarization control element. A dielectric film 112 is formed on a transparent support substrate (or film) 111 such as a glass substrate by using a deposition method such as a sputtering method, and a resist film 113 is laminated thereon (step 1). Subsequently, using electron beam lithography or the like, a desired arrangement pattern is exposed to form a mask pattern on the resist film 113 (step 2). Instead of electron beam lithography, a method of forming in a batch using near-field optical lithography or nanoimprint processing technology can also be applied. Thereafter, in order to produce a buried structure of a metal structure in the dielectric film 112, a concave pattern is produced by an etching technique such as reactive dry etching (step 3). Subsequently, a metal material is deposited by sputtering or vapor deposition to form a metal pattern 114 (step 4). Subsequently, unnecessary portions other than the metal structure are removed by a lift-off method accompanying the removal of the resist film 113, and further coated with a dielectric material 115 by a sputtering method or the like, so that the surface is flat and the dielectric film 101 The metal structures 103 arranged in the two-dimensional plane are prepared (step 5).

Next, an example of a different manufacturing method is shown in FIGS. Steps 1 and 2 are the same as the manufacturing procedure of FIG. Here, using the pattern of the resist film 113 as a mask, a metal material is deposited on the dielectric film 112 by sputtering or vapor deposition to produce the metal pattern 114 (step 3). Subsequently, unnecessary portions other than the metal structure are removed by a lift-off method that accompanies the removal of the resist film 113, and the convex metal structure 103 is manufactured. Finally, using a soft material such as the ultraviolet curable resin 116, the film 101 having the metal structure 103 which is cured by irradiating the ultraviolet ray UV to compensate for the smoothness of the surface is produced (step 4).

In the production method of FIG. 5, since a resin material is used for the film covering the metal structure 103, there is a problem in heat resistance. On the other hand, this embodiment is applied to a substrate material and a film material that are difficult to process. In the case of forming the polarization control element, it is a useful technique because a step of digging a substrate or a film is unnecessary. The material used for the support substrate or the film 111 is preferably a material having low absorption at a wavelength in the visible region in order to increase efficiency in the case of constituting a transmissive type element. , Borosilicate glass such as ZnS—SiO ₂ , optical crystal materials such as CaF ₂ , Si, ZnSe, Al ₂ O ₃ , and ZnO are used. In the case of constructing a reflective element, a material having high reflectance is preferable, and a metal film coating such as Al or Au is applied to the optical glass or optical crystal material. The film thickness at this time needs to be thicker than the skin depth at which light penetrates into the metal, and a film thickness of 30 nm or more is preferable. Moreover, what gave the total reflection coating by the dielectric multilayer film may be used. Further, when used as a beam splitter using both transmitted light and reflected light, a Cr coating or the like is used as a partial reflection film.

  Next, a specific configuration of the metal structure 103 will be described. The material of the metal structure 103 needs to be a material that can excite surface plasmons or localized surface plasmons. Here, the surface plasmon is a collective motion of electrons excited on the metal side of the interface region between the metal and the dielectric, and the localized surface plasmon is the entire metal material when the structure of the metal becomes minute. Collective motion of electrons excited over Hereinafter, both surface plasmons and localized surface plasmons are called plasmons. Plasmon couples with the electromagnetic field in the vicinity of the metal structure, is converted into a propagating light component, and is emitted to the far field. The conversion efficiency to propagating light is maximized near the resonance wavelength determined by the metal structure 103. As a metal material that can excite plasmons, any one of Au, Ag, Pt, Al, Ni, Cr, and Cu described in the third means, or an alloy material mainly composed of these, spatially combined with these. Arranged configurations and mixed materials composed of these and non-metallic materials can be used. The metal structure 103 needs to be sufficiently smaller than the diffraction limit of incident light, and in addition, in order for the light transmitted through the polarization control element 100 of this embodiment to be spatially uniform, a plurality of The unit array pattern 106 made of the metal structure 103 is also preferably smaller than the diffraction limit of light. Due to both restrictions of the metal structure 103 and the unit arrangement pattern, the size of the metal structure 103 is limited depending on the wavelength of light used. Specifically, if it is 100 nm or less, it can be used for the entire visible light region. In the light irradiated from a distance or the light observed in a distance, the arrangement and shape of the unit array pattern 106 are not observed due to the limitation due to the diffraction limit of light. However, due to the interaction between the plasmon generated in the unit array pattern 106 and the plasmon via the near-field light, the phase difference with respect to the emitted light intensity and the vibration direction changes depending on the size and arrangement of the metal structure 103. To do. Here, the near-field light refers to an electromagnetic field in a local region that exists in combination with plasmons without releasing energy into free space.

  Next, the principle of changing the polarization state by the unit array pattern 106 will be described based on the result of numerical simulation using the simplest configuration of two metal dots (for example, Au spheres). The numerical simulation utilized a finite time domain difference method (FDTD method) that solves the Maxwell equation describing the motion of an electromagnetic field by approximating it to a space-time difference equation. FIG. 6 is a model used for the simulation, in which the distance d between adjacent ends of two metal structures (Au spheres) 103 having a size (diameter) of 40 nm existing in the air is changed from 0 to 80 nm. The polarization state in the reflected far field was calculated. In order to obtain the characteristics of far-field light from the electric field distribution in the vicinity of the unit array pattern of the Au sphere 103 obtained by the FDTD method, as shown in FIG. 6A, the angle θ = 0 ° is obtained by Fourier transform of the electric field distribution. The components were extracted, and the amplitude ratio and phase difference between the x and y directions as shown in FIG. 6B were calculated. A calculation was performed to irradiate a plane wave having a vibration direction of an electric field in the direction of 45 ° from the x axis in the xy plane shown in FIG. As the optical constant of Au, refractive index n = 0.072 and k = 1.497 were used. FIG. 7 is a graph plotting the distance dependence of the amplitude ratio. In a region where d is large, the amplitude ratio approaches 1 and the polarization plane (the vibration direction of the electric field) matches the polarization direction of the incident light. I can confirm. On the other hand, the amplitude ratio increases as it approaches d = 0, that is, the polarization plane tilts in the y direction. On the other hand, FIG. 8 shows the phase difference between the x component and the y component of the electric field. As d approaches zero, the phase difference increases. When d = 0 (when the Au sphere comes into contact), the phase difference is about 45 °. This means that linearly polarized light has been converted to elliptically polarized light. From the simulation results by the FDTD method described above, it can be seen that the plane of polarization can be rotated by controlling the interval between the Au spheres, and the polarization state can be converted from, for example, linearly polarized light to elliptically polarized light.

  A similar calculation result can be obtained when an Ag sphere is used as the metal material. In this case, the wavelength region where the polarization state changes is in the vicinity of the wavelength of 400 nm, which is near the plasmon resonance wavelength of the Ag sphere, and the ultraviolet region. It was. However, the plasmon resonance wavelength, that is, the operating region of the polarization control element of this embodiment can be adjusted by the refractive index of the material covering the metal structure 103. The plasmon resonance wavelength also depends on the size of the metal structure 103, and the operating wavelength can be adjusted by controlling the size. In order to confirm the effect of the covering medium of the metal structure 103, the change in the plasmon resonance wavelength was analytically calculated using the Mie scattering theory. 9 to 11 are diagrams showing the electric field strength at the center of a single Au sphere calculated by the Mie scattering theory. FIG. 9 shows air (n = 1.0), and FIG. 10 shows a plastic film (n = 1). .3) and FIG. 11 show the results when three types of materials of polycarbonate (n = 1.5) are used as coating materials. These materials are not particularly limited, and a refractive index material having a plasmon resonance wavelength of an Au sphere in the vicinity of the center wavelengths of three colors of red, green, and blue (RGB) of the display device is selected. Moreover, FIGS. 12-14 is the calculation which performed the same calculation with respect to Ag sphere, FIG. 12 is polycarbonate (n = 1.5), FIG. 13 is ZnO (n = 2.1), FIG. It is a result at the time of applying ZnS-SiO2 (n = 2.3) as a coating material corresponding to three colors of RGB, respectively. From the above results, it is possible to select the operating wavelength of the polarization control element of this embodiment by selecting a material covering the metal structure having a suitable refractive index. 9 and 12, the plurality of curves are the results when the diameter of the Au sphere or Ag sphere is changed from 10 nm to 50 nm in increments of 10 nm (that is, FIGS. 9 to 14). A = 10 nm, b = 20 nm, c = 30 nm, d = 40 nm, e = 50 nm). As can be seen from this result, by adjusting the size of the metal structure 103, the resonance wavelength of the plasmon can be controlled within a range of about 50 nm.

In order to design the polarization control element of this embodiment, it is necessary to arrange two or more metal structures so that desired polarization characteristics appear.
FIG. 15 shows an arrangement method when 2 to 5 metal structures 103 are used (fourth to sixth means). FIG. 15A shows a case where the unit array pattern 106 formed of two metal structures 103 is used, and depends on the orientation of the unit array pattern 106 with respect to the polarization direction of incident light and the distance between the metal structures 103. As a result, the amplitude ratio and the phase difference change. That is, the functions of the optical rotator and the wave plate can be realized. FIG. 15B shows a case where the unit array pattern 106 using three metal structures 103 is used, and by adjusting the angle θ between the two array axes in addition to the interval between the metal structures 103, FIG. The polarization state can be controlled. In the case of θ = 90 ° (the right diagram in FIG. 15B), it is L-shaped. In such an arrangement, the function of a polarization selection element that extracts linearly polarized light from natural polarized light can be realized by using the effect of interference of horizontal and vertical plasmon waves in addition to an optical rotator and a wave plate. FIG. 15C shows a configuration using the unit arrangement pattern 106 of four metal structures 103, the left figure is line-symmetric with respect to the center line, the center figure is 180 ° rotationally symmetric, and the right figure is rotated 360 °. The configuration matches the original arrangement. When four metal structures 103 are used in this way, spatial symmetry can be used to control the polarization state. Thereby, in addition to the function of an optical rotator, a wave plate, and linearly polarized light selection, a function having polarization selectivity for circularly polarized light can be realized. Furthermore, as shown in FIG. 15D, by using the unit array pattern 106 of five or more metal structures 103, it is possible to control a more complicated polarization state.

  Next, the configuration of the composite array pattern based on the array of unit array patterns 106 will be described. FIGS. 16A, 16B, and 16C are each a unit arrangement pattern 106 (two metal structures 103 in the figure), but may be two or more metal structures. 2) is a top view showing a configuration example of a polarization control element having a composite array pattern in which a square lattice shape, a rectangular lattice shape, and a hexagonal lattice shape are arranged. When arranged in a hexagonal lattice, the unit array pattern 106 can be filled with the highest density. On the other hand, when arranged in a rectangular lattice, anisotropy occurs in the light intensity distribution in the transmitted or reflected far field. The symmetry and period are adjusted according to desired characteristics such as beam shape and efficiency, respectively. FIGS. 16D and 16E are configuration examples of a polarization control element having a composite array pattern in which unit array patterns 106 are arranged in stripes. The orientation of the metal structure 103 and the unit array pattern 106 are shown in FIGS. There are cases where the orientations of the arrays are orthogonal and cases where the arrangements are arranged in parallel, and the transmittance, reflectance, and polarization selectivity for incident polarized light are different. FIG. 16F is a configuration example of a polarization control element having a composite array pattern in which unit array patterns 106 are arranged concentrically. By adjusting the distance between the concentric circles, a condensing effect similar to a Fresnel lens can be realized, and a polarization control element having both polarization control characteristics and beam condensing characteristics can be realized. FIG. 16G is a configuration example of a polarization control element having a composite array pattern in which unit array patterns 106 are randomly distributed, and the polarization control characteristics are determined depending only on the orientation of the unit array pattern 106. For this reason, the requirements for the fabrication accuracy of the polarization control element of this embodiment are relaxed.

  Next, the effect at the interface of the film including the metal structure 103 will be described. FIGS. 17A and 17B are diagrams for explaining the contribution at the observation point 123 when the metal structure 103 is provided on the film 101 and when the metal structure 103 is provided inside the film 101. is there. Although only one metal structure 103 is shown for simplicity, the metal structure 103 actually forms the unit arrangement pattern 106 described above. In addition, although the configuration uses reflected light, the same applies to the case of transmitted light. In the case of FIG. 17A, the incident light 104 is scattered by the metal structure 103, but the light detected at the observation point 123 is a component of light (scattered light 121) that reaches the observation point directly from the metal structure 103. ) And a component (scattered light 122) that reaches the observation point 123 after being reflected by the interface of the film 101. This is equivalent to the presence of a virtual electric dipole 120 at the mirror image point inside the film 101 as indicated by an arrow in FIG. 17A, and the metal structure 103 is close to the interface of the film 101. In this case, the electric dipole moment of the metal structure 103 is canceled out, so that the magnitude of the electric dipole moment is reduced. On the other hand, in the case of FIG. 17B, since the metal structure 103 is arranged at a distance h from the interface between the film 101 and the film 102, the influence of the interface is small, and the magnitude of the electric dipole moment is reduced. It can be used well, that is, the polarization control characteristics such as optical rotation and phase shift of the unit array pattern 106 by the plurality of metal structures 103 can be improved. Further, the polarization characteristic can be controlled by adjusting the distance h. Since the polarization state is affected when the distance h changes by about the size of the metal structure 103, the polarization characteristics are controlled by adjusting the distance by about the size.

  As described above, the polarization control element of this example includes the material of the metal structure 103, the material of the film 101 covering the metal structure 103, the distance between the metal structures, and the array pattern (unit array pattern 106 and composite array). By adjusting the pattern h) and the distance h between the film interface and the metal structure 103, it is possible to design various polarization characteristics. In addition, since an inorganic metal material is used for polarization control, it is excellent in heat resistance and light resistance, and the metal structure 103 is included in the film, so that it is resistant to external damage. In addition, since a complicated structure is not required, a polarization control element that is easy to manufacture can be realized.

  Further, the polarization control element 100 of the present embodiment and means for modulating the polarization characteristics of the polarization control element by an external signal (for example, an electric means for applying an electric field or a voltage, a magnetic means for applying a magnetic field, and a control light are emitted. A polarization control device capable of easily controlling the polarization state of the polarization control element can be realized.

[Example 2]
The present embodiment relates to a polarization control element according to the second, third, fourth, fifth, sixth, seventh and eighth means, a polarization control method according to the tenth means, and a polarization control apparatus according to the eleventh means.
The polarization control element of this embodiment will be described with reference to FIGS. FIG. 18 is a cross-sectional view illustrating a configuration example of the polarization control element 110 of this embodiment. As in the first embodiment, the polarization control element 110 according to the present embodiment is a unit array in which a metal structure 103 having a size smaller than or equal to the diffraction limit (approximately the wavelength) of incident light is disposed adjacent to a region less than the diffraction limit. The pattern 106 has a structure that is regularly or randomly arranged. A difference from the first embodiment is that, as shown in FIG. 18A, a reflectance adjusting film 108 is provided at a position separated by a distance h from the surface on which the metal structures 106 are arranged. Further, as shown in FIG. 18B, a configuration having the reflectance adjustment film 108 in the surface layer portion may be employed.

  Similar to the description of the first embodiment, the metal structure 103 needs to use a metal material that can excite plasmons, and any of Au, Ag, Pt, Al, Ni, Cr, and Cu described in the third means. Alternatively, an alloy material mainly composed of these materials, a configuration in which these are combined and spatially arranged, or a mixed material composed of these and a non-metallic material can be used. The shape of the metal structure 103 may be an arbitrary shape as long as all the metal structures such as a columnar shape and a hemispherical shape are aligned. As shown in FIG. 15, the unit array pattern 106 composed of a plurality of metal structures 103 uses 2 to 4 metal structures 103, and the distance, orientation, and spatial symmetry between the metal structures. Apply the adjustment of gender. Further, as shown in FIG. 16, a composite array pattern composed of a plurality of unit array patterns 106 is a regular array such as a square lattice, a rectangular lattice, a hexagonal lattice, a stripe, or a concentric circle, or a random array. To place. Such an arrangement pattern of the metal structures 103 can be manufactured by the film formation by sputtering shown in FIG. 4 or FIG. 5 and the etching technique using electron beam exposure and lift-off methods. The principle of polarization control is also as described in the first embodiment, and plasmons excited in a plurality of metal structures interact with each other between adjacent metal structures via near-field light. This is because anisotropy appears in amplitude and phase with respect to the axis of the structure array.

  As shown in FIG. 18A, the films 101 and 102 disposed above and below the reflectance adjusting film 108 are those described in the eighth means, and are used as passive elements having unique functions. Dielectric materials, birefringent materials, and metal materials can be used. In addition, when used as an active element that modulates by applying an electric field or a magnetic field by an electric field applying unit or a magnetic field applying unit from the outside, a semiconductor material, an electro-optic crystal material, an electrostrictive material, or a magnetic material is used.

  The reflectance adjustment film 108, which is a feature of the polarization control element 110 of the present embodiment, plays a role of adjusting the interaction between the film interface and the metal structure 103 shown in FIG. In FIG. 17B, the reflection at the boundary surface between the film 101 and the film 102 changes the polarization characteristic at the observation point. However, the polarization characteristic is adjusted by providing the reflectance adjustment film 108 and adjusting the reflectance at the boundary surface. Can be controlled. In addition, a decrease in the amount of change in polarization characteristics due to reflection at the upper interface of the film 102 in FIG. 18A or the film 101 in FIG. 18B is suppressed by providing the reflectance adjustment film 108. It is possible.

The material constituting the reflectivity adjusting film 108 is a general thin film material, such as a metal material such as Al, Au, and Ag, MgF ₂ , CeF ₃ , Al ₂ O ₃ , AiO ₂ , ZrO ₂ , TiO ₂ , Dielectric materials such as ZnS and ZnS—SiO ₂ can be used. By combining these materials, an antireflection film, a total reflection film, or a partial reflection film can be formed as the reflectance adjustment film 108. As a result, the magnitude of the electric dipole moment at the mirror image position shown in FIG. 17B can be adjusted, and the polarization state can be controlled by the characteristics of the reflectance adjusting film 108.

  In the polarization control element of this example, in addition to the material of the metal structure 103, the material of the film 101 covering the metal structure 103, the distance between the metal structures and the arrangement pattern, the film interface and the metal structure 103 By adjusting the light interaction between the two by the configuration of the reflectance adjustment film 108, various polarization characteristics can be designed. In addition, since an inorganic metal material is used for polarization control, it is excellent in heat resistance and light resistance, and the metal structure 103 is included in the film, so that it is resistant to external damage. In addition, since a complicated structure is not required, a polarization control element that is easy to manufacture can be realized.

  Further, the polarization control element 100 of the present embodiment and means for modulating the polarization characteristics of the polarization control element by an external signal (for example, an electric means for applying an electric field or a voltage, a magnetic means for applying a magnetic field, and a control light are emitted. A polarization control device capable of easily controlling the polarization state of the polarization control element can be realized.

[Example 3]
The present embodiment relates to a polarization control element according to a ninth means, a polarization control method according to the tenth means, and a polarization control device according to the eleventh means.
The polarization control element of the present embodiment will be described based on FIGS. 4, 5, 15, 16, 19, and 20. The polarization control element of this example has a film 101 including a metal structure 103 similar to that of Example 1 or Example 2, and has a configuration in which the film 101 is laminated in a plurality of stages. FIG. 19 is a cross-sectional view showing an example of the polarization control element 130 of the present embodiment. The unit array pattern 106-1 of the metal structure 103 is formed in two two-dimensional planes inside the film 101 made of the same material. , 106-2 are formed. In FIG. 19, a two-layered structure is shown for simplicity, but a structure having two or more stages may be used. The material used for the film (or support substrate) 102 is the one described in the eighth means. When used as a passive element having a specific function, a dielectric material, a birefringent material, or a metal material is used. Available. In addition, when used as an active element that modulates by applying an electric field or magnetic field from the outside by an electric field applying means or a magnetic field applying means, a semiconductor material, an electro-optic crystal material, an electrostrictive material, or a magnetic material is used.

  Similarly to the description of the first embodiment, the polarization control element 130 of the present embodiment also needs to use a metal material that can excite plasmons. As described in the third means, Au, Ag, Pt, Any one of Al, Ni, Cr, and Cu, or an alloy material mainly composed of these materials, a structure in which these are combined and spatially arranged, and a mixed material composed of these and a non-metallic material can be used. The shape of the metal structure 103 may be an arbitrary shape as long as all the metal structures such as a columnar shape and a hemispherical shape are aligned. As shown in FIG. 15, unit array patterns 106-1 and 106-2 composed of a plurality of metal structures 103 use 2 to 4 metal structures 103, and the distance and orientation between the metal structures. Apply a spatial symmetry adjustment. Further, as shown in FIG. 16, a composite array pattern composed of a plurality of unit array patterns 106 is a regular array such as a square lattice, a rectangular lattice, a hexagonal lattice, a stripe, or a concentric circle, or a random array. To place. Such an arrangement pattern of the metal structures 103 can be manufactured by the film formation by sputtering shown in FIG. 4 or FIG. 5 and the etching technique using electron beam exposure and lift-off methods. The principle of polarization control is as described in the first embodiment, and plasmons excited in a plurality of metal structures interact with each other through near-field light, so that the axis of the metal structures is aligned. On the other hand, anisotropy appears in amplitude and phase.

  Next, an example of the function of the polarization control element 130 of this embodiment will be described. In FIG. 19, unit array patterns 106-1 and 106-2 of the same metal are used, the unit array pattern 106-1 is a 1/4 wavelength plate function (function 1), and the unit array pattern 106-2 is a polarizing plate function (function). 2), the distance between the metal structures 106, the arrangement, and the distance h from the boundary surface can be designed to realize a polarization selection element that extracts circularly polarized light from natural polarized light. Further, with the same configuration, when the film 102 in FIG. 19 is a metal film or a total reflection multilayer film, a reflection-type polarization conversion element that converts natural polarized light into only a unidirectional polarization component can be realized. Further, when the unit array patterns 106-1 and 106-2 are designed to have the same optical rotation function, an optical rotation element having a thin element and a large optical rotation angle can be realized.

  FIG. 20 is a cross-sectional view showing another configuration example of a polarization control element having different functions. In the polarization control element 140 of this configuration example, an example is shown in which different metal materials are used for the metal structures 103-1 and 103-2 in two stages. In this case, since the resonance wavelengths of plasmons excited in the metal structure are different, the polarization control in which the unit arrangement patterns 106-1 and 106-2 independently generate a polarization selection function and a phase shift function for a specific wavelength. Operates as an element. Here, the materials of the film 101 and the film 102 including the respective unit array patterns 106-1 and 106-2 need to have an appropriate refractive index in order to select an operating wavelength as desired. The example of the polarization control element of FIG. 19 or FIG. 20 has unit arrangement patterns 106-1 and 106-2 configured in two stages. However, even if the unit array pattern is configured to use a plurality of stages of three or more stages. Good.

As described above, the polarization control element of the present embodiment has been compounded by providing a single configuration having a specific polarization control function in multiple stages, thereby improving the efficiency of the polarization control function, Various polarization control functions such as polarization conversion and linear / circular polarization extraction can be realized with a single optical element.
Further, the multifunctional polarization control element of this embodiment and means for modulating the polarization characteristics of the polarization control element by an external signal (for example, electrical means for applying an electric field or voltage, magnetic means for applying a magnetic field, control light With a configuration including an optical means for irradiating and a mechanical means for applying pressure, vibration, etc. to the element, a polarization control device having various polarization control functions can be easily realized.

  As described above, according to the present invention, a polarization control element having high efficiency, high heat resistance, and high light resistance and capable of modulating polarization characteristics by an external signal, and a polarization control device using the polarization control element Can be realized. The polarization control element and the polarization control device are suitable for a display device such as a liquid crystal projector, and can be used for optical measurement technology, optical equipment, measurement equipment, and the like.

It is a conceptual diagram explaining the function of the polarization control element which concerns on this invention. FIG. 2 is a cross-sectional view illustrating a configuration example of a polarization control element according to a first embodiment of the present invention and a top view. It is sectional drawing which shows another structural example of the polarization control element of the 1st Example of this invention. It is a figure explaining an example of the preparation procedures of the polarization control element of the 1st Example of this invention. It is a figure explaining another example of the preparation procedures of the polarization control element of the 1st Example of this invention. It is a figure explaining the numerical simulation model of the unit arrangement pattern of a metal structure. It is a figure which shows the calculation result of the amplitude ratio obtained by numerical simulation. It is a figure which shows the calculation result of the phase difference obtained by numerical simulation. It is a figure which shows the wavelength dependence by the combination of Au bulb | ball and the coating material (air) derived | led-out by the Mie scattering theory. It is a figure which shows the wavelength dependence by the combination of Au bulb | ball and the coating material (plastic film) derived | led-out by the Mie scattering theory. It is a figure which shows the wavelength dependence by the combination of Au sphere derived | led-out by the Mie scattering theory, and coating material (polycarbonate). It is a figure which shows the wavelength dependence by the combination of Ag sphere derived | led-out by the Mie scattering theory, and coating material (polycarbonate). It is a figure which shows the wavelength dependence by the combination of Ag sphere derived | led-out by the Mie scattering theory, and coating material (ZnO). It is a diagram showing the wavelength dependence of the combination of derived by Mie scattering theory Ag spheres and the coating material (ZnS-SiO _2). It is a figure explaining the example of the unit arrangement | sequence pattern by a some metal structure. It is a figure explaining the example of the compound arrangement pattern by a plurality of unit arrangement patterns. It is a figure explaining the effect by the distance of a metal structure and a film interface. It is sectional drawing explaining the structural example of the polarization control element of the 2nd Example of this invention. It is sectional drawing which shows the structural example of the polarization control element of the 3rd Example of this invention. It is sectional drawing which shows another structural example of the polarization control element of the 3rd Example of this invention. It is a figure explaining prior art 1. FIG. It is a figure explaining the prior art 2. FIG. It is a figure explaining the prior art 3. FIG. It is a figure explaining prior application 1. FIG. It is a figure explaining prior application 2. FIG. It is a figure explaining prior application 3. FIG. It is a figure explaining prior application 4. FIG.

Explanation of symbols

100, 110: Polarization control element 101: Film 102: Film (or supporting substrate)
103, 103-1, 103-2: Metal structure 104: Incident light 105: Emission light 105a: Transmitted light 105b: Reflected light 106, 106-1, 106-2: Unit arrangement pattern 107: Reflective film 108: Reflectance Adjustment membrane 109: membrane (or support substrate)
130, 140: Multi-functional polarization control element

Claims (11)

By a metal material capable of exciting surface plasmons or localized surface plasmons, the dot-like metal structure of the same shape in two or more micro and mutually arranged with intervals a predetermined interval in the following areas wavelength of incident light units An array pattern,
Characterized in that it has the metal structure has one or more layers of film which supports a plurality of the composite array pattern unit array patterns are arranged with the same orientation in a two-dimensional plane of the inner membrane A polarization control element. The polarization control element according to claim 1,
A polarization control element comprising a reflectance adjusting film made of one or more materials on an end face of the film including the composite array pattern, which is close to the composite array pattern. The polarization control element according to claim 1 or 2,
The metal material constituting the metal structure is any one of gold (Au), silver (Ag), platinum (Pt), aluminum (Al), nickel (Ni), chromium (Cr), and copper (Cu). Or a combination thereof, or a polarization control element comprising an alloy material / mixed material containing these as a main component. The polarization control element according to any one of claims 1 to 3,
The polarization control element, wherein the unit array pattern is composed of two metal structures whose spacing and orientation are adjusted. The polarization control element according to any one of claims 1 to 3,
The polarization control element, wherein the unit array pattern is composed of three metal structures in which an interval, an orientation, and an angle between two axes for arranging the metal structures are adjusted. The polarization control element according to any one of claims 1 to 3,
The polarization control element, wherein the unit array pattern is composed of four or more metal structures whose spacing, orientation, and spatial symmetry are adjusted. In the polarization control element according to any one of claims 1 to 6,
The polarization control element characterized in that the spatial arrangement of the unit arrangement patterns constituting the composite arrangement pattern is any one of a square lattice, a rectangular lattice, a hexagonal lattice, a stripe, a concentric circle, and a random. In the polarization control element according to any one of claims 1 to 7,
The material constituting the film is composed of a dielectric material, a metal material, a semiconductor material, a birefringent material, an electro-optic crystal material, an electrostrictive material, a magnetic material, or a combination thereof. A polarization control element. A multifunctional polarization control element,
A polarization control element having a configuration in which the polarization control element according to claim 1 is stacked in a plurality of stages.   A polarization control method using the polarization control element according to claim 1, wherein the polarization characteristic of the polarization control element is modulated by an external signal.   A polarization control device comprising: the polarization control element according to claim 1; and means for modulating polarization characteristics of the polarization control element by an external signal.

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