JP2012123327A - Circular dichroic element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a circular dichroic element which has a degree of circular dichroism σ of 0.75 or more and an efficiency factor ε of 25 or more and has a thickness smaller than a wavelength of an incident plane wave and is capable of controlling a polarization state of a transmitted plane wave into linearly polarized light or light polarized circularly in the same direction as incident circularly polarized light or in the opposite direction.SOLUTION: A circular dichroic element 101 is used. The circular dichroic element 101 has a laminate structure of a quarter-wave plate 1 and an anisotropic transmission plate 2 and has a sub-wavelength thickness, and the quarter-wave plate is capable of converting circularly polarized light of one plane wave 5 selected from a wavelength region from 400 to 1600 nm into linearly polarized light, and the anisotropic transmission plate 2 has a high transmission axis in a linear polarization direction of the one plane wave 5.

Description

The present invention relates to a circular dichroic element that causes circular dichroism in electromagnetic waves.

Circular dichroism means that the transmittance when the incident plane wave is clockwise and counterclockwise circularly polarized light is expressed as TR and TL, respectively, when TR = TL, there is no circular dichroism, and otherwise, That is, it is defined that there is circular dichroism when TR> TL or TR <TL.
A circular dichroic element is an element exhibiting circular dichroism.
The wavelength of the incident plane wave that functions as a circular dichroic element is called the operating wavelength of the circular dichroic element.

A plane wave is defined as circularly polarized when an electric field vector of a plane wave at an arbitrarily fixed time forms a circular rotational distribution around a wave vector defining the traveling direction. Here, the plane wave is an electromagnetic wave whose distribution is represented by a function exp (ik · r−iωt). However, i is an imaginary unit, k is a wave vector of electromagnetic waves, r is a three-dimensional Euclidean space coordinate, ω is an angular frequency of electromagnetic waves, and t is time.

FIG. 23 is a conceptual diagram showing an example of counterclockwise circularly polarized light.
As shown in FIG. 23, when the electric field vector 15 at an instant fixed with respect to the wave vector 14 forms a left-handed screw-like distribution, the plane wave is defined as counterclockwise circularly polarized light. The wave vector 14 is a vector representing the traveling direction of the plane wave. In FIG. 23, the change of the electric field vector 15 for one wavelength of light is displayed in 8 steps.

FIG. 24 is a conceptual diagram showing an example of clockwise circularly polarized light.
As shown in FIG. 24, when the instantaneous radio wave vector 17 arbitrarily fixed with respect to the wave vector 16 forms a right-handed distribution, the plane wave is defined as clockwise circularly polarized light. An electric field vector 17 is generated from a wave vector 16 representing the traveling direction of a plane wave. In FIG. 24, changes in the electric field vector 17 for one wavelength of light are displayed in 8 steps.

FIG. 25 is a conceptual diagram showing an example of circular dichroism, and schematically shows a situation where circular dichroism is remarkable.
When it is assumed that the incident plane wave of the wave vector 19 is clockwise circularly polarized light 20 and the light incident on the wave vector 21 is counterclockwise circularly polarized light 22 on the circular dichroic element 18, the transmitted plane wave represented by the wave vector 23 is used. This shows a case where the transmittance TR of the transmission plane wave represented by the wave number vector 24 is 1% or less, whereas the transmittance TR of is 50% or more.

The degree of circular dichroism is quantitatively represented by the degree of circular dichroism σ defined by (TR−TL) / (TR + TL).
When there is no circular dichroism, σ = 0. When there is circular dichroism, σ ≠ 0 is always satisfied. In particular, when the transmittance of counterclockwise circularly polarized light is 0%, that is, when TL = 0, σ = 1. The situation shown in FIG. 25 corresponds to this case. On the other hand, when the transmittance of clockwise circularly polarized light is 0%, that is, TR = 0, σ = −1. As described above, the maximum circular dichroism is expressed as | σ | = 1.

A circular dichroic element can be evaluated by an efficiency factor ε defined by max (TR, TL) × | σ |.
Here, max (TR, TL) represents the larger value of TR and TL. The larger the efficiency factor ε, the better the circular dichroic element. ε = 100 is an ideal circular dichroic element. If ε ≧ 60, it is evaluated as a high-performance circular dichroic element, and if ε ≧ 25, it is evaluated as a circular dichroic element that contributes to practical use.

In addition, the circular dichroic element can be evaluated by an efficiency factor α having a structure defined by λ / d.
Here, λ represents the wavelength of light in vacuum, and d represents the thickness of the circular dichroic element. The structural efficiency factor α is an index for quantitatively expressing how thin a circular dichroic element can be realized. For example, the efficiency factor α of the structure of a circular dichroic element having a thickness d of 250 nm is 2 for light having a wavelength λ of 500 nm. In other words, when the structural efficiency factor α ≧ 1, it means that a circular dichroic element having a size smaller than the wavelength of the plane wave to be irradiated (hereinafter referred to as a sub-wavelength size) can be realized. This means that the larger the structure efficiency factor α, the thinner the circular dichroic element can be realized.
The circular dichroic element can be evaluated in a multifaceted and comprehensive manner by the circular dichroism degree σ, the efficiency factor ε, and the structural efficiency factor α.

Regarding the circular dichroism, there are many research examples regarding the circular dichroism inherent in an insulator material or a semiconductor material and the circular dichroism in a solid medium in which a magnetic ion is slightly doped. However, there are almost no studies on circular dichroic elements having a large contrast such that the circular dichroism σ exceeds 0.5.

In addition, there are many research examples of circular dichroic elements that are thick to the centimeter order. For example, a circular dichroic element having a thickness d of 1 × 10 ⁻² m for light having a wavelength λ of 500 × 10 ⁻⁹ m. Therefore, the efficiency factor α of the structure takes a very small value of 5 × 10 ⁻⁵ and is much thicker than the wavelength of light. On the other hand, there are research examples of circular dichroic elements, but there are few research examples of circular dichroic elements in which the thickness is reduced to the sub-wavelength size.
In order to achieve miniaturization of optical devices and incorporate them into microchips to realize multifunctional and low power consumption micro optical devices, it is required to realize circular dichroic elements thinner than the wavelength of light.

Furthermore, there are many research examples of circular dichroism performed at an extremely low temperature of −100 ° C. or lower, but circular dichroism is difficult to be found in a practical environment at room temperature, and particularly includes visible light and near infrared light regions. There are few research examples on circular dichroic elements that contribute to practical use in the optical wavelength region.

As a circular dichroic element, there is an element described in Patent Document 1, for example.
Patent Document 1 relates to “medium measurement surface plasmon resonance sensor having circular dichroism, circular dichroism measurement method and measurement apparatus”, and invention of a circular dichroic element using anisotropic plasmon resonance Is disclosed. The subject of the invention is mainly circular dichroism in a reflective arrangement, not a transmissive arrangement. In general, plasmon resonance is related to the fabrication of sub-wavelength sized devices, but Patent Document 1 does not have proof by numerical calculations or experiments, and its effectiveness is not clear. Further, the disclosed element can be estimated to have a circular dichroism degree of 0.2 or less, and its function as a circular dichroic element is small.

Non-Patent Document 4 describes a structure that enables a sub-wavelength sized wave plate. It shows that a wave plate having such a sub-wavelength size is made possible by an electromagnetic wave medium having an extremely large anisotropy in refractive index. This wave plate is one element for realizing the circular dichroic element of the embodiment.
In particular, a quarter wave plate is useful for circularly polarized light. A quarter-wave plate is an element that transmits incident circularly polarized light and then converts it to linearly polarized light.
A quarter-wave plate having a sub-wavelength size as shown in Non-Patent Document 4 can be obtained by optimizing the thickness so as to satisfy the above definition with respect to the incident wavelength. Therefore, the thickness of the quarter wave plate is determined to be an optimum thickness for transmitting incident circularly polarized light and then converting it to linearly polarized light.
A normal quarter-wave plate is produced by cutting an optical crystal into a plate shape and optically polishing, and a quarter-wave plate for visible light (typical wavelength is 500 nm) has a thickness of 1 mm or more.
In addition, in the quarter-wave plate, regardless of whether the thickness is a sub-wavelength, the axis with the fastest phase velocity (advanced axis) and the slowest axis (delay axis) exist in the plane, Orthogonal to each other. The formulas representing the properties are formulas (4) and (5) described later in the embodiment, and the Jones matrix represented by formula (3) represents a quarter-wave plate.
In the quarter-wave plate, the transmittance is the same regardless of whether the incident light is clockwise or counterclockwise circularly polarized light, and the transmitted light is both linearly polarized light, indicating the directions of polarized light orthogonal to each other. The value of the circular dichroism σ is 0, and the quarter wave plate is an element having no circular dichroism.

Non-Patent Document 5 describes a circular dichroic element formed by producing a spiral metal coil in a micrometer size. Specifically, it is a circular dichroic element formed by periodically arranging gold spiral structures, and the element can be configured using a structure found in the microwave region in the infrared light region. Based on this empirical rule, the structure was designed and produced. Since the dielectric constant of the metal is significantly different from that of infrared light, this structure cannot effectively exhibit circular dichroism in the visible light and near infrared light regions, and does not have the polarization operability of transmitted plane waves.

This circular dichroic element can select whether or not to excite a resonance state depending on the rotation direction of incident circularly polarized light in an infrared light region having a wavelength of 3 μm or more. In the case of incident circularly polarized light that excites the resonance state, light is absorbed by the coil and does not pass through. In the case of incident circularly polarized light that does not excite the resonance state, light passes through and a transmittance of about 90% is obtained. . Thereby, a circular dichroic element having a circular dichroism degree σ close to 1 can be obtained.

However, this design is not effective in the visible light and near infrared light regions in the following two points. First, the dielectric constant of the metal forming the coil (gold in Non-Patent Document 5) contains a large amount of light absorption components, and light is absorbed for any incident circularly polarized light. Secondly, since the resonance state of the coil structure has a cutoff (lower limit of wavelength), the wavelength at which the resonance state occurs can be brought into the visible light or near infrared light region by making the metal coil with a smaller size. I can't.

Non-Patent Document 6 describes a circular dichroic element in the near-infrared light region.
This element has a structure in which thin film layers are sandwiched so as not to directly contact fine metal pieces having the same shape in a cross shape and laminated with a twist angle. When the same cross-shaped structure is stacked with the thin film layer interposed therebetween, circular dichroism can be expressed by providing a twist angle.

The circular dichroism degree σ of Non-Patent Document 6 is a maximum of 0.4, the transmittance at that time is 7%, and the efficiency factor ε is as small as 2.8, which is not suitable for practical use. In fact, it is dark as a circular dichroic element.
Also, the polarization of the transmitted plane wave is almost the same as the incident plane wave and cannot be rotated in the opposite direction to the linearly polarized wave or the incident plane wave. Large, there is a difficulty that can not be expected to increase the transmittance.

Thus, the conventional circular dichroic element has a circular dichroism degree σ of 0.75 or more and an efficiency factor ε of 25 or more, and the thickness of the circular dichroic element is thinner than the wavelength of light. Therefore, there is a problem that it is difficult to control the polarization state of the transmitted plane wave to linearly polarized light or clockwise or counterclockwise circularly polarized light.

JP 2009-210495 A

L. Li, "New formulation of the Fourier modal method for crossed surface-relief gratings," J. Opt. Soc. Am. A, Vol. 14, p. 2758-2767 (1997). L. Li, “Formation and comparison of two recursive matrix algorithm for layered diffractive gratings,” J. Am. Opt. Soc. Am. A, Vol. 13, p. 1024-1035 (1996). A. D. Rakic, A .; B. Djurusic, J.A. M.M. Elazar, and M.M. L. Majewski, “Optical properties of metallic films for vertical-cavity optoelectronic devices,” Appl. Opt. , Vol. 37, 5271-5283 (1988). M.M. Iwanaga, “Ultracompact waveplates: Approach from materials,” Appl. Phys. Lett. , Vol. 92, 153102 (2008). J. et al. K. Gansel, M.M. Thiel, M.M. S. Decker, K.M. Bade, V .; Sail, G. et al. von Freymann, S.M. Linden, and M.M. Wegener, “Gold Helix Photometric Material as Broadband Circular Polarizer,” Science, Vol. 325, p. 1513-1515 (2009). M.M. Decker, M.M. Ruther, C.I. E. Kriegler, J. et al. Zhou, C.I. M.M. Soukoulis, S .; Linden, and M.M. Wegener, “Strong optical activity from twisted-cross photomaterials,” Opt. Lett. , Vol. 34, p. 2501-2503 (2009). M.M. Iwanaga, A .; S. Vengurkar, T .; Hatano, and T.M. Ishihara, “Reciprocal transmitters and references: An elementary profile,” Am. J. et al. Phys. Vol. 75, p. 899-903 (2007). M.M. Iwanaga, “Polarization-selective transmission in stacked two-dimensional complementary complementary slabs,” Appl. Phys. Lett. Vol. 96,083106 (2010). E. D. Palik, Handbook of Optical Constants of Solids II, Academic Press, San Diego, 1991.

The present invention has a circular dichroism degree σ of 0.75 or more and an efficiency factor ε of 25 or more, a thickness smaller than the wavelength of the incident plane wave, and the polarization state of the transmitted plane wave is linearly polarized or incident circle. It is an object of the present invention to provide a circular dichroic element which can be controlled to circularly polarized light opposite to or in the same direction as polarized light.

It is well known that the solution of the Maxwell equation, which is recognized as an equation that accurately represents phenomena related to electromagnetism, can be accurately reproduced even for electromagnetic phenomena in periodic structures.
Since calculating the transmittance when electromagnetic waves pass through the periodic structure and the polarization vector of the transmitted plane wave is an important technique in the present invention, the literature will be described below.
It is suitable to rewrite Maxwell's equations in a structure consisting of a periodic array into a form obtained by Fourier transform. For example, Non-Patent Document 1 describes a table expression in which Maxwell's equations are specifically rewritten into a Fourier transform, and describes an algorithm for solving the rewritten equations numerically at high speed and with high accuracy. Yes. By using this method, it is possible to accurately know the solution of the Maxwell equation of the eigenmode induced when the periodic plane body is irradiated with the incident plane wave.
In Non-Patent Document 2, when a solution of Maxwell's equations in a layer composed of a periodic array is obtained, scattering is used to stably calculate the transmittance and reflectance of the laminated structure using the solution. Matrix algorithm and specific expressions are described systematically.
By combining the methods of Non-Patent Documents 1 and 2, it becomes possible to calculate the transmittance and reflectance of a structure in which layers having a periodic arrangement are arbitrarily stacked as a direct result from the Maxwell equation. Therefore, the results calculated from these methods are the most reliable results in electromagnetics, and the validity of these results is already well known from comparison with many experiments.
In particular, Non-Patent Documents 7 and 8 are cited as documents showing experimental values of transmittance with respect to a plane electromagnetic wave of a periodic structure including a metal with good reproducibility by the calculation method. Non-Patent Documents 7 and 8 have experimental values related to the transmittance of periodic structures containing metal and values calculated by the above method, and the range in which the periodic length of the periodic structures is a subwavelength with respect to the wavelength of the incident plane wave In FIG. 5, the values agree within an error range of ± 5% or less. Therefore, it is presumed that the calculated value obtained with the configuration of the present application can also be obtained as an experimental value within the same error range. It is considered that the main cause of the error from the experimental value is that the structure actually produced deviates from the design according to the processing accuracy.
By calculating an electric field vector at an arbitrarily determined time of the transmitted plane wave obtained by the calculation method along the traveling direction, a polarization vector of the transmitted plane wave can be obtained. This method has already been described in Non-Patent Document 4.
Non-Patent Document 3 describes a dielectric constant over a wide wavelength range by fitting the dielectric constant of silver measured experimentally by the Brendel-Barden model.

  The inventor of the present application has discovered that there is a possibility that the above problem can be solved by using the calculations described in Non-Patent Documents 1 and 2 and the dielectric constant of silver described in Non-Patent Document 3. completed. The present invention has the following configuration.

The circular dichroic element of the present invention is a circular dichroic element having a laminated structure of a quarter-wave plate and an anisotropic transmission plate and having a sub-wavelength thickness, wherein the quarter-wave plate Can convert circular polarization of one plane wave selected from a wavelength region of not less than 400 nm and not more than 1600 nm into linear polarization, and the anisotropic transmission plate has a high transmittance axis in the linear polarization direction of the one plane wave. It is characterized by.

In the circular dichroic element of the present invention, it is preferable that the high transmittance axis of the anisotropic transmission plate forms an angle of 45 degrees with respect to the advanced axis of the quarter wavelength plate.
In the circular dichroic element of the present invention, the quarter wavelength plate is composed of an electromagnetic wave transmitting member and a negative dielectric constant member, and the negative dielectric constant member is parallel and spaced apart on one side of the quarter wavelength plate. It is preferable that a plurality of lines arranged in a constant manner are formed, and the extending direction of the lines is the advanced axis direction of the quarter-wave plate.

In the circular dichroic element of the present invention, the anisotropic transmission plate includes an electromagnetic wave transmission member and a negative dielectric constant member, and the negative dielectric constant member has the same size on one side of the anisotropic transmission plate. The plurality of lines formed by arranging the apex angles of the adjacent negative dielectric constant members close to each other and arranging them in one direction are arranged in parallel and at a constant interval. In addition, it is preferable that the negative dielectric constant member is arranged on one side of the anisotropic transmission plate so as to form a plurality of lines arranged in parallel and at constant intervals.
In the circular dichroic element of the present invention, the negative dielectric constant member is preferably a metal.
In the circular dichroic element of the present invention, the electromagnetic wave transmitting member is preferably a material having a transmittance of 70% or more for the one plane wave.

In the circular dichroic element of the present invention, it is preferable that another quarter-wave plate is laminated on the opposite surface of the anisotropic transmission plate to the quarter-wave plate.
In the circular dichroic element of the present invention, the other quarter-wave plate may be laminated such that the advanced axes of the quarter-wave plate and the other quarter-wave plate are parallel to each other. preferable.
In the circular dichroic element of the present invention, the other quarter-wave plate is preferably laminated such that the advanced axes of the quarter-wave plate and the other quarter-wave plate are orthogonal to each other. .

The circular dichroic element of the present invention is a circular dichroic element having a laminated structure of a quarter-wave plate and an anisotropic transmission plate and having a sub-wavelength thickness, wherein the quarter-wave plate Can convert circular polarization of one plane wave selected from a wavelength region of not less than 400 nm and not more than 1600 nm into linear polarization, and the anisotropic transmission plate has a high transmittance axis in the linear polarization direction of the one plane wave. Therefore, one plane wave selected from a wavelength region of 400 nm or more and 1600 nm or less can be incident and transmitted to generate circular dichroism in the transmitted plane wave, and a circular dichroism degree σ of 0.75 or more. In addition, it is possible to provide a circular dichroic element having an efficiency factor ε of 25 or more and capable of controlling the polarization state of the transmitted plane wave to circularly polarized light opposite to or the same as linearly polarized light or incident circularly polarized light. In addition, since it is a circular dichroic element with a sub-wavelength thickness, it can be easily incorporated into microchips, etc., and light-to-light conversion devices, light-to-electric conversion devices, and electricity-to-light conversion devices can be made smaller. Multifunctionality and low power consumption can be achieved.

It is a figure which shows an example of the circular dichroic element of this invention, Comprising: It is the schematic of a two-layer type circular dichroic element. It is a side view of the circular dichroic element shown in FIG. It is a top view of the unit surface of a quarter wavelength plate. It is a top view of the unit surface of an anisotropic transmission board. It is a figure which shows another example of the circular dichroic element of this invention, Comprising: It is the schematic of a 1st 3 layer type | mold circular dichroic element. It is a figure which shows another example of the circular dichroic element of this invention, Comprising: It is the schematic of a 2nd 3 layer type | mold circular dichroic element. It is a top view of the unit surface of another quarter wavelength plate. It is a graph which shows the calculation result of the transmission spectrum of a two-layer type circular dichroic element. It is a graph which shows the calculation result of the circular dichroism degree spectrum of a two-layer type circular dichroic element. It is a graph which shows the calculation result of the polarization state of the transmission plane wave of a two layer type circular dichroic element. It is a graph which shows the calculation result of the transmission spectrum of an anisotropic transmission board (thickness 210nm) single layer under linearly polarized light. It is a graph which shows the calculation result of the transmission spectrum of a 1st 3 layer type circular dichroic element. It is a graph which shows the calculation result of the circular dichroism degree spectrum of a 1st 3 layer type | mold circular dichroism element. It is a perspective view which shows the calculation result of the polarization state of the transmission plane wave of a 1st 3 layer type | mold circular dichroism element. It is a graph which shows the calculation result of the polarization state of the transmission plane wave of the 1st 3 layer type circular dichroism element. It is a graph which shows the calculation result of the transmission spectrum of the 2nd 3 layer type circular dichroism element. It is a graph which shows the calculation result of the circular dichroism degree spectrum of the 2nd 3 layer type circular dichroic element. It is a perspective view which shows the calculation result of the polarization state of the transmission plane wave of the 2nd 3 layer type circular dichroic element. It is a top view of the unit surface of an anisotropic transmission board. It is a top view of the unit surface of an anisotropic transmission board. It is a graph which shows the calculation result of the polarization state of a transmission plane wave when the layer structure which has the unit surface 31 is 100 nm in thickness. It is a transmission spectrum of a two-layer type circular dichroic element whose thickness is not optimized. It is the schematic which shows the definition of counterclockwise circularly polarized light. It is the schematic which shows the definition of clockwise rotation polarization | polarized-light. It is a conceptual diagram which shows an example of circular dichroism.

(First embodiment of the present invention: two-layer circular dichroic element)
First, the circular dichroic element which is the 1st Embodiment of this invention is demonstrated.
The function manifestation mechanism for making linearly polarized light after the two-layer element of the present invention transmits incident circularly polarized light can be shown using the Jones matrix as follows.
The Jones matrix method has already been established in optics as a method for expressing the properties of transmissive optical elements. In particular, this method is suitable when light is incident perpendicular to the element.
When the orthogonal coordinate xyz axis is given, the element and the incident light are set so that the incident surface of the element is parallel to the xy plane and the traveling direction of the incident light is the -z axis.
An electric field component (Ex, Ey) of light is taken as a basis vector, which is called a Jones vector. With this basis vector, the transmission characteristics of the optical element can be expressed as a 2 × 2 matrix, which is called the Jones matrix. Both the Jones vector and the Jones matrix are complex values to represent the light phase.

First, Jones vector _JR of clockwise circular polarization can be expressed as shown in Equation (1). Similarly, Jones vector J _L of the left-handed circularly polarized light can be expressed by the equation (2). Here, the imaginary unit is represented by i, and the Jones vector is standardized to have an absolute value of 1 (hereinafter the same).

Next, when the advanced axis of the quarter-wave plate is arranged so that it is parallel to the x-axis and the delay axis is parallel to the y-axis, the corresponding Jones matrix L ₁ is expressed as equation (3).

In general, when the Jones matrix is multiplied by the Jones matrix, the product result represents the Jones vector of transmitted light. The applied Jones vector represents the polarization of the incident light.
It can be confirmed as follows that Expression (3) is a Jones matrix representing a quarter-wave plate. As described above, the definition of the quarter wave plate is to convert circularly polarized light into linearly polarized light. When the Jones matrix L ₁ applying a Jones vector J _L of the right-handed circularly polarized light of the Jones vector J _R and the left-handed circularly polarized light, as can be seen from equation (4) and (5), is converted into linearly polarized light, respectively. The right side of Expression (4) represents a Jones vector linearly polarized in the (1, 1) direction, and the right side of Expression (5) represents a Jones vector linearly polarized in the (-1, 1) direction. Against two linearly independent Jones vector J _R and J _L, Jones matrix satisfying Equation (4) Equation (5) is uniquely determined, the table type is an expression (3). As described above, Equation (3) is a Jones matrix that represents a quarter-wave plate.
It can also be seen from the equations (4) and (5) that the linearly polarized light obtained by converting the clockwise circularly polarized light and the counterclockwise circularly polarized light by the quarter wavelength plate is orthogonal to each other.

Next, the Jones matrix L ₂ representing the anisotropic transparent plate is expressed by equation (6). However, it is assumed that the high transmittance axis is parallel to the vector (1, 1) and the low transmittance axis is parallel to the vector (-1, 1).

It can be confirmed that the expression (6) is an anisotropic transmission plate as follows. When a Jones vector representing linearly polarized light in the (1, 1) direction is applied to the Jones matrix of Equation (6), as can be seen from Equation (7), the same Jones vector as the incident polarized light represents the polarization state of the transmitted plane wave. That is, the (1, 1) direction is the high transmittance axis, and the transmittance is 100%. On the other hand, equation (8) corresponds to the case where the incident plane wave is linearly polarized light and is in the (−1, 1) direction, and indicates that the transmitted plane wave is a zero vector, that is, a transmittance of 0%. Therefore, the (-1, 1) direction is the low transmittance axis. Since the ratio of matrix components satisfying Equations (7) and (8) is uniquely determined by the matrix represented by Equation (6) for two first-order independent Jones vectors, Equation (6) is different. It was confirmed to be a Jones matrix representing a rectangular transmission plate.

As described above, it has been clarified that the quarter-wave plate and the anisotropic transmission plate have effects corresponding to the Jones matrix L ₁ and the Jones matrix L ₂ , respectively.
Note that the Jones matrix L ₁ and the Jones matrix L ₂ are idealized in order to explicitly show qualitative properties. An actual circular dichroic element has a reflection loss and an absorption loss, and the transmittance may not be 100%, but the operating principle of the circular dichroic element can be explained qualitatively in the same way (the following explanation) The same applies to).

Next, a Jones matrix M ₂ of a two-layer circular dichroic element in which a quarter-wave plate and an anisotropic transmission plate are stacked is obtained by multiplying the Jones matrix L ₁ by L ₂ from the left. The Jones matrix product corresponds to a layered stack. Concrete expression Jones matrix M ₂ is shown in equation (9).

It can be confirmed as follows that Expression (9) is a Jones matrix representing the two-layer circular dichroic element 101. When the Jones vector J _R of clockwise circular polarization and the Jones vector J _L of counterclockwise circular polarization are respectively applied in the expressions (10) and (11), the transmittance is 100% and the counterclockwise rotation with respect to the clockwise circular polarization. The transmittance is 0% for circularly polarized light. Since the ratio of the matrix components satisfying the equations (10) and (11) is uniquely determined by the matrix represented by the equation (9) with respect to two primary independent Jones vectors, the equation (9) is expressed as 2 It was confirmed that the Jones matrix representing the layered circular dichroic element 101 was obtained.
Further, as can be seen from the equation (10), the polarization state of the transmitted plane wave under clockwise circularly polarized light is linearly polarized light in the (1, 1) direction.

As described above, Equation (9) 2-layer circular dichroism element represented by the Jones matrix M ₂ of (circular dichroism element 101 of the present invention), right-handed circularly polarized light of incident circularly polarized light only And the transmitted wave is converted into linearly polarized light.
In particular, the process shown by the Jones matrix does not depend on the internal structure of the quarter-wave plate or the anisotropic transmission plate. That is, the two-layer circular dichroic element according to the first embodiment of the present invention has a universal property that is established if the conditions that each layer is a quarter-wave plate and an anisotropic transmission plate are satisfied. Became clear.

FIG. 1 is a schematic view showing an example of a circular dichroic element according to the first embodiment of the present invention. An outline is shown including an internal structure necessary for realizing a circular dichroic element with a thickness of a sub-wavelength size.
As shown in FIG. 1, the circular dichroic element 101 is a circular dichroic element configured by stacking two rectangular parallelepiped flat layers. The ¼ wavelength plate 1 having a substantially rectangular shape in plan view and the anisotropic transmission plate 2 having a substantially rectangular shape in plan view are stacked to form a schematic configuration. The two layers are shown in different sizes so that the internal structure of the anisotropic transmission plate 2 can be seen.

In FIG. 1, coordinates xyz are defined. The coordinates are set so that the advanced axis and delay axis of the quarter-wave plate 1 coincide with the xy axis. At this time, the plane wave incident perpendicularly to the xy plane travels in the −z direction. A vector defining the traveling direction of the incident plane wave is a wave vector 5.
In FIG. 2, the quarter-wave plate 1 and the anisotropic transmission plate 2 are shown in an arrangement in which the yz section of the circular dichroic element 101 is viewed from the + x side. One surface 1a and the other surface 1b of the quarter-wave plate 1 are parallel to the xy plane in the order in which the incident plane wave is irradiated. One side 2a and the other side 2b of the anisotropic transmission plate 2 are used. The other surface 1b of the quarter-wave plate 1 and the one surface 2a of the anisotropic transmission plate 2 are laminated so as to contact each other.

In FIG. 1, a quarter-wave plate 1 includes a negative dielectric constant member 3a and an electromagnetic wave transmission member 3b. The negative dielectric constant members 3a and the electromagnetic wave transmission member 3b are alternately arranged so that the interface is parallel to the y-axis. Is arranged. The arrangement direction of the negative dielectric constant member 3a and the electromagnetic wave transmission member 3b coincides with the x axis.
On one surface side of the quarter-wave plate 1, the negative dielectric constant member 3a forms a plurality of lines arranged in parallel and at constant intervals.

In FIG. 3, a partial enlarged view of the xy section of the quarter-wave plate 1, particularly a unit surface 31 is shown. Here, the unit plane refers to a unit that can be extracted from the xy cross section and can form the entire original xy cross section by repeating the unit planes adjacent to each other without gaps and without overlapping in the xy plane.
The unit surface of FIG. 3 has a length of horizontal lx and vertical ly, and includes a negative dielectric constant member 3a and an electromagnetic wave transmitting member 3b inside. The length of the negative dielectric constant member 3a in the x-axis direction is tx. The internal structure of the quarter-wave plate 1 represented by the unit surface 31 can be changed by changing the length tx. In FIG. 3, the advanced axis 3c and the delay axis 3d of the quarter-wave plate 1 are also shown. The extending direction of the line is the direction of the advanced axis 3 c of the quarter-wave plate 1.

In FIG. 4, the unit surface 41 regarding the xy cross section of the anisotropic transmission board 2 is shown. The unit surface of FIG. 4 has a length of lx and a width of ly, and includes negative dielectric constant members 4a1, 4a2, 4a3, 4a4, 4a5, 4a6 and an electromagnetic wave transmitting member 4b. The negative dielectric constant members 4a1 to 4a6 have the same shape in a square shape in plan view and have a length of horizontal sx and vertical sy.
In FIG. 4, the high transmittance axis 4c and the low transmittance axis 4d of the anisotropic transmission plate 2 are also shown.
The high transmittance axis 4 c of the anisotropic transmission plate 2 forms an angle of 45 degrees with respect to the advanced axis 3 c of the quarter-wave plate 1.

The internal structure of the anisotropic transmission plate 2 represented by the unit surface 41 has a degree of freedom in changing the number and shape of the negative dielectric constant members 4a1 to 4a6 in the arrangement. The negative dielectric constant members of the array of anisotropic transmission plates 2 are not limited to the same shape. For example, an anisotropic transmission plate 2 can be formed even if squares having different sizes are arranged in a line.

The anisotropic transmission plate 2 is formed so that the unit surfaces 41 are periodically adjacent to the xy plane, and the negative dielectric constant members 4a1, 4a2, 4a3, 4a4, 4a5, 4a6 are obliquely aligned in a straight line. It is arranged. Thereby, the line-shaped negative dielectric constant member 4a is formed. The line-shaped negative dielectric constant members 4a are arranged in parallel to each other and at equal intervals.
By having such a regular structure, the anisotropic transmission plate 2 can increase the transmittance in the direction of an arbitrary linearly polarized light when a linearly polarized wave is used as the incident plane wave. The transmittance in the direction of linearly polarized light rotated by 90 ° can be lowered. For example, in the xy plane, the transmittance in the direction of linearly polarized light parallel to the vector (1, 1) can be increased, and the transmittance in the direction of linearly polarized light parallel to the vector (-1, 1) can be decreased. Can do.

The negative dielectric constant member 3a and the negative dielectric constant members 4a1, 4a2, 4a3, 4a4, 4a5 and 4a6 are preferably made of metal. The metal type is preferably determined in consideration of an incident wavelength and a dielectric constant. By including a metal material, it is advantageous to manufacture a circular dichroic element with a thin sub-wavelength.
Examples of metals that can be used include Ag, Al, Au, and Pt. Ag and Al are particularly preferable in the visible light region. Pt is not preferable because the loss due to light absorption is large when visible light is used as the incident plane wave. Cu can be used as a metal member in the infrared light region and the microwave region.

The dielectric constant of the metal material depends on the wavelength of the incident plane wave, takes a negative value in the limit of the long wavelength, and monotonically increases toward 0 as the wavelength becomes shorter, which is convenient for an actual metal material. In addition, the wavelength at which the dielectric constant becomes 0 is defined as the effective plasma wavelength.
By reducing the in-plane ratio of the negative dielectric constant member 3a of the unit surface 31, the effective plasma wavelength can be shifted to the long wavelength side. Therefore, the transmittance of the quarter-wave plate 1 can be increased by using a plane wave in the wavelength region shorter than the effective plasma wavelength as the incident plane wave.

The electromagnetic wave transmitting member 3b and the electromagnetic wave transmitting member 4b have a transmittance of incident plane waves of preferably 70% or more, and more preferably 90% or more. Examples of the material having a high transmittance of the incident plane wave include an insulator or a semiconductor. For example, for an incident plane wave having a wavelength in the visible light region, a transparent insulator such as SiO ₂ , Al ₂ O ₃ , or MgF ₂ can be used.

For example, the plasma wavelength of silver or aluminum is in the ultraviolet region. Therefore, the unit surface 31 shown in FIG. 3 can be formed by a combination of silver and SiO ₂ or a combination of aluminum and SiO ₂ .
By reducing the in-plane ratio of the metal occupying the unit surface 31, the effective plasma wavelength can be moved from the ultraviolet light region to the visible light region and the near infrared light region.
Thereby, the operating wavelength of the quarter wavelength plate 1 of the sub-wavelength size can be moved from the ultraviolet light region to the visible light region and the near infrared light region.

Further, by considering the thickness of the quarter-wave plate 1 and selecting the wavelength of the incident plane wave, a circular dichroic element having a thickness equal to or smaller than the sub-wavelength size can be obtained.
In addition, it has been reported that the quarter wavelength plate 1 can become a quarter wavelength plate of a subwavelength size alone (Non-patent Document 4).

Next, the polarization effect of the two-layer circular dichroic element 101 according to the first embodiment of the present invention will be described.
First, as shown in FIG. 1, an incident plane wave is incident in a direction (−z direction) perpendicular to one surface 1 a of the quarter-wave plate 1.
As described above using the Jones matrix that does not depend on the electromagnetic wave of a specific wavelength, it is possible to select and use an incident plane wave from electromagnetic waves in a wide wavelength range from ultraviolet light to microwaves, corresponding to the wavelength of the incident plane wave. By using the member, the same polarization effect can be obtained. In addition, it is preferable to make a wavelength range into the range (wavelength 400nm or more) longer than ultraviolet light. This is because, when the wavelength is shorter than visible light, a negative dielectric constant member that does not have a light absorption loss has not been found so far, so that it is difficult to construct a quarter wavelength plate as exemplified by the unit surface 31.

The incident plane wave is converted from circularly polarized light to linearly polarized light inside the quarter wavelength plate 1.
The clockwise circularly polarized light and the counterclockwise circularly polarized light are converted into linearly polarized light whose directions are orthogonal to each other.

Next, the incident plane wave converted into the linearly polarized light is incident on the inside of the anisotropic transmission plate 2.
The anisotropic transmission plate 2 transmits linearly polarized light having a high transmittance axis and direction with high transmittance, while transmitting linearly polarized light in a direction orthogonal to the high transmittance axis, that is, low transmittance axis and direction, with low transmittance. Make it transparent.
Therefore, the two linearly polarized lights emitted from the other surface 2b of the anisotropic transmission plate 2 have different transmittances and exhibit circular dichroism. From these transmittances, the circular dichroism degree σ and the efficiency factor ε are calculated.
As described above, the circular dichroic element 101 according to the first embodiment of the present invention transmits only one of the clockwise or counterclockwise incident circularly polarized light and converts it into linearly polarized light. The efficiency factor ε can be increased and emitted.

(Second embodiment of the present invention: first three-layer circular dichroic element)
Next, the circular dichroic element which is the 2nd Embodiment of this invention is demonstrated. First, the function expression mechanism is shown using the Jones matrix. In the Jones matrix M ₃ ⁽¹⁾ of the first three-layer circular dichroic element, the two quarter-wave plates are stacked so that they have parallel advanced axes. It is represented by ₁ L ₂ L ₁ .

It can be confirmed that the equation (12) is a Jones matrix representing the three-layer circular dichroic element 102 as follows. When the Jones vector J _{R of} the clockwise circular polarization and the Jones vector J _L of the counterclockwise circular polarization are respectively applied in the expressions (13) and (14), the clockwise circular polarization is expressed as shown in the expression (13). The transmittance is 100%, and the transmittance is 0% for counterclockwise circularly polarized light as shown in the equation (14). Since the ratio of the matrix components satisfying the equations (13) and (14) is uniquely determined by the matrix represented by the equation (12) with respect to the two first-order independent Jones vectors, the equation (12) is expressed as 3 It was confirmed that the Jones matrix representing the layered circular dichroic element 102 was obtained.
From Expressions (13) and (14), it was shown that only clockwise circularly polarized light is transmitted, and from Expression (13), the transmitted plane wave is opposite to the incident circularly polarized light, that is, left-handed circularly polarized light.

Expression (13) is a case where the incident plane wave is clockwise circularly polarized light, and the transmitted plane wave is counterclockwise circularly polarized light, and represents the transmitted plane wave of circularly polarized light that is counterclockwise to the incident circularly polarized light.
A circular dichroic element in which the incident plane wave is counterclockwise circularly polarized and the transmission plane wave is clockwise circularly polarized light can be obtained by rotating the anisotropic transmission plate by 90 degrees.
As a result of the above derivation, the circular dichroic element is not only an individual case but also a three-layer laminated structure of a quarter-wave plate, an anisotropic transmission plate, and a quarter-wave plate. It can be realized universally regardless of the details.

FIG. 5 is a schematic view showing an example of a circular dichroic element according to the second embodiment of the present invention. An outline is shown including an internal structure necessary for realizing a circular dichroic element with a thickness of a sub-wavelength size.
As shown in FIG. 5, the circular dichroic element 102 is a three-layer type, and another quarter wavelength plate 6 having a substantially rectangular shape in plan view is laminated on the other surface 2 b side of the anisotropic transmission plate 2. Other than this, the configuration is the same as that of the two-layer circular dichroic element 101 according to the first embodiment of the present invention.

In FIG. 5, in order to show the internal structure of the anisotropic transmission plate 2 and another quarter wavelength plate 6, one end side of the quarter wavelength plate 1 and the anisotropic transmission structure plate 2 is deleted. ing. The structure is the same as that of the first embodiment of the present invention, and the area where the anisotropic transmission plate 2 and the other quarter-wave plate 6 are in contact with each other is the same, and they are stacked so as to overlap each other.

As shown in FIG. 5, another quarter-wave plate 6 has a negative dielectric constant member 7a and an electromagnetic wave transmitting member 7b. Similar to the quarter-wave plate 1, the other quarter-wave plate 6 has a structure in which negative dielectric constant members 7a and electromagnetic wave transmitting members 7b are alternately arranged in the x-axis direction and are uniform in the y-axis direction. Have.
As described in the first embodiment of the present invention, by using a metal for the negative dielectric constant member 7a, the other quarter-wave plate 6 can be made thin with a sub-wavelength.

Next, the polarization effect of the first three-layer circular dichroic element 102 according to the second embodiment of the present invention will be described.
As shown in FIG. 5, the incident plane wave is incident in a direction (−z direction) perpendicular to one surface of the quarter-wave plate 1.
The incident plane wave is converted from circularly polarized light to linearly polarized light inside the quarter wavelength plate 1.
The clockwise circularly polarized light and the counterclockwise circularly polarized light are converted into linearly polarized light whose directions are orthogonal to each other.

Next, the incident plane wave converted into the linearly polarized light is incident on the inside of the anisotropic transmission plate 2.
The anisotropic transmission plate 2 transmits linearly polarized light having a high transmittance axis and direction with high transmittance, while transmitting linearly polarized light in a direction orthogonal to the high transmittance axis, that is, low transmittance axis and direction, with low transmittance. Make it transparent.

Next, since the advanced axis of another quarter wavelength plate 6 is arranged so as to coincide with the advanced axis of the quarter wavelength plate 1, the linearly polarized light emitted from the anisotropic transmission plate 2 is It is converted into circularly polarized light that is reverse to the incident circularly polarized light. Through the above process, the light is emitted in the −z direction from the other surface of another quarter-wave plate 6.

As described above, the circular dichroic element 102 according to the second embodiment of the present invention transmits only the clockwise incident circularly polarized light and converts it to the left-handed circularly polarized light, or emits it in the counterclockwise direction. Only incident circularly polarized light can be transmitted, converted into clockwise circularly polarized light, and emitted. The ratio of the transmittance of the finally transmitted light becomes circular dichroism. From the ratio of these transmittances, the circular dichroism degree σ and the efficiency factor ε are calculated.

(Third embodiment of the present invention: second three-layer circular dichroic element)
A circular dichroic element according to a third embodiment of the present invention will be described. The Jones matrix M ₃ ⁽²⁾ representing the three-layer circular dichroic element according to the third embodiment is different from the three-layer circular dichroic element 102 in that the other quarter-wave plate 6 is placed in the xy plane. Since it is an arrangement rotated by 90 degrees, it is expressed as equation (15).

It can be confirmed as follows that Expression (15) is a Jones matrix representing the three-layer circular dichroic element 103. When the Jones vector J _R of clockwise circular polarization and the Jones vector J _L of counterclockwise circular polarization are respectively acted as shown in the equations (16) and (17), the clockwise circular polarization is obtained as shown in the equation (16). The transmittance is 100%, and the transmittance is 0% for counterclockwise circularly polarized light as shown in equation (17). Since the ratio of the matrix components satisfying the equations (16) and (17) is uniquely determined by the matrix represented by the equation (15) with respect to two primary independent Jones vectors, the equation (15) is expressed as 3 It was confirmed that the Jones matrix representing the layered circular dichroic element 103 was obtained.
From equations (16) and (17), it was shown that only clockwise circularly polarized light is transmitted, and from equation (17), the transmitted plane wave becomes circularly polarized light in the same direction as the incident circularly polarized light.
If the anisotropic transmission plate of this circular dichroic element is rotated 90 degrees in the xy plane, a circular dichroic element in which the incident plane wave is counterclockwise circularly polarized and the transmission plane wave is also counterclockwise circularly polarized is obtained. It is done.

The three circular dichroic elements according to the embodiment of the present invention are designed based on general proof using the equations (1) to (17).

FIG. 6 is a schematic view showing an example of a circular dichroic element according to the third embodiment of the present invention. An outline is shown including an internal structure necessary for realizing a circular dichroic element with a thickness of a sub-wavelength size.
In FIG. 6, by arranging the advanced axis of another quarter wavelength plate 8 in a direction orthogonal to the advanced axis of the quarter wavelength plate 1, the polarization of the transmitted plane wave is the same as the circular polarization of the incident plane wave. Circular dichroism that becomes circularly polarized light becomes possible.

FIG. 7 is a partially enlarged view of an xy sectional view of another quarter wavelength plate 8 and shows a unit surface 71 in the xy plane. The unit surface 71 in FIG. 7 coincides with the unit surface 31 in FIG. 3 rotated 90 degrees in the xy plane.
By using a metal for the negative dielectric constant member 9a, the other quarter-wave plate 8 can be a quarter-wave plate having a thin sub-wavelength.
In FIG. 7, the advanced axis 9c and the delay axis 9d of the quarter wavelength plate are shown.

The circular dichroic elements 101, 102, 103 according to the embodiment of the present invention have a laminated structure of a quarter-wave plate 1 and an anisotropic transmission plate 2, and have a sub-wavelength thickness of circular dichroism. In the element, the quarter wave plate 1 can convert circularly polarized light of one plane wave 5 selected from a wavelength region of 400 nm to 1600 nm into linearly polarized light, and the anisotropic transmission plate 2 has one plane wave 5. Therefore, it has a circular dichroism σ of 0.75 or more and an efficiency factor ε of 25 or more, and the polarization state of the transmitted plane wave is linearly polarized or incident circle. It is possible to provide a circular dichroic element that can be controlled to be circularly polarized light in the reverse direction or the same direction as the polarized light. In addition, by providing a circular dichroic element with a sub-wavelength thickness, it can be easily incorporated into a microchip, etc., and light-to-light conversion devices, light-to-electric conversion devices, and electricity-to-light conversion devices can be made smaller. Multi-function and low power consumption can be achieved.

In the circular dichroic elements 101, 102, and 103 according to the embodiment of the present invention, the high transmittance axis of the anisotropic transmission plate 2 has an angle of 45 degrees with respect to the advanced axis of the quarter-wave plate 1. With this configuration, the polarization state of the incident plane wave 5 can be changed to change the polarization state of the transmission plane wave to a circularly polarized light that is opposite or the same as the linearly polarized light or the incident circularly polarized light. By adding the anisotropic transmission plate 2, circular dichroism can be developed. Since the quarter-wave plate 1 is an element having no circular dichroism as described above, the effect of the circular dichroism in the circular dichroic elements 101, 102, 103 according to the present invention is the anisotropic transmission plate 2. Has its origin.

In the circular dichroic elements 101, 102, 103 according to the embodiment of the present invention, the quarter wavelength plate 1 is composed of a negative dielectric constant member 3a and an electromagnetic wave transmission member 3b, and on one side of the quarter wavelength plate. The negative dielectric constant member forms a plurality of lines arranged in parallel and at constant intervals, and the extending direction of the lines is the advanced axis direction of the quarter-wave plate 1, By changing the polarization state of the plane wave 5, the polarization state of the transmitted plane wave can be changed to a circularly polarized light that is opposite or the same as the linearly polarized light or the incident circularly polarized light. By using the negative dielectric constant member 3a, there is an effect of reducing the thickness of the quarter wavelength plate 1 to the sub-wavelength size.

In the circular dichroic elements 101, 102, 103 according to the embodiment of the present invention, the anisotropic transmission plate 2 includes an electromagnetic wave transmission member 4b and a negative dielectric constant member 4a. The negative dielectric constant member 4a has a plurality of quadrangular shapes of the same size, and a plurality of lines formed by arranging the apex angles of adjacent negative dielectric constant members close to each other and arranging them in one direction are parallel to each other. In addition, the negative dielectric constant members are arranged in parallel and at a constant interval on one surface side of the anisotropic transmission plate. Since it is a structure, the polarization state of an incident plane wave can be changed, and the polarization state of a transmission plane wave can be made into the circular polarization of the reverse or the same rotation as a linearly polarized light or incident circularly polarized light. Since the anisotropic transmission plate 2 has a linear structure composed of the members 4a and 4b, an anisotropic structure can be formed in the unit surface 41, and anisotropy related to the transmittance can be derived.

Since the circular dichroic elements 101, 102, 103 according to the embodiment of the present invention have a configuration in which the negative dielectric constant members 3a, 4a are metal, the circular dichroism degree σ is 0.75 or more and the efficiency factor is 25 or more. Provided is a circular dichroic element that has ε and is thinner than the wavelength of the incident plane wave, and can control the polarization state of the transmitted plane wave to circularly polarized light that is opposite or the same as linearly polarized light or incident circularly polarized light. can do. By using a metal for the negative dielectric constant members 3a and 4a, it becomes possible to cause plasmon resonance of the metal, which is advantageous in reducing the thickness of the circular dichroic element to a sub-wavelength size.

In the circular dichroic elements 101, 102, and 103 according to the embodiment of the present invention, the electromagnetic wave transmitting members 3b and 4b are composed of a material having a transmittance of one plane wave 5 of 70% or more, and thus 0.75 or more. Having a circular dichroism σ of 25 and an efficiency factor ε of 25 or more, and having a thickness smaller than the wavelength of the incident plane wave, the polarization state of the transmitted plane wave is opposite or the same as that of linearly polarized light or incident circularly polarized light. A circular dichroic element that can be controlled by circularly polarized light can be provided. By using a member having a transmittance as high as 70% or more, a region through which electromagnetic waves are efficiently transmitted can be secured in the unit surfaces 31, 41, 71, 191, and 201.

In the circular dichroic elements 102 and 103 according to the embodiment of the present invention, other quarter-wave plates 6 and 8 are laminated on the opposite surface of the anisotropic transmission plate 2 to the quarter-wave plate 1. Because of this configuration, it has a circular dichroism degree σ of 0.75 or more and an efficiency factor ε of 25 or more, and the polarization state of the transmitted plane wave can be controlled to be linearly polarized light or circularly polarized light that is opposite or the same as the incident circularly polarized light. A circular dichroic element can be provided. By laminating the other quarter-wave plates 6 and 8, there is an effect of further converting a plane wave close to linearly polarized light immediately after being transmitted through the anisotropic transmission plate into circularly polarized light. By adding other quarter-wave plates 6 and 8, the circular dichroic elements 102 and 103 can be converted into circularly polarized light from the transmitted plane wave.

In the circular dichroic element 102 according to the embodiment of the present invention, another quarter-wave plate 6 is laminated so that the advanced axes of the quarter-wave plate 1 and the other quarter-wave plate 6 are parallel to each other. Since the quarter wave plate 1 changes the polarization state of the incident plane wave and controls the polarization state of the transmission plane wave to the circularly polarized light that is opposite or the same as the linearly polarized light or the incident circularly polarized light. With the other quarter-wave plate 6, the direction of the circular polarization of the transmitted plane wave can be designated as the same or the reverse direction with respect to the circular polarization of the incident plane wave.

In the circular dichroic element 103 according to the embodiment of the present invention, another quarter-wave plate 8 is laminated so that the advanced axes of the quarter-wave plate 1 and the other quarter-wave plate 8 are orthogonal to each other. Since the quarter wave plate 1 changes the polarization state of the incident plane wave and controls the polarization state of the transmission plane wave to circularly polarized light that is opposite or the same as the linearly polarized light or the incident circularly polarized light, With another quarter wave plate 8, the direction of the circularly polarized light of the transmitted plane wave can be designated as the same or the reverse direction with respect to the circularly polarized light of the incident plane wave.

The circular dichroic element which is an embodiment of the present invention is not limited to the above embodiment, and can be implemented with various modifications within the scope of the technical idea of the present invention. Specific examples of this embodiment are shown in the following examples. However, the present invention is not limited to these examples.

(Example 1: Two-layer type circular dichroic element)
First, an example of a two-layer circular dichroic element in which a quarter-wave plate and an anisotropic transmission plate shown in FIGS. Here, the members 3a and 4a were set as metal (silver), and the members 3b and 4b were set as insulators (SiO ₂ ). Thereby, the anisotropy of the refractive index in the unit surface 31 in FIG. 3 can be increased.
The size _{l x} × _{l y} unit surface 31 and the unit surface 41 was set to 300 × 300 nm ^2. The width t _x of the negative dielectric constant member was 30 nm. At this time, the advanced axis coincides with the x axis, and the delay axis coincides with the y axis. Further, the electromagnetic wave transmitting member 4a1~4a6 at unit surface 41, the size _{s x} × _{s y} placed the area of 50 × 50 nm ² square six consecutive diagonally. The square areas were arranged in the xy plane with the corners in the vector (-1, 1) direction. The high transmittance axis is generated in the direction of vector (1, 1), and the low transmittance axis is generated in the direction of vector (-1, 1).
Under the above settings, when the incident plane wave is 855 nm, the thickness of the quarter wavelength plate is 284 nm. The thickness of the anisotropic transmission plate was 210 nm.
Next, the calculation result of the transmission spectrum when the incident plane wave was incident perpendicularly to the incident surface (xy plane) of the two-layer circular dichroic element was calculated.

In the above-described method for calculating the transmittance and the polarization state of the transmitted plane wave, with respect to specific numerical calculations related to the present invention, the orders of the vibrators used for Fourier expansion are ±± in the x and y directions, respectively. By taking the 17th order or more, the calculation accuracy was suppressed to ± 1%.
In addition, numerical calculation was implemented with respect to the case where the circular dichroic element in this application exists in the air or a vacuum. Further, as a material parameter constituting the circular dichroic element for this numerical calculation, the relative dielectric constant of silver was obtained from Non-Patent Document 3. The relative dielectric constant of SiO ₂ was 2.13, which is a well-known value in the target wavelength range. (same as below)

FIG. 8 is a graph showing the calculation results of the transmission spectrum of the circular dichroic element of Example 1. The solid line is the calculation result of the transmission spectrum when the clockwise circular polarized light is incident, and the dotted line is the calculation result of the transmission spectrum when the counterclockwise circular polarized light is incident.
As shown in FIG. 8, the transmissivity was minimum at 855 nm when it was counterclockwise circularly polarized light and decreased to 1.1%. On the other hand, in the case of clockwise circular polarization, the transmittance was 855 nm and the transmittance was 82.4%.
That is, it has been clarified that the two-layer structure shown in FIG. 1 functions as a circular dichroic element when the wavelength of the incident plane wave is 855 nm. The calculation result of the transmission spectrum was obtained by the method described above (hereinafter, this arrangement and calculation method are the same).

Next, the degree of circular dichroism was calculated from the transmission spectrum. The solid line in FIG. 9 is the degree of circular dichroism calculated directly from the transmission spectrum. At a wavelength of 855 nm, the circular dichroism σ was a maximum value of 0.97, and this value was close to the upper limit 1 of the circular dichroism.
The efficiency factor ε = 82.4 × 0.97 = 80. Also, the efficiency factor α for the structure was α = 855 / (284 + 210) = 1.73, which was the sub-wavelength size.

Next, the polarization state of the transmitted plane wave of the two-layer circular dichroic element was calculated.
FIG. 10 is a calculation result of the polarization state of the transmitted plane wave that is incident on the two-layered circular dichroic element with the clockwise circularly polarized incident plane wave, and the incident polarization vector is normalized to 1. (Hereafter, the same standardization was performed).
Here, the horizontal axis represents the electric field Ex of the x component, the vertical axis represents the electric field Ey of the y component, and the electric field components (Ex, Ey) were projected onto the plane. When one period of light was plotted, the electric field changed in the vector (1, 1) direction (the arrow direction in FIG. 10) in the xy plane. That is, the transmitted plane wave was linearly polarized light in the vector (1, 1) direction.

FIG. 11 shows the result of calculation of the transmission spectrum in order to verify whether the anisotropic transmission plate 2 of FIG. 1 is an anisotropic transmission plate having a sub-wavelength thinness alone. Show. The thickness of the anisotropic transmission plate 2 was 210 nm. The solid line is the calculation result of the transmission spectrum when the incident plane wave is linearly polarized light in the (1, 1) direction, and the dotted line is the calculation result of the transmission spectrum when the incident plane wave is linearly polarized light in the (-1, 1) direction. .
When the linearly polarized light of the incident plane wave is in the (1, 1) direction, the transmittance in the wavelength range of 800 to 950 nm of the incident plane wave was greater than 80%. On the other hand, when the linearly polarized light of the incident plane wave is in the (-1, 1) direction, the transmittance was as small as 2% or less. Therefore, it has been clarified that when the anisotropic transmission plate 2 exists alone, the anisotropic transmission plate is actually an anisotropic transmission plate having a thin sub-wavelength.
In addition, since it can verify similarly to the nonpatent literature 4 that the quarter wavelength plate 1 turns into a quarter wavelength plate of the sub wavelength thinness, it abbreviate | omits here.
In the example shown in FIG. 11, the calculation was performed with the thickness of the anisotropic transmission plate being 210 nm. The thickness of the anisotropic transmission plate is preferably 1/5 or more of the wavelength of the incident plane wave within the range in which the thickness of the entire circular dichroic element is maintained at the sub-wavelength. . At that time, attention should be paid to satisfy that the ratio of the high transmittance to the low transmittance is 70 or more at the wavelength of the incident plane wave and the high transmittance is 80% or more.

(Example 2: First three-layer circular dichroic element)
An example of the first three-layer circular dichroic element shown in FIG. 5 is shown in the same manner as in Example 1 except that another quarter-wave plate is laminated on the other side of the anisotropic transmission plate. .
As shown in FIG. 5, the calculation model of the first three-layer circular dichroic element is a 284-nm-thick quarter-wave plate and a 210-nm-thick anisotropic transmission structure plate in the order in which incident plane waves are transmitted. In addition, another quarter-wave plate having a thickness of 255 nm is laminated.
Here, the reason why the thickness of another quarter-wave plate 6 differs from the thickness of the quarter-wave plate 1 by about 10% is that the electromagnetic wave immediately after passing through the anisotropic transmission plate contains a near-field component. This is because it is not an ideal plane wave. As for the thickness of the other quarter-wave plate 6, it is necessary to optimize the transmission plane wave to circularly polarized light.
The unit surface of the quarter wavelength plate and another quarter wavelength plate was the same unit surface as shown in FIG. The unit surface of the anisotropic transmission plate is the same as the unit surface of FIG.
Next, a transmission spectrum in the case where an incident plane wave traveling in the direction of the wave vector 5 shown in FIG. 5, that is, in the −z direction, is perpendicularly incident on the incident surface (xy plane) of the three-layer circular dichroic element. The calculation result of was calculated.

FIG. 12 is a graph showing the calculation results of the transmission spectrum of the circular dichroic element of Example 2. The solid line is the calculation result of the transmission spectrum when the incident plane wave is clockwise circularly polarized light, and the dotted line is the calculation result of the transmission spectrum when it is counterclockwise circularly polarized light.
As shown in FIG. 12, near 850 nm, the transmission spectrum under counterclockwise circularly polarized light was as small as several percent or less. On the other hand, the transmittance exceeded 70% under clockwise circularly polarized light. Therefore, it was revealed that the first three-layer circular dichroic element has circular dichroism around 850 nm.

FIG. 13 is a graph showing the circular dichroism degree σ. A wavelength range in which the circular dichroism degree σ exceeds 90% exists in a wavelength range of 50 nm or more, and a large circular dichroism degree can be realized. It was.
At a wavelength of 855 nm, TR = 71.9%, TL = 1.0%, and σ = 0.97, close to the upper limit. At this time, the efficiency factor ε = 70 as a circular dichroic element, which is an efficiency that contributes to practical use. In addition, the efficiency factor α related to the thickness α = 855 / (284 + 210 + 255) = 1.1, and it was also revealed that the sub-wavelength size was thin.

FIG. 14 shows the electric field vector distribution of the transmitted plane wave at a certain time, that is, the polarization state in a three-dimensional manner when the incident plane wave with a wavelength of 855 nm is clockwise circularly polarized light. The direction and magnitude of the electric field vector corresponding to the position of the plane wave at an arbitrary time are shown.

FIG. 15 shows the calculation result of the polarization state of the transmitted plane wave that is incident on the three-layered circular dichroic element with the incident plane wave of clockwise circularly polarized light, and the intensity of the incident polarized light is normalized to 1. The electric field vector is projected onto the xy plane. The arrows in FIG. 15 indicate the direction in which the electric field vector rotates along the light traveling direction.
As shown in FIGS. 14 and 15, the transmitted plane wave was counterclockwise circularly polarized light.
From the above, the three-layer structure shown in FIG. 5 efficiently transmits only the clockwise circularly polarized incident plane wave, and converts the direction of the circularly polarized light to the opposite direction, thereby transmitting the counterclockwise circularly polarized transmitted plane wave. It was clarified that the circular dichroic element emits as

(Example 3: Second three-layer circular dichroic element)
Next, the second three-layer circular dichroic element shown in FIG. 6 is configured as shown in FIG. 6 except that the direction of another quarter-wave plate is rotated by 90 ° in the xy plane. A calculation model was created.
As shown in FIG. 6, the negative dielectric constant member 9a and the electromagnetic wave transmitting member 9b extend uniformly in the direction parallel to the x axis and are alternately distributed in the y axis direction.

Next, the calculation result of the transmission spectrum when the incident plane wave was incident perpendicularly to the incident surface (xy plane) of the three-layer circular dichroic element was calculated.
FIG. 16 is a graph showing the calculation results of the transmission spectrum of the circular dichroic element of Example 3. The solid line is the transmission spectrum when the incident plane wave is clockwise circularly polarized light, and the dotted line is the counterclockwise circularly polarized light. Is the transmission spectrum.
As shown in FIG. 16, the transmission spectrum of counterclockwise circularly polarized light takes a small value of several percent or less near the wavelength of 860 nm, while the transmission spectrum of clockwise circularly polarized light shows a transmittance exceeding 50%. It was. Further, TR at a wavelength of 855 nm was TR = 63.7%, TL = 1.1%, σ = 0.96, and it was close to the upper limit value 1 of σ. Further, the efficiency factor ε = 61, and it was a circular dichroic element useful for practical use. The efficiency factor α of the structure at a wavelength of 855 nm was 1.1, and the sub-wavelength size was thin.
FIG. 17 shows the circular dichroism degree σ, and the circular dichroism degree σ takes a maximum value exceeding 95% near the wavelength of 860 nm.

FIG. 18 shows the electric field vector distribution of a transmission plane wave at a certain time, that is, the polarization state three-dimensionally when the incident plane wave with a wavelength of 855 nm is clockwise circular polarization, and the transmission plane wave traveling in the −z direction. It is the figure which showed the locus | trajectory of the electric field vector in arbitrary time.
As shown in FIG. 18, the incident plane wave of the clockwise circularly polarized light remains the clockwise circularly polarized light even when it becomes a transmitted plane wave. It is clear that the three-layer circular dichroic element shown in FIG. 6 has a function of efficiently transmitting only clockwise circularly polarized light and keeping the direction of circularly polarized light to the same clockwise circularly polarized light as the incident plane wave. Became.

(Example 4: second two-layer circular dichroic element)
An example of a two-layered circular dichroic element for an incident plane wave wavelength of 460 nm is shown. The circular dichroic element has the unit surface 31 of FIG. 3, the quarter-wave plate having a thickness of 118 nm and the unit surface 191 of FIG. 19, and two layers of an anisotropic transmission plate having a thickness of 30 nm. It consists of a laminated structure. The unit surfaces 31 and 191 have a size lx × ly of 150 × 150 nm ² , tx on the unit surface 31 is 30 nm, and both px and py on the unit surface 191 are 50 nm. Moreover, the negative dielectric constant member in the unit surfaces 31 and 191 was a metal (silver), and the electromagnetic wave transmitting member was an insulator (SiO ₂ ). The high transmittance axis in the anisotropic transmission plate is the (1, 1) direction in the unit surface 191, and the low transmittance axis is the (-1, 1) direction.
This second two-layer circular dichroic element had a circular dichroism degree σ of 0.78 and an efficiency factor ε of 26, indicating a circular dichroism.
The incident wavelength of 460 nm in this example is shorter than that in Example 1, and the imaginary part of the dielectric constant of silver is increased to increase the absorption loss. As a result, it was considered that the efficiency factor and the like were reduced.

(Example 5: Third two-layer circular dichroic element)
An example of a two-layered circular dichroic element for an incident plane wave wavelength of 1500 nm is shown. The circular dichroic element has the unit surface 31 of FIG. 3, the quarter-wave plate having a thickness of 176 nm and the unit surface 201 of FIG. 20, and two layers of an anisotropic transmission plate having a thickness of 340 nm. It consists of a laminated structure. The unit surfaces 31 and 191 have a size lx × ly of 250 × 250 nm ² , tx of the unit surface 31 is 50 nm, and both wx and wy of the unit surface 201 are 50 nm. The five squares 12a1, 12a2, 12a3, 12a4, 12a5 are all the same shape. Moreover, the negative dielectric constant member in the unit surfaces 31 and 201 was metal (silver), and the electromagnetic wave transmitting member was semiconductor (Si). The high transmittance axis in the anisotropic transmission plate is the (1, 1) direction in the unit surface 201, and the low transmittance axis is the (-1, 1) direction.
This second two-layer circular dichroism element had a circular dichroism degree σ of 0.92 and an efficiency factor ε of 44, indicating circular dichroism. At an incident wavelength of 1500 nm in the present embodiment, since the electromagnetic wave transmitting member Si has a large dielectric constant, reflection loss increases, and thus the transmittance relatively decreases. As a result, it was considered that the efficiency factors and the like were reduced as compared with Example 1. In addition, the value of the nonpatent literature 9 was quoted for the dielectric constant of Si in a present Example.

(Comparative Example 1)
First, the polarization state of the transmitted plane wave was investigated when the structure parameters lx, ly, and tx were the same as in Example 1 except that the layer structure having the unit surface 31 existed alone and the thickness was 100 nm. . The wavelength of the incident plane wave is 855 nm. FIG. 19 shows the result, and the polarization state of the transmitted plane wave is elliptically polarized with respect to the incident circularly polarized light. Therefore, it can be seen that when the layer structure is present alone, it is a polarization conversion element. However, if the ¼ wavelength plate is used, the transmitted plane wave becomes linearly polarized light, so the layer structure is not a ¼ wavelength plate.
Next, an element in which the layer structure having a thickness of 100 nm and the anisotropic transmission plate are stacked is referred to as Comparative Example 1. The element has a structure in which the thickness of the polarization conversion element is changed by the two-layer circular dichroic element 101.
FIG. 22 shows the calculation result of the transmission spectrum of the two-layer element of Comparative Example 1. The solid line indicates the case of an incident plane wave with clockwise circular polarization, and the dotted line indicates the case of an incident plane wave with counterclockwise circular polarization. In FIG. 22, when the wavelength is 855 nm, the circular dichroism σ = (72.7-14.7) / (72.7 + 14.7) = 0.66, and the circular dichroism as compared with Example 1. The degree is falling. Note that the efficiency factor ε = 48.

While the circular dichroism degree σ of the elements of Examples 1 to 3 is 0.96 or more, in Comparative Example 1, σ is 0.66 and the efficiency factor ε = 48. It was considered that the circular dichroic element of Comparative Example 1 had a reduced degree of circular dichroism because the thickness of the polarization conversion element was not optimized.

(Comparative Example 2)
In Example 1, the wavelength of the incident plane wave is 500 nm. In this case, since the layer corresponding to 1 in FIG. 1 cannot convert the circularly polarized incident plane wave into linearly polarized light, it is not a quarter wavelength plate. Therefore, the two-layer circular dichroic element 101 does not have a laminated structure of a quarter-wave plate and an anisotropic transmission plate with respect to an incident plane wave having a wavelength of 500 nm. In this example, the degree of circular dichroism σ = (27.2-56.3) / (27.2 + 56.3) = − 0.35, and the efficiency factor ε = 20.

(Comparative Example 3)
In Example 1, the wavelength of the incident plane wave is 1500 nm. In this case, since the layer corresponding to 1 in FIG. 1 cannot convert the circularly polarized incident plane wave into linearly polarized light, it is not a quarter wavelength plate. Therefore, the two-layer circular dichroic element 101 does not have a laminated structure of a quarter-wave plate and an anisotropic transmission plate with respect to an incident plane wave having a wavelength of 1500 nm. In this example, the degree of circular dichroism σ = (44.6-28.5) / (44.6 + 28.5) = 0.22, and the efficiency factor ε = 9.8.

(Comparative Example 4)
In Example 1, the wavelength of the incident plane wave is 2000 nm. In this case, since the layer corresponding to 1 in FIG. 1 cannot convert the circularly polarized incident plane wave into linearly polarized light, it is not a quarter wavelength plate. Accordingly, the two-layer circular dichroic element 101 does not have a laminated structure of a quarter-wave plate and an anisotropic transmission plate with respect to an incident plane wave having a wavelength of 2000 nm. In this example, the circular dichroism degree σ = (44.1-30.4) / (44.1 + 30.4) = 0.18, and the efficiency factor ε = 8.1.

(Comparative Example 5)
In Example 1, the wavelength of the incident plane wave is 350 nm. In this case, since the thickness of the element is 494 nm, it is not the thickness of the sub-wavelength. Since the layer corresponding to 1 in FIG. 1 cannot convert the circularly polarized incident plane wave into linearly polarized light, it is not a quarter wavelength plate. Therefore, the two-layer circular dichroic element 101 does not have a laminated structure of a quarter wavelength plate and an anisotropic transmission plate with respect to an incident plane wave having a wavelength of 350 nm, and the thickness of the element is larger than the wavelength. . In this example, the degree of circular dichroism σ = (17.6-12.4) / (17.6 + 12.4) = 0.17, and the efficiency factor ε = 3.0.

  In Comparative Examples 2, 3, 4, and 5, in any case, the layer corresponding to the quarter-wave plate that converts the incident circularly polarized light is not optimized with respect to the thickness, so the absolute value of the circular dichroism is It was considered that it became 0.35 or less. Further, since the layer corresponding to the anisotropic transmission plate structure does not have a unit surface structure suitable for the wavelength, it was considered that the efficiency factor decreased to 20 or less.

The circular dichroic element of the present invention has a circular dichroism degree σ of 0.75 or more, an efficiency factor ε of 25 or more, a thickness smaller than the wavelength of the incident plane wave, and the polarization state of the transmitted plane wave Is a circular dichroic element that can be controlled to be linearly polarized light or circularly polarized light that is opposite or the same as that of incident circularly polarized light, and can be used in the optical device industry using spintronic materials and the like.

DESCRIPTION OF SYMBOLS 1 ... 1/4 wavelength plate, 1a ... One side, 1b ... Other side, 2 ... Anisotropic transmission plate, 2a ... One side, 2b ... Other side, 3a ... Negative dielectric constant member, 3b ... Electromagnetic wave transmission member, 3c ... Advanced Axis, 3d ... delay axis, 4a, 4a1, 4a2, 4a3, 4a5, 4a6 ... negative dielectric constant member, 4b ... electromagnetic wave transmitting member, 4c ... high transmittance axis, 4d ... low transmittance axis, 5 ... wave vector, 6 ... another quarter wave plate, 7a ... negative dielectric constant member, 7b ... electromagnetic wave transmission member, 8 ... another quarter wave plate, 9a ... negative dielectric constant member, 9b ... electromagnetic wave transmission member, 9c ... advanced shaft, 9d ... Delay axis, 10a, 10b, 10c ... Negative dielectric constant member, 10d, 10e ... Electromagnetic wave transmission member, 11a ... High transmittance axis, 11b ... Low transmittance axis, 12a1, 12a2, 12a3, 12a4, 12a5 ... Negative dielectric Rate member, 12b1, 12b2 ... electromagnetic wave transmitting member, 13a ... high Excess axis, 13b ... Low transmittance axis, 14 ... Wave vector, 15 ... Electric field vector, 16 ... Wave vector, 17 ... Electric field vector, 18 ... Circular dichroic element, 19 ... Wave vector, 20 ... Circularly circularly polarized light 21 ... wave vector, 22 ... counterclockwise circular polarization, 23 ... transmitted light wave vector under clockwise circular polarization, 24 ... transmitted light wave vector under counterclockwise circular polarization, 31 ... unit plane of quarter wave plate, 41: Unit plane of anisotropic transmission plate, 71: Unit plane of another quarter-wave plate, 101: Two-layer circular dichroic element, 102: First three-layer circular dichroic element, 103 2nd three-layer type circular dichroic element, 191 ... Unit surface of anisotropic transmission plate, 201 ... Unit surface of anisotropic transmission plate.

Claims (9)

A circular dichroic element having a laminated structure of a quarter-wave plate and an anisotropic transmission plate and having a sub-wavelength thickness, wherein the quarter-wave plate is selected from a wavelength region of 400 nm to 1600 nm The circularly polarized light of one plane wave that can be converted into linearly polarized light, and the anisotropic transmission plate has a high transmittance axis in the direction of linear polarization of the one plane wave. Sex element. 2. The circular dichroic element according to claim 1, wherein a high transmittance axis of the anisotropic transmission plate forms an angle of 45 degrees with respect to an advanced axis of the quarter-wave plate. The quarter-wave plate is composed of a negative dielectric constant member and an electromagnetic wave transmitting member, and a plurality of lines in which the negative dielectric constant member is arranged in parallel and at a constant interval on one surface side of the quarter-wave plate. 3. The circular dichroic element according to claim 1, wherein the circular dichroic element is formed, and the extending direction of the line is an advanced axis direction of the quarter-wave plate. The anisotropic transmission plate is composed of an electromagnetic wave transmission member and a negative dielectric constant member, and on one side of the anisotropic transmission plate, the negative dielectric constant member has a plurality of quadrangular shapes of the same size, adjacent to each other. A plurality of lines formed by arranging apex angles of the negative dielectric constant members close to each other and arranging them in one direction are arranged in parallel and at a constant interval, or the anisotropic transmission plate The circle according to any one of claims 1 to 3, wherein the negative dielectric constant member is arranged on one surface side so as to form a plurality of lines arranged in parallel and at constant intervals. Dichroic element.   The circular dichroic element according to claim 1, wherein the negative dielectric constant member is a metal.   The circular dichroic element according to claim 1, wherein the electromagnetic wave transmitting member is made of a material having a transmittance of 70% or more for the one plane wave.   The circle according to any one of claims 1 to 6, wherein another quarter-wave plate is laminated on a surface of the anisotropic transmission plate opposite to the quarter-wave plate. Dichroic element.   The circle according to claim 7, wherein the other quarter-wave plate is laminated so that the advanced axes of the quarter-wave plate and the other quarter-wave plate are parallel to each other. Dichroic element. 8. The second circular plate according to claim 7, wherein the another quarter-wave plate is laminated so that the advanced axes of the quarter-wave plate and the other quarter-wave plate are orthogonal to each other. Color element.