CN107340559B - High efficiency and broad band circular polarization switching device and method based on super clever surface - Google Patents

Abstract

The high-efficiency broadband circular polarization conversion device and method based on metasurface disclosed in the invention belong to the technical field of micro-nano optical application. The high-efficiency broadband circular polarization conversion device based on the metasurface disclosed in the invention is a composite structure, including a nano-antenna layer, a spacer medium layer and a metal base layer. The nano-antenna layer is used to modulate the specific phase and amplitude of the incident linearly polarized light; the spacer dielectric layer is used to accumulate the phase changes of the light waves; the metal base layer is used to reflect the light waves propagating to the surface of the metal base layer, improving the overall Conversion efficiency; the nano-antenna layer, the spacer medium layer and the metal base layer form an optical resonator as a whole, which can make the light beam propagating in the optical resonator produce the Fabry-Perot multi-beam interference effect. The invention also discloses a high-efficiency broadband circular polarization conversion method based on the metasurface realized by the circular polarization conversion device. The present invention can realize high-efficiency and broadband modulation of the outgoing circularly polarized light.

Description

Metasurface-based high-efficiency broadband circular polarization conversion device and method

technical field

The invention relates to a high-efficiency broadband circular polarization conversion device and method based on a metasurface, and belongs to the technical field of micro-nano optical applications.

Background technique

The polarization state is one of the important properties of electromagnetic waves. Controlling the polarization state of electromagnetic waves and realizing the conversion of different polarization states has a wide range of applications in optical sensing, imaging, communication, chemical analysis and other fields. The polarization state of the electromagnetic wave can be controlled by decomposing the incident light into two orthogonal beam components and then making it achieve the desired phase delay. The traditional methods of modulating the polarization state are mainly based on anisotropic materials, such as materials with birefringence properties. When the light is not incident along the main axis, different phase changes are accumulated between ordinary light and extraordinary light, and a phase difference is formed when the light exits. , so as to realize the conversion of polarization state. Generally, birefringent materials in nature include crystals and liquid crystals. The disadvantages of such traditional methods mainly include narrow bandwidth, large size, and few types of available materials, which are not conducive to the miniaturization and integration of optical devices.

In recent years, researchers have carried out a lot of research work on metamaterials. Metamaterials are a class of artificially engineered subwavelength-sized structures with novel physical properties that do not exist in materials in nature. A variety of optoelectronic functional applications based on metamaterials have been proposed and demonstrated, such as negative refraction phenomena, metalens, and "invisibility cloaks". Anisotropic metamaterials and chiral metamaterials have been used in various polarization conversion devices from microwave to visible light. However, three-dimensional metamaterials have the inconvenience of processing technology and large volume, and a feasible way to solve such difficulties is to use metasurfaces. Metasurfaces are composed of precisely designed two-dimensional arrays of subwavelength-sized metal or dielectric elements whose thicknesses are much smaller than the wavelength. Through reasonable structural design, the scattered field of each pixel can be changed point by point in its plane, thereby controlling the corresponding phase, amplitude and polarization state, and finally realizing any desired modulation of the wavefront.

Metasurfaces can broaden the working bandwidth, have better robustness and consume lower processing costs, and are increasingly used in integrated nanophotonic devices. The use of metasurfaces to control the polarization state of electromagnetic waves has attracted a large number of researchers' research interests. By precisely designing the unit structure of single-layer or multi-layer metasurfaces, a variety of polarization state control schemes can be obtained. For example, the efficiency of 96% at 685 nm can be achieved by using the structure of metal antenna-dielectric layer-metal layer. The linear polarization conversion of (Phys.Rev.Applied.80, 023807, 2009); using cascaded four-layer metal wire grid sheets, the focused light wave can be converted from a linear polarization state to a circular polarization state at a wavelength of 2 μm (Appl. Phys.Lett.102, 231116, 2013); Using a single-layer metasurface with double F-type metal holes, the broadband linear polarization conversion effect in the terahertz band can be realized, and the transmission efficiency is not more than 40% (Opt.Lett.13, 3185-8, 2015); a polarization converter based on a single-layer metasurface with a metal rod structure, which can perform broadband line-circular polarization interconversion in the near-infrared band with an efficiency not exceeding 40% (Sci.Rep.5,18106 , 2015); by combining graphene materials, linear-circular polarization conversion and linear-linear polarization conversion can be realized in broadband operation in the terahertz band, and the transmission efficiency is not higher than 50% (Opt.Lett.23, 5592-55952016) . It can be seen that among the reported metasurface polarization conversion devices, it is difficult to realize the devices with high conversion efficiency and broadband operation in the near-infrared band, which limits its application.

SUMMARY OF THE INVENTION

In order to solve the problem that it is difficult to achieve high-efficiency broadband control in the current metasurface-based polarization device, the purpose of the present invention is to provide a metasurface circular polarization conversion device based on a double mirror symmetric structure antenna, and also to provide a circular polarization conversion device based on the circular polarization The high-efficiency broadband circular polarization conversion method based on the metasurface of the conversion device realizes the high-efficiency and broadband modulation of the outgoing circularly polarized light.

The high-efficiency broadband circular polarization conversion device based on the metasurface disclosed in the invention is a composite structure, including a nano-antenna layer, a spacer medium layer and a metal base layer. The nano-antenna layer is used to generate specific phase and amplitude modulation for the incident linearly polarized light, and is composed of nano-antennas with double mirror symmetry arranged in an array. Each nano-antenna unit includes a nano-antenna. The unit cell size is much smaller than the wavelength. The spacer dielectric layer is used to accumulate the phase change of the light wave, and the material is a dielectric. The metal base layer is used for reflecting light waves propagating on the surface of the metal base layer, thereby improving the overall conversion efficiency of the device. The spacer medium layer is located between the nano-antenna layer and the metal base layer, and the thicknesses of the nano-antenna layer and the spacer medium layer satisfy the sub-wavelength range. The nano-antenna layer, the spacer medium layer and the metal base layer as a whole constitute an optical resonant cavity, which can make the light beam propagating in the optical resonant cavity produce the Fabry-Perot multi-beam interference effect.

The design method of the nano-antenna layer is as follows:

The polarization state of electromagnetic waves can be characterized by Jones matrix, and the modulation of light by planar optics is characterized by scattering matrix. The plane where the metasurface is located is a diffraction-free scattering array, and its scattering matrix is expressed as:

where θ is the angle of incidence, and a, b, c, and d are complex coefficients. The metasurface can couple the tangential electric field and the normal magnetic field. When the tangential electric field and normal magnetic field components of the incident light are the same, the excitation effect on the metasurface is also the same. At the same time, in the absence of an additional magnetic field, the Lorentz reciprocity theorem holds. According to the matrix analysis, when the metasurface receives normal incident light excitation, the matrix elements in its scattering matrix satisfy the relationship: a=d, |b|=|c| under the condition of lossless. Further, for the two-dimensional achiral unit structure, the mirror structure can be coincident with the in-plane rotation operation. Therefore, when light is normally incident on a metasurface composed of an achiral antenna structure, the normally incident and reversely incident light will interact with a pair of mirrored structures, that is, with the unit structure before and after a certain angle of rotation . By defining the off-diagonal elements in the scattering matrix, the parameters in the phase terms of the off-diagonal elements b and c are obtained Corresponds to the azimuthal angle of the forward-propagating eigenstate of the scattering matrix, and also corresponds to the azimuthal angle of the mirror symmetry line of the achiral structure under normal incidence. Therefore, rotating the metasurface composed of two-dimensional achiral units by a certain angle will lead to the rotation of the corresponding angle of the eigenstate of its scattering matrix. Due to the structural symmetry of the two-dimensional achiral unit structure, it can overlap with the original structure after rotation, that is, the scattering matrices corresponding to before and after rotation are equal. The phase relationship between the off-diagonal elements b and c is solved by rotating the relationship that the scattering matrices are equal before and after, and the expression of the scattering matrix of the metasurface composed of achiral antenna structures under normal incidence is obtained:

where κ and are the parameters in the phase terms of the off-diagonal elements b, c. For metasurfaces with birefringence properties under non-destructive conditions, a set of specific solutions are obtained by solving the parameter relationship under the constraint of energy conservation: Further write the expression of the constrained scattering matrix:

To obtain circularly polarized eigenstates, choose where n is an integer. Substituting into formula (3), the scattering matrix of the circularly polarized eigenstate can be obtained:

Therefore, the nano-antenna with double mirror symmetry is selected, and the angle between the polarization direction of the incident ray polarized light and the mirror symmetry axis of the achiral structure is set to be 45° or 135° by setting the appropriate unit period, so that the nanometer The antenna layer has a scattering matrix as shown in equation (4). It should be noted that, for the regulation of polarization, the incident light is usually decomposed into mutually perpendicular polarization components, and the final superposed polarization conversion effect is achieved by controlling the phase difference between the components. Therefore, when setting the geometric parameters of the nano-antenna layer, it is necessary to satisfy that the nano-antenna layer has different resonance frequencies for the linearly polarized light in the x and y directions, so as to ensure that the device has a wide operating band range.

The design method of the spacer dielectric layer is as follows:

In order to achieve the effect of accumulating phase, a spacer dielectric layer is used, and the spacer dielectric layer is a transparent medium for electromagnetic waves. The thickness of the spacer medium layer is adjustable, and by adjusting the thickness of the spacer medium layer, polarization conversion in different frequency ranges and circular polarization conversion effects in different rotation directions can be obtained.

The nano-antenna layer is preferably an Ω-type nano-antenna layer. The Ω-type nanoantenna has different resonance frequencies for the linearly polarized light in the x and y directions, thus ensuring the device has a wide operating band range.

The size of the Ω-type gold nano-antenna unit is in the sub-wavelength range.

The material of the spacer dielectric layer is preferably MgF ₂ .

The material of the metal base layer is preferably gold.

The invention also discloses a metasurface-based high-efficiency broadband circular polarization conversion method realized by a metasurface-based high-efficiency broadband circular polarization conversion device. The light beam incident on the surface of the metasurface-based high-efficiency broadband circular polarization conversion device is a Laser, the polarization direction of the incident light is modulated by the polarizer into linearly polarized light with an angle of 45° or 135° to the mirror symmetry axis of the device surface, and is incident on the device surface along the normal direction of the surface of the circular polarization conversion device. After the linearly polarized incident light interacts with the circular polarization conversion device, sufficient phase changes are accumulated, and the reflection is close to lossless, and the polarization state of the reflected light is circularly polarized, thereby realizing efficient and broadband modulation of the outgoing circularly polarized light.

The high-efficiency broadband circular polarization conversion device and method based on the metasurface disclosed by the invention has strong applicability in the working band in the communication optical band.

Beneficial effects:

1. The high-efficiency broadband circular polarization conversion device and method based on a metasurface disclosed in the present invention utilizes a metasurface based on a nano-antenna array with double mirror symmetry, combined with a spacer medium layer and a metal base layer, to provide a An efficient and broadband method for linear-circular conversion of the polarization state of reflected light, which works in the near-infrared band, can generate reflected light with a circularly polarized state under the vertical incidence of the linearly polarized state in the ±45° direction, and the obtained reflected circularly polarized light has super Broadband effect and ultra-high conversion efficiency, solving the problem that current metasurface polarizers are difficult to achieve high-efficiency broadband polarization control. In particular, the working band of the present invention is within the communication optical band, and has strong applicability.

2. The high-efficiency broadband circular polarization conversion device based on metasurface disclosed in the present invention is an all-solid-state, ultra-thin, planar optical component that does not require any mechanical stretching, rotation, etc. The high-efficiency broadband circular polarization conversion device and method of the bright surface can be widely used in miniaturized, miniaturized and integrated optoelectronic applications, especially in laser communication systems and polarization detection systems, which can effectively reduce its volume and weight, and can Provides an efficient and broadband modulation method for on-chip applications of integrated optics.

Description of drawings

Figure 1 is a schematic structural diagram of a high-efficiency broadband circular polarization conversion device based on metasurface; (a) a schematic diagram of a three-layer structure, (b) a schematic structural diagram of an Ω-type antenna unit; wherein: 1—nano-antenna array, 2—spacer dielectric layer, 3—metal base layer;

2 is a schematic diagram of a two-dimensional achiral unit structure and its mirror image structure;

Fig. 3 is a reflectance diagram of the normal incidence of linearly polarized light with a polarization angle of 45° on a metasurface-based high-efficiency broadband circular polarization conversion device. (a) the amplitudes of the x and y components of the reflected light, (b) the phases of the x and y components of the reflected light;

Figure 4 shows the Stokes parameter of reflected light. (a) Stokes parameters of the reflected light of the linearly polarized light with polarization angles of 45° and -45° incident on the surface of the device perpendicularly, (b) the linearly polarized light with a polarization angle of 45° incident obliquely on the metasurface-based The Stokes parameters of the reflected light obtained from the surface of the high-efficiency broadband circular polarization conversion device, where the incident angles are 15°, 30° and 45°, respectively;

Figure 5 shows the absolute value of the Stokes parameter of the reflected light when the polarization angle of the incident light varies in the range of 0° to 360°.

Detailed ways

The present invention will be described below with reference to the accompanying drawings and embodiments. The specific implementations described herein are only used to explain the present invention, and are not intended to limit the present invention.

Example 1:

In order to verify the feasibility and beneficial effects of the efficient broadband circular polarization conversion device and method based on metasurface disclosed in the present invention, a metasurface with an operating wavelength of λ=1.2 μm-1.6 μm is used as an example.

As shown in FIG. 1 , the metasurface-based high-efficiency broadband circular polarization conversion device disclosed in this embodiment is a composite structure, including an Ω-type nano-antenna layer 1 , a spacer medium layer 2 and a metal base layer 3 . The Ω-type nano-antenna layer 1 is used to generate specific phase and amplitude modulation for the incident linearly polarized light, and is composed of Ω-type nano-antennas with double mirror symmetry arranged in an array, and each Ω-type nano-antenna unit includes an Ω-type nano-antenna unit. The size of the Ω-type nano-antenna unit is much smaller than the wavelength. The spacer dielectric layer 2 is used for accumulating the phase change of the light wave, and the material is a dielectric material. The metal base layer 3 is used to reflect the light waves propagating to the surface of the metal base layer, so as to improve the overall conversion efficiency of the device. The spacer medium layer 2 is located between the nano-antenna layer and the metal base layer 3, and the thicknesses of the Ω-type nano-antenna layer 1 and the spacer medium layer 2 satisfy the sub-wavelength range. The Ω-type nano-antenna layer 1, the spacer medium layer 2 and the metal base layer 3 form an optical resonant cavity as a whole, which can make the light beam propagating in the optical resonant cavity produce the Fabry-Perot multi-beam interference effect.

The Ω-type nanoantenna has different resonance frequencies for the linearly polarized light in the x and y directions, thus ensuring the device has a wide operating band range.

The size of the Ω-type gold nano-antenna unit is in the subwavelength range.

The material of the spacer dielectric layer is MgF ₂ .

The material of the metal base layer is gold.

The design method of the nano-antenna layer is as follows:

A single unit period of a metasurface based on an Ω-type nanoantenna array contains an Ω-type metal structure, and the entire array is composed of multiple unit periodic structures arranged into a planar layer, as shown in Figure 1. The Ω-type nanoantenna is a two-dimensional achiral double mirror-symmetric structure, as shown in Fig. 2, and the scattering matrix satisfies the formula (3). The structure and size parameters of the precisely designed Ω-type nano-antenna are shown in Figure 1. The outer radius of the ring part of the Ω-type structure is 100nm, the length of the two sides and the opening is 80nm, the width is 50nm, and the period is 320nm. The structure size parameter can modulate the incident light in the near-infrared band. When the linear polarization angle of the incident light is π/4 or -π/4, the best circular polarization conversion effect is obtained, that is, the scattering matrix that satisfies the formula (4). Through the setting of the Ω-type nano-antenna layer 1, circularly polarized transmitted light and reflected light are obtained, and the two have opposite rotation directions and equal amplitudes, but the efficiencies are theoretically 50% each, and further design is needed to improve the reflected light. conversion efficiency.

The design method of the spacer dielectric layer is as follows:

The spacer dielectric layer 2 is mainly used to change the cumulative phase difference of the incident light, and by designing its thickness dimension, circularly polarized reflected light can be obtained in different frequency bands. Under different thickness conditions, circularly polarized light with different rotation directions is obtained. Here, a thickness of 50 nm is chosen as an example.

The incident light interacts with the Ω-type nano-antenna layer 1 to obtain circularly polarized eigenstate transmission and reflection, in which part of the transmission passes through the infinite reflection and transmission of the spacer dielectric layer 2 and the metal base layer 3, from the Ω-type nano-antenna layer 1 exits, superimposed with the previous part of the reflected light, and finally forms the circularly polarized reflected light. When the electromagnetic wave is decomposed into components in the x and y directions, the reflected electric field components have the same amplitude in the frequency band of 185THz ~ 250THz (corresponding to wavelengths of 1.2μm ~ 1.6μm), and the phase difference is about 90°, which is the circular polarization state, as shown in Figure 3 shown. The Stokes parameter is further used to characterize the polarization state of the reflected light. The calculation formula of the Stokes parameter is as follows:

As shown in Figure 4. When the S ₀ of the Stokes parameter is close to 1, it means that the percentage of total light intensity is close to 100%, and it has high conversion efficiency. When S ₃ of the Stokes parameter is equal to 1 or -1, it indicates that it is left-handed or right-handed circularly polarized. It can be seen from Figure 4 that when the polarization angles of the incident polarized light are 45° and -45°, through the modulation of the device, the handedness can be obtained in a wide frequency range of 187THz ~ 250THz (corresponding to wavelengths of 1.2μm ~ 1.6μm) The opposite circular polarization reflects light and the conversion efficiency is higher than 92%. The high-efficiency broadband circular polarization conversion device based on metasurface has certain flexibility and tunability. When the incident light is incident obliquely, it can obtain elliptically polarized light or approximately circularly polarized light, and the inclination range of the incident angle can reach ±45°, such as shown in Figure 4. The relationship between the polarization state of the reflected light and the polarization angle at normal incidence is shown in Figure 5. The latitude in the figure represents the absolute value of the Stokes parameter, and the longitude represents the magnitude of the polarization angle. In the case of normal incidence, when the polarization angle of incident light is not equal to 45°, the efficient broadband circular polarization conversion device based on metasurface can perform elliptical polarization conversion.

The high-efficiency broadband circular polarization conversion device based on metasurface disclosed in this embodiment is an all-solid-state, ultra-thin, planar optical component that does not require any mechanical stretching, rotation, etc. The high-efficiency broadband circular polarization conversion device and method of the bright surface can be widely used in miniaturized, miniaturized and integrated optoelectronic applications, especially in laser communication systems and polarization detection systems, which can effectively reduce its volume and weight, and can Provides an efficient and broadband modulation method for on-chip applications of integrated optics.

The above-mentioned specific descriptions further describe the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above-mentioned descriptions are only specific embodiments of the present invention, and are not intended to limit the protection of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (5)

1. the high efficiency and broad band circular polarization switching device based on super clever surface, it is characterised in that: be composite construction, including nano-antenna Layer (1), spacer dielectric layer (2) and metallic substrate layer (3)；Nano-antenna layer (1) is specific to generate to incident linearly polarized light Phase and amplitude modulation, formed by being arranged into array with the symmetrical nano-antenna of double mirror image, each nano-antenna list Member includes a nano-antenna, and the nano-antenna unit unit size is much smaller than wavelength；Spacer dielectric layer (2) is to accumulate The phase change of light wave, material selection dielectric；Metallic substrate layer (3) propagates to metallic substrate layer (3) surface for reflecting Light wave, improve the overall conversion efficiency of device；Spacer dielectric layer (2) be located at nano-antenna layer (1) and metallic substrate layer (3) it Between, the thickness of nano-antenna layer (1) and spacer dielectric layer (2) meets within the scope of sub-wavelength；Nano-antenna layer (1), interval are situated between Matter layer (2) and metallic substrate layer (3) integrally form optical resonator, and the light beam propagated in optical resonator is made to generate Fabry- Perot multiple-beam interference effect；

Described nano-antenna layer (1) design method are as follows:

The polarization state of electromagnetic wave can be characterized with Jones matrix, and planar optical device characterizes the modulation of light with collision matrix；It is super clever Plane where surface is the scattering array of salt free ligands, and collision matrix indicates are as follows:

Wherein, θ is incidence angle, and a, b, c, d are complex coefficients；Super clever surface can couple the magnetic field of tangential electric field and normal direction, when When the tangential electric field of incident light is identical with the magnetic-field component of normal direction, the excitation to super clever surface is also identical；Meanwhile Under conditions of no complementary field, Lorentz reciprocal theorem is set up；According to matrix analysis, when super clever surface receives normal incidence Light excitation when, under conditions of lossless, the matrix element in collision matrix meets relationship: a=d, | b |=| c |；Further , for two-dimentional achirality cellular construction, can be overlapped with its mirror-image structure by the rotation process in face；Therefore, when light just When being incident on the super clever surface being made of achirality antenna structure, forward entrance and reversed incident light will be with a pair of of mirror-image structures Interaction that is to say and interact with the cellular construction before and after certain angle of rotation；By defining the non-diagonal in collision matrix Member obtains the parameter in the phase term of nondiagonal element b, cThe azimuth of forward-propagating eigenstate corresponding to collision matrix, simultaneously Also correspond to the deflection of the mirror symmetry of achirality structure under the conditions of normal incidence；Therefore, two-dimentional achirality unit is constituted Super clever surface carry out the rotation of certain angle, that is, lead to the rotation of the respective angles of its collision matrix eigenstate；Since two dimension is non- The structural symmetry of chiral unit structure can be overlapped after rotating with original structure, that is to say the scattering square for corresponding to rotation front and back Battle array is equal；By the equal relationship of rotation front and back collision matrix, the phase relation between nondiagonal element b, c is solved, is obtained just The expression formula of the collision matrix on the super clever surface being made of under the conditions of incidence achirality antenna structure:

Wherein κ andIt is the parameter in the phase term of nondiagonal element b, c；For super with birefringence under the conditions of lossless Clever surface is obtained one group and is specifically solved by the parameters relationship under solution conservation of energy constraint condition:The expression formula of collision matrix after further writing out constraint:

In order to obtain the eigenstate of circular polarization, selectWherein n is integer；It is updated in formula (3), can obtain Obtain the collision matrix of circular polarization eigenstate:

Therefore, the nano-antenna with double mirror symmetry is selected, it is incident by suitable unit cycle set, and setting The polarization direction of linearly polarized light and the mirror axis angle of achirality structure are 45 ° or 135 °, have nano-antenna layer (1) The collision matrix as shown in formula (4)；It should be noted that incident light, is usually first decomposed into mutually by the regulation for polarization Vertical polarized component reaches the polarization conversion effect being finally superimposed by the phase difference between control component；Therefore, to receiving When the geometric parameter of rice antenna stack (1) is set, needs to meet nano-antenna layer (1) and have for the linearly polarized light in the direction x and y There is different resonance frequencies, so as to guarantee that device has wider service band range.

2. as described in claim 1 based on the high efficiency and broad band circular polarization switching device on super clever surface, it is characterised in that: described Spacer dielectric layer (2) design method are as follows:

In order to realize the effect of accumulated phase, using spacer dielectric layer (2), spacer dielectric layer (2) is transparent Jie for electromagnetic wave Matter；Spacer dielectric layer (2) thickness is adjustable, by control interval dielectric layer (2) thickness, can obtain inclined in different frequency scope The circular polarization conversion effect of vibration conversion and different rotation directions.

3. as claimed in claim 2 based on the high efficiency and broad band circular polarization switching device on super clever surface, it is characterised in that: described Nano-antenna layer (1) preferably Ω type nano-antenna layer (1)；Ω type nano-antenna has difference for the linearly polarized light in the direction x and y Resonance frequency, so as to guarantee device have wider service band range.

4. as claimed in claim 3 based on the high efficiency and broad band circular polarization switching device on super clever surface, it is characterised in that:

The Ω type gold nano antenna element size is in sub-wavelength range；

Described spacer dielectric layer (2) material selects MgF₂；

Metallic substrate layer (3) material selects gold.

5. the high efficiency and broad band circular polarization conversion method based on super clever surface, it is characterised in that: based on such as claim 1,2,3,4 High efficiency and broad band circular polarization switching device described in one based on super clever surface is realized, the efficient width based on super clever surface is incident to Light beam with circular polarization switching device surface is the laser that will be modulated, and is modulated to incident light polarization direction and device through the polarizer The antenna mirror axis on part surface is at 45 ° or the linearly polarized light at 135 ° of angles, along circular polarization switching device normal to a surface side To being incident on device surface；After linear polarization incident light and the interaction of circular polarization switching device, enough phase changes are accumulated, And have close to lossless reflection, the polarization state of reflected light is circular polarization, thus realize to the efficient of outgoing circularly polarized light and The modulation in broadband.