A Preparation Method of an External Chiral Metasurface and an Asymmetric Polarization Converter

Abstract

The present invention discloses a method for preparing an extrinsic chiral metasurface and an asymmetric polarization converter. The technology is based on a single-layer extrinsic chiral metasurface to achieve asymmetric reflection polarization conversion, that is, different polarization conversions in the forward and reverse directions. Even for linearly polarized light in one reflection direction, its polarization remains unchanged, while in the opposite direction, it is converted into linearly polarized light with another polarization. This technology has great application potential in applications such as different polarization state communication and computing in a reflection dual-channel; The technology is based on a single-layer extrinsic chiral metasurface to achieve asymmetric transmission polarization conversion, that is, different polarization conversions in the forward and reverse directions. Even for linearly polarized light in one propagation direction, its polarization remains unchanged, while in the opposite direction, it is converted into linearly polarized light with another polarization. This technology has great application potential in applications such as different polarization state communication and computing in a forward and reverse dual-channel.

Description

Technical Field

[0001] The present invention belongs to the field of asymmetric polarization converters, and particularly relates to a method for preparing an extrinsic chiral metasurface and an asymmetric polarization converter. Background Art

[0002] Polarization is an essential feature of electromagnetic waves. Electromagnetic waves can transmit information in different environments through different polarization states. Therefore, realizing the control and manipulation of the polarization state of the optical field is of great significance for related research in fields such as imaging, liquid crystal display, optical fiber communication, and sensing. In traditional optical systems, polarizers and wave plates are important optical components and the main tools for realizing the regulation of the polarization state of the optical field. However, these traditional optical polarization devices are no longer suitable for the requirements of miniaturized and integrated optical systems due to their large size and heavy weight.

[0003] Similar to the Faraday rotation effect, the optical field polarization conversion effect has received extensive attention because it does not require the introduction of an external magnetic field or non-commutative materials. With the emergence of metasurfaces, important progress has been made in the optical field polarization conversion of metasurfaces in the visible, near-infrared, and terahertz bands, and various functions have been realized. For example, the perpendicular conversion of the polarization direction of a linearly polarized optical field, the conversion of a linearly polarized light into a circularly polarized light, etc.

[0004] The existing asymmetric polarization conversion devices convert a linearly polarized light in one propagation direction into its orthogonal polarization during the transmission mode, and achieve zero transmission in the opposite direction. In an optical system, a reflective element is essential, which plays roles such as deflecting the optical path, reducing the volume of the instrument, and changing the upright and inverted relationship of the image. Therefore, a dual-channel reflective asymmetric polarization conversion device is very necessary.

[0005] Currently, important progress has been made in the optical field polarization conversion of metasurfaces in the microwave, visible, near-infrared, and terahertz bands, and various functions have been realized. For example, the perpendicular conversion of the polarization direction of a linearly polarized optical field, the conversion of a linearly polarized light into a circularly polarized light, etc. Among them, for the asymmetric polarization conversion function, it refers to converting a linearly polarized light in one propagation direction into its orthogonal polarization during the transmission mode and effectively reflecting the light in the opposite propagation direction.

[0006] Nowadays, most of the research on asymmetric polarization conversion is to convert a linearly polarized light in one propagation direction into its orthogonal polarization during the transmission mode and effectively reflect the light in the opposite propagation direction.

[0007] Disadvantages of the Prior Art:

[0008] It is only applicable to a single-direction polarization conversion system, which greatly limits the application range of asymmetric polarization conversion devices.

[0009] Most of the current asymmetric polarization conversion devices are composed of multiple layers of materials. The structural devices are too complex and not conducive to processing, which greatly limits the development of polarization conversion devices. Summary of the Invention

[0010] In order to solve the technical problems existing in the background art, the present invention aims to provide a method for preparing an extrinsic chiral metasurface and an asymmetric polarization converter. Based on a single-layer extrinsic chiral metasurface, asymmetric reflection polarization conversion is realized, that is, different polarization conversions are achieved in the forward and reverse directions. Even for linearly polarized light in one reflection direction, its polarization remains unchanged, and in the opposite direction, it is converted into linearly polarized light with another polarization. This technology has great application potential in applications such as different polarization state communication and computing in a reflection dual-channel; based on a single-layer extrinsic chiral metasurface to achieve asymmetric transmission polarization conversion, that is, different polarization conversions are achieved in the forward and reverse directions. Even for linearly polarized light in one propagation direction, its polarization remains unchanged, and in the opposite direction, it is converted into linearly polarized light with another polarization. This technology has great application potential in applications such as different polarization state communication and computing in a forward and reverse dual-channel.

[0011] In order to solve the technical problems, the technical solution of the present invention is:

[0012] A method for preparing an extrinsic chiral metasurface, the method comprising:

[0013] Using numerical calculations to simulate U-shaped gold extrinsic chiral metasurfaces with different parameters; then, according to the asymmetric transmission polarization conversion results, the structural size parameters are set to R = 350 nm, w = 200 nm, and the thickness is 100 nm. The array period is set to P X = 1000 nm, P y = 650 nm;

[0014] Using electron beam lithography technology, on a 1 mm thick sheet material, etch a U-shaped gold split ring resonator array with a cross-section of 5 * 5 mm 2 of.

[0015] Further, the sheet material property is quartz glass.

[0016] An asymmetric reflection polarization converter based on a single-layer extrinsic chiral metasurface, applied to the above-mentioned extrinsic chiral metasurface, the asymmetric reflection polarization converter comprising: a white light source or a laser source, a polarizer, an extrinsic chiral metasurface, a polarizer, and an optical power meter;

[0017] The beam of the white light source or the laser passes through the polarizer to form linearly polarized light. The linearly polarized light is incident on the metasurface at an angle of 45° with the normal of the metasurface, and the polarizer and the optical power meter are used to measure the polarization state of the reflected light.

[0018] Further, the transmission directions of the polarizers are all parallel to the symmetry axis direction of the U-shaped array of the external chiral metasurface, and the plane formed by the light source direction and the normal does not include the symmetry axis of the U-shaped array.

[0019] An asymmetric transmission polarization converter based on a single-layer external chiral metasurface is applied to the above-mentioned external chiral metasurface. The asymmetric transmission polarization converter includes: a white light source or a laser source, a polarizer, an external chiral metasurface, a polarizer, and an optical power meter.

[0020] The beam of the white light source or the laser passes through the polarizer to form linearly polarized light. The linearly polarized light is incident on the metasurface at an angle of 45° with the metasurface normal, and the polarization state of the transmitted light is measured with a polarizer and an optical power meter.

[0021] Further, the transmission directions of the polarizers are all parallel to the symmetry axis direction of the U-shaped array of the external chiral metasurface, and the plane formed by the light source direction and the normal does not include the symmetry axis of the U-shaped array.

[0022] Compared with the prior art, the advantages of the present invention are as follows: The present invention provides a new practical method for realizing an asymmetric reflection and transmission polarization converter, and the working frequency band is in the near-infrared, which is the core frequency band of communication, and has important application prospects in some application directions with relatively strict polarization control requirements.

[0023] Since the present invention adopts a single-layer external chiral metasurface, it has the advantages of small structural size, simple process, and easy processing.

[0024] Both directions of the present invention are for reflection, and it has great applications in future reflection dual-channel optical paths. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 、The first perspective view of an external chiral metasurface of the present invention;

[0026] Figure 2 、The second perspective view of an external chiral metasurface of the present invention;

[0027] Figure 3 、Asymmetric reflection polarization converter;

[0028] Figure 4 、Asymmetric transmission polarization converter;

[0029] Figure 5 、Polar coordinate diagram of the polarization states of the forward and backward reflected light measured when different linearly polarized lights are incident at a wavelength of 1550 nm;

[0030] Figure 6 、Polar coordinate diagram of the polarization states of the transmitted light measured when different linearly polarized lights are incident at a wavelength of 1550 nm. DETAILED DESCRIPTION OF THE INVENTION

[0031] The specific implementation manners of the present invention will be described below in conjunction with embodiments:

[0032] It should be noted that the structures, ratios, sizes, etc. shown in this specification are only used to cooperate with the content disclosed in the specification for those skilled in this technology to understand and read, and are not used to limit the implementation conditions of the present invention. Any modification of the structure, change of the proportional relationship or adjustment of the size, without affecting the effects that the present invention can produce and the purposes that can be achieved, should still fall within the scope covered by the technical content disclosed in the present invention.

[0033] At the same time, the terms such as "upper", "lower", "left", "right", "middle" and "one" cited in this specification are only for the convenience of clear narration, and are not used to limit the scope of implementation of the present invention. The change or adjustment of their relative relationships, without substantial change in the technical content, should also be regarded as the scope within which the present invention can be implemented.

[0034] Embodiment 1:

[0035] As Figure 3 shown, the specific implementation steps of a single-layer extrinsic chiral metasurface asymmetric reflection polarization converter are as follows:

[0036] As Figure 1 , 2 shown, (1) Numerical calculations are used to simulate U-shaped gold extrinsic chiral metasurfaces with different parameters; then according to the asymmetric transmission polarization conversion results of the linearly polarized light incident obliquely, the structural dimension parameters are set as R = 350 nm, w = 200 nm and the thickness is 100 nm., and the array period is set as P X = 1000 nm, P y = 650 nm;

[0037] (2) Electron beam lithography technology is used to etch a U-shaped gold split-ring resonator array with a cross-section of 5 * 5 mm 2 on a 1 mm thick sheet material, and the material property is quartz glass;

[0038] (3) The beam 3 of white light source or laser passes through the polarizer 4 to form linearly polarized light. The linearly polarized light is obliquely irradiated on the metasurface 5 at an angle of 45° with the normal of the metasurface, and the polarizer 6 and the optical power meter 7 are used to measure the polarization state of the reflected light.

[0039] The transmission directions of the polarizers are all parallel to the symmetry axis direction of the U-shaped array, and the plane of the included angle between the light source direction and the normal does not include the symmetry axis of the U-shaped array.

[0040] Appendix Figure 4Polar plots of the polarization states of the forward and backward reflected light measured when different linearly polarized lights at 1550 nm are incident.

[0041] Example 2:

[0042] As Figure 5 shown, the specific implementation steps of a single-layer extrinsic chiral metasurface-based asymmetric transmission polarization converter are as follows:

[0043] (1) Use numerical calculations to simulate U-shaped gold extrinsic chiral metasurfaces with different parameters; then, according to the asymmetric transmission polarization conversion results, set the structural dimension parameters as R = 350 nm, w = 200 nm, and the thickness as 100 nm., and set the array period as P X = 1000 nm, P y = 650 nm;

[0044] (2) Use electron beam lithography technology to etch a U-shaped gold split-ring resonator array with a cross-section of 5 * 5 mm 2 on a 1-mm-thick sheet material, and the material property is quartz glass;

[0045] (3) The light beam 3 of a white light source or a laser passes through a polarizer 4 to form linearly polarized light. The linearly polarized light is obliquely incident on the metasurface 5 at an angle of 45° with the metasurface normal, and a polarizer 6 and a power meter 7 are used to measure the polarization state of the transmitted light.

[0046] The transmission directions of the polarizer 6 are all parallel to the symmetry axis direction of the U-shaped array, and the plane formed by the light source direction and the angle with the normal does not include the symmetry axis of the U-shaped array.

[0047] Appendix Figure 6 is the polar plot of the polarization state of the transmitted light measured when different linearly polarized lights at a wavelength of 1550 nm are incident.

[0048] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the above embodiments. Within the knowledge scope of those of ordinary skill in the art, various changes can be made without departing from the gist of the present invention.

[0049] Many other changes and modifications can be made without departing from the concept and scope of the present invention. It should be understood that the present invention is not limited to specific embodiments, and the scope of the present invention is defined by the appended claims.

Claims

1. An asymmetric reflection polarization converter based on a single-layer extrinsic chiral metasurface, applied to a U-shaped gold extrinsic chiral metasurface, characterized in that The asymmetric reflection polarization converter includes: a white light source or a laser source, a polarizer, an extrinsic chiral metasurface, a polarizer, and a power meter; The beam of the white light source or the laser passes through the polarizer to form linearly polarized light, and the linearly polarized light is incident on the metasurface at an angle of 45° with respect to the normal of the metasurface; the transmission directions of the polarizers are all parallel to the symmetry axis direction of the U-shaped array of the extrinsic chiral metasurface, and the plane formed by the angle between the light source direction and the normal does not include the symmetry axis of the U-shaped array.

2. The asymmetric reflection polarization converter based on a single-layer extrinsic chiral metasurface according to claim 1, wherein The polarization state of the reflected light is measured using a polarizer and a power meter.

3. A single-layer extrinsic chiral metasurface-based asymmetric transmission polarization converter, applied to a U-shaped gold extrinsic chiral metasurface, characterized in that, The asymmetric transmission polarization converter includes: a white light source or a laser source, a polarizer, an extrinsic chiral metasurface, a polarizer, and a power meter; The beam of the white light source or the laser passes through the polarizer to form linearly polarized light, and the linearly polarized light is incident on the metasurface at an angle of 45° with respect to the normal of the metasurface; the transmission directions of the polarizers are all parallel to the symmetry axis direction of the U-shaped array of the extrinsic chiral metasurface, and the plane formed by the angle between the light source direction and the normal does not include the symmetry axis of the U-shaped array.

4. An asymmetric transmission polarization converter based on a single-layer extrinsic chiral metasurface according to claim 3, wherein The polarization state of the transmitted light is measured using a polarizer and a power meter.

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