Light-operated broadband full-polarization-state polarization converter

Abstract

The invention discloses a polarization converter of a light-operated broadband full-polarization state. The polarization converter comprises a polarization control layer and a transmission substrate layer, the polarization control layer is formed by arranging a plurality of periodic transmission units in a regular matrix in an attached mode. Each periodic transmission unit is composed of a square-shaped structure located on the periphery of the unit, a step-shaped structure located in the middle of the unit, a step-shaped hollowed-out part located on the left rear opposite angle of the unit and an L-shaped hollowed-out part located on the right front opposite angle of the unit. External laser is controlled to apply laser pulses to the photosensitive material layer of the polarization converter, so that the photosensitive material layer generates a large number of light-excited free carriers, a periodic unit resonator is formed, and polarization regulation of terahertz waves under a specific frequency band is achieved. Besides, full polarization state conversion of the terahertz waves can be realized only by adjusting the frequency of the incident terahertz waves so as to be suitable for different occasions.

Description

Technical Field

[0001] The present invention relates to the field of terahertz technology, and in particular to a polarization converter for optically controlling broadband full polarization states. Background Art

[0002] Recently, with the rapid development of network communication technology, 5G communication technology has matured and gradually commercialized. The basic theoretical research of 6G communication technology with wider communication spectrum and faster transmission rate has been gradually carried out worldwide. Terahertz communication technology is expected to achieve data transmission of up to 1Tbit / s, and is expected to become the main working frequency band of 6G communication, which is one of the best solutions for realizing 6G communication technology. As a key basic component in terahertz communication technology, terahertz polarization converter realizes effective modulation of multi-band signals by completing polarization state conversion and transmission in different frequency bands, providing important technical support and guarantee for the application of terahertz communication technology. At present, terahertz polarization converters mainly use metal composite controllable materials to design resonant structures, and realize the polarization conversion function of polarization converters by powering or heating control methods. However, terahertz polarization converters using power control methods require the power source to be directly connected to the polarization converter, and terahertz polarization conversion using heating control methods requires the heating source to be close to the polarization converter, which to a certain extent limits the application scenarios of polarization converters. In addition, after the surface structure of the existing terahertz polarization converter is determined, it can generally only achieve a single polarization state conversion, but cannot achieve full polarization state conversion. Summary of the invention

[0003] The present invention aims to solve the problem that the application scenarios of existing terahertz polarization converters are limited and it is difficult to achieve terahertz full polarization state conversion, and to provide a polarization converter with optically controlled broadband full polarization states.

[0004] To solve the above problems, the present invention is achieved through the following technical solutions:

[0005] A polarization converter with optically controlled broadband full polarization state comprises a polarization control layer and a transmission substrate layer; the polarization control layer is located on the upper surface of the transmission substrate layer and is formed by stacking an upper photosensitive material layer and a lower transmission material layer; the polarization control layer is formed by a plurality of periodic transmission units arranged in a regular matrix; each periodic transmission unit is composed of a U-shaped structure at the periphery of the unit, a stepped structure in the middle of the unit, a stepped hollow at the left rear diagonal of the unit, and an L-shaped hollow at the right front diagonal of the unit; the left side of the stepped structure is connected to the left side bar of the U-shaped structure, and the rear side of the stepped structure is connected to the rear side bar of the U-shaped structure; when in use, a terahertz wave is incident from the upper surface of the polarization control layer, passes through the polarization control layer and the transmission substrate layer, and is transmitted from the lower surface of the transmission substrate layer; when there is no laser pumping on the upper surface of the polarization control layer, the transmitted terahertz wave is not polarized; when there is laser pumping on the upper surface of the polarization control layer, the transmitted terahertz wave is polarized.

[0006] In the above scheme, the stepped structure is a three-level stepped structure.

[0007] In the above scheme, the photosensitive material layer is made of vanadium dioxide, photosensitive silicon or transition metal sulfide semiconductor; the transmission material layer is made of mica, high-resistance silicon or sapphire; and the transmission base layer is made of mica, high-resistance silicon or sapphire.

[0008] In the above solution, the material of the transmissive material layer of the polarization control layer is the same as that of the transmissive base layer.

[0009] In the above solution, the spot area of ​​the terahertz wave is smaller than or equal to the coverage area of ​​all periodic transmission units of the polarization control layer; the spot area of ​​the laser is larger than or equal to the coverage area of ​​all periodic transmission units of the polarization control layer.

[0010] In the above scheme, when there is laser pumping on the upper surface of the polarization control layer, as the frequency of the incident terahertz wave changes, the transmitted terahertz wave presents different polarization states, wherein the polarization states include right-handed circular polarization, linear polarization and left-handed circular polarization.

[0011] Compared with the prior art, the present invention uses laser pumping to generate a large number of photoexcited carriers through the photosensitive material layer of the terahertz polarization converter, so that the terahertz polarization converter forms a resonator to achieve the phase control of the terahertz wave transmitted under a specific frequency band (0.5-1.05THz), which further broadens the application scenarios of the terahertz polarization converter; in addition, the present invention does not need to change the surface structure of the terahertz polarization converter, and only needs to change the frequency of the incident terahertz wave to achieve the full polarization state conversion of the terahertz wave, which greatly improves the adaptability of the terahertz polarization converter and greatly reduces its use cost. The present invention has the characteristics of simple preparation, low cost, stable performance and wide application scenarios, and is suitable for terahertz communication and imaging and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 The figure is a schematic diagram of the three-dimensional structure of a polarization converter with optically controlled broadband full polarization states.

[0013] Figure 2 Schematic diagram of the three-dimensional structure of the polarization control layer.

[0014] Figure 3 Schematic diagram of the three-dimensional structure of a periodic transmission unit.

[0015] Figure 4 A plan view of a periodic transmission unit.

[0016] Figure 5 It is a schematic diagram of the co-polarization transmittance and cross-polarization transmittance curves of terahertz wave polarization conversion in the absence of laser pumping in the present invention.

[0017] Figure 6 It is a schematic diagram of the co-polarization transmittance and cross-polarization transmittance curves of terahertz wave polarization conversion under laser pumping in the present invention.

[0018] Figure 7 It is a schematic diagram of the ellipticity curve of the terahertz wave polarization conversion in the case of no laser pumping and with laser pumping according to the present invention.

[0019] Numbers in the figure: 1, transmission base layer; 2, polarization control layer, 21 transmission material layer, 22 photosensitive material layer. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in combination with specific examples and with reference to the accompanying drawings. It should be noted that the directional terms mentioned in the examples, such as "upper", "lower", "middle", "left", "right", "front", "back", etc., are only referenced to the directions of the accompanying drawings. Therefore, the directions used are only used for illustration and are not used to limit the scope of protection of the present invention.

[0021] See also Figure 1, a polarization converter with optically controlled broadband full polarization state, comprising a polarization control layer 2 and a transmission substrate layer 1, wherein the polarization control layer 2 further comprises a photosensitive material layer 22 and a transmission material layer 21. The photosensitive material layer 22, the transmission material layer 21 and the transmission substrate layer 1 are stacked in sequence from top to bottom. The photosensitive material layer 22 is made of a photosensitive material, such as vanadium dioxide, photosensitive silicon or a transition metal sulfide semiconductor (such as molybdenum disulfide, tungsten disulfide, platinum diselenide and molybdenum ditelluride, etc.). The transmission material layer 21 and the transmission substrate layer 1 are made of a material with high terahertz transmittance, such as mica, high-resistance silicon or sapphire, etc. In the present invention, the material of the transmission material layer 21 of the polarization control layer 2 is the same as or different from that of the transmission substrate layer 1. However, in order to simplify the process, the transmission material layer 21 and the transmission substrate layer 1 are preferably made of the same material. The overall outer contour shape of the polarization control layer 2 and the transmission substrate layer 1 can be any shape such as a circle, a square or a polygon, which does not affect the performance of the polarization converter. In a preferred embodiment of the present invention, the overall outlines of the polarization control layer 2 and the transmissive substrate layer 1 are both square; the photosensitive material layer 22 of the polarization control layer 2 is made of vanadium dioxide (VO2) with a thickness of 0.2 to 0.4 μm; the transmissive material layer 21 of the polarization control layer 2 is made of mica (KMg3(AlSi3O 10 )F2) material, the thickness of which is between 5 and 15 μm; the transmission substrate layer 1 is made of mica (KMg3 (AlSi3O 10 )F2) material, with a thickness of 0.2mm; the entire polarization converter is in the shape of a square sheet.

[0022] See also Figure 2 , the photosensitive material layer 22 and the transmission material layer 21 of the polarization control layer 2 are stacked on each other, and the surface structures of the photosensitive material layer 22 and the transmission material layer 21 are exactly the same, that is, the polarization control layer 2 is composed of a surface periodic structure composed of a plurality of periodic transmission units arranged in a regular matrix. In the present invention, the periodic transmission units on the polarization control layer 2 are formed by etching. In a preferred embodiment of the present invention, the polarization control layer 2 is composed of 8×8 periodic transmission units.

[0023] The surface periodic structure on the polarization control layer 2 is the key structure of the polarization converter. Figure 3 and 4Each periodic transmission unit is composed of a U-shaped structure at the periphery of the unit, a stepped structure in the middle of the unit, a stepped hollow at the left rear diagonal of the unit, and an L-shaped hollow at the right front diagonal of the unit. The left side of the stepped structure is connected to the left side bar of the U-shaped structure, and the rear side of the stepped structure is connected to the rear side bar of the U-shaped structure. In the present invention, the number of levels of the stepped structure is three or more. The shapes of the stepped hollowing out and the L-shaped hollowing out are both the gaps formed between the stepped structure and the U-shaped structure, among which the L-shaped hollowing out is the gap between the front side and right side of the stepped structure and the front and right side bars of the U-shaped structure, and its shape is L-shaped; the stepped hollowing out is the gap between the step surface of the stepped structure and the left and rear bars of the U-shaped structure, and its specific shape is related to the number of levels of the stepped structure: when the stepped structure has three levels of steps, the stepped hollowing out is two levels of steps; when the stepped structure has four levels of steps, the stepped hollowing out is three levels of steps, and so on.

[0024] When in use, the terahertz wave is incident from the upper surface of the polarization control layer 2, passes through the polarization control layer 2 and the transmission substrate layer 1, and is transmitted from the lower surface of the transmission substrate layer 1. In order to allow the terahertz beam on the polarization converter to pass through without obstruction, the spot area of ​​the terahertz wave is less than or equal to the coverage area of ​​all periodic transmission units of the polarization control layer 2. In the present invention, the coverage area of ​​all periodic transmission units of the polarization control layer 2 is 1.5 to 2.5 times the spot area of ​​the terahertz beam, and the terahertz wave is vertically incident from the upper surface of the polarization control layer 2. In order to ensure the excitation effect of the laser on the polarization converter, the spot area of ​​the laser is greater than or equal to the coverage area of ​​all periodic transmission units of the polarization control layer 2. In the present invention, the spot area of ​​the laser is 2 to 3 times the coverage area of ​​all periodic transmission units of the polarization control layer 2, and the laser is obliquely pumped from the upper surface of the polarization control layer 2. The laser used in the present invention has a wavelength of 800nm ​​to 1064nm and a power of 0.5W to 1.5W.

[0025] The present invention has the following two working states:

[0026] The first working state: when there is no laser pumping on the upper surface of the polarization control layer 2, the photosensitive material of the photosensitive material layer 22 of the polarization control layer 2 does not undergo a photoelectric effect, does not generate photoexcited carriers, the polarization converter does not constitute a resonator, has no polarization conversion effect, and the transmitted terahertz wave is not polarized. Figure 5 This is a schematic diagram of the co-polarization transmittance and cross-polarization transmittance curves of terahertz wave polarization conversion in the absence of laser pumping in the present invention. It can be seen from the figure that in the wide band of 0.5 to 1.05 THz, the transmitted terahertz wave is not polarized, the co-polarization transmittance in the band exceeds 70%, and the cross-polarization transmittance is 0%.

[0027] The second working state: when there is laser pumping on the upper surface of the polarization control layer 2, the photosensitive material of the photosensitive material layer 22 of the polarization control layer 2 undergoes a photoelectric effect to generate photoexcited carriers, and the polarization converter forms a resonator to achieve the regulation of the terahertz wave and produce a polarization conversion effect, and the transmitted terahertz wave is polarized. Figure 6 This is a schematic diagram of the co-polarization transmittance and cross-polarization transmittance curves of terahertz wave polarization conversion under laser pumping in the present invention. It can be seen from the figure that in the wide band of 0.5 to 1.05 THz, the transmitted terahertz wave is polarized, and the co-polarization transmittance and cross-polarization transmittance in the band exceed 18%.

[0028] When there is laser pumping on the upper surface of the polarization control layer 2, by changing the frequency of the incident terahertz wave, different polarization states (right-handed circular polarization, linear polarization and left-handed circular polarization) of the transmitted terahertz wave can be achieved. Figure 7 The figure is a schematic diagram of the ellipticity curve of the polarization conversion of the terahertz wave in the case of no laser pumping and with laser pumping of the present invention. It can be seen from the figure that within the wide band of 0.5-1.05 THz, the transmitted terahertz wave can achieve full polarization state (0-2π), and as the frequency of the incident terahertz wave increases, a complete polarization conversion effect of right-handed circular polarization-linear polarization-left-handed circular polarization-linear polarization-right-handed circular polarization of the transmitted terahertz wave appears, such as the transmitted terahertz wave at the frequencies of 0.53 THz and 1.03 THz is right-handed circular polarization, the transmitted terahertz wave at the frequency of 0.75 THz is left-handed circular polarization, and the transmitted terahertz wave at the frequencies of 0.66 THz and 0.86 THz is linearly polarized.

[0029] The present invention controls an external laser to apply laser pulses to the photosensitive material layer 22 of the polarization converter, so that a large number of photoexcited free carriers are generated to form a periodic unit resonator, thereby realizing polarization control of terahertz waves in a specific frequency band. In addition, the present invention does not need to redesign the structure, but only needs to adjust the frequency of the incident terahertz wave to achieve full polarization state conversion of terahertz waves. Compared with the prior art, the present invention can realize the full polarization state conversion function of a wide band, is suitable for different occasions, has a simple structure, and is easy to operate.

[0030] It should be noted that although the embodiments of the present invention described above are illustrative, they are not intended to limit the present invention, and therefore the present invention is not limited to the above specific embodiments. Without departing from the principles of the present invention, any other embodiments obtained by those skilled in the art under the guidance of the present invention are deemed to be within the protection of the present invention.

Claims

1. A polarization converter with optically controlled broadband full polarization state, characterized in that: It comprises a polarization control layer (2) and a transmission substrate layer (1); the polarization control layer (2) is located on the upper surface of the transmission substrate layer (1) and is formed by stacking an upper photosensitive material layer (22) and a lower transmission material layer (21); The polarization control layer (2) is composed of a plurality of periodic transmission units arranged in a regular matrix; each periodic transmission unit is composed of a U-shaped structure at the periphery of the unit, a stepped structure in the middle of the unit, a stepped hollow at the left rear diagonal of the unit, and an L-shaped hollow at the right front diagonal of the unit; the left side of the stepped structure is connected to the left side strip of the U-shaped structure, and the rear side of the stepped structure is connected to the rear side strip of the U-shaped structure; When in use, the terahertz wave is incident from the upper surface of the polarization control layer (2), passes through the polarization control layer (2) and the transmission substrate layer (1), and is transmitted from the lower surface of the transmission substrate layer (1); when there is no laser pumping on the upper surface of the polarization control layer (2), the transmitted terahertz wave is not polarized; when there is laser pumping on the upper surface of the polarization control layer (2), the transmitted terahertz wave is polarized.

2. The optically controlled broadband full polarization state polarization converter according to claim 1, characterized in that: The stepped structure is a three-level stepped structure.

3. The optically controlled broadband full polarization state polarization converter according to claim 1, characterized in that: The photosensitive material layer (22) is made of vanadium dioxide, photosensitive silicon or transition metal sulfide semiconductor; the transmission material layer (21) is made of mica, high-resistance silicon or sapphire; and the transmission base layer (1) is made of mica, high-resistance silicon or sapphire.

4. The optically controlled broadband full polarization state polarization converter according to claim 1 or 3, characterized in that: The material of the transmissive material layer (21) of the polarization control layer (2) is the same as that of the transmissive base layer (1).

5. The optically controlled broadband full polarization state polarization converter according to claim 1, characterized in that: The spot area of ​​the terahertz wave is smaller than or equal to the coverage area of ​​all periodic transmission units of the polarization control layer (2); and the spot area of ​​the laser is larger than or equal to the coverage area of ​​all periodic transmission units of the polarization control layer (2).

6. The optically controlled broadband full polarization state polarization converter according to claim 1, characterized in that: When laser pumping is applied to the upper surface of the polarization control layer (2), as the frequency of the incident terahertz wave changes, the transmitted terahertz wave presents different polarization states, wherein the polarization states include right-handed circular polarization, linear polarization and left-handed circular polarization.

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