A polarization converter for controlling broadband full polarization states by light

Abstract

The application discloses a polarization converter for controlling wideband full polarization states, comprising a polarization control layer and a transmission substrate layer; the polarization control layer is arranged in a regular matrix by a plurality of periodic transmission units; each periodic transmission unit is composed of a square structure at the periphery of the unit, a ladder structure at the middle of the unit, a ladder-shaped hollow at the left rear diagonal of the unit, and an L-shaped hollow at the right front diagonal of the unit. The application controls the external laser to exert laser pulses on the photosensitive material layer of the polarization converter, so that a large number of photoexcited carriers are generated, a periodic unit resonator is formed, and the polarization of the terahertz wave is regulated under a specific frequency band. In addition, the application can realize the full polarization state conversion of the terahertz wave by adjusting the frequency of the incident terahertz wave, 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 capable of optically controlling broadband full polarization states. Background Art

[0002] With the recent rapid development of network communication technology, 5G communication technology has matured and is gradually being commercialized. Fundamental theoretical research on 6G communication technology, featuring a wider spectrum and faster transmission rates, has begun globally. Terahertz communication technology has the potential to achieve data transmission rates of up to 1 Tbit / s and is expected to become the primary operating frequency band for 6G communication, offering one of the best solutions for its implementation. As a key component in terahertz communication technology, terahertz polarization converters convert and transmit polarization states across different frequency bands, enabling efficient modulation of multi-band signals and providing important technical support and assurance for the application of terahertz communication technology. Currently, terahertz polarization converters primarily utilize resonant structures designed with tunable metal composite materials and achieve polarization conversion through either electrical or thermal control. However, terahertz polarization converters using electrical control require a direct connection between the power source and the polarization converter, while those using thermal control require proximity between the heating source and the polarization converter. These limitations limit their application scenarios. 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 provides a polarization converter with optically controlled broadband full polarization state.

[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 states 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 corner of the unit, and an L-shaped hollow at the right front corner 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 solution, the stepped structure is a three-level stepped structure.

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

[0008] In the above solution, the transmissive material layer of the polarization control layer is made of the same material as 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, where the polarization states include right circular polarization, linear polarization and left circular polarization.

[0011] Compared with the existing technology, the present invention generates a large number of photoexcited carriers by laser pumping the photosensitive material layer of the terahertz polarization converter, thereby making the terahertz polarization converter form a resonator to achieve phase control of the terahertz wave transmitted in a specific frequency band (0.5 to 1.05 THz). This further broadens the application scenarios of the terahertz polarization converter. In addition, the present invention does not require any changes to the surface structure of the terahertz polarization converter. It only needs to change the frequency of the incident terahertz wave to achieve full polarization state conversion of the terahertz wave. This greatly improves the adaptability of the terahertz polarization converter and greatly reduces its cost of use. The present invention has the characteristics of simple preparation, low cost, stable performance and wide application scenarios, and is suitable for fields such as terahertz communication and imaging. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 It is a perspective view of the structure of the polarization converter of the present application.

[0013] Figure 2 It is a perspective view of the structure of the polarization control layer.

[0014] Figure 3 It is a perspective view of the structure of a periodical transmission unit.

[0015] Figure 4 It is a plan view of a periodical transmission unit.

[0016] Figure 5 It is a curve diagram of the co-polarization transmittance and cross-polarization transmittance of the present application in the case of no laser pumping.

[0017] Figure 6 It is a curve diagram of the co-polarization transmittance and cross-polarization transmittance of the present application in the case of laser pumping.

[0018] Figure 7 It is a curve diagram of the ellipticity of the present application in the case of no laser pumping and in the case of laser pumping.

[0019] In the figure, 1 is a transmission base layer; 2 is a polarization control layer, 21 is a transmission material layer, and 22 is a photosensitive material layer. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below with reference to the specific examples and the accompanying drawings. It should be noted that the directional terms mentioned in the examples, such as “up”, “down”, “middle”, “left”, “right”, “front”, “back” and the like, are only the directions of the accompanying drawings. Therefore, the directions used are only used for description and are not used to limit the protection scope of the present application.

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

[0022] Referring to Figure 2 , the photosensitive material layer 22 and the transmissive material layer 21 of the polarization control layer 2 are stacked with each other, and the surface structures of the photosensitive material layer 22 and the transmissive material layer 21 are completely the same, i.e. the polarization control layer 2 is composed of a surface periodic structure formed by a plurality of periodic transmission units arranged in a regular matrix. In the present application, the periodic transmission units on the polarization control layer 2 are formed by etching. In the preferred embodiment of the present application, the polarization control layer 2 is composed of 8x8 periodic transmission units.

[0023] The surface periodic structure on the polarization control layer 2 is the key structure of the polarization converter. Referring to Figure 3 and 4Each periodic transmission unit is composed of a U-shaped structure at the unit's periphery, a stepped structure in the unit's center, a stepped hollow at the unit's left rear corner, and an L-shaped hollow at the unit's right front corner. 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 stepped structure has three or more levels. The shapes of the stepped hollowing and the L-shaped hollowing are both the gaps formed between the stepped structure and the U-shaped structure. The L-shaped hollowing 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 is the gap between the stepped 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 is two levels of steps; when the stepped structure has four levels of steps, the stepped hollowing is three levels of steps, and so on.

[0024] During use, the terahertz wave is incident from the top surface of the polarization control layer 2, passes through the polarization control layer 2 and the transmissive base layer 1, and is transmitted from the bottom surface of the transmissive base layer 1. To allow the terahertz beam on the polarization converter to pass through unobstructed, 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 incident perpendicularly from the top surface of the polarization control layer 2. To ensure the laser's excitation effect 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 pumped obliquely from the top surface of the polarization control layer 2. The laser used in the present invention has a wavelength of 800 nm to 1064 nm and a power of 0.5 W to 1.5 W.

[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 produce a photoelectric effect, does not generate photoexcited carriers, the polarization converter does not constitute a resonator, there is 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. As can be seen from the figure, within the wide frequency band of 0.5 to 1.05 THz, the transmitted terahertz wave is not polarized, the co-polarization transmittance within the frequency 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, generating 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 within the wide frequency band of 0.5 to 1.05 THz, the transmitted terahertz wave is polarized, and the co-polarization transmittance and cross-polarization transmittance within the band exceed 18%.

[0028] When laser pumping is applied to the upper surface of the polarization control layer 2 , different polarization states (right-handed circular polarization, linear polarization, and left-handed circular polarization) of the transmitted terahertz wave can be achieved by changing the frequency of the incident terahertz wave. Figure 7 This is a schematic diagram of the ellipticity curve of the polarization conversion of terahertz waves in the absence of laser pumping and with laser pumping in the present invention. It can be seen from the figure that within the wide frequency band of 0.5 to 1.05 THz, the transmitted terahertz wave can achieve full polarization states (0 to 2π), and as the frequency of the incident terahertz wave increases, a complete polarization conversion effect of the transmitted terahertz wave from right-handed circular polarization to linear polarization to left-handed circular polarization to linear polarization to right-handed circular polarization occurs. For example, the transmitted terahertz wave at frequencies of 0.53 THz and 1.03 THz is right-handed circular polarization, the transmitted terahertz wave at a frequency of 0.75 THz is left-handed circular polarization, and the transmitted terahertz wave at 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, generating a large number of photoexcited free carriers, forming a periodic unit resonator, and achieving polarization control of terahertz waves within a specific frequency band. Furthermore, the present invention achieves full polarization state conversion of terahertz waves by simply adjusting the incident terahertz wave frequency without requiring structural redesign. Compared to existing technologies, the present invention achieves broadband full polarization state conversion, making it suitable for a variety of applications and featuring a simple structure and easy operation.

[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. Therefore, the present invention is not limited to the above-mentioned 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: The polarization control layer (2) 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 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 at the middle of the unit, a stepped hollow at the left rear corner of the unit, and an L-shaped hollow at the right front corner 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, wherein: 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 transmission material layer (21) of the polarization control layer (2) is the same as that of the transmission base layer (1).

5. The optically controlled broadband full-polarization state polarization converter according to claim 1, wherein: 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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