Terahertz magneto-optical material with step-type microstructure anti-reflection layer

Abstract

The invention belongs to the field of terahertz, relates to a magneto-optical material in a one-way transmission device (such as an isolator and the like), and particularly provides a terahertz magneto-optical material with a step-type microstructure anti-reflection layer. The objective of the invention is to solve the problems of low transmissivity, high emissivity, low forward transmission efficiency and the like caused by too large thickness of an existing magneto-optical material (La: YIG thick film) when a strong magneto-optical effect is realized. The anti-reflection layer based on the step type microstructure is creatively provided and arranged on the upper surface of the magneto-optical material layer, so that the anti-reflection and anti-reflection effects on terahertz waves are achieved, the forward transmission efficiency of the magneto-optical material is remarkably improved, and the application requirements of non-reciprocal one-way transmission devices (such as isolators and the like) of the terahertz frequency band are met.

Description

Technical Field

[0001] The present invention belongs to the terahertz field, relates to magneto-optical materials in non-reciprocal one-way transmission devices (such as isolators, etc.), and specifically provides a terahertz magneto-optical material with a stepped microstructure antireflection layer. Background Art

[0002] Terahertz waves widely exist in nature and even in people's daily lives. With the characteristics of strong coherence, strong penetration, low quantum energy, fast transmission rate, etc., they have relatively broad application prospects in the fields of communication, medicine, military, security inspection, and even remote sensing satellites. Especially after 5G commercialization, theoretical and technical research on 6G communication has been carried out worldwide. Among them, non-reciprocal one-way transmission devices (such as isolators, etc.) applicable to the terahertz frequency band have become the research focus.

[0003] Non-reciprocal one-way transmission devices mainly utilize the Faraday rotation effect of magneto-optical materials, requiring the materials themselves to have the characteristics of low absorption, low reflection, high transmittance, and good rotation angle. Currently, iron-containing garnet materials (RIG) have been proven to have a low absorption coefficient (α), a high Faraday rotation angle (θ F ) and a high laser-induced damage threshold (LIDT), and are widely used in the magneto-optical field. Further, by doping specified ions in the iron-containing garnet material, the lattice constant of the garnet can be changed, and thus a thick film with a thickness of several hundred micrometers can be grown by the liquid phase epitaxy growth process; for example, in the literature "Wafer-level Substrate-free YIG Single Crystal Film for Broadband Tunable Terahertz Isolator", by doping lanthanum element in yttrium iron garnet, a 3-inch wafer-level La:YIG thick film with a thickness of 305 μm was prepared, and the thickness was increased by stacking to achieve a Faraday rotation angle of 45° and an isolation degree of 23 dB, which has met the requirements of commercial terahertz isolators. However, due to the large difference in refractive index between La:YIG and air, relatively strong surface reflection will be caused, which will not only weaken the signal transmission, but the reflected terahertz waves may also have an adverse impact on the entire system.

[0004] Sub-wavelength structures have been widely used in anti-reflection applications in the visible light field. Among them, the principle of the stepped micro-structure is to etch to make the duty cycle different when the material thickness is different, forming an effect of gradually changing refractive index, thereby reducing the reflection of electromagnetic waves. It mainly includes structures such as cylindrical, hemispherical, pyramid-shaped, and conical, and all have good anti-reflection effects. For example, in patent documents CN202310843844.1 and CN202310246552.X, the stepped micro-structure is formed by photolithography and etching methods. However, for the field of terahertz anti-reflection and anti-transmission, the current etching technology for garnet is not yet mature. Therefore, the present invention selects the method of femtosecond laser micro-nano processing for processing. Moreover, there is no precedent for applying the stepped micro-structure to the field of terahertz anti-reflection and anti-transmission. Therefore, the present invention provides a RIG terahertz magneto-optical material with a stepped micro-structure anti-reflection layer. Summary of the Invention

[0005] The purpose of the present invention is to provide a terahertz magneto-optical material with a stepped micro-structure anti-reflection layer, so as to solve the problems of low transmittance, high reflectivity, and low forward transmission efficiency caused by excessive thickness when realizing a strong magneto-optical effect in existing magneto-optical materials (RIG thick films). The present invention creatively proposes an anti-reflection layer based on the stepped micro-structure, which is arranged on the upper surface of the magneto-optical material layer, thereby realizing the effect of increasing transmittance and reducing reflection of terahertz waves, significantly improving the forward transmission of the magneto-optical material to terahertz waves, and thus meeting the application requirements of non-reciprocal one-way transmission devices (such as isolators, etc.) in the terahertz frequency band.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] A terahertz magneto-optical material with a stepped micro-structure anti-reflection layer, characterized in that the terahertz magneto-optical material includes: a magneto-optical material layer and an anti-reflection layer, the anti-reflection layer is arranged on the upper surface of the magneto-optical material layer, and the terahertz wave is incident from the upper surface of the anti-reflection layer; the anti-reflection layer is composed of a base and N layers of stepped micro-structures arranged on the base, N = 1, 2, 3, and each layer of stepped micro-structure is composed of a number of stepped units arranged in a matrix. The stepped units all adopt a regular quadrangular prism structure, and the stepped units in the N layers of stepped micro-structures are arranged in an overlapping manner in one-to-one correspondence.

[0008] Further, the magneto-optical material layer adopts a RIG thick film, and the anti-reflection layer adopts a processed RIG layer.

[0009] Further, when the anti-reflection layer adopts a single-layer stepped micro-structure, N = 1; the value range of the unit period p of the single-layer stepped micro-structure is 0.12 mm to 0.18 mm, the value range of the unit spacing d is 0.04 mm to 0.06 mm; the value range of the height h of the structural unit in the single-layer stepped micro-structure is 0.06 mm to 0.1 mm.

[0010] Further, when the antireflection layer adopts a double-layer stepped microstructure, N = 2; the unit period p of the double-layer stepped microstructure ranges from 0.12 mm to 0.16 mm, the unit spacing d in the lower-layer stepped microstructure ranges from 0.03 mm to 0.05 mm, the unit spacing in the upper-layer stepped microstructure is 2d; the heights of the stepped units in the upper and lower stepped microstructures are the same, and the height h ranges from 0.06 mm to 0.1 mm.

[0011] Further, when the antireflection layer adopts a triple-layer stepped microstructure, N = 3; the unit period p of the triple-layer stepped microstructure ranges from 0.12 mm to 0.16 mm, the unit spacing d in the lower-layer stepped microstructure ranges from 0.03 mm to 0.05 mm, the unit spacing in the middle-layer stepped microstructure is 2d, and the unit spacing in the upper-layer stepped microstructure is 3d; the heights of the stepped units in the upper, middle, and lower stepped microstructures are the same, and the height h ranges from 0.06 mm to 0.1 mm.

[0012] Further, the thickness of the magneto-optical material layer is 2.2 mm to 2.5 mm, and the thickness of the base in the antireflection layer is 0.03 mm to 0.05 mm.

[0013] Based on the above technical solutions, the beneficial effects of the present invention are as follows:

[0014] The present invention provides a terahertz magneto-optical material with a stepped microstructure antireflection layer. By using the technical means of stacking a stepped microstructure and a magneto-optical material with a strong magneto-optical effect, the magneto-optical material has extremely low surface reflection and high signal transmission efficiency for terahertz waves while having strong optical rotation and isolation, thus meeting the application requirements of non-reciprocal unidirectional transmission devices (such as isolators, etc.) in the terahertz frequency band. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic structural diagram of the terahertz magneto-optical material with a stepped microstructure antireflection layer in Example 1.

[0016] Figure 2 It is a reflectivity result diagram of the terahertz magneto-optical material with a stepped microstructure antireflection layer in Example 1. Among them, (a) is the RIG surface reflectivity, (b) is the surface reflectivity of the terahertz magneto-optical material when p = 0.12 mm, (c) is the surface reflectivity of the terahertz magneto-optical material when p = 0.14 mm, (d) is the surface reflectivity of the terahertz magneto-optical material when p = 0.16 mm, (e) is the surface reflectivity of the terahertz magneto-optical material when p = 0.18 mm, and (f) is the surface reflectivity of the terahertz magneto-optical material when p = 0.2 mm.

[0017] Figure 3Transmission rate results graph of the terahertz magneto-optical material with a stepped microstructure antireflection layer in Example 1. Among them, (a) is the transmission rate of La:YIG, (b) is the transmission rate of the terahertz magneto-optical material when p = 0.12 mm, (c) is the transmission rate of the terahertz magneto-optical material when p = 0.14 mm, (d) is the transmission rate of the terahertz magneto-optical material when p = 0.16 mm, (e) is the transmission rate of the terahertz magneto-optical material when p = 0.18 mm, and (f) is the transmission rate of the terahertz magneto-optical material when p = 0.2 mm.

[0018] Figure 4 Schematic diagram of the structure of the terahertz magneto-optical material with a stepped microstructure antireflection layer in Example 2.

[0019] Figure 5 Reflectivity results graph of the terahertz magneto-optical material with a stepped microstructure antireflection layer in Example 2. Among them, (a) is the surface reflectivity of the terahertz magneto-optical material when p = 0.12 mm, (b) is the surface reflectivity of the terahertz magneto-optical material when p = 0.14 mm, (c) is the surface reflectivity of the terahertz magneto-optical material when p = 0.16 mm, (d) is the surface reflectivity of the terahertz magneto-optical material when p = 0.18 mm, and (e) is the surface reflectivity of the terahertz magneto-optical material when p = 0.2 mm.

[0020] Figure 6 Transmission rate results graph of the terahertz magneto-optical material with a stepped microstructure antireflection layer in Example 2. Among them, (a) is the transmission rate of the terahertz magneto-optical material when p = 0.12 mm, (b) is the transmission rate of the terahertz magneto-optical material when p = 0.14 mm, (c) is the transmission rate of the terahertz magneto-optical material when p = 0.16 mm, (d) is the transmission rate of the terahertz magneto-optical material when p = 0.18 mm, and (e) is the transmission rate of the terahertz magneto-optical material when p = 0.2 mm.

[0021] Figure 7 Schematic diagram of the structure of the terahertz magneto-optical material with a stepped microstructure antireflection layer in Example 3.

[0022] Figure 8 Reflectivity results graph of the terahertz magneto-optical material with a stepped microstructure antireflection layer in Example 3. Among them, (a) is the surface reflectivity of the terahertz magneto-optical material when p = 0.1 mm, (b) is the surface reflectivity of the terahertz magneto-optical material when p = 0.12 mm, (c) is the surface reflectivity of the terahertz magneto-optical material when p = 0.14 mm, (d) is the surface reflectivity of the terahertz magneto-optical material when p = 0.16 mm, (e) is the surface reflectivity of the terahertz magneto-optical material when p = 0.2 mm, and (f) is the surface reflectivity of the terahertz magneto-optical material when p = 0.24 mm.

[0023] Figure 9Transmission rate result graph of the terahertz magneto-optical material with a stepped microstructure antireflection layer in Example 3. Among them, (a) is the transmission rate of the terahertz magneto-optical material when p = 0.1 mm, (b) is the transmission rate of the terahertz magneto-optical material when p = 0.12 mm, (c) is the transmission rate of the terahertz magneto-optical material when p = 0.14 mm, (d) is the transmission rate of the terahertz magneto-optical material when p = 0.16 mm, (e) is the transmission rate of the terahertz magneto-optical material when p = 0.2 mm, and (f) is the transmission rate of the terahertz magneto-optical material when p = 0.24 mm.

[0024] Figure 10 Reflection rate and transmission rate result graph of the terahertz magneto-optical material with a stepped microstructure antireflection layer in Example 3 at multiple step heights. Among them, (a) is the reflection rate and (b) is the transmission rate.

[0025] Figure 11 Electric field distribution diagram in the x-z plane at the resonant frequency of the terahertz magneto-optical material with a stepped microstructure antireflection layer in Example 3.

[0026] Figure 12 Physical SEM image of the three-layer stepped microstructure antireflection layer in Example 3.

[0027] Figure 13 Comparison graph of the reflection rate test results between the terahertz magneto-optical material with a stepped microstructure antireflection layer and the RIG die in Example 3.

[0028] Figure 14 Comparison graph of the transmission rate test results between the terahertz magneto-optical material with a stepped microstructure antireflection layer and the RIG die in Example 3. Detailed implementation manners

[0029] To make the objectives, technical solutions, and beneficial effects of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0030] Example 1

[0031] This example provides a terahertz magneto-optical material with a stepped microstructure antireflection layer, and its structure is as Figure 1 shown, adopting a single-layer stepped microstructure; the terahertz magneto-optical material includes: a magneto-optical material layer and an antireflection layer. The magneto-optical material layer adopts an RIG thick film, and the antireflection layer adopts an RIG material layer; the antireflection layer is disposed on the upper surface of the magneto-optical material layer, and the terahertz wave is incident from the upper surface of the antireflection layer; the antireflection layer is composed of a base and a single-layer stepped microstructure disposed on the base. The single-layer stepped microstructure is composed of several step units arranged in a matrix, and the step unit adopts a regular quadrangular prism structure; the single-layer stepped microstructure is formed by etching the surface of the RIG die.

[0032] Furthermore, the value range of the unit period p of the single-layer stepped microstructure is 0.12 mm to 0.18 mm, and the value range of the unit spacing d is 0.04 mm to 0.06 mm; the value range of the height h of the structural unit in the single-layer stepped microstructure is 0.06 mm to 0.1 mm.

[0033] Furthermore, the thickness of the magneto-optical material layer is 2.2 mm to 2.5 mm, and the thickness of the base in the anti-reflection layer is 0.03 mm to 0.05 mm.

[0034] The beneficial effects of the present invention will be described in detail below in combination with simulation tests. The electromagnetic simulation software used in the simulation tests is CST (Computer Simulation Technology). Mainly using methods such as finite element, time-domain integral equation, and finite-difference time-domain for simulation, by transforming the electromagnetic field problem into a mathematical model and then using numerical methods to solve the model, the time domain and frequency domain can be analyzed. The simulation steps successively include: establishing a physical model, importing material electromagnetic parameters, setting ports and boundaries, mesh generation, simulation analysis, parameter scanning, etc.

[0035] For sub-wavelength structures, the characteristic size of the surface structure needs to be smaller than the wavelength. At this time, the high-order diffraction of electromagnetic waves will disappear, and only zero-order diffraction exists, making the surface reflectivity drop to the lowest level or even approach zero; in this embodiment, the minimum wavelength is about 0.25 mm. Therefore, the characteristic size of the stepped microstructure is controlled below 0.25 mm.

[0036] As Figure 1 shown, the single-layer stepped microstructure adopts a 2×2 structural unit. Among them, p represents the distance between the midpoints of adjacent structural units, that is, the unit period of the single-layer stepped microstructure; d represents the spacing between adjacent structural units, and the width of the structural unit is p - d. By changing the size of p, the period of the step distribution can be adjusted, and by changing the size of d while keeping the period unchanged, the step width can be adjusted.

[0037] A simulation model is established in CST. When measuring the transmittance, the model consists of two parts, and both the magneto-optical material layer and the anti-reflection layer are set as RIG materials; when measuring the reflectivity, a metal reflection layer also needs to be added to the lower surface of the magneto-optical material layer to ensure that the electromagnetic signal does not pass through the sample, so as to better measure the anti-reflection effect of the microstructure on electromagnetic waves. The metal reflection layer selects PEC material. The x and y directions are set as periodic boundary conditions, the z direction is an open space, and the polarization direction of the plane wave is along the x direction, and the propagation direction is from +z to -z.

[0038] In this embodiment, p is set to 0.12 mm, 0.14 mm, 0.16 mm, 0.18 mm, and 0.2 mm respectively, and d starts from 0.02 mm and increases with a gradient of 0.01 mm; a single magneto-optical material layer is used as a comparative example (i.e., without an antireflection layer structure), and the surface reflectivity results are as Figure 2 shown. It can be seen from the figure that for any period, when the value of d is close to p / 2, the antireflection effect is better; according to the effective medium theory (EMT), when the period of the structure is greater than the wavelength in the dielectric but less than the wavelength in free space, higher-order diffraction will cause local energy dissipation, thus generating absorption peaks at a fixed frequency; in order to be applicable to broadband isolators, it is also necessary to calculate the 10 dB bandwidth (reflectivity below -10 dB) of each group of simulation results and the average reflectivity in the range of 0.1 - 0.8 THz. The results are shown in Table 1. It can be seen from the table that when p is in the range of 0.12 - 0.18 mm, the average reflectivity is lower than -10 dB, and the bandwidth can reach a relatively high level, and the effect is the best when d is about 0.06 mm.

[0039] Table 1

[0040] p / mm d / mm at the best reflection effect 10 dB bandwidth / THz Average reflectivity / dB 0.12 0.02 0.252 -9.38 0.14 0.06 0.750 -10.91 0.16 0.06 0.666 -13.83 0.18 0.06 0.620 -13.25 0.2 0.06 0.299 -5.40

[0041] Subsequently, the transmittance of each group of structures is simulated, and the results are as Figure 3 shown. Moreover, the average transmittance is calculated in the frequency range of 0.1 - 0.6 THz, and the size of the -3 dB bandwidth (transmittance above -3 dB) is calculated. The results are shown in Table 2; it can be seen from the figure and table that when the value of p is smaller, that is, the step distribution is denser, the average transmittance is higher, but the change is not obvious. Considering the results of the previous reflection simulation, since a denser step distribution will increase the reflection to a certain extent, therefore, the most ideal value of p should be set to about 0.16 mm, and the step spacing should be 0.06 mm. At this time, the transmittance is above -3 dB in the range of 0.35 - 0.55 THz.

[0042] Table 2

[0043] p / mm d / mm at the best transmission effect 3 dB bandwidth / THz Average transmittance / dB 0.12 0.02 0.210 -2.97 0.14 0.02 0.096 -3.06 0.16 0.06 0.211 -3.10 0.18 0.06 0.173 -3.28 0.2 0.06 0.100 -3.67

[0044] Example 2

[0045] This embodiment provides a terahertz magneto-optical material with a stepped microstructure antireflection layer, and its structure is as Figure 2As shown in the figure, a double-layer stepped microstructure is adopted; the terahertz magneto-optical material includes: a magneto-optical material layer and an antireflection layer. The magneto-optical material layer uses a RIG thick film, and the antireflection layer uses a RIG material layer; the antireflection layer is disposed on the upper surface of the magneto-optical material layer, and the terahertz wave is incident from the upper surface of the antireflection layer; the antireflection layer is composed of a base and a double-layer stepped microstructure disposed on the base. Each layer of the stepped microstructure is composed of a plurality of stepped units arranged in a matrix. The stepped units in the upper and lower layers of the stepped microstructure adopt a regular quadrangular prism structure, and the stepped units in the upper and lower layers of the stepped microstructure are overlapped one by one, that is, the center points are overlapped in the vertical direction. Under this structure, the unit periods in the upper and lower layers of the stepped microstructure are the same; the double-layer stepped microstructure is formed by surface etching of a RIG material layer.

[0046] Further, the value range of the unit period p of the double-layer stepped microstructure is 0.12 mm to 0.16 mm, the value range of the unit spacing d in the lower-layer stepped microstructure is 0.03 mm to 0.05 mm, and the unit spacing in the upper-layer stepped microstructure is 2d; the stepped units in the upper and lower layers of the stepped microstructure have the same height, and the value range of the height h is 0.06 mm to 0.1 mm.

[0047] Further, the thickness of the magneto-optical material layer is 2.2 mm to 2.5 mm, and the thickness of the base in the antireflection layer is 0.03 mm to 0.05 mm.

[0048] The beneficial effects of the present invention will be described in detail below in combination with simulation tests. The simulation process is the same as that in Embodiment 1.

[0049] As Figure 4 shown, p is set to 0.12 mm, 0.14 mm, 0.16 mm, 0.18 mm, and 0.2 mm respectively, and d starts from 0.02 mm and increases in a gradient of 0.01 mm; the surface reflectivity results are as Figure 5 shown, and the average reflectivity and 10 dB bandwidth are shown in Table 3; it can be seen from the charts that compared with the single-layer stepped microstructure, the average reflectivity has decreased significantly, all below -10 dB. Among them, the average reflectivity in the range of p from 0.14 to 0.18 mm can even be reduced to below -15 dB, and the 10 dB bandwidth has also been further improved.

[0050] Table 3

[0051] p / mm d / mm at the best reflection effect 10 dB bandwidth / THz Average reflectivity / dB 0.12 0.02 0.417 -12.32 0.14 0.04 0.721 -15.67 0.16 0.04 0.714 -17.31 0.18 0.04 0.950 -15.38 0.2 0.04 0.928 -14.13

[0052] Subsequently, the transmittance of each group of structures was simulated, and the results are as Figure 6As shown, the frequency range of 0.1 - 0.6 THz was selected to calculate its average transmittance, and the magnitude of the -3 dB bandwidth (transmittance higher than -3 dB) was calculated. The results are shown in Table 4. It can be seen from the chart that compared with the single-layer stepped microstructure, the average transmittance and 3 dB bandwidth have been further improved. When p is less than 0.16 mm, the average transmittance is already higher than -3 dB. Considering the comprehensive reflection simulation results, for the stepped microstructure, when p is 0.16 mm and d is 0.14 mm, the anti-reflection and light-transmission enhancement effect on electromagnetic waves is the best.

[0053] Table 4

[0054] p / mm d / mm at the best transmission effect 3 dB bandwidth / THz Average transmittance / dB 0.12 0.03 0.411 -2.92 0.14 0.04 0.274 -2.97 0.16 0.04 0.311 -2.92 0.18 0.04 0.300 -3.23 0.2 0.04 0.145 -3.92

[0055] Example 3

[0056] This example provides a terahertz magneto-optical material with an anti-reflection layer of stepped microstructure, and its structure is as Figure 7 shown, adopting a three-layer stepped microstructure; the terahertz magneto-optical material includes: a magneto-optical material layer and an anti-reflection layer. The magneto-optical material layer uses a RIG thick film, and the anti-reflection layer uses a RIG material layer; the anti-reflection layer is arranged on the upper surface of the magneto-optical material layer, and the terahertz wave is incident from the upper surface of the anti-reflection layer; the anti-reflection layer is composed of a base and three layers of stepped microstructures arranged on the base. Each layer of stepped microstructure is composed of several stepped units arranged in a matrix. The stepped units in the upper, middle, and lower stepped microstructures adopt a regular quadrangular prism structure, and the stepped units in the upper, middle, and lower stepped microstructures are overlapped one by one, that is, the center points are overlapped in the vertical direction. Under this structure, the unit periods in the upper, middle, and lower stepped microstructures are still the same; the three-layer stepped microstructure is formed by surface etching of the RIG material layer.

[0057] Furthermore, the value range of the unit period p of the three-layer stepped microstructure is 0.12 mm to 0.16 mm, the value range of the unit spacing d in the lower stepped microstructure is 0.03 mm to 0.05 mm, the unit spacing in the middle stepped microstructure is 2d, and the unit spacing in the upper stepped microstructure is 3d; the heights of the stepped units in the upper, middle, and lower stepped microstructures are the same, and the value range of the height h is 0.06 mm to 0.1 mm.

[0058] Furthermore, the thickness of the magneto-optical material layer is 2.2 mm to 2.5 mm, and the thickness of the base in the anti-reflection layer is 0.03 mm to 0.05 mm.

[0059] The beneficial effects of the present invention will be described in detail below in combination with simulation tests. The simulation process is the same as that in Example 1.

[0060] As Figure 7As shown, p is set to 0.1 mm, 0.12 mm, 0.14 mm, 0.16 mm, 0.2 mm, and 0.24 mm respectively, and d starts from 0.02 mm and increases with a gradient of 0.01 mm; the surface reflectivity results are as Figure 8 shown. The average reflectivity and 10 dB bandwidth are shown in Table 5; as can be seen from the chart, compared with the double-layer stepped microstructure, the average reflectivity has increased again, and the 10 dB bandwidth has increased to about 0.9 THz at this time, and almost the anti-reflection effect for the entire frequency band below 1 THz has been achieved at this time.

[0061] Table 5

[0062] p / mm d / mm at the best reflection effect 10 dB bandwidth / THz Average reflectivity / dB 0.1 0.02 0.903 -12.98 0.12 0.02 0.945 -12.54 0.14 0.02 0.864 -13.67 0.16 0.04 0.864 -17.11 0.2 0.04 0.925 -18.44 0.24 0.05 0.941 -16.42

[0063] Subsequently, the transmittance of each group of structures was simulated, and the results are as Figure 9 shown. Moreover, the frequency range 0.1 - 0.6 THz was selected to calculate its average transmittance, and the magnitude of the -3 dB bandwidth (transmittance higher than -3 dB) was calculated. The results are shown in Table 6; as can be seen from the chart, when p is less than 0.16 mm, the average transmittance of the three-layer step further increases and can reach about -2.7 dB, and the 3 dB bandwidth can also reach more than 0.6 THz; however, when the p value is too high, the average transmittance decreases significantly. This is because the transmittance of the three-layer step for terahertz waves decreases significantly below 0.6 THz at this time, thereby pulling down the average transmittance in the range of 0.1 - 0.6 THz, which also limits the maximum value that p can take; combining the reflection results, when p is 0.14 mm and d is 0.02 mm, the anti-reflection and anti-transmission effects of the three-layer step structure are the best. At this time, the widths of the three-layer steps from bottom to top are 0.12, 0.1, and 0.08 mm respectively.

[0064] Table 6

[0065]

[0066]

[0067] Finally, p and d are set to 0.14 mm and 0.02 mm respectively, the height h of each layer of the step is adjusted, and the reflectivity and transmittance of the stepped microstructure at each height are simulated. The results are as Figure 10 shown, and the specific values are shown in Table 7; as can be seen from the chart, as the height increases, the average reflectivity first decreases and then increases, and the 3 dB bandwidth and average transmittance of the transmittance first increase and then decrease. After comprehensive analysis, when the height of each step is 0.08 mm, the anti-reflection and anti-transmission effects are the best.

[0068] Table 7

[0069]

[0070] Furthermore, when h = 0.08 mm is set, the electric field distribution in the x-z plane at the resonant frequency of the reflectivity is as follows Figure 11 shown. It can be more intuitively seen from the electric field distribution diagram that most of the energy is concentrated in the air gap between adjacent microstructures and is not reflected, reflecting the good antireflection effect of the present invention.

[0071] Furthermore, the physical object of the three-layer stepped microstructure antireflection layer in this embodiment is as follows Figure 12 shown, and it is processed by using the femtosecond laser micro-nano processing technology; in order to elaborate the beneficial effects of this embodiment in detail, the reflectivities of the terahertz magneto-optical material and the RIG die in this embodiment are measured by using a THz-TDS system, and the results are as follows Figure 13 shown. It can be seen from the figure that the average reflectivities of the two are -17.18 dB and -3.37 respectively, and the average reflectivity of the terahertz magneto-optical material in this embodiment is reduced by 13.81 dB. At the same time, subsequently, the transmittances of the terahertz magneto-optical material and the RIG die in this embodiment are measured by using a THz-TDS system, and the results are as follows Figure 14 shown. In the range of 0.1 - 0.6 THz, the average transmittances of the two are -1.41 dB and -2.04 respectively, and the average transmittance of the terahertz magneto-optical material in this embodiment is increased by 0.63 dB. Through the actual measurement of the magneto-optical material, it also proves that the stepped microstructure antireflection layer proposed by the present invention can achieve the effect of antireflection and antireflection enhancement.

[0072] The above is only the specific implementation manner of the present invention. Any feature disclosed in this specification, unless specifically described, can be replaced by other equivalent or similar-purpose alternative features; all the features disclosed, or all the steps in all the methods or processes, except for the mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A terahertz magneto - optical material with an antireflection layer having a stepped micro - structure, characterized in that The terahertz magneto-optical material includes: a magneto-optical material layer and an antireflection layer. The antireflection layer is disposed on the upper surface of the magneto-optical material layer, and terahertz waves are incident from the upper surface of the antireflection layer. The antireflection layer is composed of a base and N layer of stepped microstructures disposed on the base, where N = 1, 2, 3. Each layer of stepped microstructures is composed of a number of step units arranged in a matrix. The step units all adopt a regular quadrangular prism structure, and the step units in the N layer of stepped microstructures are arranged in an overlapping manner in one-to-one correspondence.

2. The terahertz magneto-optic material with a stepped microstructure antireflection layer according to claim 1, characterized in that, The magneto-optical material layer adopts a RIG thick film, and the antireflection layer adopts an etched RIG layer.

3. The terahertz magneto-optical material with a stepped microstructure antireflection layer according to claim 1, characterized in that When the antireflection layer adopts a single-layer stepped microstructure, N = 1. The value range of the unit period p of the single-layer stepped microstructure is 0.12 mm to 0.18 mm, and the value range of the unit spacing d is 0.04 mm to 0.06 mm. The value range of the height h of the structural units in the single-layer stepped microstructure is 0.06 mm to 0.1 mm.

4. The terahertz magneto-optical material with a stepped microstructure antireflection layer according to claim 1, characterized in that When the antireflection layer adopts a double-layer stepped microstructure, N = 2. The value range of the unit period p of the double-layer stepped microstructure is 0.12 mm to 0.16 mm. The value range of the unit spacing d in the lower-layer stepped microstructure is 0.03 mm to 0.05 mm, and the unit spacing in the upper-layer stepped microstructure is 2d. The heights of the step units in the upper and lower-layer stepped microstructures are the same, and the value range of the height h is 0.06 mm to 0.1 mm.

5. The terahertz magneto-optic material with a stepped microstructure antireflection layer according to claim 1, wherein When the antireflection layer adopts a triple-layer stepped microstructure, N = 3. The value range of the unit period p of the triple-layer stepped microstructure is 0.12 mm to 0.16 mm. The value range of the unit spacing d in the lower-layer stepped microstructure is 0.03 mm to 0.05 mm, the unit spacing in the middle-layer stepped microstructure is 2d, and the unit spacing in the upper-layer stepped microstructure is 3d. The heights of the step units in the upper, middle, and lower-layer stepped microstructures are the same, and the value range of the height h is 0.06 mm to 0.1 mm.

6. The terahertz magneto-optic material with a stepped microstructure antireflection layer according to claim 1, characterized in that The thickness of the magneto-optical material layer is 2.2 mm to 2.5 mm, and the thickness of the base in the antireflection layer is 0.03 mm to 0.05 mm.

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