Multi-channel independently-regulated terahertz wave beam separator

Abstract

The invention discloses a multi-channel independently-regulated terahertz beam splitter which is of a metal-medium-metal reflective structure, and the metasurface of a top patch is of an anisotropic split resonant ring structure. Wherein the metasurface is composed of N sub-metasurfaces, and the N sub-metasurfaces are spliced in any mode; the sub-metasurfaces are relatively independent, and each sub-metasurface independently controls one reflection wave beam; the size of the combined beam separator is the same as that of an incident terahertz wave light spot; each sub metasurface is composed of M units; the invention is suitable for various incident wave forms such as linearly polarized waves, circularly polarized waves and the like, and meets the requirements of diversity.

Description

Technical Field

[0001] The present invention relates to the technical field of beam splitters, and in particular to a multi-channel independently controlled terahertz beam splitter. Background Art

[0002] A beam splitter is an optical device that splits a beam of electromagnetic waves into two or more directions. It has been widely used in wireless communications, radar detection and other fields. At present, common beam splitters can reflect or transmit multiple beams in the far field. However, these beams affect each other and are difficult to control independently. As a device that can simultaneously generate and independently control beams, multi-channel beam splitters are more able to meet the needs of modern optical systems. Traditionally, this is achieved through waveguides, diffraction gratings or multilayer film cascades, which makes the device too bulky and inefficient, and therefore not suitable for compact terahertz optical systems.

[0003] Terahertz (THz) waves are electromagnetic waves with a frequency of 0.1-10THz and a wavelength of 3mm-30μm, and have received widespread attention in the fields of medicine, military, imaging, etc. However, the development of efficient and compact devices for manipulating THz waves remains challenging. Metasurfaces, as a new type of two-dimensional structure, have the ability to precisely control the amplitude, phase, and polarization of electromagnetic waves, and have the advantages of simple manufacturing and easy integration, making them easier to apply in THz systems. Among them, coded metasurfaces quantize continuous phases, further simplifying the complexity of the design, and there are many studies on this in beam splitter design.

[0004] The coded metasurface is composed of metasurface units arranged in a certain order. The order of arrangement is related to the wavefront phase, so the metasurface can achieve a variety of beam steering functions. In 2011, Capasso et al. proposed a generalized Snell's law to explain and guide the design of metasurfaces. Introducing discontinuous phases on the metasurface causes abnormal deflection of the beam, which is called a phase gradient metasurface. Phase gradient coded metasurfaces manipulate wavefronts by applying a spatially varying phase profile across the surface. This has become an effective way to precisely control the direction of electromagnetic wave transmission and helps create complex phases that are critical to efficient beam splitting.

[0005] The commonly used multi-channel beam splitters currently have major problems such as complex design, low operating frequency band, narrow bandwidth, inability to independently control the beam, polarization insensitivity, and low polarization conversion efficiency. Summary of the invention

[0006] Purpose of the invention: The purpose of the present invention is to provide a multi-channel independently controlled terahertz beam splitter to solve the problems of complex design of terahertz beam splitter, inability to independently control the far-field main beam, low polarization conversion efficiency, etc., and to achieve the far-field main beam with arbitrary deflection angle and polarization direction.

[0007] Technical solution: The multi-channel independently controlled terahertz beam splitter described in the present invention consists of a metal-dielectric-metal reflective structure, and the top-layer patch metasurface is an anisotropic split resonant ring structure; wherein the metasurface is composed of N sub-metasurfaces, and the N sub-metasurfaces are spliced ​​in an arbitrary manner; each sub-metasurface is relatively independent and each sub-metasurface independently controls a reflected beam; the size of the combined beam splitter is the same as the size of the incident terahertz wave spot; and each sub-metasurface is composed of M units.

[0008] Furthermore, the metasurface is arranged in a designed gradient phase manner, and the different arrangement of units in each sub-metasurface makes the reflected wavefront phase different, thereby deflecting the beam to different directions.

[0009] Furthermore, the designed gradient phase is arranged in a specific manner: the phase gradient is calculated by the required deflection angle according to the generalized Snell's law, and the sub-metasurface has different phase gradients or unit arrangement directions. When irradiated by a terahertz wave, a beam with a predetermined angle and polarization mode is reflected.

[0010] Furthermore, each unit reflects the incident x-line polarized terahertz wave or y-line polarized terahertz wave into a y-line polarized wave or an x-line polarized wave, and achieves a phase coverage range of 360° by rotating the resonant ring patch.

[0011] Furthermore, the medium is a polyimide material with a dielectric constant of 3.0-3.5 and a loss tangent of 0.005-0.05.

[0012] Furthermore, the thickness of the polyimide medium is 30 μm and the unit period is 103 μm.

[0013] Furthermore, the patch resonant ring width is 27 μm and the inner radius is 12 μm.

[0014] The invention provides a method for designing a multi-channel independently controlled terahertz beam splitter, comprising the following steps:

[0015] (1) The basic unit of the metasurface is established based on the anisotropic split resonant ring structure, which is a three-layer reflective structure consisting of metal-dielectric-metal. The dielectric layer is made of polyimide material with a dielectric constant of 3.0-3.5 and a loss tangent of 0.005-0.05.

[0016] (2) Optimize the structural dimensions, including unit period, dielectric thickness, and split resonant ring width, radius, opening angle and other parameters, so that the unit operates in a specific terahertz frequency band; in the unit structure optimization, the split resonant ring opening direction is 45° or -45°, the incident terahertz wave is an x ​​or y linear polarization wave, and the reflected wave should be in the direction after polarization conversion, satisfying the polarization conversion efficiency higher than 90%, and obtaining 360° phase coverage by rotating the resonant ring patch;

[0017] (3) The optimized metasurface units are arranged according to the unit distribution to obtain sub-metasurfaces, and a linearly polarized plane wave is incident to calculate the deflection angle of the reflected beam of each sub-metasurface; the sub-metasurfaces are combined together to obtain a multi-channel independently controlled beam splitter.

[0018] Furthermore, step (1) includes the following steps:

[0019] (11) According to the number of beam splitting requirements, N sub-metasurfaces are designed, corresponding to N far-field beams, which are deflected to different directions;

[0020] (12) The phase distribution of N sub-metasurfaces, i.e., the order of unit arrangement, is calculated according to the direction of beam deflection. The phase difference between adjacent units realizes the change of wavefront phase, which causes the beam to be deflected. This is designed and explained by the generalized Snell's law.

[0021] Furthermore, in step (3), the beam splitter uses linearly polarized wave incidence to achieve the target beam splitting quantity, deflection angle and polarization direction in the far field.

[0022] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The terahertz beam splitter with multi-channel independent control proposed in the present invention can realize the simultaneous generation and independent control of beams. (2) The method of combining sub-metasurfaces proposed in the present invention simplifies the difficulty of device design, and can realize an adjustable multi-channel beam splitter by replacing adjustable materials or mechanical control. (3) The beam splitter designed in the present invention can be adjusted according to the target angle and polarization requirements, and the operating frequency range can be adjusted by optimizing the unit structure parameters, which is easier to combine with practical applications. (4) The metasurface unit designed in the present invention achieves a high polarization conversion efficiency of more than 90% and a phase coverage of 360° by rotating the top layer patch, and has the advantages of wide working bandwidth. (5) The present invention is applicable to a variety of incident wave forms such as linearly polarized waves and circularly polarized waves to meet diverse needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a schematic diagram of a terahertz beam splitter of the present invention;

[0024] Figure 2 The basic structure of the super surface unit of the present invention;

[0025] Figure 3 The performance of the metasurface unit of the present invention;

[0026] Figure 4 is a far-field scattering diagram of the multi-channel beam splitter of the present invention;

[0027] Figure 5 This is the far-field scattering diagram of the multi-channel beam splitter of the present invention;

[0028] Figure 6 The performance of the metasurface unit of the present invention;

[0029] Figure 7 The phase distribution and far-field scattering diagram of the present invention;

[0030] Figure 8 The test system and results of the present invention. DETAILED DESCRIPTION

[0031] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0032] Example 1

[0033] like Figure 1 As shown, an embodiment of the present invention provides a multi-channel independently controlled terahertz beam splitter, which is composed of a metal-medium-metal reflective structure, and the top-layer patch metasurface is an anisotropic split resonant ring structure; wherein the metasurface is composed of N sub-metasurfaces, and the N sub-metasurfaces are spliced ​​in any way; each sub-metasurface is relatively independent and each sub-metasurface independently controls a reflected beam; the size of the combined beam splitter is the same as the size of the incident terahertz wave spot; each sub-metasurface is composed of M units. The metasurface is arranged in a designed gradient phase manner, and the different arrangement of units in each sub-metasurface makes the reflected wavefront phase different, so that the beam is deflected to different directions. The designed gradient phase arrangement is specifically: the phase gradient is calculated by the required deflection angle according to the generalized Snell's law, and the sub-metasurface has different phase gradients or unit arrangement directions. When irradiated by the terahertz wave, a beam with a predetermined angle and polarization mode is reflected. Each unit reflects the incident x-line polarized terahertz wave or y-line polarized terahertz wave as a y-line polarized wave or an x-line polarized wave, and achieves a phase coverage of 360° by rotating the resonant ring patch. The patch resonant ring width is 27μm and the inner radius is 12μm.

[0034] The dielectric is a polyimide material with a dielectric constant of 3.0-3.5 and a loss tangent of 0.005-0.05. The thickness of the polyimide dielectric is 30μm and the unit period is 103μm

[0035] Embodiment 2: A two-channel beam splitter with an operating frequency band of 0.8THz-1.2THz, comprising the following steps:

[0036] (1) Multi-channel beam splitter such as Figure 1 As shown, it includes metasurface unit design, sub-metasurface design, multi-channel beam splitter calculation and verification.

[0037] (2) Design Figure 2 The basic unit of the metasurface shown is a reflective structure of metal-dielectric-metal. The metal uses gold or aluminum with low loss in the terahertz band, and the dielectric is polyimide. The top patch is an anisotropic split resonant ring structure. In order to obtain high polarization conversion efficiency and full phase coverage, the optimized unit size is 30μm thick polyimide dielectric, 103μm unit period, 27μm patch resonant ring width, and 12μm inner radius. The unit is quantized in the manner of a 2-bit coded metasurface, with a total of four units, and the resonant ring opening angles are 35°, 120°, 35°, and 120° respectively. In order to obtain the maximum linear polarization conversion efficiency, the resonant ring opening directions are -45°, 45°, 45°, and -45° respectively. The four units are represented by '1', '2', '3', and '4'.

[0038] (3) By simulating and verifying the optimized unit structure, the boundaries in the x and y directions are periodic boundaries, and the z direction is an open boundary, such as Figure 3 As shown, in the range of 0.8THz-1.2THz, the polarization conversion efficiency is higher than 90%, and the phase difference of the four units is 90°.

[0039] (4) Design sub-metasurfaces with unit sequences of '1234', '12341234', '123412341234' and '1234123412341234'. In order to maintain the consistency of the structure size, the units in the four cases are periodically expanded to 12, 6, 4 and 2, respectively, and the equivalent unit period is changed accordingly. The generalized Snell's law can be used for explanation and design.

[0040]

[0041] When an electromagnetic wave passes through a i The medium with a refractive index of n r When the medium is a phase difference on the contact surface, an abnormal reflection angle is generated. After the transformation of the generalized Snell's law, when the electromagnetic wave is vertically transmitted from the air to the metasurface, the reflection angle generated is θ r .

[0042]

[0043] The theoretical deflection angles calculated according to the generalized Snell's law are 4.09°, 8.2°, 12.36°, and 25.34°, respectively.

[0044] (5) In order to reflect two independent deflected beams on the same beam splitter, it is necessary to combine two phase gradient sub-metasurfaces.

[0045] M=[AB]

[0046] B=A*

[0047] Combining the above four unit sequences A and their mirror image sequences B together, we get four 2-channel beam splitters with different beam deflection angles. Since the sub-metasurfaces are relatively independent, the main beam reflected in the far field will not be affected by other main beams.

[0048] (6) With x-polarized wave incident, the x, y, and z directions are open boundaries, and each beam splitter reflects two independent beams in the far field. The numerical simulation results are shown in Figure 4 As shown, it is consistent with the theoretical angle, and the far-field beam is a combination of the sub-metasurface deflected beams.

[0049] Embodiment 3: An adjustable four-channel beam splitter with an operating frequency band of 0.8THz-1.2THz, comprising the following steps:

[0050] (1) Based on the metasurface unit designed in Example 2, a 4-channel beam splitter is designed. The unit sequence '1234123412341234' is rotated in the directions of 90°, 180°, and 270° to obtain a total of 4 sub-metasurfaces, which are combined in a 2×2 manner to obtain 4 main beams in the -x, x, -y, and y directions.

[0051] (2) One of the sub-metasurfaces is shielded by a metal plate. The metal plate does not have the polarization deflection function and phase gradient change, so in theory a non-polarization conversion beam will be formed at the reflection center.

[0052] (3) With x-polarized wave incident, open boundaries in x, y, and z directions for simulation verification, such as Figure 5 As shown, since the metasurface unit has high polarization conversion efficiency and reflectivity, the power distribution of the main beam is relatively uniform and has good uniformity.

[0053] Embodiment 4: A four-channel beam splitter and a test scheme with an operating frequency band of 0.2THz-0.37THz, comprising the following steps:

[0054] (1) According to Figure 2The basic unit of the metasurface shown in the figure has an optimized unit size of 150μm polyimide dielectric thickness, 340μm unit period, 25μm patch resonant ring width, and 115μm inner radius. The unit is quantized in the manner of a 2-bit coded metasurface, with a total of four units, and the resonant ring opening angles are 95°, 180°, 95°, and 180°, respectively. To obtain the maximum linear polarization conversion efficiency, the resonant ring opening directions are -45°, 45°, 45°, and -45°, respectively.

[0055] (2) Calculate the polarization conversion efficiency, amplitude and phase of the four units. The x-polarized wave is incident. The x and y directions are periodic boundaries, and the z direction is an open boundary. For example, Figure 6 As shown, the polarization conversion efficiency is higher than 90% in the wide bandwidth range of 0.2THz-0.37THz, and the four units have a phase difference of 90°, which meets the design requirements of 2-bit coding metasurface.

[0056] (3) Arrange the units in the sequence of '1233412234' and combine the hypersurfaces with different orientations together, e.g. Figure 7 As shown in the figure, the numerical simulation uses x-polarized wave incident, and the incident wave uses a 20° incident angle to meet the needs of practical applications. After one sub-metasurface is shielded by a metal plate, the far-field beam presents three deflection directions and one center position, and the intensities of the four beams are close. After two sub-metasurfaces are shielded by metal plates, the far-field beam is two deflected beams and one center position beam, and the center beam is about twice the deflected beam.

[0057] (4) A commercial 150 μm polyimide film is used, a 0.2 μm thick metal layer is magnetron sputtered on one side, and a metal patch is made on the other side using a standard photolithography process to obtain a multi-channel beam splitter, and one or two of the sub-metasurfaces are shielded with a metal plate.

[0058] (5) When the reflective multi-channel beam splitter is used, the incident wave is incident at an angle of 20°, and the detector scans within the reflection area, e.g. Figure 8 As shown, the test results are consistent with the simulation results.

Claims

1. A multi-channel independently controlled terahertz beam splitter, characterized in that: It consists of a metal-dielectric-metal reflective structure, and the top-layer patch metasurface is an anisotropic split resonant ring structure; wherein, the metasurface is composed of N sub-metasurfaces, and the N sub-metasurfaces are spliced ​​in an arbitrary manner; each sub-metasurface is relatively independent and each sub-metasurface independently controls a reflected beam; the size of the combined beam splitter is the same as the size of the incident terahertz wave spot; each sub-metasurface is composed of M units.

2. A multi-channel independently controlled terahertz beam splitter according to claim 1, characterized in that: The metasurface is arranged in a designed gradient phase manner. The different arrangement of units in each sub-metasurface makes the reflected wavefront phase different, thereby deflecting the beam to different directions.

3. A multi-channel independently controlled terahertz beam splitter according to claim 2, characterized in that: The designed gradient phase is arranged in a specific manner: the phase gradient is calculated by the required deflection angle according to the generalized Snell's law, and the sub-metasurface has different phase gradients or unit arrangement directions. When irradiated by a terahertz wave, a beam with a predetermined angle and polarization mode is reflected.

4. The multi-channel independently controlled terahertz beam splitter according to claim 1, characterized in that: Each unit reflects the incident x-line polarized terahertz wave or y-line polarized terahertz wave into a y-line polarized wave or an x-line polarized wave, and achieves a phase coverage range of 360° by rotating the resonant ring patch.

5. The multi-channel independently controlled terahertz beam splitter according to claim 1, characterized in that: The medium is a polyimide material with a dielectric constant of 3.0-3.5 and a loss tangent of 0.005-0.

05.

6. The multi-channel independently controlled terahertz beam splitter according to claim 5, characterized in that: The thickness of the polyimide medium is 30μm-150μm, and the unit period is 100μm-340μm.

7. The multi-channel independently controlled terahertz beam splitter according to claim 1, characterized in that: The patch resonant ring width is 20μm-30μm, and the inner radius is 10μm-120μm.

8. A method for designing a multi-channel independently controlled terahertz beam splitter, characterized in that: The following steps are involved: (1) The basic unit of the metasurface is established based on the anisotropic split resonant ring structure, which is a three-layer reflective structure consisting of metal-dielectric-metal. The dielectric layer is made of polyimide material with a dielectric constant of 3.0-3.5 and a loss tangent of 0.005-0.

05. (2) Optimize the structural dimensions, including unit period, dielectric thickness, and split resonant ring width, radius, opening angle and other parameters, so that the unit operates in a specific terahertz frequency band; in the unit structure optimization, the split resonant ring opening direction is 45° or -45°, the incident terahertz wave is an x ​​or y linear polarization wave, and the reflected wave should be in the direction after polarization conversion, satisfying the polarization conversion efficiency higher than 90%, and obtaining 360° phase coverage by rotating the resonant ring patch; (3) The optimized metasurface units are arranged according to the unit distribution to obtain sub-metasurfaces, and a linearly polarized plane wave is incident to calculate the deflection angle of the reflected beam of each sub-metasurface; the sub-metasurfaces are combined together to obtain a multi-channel independently controlled beam splitter.

9. The method for designing a multi-channel independently controlled terahertz beam splitter according to claim 8, characterized in that: Step (1) includes the following steps: (11) According to the number of beam splitting requirements, N sub-metasurfaces are designed, corresponding to N far-field beams, which are deflected to different directions; (12) The phase distribution of N sub-metasurfaces, i.e., the order of unit arrangement, is calculated according to the direction of beam deflection. The phase difference between adjacent units realizes the change of wavefront phase, which causes the beam to be deflected. This is designed and explained by the generalized Snell's law.

10. The method for designing a multi-channel independently controlled terahertz beam splitter according to claim 8, characterized in that: In step (3), the beam splitter uses linearly polarized wave incidence to achieve the target beam splitting quantity, deflection angle and polarization direction in the far field.

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