A terahertz reflection type quasi-optical isolation system based on small-angle incidence

Abstract

This invention discloses a terahertz reflective quasi-optical isolation system based on small-angle incident light, belonging to the field of transceiver isolation technology based on reflective quasi-optical technology. The system includes: input port A, output port B, isolation port C, isolation port D, ellipsoidal mirrors M1, M2, M3, and M4, plane mirrors N1 and N2, a 90° polarization grating S1, a 45° polarization grating S2, and a reflective Faraday rotator. The reflective isolator in this invention has an incident angle close to the normal relative to the Faraday rotator and possesses very high power handling capability. Through the rational use and arrangement of various components, the energy at the -30dB edge level (99.9% of the energy) is not blocked during propagation. Furthermore, combined with a reasonable design of the beam waist conversion parameters, the collimation of the Gaussian beam during propagation is guaranteed.

Description

Technical Field

[0001] This invention belongs to the field of transceiver isolation technology based on reflective quasi-optical technology, specifically relating to a terahertz quasi-optical reflective isolation system based on small-angle incident light. Background Technology

[0002] Quasi-optical ferrite-based isolators utilize the Faraday rotation effect, a characteristic of polarization that occurs when electromagnetic waves propagate in a longitudinally magnetized ferrite medium. Simultaneously, signal transmission and reception isolation is achieved by combining grating devices and optical path design within the quasi-optical link. Researchers noted that under a certain saturation magnetization, the polarization rotation angle generated by the Faraday rotation effect is only related to the thickness of the ferrite medium. Therefore, compared to conventional waveguide devices, quasi-optical ferrite circulators are less limited by the saturation magnetization characteristics of the ferrite material, making it easier to realize broadband devices. Suitable ferrite medium thickness parameters can be obtained by combining the permanent magnet circuit and the heat dissipation requirements of the ferrite medium.

[0003] Quasi-optical Faraday rotators are the most critical components in quasi-optical beamguide isolation technology for short-millimeter-wave and terahertz radars. They not only play a vital role in protecting the transmitter but also separate the transmitted and received signals. Based on the form of the emitted wave, quasi-optical Faraday rotators can be divided into two main categories: transmission (transmission) type and reflection type. With the further improvement of high-power sources in millimeter-wave and terahertz radars, isolation technology based on transmission-type Faraday rotators is limited by power capacity bottlenecks due to the complex multilayer dielectric stacking and circumferential conduction heat dissipation mechanism of transmission-type rotators. Therefore, reflection-type quasi-optical Faraday rotators have been proposed. Compared with transmission-type quasi-optical Faraday rotators, their advantages include better heat dissipation performance, meeting the requirements of higher power applications, and lower requirements for ferrite dielectric sheet thickness.

[0004] Specifically, because the beam of a reflective quasi-optical Faraday rotator passes through the ferrite layer twice during reflection, the ferrite layer thickness is theoretically half that of a transmission Faraday rotator. Furthermore, it only requires a single-layer surface dielectric matching, making its design, fabrication, and cost lower than that of a transmission Faraday rotator. Secondly, the ferrite layer of a reflective Faraday rotator can be directly soldered to a metal backplane, allowing for rapid heat dissipation. This results in strong structural heat dissipation, whereas transmission Faraday rotators can only dissipate heat from the device's circumference, giving them a natural advantage in high power capacity.

[0005] Therefore, actively carrying out research on reflective quasi-optical technology and quasi-planar beam waveguide technology, breaking through key technologies such as theoretical design methods for reflective quasi-optical devices and design and integration of small incident angle reflective optical paths, and effectively solving the technical problem of isolation for high-power radar in the terahertz band are of great significance to promoting the development of terahertz-related application systems in my country. Summary of the Invention

[0006] This invention provides a terahertz reflective quasi-optical isolation system based on small-angle incident light. It achieves small-angle incident light with fewer components, thus realizing system compactness, reducing cost, reducing losses, and achieving high power.

[0007] The technical solution adopted in this invention is as follows:

[0008] A terahertz reflective quasi-optical isolation system based on small-angle incident light includes: an input port A, an output port B, an isolation port C, an isolation port D, ellipsoidal mirrors M1, M2, M3, and M4, plane mirrors N1 and N2, a 90° polarization grating S1, a 45° polarization grating S2, and a reflective Faraday rotator.

[0009] The Gaussian beam is fed into input port A with its polarization direction perpendicular to the grating metal strip;

[0010] The ellipsoidal mirror M1 reflects the fed Gaussian beam to the 90° polarization grating S1 after the first waist conversion.

[0011] The 90° polarization grating S1 is placed at a 45° angle to the incident Gaussian beam, so that the Gaussian beam is transmitted to the plane mirror N1.

[0012] The plane mirror N1 is tilted at an angle θ1 to the horizontal plane, reflecting the Gaussian beam to the ellipsoidal mirror M2 above the horizontal plane;

[0013] The ellipsoidal mirror M2 reflects the Gaussian beam to a reflective Faraday rotator below the horizontal plane after a second waist conversion.

[0014] The reflective Faraday rotator polarizes and rotates the incident Gaussian beam by 45° and reflects it to the ellipsoidal mirror M3 above the horizontal plane, wherein the angle between the incident Gaussian beam and the outgoing Gaussian beam is 9° to 11°.

[0015] The ellipsoidal mirror M3 reflects the Gaussian beam to the plane mirror N2 after a third waist conversion.

[0016] The plane mirror N2 is tilted at an angle θ2 to the horizontal plane, reflecting the Gaussian beam to the 45° polarization grating S2;

[0017] The 45° polarization grating S2 is placed at a 45° angle to the incident Gaussian beam, so that the Gaussian beam with a polarization rotation of 45° is transmitted to the ellipsoidal mirror M4, and the Gaussian beam with a polarization rotation angle of less than 45° is reflected to the isolation port D.

[0018] The ellipsoidal mirror M4 outputs a Gaussian beam with a polarization rotation of 45° through output port B.

[0019] The Gaussian beam reflected from output port B is transmitted in reverse, passing sequentially through ellipsoidal mirror M4, 45° polarization grating S2, plane mirror N2, ellipsoidal mirror M3, reflective Faraday rotator, ellipsoidal mirror M2, plane mirror N1, and 90° polarization grating S1, and is finally reflected to isolation port C. When the reverse-transmitted Gaussian beam passes through the reflective Faraday rotator, due to its non-reciprocity, it rotates again by 45° in the same direction, becoming a beam with its polarization direction parallel to the metal strip of the 90° polarization grating S1. When this beam is transmitted to the 90° polarization grating S1, there is almost no transmitted beam; that is, the reverse-transmitted beam is reflected to isolation port C, thus achieving isolation protection of the terahertz source.

[0020] Preferably, the 90° polarization grating S1 and the 45° polarization grating S2 are placed parallel to each other; the grating strips of the 90° polarization grating S1 are perpendicular to the horizontal plane, and the grating strips of the 45° polarization grating S2 and the grating strips of the 90° polarization grating S1 have a 45° tilt angle.

[0021] Preferably, the ellipsoidal mirrors M1, M2, and N1 are symmetrically distributed with the plane mirrors N2, M3, and M4.

[0022] Preferably, the 90° polarization grating S1 is positioned when the Gaussian beam reaches the waist state after passing through the ellipsoidal mirror M1; the reflective Faraday rotator is positioned when the Gaussian beam reaches the waist state after passing through the ellipsoidal mirror M2; and the 45° polarization grating S2 is positioned when the Gaussian beam reaches the waist state after passing through the ellipsoidal mirror M3 and the plane mirror N2.

[0023] Preferably, the tilt angle between the plane mirror N1 and the horizontal plane is θ1, and the tilt angle between the plane mirror N2 and the horizontal plane is θ2, where θ1 + θ2 = 180°.

[0024] Preferably, the mirror dimensions of ellipsoidal mirrors M1 and M4 are exactly the same as their optical parameters; the mirror dimensions of ellipsoidal mirrors M2 and M3 are exactly the same as their optical parameters; and the mirror dimensions of plane mirrors N1 and N2 are exactly the same as their optical parameters.

[0025] The beneficial effects of this invention are:

[0026] Compared to traditional waveguide modes, quasi-optical technology transmits signals by focusing electromagnetic waves in space. It operates as a Gaussian beam, with most of the energy concentrated near the propagation axis. The longitudinal propagation of the Gaussian beam exhibits planar wave characteristics, and the limited transmission path loss is primarily distributed across various mirror reflections. Furthermore, a well-designed beam waist parameter matching system can result in very low beam mirror diffraction loss.

[0027] The reflective isolator designed in this invention has an incident angle close to the normal direction relative to the Faraday rotator and has a very high power handling capability. Through the rational use and arrangement of various devices, the energy at the -30dB edge level (99.9% of the energy) is not blocked during the propagation process. Furthermore, combined with the rational design of the beam waist conversion parameters, the collimation of the Gaussian beam during propagation is guaranteed. Attached Figure Description

[0028] Figure 1 A schematic diagram of the optical path propagation of a Gaussian beam in a terahertz reflective quasi-optical isolator based on small-angle incidence;

[0029] Figure 2 Schematic diagram of a terahertz reflective quasi-optical isolator based on small-angle incident light;

[0030] Figure 3 A schematic diagram showing the propagation path of the Gaussian beam in a quasi-optical isolator and the distances between the components.

[0031] Figure 4 Schematic diagram of the dual-reflective mirror system;

[0032] Figure 5 Schematic diagram of ellipsoidal mirror section;

[0033] Figure 6 Schematic diagram of the 90° polarization grating structure;

[0034] Figure 7 Schematic diagram of the principle of a 45° polarization grating;

[0035] Figure 8 Simulation diagram of the optical path of a dual-reflection mirror system based on small-angle incident light;

[0036] Figure 9 Electric field distribution diagram of the output cross section of a dual-reflection mirror system based on small-angle incident light;

[0037] Figure 10 Electric field amplitude diagram of the output cross section of a dual-reflecting mirror system based on small-angle incident light. Detailed Implementation

[0038] The technical solution and beneficial effects of the present invention will be described in detail below with reference to the accompanying drawings.

[0039] like Figure 1 , 2As shown, this application provides a terahertz reflective quasi-optical isolation system based on small-angle incident light, comprising: an input port A, an output port B, an isolation port C, an isolation port D, ellipsoidal mirrors M1, M2, M3, and M4, plane mirrors N1 and N2, a 90° polarization grating S1, a 45° polarization grating S2, and a reflective Faraday rotator. Ellipsoidal mirrors M1, M4, N1, and N2 are placed on the same horizontal plane, ellipsoidal mirrors M2 and M3 are placed above this horizontal plane, and the reflective Faraday rotator is placed below this horizontal plane.

[0040] The Gaussian beam is fed into input port A with its polarization direction perpendicular to the grating metal strip.

[0041] The ellipsoidal mirror M1 reflects the fed Gaussian beam to the 90° polarization grating S1 after the first waist conversion.

[0042] In the 90° polarization grating S1, the grating strips are placed perpendicular to the horizontal plane, and the whole is placed at a 45° angle with the incident Gaussian beam, so that the Gaussian beam is transmitted to the plane mirror N1 with almost no loss.

[0043] The plane mirror N1 is tilted at an angle θ1 to the horizontal plane, reflecting the Gaussian beam to the ellipsoidal mirror M2 above the horizontal plane.

[0044] The ellipsoidal mirror M2 reflects the Gaussian beam to a reflective Faraday rotator below the horizontal plane after a second waist conversion.

[0045] The reflective Faraday rotator polarizes and rotates the incident Gaussian beam by 45° and reflects it to an ellipsoidal mirror M3 above the horizontal plane, wherein the angle between the incident Gaussian beam and the outgoing Gaussian beam is 10°.

[0046] The ellipsoidal mirror M3 reflects the Gaussian beam to the plane mirror N2 after a third waist conversion.

[0047] The plane mirror N2 is tilted at an angle θ2 to the horizontal plane, reflecting the Gaussian beam to the 45° polarization grating S2.

[0048] The 45° polarization grating S2 is parallel to the 90° polarization grating S1, i.e., it is placed at a 45° angle with the incident Gaussian beam. At the same time, the grating strips of the 45° polarization grating S2 and the grating strips of the 90° polarization grating S1 have a 45° tilt angle, so that the Gaussian beam with a polarization rotation of 45° is transmitted to the ellipsoidal mirror M4, and the Gaussian beam with a polarization rotation angle of less than 45° is reflected to the isolation port D.

[0049] The ellipsoidal mirror M4 outputs a Gaussian beam with a polarization rotation of 45° through output port B.

[0050] The Gaussian beam reflected from output port B is transmitted in reverse, passing sequentially through ellipsoidal mirror M4, 45° polarization grating S2, plane mirror N2, ellipsoidal mirror M3, reflective Faraday rotator, ellipsoidal mirror M2, plane mirror N1, and 90° polarization grating S1, and is finally reflected to isolation port C. When the reverse-transmitted Gaussian beam passes through the reflective Faraday rotator, due to its non-reciprocity, it rotates again by 45° in the same direction, becoming a beam with its polarization direction parallel to the metal strip of the 90° polarization grating S1. When this beam is transmitted to the 90° polarization grating S1, there is almost no transmitted beam; that is, the reverse-transmitted beam is reflected to isolation port C, thus achieving isolation protection of the terahertz source.

[0051] like Figure 3 , 4 As shown, the proposed technical measures for achieving small-angle optical path control technology are to introduce a dual-mirror system designed using physical optics methods to complete beam steering and parameter transformation. This structure can reduce the angle between the incident field and the mirror normal, thereby suppressing the occurrence of the TEM01 mode as much as possible and suppressing the cross-polarization components of the beam. The beam channel can also be optimized through this structure to ensure that the Gaussian beam waist is at the aperture of the Faraday rotator, reducing the insertion loss and ellipticity reduction caused by non-planar wavefront deviation.

[0052] Specifically, in this embodiment, the distance between ellipsoidal mirror M1 and 90° polarization grating S1 is d1, the distance between 90° polarization grating S1 and plane mirror N1 is d2, the distance between plane mirror N1 and ellipsoidal mirror M2 is d3, the distance between ellipsoidal mirror M2 and Faraday rotator is d4; the distance between ellipsoidal mirror M4 and 45° polarization grating S2 is d5, the distance between 45° polarization grating S2 and plane mirror N2 is d6, the distance between plane mirror N2 and ellipsoidal mirror M3 is d7, the distance between ellipsoidal mirror M3 and Faraday rotator is d8, and the center distance between plane mirror N1 and plane mirror N2 is L. With the center of the Faraday rotator as the axis, the left and right sides of this small-angle incident terahertz reflective quasi-optical isolator system are completely symmetrical in terms of device arrangement, that is, d1=d5, d2=d6, d3=d7, d4=d8, θ1+θ2=180°.

[0053] A 90° polarization grating S1 is placed at the position where the Gaussian beam reaches the waist state after passing through the ellipsoidal mirror M1; the reflective Faraday rotator is placed at the position where the Gaussian beam reaches the waist state after passing through the ellipsoidal mirror M2; a 45° polarization grating S2 is placed at the position where the Gaussian beam reaches the waist state after passing through the ellipsoidal mirror M3 and the plane mirror N2. Four ellipsoidal mirrors are used to achieve four waist transformations of the Gaussian beam. Let the beam waist radius after the first waist transformation be w1, the beam waist radius after the second waist transformation be w2, the beam waist radius after the third waist transformation be w3, and the beam waist radius after the fourth waist transformation be w4. Due to the symmetry of the mirror arrangement, w1 = w4 and w2 = w3.

[0054] like Figure 5 As shown, in this embodiment, ellipsoidal mirrors M1 and M4 are obtained as follows: Let the major axis of the ellipse be a, the minor axis be b, and the center be the origin. Rotate the ellipse around its major axis to obtain an ellipsoid. Then, use a cylinder with radius r1 and a central axis parallel to the y-axis to intercept the ellipsoid at coordinates (x1, y1, 0) to obtain ellipsoidal mirrors M1 and M4. The methods for obtaining ellipsoidal mirrors M2 and M3 are the same as for ellipsoidal mirror M1, where the major axis of the ellipse is a1, the minor axis is b1, the radius of the intercepting cylinder is r2, and the intercepting position coordinates are (x2, y2, 0).

[0055] In this embodiment, the operating center frequency of the entire system is 220 GHz, the distance between the Gaussian horn and the ellipsoidal mirror M1 is 100 mm, and the beam waist radius w0 of the primary beam radiated by the Gaussian horn is 1.9 mm. Considering the specific design principle of the ellipsoidal mirror and the reasonable arrangement between optical paths, the specific parameters are designed as follows:

[0056] w1 = 4.5 mm, w2 = 11.8 mm;

[0057] a=174.34mm, b=111.74mm, x1=-126.35mm, y1=50mm, r1=40mm;

[0058] a1=423.54mm, b1=308.11mm, x2=-119.15mm, y2=390.5mm, r2=25mm;

[0059] d1=220mm, d2=105mm, d3=45mm, d4=250.20mm;

[0060] θ1=70°, θ2=110°, L=27.37mm.

[0061] like Figure 6 , 7As shown, the 90° polarization grating S1 and the 45° polarization grating S2 are composed of periodically arranged cylindrical metal grating strips, wherein the radius of the metal grating strips is r = 0.05 mm and the arrangement period is g = 0.35 mm. The metal wire of the 90° polarization grating S1 is perpendicular to the polarization direction of the Gaussian beam fed from the port. When a wave with a polarization direction perpendicular to the grating strip passes through this grating, it is almost completely transmitted, and a parallel polarized wave passes through this grating, it is almost completely reflected. The grating strips in the 45° polarization grating S2 are rotated 45 degrees. When a 45° linearly polarized wave is incident on this grating, it is completely transmitted.

[0062] The key to this invention lies in a double-reflecting mirror system based on small-angle incident light. For example... Figure 8 As shown, the dual-reflection mirror system based on small-angle incident can achieve the transmission of -30dB energy (99.9% of the energy) under an incident angle of about 10°. During the transmission process, the beam is basically not blocked by the mirror or leaked from the edge of the mirror.

[0063] like Figure 9 , 10 As shown in the figure, the electric field distribution diagram at the output cross-section port of the dual-reflector system shows that the Gaussian beam distribution characteristics of the dual-reflector system are still good.

[0064] This invention primarily addresses the problems of excessive loss in the terahertz band of traditional waveguide-type isolators, low power capacity of transmission-type quasi-optical isolators, and poor matching characteristics of conventional reflective quasi-optical isolators when incident at large angles to the Faraday rotator, resulting in significant differences in polarization angles between vertically and parallelly polarized beams. Compared to traditional transmission-type quasi-optical isolators and quasi-optical isolators with 45° incident angles, this invention, based on phase matching and physical optics, designs a small-angle incident reflective optical path to improve the power capacity of the quasi-optical isolator and minimize the difference in polarization twist angles between vertically and parallelly polarized beams by the reflective Faraday rotator.

Claims

1. A terahertz reflective quasi-optical isolation system based on small-angle incident light, characterized in that, include: Input port A, output port B, isolation port C, isolation port D, ellipsoidal mirror M1, ellipsoidal mirror M2, ellipsoidal mirror M3, ellipsoidal mirror M4, plane mirror N1, plane mirror N2, 90° polarization grating S1, 45° polarization grating S2, and reflective Faraday rotator. The Gaussian beam is fed into input port A with its polarization direction perpendicular to the grating metal strip; The ellipsoidal mirror M1 reflects the fed Gaussian beam to the 90° polarization grating S1 after the first waist conversion. The 90° polarization grating S1 is placed at a 45° angle to the incident Gaussian beam, so that the Gaussian beam is transmitted to the plane mirror N1. The plane mirror N1 is tilted at an angle θ1 to the horizontal plane, reflecting the Gaussian beam to the ellipsoidal mirror M2 above the horizontal plane; The ellipsoidal mirror M2 reflects the Gaussian beam to a reflective Faraday rotator below the horizontal plane after a second waist conversion. The reflective Faraday rotator polarizes and rotates the incident Gaussian beam by 45° and reflects it to the ellipsoidal mirror M3 above the horizontal plane, wherein the angle between the incident Gaussian beam and the outgoing Gaussian beam is 9° to 11°. The ellipsoidal mirror M3 reflects the Gaussian beam to the plane mirror N2 after a third waist conversion. The plane mirror N2 is tilted at an angle θ2 to the horizontal plane, reflecting the Gaussian beam to the 45° polarization grating S2; The 45° polarization grating S2 is placed at a 45° angle to the incident Gaussian beam, so that the Gaussian beam with a polarization rotation of 45° is transmitted to the ellipsoidal mirror M4, and the Gaussian beam with a polarization rotation angle of less than 45° is reflected to the isolation port D. The ellipsoidal mirror M4 outputs a Gaussian beam with a polarization rotation of 45° through output port B. The Gaussian beam reflected from output port B is transmitted in reverse, passing sequentially through ellipsoidal mirror M4, 45° polarization grating S2, plane mirror N2, ellipsoidal mirror M3, reflective Faraday rotator, ellipsoidal mirror M2, plane mirror N1, 90° polarization grating S1, and finally reflected to isolation port C.

2. The terahertz reflective quasi-optical isolation system based on small-angle incident light as described in claim 1, characterized in that, The 90° polarization grating S1 and the 45° polarization grating S2 are placed parallel to each other; the grating strips of the 90° polarization grating S1 are perpendicular to the horizontal plane, and the grating strips of the 45° polarization grating S2 and the grating strips of the 90° polarization grating S1 have a 45° tilt angle.

3. The terahertz reflective quasi-optical isolation system based on small-angle incident light as described in claim 2, characterized in that, The 90° polarization grating S1 is positioned at the waist of the Gaussian beam after passing through the ellipsoidal mirror M1; the reflective Faraday rotator is positioned at the waist of the Gaussian beam after passing through the ellipsoidal mirror M2; and the 45° polarization grating S2 is positioned at the waist of the Gaussian beam after passing through the ellipsoidal mirror M3 and the plane mirror N2.

4. The terahertz reflective quasi-optical isolation system based on small-angle incident light as described in claim 3, characterized in that, The ellipsoidal mirrors M1, M2, and N1 are symmetrically distributed with the plane mirrors N2, M3, and M4.

5. The terahertz reflective quasi-optical isolation system based on small-angle incident light as described in claim 4, characterized in that, The tilt angle between the plane mirror N1 and the horizontal plane is θ1, and the tilt angle between the plane mirror N2 and the horizontal plane is θ2, where θ1 + θ2 = 180°.

6. The terahertz reflective quasi-optical isolation system based on small-angle incident light as described in claim 5, characterized in that, The mirror dimensions of ellipsoidal mirrors M1 and M4 are exactly the same as their optical parameters; the mirror dimensions of ellipsoidal mirrors M2 and M3 are exactly the same as their optical parameters; the mirror dimensions of plane mirrors N1 and N2 are exactly the same as their optical parameters.

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