Optical radar common aperture off-axis imaging system

Abstract

The invention relates to the technical field of optical imaging, and particularly provides an optical radar common-aperture off-axis imaging system, which comprises an off-axis reflector group, a frequency division light splitting device, a radar transceiving system and an optical imaging system, and is characterized in that the frequency division light splitting device is arranged on a rear-end light path of a secondary mirror and is used for reflecting light waves and transmitting microwaves; the frequency division light splitting device comprises a frequency selection surface, the frequency selection surface comprises an FSS pattern layer and a bias line layer, the FSS pattern layer comprises periodically arranged FSS units, the FSS units are electrically connected with a nonlinear capacitor, the bias line layer is used for applying voltage to the nonlinear capacitor according to the wave band of received microwaves, and the nonlinear capacitor is connected with the frequency selection surface. The resonant frequency of the FSS unit is tuned by changing the voltage applied to the nonlinear capacitor, so that the microwave passband frequency of the frequency division light splitting device is changed. According to the invention, the reflection wave and microwave transmission design is realized, and the problem that only single-band microwaves are transmitted and different demand tasks are difficult to adapt in a microwave and reflection wave transmission mode is solved.

Description

Technical Field

[0001] This invention belongs to the field of optical imaging technology, and particularly relates to an optical radar common aperture off-axis imaging system. Background Technology

[0002] Synthetic Aperture Radar (SAR) and optical remote sensing cameras each possess unique observational advantages, and their combination can significantly enhance observational capabilities. SAR is an active imaging device that operates in the microwave band, unaffected by lighting conditions, and capable of all-weather observation. The longer wavelength of microwaves allows for strong penetration through clouds and fog, enabling stable operation in rain, snow, fog, and other weather conditions. Furthermore, SAR can acquire target altitude information, providing some range and velocity measurement capabilities. However, SAR can only represent the electromagnetic scattering characteristics of a target within a specific wavelength band; the generated black-and-white images do not reflect true colors, and its observational capabilities may be limited in complex electromagnetic environments.

[0003] In contrast, while optical remote sensing cameras are limited in imaging during inclement weather and at night, they produce clearer, richer colors that accurately reproduce the true colors of targets, better meeting the visual needs of the human eye. Furthermore, the high resolution of optical cameras helps to reveal detailed features of the target area, facilitating target identification and description. By fusing the all-weather capabilities of SAR with the color information from optical remote sensing, the overall performance of the observation equipment is improved.

[0004] Currently, there are some solutions that combine synthetic aperture radar with optical remote sensing cameras, but they all have many shortcomings: For example, Chinese invention patent application CN112485793A, published on March 12, 2021, entitled "Optical and Radar Co-aperture Composite Imaging System and Method", uses a light-transmitting and frequency-dividing unit as a light-transmitting and reflective microwave light-transmitting and frequency-dividing device. It uses a micron-sized metal grid to reflect microwaves. However, the metal grid acts as a two-dimensional diffraction grating in the infrared band, which will produce multi-order diffraction, which has a certain impact on the imaging quality of the optical system. Even if certain technical means are adopted to effectively suppress it, it cannot be completely eliminated.

[0005] For example, Chinese invention patent application CN120468834A, published on August 12, 2025, entitled "A Co-aperture Imaging System for Optical Imaging and Radar Detection," discloses a coaxial optical system with a microwave-transmitting and reflective light-wave splitting and frequency-division unit designed for microwave transmission in the Ka band. However, the coaxial optical system suffers from central obstruction, resulting in low imaging light flux; the splitting and frequency-division unit designed only for the Ka band cannot be adapted to SAR bands (such as the X band) required for other missions, and is susceptible to electromagnetic interference. Summary of the Invention

[0006] In view of this, the present invention aims to provide an optical radar co-aperture off-axis imaging system, which solves the problems of decreased optical imaging quality caused by multi-level diffraction of metal grids in traditional light-transmitting wave-reflecting microwave schemes, the central obstruction problem in coaxial optical systems, and the difficulty in adapting to different needs and tasks in the light-transmitting wave-reflecting microwave method that only transmits a single band of microwaves.

[0007] To achieve the above objectives, the technical solution created by this invention is implemented as follows: This invention provides an optical radar common aperture off-axis imaging system, comprising: An off-axis mirror assembly, including a primary mirror and a secondary mirror, is used to receive light waves and microwaves; A frequency-division beam splitter is located in the optical path at the rear end of the secondary mirror and is used to reflect light waves and transmit microwaves. A radar transceiver system is used to receive transmitted microwaves and perform radar imaging. An optical imaging system is used to receive reflected light waves and perform optical imaging; The frequency-splitting device includes a frequency-selective surface, which includes an FSS pattern layer and a bias line layer. The FSS pattern layer includes periodically arranged FSS units. A nonlinear capacitor is electrically connected to the FSS unit. The bias line layer applies a voltage to the nonlinear capacitor according to the wavelength of the received microwave. The resonant frequency of the FSS unit is tuned by changing the voltage applied to the nonlinear capacitor.

[0008] Preferably, the secondary mirror, frequency splitter, radar transceiver system, and optical imaging system are all located outside the main optical path of the off-axis mirror group to avoid central obstruction.

[0009] Preferably, the radar transceiver system includes a defocusing feed array.

[0010] Preferably, the optical imaging system includes a beam splitter, an infrared imaging system, and a visible light imaging system. The beam splitter is used to split the light waves reflected by the frequency-splitting device into visible light and infrared light. The visible light enters the visible light imaging system for imaging, and the infrared light enters the infrared light imaging system for imaging.

[0011] Preferably, the frequency division and beam splitter is provided with a protective film, a dielectric reflective film, a frequency selective surface, quartz glass and a dielectric anti-reflective film in sequence from the front to the back. The dielectric reflective film adopts a multilayer film structure and is used to reflect light waves in the visible light band and the infrared band.

[0012] Preferably, the nonlinear capacitor is a varactor diode.

[0013] Preferably, nonlinear capacitors are provided in the capacitive gaps of the metal pattern in each FSS unit.

[0014] Preferably, the frequency selection surface further includes a digital-to-analog converter (DAC) for generating and providing a DC control voltage to the bias line layer to control the junction capacitance of each varactor diode.

[0015] Preferably, the frequency selection surface also includes an RF choke coil connected in series on the bias line layer to prevent microwave leakage to the bias line layer while allowing DC control voltage to pass through.

[0016] Preferably, the RF choke is a lumped element inductor or a high-impedance microstrip line.

[0017] Compared with the prior art, the present invention can achieve the following beneficial effects: The optical imaging and radar imaging systems of this invention share a primary mirror and a secondary mirror. A beam splitter / frequency divider is used behind the secondary mirror to separate the microwave channel and optical path. The microwave signal, after being transmitted, is transmitted and received via a radar feed for subsequent imaging processing. After passing through the beam splitter / frequency divider, a visible / infrared beam splitter is arranged in the subsequent optical path to separate visible and infrared light, which then enter their respective imaging systems and detectors for imaging. The radar imaging system and the visible / infrared optical imaging system of this invention are arranged on the same side of the primary mirror, resulting in a simple structure.

[0018] This invention employs an off-axis optical system, moving the secondary mirror and imaging system out of the main optical path, eliminating central obstruction, and improving imaging light throughput and contrast. Through asymmetric optical path design, it can effectively compensate for some aberrations while maintaining a compact structure, thus obtaining better image quality.

[0019] This invention employs frequency-selective surface technology and a broadband high-reflectivity multilayer film system to achieve efficient separation of light waves and microwaves. Utilizing frequency-selective surface technology, a miniaturized, multipole unit structure is used as the initial structure of the frequency-selective surface. The frequency-selective surface is configured in a reconfigurable / tunable manner, adaptable to different SAR frequency bands (such as switching from the X-band to the Ka-band) without hardware replacement. When encountering electromagnetic interference, the passband can be actively fine-tuned to avoid interfering frequencies. Simultaneously, through continuous combination and iteration of different band reflective film systems, the reflection bandwidth is broadened, achieving a Ka-band transmittance of over 99% and a 450-900nm and mid-wave infrared reflectance of over 98%. This method of separating and frequency-distributing light waves while transmitting microwaves avoids the optical imaging quality degradation caused by multi-level diffraction of metal grids in traditional light-transmitting and microwave-reflecting methods, effectively improving the clarity and resolution of optical imaging. Attached Figure Description

[0020] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a schematic diagram of the structure of an optical radar common aperture off-axis imaging system provided according to an embodiment of the present invention; Figure 2 This is a structural model diagram of a frequency-division and beam-splitting device provided according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the structure of a frequency selective surface provided according to an embodiment of the present invention; Figure 4 This is a schematic diagram of an FSS pattern layer provided according to an embodiment of the present invention; Figure 5 This is a schematic diagram of the bias line and tuning point circuit provided according to an embodiment of the present invention.

[0021] The reference numerals in the figures include: 1. Primary mirror; 2. Secondary mirror; 3. Frequency division and beam splitting device; 4. Radar transceiver system; 5. Three mirrors; 6. Reflector; 7. Beam splitter; 8. Visible light imaging system; 9. Infrared imaging system; 31. Protective film; 32. Dielectric reflective film; 33. Frequency selective surface; 34. Quartz glass; 35. Dielectric antireflective film; FSS pattern layer 331, bias line layer 332, RF choke 333, digital-to-analog converter 334; FSS unit 3311, varactor diode 3312. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and do not constitute a limitation thereof. Similar elements in different embodiments are referred to by associated similar element reference numerals. In the following embodiments, many details are described to facilitate a better understanding of the invention. However, those skilled in the art will readily recognize that some features may be omitted in different situations, or may be replaced by other elements, materials, or methods. In some cases, some operations related to the invention are not shown or described in the specification. This is to avoid obscuring the core parts of the invention with excessive description. For those skilled in the art, detailed description of these related operations is not necessary; they can fully understand the related operations based on the description in the specification and general technical knowledge in the art.

[0023] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined to form various implementations. Furthermore, the order of the steps or actions in the method description can be changed or adjusted in a manner readily apparent to those skilled in the art. Therefore, the various orders in the specification and drawings are merely for the clear description of a particular embodiment and do not imply a mandatory order, unless otherwise stated that a particular order must be followed.

[0024] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0025] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0026] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0027] Please see Figure 1 In one embodiment of the present invention, an optical-radar co-aperture off-axis imaging system is provided, which employs a co-aperture design for optical imaging and radar detection to achieve simultaneous imaging of the target in visible light, infrared light, and radar. Specifically, it includes: An off-axis mirror assembly, comprising a primary mirror 1 and a secondary mirror 2, is used to receive light waves and microwaves; The frequency-division and beam-splitting device 3 is located on the rear optical path of the secondary mirror 2 and is used to reflect light waves and transmit microwaves. Radar transceiver system 4 is used to receive transmitted microwaves and perform radar imaging; An optical imaging system is used to receive reflected light waves and perform optical imaging; The frequency-splitting device 3 includes a frequency selection surface 33, which includes an FSS pattern layer 331 and a bias line layer 332. The FSS pattern layer 331 includes periodically arranged FSS units 3311. A nonlinear capacitor is electrically connected to the FSS unit 3311. The bias line layer 332 applies a voltage to the nonlinear capacitor according to the wavelength of the received microwave. The resonant frequency of the FSS unit 3311 is tuned by changing the voltage applied to the nonlinear capacitor.

[0028] The optical imaging system includes a visible light imaging system 8 and an infrared imaging system 9. The radar transceiver system 4, visible light imaging system 8, and infrared imaging system 9 share a primary mirror 1 and a secondary mirror 2. The radar transceiver system 4 is used for microwave transmission and reception and subsequent imaging processing. The visible light imaging system 8 and infrared imaging system 9 are used for visible light imaging and infrared imaging of light waves, respectively. Both the primary mirror 1 and the secondary mirror 2 are made of silicon carbide. The primary mirror 1 adopts a lightweight triangular rib structure design with a back opening, significantly reducing weight while ensuring structural strength. To solve the problem of central occlusion in coaxial optical systems, an off-axis imaging system is used in this embodiment. The secondary mirror 2, the frequency-splitting device 3, the radar transceiver system 4, the visible light imaging system 8, the infrared imaging system 9, and all other optical components required in the optical path are placed outside the main optical path of the off-axis reflector group, avoiding central occlusion and improving imaging light throughput and contrast. Furthermore, an asymmetric optical path design is adopted, which can effectively compensate for some aberrations while maintaining a compact structure, resulting in better image quality.

[0029] As an optional embodiment, the radar transceiver system 4, the visible light imaging system 8, and the infrared imaging system 9 are arranged on the same side of the primary mirror 1, which simplifies the optical structure and reduces the system size.

[0030] When receiving light waves and microwaves reflected from the target, the collimated light waves and microwaves first strike the primary mirror 1. The primary mirror 1 changes the propagation direction of the light waves and microwaves, causing them to strike the secondary mirror 2. After the secondary mirror 2 reflects the light waves and microwaves, the light waves and microwaves strike the frequency division and beam splitter 3 in a parallel state.

[0031] The frequency-division beam splitter 3 is used to separate light waves and microwaves during echo imaging. The frequency-division beam splitter 3 reflects light waves and transmits microwaves. Microwaves, after being transmitted through the frequency-division beam splitter 3, are directed to the radar transceiver system 4 for radar detection and imaging. Light waves are reflected by the frequency-division beam splitter 3 to the visible light imaging system 8 and the infrared imaging system 9, achieving optical imaging.

[0032] To ensure that the light waves can enter the visible light imaging system 8 and the infrared imaging system 9 after being split by the frequency-division beam splitter 3, this embodiment of the invention further includes, in sequence, a three-mirror 5, a reflecting mirror 6, and a beam splitter 7 in the subsequent optical path of the frequency-division beam splitter 3. The light waves are first reflected by the frequency-division beam splitter 3 to the three-mirror 5. The three-mirror 5 is used for optical path reversal and aberration compensation, reflecting the compensated light waves to the reflecting mirror 6. The reflecting mirror 6 then changes the optical path direction again, reflecting the light waves to the beam splitter 7. The beam splitter 7 can split the light waves, realizing the separation of visible light and infrared light. After separation, the visible light enters the visible light imaging system 8 for visible light imaging, and the infrared light enters the infrared imaging system 9 for infrared imaging.

[0033] The microwaves transmitted through the frequency division and beam splitter 3 are then further transmitted into the radar transceiver system 4, which includes... The off-focus feed array and radar transceiver system 4 enable microwave reception, radar detection and imaging, and high-quality optical / radar simultaneous imaging.

[0034] Since the frequency-splitting and beam-splitting device 3 needs to achieve a beam-splitting and frequency-splitting method that transmits microwaves and reflects light waves, frequency-selective surface technology and spectral reflective thin film technology are used in this embodiment of the invention to separate light waves and microwaves. For example... Figure 2 As shown, the frequency-splitting device 3 includes a protective film 31, a dielectric reflective film 32, a frequency-selective surface 33, quartz glass 34, and a dielectric anti-reflective film 35 arranged sequentially from the front to the back. The protective film 31 protects the dielectric reflective film 32 and has no special optical effect on light waves or microwaves, exhibiting high transmittance characteristics. The dielectric reflective film 32 is a multilayer film structure. Since the optical imaging requirements are visible light imaging and infrared imaging, suitable film materials with high reflectivity for visible light and mid-wave infrared can be selected from metal fluorides or semiconductor materials. Multiple layers of materials with different refractive indices are stacked, and the multi-band reflective film system is continuously optimized and iterated to broaden the reflection bandwidth and ensure high transmittance to microwaves. In this embodiment of the invention, YbF3 with low refractive index for visible light and infrared, ZnSe with medium refractive index, and Ge with high refractive index are specifically used. The average refractive index of YbF3 is 1.37, the average refractive index of ZnSe is 2.46, and the average refractive index of Ge is 4. Tests showed that the dielectric reflective film 32 has a reflectivity of over 98% for the 450-900nm wavelength band and mid-wave infrared, and a transmittance of over 99% for Ka-band microwaves (frequency range between 26.5 and 40 GHz), effectively achieving the separation of light waves and microwaves. Quartz glass 34 serves as the processing substrate for the frequency division and beam splitting device 3, while the dielectric antireflective film 35 is used to reduce microwave reflection.

[0035] For the frequency selective surface 33, this embodiment of the invention utilizes frequency selective surface technology, combining a miniaturized, multi-pole unit structure as the initial structure of the frequency selective surface, and employs an optimization algorithm to optimize its macroscopic order, achieving efficient frequency division. However, since traditional FSSs can only transmit microwaves in a single band, they cannot meet the needs of different missions. When the incident microwave band changes, it is necessary to replace the frequency division and beam splitter 3 and reassemble and adjust the device, which is a complex and time-consuming process. Furthermore, it cannot avoid interfering frequencies when encountering electromagnetic interference. Therefore, in order to meet the requirements of different microwave passband frequencies and achieve dynamic spectrum adaptation, this invention configures the frequency selective surface 33 as reconfigurable / tunable. Figure 3 As shown, the frequency selection surface 33 includes an FSS pattern layer 331 and a bias line layer 332, wherein the FSS pattern layer 331 includes multiple... Figure 4 The periodically arranged FSS units 3311 are shown. The frequency selective surface 33 is essentially a two-dimensional periodic metal grid structure. Its filtering characteristics are determined by the collective resonant behavior of these countless tiny FSS units 3311. When microwaves irradiate the frequency selective surface 33, each FSS unit 3311 acts as a tiny resonator. Since all the FSS units 3311 are periodically arranged, their generated electromagnetic responses couple and superimpose with each other, ultimately exhibiting macroscopic "on" or "off" characteristics for specific frequencies.

[0036] Because the metal grid structure pattern is fixed, the resonant frequency is also fixed. Therefore, only microwaves of a specific wavelength can be used. To achieve dynamic spectrum adaptation, this invention electrically connects a nonlinear capacitor between the capacitive gaps of the metal pattern in each FSS unit 3311. The capacitance value of the nonlinear capacitor varies when different voltages are applied. For each gap in the metal pattern of each FSS unit 3311, when microwaves irradiate the FSS unit 3311, its electric field will be highly concentrated at the gap, inducing opposite charges on both sides of the gap and generating an electric field. According to the resonant frequency formula, capacitance is a key parameter that directly determines the resonant frequency. Therefore, integrating the nonlinear capacitor into the gap of the FSS unit 3311 can efficiently change the resonant frequency of the entire FSS unit 3311.

[0037] The nonlinear capacitor can be a GaAs varactor diode 3312. The specific electrical connection method is as follows: Metal pads are designed at key locations in the gaps of each FSS unit 3311, and varactor diodes 3312 are integrated on these metal pads. Fine DC bias lines are arranged in the area between the FSS units 3311 to form a bias circuit. All bias lines are connected in parallel to form a bias line layer 332, providing a unified control voltage for all varactor diodes 3312.

[0038] As an alternative embodiment, such as Figure 5As shown, the frequency selective surface 33 also includes an RF choke 333 and a digital-to-analog converter 334. A lumped element inductor or a high-impedance microstrip line is connected in series on the bias line layer 332 as the RF choke 333, making the bias circuit exhibit high impedance to microwaves, preventing microwave signals from leaking into the bias line layer, while allowing DC control voltage to pass through. Furthermore, a DC control voltage is generated by the digital-to-analog converter 334 and applied to each varactor diode 3312 through the bias line layer 332, changing the junction capacitance of the varactor diodes 3312, thereby continuously changing the resonant frequency of the FSS unit 3311. By changing the voltage applied to the nonlinear capacitor, the passband frequency of the frequency selective surface 33 is shifted, or the bandwidth is broadened or narrowed. The frequency selective surface 33 can be reconfigured and tuned to meet different task requirements. Without changing the hardware, the frequency divider / splitter 3 can transmit microwaves of different bands. Similarly, when encountering electromagnetic interference, the passband can be actively fine-tuned to avoid interfering frequencies.

[0039] In the specific imaging process, the required SAR frequency band, i.e., the incident microwave wavelength, is first determined according to the observation task. Based on the incident microwave wavelength, the digital-to-analog converter 334 generates a corresponding control voltage. This same control voltage is then applied to each varactor diode 3312 on the FSS pattern layer 331 through the bias line layer 332 and the RF choke 333. The junction capacitance of the varactor diode 3312 changes with the voltage, causing the resonant frequency of the FSS unit 3311 to shift accordingly. By changing the control voltage, different microwave transmission frequencies are achieved. When electromagnetic interference is detected at a specific frequency, the passband of the frequency selective surface 33 is slightly shifted by fine-tuning the voltage to bypass the interfered frequency, without requiring any changes to the radar hardware.

[0040] In summary, the above description is merely a preferred embodiment of this specification and is not intended to limit the scope of protection of this specification. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this specification should be included within the scope of protection of this specification.

[0041] The systems, apparatuses, modules, or units described in one or more of the above embodiments may be implemented by a computer chip or entity, or by a product having a certain function. A typical implementation device is a computer. Specifically, a computer may be, for example, a personal computer, a laptop computer, a cellular phone, a camera phone, a smartphone, a personal digital assistant, a media player, a navigation device, an email device, a game console, a tablet computer, a wearable device, or any combination of these devices.

[0042] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0043] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to interchangeably. Each embodiment focuses on describing the differences from other embodiments. In particular, the system embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments.

Claims

1. A common-aperture off-axis imaging system for optical radar, characterized in that, include: An off-axis mirror assembly, including a primary mirror and a secondary mirror, is used to receive light waves and microwaves; The frequency-division and beam-splitting device is located in the optical path at the rear end of the secondary mirror and is used to reflect light waves and transmit microwaves. A radar transceiver system is used to receive transmitted microwaves and perform radar imaging. An optical imaging system is used to receive reflected light waves and perform optical imaging; The frequency division and beam splitting device includes a frequency selective surface, which includes an FSS pattern layer and a bias line layer. The FSS pattern layer includes periodically arranged FSS units, and a nonlinear capacitor is electrically connected to the FSS unit. The bias line layer applies a voltage to the nonlinear capacitor according to the wavelength of the received microwave, and the resonant frequency of the FSS unit is tuned by changing the voltage applied to the nonlinear capacitor.

2. The optical radar common aperture off-axis imaging system according to claim 1, characterized in that, The secondary mirror, the frequency-splitting and beam-splitting device, the radar transceiver system, and the optical imaging system are all located outside the main optical path of the off-axis mirror group to avoid central obstruction.

3. The optical radar common aperture off-axis imaging system according to claim 1, characterized in that, The radar transceiver system includes a defocusing feed array.

4. The optical radar common aperture off-axis imaging system according to claim 1, characterized in that, The optical imaging system includes a beam splitter, an infrared imaging system, and a visible light imaging system. The beam splitter is used to split the light waves reflected by the frequency-splitting device into visible light and infrared light. The visible light enters the visible light imaging system for imaging, and the infrared light enters the infrared light imaging system for imaging.

5. The optical radar common aperture off-axis imaging system according to claim 1, characterized in that, The frequency division and beam splitter is provided with a protective film, a dielectric reflective film, a frequency selective surface, quartz glass, and a dielectric anti-reflective film in sequence from the front to the back. The dielectric reflective film adopts a multilayer film structure and is used to reflect light waves in the visible light band and the infrared band.

6. The optical radar common aperture off-axis imaging system according to claim 1, characterized in that, The nonlinear capacitor is a varactor diode.

7. The optical radar common aperture off-axis imaging system according to claim 1, characterized in that, The nonlinear capacitor is disposed in the capacitive gap of the metal pattern in each FSS unit.

8. The optical radar common aperture off-axis imaging system according to claim 1, characterized in that, The frequency selection surface also includes a digital-to-analog converter (DAC) for generating and providing a DC control voltage to the bias line layer to control the junction capacitance of each varactor diode.

9. The optical radar common aperture off-axis imaging system according to claim 8, characterized in that, The frequency selection surface also includes an RF choke coil connected in series on the bias line layer to prevent microwave leakage to the bias line layer while allowing DC control voltage to pass through.

10. The optical radar common aperture off-axis imaging system according to claim 9, characterized in that, The RF choke is a lumped element inductor or a high-impedance microstrip line.

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