Medium-wave infrared polarization imaging system, laser beam calibration system and image restoration method

Abstract

The invention provides a medium-wave infrared polarization imaging system, a laser beam calibration system and an image restoration method, and the system does not need complex optical path debugging and microstructure design, and only needs to directly couple a liquid crystal micro-nano polarization control device with a medium-wave focal plane detector. Based on the modulation effect of the liquid crystal micro-nano deviation control device on the incident light polarization state of a target scene under the effect of the external voltage, the corresponding relation between the polarization rotation angle and the external voltage is obtained through the calibration data of the rotation incident light of the liquid crystal micro-nano deviation control device by the controllable power supply in the laser environment; and finally, a linear polarization degree image in the target scene is obtained through inversion, so that the target scene is analyzed by replacing a traditional polarization angle with the polarization rotation angle. According to the medium-wave infrared polarization imaging system, the polarization rotation angle is used for replacing the polarization angle for parameter analysis, so that the obtained polarization image reflects polarization information on the basis of higher energy utilization rate, and electric control polarization detection of a target scene can be realized without sacrificing the resolution.

Description

Technical Field

[0001] The present invention relates to the field of infrared detection technology, and in particular, to a mid-wave infrared polarization imaging system, a laser beam calibration system, and an image restoration method. Background Art

[0002] As a transverse wave, the polarization information carried by the light emitted or reflected during the propagation of light interacting with the target object can be used to infer the physical properties of the target object, such as specific parameters like refractive index, surface roughness, humidity, dielectric constant, etc. Developing polarization imaging technology can provide more-dimensional information guarantee for target detection on the basis of traditional intensity imaging, break through the problems of blurred imaging and unclear detection in scenarios such as rainy and snowy weather and the sea surface, and can greatly improve the accuracy of target detection. The mid-wave infrared band has extensive applications in the fields of industrial manufacturing, military, atmospheric detection, and environmental monitoring. It is necessary to develop multi-dimensional new detection technologies in this band.

[0003] Currently, the developed mid-wave infrared polarization detection technologies are mainly divided into time-sharing, amplitude-division, aperture-division, focal-plane-division polarization imaging technologies, and snapshot polarization imaging technologies. The disadvantages of the former major category are generally that it is necessary to rotate the polarization element (with large energy loss, complex calculation, poor real-time performance, and requires mechanical rotation), or it is necessary to design multi-channel imaging (with complex optical paths, high precision requirements for each component, and difficult alignment), or it is necessary to design multi-detector clusters (with high cost and large system volume), or it is necessary to use microlenses (although small in volume but sacrificing spatial resolution); the latter snapshot polarization imaging requires designing a microstructure grating containing different polarization angles. Although it can achieve one-shot snapshot imaging, the actual processing is complex, the cost is high, the yield is low, the calculation amount is large, and the alignment difficulty is great.

[0004] Therefore, there is an urgent need for a mid-wave infrared polarization imaging system, a laser beam calibration system, and an image restoration method to solve the above technical problems. Summary of the Invention

[0005] The purpose of the present invention is to provide a mid-wave infrared polarization imaging system, a laser beam calibration system, and an image restoration method, which are used to solve the technical problems existing in the existing mid-wave infrared polarization detection technology, such as large energy loss, poor real-time performance, complex optical path, and high cost.

[0006] To solve the above technical problems, the present invention provides a mid-wave infrared polarization imaging system, including: A drivable power supply for outputting an external voltage; A liquid crystal micro-nano polarization control device electrically connected to the drivable power supply, for adjusting the polarization rotation angle of the light emitted from the target scene with respect to the incident light after being applied with an external voltage; The mid-wave focal plane detector is disposed closely to the light-emitting side of the liquid crystal micro-nano polarization control device, and is used to obtain the target measured images corresponding to different external voltages of the target scene; The data storage and analysis module is electrically connected to the mid-wave focal plane detector, and is used to inversely obtain the linear polarization degree image of the target scene according to the calibration data of the corresponding relationship between the external voltage and the polarization rotation angle stored in advance, and the light intensity data of the external voltage and the target measured images.

[0007] Preferably, the drivable power supply is a square wave power supply, and its frequency is 1 kHz and the duty cycle is 1:1.

[0008] Preferably, the liquid crystal micro-nano polarization control device sequentially includes a first substrate, a first electrode layer, a first alignment layer, a liquid crystal layer, a second alignment layer, a second electrode layer, and a second substrate along the propagation direction of the incident light.

[0009] Preferably, the mid-wave focal plane detector sequentially includes a mid-wave infrared band adaptation lens, a mid-wave infrared detection CMOS focal plane array, and an electronic component along the propagation direction of the incident light. One end of the electronic component is electrically connected to the mid-wave infrared detection CMOS focal plane array, and the other end of the electronic component is electrically connected to the data storage and analysis module; Wherein, the mid-wave infrared detection CMOS focal plane array is a HgCdTe infrared focal plane array, and the mid-wave infrared detection band is 3.7 μm to 4.8 μm.

[0010] Preferably, the mid-wave infrared polarization imaging system further includes a device support frame and a precision pan-tilt stabilizer. One end of the device support frame is fixedly connected to the mid-wave infrared band adaptation lens, and the precision pan-tilt stabilizer is used to carry the mid-wave focal plane detector.

[0011] Preferably, the device support frame has a receiving cavity, and the liquid crystal micro-nano polarization control device is disposed in the receiving cavity. The included angle between the liquid crystal micro-nano polarization control device and the mid-wave infrared band adaptation lens is 10° to 45°.

[0012] Correspondingly, the present invention further provides a laser beam calibration system for calibrating the calibration data of the mid-wave infrared polarization imaging system as described in any one of the above. The laser beam calibration system sequentially includes a mid-infrared optical parametric oscillator laser, a polarizer, a liquid crystal micro-nano polarization control device, an analyzer, an objective lens, an attenuator, and an optical quality analyzer along the optical signal input end to the optical signal output end; Wherein, the laser beam calibration system further includes a drivable power supply, and the drivable power supply is electrically connected to the liquid crystal micro-nano polarization control device.

[0013] Preferably, the polarization direction of the emitted light of the mid-infrared optical parametric oscillator laser and the orientation direction of the liquid crystal micro-nano polarization component close to the incident light side are both along the X axis.

[0014] Preferably, when the transmission direction of the polarizer is along the X-axis, the pixel light intensity of the CMOS surface of the optical quality analyzer is recorded within the X-direction voltage adjustment range at different external voltages, and the average surface light intensity is taken as Ix Vn ; when the transmission direction of the polarizer is along the Y-axis, the pixel light intensity of the CMOS surface of the optical quality analyzer is recorded within the Y-direction voltage adjustment range at different external voltages, and the average surface light intensity is taken as Iy Vn ; the polarization rotation angle AOP of the liquid crystal micro-nano polarization control device at different external voltages Vn is arctan(Iy Vn / Ix Vn ).

[0015] Correspondingly, the present invention further provides an image restoration method, which is applied to the mid-wave infrared polarization imaging system in any one of the above, and the method includes: S10, debugging the mid-wave infrared polarization imaging system so that it can collect the target grayscale image; S20, turning on the drivable power supply, and respectively collecting the target measured images at different external voltages through the mid-wave focal plane detector; S30, calculating the corresponding polarization rotation angles at different external voltages according to the calibration data of the corresponding relationship between the external voltage and the polarization rotation angle; S40, converting the target measured images corresponding to different polarization rotation angles into corresponding polarization angle images according to the calibration data; S50, converting the polarization angle image into the linear polarization degree image of the target scene according to the corresponding relationship of the Stokes components.

[0016] The beneficial effects of the present invention are as follows: Different from the prior art, the present invention provides a mid-wave infrared polarization imaging system, a laser beam calibration system, and an image restoration method. The above mid-wave infrared polarization imaging system does not require complex optical path debugging and micro-structure design. Only by directly coupling a liquid crystal micro-nano polarization control device with a mid-wave focal plane detector, based on the modulation effect of the liquid crystal micro-nano polarization control device on the polarization state of the incident light of the target scene under the action of an external voltage, and by calibrating the data of the liquid crystal micro-nano polarization control device to rotate the incident light by a drivable power supply in a laser environment, the corresponding relationship between the polarization rotation angle and the external voltage is obtained, and finally the degree of linear polarization image of the target scene is inversely obtained, so as to realize the analysis of the target scene by using the polarization rotation angle instead of the traditional polarization angle. The above liquid crystal micro-nano optical component is simple to manufacture, low in cost, and can effectively realize the electro-control adjustment of the polarization direction of the incident light by driving with a small voltage, which is realized only by adjusting the magnitude of the external driving voltage. There are no mechanical rotating parts during the use process, and the use requirements are low. At the same time, when the mid-wave infrared polarization imaging system obtains the polarization image corresponding to the polarization angle, it is different from the traditional polarization imaging system. The polarization rotation angle is used instead of the polarization angle for parameter analysis, so that the obtained polarization image reflects the polarization information on the basis of higher energy utilization rate, and the electro-control polarization detection of the target scene can be realized without sacrificing the resolution. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the overall architecture of the mid-wave infrared polarization imaging system provided in Embodiment 1 of the present invention; Figure 2 It is a schematic diagram of the optical path of the laser beam calibration system provided in Embodiment 1 of the present invention; Figure 3a It is a schematic diagram of the calibration light intensity change in the X direction at typical voltages of 0, 1.4Vrms, and 2.1Vrms in the laser beam calibration system provided in Embodiment 1 of the present invention; Figure 3b It is a schematic diagram of the calibration light intensity change in the Y direction at typical voltages of 0, 1.4Vrms, and 2.1Vrms in the laser beam calibration system provided in Embodiment 1 of the present invention; Figure 3c It is a schematic diagram of the calibration light intensity change without distinguishing directions at typical voltages of 0, 1.4Vrms, and 2.1Vrms in the laser beam calibration system provided in Embodiment 1 of the present invention; Figure 4 It is a schematic diagram of the relationship between the polarization rotation angle and the voltage of the liquid crystal micro-nano polarization control component obtained by the laser beam calibration system provided in Embodiment 1 of the present invention; Figure 5 It is a flowchart of the image restoration method provided in Embodiment 1 of the present invention; Figure 6a It is the target measured image of the mid-wave focal plane detector at a typical voltage of 0Vrms in the image restoration method provided in Embodiment 1 of the present invention; Figure 6b The measured target image of the mid-wave focal plane detector at a typical voltage of 1.3 Vrms in the image restoration method provided in Embodiment 1 of the present invention; Figure 6c The measured target image of the mid-wave focal plane detector at a typical voltage of 1.4 Vrms in the image restoration method provided in Embodiment 1 of the present invention; Figure 6d The measured target image of the mid-wave focal plane detector at a typical voltage of 2.0 Vrms in the image restoration method provided in Embodiment 1 of the present invention; Figure 6e The Stokes vector S0 image of the target scene in the image restoration method provided in Embodiment 1 of the present invention; Figure 6f The Stokes vector S1 image of the target scene in the image restoration method provided in Embodiment 1 of the present invention; Figure 6g The Stokes vector S2 image of the target scene in the image restoration method provided in Embodiment 1 of the present invention; Figure 6h The degree of linear polarization image of the target scene in the image restoration method provided in Embodiment 1 of the present invention; In the figure: 100 - mid-wave infrared polarization imaging system; 11 - liquid crystal micro-nano polarization control device; 12 - mid-wave focal plane detector; 121 - mid-wave infrared band adapter lens; 122 - mid-wave infrared detection CMOS focal plane array; 13 - drivable power supply; 14 - data storage and analysis module; 15 - device support frame; 16 - precision pan-tilt stabilizer; 17 - second substrate; 200 - laser beam calibration system; 21 - mid-infrared optical parametric oscillator laser; 22 - polarizer; 23 - analyzer; 24 - objective lens; 25 - attenuation sheet; 26 - optical quality analyzer. Detailed implementation manners

[0018] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0019] The object of the present invention is to address the deficiencies of the prior art and provide a mid-wave infrared polarization imaging system 100, a laser beam calibration system 200, and an image restoration method. When the mid-wave infrared polarization imaging system 100 acquires polarization images corresponding to polarization angles, it is different from traditional polarization imaging systems. It uses the polarization rotation angle instead of the polarization angle for parameter analysis, enabling the acquired polarization images to reflect polarization information based on a higher energy utilization rate, and realizing electro-controlled polarization detection of the target scene without sacrificing resolution.

[0020] The technical solution of the present invention will now be described in conjunction with specific embodiments.

[0021] Embodiment 1: Please refer to Figure 1 , Figure 1 which is a schematic diagram of the overall device structure of the mid-wave infrared polarization imaging system 100 provided in Embodiment 1 of the present invention; as can be seen from Figure 1 , the mid-wave infrared polarization imaging system 100 includes a drivable power supply 13, a liquid crystal micro-nano polarization control device 11 electrically connected to the drivable power supply 13, a mid-wave focal plane detector 12 disposed closely on the light-emitting side of the liquid crystal micro-nano polarization control device 11, and a data storage and analysis module 14 electrically connected to the mid-wave focal plane detector 12; Among them, the drivable power supply 13 is used to output an external voltage. The liquid crystal micro-nano polarization control device 11 is used to adjust the polarization rotation angle of the outgoing light compared to the incident light in the target scene after being applied with an external voltage. The mid-wave focal plane detector 12 is used to acquire the target measured images corresponding to different external voltages in the target scene; the data storage and analysis module 14 is used to inversely obtain the linear polarization degree image of the target scene based on the calibration data of the corresponding relationship between the external voltage and the polarization rotation angle stored in advance and the light intensity data of the external voltage and the target measured images.

[0022] In this Embodiment 1, the drivable power supply 13 is an alternating current power supply or a square wave power supply, preferably a square wave power supply, and its square wave power supply frequency is 1 kHz and the duty cycle is 1:1; among them, the square wave power supply is a common form of periodic power supply signal, and its output voltage periodically switches between a high level and a low level, presenting a waveform similar to a rectangle.

[0023] Specifically, a higher frequency can enable the liquid crystal micro-nano polarization control device 11 to relatively quickly respond to voltage changes at different times, and then relatively quickly adjust the polarization rotation angle of the outgoing light compared to the incident light in the target scene, which helps to obtain more optical signals in different polarization states per unit time, improving the dynamic response ability of the imaging system and the timeliness of data acquisition as a whole, so as to more efficiently obtain relevant image information of the target scene in multiple polarization states.

[0024] Specifically, the duty cycle is 1:1, which means that within a complete cycle, the time the square wave is at the high level is equal to the time it is at the low level. For the liquid crystal micro-nano polarization control device 11, such a symmetric duty cycle can provide a relatively balanced driving state. When at the high level, the device adjusts the polarization rotation angle according to the corresponding high-level voltage value, and when at the low level, it can reset the state or prepare for the next response to the high-level drive, ensuring the stability and regularity of the polarization rotation angle adjustment. This makes the changes in the target measured images obtained by the mid-wave focal plane detector 12 more repeatable and regular in different cycles, and is also more conducive to the subsequent data storage and analysis module 14 accurately retrieving the linear polarization degree image of the target scene based on stable and regular data, ensuring the accuracy and reliability of the entire imaging system operation.

[0025] In this Embodiment 1, the liquid crystal micro-nano polarization control device 11 sequentially includes a first substrate, a first electrode layer, a first alignment layer, a liquid crystal layer, a second alignment layer, a second electrode layer, and a second substrate along the propagation direction of the incident light; among them, the thickness of the liquid crystal micro-optical device is in the millimeter range, which can greatly reduce the thickness of the mid-wave infrared polarization imaging system 100 after overall integration.

[0026] Specifically, the liquid crystal micro-nano polarization control device 11 mainly operates by utilizing the electro-optical properties of liquid crystals. Before an external electric field is applied, the liquid crystal molecules in the liquid crystal layer have their initial arrangement states. When an external electric field is applied, the orientation of the liquid crystal molecules will change. Since the arrangement direction of the liquid crystal molecules is closely related to the polarization state of light, this change in orientation will adjust the polarization state of the incident light passing through the liquid crystal micro-nano polarization control device 11 once. For example, changes in the twist degree, orientation angle, etc. of the liquid crystal molecules can rotate the polarization direction of the incident linearly polarized light by a certain angle, thereby changing the polarization state of the light.

[0027] Specifically, both the first substrate and the second substrate can transmit light in the 3 - 5μm mid-wave infrared band. This provides a basic guarantee for the incident light to smoothly enter and exit the liquid crystal micro-nano polarization control device 11. As the outer support structures of the entire component, they carry the internal functional layers, ensuring the stability of the component structure and enabling the normal progress of the internal optical and electrical processes.

[0028] Specifically, the liquid crystal molecules in the liquid crystal layer are positive nematic liquid crystals, which have unique electro-optical properties. Under the action of an external electric field, the liquid crystal molecules can flexibly change their own orientations, thereby affecting the polarization state of the incident light passing through. This ability to change the polarization state is the core of realizing different working states and light intensity adjustment functions of the mid-wave infrared polarization imaging system 100.

[0029] Specifically, neither the first electrode layer nor the second electrode layer requires a patterned design. The material used is ITO with a thickness of 25 nm. At this parameter, the first electrode layer and the second electrode layer do not absorb significantly in the target infrared band and can play a good conductive role. At the same time, it is electrically connected to the external electric field using a conductive tape with good conductivity, so that the liquid crystal micro-nano polarization control device 11 can achieve the function of flexibly regulating the polarization state of the incident light.

[0030] Specifically, the molecular orientation direction of the first alignment layer is perpendicular to that of the second alignment layer. This orthogonal setting plays a key guiding role for the liquid crystal molecules in the liquid crystal layer. The liquid crystal molecules will exhibit a specific initial arrangement according to the directions of these two alignment layers when no external voltage is applied, usually forming a certain twisted structure. For example, it may cause the liquid crystal molecules to gradually twist by a certain angle from top to bottom, laying a foundation for subsequent adjusting the polarization state of light through an electric field.

[0031] In this Embodiment 1, the mid-wave focal plane detector 12 includes, in the propagation direction of the incident light, a mid-wave infrared band adaptation lens 121, a mid-wave infrared detection CMOS focal plane array 122, and an electronic component in sequence. One end of the electronic component is electrically connected to the mid-wave infrared detection CMOS focal plane array 122, and the other end of the electronic component is electrically connected to the data storage and analysis module 14. The mid-wave infrared detection CMOS (Complementary Metal-Oxide-Semiconductor) focal plane array is a HgCdTe infrared focal plane array, and the mid-wave infrared detection band is 3.7 μm to 4.8 μm.

[0032] Specifically, the electronic component plays a key connecting role. One end of it is electrically connected to the mid-wave infrared detection CMOS focal plane array 122 and can receive the electrical signal from the focal plane array. The other end is electrically connected to the data storage and analysis module 14 and is responsible for transmitting the collected signal to the data storage and analysis module 14, thereby ensuring the smoothness of the signal transmission link in the entire imaging system and laying a foundation for subsequent image generation and analysis processing.

[0033] Specifically, the mid-wave infrared detection CMOS focal plane array 122 is a HgCdTe infrared focal plane array. The HgCdTe (mercury cadmium telluride) material has excellent optoelectronic properties and has a high quantum efficiency in the mid-wave infrared band. It can effectively convert the received infrared light signal into an electrical signal. It has a good response ability to the light in the mid-wave infrared band and can more sensitively detect the light radiated or reflected by the target scene in this band range, thereby improving the detection sensitivity and imaging resolution of the imaging system for the target scene, making the obtained actual measured image of the target able to more clearly and accurately reflect the detailed features of the target scene.

[0034] Specifically, the mid-wave infrared detection band is set to 3.7 μm to 4.8 μm. In the 3.7 μm to 4.8 μm band, it has unique infrared spectral characteristics, which can help distinguish targets from the background or identify different types of targets. For the mid-wave infrared polarization imaging system 100, focusing on this band for detection and combining the analysis of polarization characteristics can obtain richer and valuable target scene information, further improving the application efficiency of the system in aspects such as target detection, identification, and scene analysis.

[0035] In this embodiment 1, the mid-wave infrared polarization imaging system 100 further includes a device support frame 15 and a precision pan-tilt stabilizer 16. One end of the device support frame 15 is fixedly connected to the mid-wave infrared band-adapted lens 121, and the precision pan-tilt stabilizer 16 is used to carry the mid-wave focal plane detector 12.

[0036] Specifically, the device support frame 15 can ensure that the lens maintains a fixed position and angle in various usage environments (such as when there is certain external force interference, vibration, etc.), so that the incident light can accurately enter the lens in the expected direction, thereby ensuring the normal progress of a series of subsequent processes such as light propagation, polarization adjustment, and detection, ensuring that the optical system is always in a good calibration state, and helping to improve the accuracy of the finally obtained target measured image and the retrieved linear polarization degree image.

[0037] Specifically, the precision pan-tilt stabilizer 16 can effectively offset external jitters such as wind force, equipment self-vibration, and human slight shaking through its internal stabilization mechanism (such as using high-precision gyroscopes, motors, etc. for real-time attitude adjustment and compensation), enabling the mid-wave focal plane detector 12 to work in a relatively stable state. In addition to the stabilization effect, the precision pan-tilt stabilizer 16 can also endow the mid-wave focal plane detector 12 with flexible pointing capabilities. It can rotate and adjust the angle in different directions as needed, facilitating imaging detection of target scenes in different directions. Moreover, when tracking and observing dynamic targets, the precision pan-tilt stabilizer 16 can accurately control the pointing of the mid-wave focal plane detector 12 according to the moving trajectory of the target, ensuring that the detector always aims at the target, thereby continuously and accurately obtaining image information of the target at different times and different polarization states, further enhancing the applicability and practicality of the entire mid-wave infrared polarization imaging system 100 in practical applications.

[0038] Furthermore, the device support frame 15 has a receiving cavity, and a liquid crystal micro-nano polarization control device 11 is arranged in the receiving cavity. The included angle between the liquid crystal micro-nano polarization control device 11 and the mid-wave infrared band-adapted lens 121 is 10° to 45°, preferably 30°.

[0039] Specifically, the accommodation cavity of the device support frame 15 provides a relatively stable installation space for the liquid crystal micro-nano polarization control device 11. This helps to protect the liquid crystal micro-nano polarization control device 11 from interference by external environmental factors (such as dust, moisture, etc.), ensuring the stability and reliability of its performance. At the same time, since the accommodation cavity is arranged inside the device support frame 15, the liquid crystal micro-nano polarization control device 11 and other components of the entire imaging system (such as the mid-wave infrared band adaptation lens 121, etc.) are more compact in spatial position, which is beneficial to reducing the loss of optical signals during transmission and ensuring the efficient and accurate transmission of optical signals between various components.

[0040] Specifically, the included angle between the liquid crystal micro-nano polarization control device 11 and the mid-wave infrared band adaptation lens 121 can greatly reduce the adverse effects of cold reflection on the imaging quality during the imaging process.

[0041] The mid-wave infrared polarization imaging system 100 provided in Embodiment 1 does not require complex optical path debugging and micro-structure design. The mid-wave infrared polarization imaging system 100 directly couples the liquid crystal micro-nano polarization control device 11 with the mid-wave focal plane detector 12. Based on the modulation effect of the helical structure formed in the twisted nematic liquid crystal cell on the polarization state of incident light, it realizes the analysis of the target scene by using the polarization rotation angle instead of the traditional polarization angle. By calibrating the data of the incident light rotated by the liquid crystal micro-nano polarization control device 11 by the drivable power supply 13 in the laser environment, the corresponding relationship between the polarization rotation angle and voltage of the outgoing light compared with the incident light is obtained, and then the linear polarization degree image of the target scene is inversely obtained. The mid-wave infrared polarization imaging system 100 as a whole adopts low-signal drive, has high integration, small volume, and low energy consumption.

[0042] Specifically, the liquid crystal micro-nano polarization component of the mid-wave infrared polarization imaging system 100 has a simple structure, is convenient to plug and unplug, is easy to couple, and has high energy utilization rate compared with the polarization component in the traditional infrared polarization imaging system; the mid-wave infrared polarization imaging system 100 adopts a support coupling mode, has a simple optical path, does not sacrifice resolution for the polarization regulation of the target scene, has good spatial consistency, can realize the dynamic adjustment of the polarization state of the target scene, has a long observation distance, and can realize 5 km long-distance polarization detection.

[0043] Please refer to Figure 2 , Figure 2 which is the optical path schematic diagram of the laser beam calibration system 200 provided in Embodiment 1 of the present invention; wherein, Embodiment 1 also provides a laser beam calibration system 200 for calibrating the calibration data of the mid-wave infrared polarization imaging system 100 as described above. The laser beam calibration system 200 sequentially includes a mid-infrared optical parametric oscillator laser 21, a polarizer 22, a liquid crystal micro-nano polarization control device 11, an analyzer 23, an objective lens 24, an attenuator 25, and an optical quality analyzer 26 along the optical signal input end to the optical signal output end; Among them, the laser beam calibration system 200 further includes a drivable power supply 13, and the drivable power supply 13 is electrically connected to the liquid crystal micro-nano polarization control device 11.

[0044] Specifically, along the optical signal transmission path, the laser beam calibration system 200 arranges a plurality of key components in sequence from the optical signal input end to the optical signal output end. First is the mid-infrared optical parametric oscillator 21. As the source of the optical signal, it can generate mid-infrared light with specific parameters such as wavelength and intensity, providing a stable and adjustable optical input for the subsequent calibration process. Then the light passes through a polarizer 22. The function of the polarizer 22 is to convert unpolarized light such as natural light into polarized light with a specific polarization direction, so that subsequent operations are carried out based on light with a determined polarization direction. Then the light reaches the liquid crystal micro-nano polarization control device 11, which can adjust the polarization rotation angle of the light under the action of the drivable power supply 13 electrically connected to it, and is an important link to achieve different polarization state controls. After that, the light passes through an analyzer 23, an objective lens 24, and an attenuation sheet 25 in sequence. The analyzer 23 is used to further screen and detect light with a specific polarization state. The objective lens 24 can perform optical operations such as focusing on the light to adapt to the reception requirements of subsequent components. The attenuation sheet 25 is used to adjust the light intensity to avoid damage to the subsequent optical quality analyzer 26 caused by excessive light intensity. Finally, the light enters the optical quality analyzer 26, which is used to analyze in detail the quality, polarization characteristics, etc. of the light after a series of processes, obtain relevant data, and thus complete the entire calibration process.

[0045] In Embodiment 1, the mid-wave infrared laser uses a mid-infrared optical parametric oscillator with a central wavelength of 4.1 μm; the polarizer 22 and the analyzer 23 adopt a wire grid structure with a transmittance of more than 70% and an extinction ratio of 300:1 in the 3 - 5 μm band; when the transmission directions of the polarizer 22 and the analyzer 23 are the same, an extinction ratio of 20000:1 can be achieved; the optical quality analyzer 26 uses a spot analyzer with high sensitivity, high resolution, and ultra-wideband wavelength coverage, and is used for measuring the dynamic energy distribution of the spot in the continuous or pulsed laser emission optical path.

[0046] In Embodiment 1, the laser beam calibration system 200 uses a beam quality analyzer to record the light intensity, with accurate data and strong analyzability. The proposed method for restoring the polarization image of the target scene is simple in calculation, easy to understand and implement, and the optical path of the laser beam calibration system 200 is simple and has strong feasibility.

[0047] In Embodiment 1, the process of calibrating the electro-optical polarization characteristics of the liquid crystal micro-nano polarization component by the laser beam calibration system 200 is as follows: Step 1, first Figure 2The laser beam calibration system 200 shown is aligned with the optical path, and various components are installed so that the polarization direction of the light emitted by the mid-infrared optical parametric oscillator laser 21, the transmission direction of the polarizer 22, and the orientation direction of the liquid crystal micro-nano polarization control component on the side close to the laser beam are all set along the X-axis; Step 2: Set the transmission direction of the analyzer 23 along the X-axis, and adjust the square wave voltage of the drivable power supply 13 from small to large. Observe the spot shape and light intensity obtained by the beam quality analyzer, and record it as the voltage adjustment range in the X direction; Step 3: Based on the state of the analyzer 23 in the previous step, precisely adjust the voltage in the recorded voltage adjustment range in the X direction with a step size of 0.5 Vrms. Record the pixel light intensity of the CMOS surface of the beam quality analyzer at each voltage value, and take the average surface light intensity Ix Vn ; Step 4: Set the transmission direction of the analyzer 23 along the Y-axis, and adjust the square wave voltage from small to large. Observe the spot shape and light intensity obtained by the beam quality analyzer, and record it as the voltage adjustment range in the Y direction; Step 5: Based on the state of the analyzer 23 in the previous step, precisely adjust the voltage in the recorded voltage adjustment range in the Y direction with a step size of 0.5 Vrms. Record the pixel light intensity of the CMOS surface of the beam quality analyzer at each voltage value, and take the average surface light intensity Iy Vn ; Step 6: Repeat three times; Step 7: Solve to obtain the polarization rotation angle AOP of the liquid crystal polarization control device at each voltage Vn The calculation formula is as follows: AOP Vn = arctan (Iy Vn / Ix Vn ) (1).

[0048] Specifically, in Step 1: Set the polarization direction of the light emitted by the mid-infrared optical parametric oscillator laser 21, the transmission direction of the polarizer 22, and the orientation direction of the liquid crystal micro-nano polarization control component on the side close to the laser beam all along the X-axis. This can ensure that the initial light polarization state is clear and unified, avoiding interference caused by inconsistent initial polarization directions to the subsequent measurement of the adjustment of the polarization rotation angle by the liquid crystal micro-nano polarization control component at different voltages, making the subsequent obtained data more comparable and accurate.

[0049] Specifically, in Step 2: The changes in the spot shape and light intensity reflect the changes in the light polarization state by the liquid crystal micro-nano polarization control component under different voltage drives. Determining the voltage adjustment range in the X direction can clarify the approximate interval for subsequent precise voltage adjustment, avoiding voltage adjustment beyond the reasonable range and affecting the accuracy and effectiveness of the calibration.

[0050] Specifically, in step three: the voltage is precisely adjusted in steps of 0.5Vrms. This small-step adjustment can more accurately capture the details of the change in light intensity with voltage. Record the pixel light intensity at each voltage value and take the average surface light intensity Ix Vn , in order to obtain more representative and stable data, reduce the errors caused by factors such as the fluctuations of individual pixels on the final result, and make the results calculated based on these data more reliable in the follow-up.

[0051] Specifically, in step six: repeat the above process from determining the voltage adjustment range to precisely adjusting the voltage and recording the light intensity data multiple times, so that the finally accumulated data set is more rich and comprehensive. When calculating key parameters such as the polarization rotation angle in the follow-up, comprehensive analysis can be carried out based on multiple groups of data, so as to obtain more accurate results that can better reflect the true performance of the liquid crystal micro-nano polarization control component.

[0052] Specifically, in step seven: the above polarization rotation angle formula is based on the ratio relationship of light intensity in the X and Y directions, and the inverse trigonometric function is used to determine the size of the polarization rotation angle. The polarization rotation angle calculated in this way can intuitively reflect the actual adjustment effect of the liquid crystal micro-nano polarization control component on the light polarization rotation angle under different voltage drives, providing an accurate calibration data basis for accurately using this component for polarization adjustment in the mid-wave infrared polarization imaging system 100 and accurately obtaining the linear polarization degree image of the target scene, etc. in the follow-up.

[0053] Please refer to Figures 3a to 3b , Figure 3a , which is a schematic diagram of the calibration light intensity change in the X direction of the laser beam calibration system 200 provided in Embodiment 1 of the present invention under typical voltages of 0, 1.4Vrms, and 2.1Vrms; Figure 3b , which is a schematic diagram of the calibration light intensity change in the Y direction of the laser beam calibration system 200 provided in Embodiment 1 of the present invention under typical voltages of 0, 1.4Vrms, and 2.1Vrms; among them, from Figures 3a to 3b it can be seen that the initial light intensity response of the light spot in the X direction is almost 0, and it appears from nothing after adding voltage, while the change law of the light intensity collected in the Y direction is exactly the opposite, indicating that when there is no voltage drive, this liquid crystal polarization control device rotates the originally X-direction polarized light to the Y direction, and under voltage drive, the polarization rotation effect of this liquid crystal polarization control component on the incident light polarization plane gradually disappears, and its polarization direction turns back from the Y direction to the X direction.

[0054] Please refer to Figure 3c , Figure 3c , which is a schematic diagram of the calibration light intensity change without distinguishing directions of the laser beam calibration system 200 provided in Embodiment 1 of the present invention under typical voltages of 0, 1.4Vrms, and 2.1Vrms; from Figure 3c it can be seen that after removing the effects of the analyzer 23 and the liquid crystal micro-nano polarization control component, the overall light intensity decreases slightly and there is always a response.

[0055] Please refer to Figure 4 , Figure 4 , which is a schematic diagram showing the relationship between the polarization rotation angle of the liquid crystal micro-nano polarization control component and the voltage obtained by the laser beam calibration system 200 provided in Embodiment 1 of the present invention; as can be seen from Figure 4 , when there is no voltage applied, the liquid crystal polarization control component rotates the incident linearly polarized light by 90°; under the action of an external square wave voltage, when the external square wave voltage reaches the working threshold voltage of 0.9Vrms (the voltage at which the liquid crystal starts to twist), the optical rotation ability gradually disappears, and until 1.6Vrms, the optical rotation ability almost completely disappears. Among them, the relationship between the typical polarization rotation angle readings and the voltage is as follows: 90° corresponds to the voltage before 0.9Vrms, 60° corresponds to 1.3Vrms, 30° corresponds to 1.4Vrms, and 0° corresponds to the voltage after 1.6Vrms.

[0056] Please refer to Figure 5 , Figure 5 , which is a flowchart of the image restoration method provided in Embodiment 1 of the present invention; among them, the specific steps of the above image restoration method are as follows: S10, debug the mid-wave infrared polarization imaging system 100 so that it can collect the target gray-scale image.

[0057] Specifically, step S10 further includes: First, provide the mid-wave infrared polarization imaging system 100 and connect it to the computer image acquisition card to collect images; secondly, turn on the computer power supply and wait for cooling. After about 8 minutes of cooling, the computer image acquisition card can collect the target gray-scale image.

[0058] S20, turn on the drivable power supply 13, and respectively collect the target measured images at different external voltages through the mid-wave focal plane detector 12.

[0059] S30, calculate the corresponding polarization rotation angles at different external voltages according to the calibration data of the corresponding relationship between the external voltage and the polarization rotation angle.

[0060] Specifically, step S30 further includes: Specifically, adjust the external square wave power supply connected to the liquid crystal polarization control component according to the calibration data provided by the laser beam calibration system 200, respectively collect the target measured images at four calibration typical voltages of 0Vrms, 1.3Vrms, 1.4Vrms, and 2Vrms, and calculate the corresponding polarization rotation angles at different external voltages.

[0061] At this time, the polarization rotation angle corresponding to the 0Vrms target measured image is 90°, the polarization rotation angle corresponding to the 1.3Vrms target measured image is 60°, the polarization rotation angle corresponding to the 1.4Vrms target measured image is 30°, and the polarization rotation angle corresponding to the 2Vrms target measured image is 0°.

[0062] S40. Convert the target measured images corresponding to different polarization rotation angles into corresponding polarization angle images according to the calibration data.

[0063] Specifically, the step S40 further includes: Convert the above four images into corresponding 0° polarization angle image, 30° polarization angle image, 60° polarization angle image and 90° polarization angle image according to the light intensity data calibrated by the laser beam calibration system 200.

[0064] Further, in the laser calibration environment, taking the conversion of the target measured image with a polarization rotation angle of 30° in step S30 into a 30° polarization angle image as an example: Set the overall average light intensity of the light spot when the polarization rotation angle is 30° as a (known quantity, provided by the calibration data provided by the laser beam calibration system 200), and the average light intensity of the light spot at a polarization angle of 30° as b (known quantity, related to the incident light intensity and transmittance); the image A obtained during actual imaging is at a polarization rotation angle of 30°, and it is converted into a 30° polarization angle image B according to the light intensity ratio, and the corresponding relationship satisfies B = A * b / a. The light intensity of each pixel of image B (characterized as the gray value of the grayscale image) can be converted according to the light intensity ratio to obtain a 30° polarization angle image.

[0065] S50. Convert the polarization angle image into a linear polarization degree image of the target scene according to the corresponding relationship of each Stokes component.

[0066] Specifically, the step S50 further includes: The Stokes vector is originally a four-dimensional vector used to completely describe the polarization state of light, S = (S0, S1, S2, S3); where S0 represents the total intensity of light, which is the sum of the light intensities in all polarization directions; S1 is related to the horizontal and vertical linear polarization components; S2 is related to the ±45° linear polarization components; S3 is related to the left-handed and right-handed circular polarization components. In the present invention, the circular polarization component S3 is ignored, and the Stokes vector becomes S = (S0, S1, S2), which means that in this calculation and processing method, the linear polarization characteristics of light are mainly concerned, and the influence of circular polarization is not considered.

[0067] Specifically, the light intensity ratio conversion relationships between S0, S1, S2, the linear polarization degree DoLP and the 0°, 30°, 60° and 90° polarization angle images are as follows: (2); (3); (4); (5); Among them, I0, I 30 , I 60 and I 90 respectively represent the outgoing light intensities of the polarization angle images with polarization angles of 0°, 30°, 60°, and 90°.

[0068] Please refer to Figures 6a to 6d , Figure 6a which is the measured target image of the mid-wave focal plane detector 12 at a typical voltage of 0Vrms in the image restoration method provided in Embodiment 1 of the present invention; Figure 6b which is the measured target image of the mid-wave focal plane detector 12 at a typical voltage of 1.3Vrms in the image restoration method provided in Embodiment 1 of the present invention; Figure 6c which is the measured target image of the mid-wave focal plane detector 12 at a typical voltage of 1.4Vrms in the image restoration method provided in Embodiment 1 of the present invention; Figure 6d which is the measured target image of the mid-wave focal plane detector 12 at a typical voltage of 2.0Vrms in the image restoration method provided in Embodiment 1 of the present invention; Among them, from Figures 6a to 6d it can be seen that at several voltages at different materials (such as the car body part), the gray values have obvious changes, but the overall light intensity changes little, indicating that the polarization imaging system realizes the polarization regulation of the target with low energy loss.

[0069] Please refer to Figures 6e to 6h , Figure 6e which is the Stokes vector S0 image of the target scene in the image restoration method provided in Embodiment 1 of the present invention; Figure 6f which is the Stokes vector S1 image of the target scene in the image restoration method provided in Embodiment 1 of the present invention; Figure 6g which is the Stokes vector S2 image of the target scene in the image restoration method provided in Embodiment 1 of the present invention; Figure 6h which is the degree of linear polarization image of the target scene in the image restoration method provided in Embodiment 1 of the present invention; Among them, from Figures 6e to 6h it can be seen that extracting the target contour in a timely manner can reflect the surface characteristics of different materials and reduce image glare.

[0070] The polarization image restoration method of the target scene provided by the present invention can inversely calculate a polarization image with polarization characteristics based on the calibration data of the liquid crystal micro-nano polarization device in a laser environment and the image directly obtained by the mid-wave infrared polarization imaging system 100. The principle of this method is simple, and it uses the rotation angle regulation characteristic of the liquid crystal micro-nano polarization component to realize the polarization analysis of the target scene.

[0071] Differing from the prior art, the mid-wave infrared polarization imaging system 100, the laser beam calibration system 200, and the image restoration method provided by the present invention have the following advantages: (1) The liquid crystal micro-nano polarization device in the mid-wave infrared polarization imaging system 100 is simple to manufacture, low in cost, and can effectively realize the electro-control adjustment of the polarization direction of incident light with a small voltage drive. It is achieved only by adjusting the magnitude of the externally connected drive voltage. There are no mechanical rotating parts during use, and the usage requirements are low.

[0072] (2) When the mid-wave infrared polarization imaging system 100 acquires polarization images corresponding to polarization angles, it is different from traditional polarization imaging systems. It does not only consider certain polarization angles (with 50% energy loss), but instead uses the polarization rotation angle to replace the polarization angle for parameter analysis, enabling the acquired polarization images to reflect polarization information on the basis of higher energy utilization efficiency.

[0073] (3) The mid-wave infrared polarization imaging system 100 can achieve electro-control polarization detection of the target scene without sacrificing resolution.

[0074] (4) The laser beam calibration system 200 has reliable data, strong analyzability, and high repeatability.

[0075] (5) The proposed method for restoring the polarization image of the target scene has a simple principle, simple calculation, and strong comprehensibility.

[0076] It should be noted that the above embodiments all belong to the same inventive concept. The descriptions of the embodiments have their own emphases. For the parts not described in detail in individual embodiments, reference can be made to the descriptions in other embodiments.

[0077] The above embodiments only represent the implementation manners of the present invention. Their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be pointed out that for those of ordinary skill in the art, without departing from the inventive concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the invention patent should be subject to the appended claims.

Claims

1. A mid-wave infrared polarization imaging system, characterized in that, Comprising: A drivable power supply for outputting an external voltage; A liquid crystal micro-nano polarization control device electrically connected to the drivable power supply, for adjusting the polarization rotation angle of the outgoing light compared to the incident light in the target scene after being applied with the external voltage; A mid-wave focal plane detector disposed closely on the light-emitting side of the liquid crystal micro-nano polarization control device, for acquiring target measured images of the target scene under different external voltages; A data storage and analysis module electrically connected to the mid-wave focal plane detector, for inversely calculating the linear polarization degree image of the target scene based on the calibration data of the corresponding relationship between the external voltage and the polarization rotation angle stored in advance, the external voltage, and the light intensity data of the target measured images; 2. The mid-wave infrared polarization imaging system according to claim 1, wherein The drivable power supply is a square wave power supply with a frequency of 1 kHz and a duty cycle of 1:

1.

3. The mid-wave infrared polarization imaging system according to claim 1, wherein The liquid crystal micro-nano polarization control device sequentially includes a first substrate, a first electrode layer, a first alignment layer, the liquid crystal layer, a second alignment layer, a second electrode layer, and a second substrate along the propagation direction of the incident light.

4. The mid-wave infrared polarization imaging system according to claim 1, characterized in that, The mid-wave focal plane detector sequentially includes a mid-wave infrared band-adapted lens, a mid-wave infrared detection CMOS focal plane array, and an electronic component along the propagation direction of the incident light. One end of the electronic component is electrically connected to the mid-wave infrared detection CMOS focal plane array, and the other end of the electronic component is electrically connected to the data storage and analysis module; Wherein, the mid-wave infrared detection CMOS focal plane array is a HgCdTe infrared focal plane array, and the mid-wave infrared detection band is 3.7 μm to 4.8 μm.

5. The mid-wave infrared polarization imaging system according to claim 4, wherein The mid-wave infrared polarization imaging system further includes a device support frame and a precision pan-tilt stabilizer. One end of the device support frame is fixedly connected to the mid-wave infrared band-adapted lens, and the precision pan-tilt stabilizer is used to carry the mid-wave focal plane detector.

6. The mid-wave infrared polarization imaging system according to claim 5, wherein The device support frame has a receiving cavity, and the liquid crystal micro-nano polarization control device is disposed in the receiving cavity. The included angle between the liquid crystal micro-nano polarization control device and the mid-wave infrared band-adapted lens is 10° to 45°.

7. A laser beam calibration system for calibrating the calibration data of the mid-wave infrared polarization imaging system according to any one of claims 1 to 6, characterized in that, The laser beam calibration system sequentially includes a mid-infrared optical parametric oscillator laser, a polarizer, the liquid crystal micro-nano polarization control device, an analyzer, an objective lens, an attenuator, and an optical quality analyzer along the optical signal input end to the optical signal output end; Wherein, the laser beam calibration system further includes the drivable power supply, and the drivable power supply is electrically connected to the liquid crystal micro-nano polarization control device.

8. The laser beam calibration system according to claim 7, characterized in that, The polarization direction of the outgoing light of the mid-infrared optical parametric oscillator laser and the orientation direction of the liquid crystal micro-nano polarization component close to the incident light side are both along the X axis.

9. The laser beam calibration system according to claim 8, wherein, When the transmission direction of the polarizer is along the X-axis, the pixel light intensity of the CMOS surface of the optical quality analyzer is recorded under different external voltages within the X-direction voltage adjustment range, and the average surface light intensity is taken as Ix Vn ; when the transmission direction of the polarizer is along the Y-axis, the pixel light intensity of the CMOS surface of the optical quality analyzer is recorded under different external voltages within the Y-direction voltage adjustment range, and the average surface light intensity is taken as Iy Vn ; the polarization rotation angle AOP of the liquid crystal micro-nano polarization control device under different external voltages Vn is arctan (Iy Vn / Ix Vn ).

10. An image restoration method, applied to the mid-wave infrared polarization imaging system according to any one of claims 1 to 6, characterized in that, The method includes: S10, debugging the mid-wave infrared polarization imaging system to enable it to collect target grayscale images; S20, turning on the drivable power supply, and respectively collecting target measured images under different external voltages through the mid-wave focal plane detector; S30, calculating the corresponding polarization rotation angles under different external voltages according to the calibration data of the corresponding relationship between the external voltage and the polarization rotation angle; S40, converting the target measured images corresponding to different polarization rotation angles into corresponding polarization angle images according to the calibration data; S50. Convert the polarization angle image into the linear polarization degree image of the target scene according to the corresponding relationship of Stokes components.

Images