A full-spectrum adjustable polarization reference light source for an infrared polarization imaging system and a radiation polarization joint calibration method

Abstract

The application discloses a full-spectrum adjustable polarization reference light source for an infrared polarization imaging system and a radiation polarization joint calibration method. The reference light source comprises: an infrared light source module for providing stable and controllable infrared radiation output; a polarization state generator module provided with a transmission light path and a reflection light path, adjustable polarization modulation units are arranged in the two paths respectively, and light path compensation components and beam synthesis components are configured to realize the output of any S1, S2 and linear combination polarization states; a system calibration and verification module for real-time measurement of the actual Stokes parameters of the output light beam; and a control module for closed-loop correction of the polarization modulation parameters according to the error between the target parameters and the actual measurement results. Through the double-light-path cooperative modulation and online Stokes parameter measurement feedback mechanism, the output accuracy and controllability of the reference polarization light are significantly improved, and the joint implementation of radiation calibration, image plane uniformity calibration and image element polarization direction calibration can be realized on the same platform.

Description

Technical Field

[0001] This invention belongs to the field of infrared polarization detection, polarization calibration and infrared testing technology, specifically involving a full-spectrum tunable polarization reference light source and a radiation polarization joint calibration method for infrared polarization imaging systems. Background Technology

[0002] Infrared polarization imaging systems, building upon traditional infrared intensity information, can further acquire characteristic parameters such as the polarization degree and direction of a target. This makes them valuable for applications in complex background target detection, camouflage identification, remote sensing monitoring, and optoelectronic countermeasures. To ensure the accuracy of polarization measurement results, infrared polarization imaging systems typically require both radiometric and polarization calibration.

[0003] In existing infrared polarization imaging calibration schemes, a common approach is to use a blackbody radiation source with a single rotatable polarizer to generate linearly polarized light in different directions, and then analyze the output response of the system under test to achieve polarization direction calibration or radiation response calibration. This type of scheme has the following shortcomings:

[0004] (1) The output polarization state type is singular, making it difficult to achieve high-precision controllable polarization reference output.

[0005] Existing technologies mostly use a "blackbody radiation source + single rotating polarizer" method to generate reference light, which can usually only output a few linear polarization states with fixed azimuth angles. It is difficult to achieve precise modulation of the Stokes parameters of any target, especially the combination of different linear polarization components, and cannot meet the high-precision, multi-state calibration requirements of infrared polarization imaging systems.

[0006] (2) Lack of online measurement and closed-loop correction capability for actual output polarization state

[0007] Existing solutions typically assume that the polarizer setting angle corresponds to the target output polarization state. However, in practical systems, polarization element errors, optical path asymmetry, material dispersion, and assembly / adjustment deviations can all cause the actual output polarization state to deviate from the theoretical value. Due to the lack of online Stokes parameter detection and error feedback mechanisms, the reference polarized light itself has uncertainties, which in turn affects calibration accuracy.

[0008] (3) The calibration functions are scattered, making it difficult to achieve joint radiation-polarization calibration.

[0009] In the existing technology, broadband radiometric calibration, image plane uniformity calibration and pixel polarization direction calibration are usually completed by different devices and different processes. The test conditions are not uniform, the efficiency is low, and it is easy to introduce inconsistencies between various parameters, making it difficult to meet the requirements of infrared polarization imaging systems for overall consistency and joint calibration.

[0010] (4) It is difficult to meet the requirements of high stability and high uniformity polarization reference output under wide-band infrared conditions.

[0011] Under long-wave infrared conditions, radiation intensity, optical path uniformity, polarization purity, output aperture and system stability need to meet high requirements at the same time. However, existing technologies often cannot meet these performance indicators, which means they can only be used for low-precision experimental verification and cannot support the high-precision calibration of engineered infrared polarization imaging systems.

[0012] (5) The complex sources of error of the infrared polarization imaging system under test were not fully considered.

[0013] Infrared polarization imaging systems not only suffer from non-uniform radiation response but are also affected by various factors such as differences in transmittance of micro-polarizers, differences in extinction ratios, polarization direction deviations, lens polarization effects, detector noise, and instantaneous field-of-view errors. Existing calibration techniques typically only correct for single error sources and lack a unified calibration scheme for system-level comprehensive errors, resulting in limited accuracy in the final polarization measurement.

[0014] In summary, existing infrared polarization imaging system calibration techniques suffer from the following shortcomings: First, the reference light source output polarization state type is relatively simple, making it difficult to achieve high-precision, flexible, and controllable modulation of the target Stokes parameters. Second, existing solutions generally lack the ability to measure and correct the actual output polarization state online, leading to error accumulation in the reference polarized light itself. Third, radiometric calibration, image plane uniformity calibration, and pixel polarization direction calibration are usually separated, making it difficult to achieve joint calibration under a unified platform and operating conditions. Fourth, under wide-band infrared operating conditions, existing technologies cannot simultaneously meet multiple performance requirements such as radiance, uniformity, stability, and polarization purity. Fifth, existing calibration methods do not adequately consider system-level error sources such as micro-polarizer non-ideality, lens polarization effect, detector noise, and instantaneous field-of-view error, resulting in limited adaptability of calibration results to complex actual operating conditions. Therefore, there is an urgent need to propose a full-spectrum tunable polarization reference light source and calibration method that can output high-precision controllable polarization reference light, has online closed-loop correction capability, and can achieve radiation-polarization joint calibration, so as to improve the overall calibration accuracy and engineering application capability of infrared polarization imaging systems. Summary of the Invention

[0015] To address the aforementioned technical problems, this invention provides a full-spectrum tunable polarization reference light source and a joint calibration method for radiation polarization in infrared polarization imaging systems. The core technical solution includes:

[0016] A full-spectrum tunable polarization reference light source for an infrared polarization imaging system includes:

[0017] Infrared light source module, used to provide stable and controllable infrared radiation output;

[0018] A polarization state generator module is disposed in the output optical path of the infrared light source module and is used for polarization modulation, optical path compensation, beam combining and collimation output of infrared radiation. The polarization state generator module includes at least a transmission optical path and a reflection optical path, and adjustable polarization modulation units are respectively disposed in the two optical paths. The target polarization state is generated by adjusting the working parameters of the polarization modulation units in the two optical paths.

[0019] The system calibration and verification module, located at the output of the polarization state generator module, is used to measure and verify the actual polarization state of the output infrared reference light; and,

[0020] The control module is electrically connected to the infrared light source module, the polarization state generator module, and the system calibration and verification module, respectively. It is used to receive the measurement results of the system calibration and verification module and perform closed-loop correction on the modulation parameters in the polarization state generator module based on the error feedback information between the target Stokes parameters and the actual measured Stokes parameters.

[0021] A method for joint calibration of radiation and polarization specifically includes the following steps:

[0022] Step 1: Set a fixed temperature for the blackbody radiation source. After the temperature stabilizes, continuously acquire several sets of images at that temperature. Since the camera acquires four images with different polarization directions (0°, 45°, 90°, and 135°) at a time, under a fixed irradiance, divide the images into four image sets: 0°, 45°, 90°, and 135°. Each image set contains several images with the same polarization direction. Then, average each image set, and then average the average of the average images to obtain the 0°, 45°, 90°, and 135° responses under the same irradiance. The responses are represented by DN values.

[0023] ;

[0024] In the formula, For the first The output signal of each pixel The total number of pixels, This is the average value output for each pixel;

[0025] Step 2: With the camera fixed, change the temperature of the blackbody radiation source and repeat the image grouping, calculation, and DN value acquisition operations from Step 1.

[0026] Step 3: Plot a linear graph with the equivalent blackbody brightness temperature of the blackbody radiation source on the x-axis and the mean value of the images acquired by the camera in the four polarization directions on the y-axis to obtain the linear fitting equation and correlation coefficient.

[0027] The present invention has the following beneficial effects:

[0028] (1) A full-spectrum tunable polarization reference light source architecture for infrared polarization imaging systems was constructed:

[0029] This invention does not employ the traditional simple structure of "blackbody radiation source + single rotating polarizer". Instead, it constructs a full-spectrum tunable polarization reference light source system consisting of an infrared light source module, a polarization state generator module, a system calibration and verification module, and a control module. This enables the reference light source to simultaneously possess infrared radiation output, polarization state generation, state verification, and closed-loop control functions, significantly improving the functional integration and engineering applicability of the reference light source.

[0030] (2) A polarization state generation mechanism based on the synergy of the transmission and reflection optical paths was proposed:

[0031] This invention, by setting up a transmission optical path and a reflection optical path, and arranging polarization modulation units in each of the two optical paths, can generate arbitrary S1 polarization states, arbitrary S2 polarization states, and linear combinations of the two polarization states. This overcomes the problems of limited reference polarization types and limited output states in existing technologies. Compared to traditional schemes that can only output a few fixed linear polarization states, this invention has significant advantages in terms of adjustable polarization state range, output flexibility, and calibration adaptability.

[0032] (3) The online Stokes parameter measurement and closed-loop correction mechanism improves the accuracy of the reference polarized light output:

[0033] This invention uses an infrared polarization analyzer to measure the actual Stokes parameters of the output reference light in real time and feeds the measurement results back to the control module. The polarization modulation parameters are then corrected in a closed-loop manner through error matrix analysis and optimization algorithms. Compared to existing open calibration schemes that rely on theoretical angle settings and lack output verification, this invention can significantly reduce polarization output deviations caused by device errors, assembly errors, and environmental disturbances, thereby improving the accuracy and repeatability of the reference polarized light from the source.

[0034] (4) Through optical path compensation and beam combining design, the output consistency of the two optical paths is improved:

[0035] This invention introduces an optical path compensation component and a beam combining component during the polarization state generation process to match and compensate for the equivalent optical path, aberration, and phase relationship between the transmitted and reflected optical paths, and then combines the two polarized beams into a single output optical path. This design effectively solves the common problems of path asymmetry and output polarization mismatch in multi-path systems, improves the purity, stability, and spatial consistency of the reference polarized light, and is particularly suitable for high-precision polarization output under wide-band infrared conditions.

[0036] (5) Integrated implementation of radiation calibration and polarization calibration has been achieved:

[0037] This invention is not limited to the determination of a single polarization direction, but can complete broadband radiometric calibration, image plane uniformity calibration, and pixel polarization direction calibration under the same reference light source platform, the same optical path system, and unified test conditions. Compared with the existing technology that implements different calibration tasks separately and with fragmented processes, this invention effectively improves test efficiency, reduces systematic errors caused by switching between different test conditions, and enhances the consistency and self-consistency among various calibration parameters.

[0038] (6) Improved the controllability and accuracy of the reference polarized light output:

[0039] This invention constructs an integrated reference light source system consisting of an infrared light source module, a polarization state generator module, a system calibration and verification module, and a control module. This system enables stable output of multiple target polarization states, no longer limited to traditional linearly polarized light with a few fixed azimuth angles. This significantly improves the tunability and output accuracy of the infrared polarized reference light.

[0040] (7) Online measurement and closed-loop correction of the output polarization state were achieved:

[0041] This invention utilizes an infrared polarization analyzer to measure the actual Stokes parameters of the output beam in real time and feeds the measurement results back to the control module to perform closed-loop correction of the polarization modulation parameters. This effectively reduces the output deviation caused by device errors, assembly errors, and environmental disturbances, thereby improving the reliability and repeatability of the reference polarized light from the source.

[0042] (8) Integrated implementation of radiation calibration and polarization calibration has been achieved:

[0043] This invention can complete broadband radiometric calibration, image plane uniformity calibration, and pixel polarization direction calibration on the same platform, with the same optical path and under the same test conditions. It avoids the problems of complex process, inconsistent conditions, and error superposition caused by different calibration tasks being carried out separately in the prior art, and improves the overall calibration efficiency and parameter consistency.

[0044] (9) Suitable for wide-band infrared high-precision calibration requirements:

[0045] This invention, through the coordinated design of the infrared light source, polarization modulation structure, optical path compensation structure, and collimation structure, enables the reference light source to maintain radiance, uniformity, stability, and polarization purity under wide-band infrared conditions, thus better meeting the high-precision calibration requirements of engineered infrared polarization imaging systems.

[0046] (10) Improved adaptability and compensation capability for system-level errors:

[0047] This invention not only optimizes the reference light source itself, but also works with an infrared polarization imaging system to comprehensively calibrate and correct factors such as the non-ideal nature of micro-polarizers, non-uniform pixel response, lens polarization effect, detector noise, and instantaneous field of view error. Therefore, it can effectively improve the polarization measurement accuracy of the system under actual complex working conditions.

[0048] In summary, this invention enables high-precision controllable polarization reference light output and completes radiation-polarization joint closed-loop calibration on a unified platform. This not only improves the calibration accuracy, consistency, and repeatability of the infrared polarization imaging system, but also enhances its applicability in wide-band, complex working conditions, and engineering applications, demonstrating significant technical advantages and application value. Attached Figure Description

[0049] Figure 1 This is a structural diagram of a full-spectrum tunable polarization reference light source unit.

[0050] Figure 2 This is a schematic diagram of the composition of a full-spectrum tunable polarization reference light source unit.

[0051] Figure 3 This is a schematic diagram of the unit structure of a full-spectrum tunable polarization reference light source;

[0052] Figure 4 A framework diagram of the blackbody calibration source;

[0053] Figure 5 This is a schematic diagram of a polarization state generator;

[0054] Figure 6 This is a schematic diagram of phase delay;

[0055] Figure 7 This is a schematic diagram of polarization detection.

[0056] Figure 8 Infrared DN values ​​of blackbody radiation sources at different temperatures;

[0057] Figure 9 The curve showing the relationship between infrared DN value and radiance in a polarization imager;

[0058] Figure 10 This is the calibration coefficient for the uniformity of a polarization direction region in a polarization imager.

[0059] Figure 11 This is the calibration coefficient for the uniformity of another polarization direction region of the polarization imager;

[0060] Figure 12 This is the calibration coefficient for the uniformity of another polarization direction region of the polarization imager;

[0061] Figure 13This is the calibration coefficient for the uniformity of another polarization direction region of the polarization imager;

[0062] Figure 14 This is a schematic diagram of the experimental setup for polarization direction calibration of a polarization imager. Detailed Implementation

[0063] 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 embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other. To achieve the above objectives, this invention adopts the following technical solution.

[0064] like Figures 1-3 As shown, the present invention first constructs a full-spectrum tunable polarization reference light source for infrared polarization imaging systems, including an infrared light source module, a polarization state generator module, a system calibration and verification module, and a control module.

[0065] The infrared light source module is used to provide stable and controllable infrared radiation output. It preferably uses a blackbody radiation source as the basic radiation source and combines it with a temperature control system to achieve continuous adjustment of different radiance levels. At the same time, the infrared light source module is preferably equipped with a Dewar chamber or an equivalent low-temperature vacuum environment unit to improve the working stability of the light source and reduce the impact of external thermal disturbances on the output radiation.

[0066] The polarization state generator module is used to polarize the infrared radiation output by the infrared light source module. The module includes at least a transmission optical path and a reflection optical path, each with an adjustable polarization modulation unit. By adjusting the operating parameters of the polarization modulation units in the two optical paths, the target polarization state can be generated. The polarization modulation units employ rotatable linear polarizers, arranged in the transmission and reflection optical paths respectively. By independently controlling the azimuth angles of the two polarizers, arbitrary S1 polarization state, arbitrary S2 polarization state, or a linear combination of both can be output. When the polarization components output from the two optical paths meet the equivalent condition, near-unpolarized infrared reference light mainly containing the S0 component can also be generated.

[0067] To reduce the optical differences between the transmitted and reflected optical paths, this invention incorporates an optical path compensation component in the polarization state generator module. This component compensates for the equivalent optical path length, aberration characteristics, and phase differences between the two optical paths. The optical path compensation component includes a germanium compensation plate or other compensation elements suitable for the infrared band. After compensation, the two optical paths are coupled to the same output optical path via a beam combining component to obtain an infrared reference light output with the target polarization state.

[0068] To ensure that the output beam meets the requirements of the infrared polarization imaging system under test, filling both the field of view and the aperture, this invention further incorporates a collimating optical component. This collimating optical component shapes the infrared polarized light output from the polarization state generator module into a parallel beam. Preferably, it employs one or more combinations of off-axis parabolic mirrors, germanium lenses, and silicon lenses to balance wideband adaptability, polarization distortion control, and engineering feasibility.

[0069] The system calibration and verification module is used to measure and verify the actual polarization state of the output infrared reference light, preferably including an infrared polarization analyzer. The infrared polarization analyzer measures the Stokes parameters of the output beam and sends the measurement results to the control module. The control module receives the target Stokes parameters and the actual measured Stokes parameters, constructs error feedback information, and corrects the modulation parameters in the polarization state generator module based on the error feedback information, forming a closed-loop control of the output polarization state. The control module uses the least squares method or other optimization algorithms to iteratively correct the polarizer angles or equivalent modulation parameters in the transmission and reflection optical paths until the output polarization state meets the preset accuracy requirements.

[0070] like Figure 2 As shown, the full-spectrum tunable polarization reference light source unit mainly includes an infrared light source module, a polarization state generator module, a system calibration and verification module, and a control box. The infrared light source module provides stable and controllable infrared radiation input and is the radiation source of the entire system. The polarization state generator module is located on the output optical path of the infrared light source module and is used for polarization modulation, optical path compensation, beam combining, and collimation output of the infrared radiation. The system calibration and verification module is located at the output end of the polarization state generator module and is used to measure and verify the actual polarization state of the output reference light. The control box is electrically connected to the infrared light source module, the polarization state generator module, and the system calibration and verification module, and is used to complete temperature control, drive control, data acquisition, status display, and closed-loop feedback adjustment. These modules together constitute a joint calibration platform capable of outputting high-precision, controllable polarization reference light.

[0071] The infrared light source module includes a blackbody radiation source and a Dewar chamber. The blackbody radiation source generates broadband, radiance-adjustable infrared radiation, simulating targets with different radiation intensities by adjusting the blackbody temperature. The Dewar chamber provides a low-temperature vacuum environment for the blackbody radiation source, reducing external heat exchange and environmental radiation interference, and improving the stability and uniformity of the output radiation. The infrared radiation output from the infrared light source module first enters the polarization state generator module.

[0072] The polarization state generator module includes a transmission optical path T, a reflection optical path R, a polarization modulation unit, an optical path compensation component, a beam combining component, and a collimating optical component. The transmission optical path T and the reflection optical path R respectively receive infrared radiation from the infrared light source module and each has a polarization modulation unit within its respective optical path. The polarization modulation unit is preferably a rotatable linear polarizer; by adjusting the azimuth angle of the polarizer in the transmission and reflection optical paths, different polarization components can be modulated and output. Specifically, the polarization modulation units in the transmission and reflection optical paths can generate linear polarization states in different directions, such as 0°, 45°, 90°, and 135°, and further achieve arbitrary S1 polarization state, arbitrary S2 polarization state, or a linear combination of both through the combination of the two polarization components.

[0073] The optical path compensation component is installed in the transmission optical path T and the reflection optical path R to compensate for the equivalent optical path length, aberration, and phase delay of the two optical paths. It is preferably implemented using a germanium compensation plate to reduce the output polarization deviation caused by path differences between the two optical paths. The compensated transmission and reflection optical paths then enter a beam combining component, which combines two infrared beams with different polarization states into a single output optical path to obtain an infrared reference beam with the target polarization state. The combined output beam then enters a collimating optical component, which can employ one or more of an off-axis parabolic mirror, a germanium lens, or a silicon lens. This component shapes the output infrared polarized light into a parallel beam, ensuring it fills both the field of view and the aperture of the infrared polarization imaging system under test.

[0074] The system calibration and verification module is located at the output end of the polarization state generator module, and preferably includes an infrared polarization analyzer and an auxiliary alignment displacement stage. The infrared polarization analyzer receives the collimated output infrared polarized reference light and measures its Stokes parameters to determine the deviation between the current output polarization state and the target polarization state. The auxiliary alignment displacement stage precisely adjusts the positional relationship between the system calibration and verification module and the output optical axis to ensure accurate coaxiality between the detection optical path and the reference light output optical path. The Stokes parameters measured by the system calibration and verification module are further transmitted to the control box for error feedback and closed-loop correction of the output polarization state.

[0075] The control box includes a control host, a drive control module, a temperature and vacuum measurement module, and related electrical control interfaces. The control host is used to uniformly manage the operation of the entire reference light source unit; the drive control module is used to control the blackbody temperature adjustment in the infrared light source module and the polarizer rotation drive in the polarization state generator module; the temperature and vacuum measurement module is used to monitor the temperature, vacuum, and related operating status of the Dewar chamber in real time; the control box also receives the polarization measurement results output by the system calibration and verification module, and performs closed-loop correction on the polarization modulation parameters in the transmission path T and the reflection path R based on the deviation between the target Stokes parameters and the actual Stokes parameters, thereby realizing the stable output and joint calibration function of the full-spectrum adjustable polarization reference light source.

[0076] From the perspective of optical path position, the infrared radiation propagation direction of the system is as follows: the infrared radiation output from the blackbody radiation source enters the polarization modulation unit through the transmission optical path T and the reflection optical path R respectively. After polarization modulation is completed in the two paths, the equivalent optical path is compensated by the optical path compensation component. Then, the two beams are combined into a unified output beam by the beam combining component. Subsequently, it is output as a parallel infrared polarization reference light through the collimating optical component, and finally enters the system calibration and verification module for polarization state measurement and verification. At the same time, the measurement results of the system calibration and verification module are fed back to the control box. The control box coordinates and controls the aforementioned functional modules and corrects the parameters, forming a complete closed-loop working link of "infrared radiation generation, dual-optical-path polarization modulation, compensation and combining, collimation output, polarization verification, and feedback control".

[0077] Based on the aforementioned full-spectrum tunable polarization reference light source, this invention further proposes a radiation-polarization joint calibration method, comprising the following steps:

[0078] The first step is to start the infrared light source module, set the temperature of the blackbody radiation source, and output stable infrared radiation after the temperature stabilizes.

[0079] The second step is to control the polarization modulation units in the transmission and reflection optical paths according to the Stokes parameters of the target to be output, so that the reference light source outputs the target polarization state.

[0080] The third step is to use the system calibration and verification module to measure the actual Stokes parameters of the current output infrared reference light.

[0081] The fourth step is to compare the target Stokes parameters with the actual measured Stokes parameters to generate an error matrix or error feedback quantity.

[0082] Fifth, the control module corrects the modulation parameters in the polarization state generator module based on the error feedback results, and repeats the output-measurement-correction process until the output polarization state reaches the preset polarization accuracy requirement.

[0083] The sixth step is to use the infrared polarization reference light after closed-loop correction to perform joint calibration on the infrared polarization imaging system under test.

[0084] The joint calibration includes at least one or more of the following: broadband radiometric calibration, image plane uniformity calibration, and pixel polarization direction calibration. Specifically, the broadband radiometric calibration establishes a correspondence between the output DN value and the input radiance of the system under test by changing the temperature of the blackbody radiation source; the image plane uniformity calibration constructs uniformity correction coefficients for each pixel or polarization channel through image response analysis under a uniform radiation field; the pixel polarization direction calibration acquires the response curves of each polarization channel by placing an external linear polarizer in front of the system under test and gradually rotating it within a predetermined angle range, and then obtaining the actual polarization resolution direction of each channel or pixel through curve fitting.

[0085] This invention achieves high-precision and controllable output of infrared polarization reference light by constructing a dual-path polarization state generation structure, an online Stokes parameter measurement structure, and a closed-loop correction control structure. At the same time, by performing radiometric calibration, uniformity calibration, and polarization direction calibration on the same platform, it realizes the joint radiometric-polarization closed-loop calibration of the infrared polarization imaging system, thereby improving the consistency, accuracy, and engineering applicability of the calibration results.

[0086] In detail, (1) blackbody radiation source

[0087] like Figure 4 As shown, a blackbody radiation source consists of a radiating surface, a heating system, a cooling system, and a control system.

[0088] The radiating surface includes a substrate material, a microstructure disposed on the surface of the substrate material, and a high-emission coating covering the surface of the microstructure. The substrate material is preferably copper, which is used to provide mechanical support and heat conduction channels. The microstructure is used to enhance multiple reflections of the surface and improve the equivalent emissivity. The high-emission coating is used to improve the radiation emission performance of the target in the infrared band. The three together constitute the radiation output surface of the blackbody infrared radiation calibration source.

[0089] The refrigeration system includes a refrigeration plate, various valves, a liquid nitrogen Dewar, and pipes. The liquid nitrogen Dewar provides the cryogenic refrigeration medium, the various valves regulate and switch the flow rate and operating mode of the refrigeration medium, the pipes form the refrigeration medium delivery path, and the refrigeration plate is thermally connected to the radiant surface for cooling control. The refrigeration system can use liquid nitrogen for rapid cooling when switching from high to low temperature, and use nitrogen to mitigate and correct temperature overshoot.

[0090] The heating system includes a heater, a heating power supply, a heat regulation plate, and a heat insulation plate. The heater converts electrical energy into heat energy and heats the radiating surface. The heating power supply provides adjustable power input to the heater. The heat regulation plate evenly distributes and transfers the heat generated by the heater to the radiating surface. The heat insulation plate reduces heat loss to non-working areas. The heating system achieves stable heating and uniform temperature control of the blackbody infrared radiation calibration source through the heat transfer relationship between the heating power supply, heater, heat regulation plate, and radiating surface.

[0091] The control system includes a heating control system, a cooling control system, and a data acquisition unit. The heating control system controls the heating system to raise the temperature and regulate the temperature of the radiating surface, while the cooling control system controls the cooling system to rapidly cool the radiating surface and suppress overshoot. The data acquisition unit collects real-time information on the temperature, power, and operating status of the radiating surface. The control system adjusts the heating control system and the cooling control system based on the collected feedback information, thereby achieving closed-loop temperature control of the blackbody infrared radiation calibration source.

[0092] In addition to the above system, it also needs to include cryogenic baffles and other auxiliary materials and devices for providing electrical, liquid nitrogen and other supplies.

[0093] (2) Polarization state generator module

[0094] The polarization state generator module is used to generate and dynamically control the polarization state of light. Its core components include a polarization modulator, optical path compensation, and beam combining components.

[0095] The polarization modulator consists of two rotating linear polarizers. By adjusting the angle of the polarizers, the polarization state of the emitted light is controlled, generating any S1 polarization state, S2 polarization state, or a linear combination of S1 and S2. Furthermore, the polarization components of S1 and S2 in the combination must exhibit a dependent coupling relationship. For example... Figure 5 As shown, Figure 5 This diagram illustrates the principle of a polarization state generator. The left image shows the generation principle of the S1 polarization component, and the right image shows the generation principle of the S2 polarization component. The cylindrical component is the main body of the polarization state generator, the horizontal line is the principal optical axis, and the tilted sheet-like component on the right is a rotatable polarization modulation unit. The arrow bundles represent linear polarization components in different directions. In the left image, the target S1 polarization state is generated by superimposing 0° / 90° orthogonal linear polarization components; in the right image, the target S2 polarization state is generated by superimposing 45° / -45° linear polarization components. By rotating the polarization modulation unit, the proportional relationship between the polarization components can be adjusted, thereby achieving the output of S1, S2, and their linear combinations of polarization states.

[0096] 1) S1 component synthesis:

[0097] a) Generate arbitrary S1 polarization components by superimposing the linear polarization states at 0 degrees (T source) and 90 degrees (R source).

[0098] b) When 90-degree linearly polarized light is injected into the reflected light path (R light path), or 0-degree linearly polarized light is injected into the transmitted light path (T light path), pure 90-degree or 0-degree polarization states can be generated respectively.

[0099] 2) Generating the S2 component requires inverse derivation of the input polarization state through Miller matrix calculation:

[0100] a) Input 51-degree linearly polarized light from T light source to output 45-degree polarized light;

[0101] b) Input 35-degree linearly polarized light from the R light source to output -45-degree polarized light;

[0102] c) Generating a pure S2 polarization state: Injecting a -45 degree polarization state in the R optical path requires 54.64 degrees of linearly polarized light input, while generating a +45 degree polarization state in the T optical path requires 39.08 degrees of linearly polarized light input.

[0103] 3) When the polarization state of the T / R light source is equivalent, the output is unpolarized (S1 / S2 components are zero), that is, it generates arbitrary S0 components only.

[0104] When the full-spectrum tunable polarization reference light source is in operation, the polarizer is rotated sequentially to 0°, 45°, 90°, and 135° (-45°) directions, and data is collected respectively. The linear Stokes components are calculated as follows:

[0105] ;

[0106] linear polarization degree and polarization direction for:

[0107] ;

[0108] An optical path compensator refers to a germanium (Ge) compensator plate, which achieves equivalent optical path matching in the transmission optical path (T) and reflection optical path (R) of a PSG, thereby making the distortion and field curvature of the two optical paths consistent.

[0109] A beam combining component is used to merge projection and reflection light paths with different polarization states into a single optical path to obtain the optimal S1 or S2 polarization state. For example... Figure 6 As shown, Figure 6This diagram illustrates the phase delay principle, primarily including germanium compensation plates positioned in the transmission and reflection optical paths, the input light source location, and the output receiver. The input reference light, incident from the lower left, enters the corresponding germanium compensation plates via two different paths. Refraction occurs at preset incident angles, resulting in phase delay compensation. This ensures that the two optical paths achieve approximately identical equivalent optical path lengths and phase conditions upon reaching the output. By adjusting the installation angle and position of the germanium compensation plates, the optical path difference and phase mismatch between the transmission and reflection optical paths can be further corrected, thereby improving the consistency of polarization state synthesis and the output polarization accuracy.

[0110] The spectral polarization analyzer is used to measure and analyze the polarization state of the output infrared polarization reference light, obtain its Stokes parameters or corresponding polarization characteristic parameters, and feed the measurement results back to the control system to realize the verification and closed-loop correction of the polarization state of the reference light source output.

[0111] In engineering, the Stokes vector is used to define the degree of polarization.

[0112] ;

[0113] In a polarized radiation source, the emitted light is partially polarized. Since partially polarized light can be considered as a mixture of fully linearly polarized light and natural light, .

[0114] ;

[0115] For any quasi-monochromatic plane wave from the target being detected, its polarization information can be expressed using the Stokes vector. To characterize.

[0116] like Figure 7 As shown, the Muller matrix of the analyzer that passes through the axis at an angle θ to the X-axis is:

[0117] ;

[0118] In the formula, n is the transmittance coefficient of the device, and the Stokes vector of the beam to be measured is assumed to be... Then the Stokes vector of the beam after the analyzer is:

[0119] ;

[0120] Since the first row of the Stokes vector represents the total intensity of the light wave, and the photodetector can only measure this intensity value, we only care about the value of the first row in the above equation. The calculated Stokes vector of the beam incident on detector D is:

[0121] ;

[0122] The light intensity value measured by the photodetector is:

[0123] ;

[0124] The design measurement method involves taking N consecutive measurements within the range of 0° to 180°, and assuming the analyzer angle is θ during the j-th measurement. The result of the j-th measurement should satisfy the following formula.

[0125] ;

[0126] ;

[0127] ;

[0128] ;

[0129] All the above formulas have the same coefficient, which cancels out the calculation of the degree of polarization:

[0130] ;

[0131] This invention provides a radiometric calibration method. Radiometric calibration establishes a linear relationship between the camera's DN value and the radiance of a radiation source. Radiometric calibration is a prerequisite for other preprocessing operations on the camera. The output energy of a blackbody radiation source is linearly related to the current, and the camera's response is linearly related to the received radiance. Therefore, a linear conversion relationship can be established by detecting the linear relationship between the camera's response and the radiation source radiance.

[0132] Specifically, the following steps are included:

[0133] Step 1: Set a fixed temperature for the blackbody radiation source. After the temperature stabilizes, continuously acquire 10 sets of images at that temperature. Since the camera acquires images with four different polarization directions (0°, 45°, 90°, and 135°) at a time, under a fixed irradiance, divide the 10 sets of images into four image sets: 0°, 45°, 90°, and 135°. Each image set contains 10 images with the same polarization direction. Then, average each image set, and then average the average of the average images to obtain the 0°, 45°, 90°, and 135° direction responses under the same irradiance. The responses are represented by DN values.

[0134] ;

[0135] In the formula, For the first The output signal of each pixel The total number of pixels, This is the average value output for each pixel;

[0136] Step 2: With the camera fixed, change the temperature of the blackbody radiation source and repeat the image grouping, calculation, and DN value acquisition operations from Step 1.

[0137] Step 3: Plot a linear graph with the equivalent blackbody brightness temperature of the blackbody radiation source on the x-axis and the mean value of the images acquired by the camera in the four polarization directions on the y-axis to obtain the linear fitting equation and correlation coefficient.

[0138] Test steps and results:

[0139] By adjusting the temperature of the blackbody radiation source, infrared polarization images were captured under different temperature conditions, and broadband absolute radiometric calibration was performed. Eight temperature points were set for the blackbody radiation source: 36.1℃, 38℃, 41.1℃, 43.2℃, 45℃, 47℃, 55.6℃, and 65.8℃. The captured images are shown below. Figure 8 As shown.

[0140] The radiance of the blackbody under different temperature conditions was calculated, and the absolute calibration coefficients of the polarization imager in normal temperature mode were fitted based on the infrared DN values ​​of the blackbody region. Statistical data are shown in Table 1.

[0141] Table 1 Correlation Table between Blackbody Radiance and Infrared DN Value

[0142]

[0143] The fitted curve is as follows Figure 9 As shown.

[0144] The obtained absolute calibration coefficients of the polarization imager are K: 0.5497, B: -3950, and the calibration formula is:

[0145] ;

[0146] In the formula, For radiance, To calibrate the DN value.

[0147] (5) Image plane uniformity calibration

[0148] In infrared polarization cameras, if the target field of view is uniform, then the ideal image output signal will also be uniform. However, many factors often cause images to be non-uniform: non-uniformity in some optical lenses and thin films during camera manufacturing; non-uniformity of filter transmittance within a certain spectral range; and non-uniformity of the photosensitive elements in the imaging device. Non-uniformity of the photosensitive elements is caused by inhomogeneity in the manufacturing process and materials; the larger the scale of the device, the more prominent the uniformity problem becomes. All these non-uniformity problems can be corrected using uniformity calibration.

[0149] Within the linear response range of the infrared polarization camera, the ratio of the standard deviation to the mean of the acquired images is used. The non-uniformity of the detector is represented by the following formula:

[0150] ;

[0151] In the formula, M×N is the total number of detector elements in the CCD. This represents the average response of all pixels. This represents the non-uniformity parameter of the detector response.

[0152] The calibration experiment method is as follows:

[0153] To correct for non-uniformity in the response, the correction coefficient for each pixel must first be calculated.

[0154] Step 1: Under typical operating conditions, the polarization imager performs 50 measurements with the entrance aperture of the infrared polarization camera blocked. The dark current is obtained by averaging the grayscale values ​​of these images. ;

[0155] Step 2: After aligning the entrance aperture of the infrared polarization camera with the light source, perform 50 measurements. Analyze the DN values ​​from the obtained images and calculate their mean and variance:

[0156] ;

[0157] In the formula, This represents the average DN of the image obtained from 50 measurements. The average value of DN represents the dark current; parameters are defined.

[0158] Step 3: The obtained radiation calibration coefficients are:

[0159] ;

[0160] Step 4: Multiply each pixel by its corresponding calibration coefficient to complete the correction of each channel image;

[0161] Step 5: Calculate the non-uniformity parameters again for the processed image. To verify the image plane uniformity correction results;

[0162] Uniformity calibration first involves photographing uniform blackbodies at different temperatures within a fixed integration time. The ratio of the DN value of each pixel to the mean value is compared, and these ratios are statistically analyzed as uniformity calibration coefficients. The experiment divides the camera into four regions with different polarization directions, calculating the uniformity calibration coefficients for each region. Simultaneously, calibration coefficients are calculated at both low and high integration times. For example... Figures 10-13 As shown, these are the calibration coefficients for the uniformity of the four polarization direction regions of the polarization imager.

[0163] (6) Pixel polarization direction calibration

[0164] The most significant characteristic of an infrared polarization focal plane is that it exhibits different responses to changes in the polarization state of the incident radiation, demonstrating polarization response characteristics. Unlike analyzing temperature response curves, it is necessary to maintain the intensity of the radiation source output at a fixed value. Different polarization states are modulated by adding a polarizer in front of the radiation source. A schematic diagram of polarization modulation is shown below. Figure 14 As shown.

[0165] The infrared polarization camera is placed in front of an external polarizer. The external polarizer is rotated continuously, and the rotation is paused every 1°. The pixel response under the current polarization direction is collected to obtain the polarization response curves of the pixels in the four channels.

[0166] Throughout the experiment, the temperature was maintained between 20°C and 23°C, and the humidity was kept below 60%. The infrared polarization camera was mounted on an adjustable work platform. The work platform was adjusted so that the camera's aperture was centered on the large-aperture blackbody radiation source, and the camera's optical axis was perpendicular to the blackbody radiation source.

[0167] To improve the accuracy of the data acquired by the polarization imaging detection system, measurements were taken along the four polarization transmission axes of the system to verify whether the orientations of the four polarizers were correctly designed and fixed at 0°, 45°, 90°, and 135°. Curve fitting was used to detect the polarizer orientation angle error. The polarization orientation calibration experiment method is as follows:

[0168] Step 1: Place a polarizer between the blackbody radiation source and the camera, rotate the linear polarizer within the range of 0°-180°, and continuously acquire 10 sets of images at 1° intervals. Take the average image as the acquired image for that angle.

[0169] Step 2: Use a data fitting tool to perform curve fitting between each rotation angle and the image mean;

[0170] Step 3: Obtain the maximum points of the fitted curves for the three polarization directions from the fitted curves;

[0171] Step 4: Take the angle corresponding to the maximum value of the first fitted curve as the polarization analysis direction of the 0° polarization direction, and then the polarization direction angle detection result of the polarization camera can be obtained.

[0172] Pixel polarization direction determination is achieved by measuring the radiation intensity of a linearly polarized light source with a known polarization direction, obtaining the DN value of each pixel of the camera with each polarization direction, and finding the sensitive polarization direction angle of each pixel through fitting. Finally, the specific angles of the four polarization directions on the image plane are obtained, as shown in Table 2.

[0173] Table 2. Relative polarization direction measurements from the polarization imager

[0174]

Claims

1. A full-spectrum tunable polarization reference light source for an infrared polarization imaging system, characterized in that, include: Infrared light source module, used to provide stable and controllable infrared radiation output; A polarization state generator module is disposed in the output optical path of the infrared light source module and is used for polarization modulation, optical path compensation, beam combining and collimation output of infrared radiation. The polarization state generator module includes at least a transmission optical path and a reflection optical path, and adjustable polarization modulation units are respectively disposed in the two optical paths. The target polarization state is generated by adjusting the working parameters of the polarization modulation units in the two optical paths. The system calibration and verification module, located at the output of the polarization state generator module, is used to measure and verify the actual polarization state of the output infrared reference light; and, The control module is electrically connected to the infrared light source module, the polarization state generator module, and the system calibration and verification module, respectively. It is used to receive the measurement results of the system calibration and verification module and perform closed-loop correction on the modulation parameters in the polarization state generator module based on the error feedback information between the target Stokes parameters and the actual measured Stokes parameters.

2. The full-spectrum tunable polarization reference light source for an infrared polarization imaging system according to claim 1, characterized in that, The infrared light source module includes a blackbody radiation source and a Dewar chamber; the blackbody radiation source is used to generate wide-band, adjustable-radiance infrared radiation, and the Dewar chamber is used to provide a low-temperature vacuum environment for the blackbody radiation source.

3. The full-spectrum tunable polarization reference light source for an infrared polarization imaging system according to claim 1, characterized in that, The polarization state generator module further includes an optical path compensation component, a beam combining component, and a collimating optical component; the optical path compensation component is disposed in the transmission optical path and the reflection optical path, and is used to match and compensate for the equivalent optical path, aberration, and phase delay of the two optical paths; the beam combining component is used to combine two infrared lights with different polarization states into the same output optical path; the collimating optical component is used to shape the output infrared polarized light into a parallel beam.

4. The full-spectrum tunable polarization reference light source for an infrared polarization imaging system according to claim 3, characterized in that, The optical path compensation component includes a germanium compensation plate; the collimating optical component adopts one or more of the following structures: off-axis parabolic mirror, germanium lens, and silicon lens.

5. A full-spectrum tunable polarization reference light source for an infrared polarization imaging system according to claim 1, characterized in that, The adjustable polarization modulation unit uses a rotatable linear polarizer; by independently controlling the azimuth angle of the polarizer in the transmission and reflection optical paths, it can achieve the output of any S1 polarization state, any S2 polarization state, or a linear combination of the two polarization states.

6. A full-spectrum tunable polarization reference light source for an infrared polarization imaging system according to claim 1, characterized in that, The system calibration and verification module includes an infrared polarization analyzer and an auxiliary alignment displacement stage. The infrared polarization analyzer is used to measure the Stokes parameters of the output beam, and the auxiliary alignment displacement stage is used to adjust the positional relationship between the system calibration and verification module and the output optical axis to ensure that the detection optical path and the reference output optical path are accurately coaxial.

7. A full-spectrum tunable polarization reference light source for an infrared polarization imaging system according to claim 1, characterized in that, The control module uses the least squares method to iteratively correct the polarization modulation parameters in the transmission and reflection optical paths until the output polarization state meets the preset accuracy requirements.

8. A full-spectrum tunable polarization reference light source for an infrared polarization imaging system according to claim 1, characterized in that, The control module includes a control host, a drive control module, and a temperature and vacuum measurement module; the drive control module is used to control the blackbody temperature adjustment in the infrared light source module and the polarizer rotation drive in the polarization state generator module; the temperature and vacuum measurement module is used to monitor the temperature, vacuum level, and related working status of the Dewar chamber in real time.

9. A method for joint calibration of radiation and polarization, characterized in that, Specifically, the following steps are included: Step 1: Set a fixed temperature for the blackbody radiation source. After the temperature stabilizes, continuously acquire several sets of images at that temperature point. Acquire four images with different polarization directions at 0°, 45°, 90°, and 135° simultaneously. Under a fixed irradiance, divide the images into four image sets: 0°, 45°, 90°, and 135°. Each image set contains several images with the same polarization direction. Then, average each image set, and then average the average of the average images to obtain the 0°, 45°, 90°, and 135° responses under the same irradiance. The responses are represented by DN values. ； In the formula, For the first The output signal of each pixel The total number of pixels, This is the average value output for each pixel; Step 2: With the camera fixed, change the temperature of the blackbody radiation source and repeat the image grouping, calculation, and DN value acquisition operations from Step 1. Step 3: Plot a linear graph with the equivalent blackbody brightness temperature of the blackbody radiation source on the x-axis and the mean value of the images acquired by the camera in the four polarization directions on the y-axis to obtain the linear fitting equation and correlation coefficient.

10. The radiation polarization joint calibration method according to claim 9, characterized in that, The calibration formula for a polarization imager is: ； In the formula, For radiance, Here, DN is the value, and K and B are scaling factors.

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