System and method for testing polarization performance of a focal plane polarized image sensor

Abstract

The application discloses a kind of focal plane polarization image sensor polarization performance test system and method, the method includes driving polarization image sensor to carry out imaging, under no light condition, multiple acquisition image data, under the illumination of constant light power light source, rotate Brewster polarizer and multiple acquisition image data at each rotation angle, then after mean processing, select the target pixel region in the middle of the collected image, polarization modulation parameter can be calculated from the measured data according to least square criterion, finally, polarization principal axis offset and polarization efficiency are obtained according to polarization modulation parameter.The application considers the influence of dark signal on test result, and polarization performance is characterized by three parameters of polarization modulation parameter, polarization principal axis offset and polarization efficiency, the test result is high in accuracy, and the modular design of test system is suitable for a variety of focal plane polarization image sensors.

Description

Technical Field

[0001] The present invention relates to the technical field of polarization imaging, and in particular to a system and method for testing the polarization performance of a split-focus plane polarization image sensor. Background Art

[0002] Polarization offers a richer range of information and significant advantages in the field of image vision. The human eye cannot directly capture polarization information, requiring the assistance of polarization imaging devices. Among these, focal plane polarization imaging devices are a hot topic due to their compact size, high integration, excellent temporal resolution, and flexible application scenarios.

[0003] While conventional image sensors have dedicated performance testing methods, polarization performance testing methods for polarization image sensors are less well-researched. For split-focal plane polarization image sensors, common polarization performance testing methods often focus solely on the linear polarization grating on the sensor surface, using transmittance and extinction ratio as primary performance parameters to evaluate the linear polarization grating. This method has the advantage of ensuring good performance of the linear polarization grating on the sensor surface and ensuring complete polarization imaging. However, its disadvantage is that it isolates the split-focal plane polarization image sensor from a single unit, ignoring errors introduced by the overall polarization imaging. Summary of the Invention

[0004] The purpose of the present invention is to provide a test system for the polarization performance of a split-focus plane polarization image sensor.

[0005] The technical solution for achieving the purpose of the present invention is: a test system for polarization performance of a split-focus plane polarization image sensor, comprising: a data processing component, a modular imaging component, and an optical system;

[0006] The modular imaging assembly is used to provide peripheral circuits of the polarization image sensor and realize power supply and signal connections;

[0007] The optical system is used to provide the polarization image sensor with linearly polarized light required for testing;

[0008] The data processing component is used to control the polarization image sensor to work and perform real-time polarization imaging to obtain polarization image data required for testing.

[0009] Preferably, the data processing component includes: an FPGA chip, an image acquisition card, and a host computer. The FPGA chip realizes the driving of the image sensor and the serial-to-parallel conversion and decoding and restoration of the image data; the image acquisition card realizes the image display of the data on the host computer; and the host computer controls the entire operation process, including the rotation of the Brewster polarizer in the optical system, the configuration of the image sensor working mode, and the storage and calculation of the collected image data.

[0010] Preferably, the modular imaging component includes a chip board, a probe board and an interface board. The chip board contains the layout and wiring of the image sensor peripheral circuit, and is provided with an adaptive test base to lead the pins of the image sensor to the probe points on the chip board; the probe board contains probes for realizing signal connection between the chip board and the interface board; the interface board has a signal connector and a power connector connected to the probe points to realize power and signal connection with other devices.

[0011] Preferably, the optical system includes a point light source, a telecentric mirror, an optical power meter and a Brewster polarizer. The point light source and the telecentric mirror are used to emit parallel uniform light, and the uniform light reaches the photosensitive surface of the image sensor after passing through the Brewster polarizer; the optical power meter is used to measure the optical power of the outgoing light; the Brewster polarizer contains multiple pieces of parallel square glass, and polarizes the transmitted light according to Brewster's law. The polarizer can rotate freely 360° around the optical axis to achieve modulation of linear polarized light at different angles.

[0012] Another object of the present invention is to provide a method for testing the polarization performance of a split-focus plane polarization image sensor, comprising the following steps:

[0013] Step 1: Place the polarization image sensor to be tested vertically in the optical path, power on the entire test system, and return the Brewster polarizer to 0°;

[0014] Step 2: Under the control of the host computer, the FPGA chip generates a drive signal, which is transmitted to the focal plane polarization image sensor through the interface board, the probe board, and the chip board. The polarization image sensor is driven to perform imaging according to the configured working mode. The imaging data is converted from serial to parallel and decoded by the FPGA chip, and the imaging results are displayed on the host computer by the image acquisition card.

[0015] Step 3: Control the image sensor to collect images under dark conditions, save the collected image data to the host computer, take the average value of multiple collections, and use the obtained image data I d Indicates dark signal;

[0016] Step 4: Control the power of the point light source to be constant, use the optical power meter to measure the light power P, rotate the Brewster polarizer, and at each rotation angle Perform image acquisition, save the acquired image data to the host computer, take the average value of multiple acquisitions, and obtain image data at various angles arrive

[0017] Step 5: Select a pixel area in the image, and obtain the polarization modulation parameters m0(x, y), m1(x, y), and m2(x, y) of each pixel using the least squares criterion based on the image grayscale value data of the pixel area;

[0018] Step 6: Calculate the polarization axis offset Δ(x, y) and polarization efficiency η of each pixel based on the definition of polarization modulation parameters. P (x, y).

[0019] Preferably, the relationship between the polarization modulation parameter and the image gray value data in step 5 is:

[0020]

[0021] in, represents the pseudo-inverse of the matrix, is the rotation angle of the Brewster polarizer, m0(x, y), m1(x, y), m2(x, y) are the polarization modulation parameters of each pixel, I d (x, y) is the dark signal of each pixel, P is the light power, The angle of the Brewster polarizer under the illumination of a light source with a light power of P is The image grayscale value collected by each pixel of the time-division focal plane polarization image sensor.

[0022] Preferably, the relationship between the polarization modulation parameter, polarization axis offset, and polarization efficiency described in step 6 is:

[0023]

[0024]

[0025] Where k1 is the primary transmittance of the linear polarization grating of the focal plane polarization image sensor, k2 is the secondary transmittance, θ(x, y) is the polarization axis angle of each pixel, and θ ideal (x, y) is the ideal polarization axis angle of each pixel, Δ(x, y) is the polarization axis offset of each pixel, and η P (x, y) is the polarization efficiency of each pixel.

[0026] Compared with the existing technology, the present invention has the following significant advantages: the test system of the present invention adopts a modular design and can be adapted to a variety of focal plane polarization image sensors by replacing different chip boards; the test method of the present invention takes into account the influence of dark signals on test results, and uses three parameters: polarization modulation parameter, polarization main axis offset, and polarization efficiency to characterize the polarization performance of the focal plane polarization image sensor. The measurement results are highly accurate and are more conducive to the restoration and calibration of Stokes parameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is an overall block diagram of the polarization performance test system of the split-focus plane polarization image sensor of the present invention.

[0028] Figure 2 It is a schematic structural diagram of the chip board in the modular imaging assembly of the present invention.

[0029] Figure 3 It is a schematic structural diagram of the probe card in the modular imaging assembly of the present invention.

[0030] Figure 4 It is a schematic structural diagram of the interface board in the modular imaging assembly of the present invention.

[0031] Figure 5 It is a flow chart of the polarization performance testing method of the split-focus plane polarization image sensor of the present invention. DETAILED DESCRIPTION

[0032] The present invention will be described in further detail below with reference to the accompanying drawings. The embodiments described with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be construed as limiting the present invention.

[0033] First, the polarization performance test system of the split-focus plane polarization image sensor proposed in accordance with an embodiment of the present invention will be described with reference to the accompanying drawings. Figure 1 The polarization performance testing system of the focal plane polarization image sensor includes: a data processing component, a modular imaging component and an optical system.

[0034] The data processing component includes an FPGA chip, an image acquisition card, and a host computer. The FPGA chip drives the image sensor and processes image data; the image acquisition card displays the data on the host computer; and the host computer controls the entire operation process. This component controls the polarization image sensor, performs real-time polarization imaging on the host computer, and acquires the polarization image data required for testing.

[0035] Modular imaging components include: chip board, probe board, interface board. Figure 2 The chip board contains the layout and wiring of the peripheral circuits, and is equipped with an adaptive test base to lead the sensor pins to the 180 probe points on the chip board; combined with Figure 3 The probe board contains 180 probes for signal connection between the chip board and the interface board; Figure 4 The interface board has two 68-pin differential signal connectors and two power connectors. These connectors connect to 180 probe points on the interface board, enabling power and signal connections to other devices. This section provides peripheral circuitry for the image sensor, enabling power and signal connections, and can be adapted to different models of focal plane polarization image sensors by replacing the chip board.

[0036] The optical system includes a point light source and telecentric lens, an optical power meter, and a Brewster polarizer. The point light source and telecentric lens emit parallel, uniform light, which then passes through the Brewster polarizer and reaches the photosensitive surface of the image sensor. The optical power meter measures the optical power of the outgoing light. The Brewster polarizer, consisting of multiple parallel square glass sheets, polarizes transmitted light according to Brewster's law, achieving excellent polarization. Furthermore, the polarizer can rotate 360° around the optical axis, producing linearly polarized light at varying angles. This component provides the optical path required for testing.

[0037] Next, a polarization performance testing method for a split-focus plane polarization image sensor according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[0038] Combine Figure 5 The steps of the polarization performance test method of the focal plane polarization image sensor are as follows:

[0039] Step 1: Place the image sensor to be tested vertically aligned with the optical path, power on the entire test system, and return the Brewster polarizer to 0°.

[0040] Step 2: Under the control of the host computer, the FPGA chip generates a driving signal, which is transmitted to the focal plane polarization image sensor through the interface board, the probe board, and the chip board. The polarization image sensor is driven to perform imaging according to the configured working mode. The imaging data is converted from serial to parallel and decoded and restored by the FPGA chip, and the imaging results are displayed on the host computer by the image acquisition card.

[0041] The focal plane polarization image sensor integrates a linear polarization grating in units of pixels on the focal plane of the image sensor, so that each pixel in the acquired image individually presents the polarization state of the corresponding point in the target scene according to a predetermined polarization direction. Therefore, the pixel model of the focal plane polarization image sensor is: the incident Stokes parameter S = (S0, S1, S2, ×) T After passing through the linear polarization grating on the sensor surface, we get S′=(S0′,×,×,×) T , which is then received by the photoelectric sensor and outputs a polarization image. The total light intensity S′0 after passing through the grating is

[0042]

[0043] Wherein, k1 and k2 are the primary and secondary transmittances of the linear polarization grating, and θ is the angle of the polarization grating for each pixel.

[0044] The grayscale image I output by the photoelectric sensor is expressed as

[0045] I=ηgS′0+d

[0046] For a single pixel, the relationship between the grayscale value I of the polarization image and the Stokes parameter S is expressed as

[0047]

[0048] The above formula is the measurement equation, which is the basis for measuring the polarization performance parameters of the camera.

[0049] Divide the pixel's response coefficient to the three Stokes parameters by The image is scaled by the mean value, and the result of scaling is the modulation parameters m0, m1, and m2:

[0050]

[0051]

[0052]

[0053] Among them, x and y represent pixel coordinates, X and Y represent the number of pixels. By introducing modulation parameters and pixel coordinates, a new measurement equation can be obtained:

[0054] I(x,y)=m0(x,y)S0(x,y)+m1(x,y)S1(x,y)+m2(x,y)S2(x,y)+d(x,y)

[0055] The pixel linear polarization grating is designed with four main axis directions: 0°, 45°, 90°, and 135°. Under ideal conditions:

[0056]

[0057]

[0058]

[0059]

[0060]

[0061]

[0062] The closer the parameters of the focal plane image sensor to be tested are to the ideal values, the better its polarization performance is.

[0063] Step 3: Control the image sensor to collect images under dark conditions, save the collected image data to the host computer, take the average value of multiple collections to reduce random noise, and obtain image data I d , the dark signal can be determined from this set of images, specifically expressed as

[0064] d(x, y) = Id (x, y)

[0065] Step 4: Control the power of the point light source to be constant, use the optical power meter to measure the light power P, rotate the Brewster polarizer, and at each rotation angle The image data is collected and saved to the host computer. The average value of multiple acquisitions is taken to reduce random noise and obtain image data at various angles. arrive The relationship with the polarization modulation parameter is expressed as

[0066]

[0067] Step 5: Select a pixel area in the image. According to the image gray value data of this area, the polarization modulation parameters m0(x, y), m1(x, y), and m2(x, y) of each pixel can be obtained by the least squares criterion. The relationship between the polarization modulation parameters and the image gray value data is:

[0068]

[0069] in, represents the pseudo-inverse of the matrix, is the rotation angle of the Brewster polarizer.

[0070] Step 6: Calculate the polarization axis offset Δ(x, y) and polarization efficiency η of each pixel based on the definition of polarization modulation parameters. P (x, y). The relationship between polarization modulation parameters, polarization axis offset, and polarization efficiency is:

[0071]

[0072]

[0073] The testing method of the embodiment of the present invention takes into account the influence of dark signals on the test results, and uses three parameters: polarization modulation parameter, polarization principal axis offset, and polarization efficiency to characterize the polarization performance of the focal plane polarization image sensor. The measurement results are highly accurate and are more conducive to the restoration and calibration of the Stokes parameters.

[0074] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

[0075] It should be understood that in order to simplify the present invention and help those skilled in the art understand the various aspects of the present invention, in the above description of the exemplary embodiments of the present invention, various features of the present invention are sometimes described in a single embodiment or described with reference to a single figure. However, the present invention should not be interpreted as if all the features included in the exemplary embodiments are essential technical features of the claims of this patent.

[0076] It should be understood that the modules, units, components, etc. included in the device of one embodiment of the present invention can be adaptively changed to be installed in a device different from the embodiment. The different modules, units, or components included in the device of the embodiment can be combined into a single module, unit, or component, or they can be divided into multiple sub-modules, sub-units, or sub-components.

Claims

1. A method for testing polarization performance of a focal plane polarization image sensor, characterized in that: Based on the test system, the test system includes: a data processing component, a modular imaging component and an optical system; The data processing component includes: FPGA chip, image acquisition card and host computer; The modular imaging assembly includes a chip board, a probe board, and an interface board; The optical system includes a point light source, a telecentric mirror, an optical power meter and a Brewster polarizer; The specific test steps are as follows: Step 1: Place the polarization image sensor to be tested vertically in the optical path, power on the entire test system, and return the Brewster polarizer to 0°; Step 2: Under the control of the host computer, the FPGA chip generates a drive signal, which is transmitted to the focal plane polarization image sensor through the interface board, the probe board, and the chip board. The polarization image sensor is driven to perform imaging according to the configured working mode. The imaging data is converted from serial to parallel and decoded by the FPGA chip, and the imaging results are displayed on the host computer by the image acquisition card. Step 3: Control the image sensor to collect images under dark conditions, save the collected image data to the host computer, take the average value of multiple collections, and use the obtained image data I d Indicates dark signal; Step 4: Control the power of the point light source to be constant, use the optical power meter to measure the light power P, rotate the Brewster polarizer, and at each rotation angle Perform image acquisition, save the acquired image data to the host computer, take the average value of multiple acquisitions, and obtain image data at various angles arrive Step 5: Select a pixel area in the image and obtain the polarization modulation parameters m0(x, y), m1(x, y), and m2(x, y) of each pixel using the least squares criterion based on the image grayscale value data of the pixel area. Specifically, in, represents the pseudo-inverse of the matrix, is the rotation angle of the Brewster polarizer, m0(x,y), m1(x,y), m2(x,y) are the polarization modulation parameters of each pixel, I d (x,y) is the dark signal of each pixel, P is the light power, The angle of the Brewster polarizer under the illumination of a light source with a light power of P is The grayscale value of the image collected by each pixel of the time-division focal plane polarization image sensor; Step 6: Calculate the polarization axis offset Δ(x, y) and polarization efficiency η of each pixel based on the definition of polarization modulation parameters. P (x,y), specifically: Where k1 is the primary transmittance of the linear polarization grating of the focal plane polarization image sensor, k2 is the secondary transmittance, θ(x,y) is the polarization axis angle of each pixel, and θ ideal (x, y) is the ideal polarization axis angle of each pixel, Δ(x, y) is the polarization axis offset of each pixel, η P (x,y) is the polarization efficiency of each pixel.

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