CN111982287A - Method for correcting spatial modulation polarization imaging parameters by incident light with tunable bandwidth - Google Patents

Abstract

The invention provides a method for correcting spatial modulation polarization imaging parameters for incident light with a tunable bandwidth. The process includes: A1, finding the position a1 where the Stokes vector S1 of the incident light with a narrow bandwidth of central wavelength λ1 is modulated in the frequency domain; A2, adjusting the bandwidth d and reducing the central wavelength λ1 of the incident light through a tunable filter, when the polarization When the degree DOP changes, subtract the half of the bandwidth d/2 from the central wavelength λ1 to obtain the minimum wavelength λ2 without aliasing in this band; A3, increase the central wavelength of the incident light and adjust the bandwidth d through the tunable filter, when When the degree of polarization DOP changes, add the center wavelength λ1 to half of the bandwidth d/2 to obtain the maximum wavelength λ3 without aliasing in this band; A4, obtain the minimum wavelength λ2 without aliasing in this band and the modulated Calculate the overall coefficient t1 of the polarization imaging system at the position a1; A5, calculate the overall coefficient t2 of the polarization imaging system through the obtained minimum wavelength λ3 and a1+1 without aliasing in this band, and compare and detect the two coefficients . The invention can be used for the measurement and correction of the parameters of the broadband spatial modulation polarization imaging equipment, and can be widely used in the fields of broadband polarization remote sensing imaging and the like.

Description

A method for correcting spatially modulated polarization imaging parameters for incident light with tunable bandwidth

(1) Technical field

The invention relates to a method for tunable bandwidth incident light to correct spatial modulation polarization imaging parameters, which can be used for parameter measurement and correction of broadband spatial modulation polarization imaging equipment, and belongs to the field of polarization remote sensing imaging.

(2) Background technology

Polarization is one of the important characteristics of light. The characteristics of polarization can reflect the corresponding properties of the target. Different targets have their own unique polarization characteristics. Therefore, the reconnaissance and identification of the target can be realized through the imaging of polarized light, which is very important in optical remote sensing. It has strong applicability and also plays a role in environmental monitoring, hidden target recognition and ophthalmic disease diagnosis. Polarization represents the transverse wave characteristics of light waves, and light waves can be divided into polarized light and unpolarized light according to the polarization state of light waves. The polarization state of light waves changes through reflection and refraction, and polarization is used to represent the basic properties of objects such as physics. In the process of light wave transmission, its inherent polarization characteristics will change with the physical properties of matter, but it cannot be observed. With the vigorous development of polarization image detection technology, emerging directions such as polarization information visualization, measurement information dimension expansion, and simultaneous detection have made polarization imaging detection a very meaningful research. In applications, the Stokes vector method (S0, S1, S2, S3) is commonly used to represent the polarization state of light, and the present invention analyzes the position where the Stokes vector S1 moves in the frequency domain after being modulated.

The spatial modulation polarization imaging system is based on a Savart mirror composed of birefringent crystals, and is composed of a half-wave plate, an analyzer and an imaging camera, as shown in Figure 1. The modulated incident light enters the polarizer group and is divided into four coherent beams by the polarizer group to form an interference image. After demodulation, the polarization information of the target can be obtained. In the frequency domain, when the wavelength changes within a pixel, the DOP will not change. When the wavelength continues to change, the signal that should be in the 0 pixel will enter the 1 pixel, and the DOP will also occur. The wavelength when the DOP does not change is the maximum wavelength of this band, as shown in Figure 2. Since the entire polarization imaging system is composed of optical elements, in addition to measuring and calibrating their respective parameters, it is also necessary to measure and calibrate the overall parameters of the imaging system.

The invention discloses a method for correcting spatial modulation polarization imaging parameters of incident light with a tunable bandwidth, which is to adjust the center wavelength and bandwidth of incident light through a tunable filter to obtain the wavelength corresponding to the edge when the degree of polarization DOP changes. The overall parameters of the polarization imaging system are deduced from the actually measured wavelengths, and the parameters calculated from the results are more accurate. for reference.

(3) Contents of the invention

The purpose of the present invention is to provide a method for correcting spatial modulation polarization imaging parameters of incident light with tunable bandwidth, which is convenient for detection and accurate in calibration parameters.

The purpose of this invention is to realize through the following technical means:

A method for correcting spatially modulated polarization imaging parameters for incident light with a tunable bandwidth, comprising:

A1, find the position a1 where the Stokes vector S1 of the incident light with a narrow bandwidth of central wavelength λ1 is modulated in the frequency domain;

A2, adjust the bandwidth d and reduce the center wavelength λ1 of the incident light through a tunable filter. When the degree of polarization DOP changes, subtract half of the bandwidth d/2 from the center wavelength λ1 to obtain the minimum wavelength without aliasing in this band λ2;

A3, increase the center wavelength of the incident light and adjust the bandwidth d through the tunable filter, when the polarization degree DOP changes, add the center wavelength λ1 to half of the bandwidth d/2 to obtain the maximum wavelength λ3 without aliasing in this band ;

A4, calculate the overall parameter t1 of the polarization imaging system by obtaining the minimum wavelength λ2 and the modulated position a1 when this band does not have aliasing;

A5: Calculate the overall parameter t2 of the polarization imaging system through the obtained minimum wavelength λ3 and a1+1 when no aliasing occurs in this band, and compare and detect the two coefficients.

Further, the tuned incident light in the step A1 will be divided into four coherent beams after entering the polarizer group, and then an interferogram containing all polarization information is formed in the camera, and the target can be obtained by transforming the interferogram. The Stokes vector S1 moves to position a1 in the frequency domain.

Further, in the steps A4 and A5, the wavelength of the incident light and the overall parameters of the polarization imaging system satisfy a certain relationship, and the formula is:

where Δ represents the transverse shear of a single birefringent crystal, D represents the size of the imaging camera pixel, N represents the number of rows or columns of the imaging camera, f represents the focal length of the imaging camera, and a represents the signal moving in the frequency domain after being modulated The position of λ represents the wavelength of the incident light, so the overall parameters of the two polarization imaging systems are obtained:

The parameter formula of the polarization imaging system is determined that the relevant parameters remain unchanged, so the two obtained parameters should be the same, which can be used to verify whether the method is correct.

Beneficial effects of the present invention: The present invention is a method for tunable bandwidth incident light to correct spatially modulated polarization imaging parameters. Compared with other methods, the accuracy of measurement and calibration is more accurate, the application is more flexible, and the system equipment does not need to be disassembled for measurement. Calibration can perform measurement and correction on the entire imaging system equipment. At the same time, it can also provide a reference for the subsequent measurement and calibration of each optical element of the polarization imaging system, especially when the influence between the optical elements needs to be considered, the integrity standard can be given.

(4) Description of drawings

FIG. 1 is a schematic structural diagram of a spatially modulated polarization imaging system based on tunable bandwidth incident light correction. It consists of a tunable filter 1, a polarizer group 2 and an imaging camera 3.

FIG. 2 is a distribution diagram of each decomposition component of wide-bandwidth incident light in the frequency domain. It mainly shows that the 0th-order components and 1st-order components of the incident light of different wavelengths in the frequency domain are distributed in the 0 pixel and 1 pixel respectively. When the same order components of the different wavelengths of incident light are in the same pixel range , the polarization degree after demodulation will not change.

3 is a flow chart of a method for correcting spatially modulated polarization imaging parameters for incident light with a tunable bandwidth according to the present invention.

(5) Specific implementation methods

The present invention will be further described below in conjunction with specific embodiments.

As shown in FIG. 3 , a method for correcting spatially modulated polarization imaging parameters for incident light with a tunable bandwidth of the present invention includes:

A1, find the position a1 where the Stokes vector S1 of the incident light with a narrow bandwidth of central wavelength λ1 is modulated in the frequency domain;

A2, adjust the bandwidth d and reduce the center wavelength λ1 of the incident light through a tunable filter. When the degree of polarization DOP changes, subtract half of the bandwidth d/2 from the center wavelength λ1 to obtain the minimum wavelength without aliasing in this band λ2;

A3, increase the center wavelength of the incident light and adjust the bandwidth d through the tunable filter, when the polarization degree DOP changes, add the center wavelength λ1 to half of the bandwidth d/2 to obtain the maximum wavelength λ3 without aliasing in this band ;

A4, calculate the overall parameter t1 of the polarization imaging system by obtaining the minimum wavelength λ2 and the modulated position a1 when this band does not have aliasing;

A5: Calculate the overall parameter t2 of the polarization imaging system through the obtained minimum wavelength λ3 and a1+1 when no aliasing occurs in this band, and compare and detect the two coefficients.

Specifically, in the step 2, when a linear polarizer is added in front of the device, the polarization degree DOP=1 obtained by demodulation and calculation when the incident light changes to the linearly polarized light of the sound without aliasing. Aliasing occurs.

Specifically, the overall parameter t1 of the calculated polarization imaging system can be obtained through a theoretical formula: t1=ΔDN/f=a1×λ2;

Specifically, the overall parameter t2 of the calculated polarization imaging system can be obtained through a theoretical formula: t2=ΔDN/f=(a1+1)×λ3;

Further, the comparison and detection of the two coefficients can detect whether the obtained overall parameter result of the imaging system is correct, which is a self-detection method.

The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to specific embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced. Without departing from the spirit and scope of the technical solutions of the present invention, all of them should be included in the scope of the claims of the present invention. The technologies, shapes and structural parts that are not described in detail in the present invention are all known technologies.

Claims (3)

1. a method for tunable bandwidth incident light correction spatial modulation polarization imaging parameter, is characterized in that, the concrete process of this method comprises the steps: A1, find the position a1 where the Stokes vector S1 of the incident light with a narrow bandwidth of central wavelength λ1 is modulated in the frequency domain; A2, adjust the bandwidth d and reduce the center wavelength λ1 of the incident light through a tunable filter. When the degree of polarization DOP changes, subtract half of the bandwidth d/2 from the center wavelength λ1 to obtain the minimum wavelength without aliasing in this band λ2; A3, increase the center wavelength of the incident light and adjust the bandwidth d through the tunable filter, when the polarization degree DOP changes, add the center wavelength λ1 to half of the bandwidth d/2 to obtain the maximum wavelength λ3 without aliasing in this band ; A4, calculate the overall parameter t1 of the polarization imaging system by obtaining the minimum wavelength λ2 and the modulated position a1 when this band does not have aliasing; A5: Calculate the overall parameter t2 of the polarization imaging system through the obtained minimum wavelength λ3 and a1+1 when no aliasing occurs in this band, and compare and detect the two coefficients. 2. the method for a kind of tunable bandwidth incident light correction spatial modulation polarization imaging parameter according to claim 1, is characterized in that: adjust the center wavelength and bandwidth of incident light by tunable filter, obtain when polarization degree changes. The corresponding wavelength, and then the overall parameters of the polarization imaging system are calculated through the relationship between the wavelength and the polarization imaging system. 3. The method for correcting spatially modulated polarization imaging parameters of incident light with a tunable bandwidth according to claim 1, characterized in that: obtaining a more accurate wavelength by trying different tuning sequences in a changing direction, and calculating a more accurate wavelength. Overall parameters of the polarization imaging system. At the same time, the overall parameters of the light of the other polarization imaging system are calculated in the other direction of change, and the comparison of the two can be used to check the correctness of the results.

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