CN111982287B - Method for correcting spatial modulation polarization imaging parameters by incident light with tunable bandwidth - Google Patents
Method for correcting spatial modulation polarization imaging parameters by incident light with tunable bandwidth Download PDFInfo
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Abstract
The invention provides a method for correcting space modulation polarization imaging parameters based on tunable bandwidth incident light. The process comprises the following steps: a1, finding the position a1 where the Stokes vector S1 of the center wavelength λ 1 narrow bandwidth incident light is modulated in the frequency domain; a2, adjusting the bandwidth d and reducing the central wavelength lambda 1 of the incident light through a tunable filter, and when the degree of polarization DOP changes, subtracting half d/2 of the bandwidth from the central wavelength lambda 1 to obtain the minimum wavelength lambda 2 when the band is not subjected to aliasing; a3, increasing the central wavelength and the adjusting bandwidth d of the incident light through a tunable filter, and obtaining the maximum wavelength lambda 3 when the band is not aliased from the central wavelength lambda 1 plus half d/2 of the bandwidth when the degree of polarization DOP is changed; a4, calculating the coefficient t1 of the whole polarization imaging system according to the formula t1 ═ Δ DN/f ═ a1 × λ 2 by the obtained minimum wavelength λ 2 when aliasing does not occur in the wavelength band and the modulated position a 1; a5 calculates a parameter t2 of the entire polarization imaging system from the obtained maximum wavelength λ 3 and a1+1 when aliasing does not occur in this wavelength band according to the formula t2 ═ Δ DN/f ═ λ 3 × (a1+1), and compares and detects two coefficients t1 and t 2. The invention can be used for measuring and correcting parameters of broadband space modulation polarization imaging equipment, and can be widely used in the fields of broadband polarization remote sensing imaging and the like.
Description
(I) technical field
The invention relates to a method for correcting spatial modulation polarization imaging parameters by tunable bandwidth incident light, which can be used for measuring and correcting parameters of broadband spatial modulation polarization imaging equipment and belongs to the field of polarization remote sensing imaging.
(II) background of the invention
The polarization is one of the important characteristics of light, the corresponding properties of targets can be reflected by the polarization characteristics, and different targets have respective unique polarization characteristics, so that the targets can be detected and identified by imaging of the polarized light, the method has strong applicability in the aspect of optical remote sensing, and plays a role in environmental monitoring, hidden target identification and ophthalmic disease diagnosis. Polarization represents the transverse wave characteristic of a light wave, and the light wave can be divided into polarized light and unpolarized light according to the polarization state of the light wave. The polarization state of the light wave can be changed through reflection and refraction, and the polarization is used for representing the physical basic properties of an object. The inherent polarization characteristics of light waves change with the physical properties of matter during their transmission, but they cannot be observed. With the rapid development of the polarization image detection technology, the polarization imaging detection becomes a very meaningful study in emerging directions of polarization information visualization, measurement information dimension expansion, simultaneous detection and the like. In application, the polarization state of light is represented by a Stokes vector method (S0, S1, S2, S3), and the present invention analyzes the position of the Stokes vector S1 which is modulated and then moved in the frequency domain.
The spatial modulation polarization imaging system is based on a Savart mirror formed by 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 set, is divided into four coherent light beams by the polarizer set to form an interference image, and the interference image is demodulated to obtain the polarization information of the target. In the frequency domain, the DOP does not change when the DOP moves within one pixel along with the wavelength change, when the wavelength continues to change, the signal which should be in the pixel 0 enters the pixel 1, and the DOP changes accordingly, and the wavelength when the DOP does not change is the maximum wavelength of the band, as shown in fig. 2. Since the whole polarization imaging system is composed of individual optical elements, it is necessary to measure and calibrate their respective parameters, and to measure and calibrate the parameters of the whole polarization imaging system.
The invention discloses a method for correcting space modulation polarization imaging parameters by incident light with tunable bandwidth, which is to adjust the central wavelength and bandwidth of the incident light through a tunable optical filter to obtain the wavelength corresponding to the edge when the degree of polarization DOP changes. The whole parameters of the polarization imaging system are reversely deduced through the actually measured wavelength, the accuracy of the parameters calculated by the result is higher, the calibration of the parameters of the polarization imaging system is completed, and meanwhile, the reference can be provided for the subsequent measurement and calibration of each optical element of the polarization imaging system.
Disclosure of the invention
The invention aims to provide a method for correcting space modulation polarization imaging parameters by incident light with tunable bandwidth, which is convenient to detect and accurate in calibration parameters.
The purpose of the invention is realized by the following technical means:
a method for correcting spatially modulated polarization imaging parameters based on tunable bandwidth incident light, comprising:
a1, finding the position a1 where the Stokes vector S1 of the center wavelength λ 1 narrow bandwidth incident light is modulated in the frequency domain;
a2, adjusting bandwidth d and reducing central wavelength λ 1 of incident light through a tunable filter, and when the degree of polarization DOP changes, subtracting half d/2 of the bandwidth from the central wavelength λ 1 to obtain the minimum wavelength λ 2 when the band is not subjected to aliasing;
a3, increasing the central wavelength and the adjusting bandwidth d of the incident light through a tunable filter, and obtaining the maximum wavelength lambda 3 when the band is not aliased from the central wavelength lambda 1 plus half d/2 of the bandwidth when the degree of polarization DOP is changed;
a4, calculating the parameter t1 of the whole polarization imaging system according to the formula t1 ═ Δ DN/f ═ a1 × λ 2 by the obtained minimum wavelength λ 2 when aliasing does not occur in the waveband and the obtained modulated position a 1;
a5 calculates a parameter t2 of the entire polarization imaging system from the obtained maximum wavelength λ 3 and a1+1 when aliasing does not occur in this wavelength band according to the formula t2 ═ Δ DN/f ═ λ 3 × (a1+1), and compares and detects two coefficients t1 and t 2.
Further, the tuned incident light in the step a1 is divided into four coherent light beams after entering the polarizer set, an interferogram containing all polarization information is formed in the camera, and the position a1 of the Stokes vector S1 of the target moving in the frequency domain can be obtained by transforming the interferogram.
Further, the wavelength of the incident light and the overall parameters of the polarization imaging system in the steps a4 and a5 satisfy a certain relationship, and the formula is as follows:
wherein Δ represents the transverse shearing amount of a single birefringent crystal, D represents the size of an imaging camera pixel, N represents the number of rows or columns of the imaging camera, f represents the focal length of the imaging camera, a represents the position of a signal moving in a frequency domain after being modulated, and λ represents the wavelength of incident light, so that the overall parameters of two polarization imaging systems are obtained:
the parameter formula of the polarization imaging system is determined to be the same with the relevant parameters, so that the two obtained parameters should be the same and can be used for verifying whether the method is correct.
The invention has the beneficial effects that: the invention is a method for correcting space modulation polarization imaging parameters based on tunable bandwidth incident light, compared with other methods, the precision of measurement calibration is more accurate, the application is more flexible, and the whole imaging system equipment can be measured and corrected without disassembling the system equipment for respective measurement calibration. And meanwhile, the device also can provide reference for subsequent measurement and calibration of each optical element of the polarization imaging system, and particularly can provide an integral standard when the influence between the optical elements needs to be considered.
Description of the drawings
FIG. 1 is a schematic diagram of a structure for a tunable bandwidth-based incident light correction spatially modulated polarization imaging system. The device consists of a tunable optical filter 1, a polarizer group 2 and an imaging camera 3.
Figure 2 is a distribution diagram of the components of decomposition of wide bandwidth incident light in the frequency domain. The method mainly shows that the 0-level component and the 1-level component of incident light with different wavelengths in a frequency domain are respectively distributed in a 0 pixel and a1 pixel, and when the same-level components of the incident light with different wavelengths are in the same pixel range, the demodulated polarization degree cannot be changed.
FIG. 3 is a flow chart of a method for incident light correction spatially modulated polarization imaging parameters with tunable bandwidth according to the present invention.
(V) detailed description of the preferred embodiments
The invention is further illustrated below with reference to specific examples.
As shown in fig. 3, a method for correcting spatially modulated polarization imaging parameters by tunable bandwidth incident light according to the present invention includes:
a1, finding the position a1 where the Stokes vector S1 of the center wavelength λ 1 narrow bandwidth incident light is modulated in the frequency domain;
a2, adjusting the bandwidth d and reducing the central wavelength lambda 1 of the incident light through a tunable filter, and when the degree of polarization DOP changes, subtracting half d/2 of the bandwidth from the central wavelength lambda 1 to obtain the minimum wavelength lambda 2 when the band is not subjected to aliasing;
a3, increasing the central wavelength and the adjusting bandwidth d of the incident light through a tunable filter, and obtaining the maximum wavelength lambda 3 when the band is not aliased from the central wavelength lambda 1 plus half d/2 of the bandwidth when the degree of polarization DOP is changed;
a4, calculating the parameter t1 of the whole polarization imaging system according to the formula t1 ═ Δ DN/f ═ a1 × λ 2 by the obtained minimum wavelength λ 2 and the obtained modulated position a1 when the band is not aliased;
a5 calculates a parameter t2 of the entire polarization imaging system from the obtained maximum wavelength λ 3 and a1+1 when aliasing does not occur in this wavelength band according to the formula t2 ═ Δ DN/f ═ λ 3 × (a1+1), and compares and detects two coefficients t1 and t 2.
Specifically, in the step 2, when a linear polarizer is added in front of the device, the polarization degree DOP obtained through demodulation calculation is 1 when the incident light changes into linearly polarized light and no aliasing occurs, and when the DOP changes, the aliasing phenomenon occurs in the frequency domain.
Specifically, the parameter t1 of the whole calculation polarization imaging system can be obtained by a theoretical formula, i.e., t1 ═ Δ DN/f ═ a1 × λ 2;
specifically, the parameter t2 of the whole calculation polarization imaging system can be obtained by a theoretical formula, that is, t2 ═ Δ DN/f ═ a1+1 × λ 3;
further, the two coefficients are compared and detected to detect whether the obtained parameter result of the whole imaging system is correct, so that the method is a self-detection method.
Although the present invention has been described in detail with reference to specific embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the invention as defined in the appended claims. The techniques, shapes, and structural parts not described in detail in the present invention are all known techniques.
Claims (3)
1. A method for correcting spatial modulation polarization imaging parameters based on tunable bandwidth incident light of spatial modulation polarization imaging is characterized in that the specific process of the method comprises the following steps:
a1, finding the position a1 where the Stokes vector S1 of the center wavelength λ 1 narrow bandwidth incident light is modulated in the frequency domain;
a2, adjusting the bandwidth d and reducing the central wavelength lambda 1 of the incident light through a tunable filter, and when the degree of polarization DOP changes, subtracting half d/2 of the bandwidth from the central wavelength lambda 1 to obtain the minimum wavelength lambda 2 when the band is not subjected to aliasing;
a3, increasing the central wavelength and the adjusting bandwidth d of the incident light through a tunable filter, and obtaining the maximum wavelength lambda 3 when the band is not aliased from the central wavelength lambda 1 plus half d/2 of the bandwidth when the degree of polarization DOP is changed;
a4, calculating the parameter t1 of the whole polarization imaging system according to the formula t1 ═ Δ DN/f ═ a1 × λ 2 by the obtained minimum wavelength λ 2 when aliasing does not occur in the waveband and the obtained modulated position a 1;
a5 calculates a parameter t2 of the entire polarization imaging system from the obtained maximum wavelength λ 3 and a1+1 when aliasing does not occur in this wavelength band according to the formula t2 ═ Δ DN/f ═ λ 3 × (a1+1), and compares and detects two coefficients t1 and t 2.
2. The method of claim 1 for correcting spatially modulated polarization imaging parameters based on tunable bandwidth incident light for spatially modulated polarization imaging, comprising: the central wavelength and the bandwidth of incident light are adjusted through the tunable optical filter, the corresponding wavelength when the polarization degree changes is obtained, 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 of claim 1 for correcting spatially modulated polarization imaging parameters based on tunable bandwidth incident light for spatially modulated polarization imaging, comprising: and (3) obtaining more accurate wavelength by trying different tuning sequences in one changing direction, calculating the overall parameters of a more accurate polarization imaging system, simultaneously calculating the overall parameters of light of another polarization imaging system in the other changing direction, and comparing the two parameters to detect the correctness of the result.
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| CN109115339A (en) * | 2018-05-16 | 2019-01-01 | 中北大学 | One kind being based on AOTF and intensity modulated high speed high spectrum full polarization imaging device and method |
| CN111537065A (en) * | 2020-04-30 | 2020-08-14 | 桂林电子科技大学 | Bandwidth design method for spatial modulation full-polarization imaging system |
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| WO2003016844A1 (en) * | 2001-08-14 | 2003-02-27 | Terapulse, Inc. | Apparatus and methods for polarization measurements |
| CN103698015B (en) * | 2014-01-06 | 2015-10-14 | 清华大学深圳研究生院 | Polarization Detection instrument and detection method |
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| CN109115339A (en) * | 2018-05-16 | 2019-01-01 | 中北大学 | One kind being based on AOTF and intensity modulated high speed high spectrum full polarization imaging device and method |
| CN111537065A (en) * | 2020-04-30 | 2020-08-14 | 桂林电子科技大学 | Bandwidth design method for spatial modulation full-polarization imaging system |
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| 通道调制型偏振成像系统的波段宽度限制判据;张宁等;《物理学报》;20160308;第074210-1页至第074210-07页 * |
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