阅读说明：本技术 一种用于空间调制全偏振成像系统的带宽设计方法 (Bandwidth design method for spatial modulation full-polarization imaging system ) 是由 叶松 郝平波 张文涛 张紫杨 陈妮艳 李树 汪杰君 王方原 王新强 甘永莹 于 2020-04-30 设计创作，主要内容包括：本发明公开了一种用于空间调制全偏振成像系统的带宽设计方法,其特征在于,包括如下步骤：1)通过空间调制全偏振成像系统数学模型推导干涉光强与Stokes参量之间的关系式；2)确定S<Sub>1</Sub>、S<Sub>23</Sub>通道的主瓣信息；3)获取空间调制全偏振成像系统的极限带宽；4)设计空间调制全偏振成像系统的带宽。这种方法可作为系统带宽设计依据,进而选择满足带宽要求的滤光器件,在保证解调精度的前提下可获得最大的光通量、可提高探测系统的灵敏度及信噪比。(The invention discloses a bandwidth design method for a space modulation full-polarization imaging system, which is characterized by comprising the following steps of: 1) deducing a relational expression between interference light intensity and Stokes parameters through a space modulation full-polarization imaging system mathematical model; 2) determination of S 1 、S 23 Main lobe information of the channel; 3) acquiring the limit bandwidth of a spatial modulation full-polarization imaging system; 4) the bandwidth of the spatially modulated full polarization imaging system is designed. The method can be used as a design basis of system bandwidth, and further selects a filter device meeting the bandwidth requirement, so that the maximum luminous flux can be obtained on the premise of ensuring demodulation precision, and the sensitivity and the signal-to-noise ratio of a detection system can be improved.)

1. A bandwidth design method for a spatial modulation full-polarization imaging system is characterized by comprising the following steps:

1) deducing a relation between interference light intensity and Stokes parameters through a space modulation full-polarization imaging system mathematical model: the spatial modulation full-polarization imaging system structure comprises a light filter, a first Savart polarizer, a half-wave plate, a second Savart polarizer, an analyzer, an imaging lens and a CCD detector which are sequentially arranged, incident light passes through the light filter and is incident to the first Savart polarizer, and sequentially passes through the half-wave plate, the second Savart polarizer and the analyzer to realize double refraction light splitting, vibration direction rotation and double refraction light splitting again to form four light beams, the four light beams are converged on a focal plane of the CCD detector through the imaging lens to generate interference, a polarization interference intensity image is recorded through the CCD detector, a main optical axis is set as an x axis, an xy coordinate system is constructed, and according to a wave optics theory, the relationship between interference light intensity and Stokes parameters S0-S3 is deduced as follows:

where I is the output interference intensity, S₀-S₃The method comprises the steps of inputting Stokes parameters, wherein omega is a carrier frequency, f is a back focal length of an imaging lens, delta is a transverse shearing quantity introduced by a first Savart polarizer and a second Savart polarizer, lambda is a central wavelength of incident light, and x_i、y_iAs image plane coordinates, S₂₃Is S₂And S₃Combining complex vectors, wherein i is an imaginary number, cos () is a cosine function, pi is an arc value corresponding to a circumference ratio of 180 degrees, and arg () represents an argument;

2) determination of S₁、S₂₃Main lobe information of the channel: derivation of S using discrete Fourier transform₁、S₂₃Spectral function expression of channel to determine S₁、S₂₃Main lobe information of the channel, for a spatially modulated full polarization imaging system, over an integration range [ -L, L]And (3) internally performing two-dimensional discrete Fourier transform on the formula (1), wherein L is the imaging area on the focal plane to obtain a formula (3):

wherein u, v represent coordinates of the frequency domain;

3) obtaining the limit bandwidth of a spatial modulation full-polarization imaging system: when the peak value of a certain wavelength in the channel is superposed with the first-level zero point of the central wavelength, the peak value of the certain wavelength and the first-level zero point of the central wavelength are just positioned at the superposed boundary of the channel, the wavelength is defined as the limit wavelength of the effective spectral bandwidth corresponding to the central wavelength, the range between the limit wavelengths corresponding to the two first-level zero points is the limit bandwidth range, and for S, the peak value of the certain wavelength in the channel is superposed with the first-₁Channel, S₁Channel spectrum function expression F₁Is formula (4):

in the formula，F₁Denotes S₁A function expression corresponding to the frequency domain, where A is the amplitude of the signal and F () represents S₁The expression of the fourier transform of (a),

the first order zero of the center wavelength satisfies equation (5):

2πL(Ω₀-u)＝±π (5)，

obtaining S according to the formula (5)₁The corresponding limiting spectral bandwidth range is of formula (6):

can obtain S in the same way₂₃The corresponding limiting spectral bandwidth range is formula (7):

compare equation (6) with equation (7) becauseSo S₂₃The corresponding limit spectral bandwidth range is the limit bandwidth of the space modulation full-polarization imaging system;

4) designing the bandwidth of a spatial modulation full-polarization imaging system: and 3) taking the limit bandwidth obtained in the step 3) as a system bandwidth design basis, wherein the bandwidth cannot exceed the limit bandwidth obtained in the step 3) during system design.

2. The bandwidth design method for the spatially modulated full polarization imaging system according to claim 1, wherein the first Savart polarizer and the second Savart polarizer are both made of two Savart single plates with equal thickness, i.e. uniaxial birefringent crystals, and the optical axis direction of the second Savart polarizer is orthogonal to the optical axis direction of the first Savart polarizer.

Technical Field

The invention relates to the field of polarization imaging detection, in particular to a bandwidth design method for a space modulation full-polarization imaging system.

Background

In recent years, the polarization imaging technology is a new detection technology newly developed in the field of optical remote sensing in recent years, and is paid attention by researchers at home and abroad. As a new remote sensing detection technology, the polarization imaging technology can simultaneously acquire the intensity information and the polarization information of a target object, and the technology is widely applied to the application fields of space remote sensing, agriculture and forestry analysis, military reconnaissance, atmospheric detection, environmental monitoring and the like.

With the research and development of the polarization detection technology, the detection accuracy and real-time performance requirements for the polarization data are higher and higher. The traditional time-sharing polarization image detection method realizes time-sharing measurement through a rotating part, but due to a complex mechanical structure and an optical system, the problems of noise, pixel mismatching and the like can be caused, and the detection, real-time measurement and the like of a moving object have limitations. Until the beginning of the 21 st century, the spatial modulation polarization imaging technology has gradually become a research hotspot due to the advantages of high spatial resolution, capability of simultaneously obtaining a plurality of Stokes parameters, compactness, no moving device, imaging of dynamic targets and the like. In 2003, Oka et al, university of Arizona, USA, proposed a polarization imaging detector based on a birefringent wedge prism, which realizes simultaneous detection of different polarization parameters of the same target, and the system has the advantages of miniaturization, compactness and capability of using snapshot imaging; in 2006, Oka proposed a monochromatic light polarization imaging system based on the Savart polarizer type.

The spatial modulation full-polarization imaging system based on the Savart polarization modulator can adopt a focal plane array detector to simultaneously acquire full Stokes parameters of a target, but the system is only suitable for monochromatic light, for the polychromatic light, channel aliasing occurs in a frequency domain, the demodulation precision of Stokes parameters is reduced, and even demodulation cannot be performed, so that, the system has strict limitation on the bandwidth, realizes monochromatic light modulation by controlling the front narrow-band filter, the limitation of the system bandwidth reduces the sensitivity and the signal-to-noise ratio of the detection system, the spatial modulation full-polarization imaging system can effectively demodulate the Stokes parameters within the limit bandwidth range, the demodulation precision of the Stokes parameters is seriously reduced and even demodulation cannot be carried out within the limit bandwidth range, the effective bandwidth design method can ensure the demodulation precision of the spatial modulation full-polarization imaging system, and meanwhile, the sensitivity and the signal-to-noise ratio of the detection system are improved.

Disclosure of Invention

The present invention is directed to overcoming the disadvantages of the prior art and providing a bandwidth design method for a spatially modulated full-polarization imaging system. The method can be used as a design basis of system bandwidth, and further selects a filter device meeting the bandwidth requirement, so that the maximum luminous flux can be obtained on the premise of ensuring demodulation precision, and the sensitivity and the signal-to-noise ratio of a detection system can be improved.

The technical scheme for realizing the purpose of the invention is as follows:

a bandwidth design method for a spatial modulation full polarization imaging system comprises the following steps:

1) deducing a relation between interference light intensity and Stokes parameters through a space modulation full-polarization imaging system mathematical model: the spatial modulation full-polarization imaging system structure comprises an optical filter, a first Savart polarizer, a half-wave plate, a second Savart polarizer, an analyzer, an imaging lens and a CCD detector which are sequentially arranged, incident light passes through the optical filter and enters the first Savart polarizer, and passes through the half-wave plate, the second Savart polarizer and the analyzer in sequence, so that birefringent light splitting, vibration direction rotation and birefringent light splitting again are realized, and then the spatial modulation full-polarization imaging system structure is formedFour beams of light are converged on a focal plane of a CCD detector through an imaging lens to generate interference, a polarization interference intensity image is recorded through the CCD detector, a main optical axis is set as an x axis, an xy coordinate system is constructed, and interference light intensity and Stokes parameters S are deduced according to a wave optics theory₀-S₃The relationship of (1) is:

where I is the output interference intensity, S₀-S₃The method comprises the steps of inputting Stokes parameters, wherein omega is a carrier frequency, f is a back focal length of an imaging lens, delta is a transverse shearing quantity introduced by a first Savart polarizer and a second Savart polarizer, lambda is a central wavelength of incident light, and x_i、y_iAs image plane coordinates, S₂₃Is S₂And S₃Combining complex vectors, wherein i is an imaginary number, cos () is a cosine function, pi is an arc value corresponding to a circumference ratio of 180 degrees, and arg () represents an argument;

2) determination of S₁、S₂₃Main lobe information of the channel: derivation of S using discrete Fourier transform₁、S₂₃Spectral function expression of channel to determine S₁、S₂₃Main lobe information of the channel, for a spatially modulated full polarization imaging system, over an integration range [ -L, L]And (3) internally performing two-dimensional discrete Fourier transform on the formula (1), wherein L is the imaging area on the focal plane to obtain a formula (3):

wherein u, v represent coordinates of the frequency domain;

3) obtaining the limit bandwidth of a spatial modulation full-polarization imaging system: in order to demodulate the parameter information of each Stokes completely, each channel must ensure the integrity of the main lobe information thereof, and the peak value of a certain wavelength in the channel can be known according to the Rayleigh criterionWhen the wavelength is superposed with the first-level zero point of the central wavelength, the two are just positioned at the superposed boundary of the channels, the wavelength is defined as the limit wavelength of the effective spectral bandwidth corresponding to the central wavelength, the range between the limit wavelengths corresponding to the two first-level zero points is the limit bandwidth range, and for S, the maximum bandwidth range is defined as the range between the limit wavelengths corresponding to the two first-level zero points₁Channel, S₁Channel spectrum function expression F₁Is formula (4):

in the formula, F₁Denotes S₁A function expression corresponding to the frequency domain, where A is the amplitude of the signal and F () represents S₁The expression of the fourier transform of (a),

the first order zero of the center wavelength satisfies equation (5):

2πL(Ω₀-u)＝±π (5)，

obtaining S according to the formula (5)₁The corresponding limiting spectral bandwidth range is of formula (6):

can obtain S in the same way₂₃The corresponding limiting spectral bandwidth range is formula (7):

compare equation (6) with equation (7) becauseSo S₂₃The corresponding limit spectral bandwidth range is the limit bandwidth of the space modulation full-polarization imaging system;

4) designing the bandwidth of a spatial modulation full-polarization imaging system: and 3) taking the limit bandwidth obtained in the step 3) as a system bandwidth design basis, wherein the bandwidth cannot exceed the limit bandwidth obtained in the step 3) during system design.

The first Savart polarizer and the second Savart polarizer are both composed of two Savart single plates with equal thickness, namely uniaxial birefringent crystals, and the optical axis direction of the second Savart polarizer is orthogonal to that of the first Savart polarizer.

According to the technical scheme, the spatial modulation full-polarization imaging system can effectively demodulate Stokes parameters within a limit bandwidth range, the limit bandwidth of the system is calculated to serve as a system bandwidth design basis, the filter device meeting the bandwidth requirement is selected, the maximum luminous flux is ensured as far as possible on the premise of ensuring demodulation precision, and a reference basis is provided for the overall design of the spatial modulation full-polarization imaging system.

The method can be used as a design basis of system bandwidth, and further selects a filter device meeting the bandwidth requirement, so that the maximum luminous flux can be obtained on the premise of ensuring demodulation precision, and the sensitivity and the signal-to-noise ratio of a detection system can be improved.

Drawings

FIG. 1 is a schematic flow chart of a design method in an embodiment;

FIG. 2 is a schematic structural diagram of a spatially modulated full-polarization imaging system according to an embodiment;

FIG. 3 shows S of the input test in the example₀-S₃A parametric image;

fig. 4 is a diagram illustrating demodulation results of different bandwidths in the embodiment.

Detailed Description

The invention will be further elucidated with reference to the drawings and examples, without however being limited thereto.