Stokes vector measurement system and method based on model optimization

Abstract

The present invention discloses a Stokes vector measurement system and method based on model optimization, relating to the technical field of optical measuring instruments. The system comprises a first photoelastic modulator, a second photoelastic modulator, an analyzer, a light intensity collector, and a computer. The present invention treats system parameters such as the optical element's principal optical axis deflection angle, the incident angle of the vector light beam, the photoelastic modulator's modulation phase delay peak value, and the static phase delay as optimizable parameters. The Stokes vector is obtained by fitting actual measurement data with model simulation data. Compared with existing measurement systems, the present invention fully considers the impact of errors in the system parameters themselves, correcting these errors through model optimization, thereby improving measurement accuracy.

Description

Technical Field

[0001] The present invention relates to the technical field of optical measuring instruments, and in particular to a Stokes vector measurement system and method based on model optimization. Background Art

[0002] The photoelastic modulator is an electro-optically coupled system that uses the inverse piezoelectric effect and the photoelastic effect to achieve electro-optical modulation. It mainly consists of two parts: an optical component and an excitation circuit. It can be widely used in the field of high-speed elliptical polarization optical measurement. Under the action of the excitation circuit, the optical component can produce a periodic birefringence phase delay, thereby periodically phase modulating the light passing through. By measuring the Stokes vector, the polarization state of different light beams can be determined, and it can be widely used in the study of changes in the polarization characteristics of vector light beams. Using a photoelastic modulator to measure the polarization modulation of a vector light beam to obtain the Stokes vector is a common method that can meet the measurement requirements of most polarized light. This method has a series of advantages such as no mechanical vibration influence, a large acceptable incident angle, a high modulation frequency, and a fast measurement speed. It has played a positive role in promoting the fields of optics, biophysics, physical chemistry, and materials research.

[0003] Existing methods for measuring polarization modulation of vector light beams using photoelastic modulators (PEMs) are primarily based on difference frequency modulation and frequency component extraction. The PEMs utilize frequency superposition of two PEMs operating at different frequencies to modulate the vector light beam, generating a high-frequency modulation component carrying the measured object. The appropriate frequency component is then extracted and processed using a lock-in amplifier to obtain the Stokes vector parameter. These methods treat various system parameters, such as the principal optical axis deflection angle of the optical element, the incident angle of the vector light beam, and the peak and static phase delay of the PEM, as known constants. However, these system parameters can deviate due to installation errors, optical path alignment errors, and changes in the external environment, including temperature and pressure. Even relatively small deviations can significantly impact the final Stokes vector measurement result, reducing measurement accuracy. Summary of the Invention

[0004] The embodiments of the present invention provide a Stokes vector measurement system and method based on model optimization, thereby solving the technical problem of low precision of Stokes vector measurement results in the prior art and improving the measurement accuracy of the Stokes vector.

[0005] On the one hand, the present invention provides the following technical solutions through an embodiment of the present invention:

[0006] A Stokes vector measurement system based on model optimization includes a first photoelastic modulator, a second photoelastic modulator, an analyzer, a light intensity collector, and a computer;

[0007] The first photoelastic modulator, the second photoelastic modulator, the analyzer and the light intensity collector are sequentially arranged on the incident optical path of the vector light beam to be measured; the light intensity collector is connected to the computer;

[0008] The computer is used to collect the actual light intensity time-varying signal output by the light intensity collector, obtain the incident angle of the vector light beam to be measured, obtain the main optical axis deflection angles of the first photoelastic modulator, the second photoelastic modulator and the analyzer, and obtain the peak value and static phase delay of the modulation phase delay of the first photoelastic modulator and the second photoelastic modulator;

[0009] The computer is also used to establish a light intensity time-varying signal simulation model with the Stokes vector simulation, the incident angle simulation, the main optical axis deflection angle simulation, the modulation phase delay peak simulation and the static phase delay simulation as inputs and the simulated Stokes vector as output;

[0010] The computer is also used to change the Stokes vector simulation quantity, and when changing the Stokes vector simulation quantity, change at least one of the incident angle simulation quantity, the main optical axis deflection angle simulation quantity, the modulation phase delay peak simulation quantity and the static phase delay simulation quantity, so as to optimize the fitting of the first component of the simulated Stokes vector and the actual light intensity time-varying signal, and output the Stokes vector simulation quantity so that the error between the actual light intensity time-varying signal and the first component meets the requirements.

[0011] Preferably, the Stokes vector measurement system based on model optimization further includes an incident light converging collimator, and the vector light beam to be measured reaches the first photoelastic modulator through the incident light converging collimator.

[0012] Preferably, the acquisition frequency of the actual light intensity time-varying signal is greater than twice the operating frequency of the first photoelastic modulator, and / or the acquisition frequency of the actual light intensity time-varying signal is greater than twice the operating frequency of the second photoelastic modulator.

[0013] On the other hand, the present invention also provides the following technical solutions:

[0014] A Stokes vector measurement method based on model optimization, comprising:

[0015] Setting the main optical axis deflection angles of the first photoelastic modulator, the second photoelastic modulator, and the analyzer, collecting the actual light intensity time-varying signal output by the light intensity collector, obtaining the incident angle of the vector light beam to be measured, and obtaining the peak value and static phase delay of the modulation phase delay of the first photoelastic modulator and the second photoelastic modulator;

[0016] Establish a light intensity time-varying signal simulation model with Stokes vector simulation, incident angle simulation, main optical axis deflection angle simulation, modulation phase delay peak simulation and static phase delay simulation as input and simulated Stokes vector as output;

[0017] Change the Stokes vector simulation quantity, and when changing the Stokes vector simulation quantity, change at least one of the incident angle simulation quantity, the main optical axis deflection angle simulation quantity, the modulation phase delay peak simulation quantity and the static phase delay simulation quantity, so as to optimize the fitting of the first component of the simulated Stokes vector and the actual light intensity time-varying signal, and output the Stokes vector simulation quantity so that the error between the actual light intensity time-varying signal and the first component meets the requirements.

[0018] Preferably, the light intensity time-varying signal simulation model is:

[0019] S out =M A ·R(A)·R(-M2)·M pem2 ·R(M2)·R(-M1)·M pem1 ·R(M1)·D(α)·S in ;

[0020] in:

[0021]

[0022] δ i =δ i (t) = Θ i ·sin(2πF i t)+δ Si , (i=1,2);

[0023] S out is the simulated Stokes vector; M1, M2, and A are the simulated values of the main optical axis deflection angles of the first photoelastic modulator, the second photoelastic modulator, and the analyzer, respectively; M pem1 、M pem2 、M A are the Mueller matrices of the first photoelastic modulator, the second photoelastic modulator, and the analyzer respectively; R(θ) represents the rotation transformation matrix with a rotation angle of θ, θ = A, -M2, M2, -M1, or M1; when i = 1, θ i , δ Si 、F i are respectively the peak simulation value of the modulation phase delay, the static phase delay simulation value, and the operating frequency of the first photoelastic modulator; when i=2, Θ i , δ Si 、F iare respectively the simulated value of the modulation phase delay peak value, the simulated value of the static phase delay value, and the operating frequency of the second photoelastic modulator; t is time; α is the simulated value of the incident angle, and D(α) is the correction matrix related to α; S in is the Stokes vector simulation quantity.

[0024] Preferably, in the light intensity time-varying signal simulation model:

[0025]

[0026] Preferably, in the light intensity time-varying signal simulation model:

[0027]

[0028] Preferably, the actual light intensity time-varying signal and the first component are optimized and fitted using the least squares method.

[0029] Preferably, the Stokes vector simulation amount is changed, and when changing the Stokes vector simulation amount, at least one of the incident angle simulation amount, the main optical axis deflection angle simulation amount, the modulation phase delay peak simulation amount, and the static phase delay simulation amount is changed to optimize the fitting of the first component of the simulated Stokes vector and the actual light intensity time-varying signal, and output the Stokes vector simulation amount so that the error between the actual light intensity time-varying signal and the first component meets the requirement, including:

[0030] Given initial values of the Stokes vector simulation quantity, the incident angle simulation quantity, the main optical axis deflection angle simulation quantity, the modulation phase delay peak simulation quantity, and the static phase delay simulation quantity, the initial values are substituted into the light intensity time-varying signal simulation model to calculate the simulated Stokes vector, and the first component of the simulated Stokes vector is extracted as the simulated light intensity time-varying signal;

[0031] If the error between the simulated light intensity time-varying signal and the actual light intensity time-varying signal is less than a preset error threshold, outputting the initial value of the Stokes vector simulation quantity;

[0032] If the error between the simulated light intensity time-varying signal and the actual light intensity time-varying signal is not less than a preset error threshold, the Stokes vector simulation quantity is corrected, and at the same time, at least one of the incident angle simulation quantity, the main optical axis deflection angle simulation quantity, the modulation phase delay peak simulation quantity and the static phase delay simulation quantity is corrected, until the error between the simulated light intensity time-varying signal and the actual light intensity time-varying signal is less than the preset error threshold, and the Stokes vector simulation quantity at this time is output.

[0033] One or more technical solutions provided in the embodiments of the present invention have at least the following technical effects or advantages:

[0034] System parameters such as the deflection angle of the main optical axis of the optical element, the incident angle of the vector light beam, the peak value of the modulation phase delay of the photoelastic modulator and the static phase delay are all treated as optimizable parameters, and the actual measurement data and model simulation data are fitted to obtain the Stokes vector. Compared with the existing measurement system, the present invention fully considers the influence of the errors of the system parameters themselves, and these errors can be corrected through model optimization, thereby improving the measurement accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following is a brief introduction to the drawings required for use in the description of the embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0036] Figure 1 A structural block diagram of a Stokes vector measurement system based on model optimization according to the present invention;

[0037] Figure 2 Another structural block diagram of the Stokes vector measurement system based on model optimization of the present invention;

[0038] Figure 3 This is a flow chart of the Stokes vector measurement method based on model optimization of the present invention. DETAILED DESCRIPTION

[0039] The embodiments of the present invention solve the technical problem of low precision of Stokes vector measurement results in the prior art by providing a Stokes vector measurement system and method based on model optimization.

[0040] The technical solution of the embodiment of the present invention is to solve the above technical problems, and the overall idea is as follows:

[0041] A Stokes vector measurement system based on model optimization, such as Figure 1 As shown, it includes a first photoelastic modulator, a second photoelastic modulator, an analyzer, a light intensity collector and a computer;

[0042] The first photoelastic modulator, the second photoelastic modulator, the analyzer and the light intensity collector are sequentially arranged on the incident optical path of the vector light beam to be measured; the light intensity collector is used to collect the actual light intensity time-varying signal after modulation and upload it to the computer;

[0043] The computer is used to collect the actual light intensity time-varying signal output by the light intensity collector, obtain the incident angle of the vector light beam to be measured, obtain the main optical axis deflection angles of the first photoelastic modulator, the second photoelastic modulator and the analyzer, and obtain the peak value and static phase delay of the modulation phase of the first photoelastic modulator and the second photoelastic modulator;

[0044] The computer is also used to establish a light intensity time-varying signal simulation model with Stokes vector simulation, incident angle simulation, main optical axis deflection angle simulation, modulation phase delay peak simulation and static phase delay simulation as inputs and simulated Stokes vector as output;

[0045] The computer is also used to change the Stokes vector simulation quantity, and when changing the Stokes vector simulation quantity, change at least one of the incident angle simulation quantity, the main optical axis deflection angle simulation quantity, the modulation phase delay peak simulation quantity and the static phase delay simulation quantity, so as to optimize the fitting of the first component of the simulated Stokes vector and the actual light intensity time-varying signal, and output the Stokes vector simulation quantity so that the error between the actual light intensity time-varying signal and the first component meets the requirements.

[0046] In order to better understand the above technical solution, the above technical solution will be described in detail below with reference to the accompanying drawings and specific implementation methods.

[0047] First, the term "and / or" as used herein simply describes a relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can represent: A alone, A and B together, or B alone. Furthermore, the character " / " in this document generally indicates an "or" relationship between the associated objects.

[0048] In this embodiment, if the incident direction of the vector light beam to be measured is absolutely parallel to the optical axis of the rear optical element, there will be no error in the incident angle caused by the installation of the optical element, and the vector light beam to be measured does not need to be collimated. However, when the optical element is actually installed, it is not possible to ensure that the incident direction of the vector light beam to be measured is absolutely parallel to the optical axis of the optical element. The error in the incident angle caused by the installation of the optical element will reduce the measurement accuracy of the Stokes vector. For this reason, Figure 2 As shown, the model-optimized Stokes vector measurement system of this embodiment preferably further includes an incident light converging collimator, through which the vector beam to be measured reaches the first photoelastic modulator. The incident light converging collimator can adjust the vector beam to be measured to be parallel to the optical axis of the rear optical element, eliminating the error in the incident angle caused by the installation of the optical element, thereby improving the measurement accuracy of the Stokes vector.

[0049] The Stokes vector is a four-dimensional vector used to represent any polarization state including the degree of polarization.

[0050] In this embodiment, the first photoelastic modulator and the second photoelastic modulator are both photoelastic modulators (PEMs), which usually use a piezoelectric material (such as piezoelectric ceramics) driven by voltage to apply different mechanical forces on an isotropic optical material (such as fused quartz), thereby changing the birefringence properties of the optical material to modulate the phase difference between o-light and e-light passing through the photoelastic modulator.

[0051] In this embodiment, the first and second photoelastic modulators have the same operating frequency. The computer acquires the actual time-varying light intensity signal at a frequency greater than twice the operating frequency of the first photoelastic modulator, and / or the computer acquires the actual time-varying light intensity signal at a frequency greater than twice the operating frequency of the second photoelastic modulator. According to the sampling theorem, a frequency greater than twice the operating frequency will prevent distortion of the acquired actual time-varying light intensity signal.

[0052] In this embodiment, the established light intensity time-varying signal simulation model is:

[0053] S out =M A ·R(A)·R(-M2)·M pem2 ·R(M2)·R(-M1)·M pem1 ·R(M1)·D(α)·S in ;

[0054] in:

[0055]

[0056] δ i =δ i (t) = Θ i ·sin(2πF i t)+δ Si , (i=1,2);

[0057] S out is the simulated Stokes vector; M1, M2, and A are the simulated values of the main optical axis deflection angles of the first photoelastic modulator, the second photoelastic modulator, and the analyzer respectively; M pem1 、M pem2 、M A are the Mueller matrices of the first photoelastic modulator, the second photoelastic modulator, and the analyzer respectively; R(θ) represents the rotation transformation matrix with a rotation angle of θ, θ=A, -M2, M2, -M1, or M1; when i=1, Θ i , δ Si 、F i are respectively the peak simulation value of the modulation phase delay, the static phase delay simulation value, and the operating frequency of the first photoelastic modulator; when i=2, Θi , δ Si 、F i are the peak simulation value of the modulation phase delay, the static phase delay simulation value, and the operating frequency of the second photoelastic modulator respectively; t is time; α is the incident angle simulation value, and D(α) is the correction matrix related to α; S in is the Stokes vector simulation quantity. Among them, the Mueller matrix is a fourth-order matrix used to represent the effect of optical elements (polarizers, etc.) on the transformation of polarization state of light.

[0058] In the simulation model of time-varying light intensity signal:

[0059]

[0060] Assuming that various system parameters such as the main optical axis deflection angle of the optical element, the incident angle of the vector beam, the peak value of the modulation phase delay of the photoelastic modulator and the static phase delay do not deviate, S out The first component of should be equal to the actual light intensity time-varying signal, α is equal to the incident angle of the vector light beam to be measured, M1, M2, and A are equal to the main optical axis deflection angles of the first photoelastic modulator, the second photoelastic modulator, and the analyzer respectively; when i = 1, Θ i , δ Si are equal to the peak value of the modulation phase delay and the static phase delay of the first photoelastic modulator respectively; when i=2, Θ i , δ Si are respectively equal to the peak value of the modulation phase delay and the static phase delay of the second photoelastic modulator; S in Equal to the Stokes vector of the vector beam to be measured.

[0061] Generally, after the Stokes vector measurement system is built, the system parameters of each optical element will be set. Assuming that the various system parameters such as the main optical axis deflection angle of the optical element, the incident angle of the vector light beam, the modulation phase delay peak value and the static phase delay of the photoelastic modulator do not deviate, the actual light intensity time-varying signal collected can be used as S out The first component of S is obtained by back-calculating out Substituted into the light intensity time-varying signal simulation model, the calculated S in It can be used as the Stokes vector of the vector beam to be measured, and the result can be considered accurate. However, in reality, various system parameters such as the deflection angle of the main optical axis of the optical element, the incident angle of the vector beam, the peak value of the modulation phase delay of the photoelastic modulator and the static phase delay will produce deviations. If the actual light intensity time-varying signal collected is used as S out The first component of S is obtained by back-calculating out Substituting into the light intensity time-varying signal simulation model, the calculated S inIt is not the true value of the Stokes vector of the vector beam to be measured, and the result is inaccurate.

[0062] In the computer of this embodiment, the least squares method is used to optimize the fitting of the actual light intensity time-varying signal and the first component. Specifically, the Stokes vector simulation amount is changed, and when changing the Stokes vector simulation amount, at least one of the incident angle simulation amount, the main optical axis deflection angle simulation amount, the modulation phase delay peak simulation amount, and the static phase delay simulation amount is changed to optimize the fitting of the first component of the simulated Stokes vector and the actual light intensity time-varying signal, and output the Stokes vector simulation amount so that the error between the actual light intensity time-varying signal and the first component meets the requirements, including:

[0063] Step 1: Given initial values of the Stokes vector simulation, the incident angle simulation, the main optical axis deflection angle simulation, the modulation phase delay peak simulation, and the static phase delay simulation, the initial values are substituted into the light intensity time-varying signal simulation model to calculate the simulated Stokes vector, and the first component of the simulated Stokes vector is extracted as the simulated light intensity time-varying signal;

[0064] Step 2: If the error between the simulated light intensity time-varying signal and the actual light intensity time-varying signal is less than a preset error threshold, outputting the initial value of the Stokes vector simulation quantity;

[0065] Step three: If the error between the simulated light intensity time-varying signal and the actual light intensity time-varying signal is not less than the preset error threshold, the Stokes vector simulation quantity is corrected, and at the same time, at least one of the incident angle simulation quantity, the main optical axis deflection angle simulation quantity, the modulation phase delay peak simulation quantity and the static phase delay simulation quantity is corrected until the error between the simulated light intensity time-varying signal and the actual light intensity time-varying signal is less than the preset error threshold, and the Stokes vector simulation quantity at this time is output.

[0066] In step 1, the system parameters of each optical element set after the Stokes vector measurement system is built can be used as the initial values of the incident angle simulation, the main optical axis deflection angle simulation, the modulation phase delay peak simulation and the static phase delay simulation. The true value of the Stokes vector of the vector beam to be measured can be estimated first, and the estimated value of the true value can be used as the Stokes vector simulation value S in If it is assumed that various system parameters such as the main optical axis deflection angle of the optical element, the incident angle of the vector beam, the peak value of the modulation phase delay of the photoelastic modulator and the static phase delay do not produce deviations, and the given Stokes vector simulation quantity S in The initial value of is exactly the true value of the Stokes vector of the vector beam to be measured, then the simulated light intensity time-varying signal calculated by the initial values of each parameter should be equal to the actual light intensity time-varying signal collected.

[0067] In step 2, the error between the simulated light intensity time-varying signal and the actual light intensity time-varying signal meets the requirements. This can be achieved by the simulated light intensity time-varying signal and the actual light intensity time-varying signal being equal, or by the error between the simulated light intensity time-varying signal and the actual light intensity time-varying signal being less than a preset error threshold. If the error between the simulated light intensity time-varying signal and the actual light intensity time-varying signal obtained through the initial value calculation meets the requirements, the output initial value of the Stokes vector simulation is used as the true value of the Stokes vector of the vector beam to be measured.

[0068] In step three, if the error between the simulated light intensity time-varying signal obtained by the initial value calculation and the actual light intensity time-varying signal does not meet the requirements, the Stokes vector simulation quantity will be continuously changed, and at the same time, at least one of the incident angle simulation quantity, the main optical axis deflection angle simulation quantity, the modulation phase delay peak simulation quantity and the static phase delay simulation quantity will be changed. That is, if it is believed that a system parameter will cause deviation, the simulation quantity of that system parameter will be changed. If it is believed that the main optical axis deflection angle of the optical element, the incident angle of the vector light beam, the modulation phase delay peak value and the static phase delay of the photoelastic modulator will all cause deviations, the incident angle simulation quantity, the main optical axis deflection angle simulation quantity, the modulation phase delay peak simulation quantity and the static phase delay simulation quantity will be changed until the error between the simulated light intensity time-varying signal and the actual light intensity time-varying signal meets the requirements. At this time, the Stokes vector simulation quantity that makes the error between the actual light intensity time-varying signal and the simulated light intensity time-varying signal meet the requirements is used as the true value of the Stokes vector of the vector light beam to be measured.

[0069] In this embodiment, system parameters such as the deflection angle of the main optical axis of the optical element, the incident angle of the vector light beam, the peak value of the modulation phase delay and the static phase delay of the photoelastic modulator are processed as optimizable parameters, and the actual measurement data and model simulation data are fitted to obtain the Stokes vector. Compared with the existing measurement system, this embodiment fully considers the influence of the errors of the system parameters themselves, and these errors can be corrected through model optimization, thereby improving the measurement accuracy.

[0070] Furthermore, the least squares method is used to fit actual measurement data with model simulation data, and measurement results are obtained through fitting analysis of the light intensity time-domain signal. Instead of using harmonic approximation, the time-domain modulation signal containing all harmonic components is analyzed, further improving measurement accuracy. Existing measurement systems, on the other hand, discard higher-order harmonic components and obtain measurement results using the amplitude of harmonic components through first- and second-order harmonic approximations, which reduces measurement accuracy.

[0071] In addition, existing measurement systems require a high-precision lock-in amplifier to extract the frequency components of the modulated signal, which increases the cost of the measurement solution. This embodiment does not involve frequency multiplication signal extraction, and the measurement system does not require a lock-in amplifier, reducing system hardware costs.

[0072] This embodiment also provides a Stokes vector measurement method based on model optimization, such as Figure 3 As shown, including:

[0073] Step S1, setting the main optical axis deflection angles of the first photoelastic modulator, the second photoelastic modulator, and the analyzer, collecting the actual light intensity time-varying signal output by the light intensity collector, obtaining the incident angle of the vector light beam to be measured, and obtaining the peak value and static phase delay of the modulation phase delay of the first photoelastic modulator and the second photoelastic modulator;

[0074] Step S2, establishing a light intensity time-varying signal simulation model with the Stokes vector simulation, the incident angle simulation, the main optical axis deflection angle simulation, the modulation phase delay peak simulation and the static phase delay simulation as inputs and the simulated Stokes vector as output;

[0075] Step S3, changing the Stokes vector simulation quantity, and changing at least one of the incident angle simulation quantity, the main optical axis deflection angle simulation quantity, the modulation phase delay peak simulation quantity and the static phase delay simulation quantity when changing the Stokes vector simulation quantity, so as to optimize the fitting of the first component of the simulated Stokes vector and the actual light intensity time-varying signal, and output the Stokes vector simulation quantity so that the error between the actual light intensity time-varying signal and the first component meets the requirements.

[0076] In this embodiment, the first and second photoelastic modulators have the same operating frequency, and the acquisition frequency of the actual light intensity time-varying signal is greater than twice the operating frequency of the first photoelastic modulator, and / or the acquisition frequency of the actual light intensity time-varying signal is greater than twice the operating frequency of the second photoelastic modulator. According to the sampling theorem, an acquisition frequency greater than twice the operating frequency will prevent distortion of the acquired actual light intensity time-varying signal.

[0077] In this embodiment, system parameters such as the deflection angle of the main optical axis of the optical element, the incident angle of the vector light beam, the peak value of the modulation phase delay of the photoelastic modulator, and the static phase delay are all processed as optimizable parameters, and the actual measurement data and model simulation data are fitted to obtain the Stokes vector. Compared with the existing measurement method, this embodiment fully considers the influence of the error of the system parameters themselves, and these errors can be corrected through model optimization, thereby improving the measurement accuracy. In addition, the existing measurement method requires the use of a high-precision phase-locked amplifier to extract the frequency component of the modulated signal, which increases the cost of the measurement solution. This method does not involve the extraction of frequency-doubled signals, and a phase-locked amplifier is not required in the measurement system, which reduces the system hardware cost.

[0078] Conventional measurement methods typically set up the Stokes vector measurement system by setting the system parameters for each optical component. This requires a complex calibration process before use, necessitating calibration of any system parameters that may have deviations. In step S1 of this embodiment, the principal optical axis deflection angle only needs to be set once for each of the first and second photoelastic modulators and the analyzer, eliminating the complex calibration process.

[0079] Among them, the simulation model of the light intensity time-varying signal is:

[0080] S out =M A ·R(A)·R(-M2)·M pem2 ·R(M2)·R(-M1)·M pem1 ·R(M1)·D(α)·S in ;

[0081] in:

[0082]

[0083] δ i =δ i (t) = Θ i ·sin(2πF i t)+δ Si , (i=1,2);

[0084] S out is the simulated Stokes vector; M1, M2, and A are the simulated values of the main optical axis deflection angles of the first photoelastic modulator, the second photoelastic modulator, and the analyzer respectively; M pem1 、M pem2 、M A are the Mueller matrices of the first photoelastic modulator, the second photoelastic modulator, and the analyzer respectively; R(θ) represents the rotation transformation matrix with a rotation angle of θ, θ=A, -M2, M2, -M1, or M1; when i=1, Θ i , δ Si 、F i are respectively the peak simulation value of the modulation phase delay, the static phase delay simulation value, and the operating frequency of the first photoelastic modulator; when i=2, Θ i , δ Si 、F i are the peak simulation value of the modulation phase delay, the static phase delay simulation value, and the operating frequency of the second photoelastic modulator respectively; t is time; α is the incident angle simulation value, and D(α) is the correction matrix related to α; S in is the Stokes vector simulation quantity. Among them, the Mueller matrix is a fourth-order matrix used to represent the effect of optical elements (polarizers, etc.) on the transformation of polarization state of light.

[0085] In the simulation model of time-varying light intensity signal:

[0086]

[0087] Assuming that various system parameters such as the main optical axis deflection angle of the optical element, the incident angle of the vector beam, the peak value of the modulation phase delay of the photoelastic modulator and the static phase delay do not deviate, S out The first component of should be equal to the actual light intensity time-varying signal, α is equal to the incident angle of the vector light beam to be measured, M1, M2, and A are equal to the main optical axis deflection angles of the first photoelastic modulator, the second photoelastic modulator, and the analyzer respectively; when i = 1, Θ i , δ Si are equal to the peak value of the modulation phase delay and the static phase delay of the first photoelastic modulator respectively; when i=2, Θ i , δ Si are respectively equal to the peak value of the modulation phase delay and the static phase delay of the second photoelastic modulator; S in Equal to the Stokes vector of the vector beam to be measured.

[0088] In step S3, the least square method is used to optimize the fitting of the actual light intensity time-varying signal and the first component. Specifically, step S3 includes:

[0089] Given initial values of the Stokes vector simulation quantity, the incident angle simulation quantity, the main optical axis deflection angle simulation quantity, the modulation phase delay peak simulation quantity, and the static phase delay simulation quantity, the initial values are substituted into the light intensity time-varying signal simulation model to calculate the simulated Stokes vector, and the first component of the simulated Stokes vector is extracted as the simulated light intensity time-varying signal;

[0090] If the error between the simulated light intensity time-varying signal and the actual light intensity time-varying signal is less than a preset error threshold, the initial value of the Stokes vector simulation quantity is output;

[0091] If the error between the simulated light intensity time-varying signal and the actual light intensity time-varying signal is not less than the preset error threshold, the Stokes vector simulation quantity is corrected, and at the same time, at least one of the incident angle simulation quantity, the main optical axis deflection angle simulation quantity, the modulation phase delay peak simulation quantity and the static phase delay simulation quantity is corrected until the error between the simulated light intensity time-varying signal and the actual light intensity time-varying signal is less than the preset error threshold, and the Stokes vector simulation quantity at this time is output.

[0092] This embodiment uses the least squares method to fit actual measurement data and model simulation data, obtaining measurement results through fitting analysis of the light intensity time-domain signal. Instead of employing harmonic approximation, it analyzes the time-domain modulation signal containing all harmonic components, further improving measurement accuracy. Existing measurement systems, on the other hand, discard higher-order harmonic components and instead use first- and second-order harmonic approximations to obtain measurement results using harmonic component amplitudes, which reduces measurement accuracy.

[0093] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0094] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A Stokes vector measurement system based on model optimization, characterized in that: The device comprises a first photoelastic modulator, a second photoelastic modulator, a polarizer, a light intensity collector and a computer; The first photoelastic modulator, the second photoelastic modulator, the analyzer and the light intensity collector are sequentially arranged on the incident optical path of the vector light beam to be measured; the light intensity collector is connected to the computer; The computer is used to collect the actual light intensity time-varying signal output by the light intensity collector, obtain the incident angle of the vector light beam to be measured, obtain the main optical axis deflection angles of the first photoelastic modulator, the second photoelastic modulator and the analyzer, and obtain the peak value and static phase delay of the modulation phase delay of the first photoelastic modulator and the second photoelastic modulator; The computer is also used to establish a light intensity time-varying signal simulation model with the Stokes vector simulation, the incident angle simulation, the main optical axis deflection angle simulation, the modulation phase delay peak simulation and the static phase delay simulation as inputs and the simulated Stokes vector as output; The computer is further configured to provide initial values of the Stokes vector simulation value, the incident angle simulation value, the main optical axis deflection angle simulation value, the modulation phase delay peak simulation value, and the static phase delay simulation value, substitute the initial values into the light intensity time-varying signal simulation model to calculate the simulated Stokes vector, and extract the first component of the simulated Stokes vector as the simulated light intensity time-varying signal; If the error between the simulated light intensity time-varying signal and the actual light intensity time-varying signal is less than a preset error threshold, outputting the initial value of the Stokes vector simulation quantity; If the error between the simulated light intensity time-varying signal and the actual light intensity time-varying signal is not less than a preset error threshold, the Stokes vector simulation value is corrected, and at the same time, at least one of the incident angle simulation value, the main optical axis deflection angle simulation value, the modulation phase delay peak simulation value, and the static phase delay simulation value is corrected until the error between the simulated light intensity time-varying signal and the actual light intensity time-varying signal is less than the preset error threshold, and the Stokes vector simulation value at this time is output; The light intensity time-varying signal simulation model is: ； in: ； ； ； is the simulated Stokes vector; 、 and A are respectively the simulated values of the principal optical axis deflection angles of the first photoelastic modulator, the second photoelastic modulator and the analyzer; 、 、 are Mueller matrices of the first photoelastic modulator, the second photoelastic modulator, and the analyzer respectively; The rotation angle is The rotation transformation matrix, =A、 、 、 or ; When i=1, 、 、 are respectively the simulated value of the peak value of the modulation phase delay, the simulated value of the static phase delay, and the operating frequency of the first photoelastic modulator; when i=2, 、 、 are respectively the simulated value of the peak value of the modulation phase delay, the simulated value of the static phase delay, and the operating frequency of the second photoelastic modulator; t is time; is the incident angle simulation quantity, For the relevant correction matrix; is the Stokes vector simulation quantity.

2. The Stokes vector measurement system based on model optimization according to claim 1, characterized in that: It also includes an incident light converging collimator, and the vector light beam to be measured reaches the first photoelastic modulator through the incident light converging collimator.

3. The Stokes vector measurement system based on model optimization according to claim 1, characterized in that: The acquisition frequency of the actual light intensity time-varying signal is greater than twice the operating frequency of the first photoelastic modulator, and / or the acquisition frequency of the actual light intensity time-varying signal is greater than twice the operating frequency of the second photoelastic modulator.

4. A Stokes vector measurement method based on model optimization, characterized in that: The Stokes vector measurement system based on model optimization applied to any one of claims 1 to 3 comprises: Setting the main optical axis deflection angles of the first photoelastic modulator, the second photoelastic modulator, and the analyzer, collecting the actual light intensity time-varying signal output by the light intensity collector, obtaining the incident angle of the vector light beam to be measured, and obtaining the peak value and static phase delay of the modulation phase delay of the first photoelastic modulator and the second photoelastic modulator; Establish a light intensity time-varying signal simulation model with Stokes vector simulation, incident angle simulation, main optical axis deflection angle simulation, modulation phase delay peak simulation and static phase delay simulation as input and simulated Stokes vector as output; Change the Stokes vector simulation quantity, and when changing the Stokes vector simulation quantity, change at least one of the incident angle simulation quantity, the main optical axis deflection angle simulation quantity, the modulation phase delay peak simulation quantity and the static phase delay simulation quantity, so as to optimize the fitting of the first component of the simulated Stokes vector and the actual light intensity time-varying signal, and output the Stokes vector simulation quantity so that the error between the actual light intensity time-varying signal and the first component meets the requirements.

5. The Stokes vector measurement method based on model optimization according to claim 4, characterized in that: In the light intensity time-varying signal simulation model: 。 6. The Stokes vector measurement method based on model optimization according to claim 4, characterized in that: In the light intensity time-varying signal simulation model: 。 7. The Stokes vector measurement method based on model optimization according to any one of claims 4 to 6, characterized in that: The actual light intensity time-varying signal and the first component are optimized and fitted using the least squares method.

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