A photoelastic modulator calibration system and method

Abstract

The present invention discloses a photoelastic modulator calibration system and method, which relates to the technical field of optical measurement instruments. The system includes a laser light source, a polarizer, a photoelastic modulator, an analyzer, a light intensity collector, and a computer. By establishing a simulation model of the time-varying light intensity signal, the present invention optimally fits the first component of the simulated Stokes vector and the actual time-varying light intensity signal, and takes the peak simulation value of the modulation phase delay amount that makes the error between the actual time-varying light intensity signal and the first component meet the requirements as the final calibration value of the peak modulation phase delay amount of the photoelastic modulator, and takes the simulation value of the static phase delay amount that makes the error between the actual time-varying light intensity signal and the simulated time-varying light intensity signal meet the requirements as the final calibration value of the static phase delay amount of the photoelastic modulator, so as to accurately calibrate the peak modulation phase delay amount and the static phase delay amount of the photoelastic modulator.

Description

Technical Field

[0001] The present invention relates to the technical field of optical measuring instruments, and particularly to a photoelastic modulator calibration system and method. Background Art

[0002] A photoelastic modulator is a system for electro-optic modulation of power optical coupling based on the inverse piezoelectric effect and the photoelastic effect. It mainly consists of two parts: an optical component and an excitation circuit, and can be widely used in the field of high-speed ellipsometric optical measurement. Under the action of the excitation circuit, the optical component can generate a periodic birefringent phase delay to perform periodic phase modulation on the passing light.

[0003] During the actual working process, the peak value of the modulation phase delay amount and the working frequency (i.e., the modulation period of the phase delay amount) of the photoelastic modulator may change due to the influence of the external environment (such as temperature), resulting in a deviation between the actual modulation phase delay amount peak value and the static phase delay amount and the set value. Moreover, the accuracy of these two parameters will directly affect the accuracy of the final ellipsometric optical measurement result. Therefore, during the actual use process, it is necessary to accurately calibrate the peak value of the modulation phase delay amount and the static phase delay amount of the photoelastic modulator. Summary of the Invention

[0004] Embodiments of the present invention provide a photoelastic modulator calibration system and method, which solve the technical problem of how to accurately calibrate the peak value of the modulation phase delay amount and the static phase delay amount of the photoelastic modulator, and achieve...

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

[0006] A photoelastic modulator calibration system includes a laser light source, a polarizer, a photoelastic modulator, an analyzer, a light intensity collector, and a computer;

[0007] The polarizer, the photoelastic modulator, the analyzer, and the light intensity collector are sequentially arranged on the optical path of the laser light source, and the light intensity collector is connected to the computer;

[0008] The computer is used to collect the actual time-varying light intensity signal output by the light intensity collector and obtain the main optical axis deflection angles of the polarizer, the photoelastic modulator, and the analyzer;

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

[0010] The computer is also used to change the Stokes vector simulation quantity, the peak simulation quantity of the modulation phase delay quantity, and the simulation quantity of the static phase delay quantity, so as to optimize the fitting between the first component of the simulated Stokes vector and the actual time-varying light intensity signal, and output the peak simulation quantity of the modulation phase delay quantity and the simulation quantity of the static phase delay quantity that make the error between the actual time-varying light intensity signal and the first component meet the requirements.

[0011] Preferably, the acquisition frequency of the actual time-varying light intensity signal is greater than twice the operating frequency of the photoelastic modulator.

[0012] Preferably, the least squares method is used to optimize the fitting between the actual time-varying light intensity signal and the first component.

[0013] Preferably, in the computer, the changing of the Stokes vector simulation quantity, the peak simulation quantity of the modulation phase delay quantity, and the simulation quantity of the static phase delay quantity to optimize the fitting between the first component of the simulated Stokes vector and the actual time-varying light intensity signal, and outputting the peak simulation quantity of the modulation phase delay quantity and the simulation quantity of the static phase delay quantity that make the error between the actual time-varying light intensity signal and the first component meet the requirements includes:

[0014] Given the initial values of the Stokes vector simulation quantity, the peak simulation quantity of the modulation phase delay quantity, and the simulation quantity of the static phase delay quantity, substitute the initial values into the time-varying light intensity signal simulation model to calculate the simulated Stokes vector, and extract the first component in the simulated Stokes vector as the simulated time-varying light intensity signal;

[0015] If the error between the simulated time-varying light intensity signal and the actual time-varying light intensity signal is less than the preset error threshold, output the initial values of the peak simulation quantity of the modulation phase delay quantity and the simulation quantity of the static phase delay quantity;

[0016] If the error between the simulated time-varying light intensity signal and the actual time-varying light intensity signal is not less than the preset error threshold, correct the Stokes vector simulation quantity, the peak simulation quantity of the modulation phase delay quantity, and the simulation quantity of the static phase delay quantity until the error between the simulated time-varying light intensity signal and the actual time-varying light intensity signal is less than the preset error threshold, and output the peak simulation quantity of the modulation phase delay quantity and the simulation quantity of the static phase delay quantity at this time.

[0017] On the other hand, the present invention also provides the following technical solution:

[0018] A method for calibrating a photoelastic modulator, comprising:

[0019] Set the main optical axis deflection angles of the polarizer, photoelastic modulator, and analyzer respectively and calibrate them, and collect the actual time-varying light intensity signal output by the light intensity collector;

[0020] Establish a time-varying light intensity signal simulation model with the Stokes vector simulation quantity, the main optical axis deflection angle, the modulation phase delay quantity peak simulation quantity, and the static phase delay quantity simulation quantity as inputs and the simulated Stokes vector as the output;

[0021] Change the Stokes vector simulation quantity, the modulation phase delay quantity peak simulation quantity, and the static phase delay quantity simulation quantity to optimize the fitting of the first component of the simulated Stokes vector and the actual time-varying light intensity signal, and output the modulation phase delay quantity peak simulation quantity and the static phase delay quantity simulation quantity that make the error between the actual time-varying light intensity signal and the first component meet the requirements.

[0022] Preferably, the time-varying light intensity signal simulation model is:

[0023] S out =M A ·R(A)·R(-M)·M pem ·R(M)·R(-P)·M P ·R(P)·S in ;

[0024] Where:

[0025] δ=δ(t)=Θ·sin(2πFt)+δ S ;

[0026] S out is the simulated Stokes vector; P, M, and A are the main optical axis deflection angles of the polarizer, the photoelastic modulator, and the analyzer respectively; M P , M pem and M A are the Mueller matrices of the polarizer, the photoelastic modulator, and the analyzer respectively; R(θ) represents a rotation transformation matrix with a rotation angle of θ, θ = A, -M, M, -P, or P; Θ is the modulation phase delay quantity peak simulation quantity; F is the operating frequency of the photoelastic modulator; t is time; δ S is the static phase delay quantity simulation quantity, and S in is the Stokes vector simulation quantity.

[0027] Preferably, in the time-varying light intensity signal simulation model:

[0028]

[0029] Preferably, in the time-varying light intensity signal simulation model:

[0030]

[0031] Preferably, the least squares method is used to optimize the fitting of the actual time-varying optical intensity signal and the first component.

[0032] Preferably, by changing the simulation quantity of the Stokes vector, the peak simulation quantity of the modulation phase delay, and the simulation quantity of the static phase delay, to optimize the fitting of the first component of the simulated Stokes vector and the actual time-varying optical intensity signal, and output the peak simulation quantity of the modulation phase delay and the simulation quantity of the static phase delay that satisfy the requirement of the error between the actual time-varying optical intensity signal and the first component, including:

[0033] Given the initial values of the simulation quantity of the Stokes vector, the peak simulation quantity of the modulation phase delay, and the simulation quantity of the static phase delay, substitute the initial values into the time-varying optical intensity signal simulation model to calculate the simulated Stokes vector, and extract the first component in the simulated Stokes vector as the simulated time-varying optical intensity signal;

[0034] If the error between the simulated time-varying optical intensity signal and the actual time-varying optical intensity signal is less than the preset error threshold, output the initial values of the peak simulation quantity of the modulation phase delay and the simulation quantity of the static phase delay;

[0035] If the error between the simulated time-varying optical intensity signal and the actual time-varying optical intensity signal is not less than the preset error threshold, correct the simulation quantity of the Stokes vector, the peak simulation quantity of the modulation phase delay, and the simulation quantity of the static phase delay until the error between the simulated time-varying optical intensity signal and the actual time-varying optical intensity signal is less than the preset error threshold, and output the peak simulation quantity of the modulation phase delay and the simulation quantity of the static phase delay at this time.

[0036] One or more technical solutions provided in the embodiments of the present invention have at least the following technical effects or advantages:

[0037] By establishing a time-varying optical intensity signal simulation model, optimizing the fitting of the first component of the simulated Stokes vector and the actual time-varying optical intensity signal, taking the peak simulation quantity of the modulation phase delay that satisfies the requirement of the error between the actual time-varying optical intensity signal and the first component as the final calibration value of the peak modulation phase delay of the photoelastic modulator, and taking the simulation quantity of the static phase delay that satisfies the requirement of the error between the actual time-varying optical intensity signal and the simulated time-varying optical intensity signal as the final calibration value of the static phase delay of the photoelastic modulator, the peak modulation phase delay and the static phase delay of the photoelastic modulator can be accurately calibrated. Description of the Drawings

[0038] To more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0039] Figure 1 It is a schematic structural diagram of the photoelastic modulator calibration system of the present invention;

[0040] Figure 2 It is a flowchart of the photoelastic modulator calibration method of the present invention. Specific embodiments

[0041] By providing a photoelastic modulator calibration system and method in the embodiments of the present invention, the technical problem of how to accurately calibrate the peak value of the modulation phase delay amount and the static phase delay amount of the photoelastic modulator is solved.

[0042] The general idea of the technical solution in the embodiments of the present invention to solve the above technical problem is as follows:

[0043] A photoelastic modulator calibration system, as Figure 1 shown, includes a laser light source, a polarizer, a photoelastic modulator, an analyzer, a light intensity collector and a computer;

[0044] The polarizer, the photoelastic modulator, the analyzer, and the light intensity collector are sequentially arranged on the optical path of the laser light source, and the light intensity collector is connected to the computer;

[0045] The computer is used to collect the actual time-varying light intensity signal output by the light intensity collector and obtain the deflection angles of the main optical axes of the polarizer, the photoelastic modulator, and the analyzer;

[0046] The computer is also used to establish a light intensity time-varying signal simulation model with the Stokes vector simulation quantity, the main optical axis deflection angle, the modulation phase delay amount peak simulation quantity, and the static phase delay amount simulation quantity as inputs and the simulated Stokes vector as the output;

[0047] The computer is also used to change the Stokes vector simulation quantity, the modulation phase delay amount peak simulation quantity, and the static phase delay amount simulation quantity to optimize the fitting of the first component of the simulated Stokes vector and the actual time-varying light intensity signal, and output the modulation phase delay amount peak simulation quantity and the static phase delay amount simulation quantity that make the error between the actual time-varying light intensity signal and the first component meet the requirements.

[0048] To better understand the above technical solution, the following will describe the above technical solution in detail in combination with the accompanying drawings of the specification and specific embodiments.

[0049] First, it should be noted that the term "and / or" appearing in this article is merely a description of the association relationship between associated objects, indicating that there can be three relationships. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone. Additionally, the character " / " in this article generally represents an "or" relationship between the associated objects before and after.

[0050] In this embodiment, the laser light source is used to generate stable laser light (the laser wavelength, laser intensity, and polarization state remain unchanged). The laser light generated by the laser light source becomes linearly polarized light after passing through a polarizer (the main optical axis deflection angle is P and remains unchanged during the calibration process), and the linearly polarized light passes through an acousto-optic modulator (the main optical axis deflection angle is M and remains unchanged during the calibration process) for phase modulation and then passes through an analyzer (the main optical axis deflection angle is A and remains unchanged during the calibration process). The polarization component along the analyzer optical axis direction can pass through and is then converted into a voltage signal by a light intensity collector and uploaded to a computer for analysis and processing.

[0051] Among them, the acquisition frequency of the computer for collecting the actual time-varying light intensity signal is greater than twice the working frequency of the acousto-optic modulator. According to the sampling theorem, the acquisition frequency greater than twice the working frequency will not cause distortion of the collected actual time-varying light intensity signal.

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

[0053] S out =M A ·R(A)·R(-M)·M pem ·R(M)·R(-P)·M P ·R(P)·S in ;

[0054] Where:

[0055] δ = δ(t) = Θ·sin(2πFt) + δ S ;

[0056] S out is the simulated Stokes vector; P, M, and A are the main optical axis deflection angles of the polarizer, acousto-optic modulator, and analyzer respectively; M P , M pem and M A are the Mueller matrices of the polarizer, acousto-optic modulator, and analyzer respectively; R(θ) represents the rotation transformation matrix with a rotation angle of θ, where θ = A, -M, M, -P, or P; Θ is the peak simulation value of the modulation phase delay; F is the working frequency of the acousto-optic modulator; t is the time; δ S is the simulated value of the static phase delay; S in is the simulated value of the Stokes vector.

[0057] In the simulation model of the time-varying optical intensity signal:

[0058]

[0059] Among them, P, M, and A are the deflection angles of the main optical axes of the polarizer, photoelastic modulator, and analyzer that are set and calibrated. During the calibration process, P, M, and A remain unchanged.

[0060] After building the photoelastic modulator calibration system in this embodiment, the deflection angles of the main optical axes of the polarizer, photoelastic modulator, and analyzer will be set and calibrated, and the peak value of the modulation phase delay, static phase delay, and working frequency of the photoelastic modulator will also be set. During the actual working process, assuming that the peak value of the modulation phase delay and the working frequency (i.e., the modulation period of the phase delay) of the photoelastic modulator will not change due to the influence of the external environment (such as temperature), and there is no deviation between the actual peak value of the modulation phase delay and the static phase delay and the set values, then S out The first component of should be equal to the actually collected time-varying optical intensity signal, Θ is equal to the peak value of the modulation phase delay of the photoelastic modulator, and δ S is equal to the static phase delay of the photoelastic modulator, and S in is equal to the Stokes vector of the polarized light generated by the laser light source.

[0061] In the computer of this embodiment, the least squares method is used to optimize the fitting between the actual time-varying optical intensity signal and the first component. Specifically, in the computer, the simulation quantity of the Stokes vector, the simulation quantity of the peak value of the modulation phase delay, and the simulation quantity of the static phase delay are changed to optimize the fitting between the first component of the simulated Stokes vector and the actual time-varying optical intensity signal, and the simulation quantity of the peak value of the modulation phase delay and the simulation quantity of the static phase delay that make the error between the actual time-varying optical intensity signal and the first component meet the requirements are output, including:

[0062] Step 1: Given the initial values of the simulation quantity of the Stokes vector, the simulation quantity of the peak value of the modulation phase delay, and the simulation quantity of the static phase delay, substitute the initial values into the simulation model of the time-varying optical intensity signal to calculate the simulated Stokes vector, and extract the first component in the simulated Stokes vector as the simulated time-varying optical intensity signal;

[0063] Step 2: If the error between the simulated time-varying optical intensity signal and the actual time-varying optical intensity signal is less than the preset error threshold, then output the initial values of the simulation quantity of the peak value of the modulation phase delay and the simulation quantity of the static phase delay;

[0064] Step 3: If the error between the simulated time-varying light intensity signal and the actual time-varying light intensity signal is not less than the preset error threshold, correct the simulated Stokes vector, the peak simulated modulation phase delay, and the simulated static phase delay until the error between the simulated time-varying light intensity signal and the actual time-varying light intensity signal is less than the preset error threshold, and output the peak simulated modulation phase delay and the simulated static phase delay at this time.

[0065] In Step 1, the peak modulation phase delay and the static phase delay of the photoelastic modulator set after the Stokes vector measurement system mentioned above is built can be used as the initial values of Θ and δ respectively. S First, estimate the true value of the Stokes vector of the polarized light generated by the laser source, and use the estimated value of the true value as the initial value of the simulated Stokes vector S. in Assume that the peak modulation phase delay and the operating frequency (i.e., the modulation period of the phase delay) of the photoelastic modulator will not change due to the influence of the external environment (such as temperature), there is no deviation between the actual peak modulation phase delay and the static phase delay and the set values, and the given initial value of the simulated Stokes vector S in happens to be the true value of the Stokes vector of the polarized light generated by the laser source. Then, the simulated time-varying light intensity signal calculated through the initial values of the simulated Stokes vector, the peak simulated modulation phase delay, and the simulated static phase delay, and the main optical axis deflection angles of the polarizer, the photoelastic modulator, and the analyzer should be equal to the actually collected time-varying light intensity signal.

[0066] In Step 2, if the error between the simulated time-varying light intensity signal and the actual time-varying light intensity signal meets the requirements, it can be that the simulated time-varying light intensity signal is equal to the actual time-varying light intensity signal, or the error between the simulated time-varying light intensity signal and the actual time-varying light intensity signal is less than the preset error threshold. If the error between the simulated time-varying light intensity signal calculated through the initial values and the actual time-varying light intensity signal meets the requirements, then the initial value of the output peak simulated modulation phase delay is used as the final calibrated value of the peak modulation phase delay of the photoelastic modulator, and the output simulated static phase delay is used as the final calibrated value of the static phase delay of the photoelastic modulator.

[0067] In step 3, if the error between the simulated time-varying optical intensity signal calculated from the initial values and the actual time-varying optical intensity signal does not meet the requirements, the simulated Stokes vector will be continuously changed, and at the same time, the peak simulated value of the modulation phase delay and the simulated value of the static phase delay will be changed until the error between the simulated time-varying optical intensity signal and the actual time-varying optical intensity signal meets the requirements. At this time, the peak simulated value of the modulation phase delay that makes the error between the actual time-varying optical intensity signal and the simulated time-varying optical intensity signal meet the requirements is used as the final calibration value of the peak modulation phase delay of the photoelastic modulator, and the simulated value of the static phase delay that makes the error between the actual time-varying optical intensity signal and the simulated time-varying optical intensity signal meet the requirements is used as the final calibration value of the static phase delay of the photoelastic modulator.

[0068] In this embodiment, by establishing an optical intensity time-varying signal simulation model with the simulated Stokes vector, the main optical axis deflection angle, the peak simulated value of the modulation phase delay, and the simulated value of the static phase delay as inputs and the simulated Stokes vector as the output, and changing the simulated Stokes vector, the peak simulated value of the modulation phase delay, and the simulated value of the static phase delay, the first component of the simulated Stokes vector and the actual optical intensity time-varying signal are optimized and fitted. The peak simulated value of the modulation phase delay that makes the error between the actual optical intensity time-varying signal and the first component meet the requirements is used as the final calibration value of the peak modulation phase delay of the photoelastic modulator, and the simulated value of the static phase delay that makes the error between the actual optical intensity time-varying signal and the simulated optical intensity time-varying signal meet the requirements is used as the final calibration value of the static phase delay of the photoelastic modulator, so as to accurately calibrate the peak modulation phase delay and the static phase delay of the photoelastic modulator.

[0069] This embodiment also provides a method for calibrating a photoelastic modulator, as Figure 2 shown, including:

[0070] Step S1: Respectively set the main optical axis deflection angles of the polarizer, the photoelastic modulator, and the analyzer and perform calibration, and collect the actual optical intensity time-varying signal output by the optical intensity collector;

[0071] Step S2: Establish an optical intensity time-varying signal simulation model with the simulated Stokes vector, the main optical axis deflection angle, the peak simulated value of the modulation phase delay, and the simulated value of the static phase delay as inputs and the simulated Stokes vector as the output;

[0072] Step S3: Change the simulated Stokes vector, the peak simulated value of the modulation phase delay, and the simulated value of the static phase delay to optimize and fit the first component of the simulated Stokes vector and the actual optical intensity time-varying signal, and output the peak simulated value of the modulation phase delay and the simulated value of the static phase delay that make the error between the actual optical intensity time-varying signal and the first component meet the requirements.

[0073] In step S2, the established simulation model of the time-varying optical intensity signal is as follows:

[0074] S out = M A ·R(A)·R(-M)·M pem ·R(M)·R(-P)·M P ·R(P)·S in ;

[0075] Where:

[0076] δ = δ(t) = Θ·sin(2πFt) + δ S ;

[0077] S out is the simulated Stokes vector; P, M, and A are the principal axis deflection angles of the polarizer, photoelastic modulator, and analyzer, respectively; M P , M pem and M A are the Mueller matrices of the polarizer, photoelastic modulator, and analyzer, respectively; R(θ) represents the rotation transformation matrix with a rotation angle of θ, where θ = A, -M, M, -P, or P; Θ is the peak simulation value of the modulation phase delay; F is the working frequency of the photoelastic modulator; t is time; δ S is the simulation value of the static phase delay, and S in is the simulation value of the Stokes vector.

[0078] In the simulation model of the time-varying optical intensity signal:

[0079]

[0080] Among them, P, M, and A are the principal axis deflection angles of the polarizer, photoelastic modulator, and analyzer that are set and calibrated, and P, M, and A remain unchanged during the calibration process.

[0081] In step S3, the least squares method is used to optimize the fitting of the actual time-varying optical intensity signal and the first component. Step S3 specifically includes:

[0082] Given the initial values of the simulation value of the Stokes vector, the peak simulation value of the modulation phase delay, and the simulation value of the static phase delay, substitute the initial values into the simulation model of the time-varying optical intensity signal to calculate the simulated Stokes vector, and extract the first component in the simulated Stokes vector as the simulated time-varying optical intensity signal;

[0083] If the error between the simulated time-varying optical intensity signal and the actual time-varying optical intensity signal is less than the preset error threshold, output the initial values of the peak simulation value of the modulation phase delay and the simulation value of the static phase delay;

[0084] If the error between the simulated time-varying optical intensity signal and the actual time-varying optical intensity signal is not less than the preset error threshold, correct the simulated Stokes vector, the peak simulated modulation phase delay, and the simulated static phase delay until the error between the simulated time-varying optical intensity signal and the actual time-varying optical intensity signal is less than the preset error threshold, and output the peak simulated modulation phase delay and the simulated static phase delay at this time.

[0085] In this embodiment, a simulation model of the time-varying optical intensity signal is established with the simulated Stokes vector, the main optical axis deflection angle, the peak simulated modulation phase delay, and the simulated static phase delay as inputs and the simulated Stokes vector as the output. By changing the simulated Stokes vector, the peak simulated modulation phase delay, and the simulated static phase delay, the first component of the simulated Stokes vector is optimized and fitted with the actual time-varying optical intensity signal. The peak simulated modulation phase delay that makes the error between the actual time-varying optical intensity signal and the first component meet the requirements is used as the final calibration value of the peak modulation phase delay of the photoelastic modulator, and the simulated static phase delay that makes the error between the actual time-varying optical intensity signal and the simulated time-varying optical intensity signal meet the requirements is used as the final calibration value of the static phase delay of the photoelastic modulator, so as to accurately calibrate the peak modulation phase delay and the static phase delay of the photoelastic modulator.

[0086] Generally, a calibration method based on Bessel function decomposition can also be used to calibrate the peak value of the modulation phase delay and the static phase delay of the photoelastic modulator. The calibration system based on Bessel function decomposition usually consists of two parts: an optical measurement module and a signal processing module. The optical measurement module is composed of a laser, a polarization beam splitter prism, a phase compensation wave plate, the photoelastic modulator to be calibrated, and a mirror, which jointly complete the modulation of the polarization state of the incident light. The signal processing module is composed of a photodetector, a signal conditioner, a lock-in amplifier, and a computer. The basic principle of the above method is to make the photoelastic modulator to be calibrated work in a stable state, modulate the incident signal light generated by the laser, and then obtain the amplitudes of the corresponding harmonic components (such as the fundamental harmonic and the second harmonic, etc.) in the modulated light intensity signal measured by the photodetector through the lock-in amplifier. The computer processes these amplitudes to obtain the corresponding peak value of the phase delay as the calibration value of the modulation phase delay of the photoelastic modulator, and the working frequency can be directly obtained from the lock-in amplifier, so that the corresponding static phase delay can be obtained and used as the calibration value of the static phase delay of the photoelastic modulator. The above method requires setting different deflection angles of the analyzer for multiple measurements, and then performing data fitting on the results of multiple measurements. The measurement process is relatively complex. Since the angular errors between optical elements will directly affect the final calibration result, multiple rotations of the deflection angle of the analyzer may increase the uncertainty of the calibration result. It is necessary to limit the range of the deflection angle difference between the polarizer and the analyzer to ensure that the amplitude of the frequency doubling signal in the modulation signal is equivalent to the amplitude of the second harmonic signal. Otherwise, the influence of system noise will increase sharply, which results in the limitation of the calibration range of the photoelastic modulator. Only the frequency doubling and second harmonic signal components in the modulation signal are extracted for analysis and processing, ignoring the DC component and other high-frequency components. In principle, it is only an approximate processing method, which will increase the uncertainty of the calibration result.

[0087] In this embodiment, only the main optical axis deflection angles of the polarizer, the photoelastic modulator, and the analyzer are set and calibrated once. During the calibration process, the main optical axis deflection angles of the polarizer, the photoelastic modulator, and the analyzer, as well as the working frequency of the photoelastic modulator, remain unchanged. There is no need to change the experimental conditions for multiple measurements, thus reducing the complexity of the calibration process. The calibration process is faster, ensuring the certainty of the calibration result. Moreover, the calibration result is obtained through the fitting analysis of the time-varying light intensity signal. The low-order harmonic approximation is not adopted, and all harmonic components in the signal are retained, improving the accuracy of the calibration result. Since there is no extraction of the frequency doubling signal, the lock-in amplifier is not required in the calibration system, reducing the cost of the calibration system.

[0088] Although the preferred embodiments of the present invention have been described, additional changes and modifications can be made to these embodiments by those skilled in the art once they learn of the basic inventive concept. Therefore, the appended claims are intended to be construed to include the preferred embodiments as well as all changes and modifications that fall within the scope of the present invention.

[0089] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A photoelastic modulator calibration system, characterized in that It includes a laser light source, a polarizer, a photoelastic modulator, an analyzer, a light intensity collector and a computer; The polarizer, the photoelastic modulator, the analyzer, and the light intensity collector are sequentially arranged on the optical path of the laser light source, and 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 and obtain the main optical axis deflection angles of the polarizer, the photoelastic modulator, and the analyzer; The computer is further used to establish a light intensity time-varying signal simulation model with the Stokes vector simulation quantity, the main optical axis deflection angle, the modulation phase delay quantity peak simulation quantity, and the static phase delay quantity simulation quantity as inputs and the simulated Stokes vector as the output; The computer is further used to give initial values of the Stokes vector simulation quantity, the modulation phase delay quantity peak simulation quantity, and the static phase delay quantity simulation quantity, substitute the initial values into the light intensity time-varying signal simulation model to calculate the simulated Stokes vector, and extract the first component in 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, the initial values of the modulation phase delay quantity peak simulation quantity and the static phase delay quantity simulation quantity are output; 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, the modulation phase delay quantity peak simulation quantity, and the static phase delay quantity simulation quantity are 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 modulation phase delay quantity peak simulation quantity and the static phase delay quantity simulation quantity at this time are output; The light intensity time-varying signal simulation model is: ； Wherein: ； ； is the simulated Stokes vector; P, M, and A are the deflection angles of the main optical axes of the polarizer, the photoelastic modulator, and the analyzer, respectively; , and are the Mueller matrices of the polarizer, the photoelastic modulator, and the analyzer, respectively; represents the rotation transformation matrix with a rotation angle of , = A, -M, M, -P, or P; is the peak simulation value of the modulation phase delay; F is the operating frequency of the photoelastic modulator; t is time; is the simulation value of the static phase delay, is the simulation value of the Stokes vector.

2. The photoelastic modulator calibration system according to claim 1, wherein The acquisition frequency of the actual light intensity time-varying signal is greater than twice the operating frequency of the photoelastic modulator.

3. The photoelastic modulator calibration system according to claim 1, characterized in that The least squares method is used to optimize and fit the actual light intensity time-varying signal and the first component.

4. A method for calibrating a photoelastic modulator, characterized in that, Applied to the photoelastic modulator calibration system according to any one of claims 1-3, it includes: Respectively set the main optical axis deflection angles of the polarizer, the photoelastic modulator, and the analyzer and calibrate them, and collect the actual light intensity time-varying signal output by the light intensity collector; Establish a light intensity time-varying signal simulation model with the Stokes vector simulation quantity, the main optical axis deflection angle, the modulation phase delay quantity peak simulation quantity, and the static phase delay quantity simulation quantity as inputs and the simulated Stokes vector as the output; Change the Stokes vector simulation quantity, the modulation phase delay quantity peak simulation quantity, and the static phase delay quantity simulation quantity to optimize and fit the first component of the simulated Stokes vector and the actual light intensity time-varying signal, and output the modulation phase delay quantity peak simulation quantity and the static phase delay quantity simulation quantity that make the error between the actual light intensity time-varying signal and the first component meet the requirements.

5. The photoelastic modulator calibration method according to claim 4, wherein In the light intensity time-varying signal simulation model: 。 6. The photoelastic modulator calibration method according to claim 4, characterized in that In the light intensity time-varying signal simulation model: 。 7. The method for calibrating a photoelastic modulator according to any one of claims 4 to 6, characterized in that, The least squares method is used to optimize and fit the actual light intensity time-varying signal and the first component.

8. The photoelastic modulator calibration method according to claim 7, characterized in that, Changing the simulated Stokes vector quantity, the peak simulated modulation phase delay quantity, and the simulated static phase delay quantity to optimize the fitting of the first component of the simulated Stokes vector and the actual time-varying optical intensity signal, and outputting the peak simulated modulation phase delay quantity and the simulated static phase delay quantity that make the error between the actual time-varying optical intensity signal and the first component meet the requirements, including: Given the initial values of the simulated Stokes vector quantity, the peak simulated modulation phase delay quantity, and the simulated static phase delay quantity, substituting the initial values into the time-varying optical intensity signal simulation model to calculate the simulated Stokes vector, and extracting the first component in the simulated Stokes vector as the simulated time-varying optical intensity signal; If the error between the simulated time-varying optical intensity signal and the actual time-varying optical intensity signal is less than the preset error threshold, output the initial values of the peak simulated modulation phase delay quantity and the simulated static phase delay quantity; If the error between the simulated time-varying optical intensity signal and the actual time-varying optical intensity signal is not less than the preset error threshold, correct the simulated Stokes vector quantity, the peak simulated modulation phase delay quantity, and the simulated static phase delay quantity until the error between the simulated time-varying optical intensity signal and the actual time-varying optical intensity signal is less than the preset error threshold, and output the peak simulated modulation phase delay quantity and the simulated static phase delay quantity at this time.

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