Global calibration and measurement method and device for a polarimeter

Abstract

The present application relates to a kind of global calibration and measuring method and device of polarimeter, first, the full-wave band light intensity information of standard sample in measurement system is measured, and the measured Fourier coefficient of standard sample is obtained by Fourier transform to light intensity information;Using the measured Fourier coefficient of standard sample and its theoretical Fourier coefficient, global system parameter is iteratively fitted;Then, the full-wave band light intensity information of the sample to be measured is measured, and the Fourier coefficient of the sample to be measured is obtained by Fourier transform to light intensity information;Using global system parameter and the Fourier coefficient of the sample to be measured, the full-wave band polarization of the sample to be measured is calculated.The present application carries out global system calibration and measurement by global system parameter, avoids the overfitting phenomenon generated by fitting system parameter by wavelength-by-wavelength method.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of spectral measurement, in particular to a global calibration and measurement method of a polarization degree measuring instrument. BACKGROUND

[0002] Polarization degree is an important physical quantity for describing polarized light. The polarization effect of light has a certain influence on the measurement accuracy of optical instruments, because optical devices have lattice directions, and therefore there is polarization sensitivity. When detecting the accuracy of optical devices, it is essential to measure the polarization degree of the optical signal. The polarization degree measuring instrument is widely used in optical device process monitoring due to its non-contact, non-destructive, fast, high-precision and other advantages.

[0003] The basic configuration of the polarization degree measuring instrument includes (as shown in Figure 2 The basic configuration of the polarization degree measuring instrument includes (as shown in

[0004] In the calibration and measurement process of the common polarization degree measuring instrument, the system parameters are fitted by the method of fitting by wavelength, and then the polarization degree is calculated by using the system parameters. However, this method is prone to overfitting phenomenon, so that the accurate system parameters cannot be obtained, and the accurate polarization degree of the measured sample cannot be obtained. SUMMARY

[0005] The present application provides a global calibration and measurement method and device of a polarization degree measuring instrument, which avoids the overfitting phenomenon caused by fitting the system parameters by wavelength.

[0006] The technical solution of the present application to solve the above technical problems is as follows:

[0007] On the one hand, the present application provides a global calibration and measurement method of a polarization degree measuring instrument, comprising:

[0008] Measuring the full-waveband light intensity information of the standard sample in the measurement system, and performing Fourier transform on the light intensity information to obtain the measured Fourier coefficient of the standard sample;

[0009] Using the measured Fourier coefficient of the standard sample and its theoretical Fourier coefficient, the global system parameters are iteratively fitted;

[0010] Measuring the full-waveband light intensity information of the measured sample, and performing Fourier transform on the light intensity information to obtain the Fourier coefficient of the measured sample;

[0011] Using the global system parameters and the Fourier coefficient of the measured sample, the full-waveband polarization degree of the measured sample is calculated.

[0012] Further, the fitting iteration method of the global system parameter comprises a traversal method, a global optimization method and a local optimization algorithm.

[0013] Further, the global system parameter comprises a central wavelength of the polarizing wave plate, an optical axis angle and an initial azimuth angle of the polarizing wave plate and the polarizing plate.

[0014] Further, the polarizing wave plate is a composite wave plate.

[0015] In another aspect, the application provides a global calibration and measurement device of a polarization degree measuring instrument, comprising:

[0016] The measurement module is used for measuring full-band light intensity information of the standard sample in the measurement system, and performing Fourier transform on the light intensity information to obtain measured Fourier coefficients of the standard sample;

[0017] The fitting module is used for fitting and iterating the global system parameter by using the measured Fourier coefficients of the standard sample and the theoretical Fourier coefficients thereof.

[0018] The measurement module is used for measuring full-band light intensity information of the standard sample in the measurement system, and performing Fourier transform on the light intensity information to obtain measured Fourier coefficients of the standard sample;

[0019] The polarization degree calculation module is used for calculating the full-band polarization degree of the sample to be measured by using the global system parameter and the Fourier coefficients of the sample to be measured.

[0020] Further, the fitting iteration method of the global system parameter adopted by the fitting module comprises a traversal method, a global optimization method and a local optimization algorithm.

[0021] Further, the global system parameter comprises a central wavelength of the polarizing wave plate, an optical axis angle and an initial azimuth angle of the polarizing wave plate and the polarizing plate.

[0022] The application has the following beneficial effects: the global system calibration and measurement are performed by using the global system parameter (comprising a plurality of central wavelengths and a plurality of optical axis angles of the polarizing wave plate, and an initial azimuth angle of the polarizing wave plate and the polarizing plate), so that the overfitting phenomenon caused by the fitting system parameter in the wavelength-by-wavelength method is avoided. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 A global calibration and measurement method flowchart of a polarization degree measuring instrument is provided for the embodiment of the application.

[0024] Figure 2 A basic configuration diagram of the polarization degree measuring instrument is provided.

[0025] Figure 3 A global calibration and measurement device structure diagram of a polarization degree measuring instrument is provided for the embodiment of the application. DETAILED DESCRIPTION

[0026] The principles and features of the present application are described below in conjunction with the accompanying drawings, in which the examples are presented only to explain the present application and are not intended to limit the scope of the present application.

[0027] As shown in the figure, the embodiment of the present application provides a global calibration and measurement method flow chart of a polarization degree measuring instrument. The method comprises the following steps: Figure 1

[0028] S1, measuring the full-band light intensity information of the standard sample in the measurement system, and performing Fourier transform on the light intensity information to obtain the measured Fourier coefficients of the standard sample.

[0029] In this step, a spectrometer or other measuring equipment can be used to obtain the full-band light intensity information of the standard sample.

[0030] S2, using the measured Fourier coefficients in step S1 and the theoretical Fourier coefficients of the standard sample to perform fitting iteration, the global system parameters of the polarization degree measuring instrument can be obtained. Here, the global system parameters of the polarization degree measuring instrument include the center wavelength of the polarizing plate, the optical axis angle, and the initial azimuth angle of the polarizing plate and the polarizing plate.

[0031] In this embodiment, the polarizing plate is a composite wave plate. The fitting iteration implementation method includes but is not limited to the traversal method, the global optimization method (such as the particle swarm algorithm, the ant colony algorithm, etc.) and the local optimization algorithm (such as the Levenberg-Marquardt method, the Newton method, the gradient descent method, the conjugate gradient method, etc.).

[0032] S3, measuring the full-band light intensity information of the sample to be measured, and performing Fourier transform on the light intensity information to obtain the Fourier coefficients of the sample to be measured.

[0033] In this step, a spectrometer or other measuring equipment is also used to obtain the full-band light intensity information of the sample to be measured.

[0034] S4, using the global system parameters and the Fourier coefficients of the sample to be measured to calculate the full-band polarization degree of the sample to be measured.

[0035] Using the global system parameters of the polarization degree measuring instrument obtained in step S2 and the Fourier coefficients of the sample to be measured, the Stokes vector of the sample to be measured is calculated, and then the full-band polarization degree of the sample to be measured is calculated using the Stokes vector.

[0036] The following formula is a general calibration and measurement mathematical model:

[0037] S out =[M A ​R(A + p1) x [R(-w1t - C1 - q1) M(5i) R(w1t + C1 + q1)] x S in (1)

[0038] In the formula, M A is the Mueller matrix of the polarizer of the analyzer, p1 is the rotation angle of the analyzer, q1 is the azimuth angle of the analyzer, w1 is the rotation speed of the motor, M(5i) is the phase retardation Mueller matrix of the analyzer, R is the rotation matrix, A and C1 are the initial azimuth angles of the analyzer and the polarizer, and S in is the Stokes vector of the standard sample or the sample to be measured, S out is the output Stokes vector. In the prior art, the system parameters are obtained by iterative calculation through wavelength-by-wavelength measurement. In the wavelength-by-wavelength measurement, A + p1 and C1 + q1 are usually calculated as a whole. Due to the wavelength-by-wavelength fitting, the noise and other interference information of the measurement are fitted into the system parameters, resulting in overfitting.

[0039] In the present embodiment, the analyzer is a composite wave plate, and the system parameters p1, q1 and 5i have the following relationship with the global system parameters of the composite wave plate model:

[0040]

[0041] In the formula, wvl is the wavelength, l i is the center wavelength of the i-th wave plate of the composite wave plate model, is the azimuth angle between the i+1-th wave plate and the first wave plate of the composite wave plate model, and M wp is the equivalent Mueller matrix of the composite wave plate.

[0042] The Stokes vector has the following relationship with the degree of polarization DOP of the standard sample or the sample to be measured:

[0043]

[0044] In the formula, S0, S1, S2 and S3 are the components of the Stokes vector, S0 is the measured light intensity, S1 and S2 represent the direction and intensity of linear polarization, S3 represents the circular polarization component, and DOP is the degree of polarization.

[0045] The measured light intensity information S0 of the standard sample is subjected to Fourier transform to obtain the measured Fourier coefficients, and then the measured Fourier coefficients are iterated with the theoretical Fourier coefficients to obtain the global system parameters of the composite wave plate model, i.e. the center wavelengths l1, l2... l n , the azimuth angles and the initial azimuth angles C1 and A of the composite wave plate and the polarizer.

[0046] According to the measured light intensity information of the sample, Fourier transform is performed to obtain Fourier coefficients of the sample. n , the initial azimuth angle C1 and A of the polarizing wave plate and the polarizing plate The Stokes vector of the sample is calculated, and the degree of polarization DOP of the sample is calculated according to formula (3).

[0047] In addition to using a single standard sample for global system parameter calibration, a plurality of samples can also be used for global calibration. The mathematical model is as follows:

[0048] [S out1 S out2 ] = [M A R(A + p1)] * [R(-ω1t-C1-θ1)M(δ1)R(ω1t+C1+θ1)] * [S in1 S in2 ]

[0049] Where S in1 S in2 is the Stokes vector of the standard sample 1 and the standard sample 2, and S out1 S out2 is the exit Stokes vector of the sample 1 and the sample 2. The change from case 1 is that S in becomes [S in1 S in2 ], and S out becomes [S out1 S out2 ], so in the system calibration, the measured Fourier coefficients of the two groups of samples and the theoretical Fourier coefficients are used to iteratively calibrate the global system parameters of the wave plate model, that is, the center wavelengths λ1, λ2... λ n , the initial azimuth angle C1 and A of the polarizing wave plate and the polarizing plate Then, according to the measured Fourier coefficients of the sample and the global system parameters calibrated by the two groups of standard samples, the Stokes vector of the sample is calculated, and finally the degree of polarization DOP of the sample is calculated according to formula (3).

[0050] Compared with using a single standard sample for global system parameter calibration, using the measured results of a plurality of samples for global calibration further avoids measurement errors introduced by the differences of the samples themselves or the influence of the external environment.

[0051] On the basis of the above embodiment, the embodiment of the application further provides a global calibration and measurement device of a polarization degree measuring instrument, comprising:

[0052] The measuring module is configured to measure full-band light intensity information of the standard sample in the measuring system, and perform Fourier transform on the light intensity information to obtain measured Fourier coefficients of the standard sample;

[0053] The fitting module is configured to iteratively fit the global system parameters by using the measured Fourier coefficients of the standard sample and the theoretical Fourier coefficients of the standard sample;

[0054] The measuring module is configured to measure full-band light intensity information of the standard sample in the measuring system, and perform Fourier transform on the light intensity information to obtain measured Fourier coefficients of the standard sample;

[0055] The polarization degree calculation module is configured to calculate the full-band polarization degree of the sample under test by using the global system parameters and the Fourier coefficients of the sample under test.

[0056] Further, the fitting module employs a fitting iteration method of the global system parameters, which includes a traversal method, a global optimization method and a local optimization algorithm.

[0057] Further, the global system parameters include a central wavelength of the polarizing plate, an optical axis angle and an initial azimuth angle of the polarizing plate and the polarizer.

[0058] Although the preferred embodiments of the present application have been described, those skilled in the art who understand the basic inventive concept can make additional changes and modifications to the embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0059] Obviously, those skilled in the art can make various modifications and variations to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and equivalent technologies thereof, the present application is also intended to include these modifications and variations.

Claims

1. A global calibration and measurement method for a polarization degree measuring instrument, characterized in that, include: The light intensity information of the standard sample in the full-band measurement system is measured, and the light intensity information is Fourier transformed to obtain the measured Fourier coefficients of the standard sample. The global system parameters are obtained by fitting and iterating using the measured Fourier coefficients and theoretical Fourier coefficients of the standard sample. Measure the light intensity information of the sample under test across the entire wavelength range, and perform Fourier transform on the light intensity information to obtain the Fourier coefficients of the sample under test. The full-band polarization degree of the sample under test is calculated using the global system parameters and the Fourier coefficients of the sample under test. The global system parameters include the center wavelength of the polarizer, the optical axis angle, and the initial azimuth angle of the polarizer and the polarizer. The polarizer is a composite waveplate.

2. The method according to claim 1, characterized in that, The fitting and iterative methods for the global system parameters include: traversal methods, global optimization methods, or local optimization algorithms.

3. A global calibration and measurement device for a polarization degree measuring instrument, characterized in that, include: The measurement module is used to measure the light intensity information of the standard sample across the entire wavelength range of the measurement system, and to perform Fourier transform on the light intensity information to obtain the measured Fourier coefficients of the standard sample. The fitting module uses the measured Fourier coefficients and theoretical Fourier coefficients of the standard sample to fit and iterate the global system parameters. The measurement module is also used to measure the full-band light intensity information of the sample under test, and to perform Fourier transform on the light intensity information to obtain the Fourier coefficients of the sample under test. The polarization degree calculation module calculates the full-band polarization degree of the sample under test using global system parameters and the Fourier coefficients of the sample under test. The global system parameters include the center wavelength of the polarizer, the optical axis angle, and the initial azimuth angle of the polarizer and the polarizer. The polarizer is a composite waveplate.

4. The apparatus according to claim 3, characterized in that, The fitting module employs iterative methods for fitting global system parameters, including: traversal method, global optimization method, or local optimization algorithm.

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