Stepping phase inversion method, device and equipment of birefringence interference imager

Abstract

The invention discloses a stepping phase inversion method, a stepping phase inversion device and stepping phase inversion equipment for a birefringence interference imager, relates to the technical field of optical detection instrument measurement, and widens the requirement on an external calibration light source, namely the external calibration light source is unstable and is not stable. Meanwhile, the response of the birefringence interference imager to the light source intensity can be the same or different in the stepping phase inversion experiment, and the actual situation of the birefringence interference imager is met; meanwhile, the total phase interval among a series of interference intensity values obtained through stepping phase inversion is random and unknown, the step length of wavelength change of a laser is not required, a high-precision tunable laser does not need to be used, the stepping phase inversion difficulty of the birefringence interference imager is greatly reduced, and the accuracy of the birefringence interference imager is improved. Errors of external regulation and control hypothesis are avoided from the theoretical level, stepping phase inversion can be easily carried out to obtain the stepping phase, and the inversion precision is improved.

Description

Technical Field

[0001] The present invention relates to the field of optical detection instrument measurement technology, and in particular to a step phase inversion method, device and equipment for a birefringence interference imager. Background Art

[0002] Birefringence interferometry has very important applications in the fields of atmospheric remote sensing, plasma flow detection and carbon dioxide monitoring. In the field of plasma flow detection, birefringence interferometry can be used to measure relevant parameters of plasma and help study the characteristics and behavior of plasma. Birefringence interferometry imaging technology utilizes the independent propagation characteristics of two characteristic polarization states in birefringent crystals. Through the analysis and processing of interference phenomena, rich information about the detected object can be obtained. The naturally formed aurora and airglow in the atmosphere are used as light sources, and the interference pattern information of the airglow spectrum is detected to obtain information on the high-altitude atmospheric wind field. There is no need to emit lasers, which has great advantages.

[0003] In recent years, birefringence interferometry has been routinely used in nuclear fusion energy research, such as in magnetic confinement plasma experiments such as tokamaks. The same technology has been shown to be useful for measuring wind speed in the upper atmosphere; however, the lower speeds (less than 200 m / s) compared to the speeds at the edge of nuclear fusion experiments (less than 4 km / s) make this application more challenging. To achieve sensitivity to Doppler shifts of this magnitude, approximately 10 3 or 10 4 Therefore, in the field of atmospheric wind field detection, a more complex four-partition birefringence interferometer imager is usually used for wind speed detection. The detection accuracy of this type of birefringence interferometer is mainly restricted by the accuracy of the step phase of the four partitions, that is, the accuracy of the step phase calibration will affect the accuracy of wind speed detection; if there is a deviation in the phase calibration in the initial stage, the subsequent measurement and imaging results will inevitably be affected; in the process of detecting the atmospheric wind field through airglow radiation, a small phase calibration error will lead to inaccurate wind speed detection results; therefore, in the installation stage of the birefringence interferometer, it is necessary to accurately invert its step phase through experiments to ensure the detection accuracy of atmospheric wind speed.

[0004] The main difficulty of the stepped phase inversion of the birefringence interferometer is that its four intensities are obtained statically and simultaneously, and it is impossible to obtain a series of interference intensity values ​​with uniform total phase intervals by precisely controlling the movement of the moving mirror like the Michelson imaging interferometer with a moving mirror. When the total phase interval is uniform, the series of interference intensity values ​​used for stepped phase inversion can make a better cosine curve, and the stepped phase can be obtained directly by fitting the cosine curve parameters.

[0005] However, the birefringence interferometer cannot obtain interference intensity values ​​with very uniform total phase intervals. It can only obtain a series of interference intensity values ​​with randomly changing total phases through external control. These interference intensity values ​​cannot directly produce a cosine curve, so it is difficult to obtain a stepped phase using this method. Summary of the invention

[0006] The embodiments of the present invention provide a step-phase inversion method, device and equipment for a birefringence interferometer, which can solve the problem in the prior art that the existing birefringence interferometer cannot obtain interference intensity values ​​with very uniform total phase intervals, and can only obtain a series of interference intensity values ​​with randomly changing total phases through external control. These interference intensity values ​​cannot directly produce a cosine curve, so it is difficult to obtain the step-phase in this way.

[0007] An embodiment of the present invention provides a step-by-step phase inversion method for a birefringence interferometer imager, comprising the following steps:

[0008] Obtain the interference intensity values ​​of the four partitions of the birefringence interferometer in the step phase inversion experiment, and combine the interference intensity values ​​of the four partitions in pairs to construct a Lissajous scatter plot;

[0009] The Lissajous scatter plot is fitted with an ellipse, and the relative intensity coefficients, instrument modulation and step phase of the two partitions in each combination are determined according to the ellipse parameters, and the reference phase of the wavelength scanning of the external calibration light source is obtained by combining the interference intensity values ​​of the four partitions;

[0010] The relative intensity coefficients of the two partitions in each combination, the instrument modulation, the step phase, the interference intensity value and the reference phase are used to update the initial value of the light source intensity of the external calibration light source, and the interference intensity values ​​of the four partitions are updated at the same time;

[0011] According to the updated interference intensity values ​​of the four partitions, the reference phase of the wavelength scanning of the external calibration light source and the light source intensity value of the external calibration light source are cyclically iterated until the difference between the light source intensities after two updates is less than a fixed value, and the step phase obtained in this iteration is output to complete the step phase inversion of the birefringence interferometer imager.

[0012] Preferably, the wavelength scanning comprises:

[0013] The wavelength scanning is performed by adjusting the current of the laser to change its wavelength, thereby causing changes in the interference intensity values ​​of the four partitions of the birefringence interferometer in the step phase inversion experiment, and obtaining a series of different interference intensity values ​​as input of the birefringence interferometer parameter calibration algorithm.

[0014] Preferably, the obtaining of the reference phase comprises:

[0015] The Lissajous scatter plot is fitted with an ellipse, and the relative intensity coefficients of the two partitions in each combination are determined according to the coordinates of the center position of the ellipse; the instrument modulation is determined according to the height and width of the ellipse; and the step phase is determined according to the zero point coordinates of the ellipse;

[0016] According to the relative intensity coefficient of the two partitions in each combination, the instrument modulation, the step phase and the interference intensity value of the four partitions, the reference phase of the wavelength scanning of the external calibration light source is obtained; the equation for obtaining the reference phase is:

[0017]

[0018] in: Represents the interference intensity values ​​of the four partitions; represents the step phase; i and j represent the i-th step in the j-th measurement of the birefringence interferometer in the step phase inversion experiment; Φ j represents the reference phase; n represents the number of steps in each measurement in the step phase inversion experiment; Indicates the initial step phase.

[0019] Preferably, updating the interference intensity values ​​of the four subareas includes:

[0020] Using the relative intensity coefficients of the two partitions in each combination, the instrument modulation, the step phase, the interference intensity values ​​of the four partitions and the reference phase, the initial value of the light source intensity of the outer boundary calibration light source is updated to obtain the updated light source intensity;

[0021] The updated interference intensity values ​​of the four partitions are obtained by using the relative intensity coefficients of the two partitions in each combination, the instrument modulation, the step phase, the reference phase and the updated light source intensity.

[0022] Preferably, the equation for updating the initial value of the light source intensity of the outer boundary calibration light source is:

[0023]

[0024] in: Indicates the intensity of the light source; Represents the interference intensity value of the four partitions; A i represents the relative strength coefficient of the two partitions in each combination; U i Indicates the instrument modulation degree; Indicates the step phase; Φ j represents the reference phase; n represents the number of steps in each measurement in the stepped phase inversion experiment; i represents the number of steps.

[0025] Preferably, the stepping phase obtained by outputting the current iteration includes:

[0026] In a set birefringence interferometer in a step phase inversion experiment, a total of m measurements are performed, each measurement has 4 steps, and each step corresponds to a partition. Then the interference intensity of a point in the experiment at the i-th step in the j-th measurement is:

[0027]

[0028] in: Represents the interference intensity values ​​of the four partitions; Indicates the intensity of the light source; A i represents the relative strength coefficient of the two partitions in each combination; U i Indicates the instrument modulation degree; Indicates the step phase; Φ j Indicates the reference phase;

[0029] When the difference between the light source intensity values ​​of the outer boundary calibration light source of two loop iterations is less than a fixed value, the step phase obtained in this loop iteration is the inverted step phase;

[0030] The light source intensity difference is:

[0031]

[0032] Among them: ε represents the difference in light source intensity after two updates; k represents the number of iterations; Represents the updated light source intensity obtained at the kth iteration; represents the updated light source intensity obtained at the k+1th iteration; m represents the number of measurements performed in the stepped phase inversion experiment.

[0033] The embodiment of the present invention further provides a step phase inversion device for a birefringence interferometric imager, comprising:

[0034] An extraction module is used to obtain the interference intensity values ​​of four partitions of the birefringence interferometer in the step phase inversion experiment, and to combine the interference intensity values ​​of the four partitions in pairs to construct a Lissajous scatter plot;

[0035] The inversion module is used to perform ellipse fitting on the Lissajous scatter plot, determine the relative intensity coefficient, instrument modulation and step phase of the two partitions in each combination according to the ellipse parameters, and obtain the reference phase of the wavelength scanning of the external calibration light source by combining the interference intensity values ​​of the four partitions;

[0036] The relative intensity coefficients of the two partitions in each combination, the instrument modulation, the step phase, the interference intensity value and the reference phase are used to update the initial value of the light source intensity of the external calibration light source, and the interference intensity values ​​of the four partitions are updated at the same time;

[0037] The iterative update module is used to cyclically iterate the reference phase of the wavelength scanning of the external calibration light source and the light source intensity value of the external calibration light source according to the interference intensity values ​​of the four partitions after the update, until the difference between the light source intensities after two updates is less than a fixed value, output the step phase obtained in this iteration, and complete the step phase inversion of the birefringence interferometer imager.

[0038] An embodiment of the present invention further provides an electronic device, including a memory and a processor;

[0039] The memory is used to store computer programs;

[0040] The processor is used to implement the steps of the step phase inversion method of a birefringence interferometer imager as described above when executing the computer program stored in the memory.

[0041] The embodiments of the present invention provide a step phase inversion method, device and equipment for a birefringence interferometric imager. Compared with the prior art, the advantages thereof are as follows:

[0042] The present invention does not need to consider the instability of an external calibration light source, and the random changes of the four partitions when the interference intensity of the four partitions is obtained in the step phase inversion experiment of the birefringence interferometer. Specifically, the interference intensity values ​​of the four partitions are obtained in the experiment, and two combinations are used to perform ellipse fitting, and the relative intensity coefficient, instrument modulation, step phase and reference phase are obtained by using ellipse coordinate parameters, and the reference phase and the light source intensity value of the external calibration light source are cyclically iterated to perform inversion; when the interference intensity of the four partitions is obtained, the total phase interval between a series of interference intensity values ​​is random and unknown, and no external regulation is required, and no high-precision tunable laser is required, which greatly reduces the difficulty of step phase inversion of the birefringence interferometer, and can easily perform step phase inversion. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 A schematic diagram of the overall process of a step-by-step phase inversion method for a birefringence interferometer imager provided by an embodiment of the present invention;

[0044] Figure 2 A schematic diagram of the change of the interference intensity of four partitions in a calibration scanning experiment of a step phase inversion method of a birefringence interferometer provided by an embodiment of the present invention;

[0045] Figure 3 A schematic diagram of an iterative convergence process of a step phase inversion method for a birefringence interferometric imager provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0046] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below.

[0047] See also Figure 1 , an embodiment of the present invention provides a step-by-step phase inversion method for a birefringence interferometer imager, comprising the following steps:

[0048] Step 1: Preset a set of light intensity The initial value of .

[0049] Step 2: The four-partition interference intensity values ​​obtained in the step phase inversion experiment According to the pairwise partition combination, a Lissajous scatter plot is made.

[0050] Step 3: Fit the Lissajous scatter plot to an ellipse. According to the ellipse geometric parameters, the relative intensity coefficient A of the two partitions of each combination i Determined by the coordinates of the center of the ellipse, the instrument modulation degree U i Determined by the width and height of the ellipse, the step phase Calculated from the zero point coordinates of the ellipse.

[0051] Step 4: The relative intensity coefficient A of the four partitions is obtained i 、Instrument modulation U i and step phase And the four-partition interference intensity values ​​obtained in the step phase inversion experiment Calculate the reference phase Φ j .

[0052] Step 5: Use the following formula to calculate the light intensity The value of is updated as follows:

[0053]

[0054] in: Indicates the intensity of the light source; Represents the interference intensity value of the four partitions; A i represents the relative strength coefficient of the two partitions in each combination; U i Indicates the instrument modulation degree; Indicates the step phase; Φ j represents the reference phase; n represents the number of steps in each measurement in the stepped phase inversion experiment; i represents the number of steps.

[0055] Step 6: Use the relative intensity coefficient A of the four partitions obtained in step 3 i 、Instrument modulation U i and step phase In step 4, the reference phase Φ is obtained. j , and the light intensity obtained in step 5 Substitute into the model A series of new four-partition interference intensity values ​​are calculated

[0056] Step 7: Use the updated Restart from step 2 and continue iterating until two adjacent loops have The difference ε between them is less than a certain value s, and ε can be expressed as:

[0057]

[0058] Where: k represents the number of iterations. The step phase obtained in this iteration This is the final step phase inversion result.

[0059] More specifically, according to the technical characteristics of the birefringence interferometer, the requirements for the external boundary calibration light source are relaxed, and it is assumed that the intensity of the external light source is unstable and the wavelength is also unstable; therefore, the light source intensity in the step phase inversion experiment of the birefringence interferometer will change with the wavelength scanning and is unknown, and the responses of the four partitions to the light source intensity will also be different, and the total phase interval between all the obtained series of interference intensity values ​​for step phase inversion is random and unknown; in a step phase inversion experiment, a total of m measurements are performed, and each measurement has n steps (because it is a static four-partition, so n=4), then the interference intensity of a point in the field of view in the i-th step in the j-th measurement is:

[0060]

[0061] Where: Φ j Indicates the total phase (including the reference phase and the additional phase caused by the wavelength change of the light source); U i Indicates the instrument modulation degree; represents the step phase. The difference between the above formula and the prior art is that the average intensity A in the nonlinear least squares calibration model is j Change to This means that the four partitions can respond differently to the light intensity. i is called the relative intensity coefficient. It is called the light source intensity.

[0062] The four-partition interference pattern obtained in the calibration experiment changes as follows Figure 2 As shown, a semiconductor laser with a wavelength of 1310nm was used in the experiment, and the wavelength was scanned by adjusting the laser working current; the interference intensity of the four partitions changed irregularly with the wavelength scanning, and it was impossible to directly perform cosine curve fitting, and the light source intensity changed with the wavelength scanning, and the average intensity of the four partitions was also different; the step phase inversion algorithm of the birefringence interferometer proposed in the present invention is insensitive to such non-smooth and irregular intensity changes, and can efficiently extract the step phase information therein.

[0063] like Figure 3 As shown in the figure, the iterative convergence process of the present invention is demonstrated; the change of the calibration light source intensity with the wavelength scanning is corrected in the iterative process, and finally it is well distributed on a fitting ellipse, realizing the step phase Inversion; the method of the present invention makes the modeling of calibration experimental conditions more accurate, the model has universal applicability, improves the accuracy of step phase inversion of the birefringence interferometer, and at the same time has a certain degree of intuitiveness, which makes it easy to monitor abnormal situations in the calibration experiment.

[0064] The invention can realize the step phase inversion under the condition of the instability of the external calibration light source; the existing technology requires the use of a high-precision tunable laser, and the experimental conditions such as temperature control are demanding; the method of the invention can relax the requirements for the external calibration light source, and at the same time, the responses of the four partitions inside the birefringence interferometer to the light source intensity can be different, which is in line with the actual situation of the instrument; and the basic model used in the invention assumes that the intensity of the external light source is unstable and the wavelength is also unstable; in the step phase inversion experiment of the birefringence interferometer, the light source intensity can change with the wavelength scanning and is unknown, and at the same time, the responses of the four partitions to the light source intensity can also be different, and the total phase intervals between all the obtained series of interference intensity values ​​for step phase inversion can be random and unknown, there is no requirement for the step length of the laser wavelength change, and there is no need to use a high-precision tunable laser. The calibration can be completed by collecting data in the way of adjusting the current using an ordinary laser, which greatly reduces the difficulty of the step phase inversion of the birefringence interferometer, avoids the error of the model assumption from the theoretical level, and improves the inversion accuracy.

[0065] The embodiment of the present invention further provides a step phase inversion device for a birefringence interferometric imager, comprising:

[0066] The extraction module is used to obtain the interference intensity values ​​of the four partitions of the birefringence interferometer in the step phase inversion experiment, and to combine the interference intensity values ​​of the four partitions in pairs to construct a Lissajous scatter plot.

[0067] The inversion module is used to perform ellipse fitting on the Lissajous scatter plot, determine the relative intensity coefficients, instrument modulation and step phase of the two partitions in each combination according to the ellipse parameters, and combine the interference intensity values ​​of the four partitions to obtain the reference phase of the wavelength scanning of the external calibration light source.

[0068] The relative intensity coefficients of the two partitions in each combination, the instrument modulation, the step phase, the interference intensity value and the reference phase are used to update the initial value of the light source intensity of the external calibration light source, and the interference intensity values ​​of the four partitions are updated simultaneously.

[0069] The iterative update module is used to cyclically iterate the reference phase of the wavelength scanning of the external calibration light source and the light source intensity value of the external calibration light source according to the interference intensity values ​​of the four partitions after the update, until the difference between the light source intensities after two updates is less than a fixed value, output the step phase obtained in this iteration, and complete the step phase inversion of the birefringence interferometer imager.

[0070] An embodiment of the present invention further provides an electronic device, including a memory and a processor.

[0071] The memory is used to store computer programs.

[0072] When the processor is used to execute the computer program stored in the memory, the steps of the above-mentioned step phase inversion method of a birefringence interference imager are implemented.

[0073] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A step phase inversion method for a birefringence interferometer imager, characterized in that: The following steps are involved: Obtain the interference intensity values ​​of the four partitions of the birefringence interferometer in the step phase inversion experiment, and combine the interference intensity values ​​of the four partitions in pairs to construct a Lissajous scatter plot; The Lissajous scatter plot is fitted with an ellipse, and the relative intensity coefficients, instrument modulation and step phase of the two partitions in each combination are determined according to the ellipse parameters, and the reference phase of the wavelength scanning of the external calibration light source is obtained by combining the interference intensity values ​​of the four partitions; The relative intensity coefficients of the two partitions in each combination, the instrument modulation, the step phase, the interference intensity value and the reference phase are used to update the initial value of the light source intensity of the external calibration light source, and the interference intensity values ​​of the four partitions are updated at the same time; According to the updated interference intensity values ​​of the four partitions, the reference phase of the wavelength scanning of the external calibration light source and the light source intensity value of the external calibration light source are cyclically iterated until the difference between the light source intensities after two updates is less than a fixed value, and the step phase obtained in this iteration is output to complete the step phase inversion of the birefringence interferometer imager.

2. The step phase inversion method of a birefringence interferometer according to claim 1, characterized in that: The wavelength scanning comprises: The wavelength scanning is performed by adjusting the current of the laser to change its wavelength, thereby causing changes in the interference intensity values ​​of the four partitions of the birefringence interferometer in the step phase inversion experiment, and obtaining a series of different interference intensity values ​​as input of the birefringence interferometer parameter calibration algorithm.

3. The step phase inversion method of a birefringence interferometer according to claim 1, characterized in that: The obtaining of the reference phase comprises: The Lissajous scatter plot is fitted with an ellipse, and the relative intensity coefficients of the two partitions in each combination are determined according to the coordinates of the center position of the ellipse; the instrument modulation is determined according to the height and width of the ellipse; and the step phase is determined according to the zero point coordinates of the ellipse; According to the relative intensity coefficient of the two partitions in each combination, the instrument modulation, the step phase and the interference intensity value of the four partitions, the reference phase of the wavelength scanning of the external calibration light source is obtained; the equation for obtaining the reference phase is: in: Represents the interference intensity values ​​of the four partitions; represents the step phase; i and j represent the i-th step in the j-th measurement of the birefringence interferometer in the step phase inversion experiment; Φ j represents the reference phase; n represents the number of steps in each measurement in the step phase inversion experiment; Indicates the initial step phase.

4. The step phase inversion method of a birefringence interferometer imager according to claim 1, characterized in that: The updating of the interference intensity values ​​of the four partitions includes: Using the relative intensity coefficients of the two partitions in each combination, the instrument modulation, the step phase, the interference intensity values ​​of the four partitions and the reference phase, the initial value of the light source intensity of the outer boundary calibration light source is updated to obtain the updated light source intensity; The updated interference intensity values ​​of the four partitions are obtained by using the relative intensity coefficients of the two partitions in each combination, the instrument modulation, the step phase, the reference phase and the updated light source intensity.

5. The step phase inversion method of a birefringence interferometer imager according to claim 4, characterized in that: The equation for updating the initial value of the light source intensity of the outer boundary calibration light source is: in: Indicates the intensity of the light source; Represents the interference intensity value of the four partitions; A i represents the relative strength coefficient of the two partitions in each combination; U i Indicates the instrument modulation degree; Indicates the step phase; Φ j represents the reference phase; n represents the number of steps in each measurement in the stepped phase inversion experiment; i represents the number of steps.

6. The step phase inversion method of a birefringence interferometer imager according to claim 1, characterized in that: The step phase obtained by outputting this iteration includes: In a set birefringence interferometer in a step phase inversion experiment, a total of m measurements are performed, each measurement has 4 steps, and each step corresponds to a partition. Then the interference intensity of a point in the experiment at the i-th step in the j-th measurement is: in: Represents the interference intensity values ​​of the four partitions; Indicates the intensity of the light source; A i represents the relative strength coefficient of the two partitions in each combination; U i Indicates the instrument modulation degree; Indicates the step phase; Φ j Indicates the reference phase; When the difference between the light source intensity values ​​of the outer boundary calibration light source of two loop iterations is less than a fixed value, the step phase obtained in this loop iteration is the inverted step phase; The light source intensity difference is: Among them: ε represents the difference in light source intensity after two updates; k represents the number of iterations; Represents the updated light source intensity obtained at the kth iteration; represents the updated light source intensity obtained at the k+1th iteration; m represents the number of measurements performed in the stepped phase inversion experiment.

7. A step phase inversion device for a birefringence interferometric imager, characterized in that: include: An extraction module is used to obtain the interference intensity values ​​of four partitions of the birefringence interferometer in the step phase inversion experiment, and to combine the interference intensity values ​​of the four partitions in pairs to construct a Lissajous scatter plot; The inversion module is used to perform ellipse fitting on the Lissajous scatter plot, determine the relative intensity coefficient, instrument modulation and step phase of the two partitions in each combination according to the ellipse parameters, and obtain the reference phase of the wavelength scanning of the external calibration light source by combining the interference intensity values ​​of the four partitions; The relative intensity coefficients of the two partitions in each combination, the instrument modulation, the step phase, the interference intensity value and the reference phase are used to update the initial value of the light source intensity of the external calibration light source, and the interference intensity values ​​of the four partitions are updated at the same time; The iterative update module is used to cyclically iterate the reference phase of the wavelength scanning of the external calibration light source and the light source intensity value of the external calibration light source according to the interference intensity values ​​of the four partitions after the update, until the difference between the light source intensities after two updates is less than a fixed value, output the step phase obtained in this iteration, and complete the step phase inversion of the birefringence interferometer imager.

8. An electronic device, characterized in that: include: Memory and processor; The memory is used to store computer programs; The processor is used to implement the steps of the step phase inversion method of a birefringence interferometric imager as described in any one of claims 1 to 6 when executing the computer program stored in the memory.

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