Stepping Phase Inversion Method, Device and Equipment for a Birefringence Interferometric Imager

Abstract

The present invention discloses a stepped phase inversion method, device and equipment for a birefringent interference imager, which relates to the technical field of optical detection instrument measurement. The present invention relaxes the requirements for the external calibration light source, that is, the external calibration light source is unstable, and at the same time, the responses of the four partitions of the birefringent interference imager to the light source intensity in the stepped phase inversion experiment can be the same or different, which is in line with the actual situation of the birefringent interference imager; at the same time, the total phase interval between a series of interference intensity values obtained for stepped phase inversion is random and unknown, there is no requirement for the step size of the laser wavelength change, and there is no need to use a high-precision tunable laser, which greatly reduces the difficulty of stepped phase inversion of the birefringent interference imager, avoids the error of the external regulation hypothesis from the theoretical level, can easily perform stepped phase inversion to obtain the stepped phase, and improves the inversion accuracy.

Description

Technical Field

[0001] The present invention relates to the technical field of optical detection instrument measurement, and particularly relates to a stepping phase inversion method, device and equipment for a birefringence interferometer imager. Background Art

[0002] Birefringence interferometer imagers have very important applications in fields such as atmospheric remote sensing detection, plasma flow detection, and carbon dioxide monitoring; in the field of plasma flow detection, birefringence interferometer imagers can be used to measure relevant parameters of plasma to help study the characteristics and behaviors of plasma; birefringence interference imaging technology utilizes the independent propagation characteristics of two characteristic polarization states in a birefringent crystal; by analyzing and processing the interference phenomenon, rich information about the detected object can be obtained. Using natural aurora and airglow in the atmosphere as the light source, by detecting the interference pattern information of airglow spectral lines, information about the upper atmospheric wind field can be obtained without the need to emit lasers, which has great superiority.

[0003] In recent years, birefringence interferometer imagers have been routinely used in magnetic confinement plasma experiments such as tokamaks in the field of nuclear fusion energy research, and the same technology has been proven to be applicable to measuring the wind speed in the upper atmosphere; however, compared with the speed at the edge of nuclear fusion experiments (less than 4 km / s), a lower speed (less than 200 m / s) poses greater challenges for this application. To achieve sensitivity to Doppler frequency shifts of this magnitude, approximately 10 3 or 10 4 large interferometer delays of waves are required; therefore, in the field of atmospheric wind field detection, birefringence interferometer imagers in a more complex four-zone form are usually used for wind speed detection. The detection accuracy of such birefringence interferometer imagers is mainly restricted by the stepping phase accuracy of the four zones, that is, the accuracy of stepping phase calibration will affect the accuracy of wind speed detection; if there are deviations in phase calibration at the initial stage, then subsequent measurement and imaging results will inevitably be affected; during the process of detecting the atmospheric wind field through airglow radiation, tiny phase calibration errors will lead to inaccurate wind speed detection results; therefore, during the installation and adjustment stage of the birefringence interferometer imager, it is necessary to accurately invert its stepping phase through experiments to ensure the detection accuracy of atmospheric wind speed.

[0004] The main difficulty in inverting the stepping phase of a birefringence interferometer imager is that its four intensities are obtained statically and simultaneously, and it is impossible to obtain a series of interference intensity values with a uniform total phase interval like a Michelson imaging interferometer with a moving mirror; when the total phase interval is uniform, a series of interference intensity values used for stepping phase inversion can form a good cosine curve, and the stepping phase can be directly obtained by fitting the parameters of the cosine curve.

[0005] However, a birefringent interference imager cannot obtain interference intensity values with a very uniform total phase interval. Instead, it can only obtain a series of interference intensity values with randomly varying total phases through external regulation. These interference intensity values cannot directly form a cosine curve, so it is difficult to obtain the stepping phase in this way. Summary of the Invention

[0006] An embodiment of the present invention provides a method, device, and equipment for inverse stepping phase of a birefringent interference imager, which can solve the problem in the prior art that a birefringent interference imager cannot obtain interference intensity values with a very uniform total phase interval. Instead, it can only obtain a series of interference intensity values with randomly varying total phases through external regulation. These interference intensity values cannot directly form a cosine curve, so it is difficult to obtain the stepping phase in this way.

[0007] An embodiment of the present invention provides a method for inverse stepping phase of a birefringent interference imager, including the following steps:

[0008] Obtain the interference intensity values of four partitions in the inverse stepping phase experiment of the birefringent interference imager, and combine the interference intensity values of the four partitions in pairs to construct a Lissajous scatter plot;

[0009] Perform elliptical fitting on the Lissajous scatter plot, determine the relative intensity coefficient, instrument modulation degree, and stepping phase of two partitions within each combination according to the elliptical parameters, and combine the interference intensity values of the four partitions to obtain the reference phase of the external calibration light source wavelength scan;

[0010] Use the relative intensity coefficient, instrument modulation degree, stepping phase, interference intensity value, and reference phase of two partitions within each combination to update the initial value of the light source intensity of the external calibration light source, and simultaneously update the interference intensity values of the four partitions;

[0011] According to the updated interference intensity values of the four partitions, cyclically iterate the reference phase of the external calibration light source wavelength scan and the light source intensity value of the external calibration light source until the difference between the light source intensities after two updates is less than a fixed value, output the stepping phase obtained in this iteration, and complete the inverse stepping phase of the birefringent interference imager.

[0012] Preferably, the wavelength scan includes:

[0013] The wavelength scan is achieved by adjusting the current of the laser to change its wavelength, thereby causing changes in the interference intensity values of the four partitions in the inverse stepping phase experiment of the birefringent interference imager, and obtaining a series of different interference intensity values as the input of the parameter calibration algorithm of the birefringent interference imager.

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

[0015] Perform elliptical fitting on the Lissajous scatter plot, and determine the relative intensity coefficients of the two partitions within each combination according to the coordinates of the ellipse center position; determine the instrument modulation degree according to the height and width of the ellipse; determine the stepping phase according to the zero point coordinates of the ellipse.

[0016] According to the relative intensity coefficients of the two partitions within each combination, the instrument modulation degree, the stepping phase, and the interference intensity values of the four partitions, obtain the reference phase for the wavelength scanning of the external calibration light source; the equation for obtaining the reference phase is:

[0017]

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

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

[0020] Use the relative intensity coefficients of the two partitions within each combination, the instrument modulation degree, the stepping phase, the interference intensity values of the four partitions, and the reference phase to update the initial value of the light source intensity of the external calibration light source, and obtain the updated light source intensity;

[0021] Use the relative intensity coefficients of the two partitions within each combination, the instrument modulation degree, the stepping phase, the reference phase, and the updated light source intensity to obtain the updated interference intensity values of the four partitions.

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

[0023]

[0024] Where: represents the light source intensity; represents the interference intensity values of the four partitions; A i represents the relative intensity coefficients of the two partitions within each combination; U i represents the instrument modulation degree; represents the stepping phase; Φ j represents the reference phase; n represents the number of steps in each measurement in the stepping phase inversion experiment; i represents the number of steps.

[0025] Preferably, the output of the stepping phase obtained in this iteration includes:

[0026] In the step - phase inversion experiment of a set one - time birefringence interferometric imager, a total of m measurements are carried out. There are 4 steps in each measurement, and each step corresponds to a partition. Then the interference intensity of a point in the j - th measurement at the i - th step in the experiment is:

[0027]

[0028] Where: represents the interference intensity values of the four partitions; represents the light source intensity; A i represents the relative intensity coefficient of two partitions within each combination; U i represents the instrument modulation; represents the step phase; Φ j represents the reference phase;

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

[0030] The difference in the light source intensity is:

[0031]

[0032] Where: ε represents the difference in the light source intensity after two updates; k represents the iteration number label; represents the updated light source intensity obtained at the k - th iteration; represents the updated light source intensity obtained at the (k + 1) - th iteration; m represents the number of measurements carried out in the step - phase inversion experiment.

[0033] An embodiment of the present invention also provides a step - phase inversion device for a birefringence interferometric imager, including:

[0034] An extraction module, configured to obtain the interference intensity values of four partitions in the step - phase inversion experiment of the birefringence interferometric imager, combine the interference intensity values of the four partitions in pairs, and construct a Lissajous scatter plot;

[0035] An inversion module, configured to perform elliptical fitting on the Lissajous scatter plot, determine the relative intensity coefficient, instrument modulation, and step phase of two partitions within each combination according to the elliptical parameters, and combine the interference intensity values of the four partitions to obtain the reference phase of the external calibration light source wavelength scan;

[0036] Update the initial value of the light source intensity of the external calibration light source by using the relative intensity coefficient, instrument modulation, step phase, interference intensity value, and reference phase of two partitions within each combination, and simultaneously update the interference intensity values of the four partitions;

[0037] An iterative update module is used to cyclically and iteratively determine the reference phase of the external calibration light source wavelength scan and the light source intensity value of the external calibration light source according to the updated interference intensity values of the four partitions until the difference between the light source intensities after two updates is less than a fixed value, and output the step phase obtained in this iteration, completing the step phase inversion of the birefringence interferometric imager.

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

[0039] The memory is used to store a computer program;

[0040] When the processor executes the computer program stored in the memory, it implements the steps of the step phase inversion method of a birefringence interferometric imager as described above.

[0041] An embodiment of the present invention provides a step phase inversion method, device and equipment for a birefringence interferometric imager. Compared with the prior art, its beneficial effects are as follows:

[0042] The present invention does not need to consider the instability of the external calibration light source and the random changes of the four partitions when obtaining the interference intensity of the four partitions in the step phase inversion experiment of the birefringence interferometric imager. Specifically, by obtaining the interference intensity values of the four partitions in the experiment, and performing elliptical fitting on two combinations, using the elliptical coordinate parameters to obtain the relative intensity coefficient, instrument modulation degree, step phase and reference phase, and at the same time cyclically iterating the reference phase and the light source intensity value of the external calibration light source for inversion; when the present invention obtains the interference intensity of the four partitions, the total phase interval between a series of interference intensity values is random and unknown, without the need for external regulation and without the use of a high-precision tunable laser, greatly reducing the difficulty of step phase inversion of the birefringence interferometric imager, and making it easier to perform step phase inversion. Description of the Drawings

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

[0044] Figure 2 It is a schematic diagram of the change of the four-partition interference intensity in a single calibration scan experiment of a step phase inversion method for a birefringence interferometric imager provided by an embodiment of the present invention;

[0045] Figure 3 It is a schematic diagram of the iterative convergence process of a step phase inversion method for a birefringence interferometric imager provided by an embodiment of the present invention. Detailed Embodiments

[0046] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following provides a detailed description of the specific embodiments of the present invention with reference to the accompanying drawings. Many specific details are set forth in the following description to facilitate a thorough 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 departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

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

[0048] Step 1: Preset a set of initial values of the light source intensity .

[0049] Step 2: Combine the four-zone interference intensity values obtained in the step phase inversion experiment in pairs by partition to create a Lissajous scatter plot.

[0050] Step 3: Perform ellipse fitting on the Lissajous scatter plot. According to the elliptical geometric parameters, the relative intensity coefficient A i of the two partitions in each combination is determined by the coordinates of the ellipse center position, the instrument modulation degree U i is determined by the width and height of the ellipse, and the step phase is calculated from the zero-point coordinates of the ellipse.

[0051] Step 4: Calculate the reference phase Φ i from the obtained relative intensity coefficients A i of the four partitions, the instrument modulation degree U , the step phase , and the four-zone interference intensity values obtained in the step phase inversion experiment j .

[0052] Step 5: Update the value of the light source intensity using the following formula:

[0053]

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

[0055] Step 6: Use the relative intensity coefficients A of the four partitions obtained in Step 3 i , the instrument modulation degree U i and the step phase the reference phase Φ obtained in Step 4 j , and the light source intensity obtained in Step 5 Substitute them into the model formula to calculate a series of new four-partition interference intensity values

[0056] Step 7: Use the updated and start from Step 2 again, continuously iterate the loop until the difference ε between two adjacent loops is less than a specific value s. ε can be expressed as:

[0057]

[0058] where: k represents the iteration number label. The step phase obtained in this iteration is the final step phase inversion result

[0059] More specifically, according to the technical characteristics of the birefringence interferometric imager, the requirements for the external calibration light source are relaxed. Assume that the intensity of the external light source is unstable and the wavelength is also unstable. Therefore, in the step phase inversion experiment of the birefringence interferometric imager, the light source intensity will change with the wavelength scan and is unknown. At the same time, the responses of the four partitions to the light source intensity will also be different. The total phase intervals between a series of interference intensity values obtained for step phase inversion are all random and unknown. In a step phase inversion experiment, a total of m measurements are performed, and each measurement has n steps (since it is a static four-partition, so n = 4). Then the interference intensity of the i-th step in the j-th measurement at a certain point in the field of view is:

[0060]

[0061] where: Φ j represents the total phase (including the reference phase and the additional phase caused by the change in the light source wavelength); U i represents 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 non-linear least squares calibration model is changed to j which means that the responses of the four partitions to the light source intensity can be different. At this time, A is called the relative intensity coefficient, and i is called the light source intensity In the calibration experiment, the changes in the four-partition interference pattern obtained are as follows

[0062] ​Figure 2 As shown in the figure, a semiconductor laser with a wavelength of 1310 nm was used in the experiment, and wavelength scanning was performed by adjusting the operating current of the laser; the interference intensities of the four partitions changed irregularly with wavelength scanning, and it was impossible to directly perform cosine curve fitting. Moreover, the light source intensity changed with wavelength scanning, and the average intensities of the four partitions were also different; the step-phase inversion algorithm of the birefringence interferometric imager proposed by the present invention was insensitive to such non-smooth and irregular intensity changes and could efficiently extract the step-phase information therein.

[0063] As Figure 3 shown, the iterative convergence process of the present invention is demonstrated; the change of the calibration light source intensity with wavelength scanning was corrected during the iterative process and finally well distributed on a fitting ellipse, realizing the inversion of the step phase. The method of the present invention is more accurate in modeling the calibration experimental conditions, the model has universality, improves the accuracy of step-phase inversion of the birefringence interferometric imager, and at the same time has a certain intuitiveness and is easy to monitor abnormal conditions in the calibration experiment.

[0064] The present invention can realize step-phase inversion under the condition of unstable external calibration light source; in the existing technologies, it is required to use a high-precision tunable laser, and the experimental conditions such as temperature control are demanding; the method of the present invention can relax the requirements for the external calibration light source. At the same time, the responses of the four partitions inside the birefringence interferometric imager to the light source intensity can be different, which conforms to the actual situation of the instrument; and the basic model used in the present invention assumes that the external light source intensity is unstable and the wavelength is also unstable; in the step-phase inversion experiment of the birefringence interferometric imager, the light source intensity can change with 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. The total phase interval between a series of interference intensity values obtained for step-phase inversion can be random and unknown, there is no requirement for the step size of the laser wavelength change, and there is no need to use a high-precision tunable laser. Data can be collected by adjusting the current of an ordinary laser to complete the calibration, which greatly reduces the difficulty of step-phase inversion of the birefringence interferometric imager, avoids the error of model assumptions from the theoretical level, and improves the inversion accuracy.

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

[0066] An extraction module, configured to obtain the interference intensity values of four partitions in the step-phase inversion experiment of the birefringence interferometric imager, and combine the interference intensity values of the four partitions in pairs to construct a Lissajous scatter plot.

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

[0068] Update the initial value of the light source intensity of the external calibration light source by using the relative intensity coefficients, instrument modulation degrees, step phases, interference intensity values, and reference phase of the two partitions within each combination, and simultaneously update the interference intensity values of the four partitions.

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

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

[0071] The memory is used to store a computer program.

[0072] When the processor is used to execute the computer program stored in the memory, it realizes the steps of the above method for inverting the step phase of a birefringent interference imager.

[0073] The above embodiments only represent several implementation manners of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the invention patent should be subject to the appended claims.

Claims

1. A step phase inversion method for a birefringence interference imager, characterized in that, Including the following steps: Obtain the interference intensity values of four partitions in the step phase inversion experiment of the birefringence interferometric imager, and combine the interference intensity values of the four partitions in pairs to construct a Lissajous scatter plot; Perform elliptical fitting on the Lissajous scatter plot, determine the relative intensity coefficient, instrument modulation degree, and step phase of two partitions within each combination according to the elliptical parameters, and combine the interference intensity values of the four partitions to obtain the reference phase of the external calibration light source wavelength scan; Update the initial value of the light source intensity of the external calibration light source using the relative intensity coefficient, instrument modulation degree, step phase, interference intensity value, and reference phase of two partitions within each combination, and simultaneously update the interference intensity values of the four partitions; Iteratively cycle the reference phase of the external calibration light source wavelength scan and the light source intensity value of the external calibration light source according to the updated interference intensity values of the four partitions until the difference between the light source intensities after two updates is less than a fixed value, and output the step phase obtained in this iteration to complete the step phase inversion of the birefringence interferometric imager.

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

3. The step phase inversion method of a birefringence interference imager according to claim 1, characterized in that, The obtaining of the reference phase includes: Perform elliptical fitting on the Lissajous scatter plot, and determine the relative intensity coefficient of two partitions within each combination according to the elliptical center position coordinates; determine the instrument modulation degree according to the height and width of the ellipse; determine the step phase according to the zero point coordinates of the ellipse; According to the relative intensity coefficient, instrument modulation degree, step phase of two partitions within each combination, and the interference intensity values of the four partitions, obtain the reference phase of the external calibration light source wavelength scan; the equation for obtaining the reference phase is: in: ; Represents the interference intensity values ​​of the four partitions; Indicates the step phase; i and j represents the first step of the birefringence interferometer in the step phase inversion experiment. j The first measurement i Sub-step; Indicates the reference phase; n represents the number of steps in each measurement in the stepped phase inversion experiment; Indicates the initial step phase.

4. The step phase inversion method of a birefringence interference imager according to claim 1, characterized in that The updating of the interference intensity values of the four partitions includes: Update the initial value of the light source intensity of the external calibration light source using the relative intensity coefficient, instrument modulation degree, step phase, interference intensity values of the four partitions, and reference phase to obtain the updated light source intensity; Obtain the updated interference intensity values of the four partitions using the relative intensity coefficient, instrument modulation degree, step phase, reference phase, and updated light source intensity of two partitions within each combination.

5. A step phase inversion method for a birefringence interference imager according to claim 4, characterized in that, The equation for updating the initial value of the light source intensity of the external calibration light source is: Wherein: Represents the light source intensity; Represents the interference intensity values of four partitions; Represents the relative intensity coefficient of two partitions within each combination; Represents the instrument modulation degree; Represents the stepped phase; Represents the reference phase; n Represents the number of steps in each measurement during the stepped phase inversion experiment; i Represents the number of stepped times.

6. The step phase inversion method of a birefringence interference imager according to claim 1, characterized in that, The output of the step phase obtained in this iteration includes: In the step phase inversion experiment of a set one-time birefringence interferometric imager, a total of m measurements were carried out. There are 4 steps in each measurement, and each step corresponds to a partition. Then the interference intensity of a point in the experiment at the j th measurement and the i th step is: Wherein: Represents the interference intensity values of four partitions; Represents the light source intensity; Represents the relative intensity coefficient of two partitions within each combination; Represents the instrument modulation degree; Represents the stepped phase; Represents the reference phase; When the difference between the light source intensity values of the external calibration light source in two cyclic iterations is less than a fixed value, the step phase obtained in this cyclic iteration is the inverted step phase; The difference in light source intensity is: Wherein: represents the difference in light source intensity after two updates; k represents the iteration number tag; represents the k updated light source intensity obtained at the -th iteration; k represents the updated light source intensity obtained at the m k +1-th iteration; represents the number of measurements performed in the step phase inversion experiment.

7. A stepped phase inversion device for a birefringence interference imager, characterized in that, Including: An extraction module for obtaining the interference intensity values of four partitions in the step phase inversion experiment of the birefringence interferometric imager, and combining the interference intensity values of the four partitions in pairs to construct a Lissajous scatter plot; An inversion module, which is used to perform elliptical fitting on the Lissajous scatter plot, determine the relative intensity coefficients, instrument modulation degrees, and step phases of the two partitions within each combination according to the elliptical parameters, and combine the interference intensity values of the four partitions to obtain the reference phase for the wavelength scanning of the external calibration light source; Update the initial value of the light source intensity of the external calibration light source by using the relative intensity coefficients, instrument modulation degrees, step phases, interference intensity values, and reference phase of the two partitions within each combination, and simultaneously update the interference intensity values of the four partitions; An iterative update module, which is used to cyclically iterate the reference phase for the wavelength scanning of the external calibration light source and the light source intensity value of the external calibration light source according to the updated interference intensity values of the four partitions 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 birefringent interferometric imager.

8. An electronic device, characterized in that, It includes: A memory and a processor; The memory is used to store computer programs; When the processor is used to execute the computer programs stored in the memory, it realizes the steps of a method for step phase inversion of a birefringent interferometric imager according to any one of claims 1 to 6.

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