Polarization phase difference measurement and calibration method, and polarization phase difference measurement and calibration system

Abstract

A polarization phase difference measurement and calibration method, and a polarization phase difference measurement and calibration system (100). The polarization phase difference measurement and calibration method is based on an interference pattern acquisition apparatus (1), wherein the interference pattern acquisition apparatus (1) comprises a plurality of polarization units (121), each polarization unit (121) comprises four linear polarization micro-elements (1211), the polarization angle difference between every two adjacent linear polarization micro-elements among the four linear polarization micro-elements (1211) is 45°, and each linear polarization micro-element (1211) allows a polarized light beam of a corresponding polarization direction to pass through same, so as to form a corresponding four-frame interference pattern. The polarization phase difference measurement and calibration method comprises: acquiring a plurality of four-frame interference patterns, and determining a synthesized interference pattern from interference patterns of a corresponding frame in the four-frame interference patterns, so as to determine a four-frame synthesized interference pattern (S10); on the basis of the four-frame interference patterns, determining ellipse expressions corresponding thereto, and on the basis of the ellipse expressions, determining ellipse coefficients (S20); and on the basis of the ellipse coefficients, performing fitting to obtain an ellipse graph, and on the basis of the degree of deviation of the ellipse graph relative to a standard circle graph, determining a polarization phase difference (S30).

Description

Polarization phase difference detection calibration method and polarization phase difference detection calibration system

[0001] Related applications

[0002] This application claims priority to Chinese patent application No. 202311535327.4 filed on November 15, 2023, the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present application relates to the technical field of optical isolation detection and calibration, and in particular to a polarization phase difference detection and calibration method and a polarization phase difference detection and calibration system. Background Art

[0004] In industrial fiber lasers, optical isolators are used to protect the light source from the adverse effects of back-reflected signals. Back-reflected signal light can damage the laser, causing it to experience mode hopping, amplitude variations, or frequency shifts. The effects of this back-reflected light are particularly pronounced in high-power lasers, where it can also cause unstable output power and power spikes, potentially damaging the laser.

[0005] The current main approach to addressing the back-reflected light problem encountered by high-power lasers is to introduce an optical isolator at the output end. This utilizes the non-polarization and non-reciprocal properties of optical isolators to change the path of the back-reflected light, thereby preventing the back-reflected light from returning to the laser. In other words, the quality of the optical isolator's polarization characteristics directly affects its ability to intercept back-reflected light, and the quality of the polarization characteristics is mainly measured by the polarization difference. The existing technology lacks a method for detecting the polarization difference of optical isolators, making it difficult to evaluate the quality of optical isolators, which in turn affects the quality control of high-power lasers.

[0006] Summary of the Invention

[0007] The main purpose of this application is to propose a polarization phase difference detection calibration method and a polarization phase difference detection calibration system, aiming to solve the problem in the prior art of lacking a method for detecting the polarization phase difference of an optical isolator and difficulty in evaluating the quality of the optical isolator.

[0008] To achieve the above-mentioned purpose, the polarization phase difference detection calibration method proposed in this application is based on an interference pattern acquisition device, and the interference pattern acquisition device includes a quarter-wave plate, a polarization structure and a detection camera arranged in sequence along the light output direction of the optical isolator. The polarization structure includes multiple groups of polarization units, each of the polarization units includes four linear polarization elements, and the polarization angles of the four linear polarization elements differ by 45°. Each of the linear polarization elements can transmit a polarized light beam in the corresponding polarization direction to form a corresponding four-frame interference pattern, and the detection camera is used to detect the interference pattern.

[0009] The polarization phase difference detection and calibration method includes the following steps: obtaining multiple groups of four-frame interference patterns, and determining a synthetic interference pattern from the interference patterns of corresponding frames in each group of four-frame interference patterns to determine four-frame synthetic interference patterns; determining an ellipse expression corresponding to the four-frame synthetic interference patterns, and determining an ellipse coefficient based on the ellipse expression; fitting an ellipse figure based on the ellipse coefficient, and determining the polarization phase difference based on the degree of deviation of the ellipse figure from a standard circle figure.

[0010] In one embodiment, an ellipse expression corresponding to the four frames of interference patterns is determined, and an ellipse coefficient is determined based on the ellipse expression, including: determining a trigonometric function expression of the four frames of synthetic interference patterns, and transforming the four trigonometric function expressions to construct a corresponding ellipse expression; fitting and solving the ellipse expression using the least squares method to construct a least squares expression; and solving the first-order partial derivative of the least squares expression to obtain the ellipse coefficient.

[0011] In one embodiment, the trigonometric function expression of the synthetic interference pattern is as follows: I1=A+Bcos(φ+ε1) (1) I3=A+Bcos(φ+π+ε3) (3)

[0012] Wherein, A and B are the background intensity and modulation amplitude of the optical isolator, respectively, φ is the true phase, and ε1, ε2, ε3 and ε4 are the phase differences caused by the polarization difference of the polarization optical element.

[0013] In one embodiment, the four trigonometric expressions are transformed to construct corresponding elliptic expressions, including: transforming the trigonometric expressions (1) to (4) to eliminate the DC term A. The intermediate mathematical expression after the transformation is as follows: N = I4 - I2 = a x sinΦ (5) D=I1-I3=a y cos(Φ+ε) (6)

[0014] Among them, in the above intermediate mathematical expression,

[0015] An ellipse expression is constructed according to the intermediate mathematical expressions (5) and (6), and the ellipse expression is as follows:

[0016] In one embodiment, the elliptic expression is fitted and solved using the least squares method to construct a least squares expression, including: fitting and solving the elliptic expression (7) to construct the least squares expression as follows:

[0017] The elliptic coefficient can be obtained by solving the first-order partial derivative of the least squares expression.

[0018] In one embodiment, after the steps of fitting an ellipse figure according to the ellipse coefficients and obtaining the polarization difference according to the degree of deviation of the ellipse figure from the standard circle figure, the method further includes: correcting the polarization difference according to a correction mathematical expression to determine a correction angle;

[0019] The correction mathematical expression is as follows:

[0020] The solution formula for the correction angle is as follows:

[0021] in, Combining the elliptic coefficients, we can solve a x and a y , and then solve for θ.

[0022] In one embodiment, multiple sets of the four interference patterns are acquired using an interval sampling method. To achieve the above purpose, the polarization phase difference detection and calibration system proposed in this application is used to detect and calibrate the polarization phase difference of optical isolators. The polarization phase difference detection and calibration system includes: an interference pattern acquisition device, including a quarter-wave plate, a polarization structure, and a detection camera arranged in sequence along the light output direction of the optical isolator, the polarization structure including multiple polarization units, each of the polarization units including four linear polarization elements, the polarization angles of the four linear polarization elements differing by 45°, each of the linear polarization elements being able to transmit a polarized light beam of a corresponding polarization direction to form a corresponding four-frame interference pattern; and a detection and calibration control device electrically connected to the detection camera to quantitatively solve the polarization phase difference of the optical isolator based on the multiple sets of the four interference patterns.

[0023] In one embodiment, the detection calibration control device includes a memory, a processor, and a polarization phase difference detection calibration program stored in the memory, and the processor executes the polarization phase difference detection calibration program to implement any of the steps of the polarization phase difference detection calibration method described above.

[0024] In one embodiment, the plurality of polarization units are arranged in a rectangular array.

[0025] In the technical solution provided in the present application, the multiple groups of four-frame interference patterns obtained by the detection camera all contain polarization phase difference information of the optical isolator. Therefore, the final four-frame synthetic interference pattern can be determined by image synthesis, and these four-frame synthetic interference patterns are converted into ellipse equations and the ellipse coefficients are solved. Then, an ellipse figure is fitted according to the ellipse coefficients. Finally, the corresponding polarization phase difference can be determined according to the degree to which the ellipse figure deviates from the standard circle figure. In this way, the quantitative solution of the polarization phase difference of the optical isolator is completed, and the evaluation of the polarization characteristics of the optical isolator is realized, which is beneficial to the quality control of high-power lasers. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0027] FIG1 is a schematic diagram of the structure of an electronic device in a hardware operating environment according to an embodiment of the present application;

[0028] FIG2 is a flow chart of an embodiment of a polarization phase difference detection calibration method provided by the present application;

[0029] FIG3 is a schematic diagram of a detailed process of step S20 in FIG2 ;

[0030] FIG4 is a schematic diagram of the related structures of an interference pattern acquisition device and an optical isolator in one embodiment of a polarization phase difference detection and calibration system provided by the present application;

[0031] FIG5 is a schematic diagram of a planar structure of the polarization structure in FIG4 ;

[0032] FIG6 is an ellipse figure fitted according to the ellipse coefficient (before polarization aberration correction);

[0033] FIG7 is an ellipse figure fitted according to the ellipse coefficient (after polarization aberration correction).

[0034] Description of Figure Numbers:

[0035] The realization of the objectives, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0036] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0037] It should be noted that if directional indications are involved in the embodiments of the present application, such directional indications are only used to explain the relative positional relationship, movement status, etc. between the components under a certain specific posture. If the specific posture changes, the directional indication will also change accordingly.

[0038] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present application, the descriptions of "first", "second", etc. are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of such features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the fact that they can be implemented by ordinary technicians in this field. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by this application.

[0039] Refer to Figure 1, which is a schematic diagram of the electronic device structure of the hardware operating environment involved in the embodiment of the present application.

[0040] As shown in Figure 1, the electronic device may include: a processor 1001, such as a central processing unit (CPU), a communication bus 1002, a user interface 1003, a network interface 1004, and a memory 1005. Among them, the communication bus 1002 is used to realize the connection and communication between these components. The user interface 1003 may include a display screen (Display), an input unit such as a keyboard (Keyboard), and the user interface 1003 may also include a standard wired interface and a wireless interface. The network interface 1004 may include a standard wired interface and a wireless interface (such as a wireless fidelity (WI-FI) interface). The memory 1005 may be a high-speed random access memory (RAM) or a stable non-volatile memory (NVM), such as a disk storage. The memory 1005 may also be a storage device independent of the aforementioned processor 1001.

[0041] Those skilled in the art will appreciate that the structure shown in FIG1 does not limit the electronic device and may include more or fewer components than shown, or combine certain components, or arrange the components differently.

[0042] As shown in FIG. 1 , the memory 1005 as a storage medium may include an operating system, a network communication module, a user interface module, and a vehicle braking control program.

[0043] In the electronic device shown in Figure 1, the network interface 1004 is mainly used to connect to the external network and communicate data with other network devices; the user interface 1003 is mainly used to connect to the user device and communicate data with the user device; the electronic device of the present application calls the polarization phase difference detection calibration program stored in the memory 1005 through the processor 1001, and executes the polarization phase difference detection calibration method provided in the embodiment of the present application.

[0044] In industrial fiber lasers, optical isolators are used to protect the light source from the adverse effects of back-reflected signals. Back-reflected signal light can damage the laser, causing it to experience mode hopping, amplitude variations, or frequency shifts. The effects of this back-reflected light are particularly pronounced in high-power lasers, where it can also cause unstable output power and power spikes, potentially damaging the laser.

[0045] The current main approach to addressing the back-reflected light problem encountered by high-power lasers is to introduce an optical isolator at the output end. This utilizes the non-polarization and non-reciprocal properties of optical isolators to change the path of the back-reflected light, thereby preventing the back-reflected light from returning to the laser. In other words, the quality of the optical isolator's polarization characteristics directly affects its ability to intercept back-reflected light, and the quality of the polarization characteristics is mainly measured by the polarization difference. The existing technology lacks a method for detecting the polarization difference of optical isolators, making it difficult to evaluate the quality of optical isolators, which in turn affects the quality control of high-power lasers.

[0046] In view of this, the present application proposes a polarization phase difference detection calibration method and a polarization phase difference detection calibration system, which aim to solve the problems in the prior art of lacking a method for detecting the polarization phase difference of an optical isolator and difficulty in evaluating the quality of the optical isolator. Figure 2 is a flow chart of an embodiment of the polarization phase difference detection calibration method provided by the present application; Figure 3 is a detailed flow chart of step S20 in Figure 2; Figure 4 is a schematic diagram of the related structures of the interference pattern acquisition device and the optical isolator in an embodiment of the polarization phase difference detection calibration system provided by the present application; Figure 5 is a schematic diagram of the planar structure of the polarization structure in Figure 4; Figure 6 is an elliptical figure fitted according to the elliptical coefficient (before polarization phase difference correction); and Figure 7 is an elliptical figure fitted according to the elliptical coefficient (after polarization phase difference correction).

[0047] 4 to 7 , the polarization phase difference detection and calibration system 100 proposed in the present application is used to detect and calibrate the polarization phase difference of optical isolation. The optical isolator 200 includes a first birefringent crystal 2, a half-wave plate 3, an optical rotator 4, and a second birefringent crystal 5 arranged in sequence along the propagation direction of the laser beam. Due to the birefringence effect of the first birefringent crystal 2 itself, the laser beam incident on the first birefringent crystal 2 is split into two beams of light, one being an ordinary beam and the other being an extraordinary beam. The ordinary beam continues to propagate along a straight line, while the propagation direction of the extraordinary beam changes, deviating from the propagation direction of the incident laser beam by a certain angle. Since air is an isotropic medium, the propagation direction of the two beams of light emitted from the first birefringent crystal 2 returns to the original propagation direction, but the polarization states of the two beams of light are perpendicular to each other. The two beams of light emitted from the first birefringent crystal 2 then pass through the half-wave plate 3. The polarization directions of the two light beams emitted from the half-wave plate 3 are each rotated by 45° after entering the optical rotator plate 4. The polarization directions of the two light beams emitted from the first birefringent crystal 2 are each rotated by 90° after passing through the half-wave plate 3 and the optical rotator plate 4, respectively. That is, the ordinary light originally in the first birefringent crystal 2 becomes extraordinary light after passing through the half-wave plate 3 and the optical rotator plate 4, and the extraordinary light originally in the first birefringent crystal 2 becomes ordinary light after passing through the half-wave plate 3 and the optical rotator plate 4. The two light beams emitted from the optical rotator plate 4 have their polarization states changed, that is, rotated by 90°. After entering the second birefringent crystal 5, considering the birefringence characteristics of the second birefringent crystal 5, the two light beams are finally combined into a light beam by the second birefringent crystal 5 and emitted from the optical isolator 200. This light beam is a pair of linearly polarized lights with orthogonal polarization states and a polarization phase difference.

[0048] The polarization phase difference detection and calibration system 100 includes an interference pattern acquisition device 1 and a detection calibration control device. The interference pattern acquisition device 1 includes a quarter-wave plate 11, a polarization structure 12 and a detection camera 13 arranged in sequence along the light output direction of the optical isolator 200. The polarization structure 12 includes multiple polarization units 121, each of the polarization units 121 includes four linear polarization elements 1211, and the polarization angles of the four linear polarization elements 1211 differ by 45°. Each of the linear polarization elements 1211 can transmit a polarized light beam in the corresponding polarization direction to form a corresponding four-frame interference pattern.

[0049] The detection calibration control device is electrically connected to the detection camera 13 to quantitatively determine the polarization phase difference of the optical isolator 200 based on the four interference pattern groups.

[0050] Among them, multiple groups of four-frame interference patterns can be obtained through multiple groups of polarization units 121, and more accurate polarization phase difference information can be finally obtained by fitting through multiple groups of four-frame interference patterns, which can weaken the adverse effect of excessive deviation of individual four-frame interference patterns on the polarization phase difference information of the optical isolator 200; it can be understood that since the four-frame interference patterns already contain polarization phase difference information, the quantitative solution of the polarization phase difference from the interference pattern can be obtained by mathematical transformation in a variety of ways, and this embodiment does not limit it.

[0051] In the technical solution provided by the present application, since the light beam emitted from the optical isolator 200 is a pair of linearly polarized lights with orthogonal polarization states and polarization phase difference, the light beam is converted into a pair of left-handed circularly polarized lights after passing through the quarter-wave plate 11. Since the polarization structure 12 includes a plurality of polarization units 121, and each of the polarization units 121 is composed of four linear polarization micro-elements 1211, and the polarization angles of the four linear polarization micro-elements 1211 differ by 45° (please refer to FIG. 5, wherein the same polarization unit 12 1 includes a first linear polarization element 1211a, a second linear polarization element 1211b, a third linear polarization element 1211c, and a fourth linear polarization element 1211d. It is clear that the polarization angles of the first linear polarization element 1211a and the second linear polarization element 1211b differ by 45°, the polarization angles of the second linear polarization element 1211b and the third linear polarization element 1211c differ by 45°, and the polarization angles of the third linear polarization element 1211c and the fourth linear polarization element 1211d differ by 45°. The angle difference is 45°, and the polarization angle of the fourth linear polarization element 1211d and the first linear polarization element 1211a differs by 45°). After the pair of left-handed circularly polarized light passes through the four linear polarization elements 1211, four interference patterns are formed. The phase difference of the two adjacent interference patterns is 90°. The strength of the interference fringes in the interference pattern can reflect the polarization angle of the pair of left-handed circularly polarized light and the corresponding linear polarization element 1211. In this way, the polarization phase difference information of the optical isolator 200 can be transmitted through the four frames. The four interference patterns are shown in the form of interference patterns. The detection and calibration control device can quantitatively solve the polarization phase difference information of the optical isolator 200 contained therein by performing mathematical transformation on the four interference patterns. This ultimately solves the problem of the lack of a method for detecting the polarization phase difference of the optical isolator 200 in the prior art, and achieves an in-depth evaluation of the quality of the optical isolator 200. As a result, the optical isolator 200 with excellent polarization characteristics can be selected for use in high-power lasers, thus achieving quality control of the high-power laser.

[0052] Since the polarization structure 12 includes a plurality of polarization units 121, there are various ways to arrange the plurality of polarization units 121, for example, they can be arranged linearly or in a circular array. In the present embodiment, the plurality of polarization units 121 are arranged in a rectangular array. Such an arrangement is more conducive to the dense arrangement of the plurality of polarization units 121, making it easier for the laser beam to pass through the plurality of polarization units 121, thereby presenting a plurality of four-frame interference patterns. At the same time, such a dense array arrangement is conducive to the miniaturization of the polarization structure 12.

[0053] In this embodiment, the detection calibration control device includes a memory, a processor, and a polarization phase difference detection calibration program stored in the memory. The processor executes the polarization phase difference detection calibration program to implement the steps of the polarization phase difference detection calibration method provided in this application.

[0054] Please refer to Figures 2 to 3. The polarization phase difference detection calibration method is based on an interference pattern acquisition device 1. The interference pattern acquisition device 1 includes a quarter-wave plate 11, a polarization structure 12 and a detection camera 13 arranged in sequence along the light output direction of the optical isolator 200. The polarization structure 12 includes multiple groups of polarization units 121, each of the polarization units 121 includes four linear polarization elements 1211, and the polarization angles of the four linear polarization elements 1211 differ by 45°. Each linear polarization element 1211 can transmit a polarized light beam in the corresponding polarization direction to form a corresponding four-frame interference pattern. The detection camera 13 is used to detect the interference pattern.

[0055] The polarization phase difference detection calibration method comprises the following steps:

[0056] S10 , obtaining multiple groups of the four-frame interference patterns, and synthesizing interference patterns of corresponding frames in each group of the four-frame interference patterns to determine four-frame synthesized interference patterns.

[0057] Among them, the detection camera 13 can detect multiple groups of four interference patterns, each group of four interference patterns is formed by the corresponding polarization unit 121. Multiple groups of four interference patterns can be formed by multiple groups of polarization units 121, and each group of four interference patterns includes four separate interference patterns with a phase difference of 90° between each other. The interference patterns of corresponding frames in the multiple groups of four interference patterns can be synthesized into one synthetic interference pattern through image processing to finally obtain four synthetic interference patterns. The synthetic interference pattern is closer to the real interference pattern than a single interference pattern. Therefore, it can better contain the real polarization phase difference information of the optical isolator 200.

[0058] S20 , determining an ellipse expression corresponding to the four frames of synthetic interference patterns, and determining an ellipse coefficient according to the ellipse expression.

[0059] Among them, the corresponding ellipse expression can be determined according to the four-frame synthetic interference pattern through data conversion, and the ellipse coefficient can be solved by formula transformation of the ellipse expression. There can be many forms of data conversion and company transformation methods, which are not limited in this embodiment, as long as the polarization phase difference information contained in the four-frame synthetic interference pattern can be expressed in the form of a formula or coefficient.

[0060] S30 , fitting an ellipse figure according to the ellipse coefficients, and determining the polarization difference according to the degree of deviation of the ellipse figure from a standard circle figure.

[0061] Among them, the elliptical figure fitted according to the elliptical coefficient is the graphical manifestation of the polarization difference, and the standard circle figure is the one without polarization difference. The degree of deviation of the elliptical figure from the standard circle figure can determine the size of the polarization difference, that is, the flatter the elliptical figure, the greater the polarization difference, and the closer the elliptical figure is to a circle, the smaller the polarization difference. There is a certain intrinsic relationship between the two, which will not be elaborated in this embodiment.

[0062] In the technical solution provided in the present application, the multiple groups of four-frame interference patterns obtained by the detection camera 13 all contain the polarization phase difference information of the optical isolator 200. Therefore, the final four-frame synthetic interference pattern can be determined by image synthesis, and these four-frame synthetic interference patterns are converted into an ellipse equation and the ellipse coefficient is solved. Then, an ellipse figure is fitted according to the ellipse coefficient. Finally, the corresponding polarization phase difference can be determined according to the degree to which the ellipse figure deviates from the standard circle figure. In this way, the quantitative solution of the polarization phase difference of the optical isolator 200 is completed, and the evaluation of the polarization characteristics of the optical isolator 200 is realized, which is beneficial to the quality control of high-power lasers.

[0063] Referring to FIG. 3 , in this embodiment, the ellipse expression corresponding to the four interference patterns is determined according to the four interference patterns, and the ellipse coefficient is determined according to the ellipse expression, including:

[0064] S21. Determine trigonometric function expressions of the four frames of synthetic interference patterns, and transform the four trigonometric function expressions to construct corresponding ellipse expressions; wherein the ellipse expressions can be conveniently constructed through trigonometric function expressions.

[0065] S22. Fitting and solving the ellipse expression by using the least square method to construct a least square expression; wherein, by constructing the least square expression, it is convenient to solve the ellipse coefficient.

[0066] S23. Solve the first-order partial derivative of the least squares expression to obtain the elliptic coefficient. In order to fit the optimal solution using the least squares method, it is necessary to find the minimum value of the formula. The minimum value occurs where the first-order partial derivative is zero. Therefore, the first-order partial derivative of the least squares expression is solved and set to 0 to obtain the elliptic coefficient.

[0067] In some embodiments, the trigonometric function expression of the synthetic interference pattern is as follows: I1=A+Bcos(φ+ε1) (1) I3=A+Bcos(φ+π+ε3) (3)

[0068] Wherein, A and B are the background intensity and modulation amplitude of the optical isolator 200, respectively; φ is the true phase; ε1, ε2, ε3 and ε4 are the phase differences caused by the polarization difference of the polarization optical element.

[0069] In some embodiments, the four trigonometric expressions are transformed to construct corresponding elliptic expressions, including: transforming the trigonometric expressions (1) to (4) to eliminate the DC term A, and the intermediate mathematical expression after the transformation is as follows: N = I4 - I2 = a x sinΦ (5) D=I1-I3=a y cos(Φ+ε) (6)

[0070] Among them, in the above intermediate mathematical expression,

[0071] An elliptic expression is constructed according to the intermediate mathematical expressions (5) and (6), and the elliptic expression is as follows:

[0072] Considering that the detection camera 13 acquires multiple sets of four-frame interference patterns, and the detection calibration control device can acquire multiple sets of trigonometric function expressions (four trigonometric function expressions converted from the same set of four-frame interference patterns constitute one set), that is, a series of different N and D can be acquired. In some embodiments, the least squares method is used to fit and solve the ellipse expression to construct a least squares expression, including:

[0073] The ellipse expression (7) is fitted and solved to construct the least squares expression as follows:

[0074] The elliptic coefficient can be obtained by solving the first-order partial derivative of the least squares expression.

[0075] If the least squares expression (8) is to be fitted to the optimal solution, it is necessary to solve the minimum value of w. Considering that the minimum value appears where the first-order partial derivative is zero, the first-order partial derivative of the least squares expression (8) is solved and set to zero, and then the ellipse coefficient can be solved. According to the ellipse coefficient, an ellipse figure as shown in FIG6 can be fitted. At this time, the ellipse figure deviates greatly from the standard circle figure, and the polarization difference it reflects is also large.

[0076] Through analysis, it can be seen that the optical isolator 200 is generally composed of a first birefringent crystal 2, a half-wave plate 3, an optical rotator 4 and a second birefringent crystal 5. The causes of polarization difference generally include: (1) quality defects of the half-wave plate 3 and its direction error; (2) quality defects of the optical rotator 4 and its direction error; (3) quality defects of the birefringent crystal and errors caused by assembly. Analysis shows that the errors caused by the quality defects of the above optical components themselves cannot be changed, but the directions of the half-wave plate 3 and the optical rotator 4 can be adjusted to correct the polarization difference. In view of this, in some embodiments, after the step of fitting an elliptical figure according to the elliptical coefficient and obtaining the polarization difference according to the degree of deviation of the elliptical figure from the standard circular figure, the following steps are also included:

[0077] Correcting the polarization phase difference according to a correction mathematical expression to determine a correction angle;

[0078] The correction mathematical expression is as follows:

[0079] The solution formula for the correction angle is as follows:

[0080] in, Combining the elliptic coefficients, we can solve a x and a y , and then solve for θ.

[0081] By solving the ellipse coefficient, we can get the size of the major axis and minor axis of the ellipse, that is, a x with a y The magnitude of the polarization difference can also be determined, and the direction of the polarization difference can also be known. By solving the correction mathematical expression, the correction angle θ can be determined. By adjusting the half-wave plate 3 and / or the optical rotator 4 by an angle θ along the correction direction of the obtained polarization difference, the polarization difference of the optical isolator 200 can be corrected, thereby improving the performance of the optical isolator 200 in intercepting back-reflected light.

[0082] Please refer to Figures 6 and 7. In Figure 6, the phase difference is not calibrated, and the elliptical figure deviates greatly from the standard circle figure. x and a yThe correction direction of the polarization difference can also be reflected. In FIG7 , the polarization difference is corrected, that is, the optical rotator 4 or the half-wave plate 3 of the optical isolator 200 is adjusted according to the correction angle θ and the known correction direction. The polarization difference after correction is finally reflected as a graph close to a circle as shown in FIG7 , which means that the polarization difference is suppressed and the polarization difference is small at this time.

[0083] In this embodiment, the four interference patterns of the plurality of groups are acquired by using an interval sampling method, which can reduce the sampling amount and the pressure on the detection and calibration control device to process the graphics, while ensuring the representativeness of the graphics data.

[0084] Furthermore, as used herein, the terms "comprises," "comprising," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or system that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or system. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not preclude the presence of additional identical elements in the process, method, article, or system that includes the element.

[0085] The serial numbers of the above embodiments of the present application are for description only and do not represent the advantages or disadvantages of the embodiments.

[0086] Through the description of the above embodiments, those skilled in the art can clearly understand that the above embodiment methods can be implemented by means of software plus the necessary general hardware platform, or of course by hardware, but in many cases the former is a better embodiment. Based on this understanding, the technical solution of the present application, or the part that contributes to the prior art, can be embodied in the form of a software product, which is stored in a storage medium (such as a read-only memory (ROM) / RAM, a magnetic disk, or an optical disk), and includes a number of instructions for enabling a terminal device (which can be a mobile phone, a computer, a server, or a network device, etc.) to execute the methods described in each embodiment of the present application.

[0087] The above are only some embodiments of the present application and are not intended to limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A polarization phase difference detection calibration method based on an interference pattern acquisition device, wherein: The interference pattern acquisition device includes a quarter wave plate, a polarization structure and a detection camera which are sequentially arranged along the light output direction of the optical isolator, the polarization structure includes a plurality of polarization units, each of the polarization units includes four linear polarization micro-elements, the polarization angles of the four linear polarization micro-elements differ by 45°, each of the linear polarization micro-elements can transmit a polarized light beam in a corresponding polarization direction to form corresponding four-frame interference patterns, and the detection camera is used to detect the interference pattern; The polarization phase difference detection calibration method comprises the following steps: Acquire multiple groups of the four-frame interference patterns, and determine a synthetic interference pattern from the interference patterns of the corresponding frames in each group of the four-frame interference patterns to determine four-frame synthetic interference patterns; Determine an ellipse expression corresponding to the four frames of synthetic interference patterns, and determine an ellipse coefficient according to the ellipse expression; and An ellipse figure is fitted according to the ellipse coefficients, and the polarization difference is determined according to the degree of deviation of the ellipse figure from a standard circle figure.

2. The polarization phase difference detection calibration method according to claim 1, wherein: Determining an ellipse expression corresponding to the four interference patterns according to the four interference patterns, and determining an ellipse coefficient according to the ellipse expression, including: Determine the trigonometric function expressions of the four frames of synthetic interference patterns, and transform the four trigonometric function expressions to construct corresponding elliptical expressions; The elliptic expression is fitted and solved by the least square method to construct a least square expression; and the first-order partial derivative of the least square expression is solved to obtain the elliptic coefficient.

3. The polarization phase difference detection calibration method according to claim 2, wherein: The trigonometric function expression of the synthetic interference pattern is as follows: I1=A+Bcos(φ+ε1) (1) I3=A+Bcos(φ+π+ε3) (3) Wherein, A and B are the background intensity and modulation amplitude of the optical isolator respectively, φ is the real phase, and ε1, ε2, ε3 and ε4 are the phase differences caused by the polarization phase difference of the polarization optical element.

4. The polarization phase difference detection calibration method according to claim 3, wherein: The four trigonometric function expressions are transformed to construct corresponding ellipse expressions, including: The trigonometric function expressions (1) to (4) are transformed to eliminate the DC term A. The intermediate mathematical expressions after the transformation are as follows: N=I4-I2=a x sinΦ (5) D=I1-I3=a y cos(Φ+ε) (6) Among them, in the above intermediate mathematical expression, An elliptic expression is constructed based on the intermediate mathematical expressions (5) and (6), wherein the elliptic expression as follows:

5. The polarization phase difference detection calibration method according to claim 4, wherein: The elliptic expression is fitted and solved by using the least square method to construct a least square method expression, including: The elliptic expression (7) is fitted and solved to construct the least squares expression as follows: The elliptic coefficient can be obtained by solving the first-order partial derivative of the least squares expression.

6. The polarization phase difference detection calibration method according to claim 5, wherein: After the step of fitting an ellipse figure according to the ellipse coefficient and obtaining the polarization difference according to the degree of deviation of the ellipse figure from the standard circle figure, the method further includes: The polarization phase difference is corrected according to a correction mathematical expression to determine a correction angle; The correction mathematical expression is as follows: The solution formula for the correction angle is as follows: in, Combining the elliptic coefficients, we can solve for a x and a y , and then solve for θ.

7. The polarization phase difference detection calibration method according to any one of claims 1 to 6, wherein: The multiple groups of the four-frame interference patterns are acquired by using an interval sampling method.

8. A polarization phase difference detection and calibration system, used for detecting and calibrating the polarization phase difference of optical isolation, wherein: The polarization phase difference detection calibration system comprises: An interference pattern acquisition device, comprising a quarter wave plate, a polarization structure and a detection camera arranged in sequence along the light output direction of the optical isolator, wherein the polarization structure comprises a plurality of polarization units, each of the polarization units comprises four linear polarization micro-elements, the polarization angles of the four linear polarization micro-elements differ by 45°, and each of the linear polarization micro-elements can transmit a polarized light beam in a corresponding polarization direction to form corresponding four-frame interference patterns; and The detection calibration control device is electrically connected to the detection camera to quantitatively solve the polarization phase difference of the optical isolator according to multiple groups of the four-frame interference patterns.

9. The polarization phase difference detection calibration system according to claim 8, wherein: The detection calibration control device comprises a memory, a processor and a polarization phase difference detection calibration program stored in the memory, and the processor executes the polarization phase difference detection calibration program to implement the steps of the polarization phase difference detection calibration method according to any one of claims 1 to 7.

10. The polarization phase difference detection calibration system according to claim 8, wherein: The plurality of polarization units are arranged in a rectangular array.

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