MZI (Mach Zehnder Interference) structure not influenced by polarization state of input light and adjusting method thereof

Abstract

The invention discloses an MZI structure not influenced by the polarization state of input light and an adjusting method thereof, and the method comprises the steps: carrying out the vibration reduction packaging of an MZI, and integrating an optical fiber polarization controller on one arm; stokes vectors of incident light and emergent light are measured by using a polarization analyzer, a rotation matrix of each part of a light path is fitted through a singular value decomposition method, and an optical fiber polarization controller is adjusted according to a result, so that polarization rotation transformation of two arms is consistent; polarization conversion of two arms of the interferometer is equivalent to rotation of a Stokes vector on a Poincare sphere around an axis. According to the method, MZI adjustment is carried out based on the polarization rotation transformation characteristic of the light path in the Stokes space, the problem of interference signal amplitude fluctuation caused by incident light polarization state change is solved through one-time calibration, complex electric feedback control is avoided, the system stability and reliability are remarkably improved, and the method is suitable for optical fiber sensing and related fields.

Description

Technical Field

[0001] The present invention relates to the technical field of fiber optic sensing, and particularly to an MZI structure that is not affected by the polarization state of the input light and its adjustment method. Background Art

[0002] Fiber optic sensing technology has been around for nearly fifty years since its inception. Its basic principle is to detect the change in characteristic parameters of the optical signal in the fiber caused by external environmental changes, so as to realize the detection and perception of external disturbances. As an important fiber optic sensor device, the Mach-Zehnder interferometer (MZI) has been widely used in the fields of high-precision measurement and high-sensitivity sensing.

[0003] However, fiber optic interference systems often face the problem of random changes in the polarization state of the input light. For example, factors such as unstable polarization state of the light source, external environmental changes, and mechanical vibrations. The change in the polarization state of the input light will cause random fluctuations in the polarization state of the light propagating in the MZI. This kind of fluctuation will cause the inconsistency of the polarization directions of the light emerging from the two arms, and the interference phenomenon requires the polarization directions of the two optical signals to be consistent. Therefore, the random change in the polarization state will significantly reduce the visibility of the interference signal, manifested as the fluctuation of the interference signal amplitude. When the polarization states of the two interfering lights are completely orthogonal, the amplitude of the interference signal will drop to zero, resulting in the so-called "polarization fading" phenomenon, which will seriously affect the performance and stability of the system.

[0004] Although polarization-maintaining fibers can limit the change in the polarization state in the fiber, the MZI structure composed of all polarization-maintaining fibers has a high cost. In addition, when the polarization state of the input light changes randomly, the all-polarization-maintaining structure will lose its function of maintaining the polarization state. Moreover, in order to achieve specific functions (such as measuring line width, introducing frequency shift, etc.), it is necessary to insert a long fiber or other optical devices, resulting in the inability to use the polarization-maintaining structure. The other main technologies adopted are the polarization diversity scheme and the electrical feedback polarization controller scheme. The polarization diversity scheme uses a polarization beam splitter and multiple receivers to receive signals of different polarization states, but this scheme not only greatly increases the cost of the system, but also brings additional system complexity. The electrical feedback polarization controller scheme realizes the stability of the system by adjusting the polarization state in real time, but this scheme also leads to an increase in the hardware complexity and cost of the system, and it is difficult to cope with when the polarization state changes very quickly.

[0005] Therefore, developing an MZI that is not affected by the polarization state of the input light and has the characteristics of low cost and easy maintenance is of great significance for improving the performance, stability and reliability of the system. Summary of the Invention

[0006] The problems to be solved by the present invention are as follows: to provide an MZI structure that is not affected by the polarization state of the input light and its adjustment method, so that the MZI structure is not affected by the change of the polarization state of the input light, and effectively suppress the problem of the amplitude fluctuation of the interference signal caused by the random change of the polarization state of the input light.

[0007] The present invention adopts the following technical solutions: an MZI structure that is not affected by the polarization state of the input light, which is characterized by comprising: a first coupler, an optical device X, a first polarization controller, an optical device Y, and a second coupler.

[0008] The optical signal enters the MZI structure through the incident end of the first coupler and is divided into two optical signals A1 and A2 by the first coupler; the optical signal of the A1 path enters the input end of the second coupler after passing through the optical device X and the first polarization controller in sequence, and the optical signal of the A2 path enters the input end of the second coupler after passing through the optical device Y; and they are combined into one path for output by the second coupler.

[0009] Preferably, both the sensing optical fiber and the transmission optical fiber used in the optical path of the MZI structure are ordinary single-mode optical fibers; the optical device X and the optical device Y are single or serially combined delay optical fibers, frequency shifters, and optical amplifiers.

[0010] The technical solution of the present invention also provides: an adjustment method for an MZI structure that is not affected by the polarization state of the input light, which is applied to the above MZI structure and comprises the following steps:

[0011] S1. Fix the MZI structure in a heat-insulating and vibration-damping box, and connect a second polarization controller to the input end of the MZI structure;

[0012] S2. Disconnect the optical signal of the A1 path of the MZI structure, adjust the second polarization controller to change the polarization state of the incident light, and record the Stokes vectors of the input light and the output light of the MZI through a polarization analyzer; according to the combination of the Stokes vectors of the input light and the output light of the MZI, fit out the rotation matrix R of the optical signal of the A2 path by the singular value decomposition method A2 ;

[0013] S3. Disconnect the optical signal of the A2 path, connect the optical signal of the A1 path, adjust the second polarization controller to change the polarization state of the incident light, and record the Stokes vectors of the input light, the output light of the MZI, and the output light after the first polarization controller through a polarization analyzer;

[0014] According to the combination of the Stokes vectors of the input light of the MZI and the output light after the first polarization controller, fit out the rotation matrix R of the optical signal of the A1 path from the first coupler to the optical path of the first polarization controller by the singular value decomposition method A1前 ;

[0015] According to the combination of the Stokes vectors of the output light after the first polarization controller and the output light of the MZI, the rotation matrix R of the optical path of the optical signal on the A1 path from the first polarization controller to the second coupler is fitted by the singular value decomposition method. A1后 ;

[0016] S4. Based on the obtained rotation matrix R A1前 , R A1后 and R A2 , solve the target rotation matrix R 目标 of the first polarization controller, so that the overall rotation matrix R' A1 of the optical signal on the A1 path is equal to R A2 ;

[0017] Adjust the first polarization controller until the equivalent rotation axis f PC in the Stokes space and the equivalent rotation angle θ PC are the same as R 目标 , so that the polarization rotation transformation of the optical signals on the A1 and A2 paths is consistent;

[0018] S5. After the adjustment is completed, remove the second polarization controller and the polarization analyzer, and restore the MZI structure to the normal state.

[0019] Preferably, the internal filling of the heat insulation and vibration damping box is a high-density heat insulation sponge, which has the dual functions of vibration damping and heat insulation, and is used to reduce the influence of environmental temperature changes and mechanical vibrations on the stability of the interferometer.

[0020] Preferably, the Stokes space system is described by the Stokes vector S = [S0, S1, S2, S3] T , which describes the intensity and polarization characteristics of the light beam. The relationship between each Stokes parameter and the light field intensity is as follows:

[0021]

[0022] where E x , E y respectively represent the components of the light field in the x and y directions, and δ is the phase delay amount between the two orthogonal components; S0 represents the total light intensity, S1 describes the intensity difference between the linearly polarized states in the 0° and 90° directions, S2 describes the intensity difference between the linearly polarized states in the 45° and 135° directions, and S3 reflects the intensity difference between the right-handed and left-handed circularly polarized components.

[0023] The physical essence of the rotation matrix is to describe the direction of the polarization state rather than the change in light intensity. Therefore, the rotation transformation of the polarization state is only reflected in the dimensions of S1, S2, and S3, and only S1, S2, and S3 are required to completely describe the rotation axis and the rotation angle.

[0024] The three-dimensional space composed of S1, S2, and S3 is called the Stokes space, and the Mueller matrix is used to describe the polarization device in the Stokes space:

[0025]

[0026] where m ij represents the matrix element of the Mueller matrix M, i = 1, 2,..., 4, j = 1, 2,..., 4.

[0027] The effect of the device on the polarization state of light can be regarded as left - multiplying the Stokes vector of light by the Mueller matrix of the device. For a lossless polarization - transforming device, its Mueller matrix has the following form:

[0028]

[0029] Therefore, a 3×3 Mueller matrix R 3×3 can be used to describe it. When light passes through a polarization device, the effect of the device on the polarization state of light can be regarded as applying a rotation transformation to this point in Stokes space. The effect of the polarization device can be represented as a rotation around a certain axis of the Poincaré sphere, that is, the Mueller matrix of the polarization device can be equivalent to a rotation matrix in Stokes space.

[0030] Preferably, the rotation matrix of the optical path can be calculated through the following steps:

[0031] S2.1. Adjust the second polarization controller, and use a polarization analyzer to measure the Stokes vectors of at least three groups of input and output polarization state combinations of this section of the optical path. The three groups of input lights are respectively denoted as b1, b2, and b3, and the corresponding output lights are respectively denoted as w1, w2, and w3:

[0032]

[0033] where b ij represents the Stokes parameter of the input light, and w ij represents the Stokes parameter of the output light;

[0034] S2.2. Take the input - output Stokes vectors as column vectors respectively and combine them into a matrix:

[0035]

[0036] S2.3. Calculate the covariance matrix H:

[0037] H = WB T

[0038] Perform singular - value decomposition on the covariance matrix H to obtain:

[0039]

[0040] where U and V svdis an orthogonal matrix, Σ is a diagonal matrix of singular values, and the orthogonal matrices U and V svd The column vectors of respectively correspond to the left and right singular vectors of the covariance matrix.

[0041] Based on the result of singular value decomposition, calculate the rotation matrix R:

[0042] R = V svd U T .

[0043] Preferably, both the first polarization controller and the second polarization controller are three-ring fiber polarization controllers, and the phase delay amounts of the three fiber rings of the three-ring fiber polarization controller are π / 2, π, and π / 2 respectively.

[0044] In the Stokes space, the action of a polarization device on the polarization state of light can be regarded as left-multiplying the Stokes vector of the light by the Mueller matrix of the device, and can be equivalently represented as a rotation around an axis of the Poincaré sphere in the Stokes space. When polarization-dependent loss is ignored, the Mueller matrix of a polarization device can be equivalent to a rotation matrix in the Stokes space.

[0045] Therefore, the rotation matrix R of the three-ring fiber polarization controller PC can be expressed as:

[0046] R PC (θ1,θ2,θ3) = M QWP (θ3)M HWP (θ2)M QWP (θ1)

[0047] where θ1, θ2, and θ3 are the angles of the three fiber rings of the three-ring fiber polarization controller respectively, and M QWP (θ1), M QWP (θ2), M QWP (θ3) are the Mueller matrices of the first, second, and third fiber rings of the three-ring fiber polarization controller respectively, and the expressions are respectively:

[0048]

[0049] The Stokes space equivalent rotation angle θ of the three-ring fiber polarization controller can be calculated PC and the equivalent rotation axis f PC :

[0050]

[0051] where tr(R PC (θ1,θ2,θ3)) = R 11 + R 22 + R 33 is the rotation matrix R PCTrace of R ij Denote R PC as the matrix elements of R

[0052] Before the experiment starts, the angles of the three fiber loops of the first polarization controller need to be adjusted to the same value. At this time, the polarization state of the light passing through the first polarization controller will not change.

[0053] Preferably, the adjustment process of the first polarization controller includes the following steps:

[0054] S4.1. Based on the rotation matrices R A1前 , R A1后 and R A2 , calculate the target state of the first polarization controller to make the rotation matrix R' A1 of path A1 equal to R A2 :

[0055] R′ A1 = R A1后 R 目标 R A1前 = R A2

[0056] Thus, determine the target rotation matrix R 目标 :

[0057]

[0058] Decompose the target rotation matrix R 目标 into the equivalent rotation angle θ 目标 and the equivalent rotation axis f 目标 :

[0059]

[0060]

[0061] where tr(R 目标 ) = R 11 + R 22 + R 33 is the trace of the rotation matrix.

[0062] S4.2. By the least squares method, find the adjustment angles θ1, θ2, and θ3 of the three fiber loops of the first polarization controller to make the equivalent rotation axis and equivalent rotation angle of the first polarization controller after adjustment consistent with the target.

[0063] Establish a multi-dimensional residual function:

[0064] F(θ1, θ2, θ3) = [Δf; Δθ]

[0065] where Δf = f PC(θ1, θ2, θ3)-f 目标 is the residual between the Stokes space equivalent rotation axis of the first polarization controller and the target equivalent rotation axis, Δθ = θ PC (θ1, θ2, θ3)-θ 目标 is the residual between the Stokes space equivalent rotation angle of the first polarization controller and the target equivalent rotation angle. Select appropriate initial angles and tolerances to minimize the residual norm to obtain the optimal θ1, θ2, and θ3.

[0066] S4.3. According to the calculated angles, adjust the three fiber loops of the first polarization controller to make the polarization rotation transformations of the A1 and A2 paths consistent.

[0067] The technical solution of the present invention also provides: an electronic device, including:

[0068] one or more processors;

[0069] a storage device storing one or more programs thereon;

[0070] When the one or more programs are executed by the one or more processors, the one or more processors implement the MZI structure adjustment method that is not affected by the input light polarization state described above.

[0071] The technical solution of the present invention also provides a computer-readable storage medium storing a computer program, and when the program is executed by a processor, it implements the steps in any of the above MZI structure adjustment methods that are not affected by the input light polarization state.

[0072] Compared with the prior art, the present invention adopts the above technical solutions and has the following technical effects:

[0073] 1. The MZI structure of the present invention adjusts according to the polarization rotation transformation characteristics of the optical path in the Stokes space, can adapt to the change of the input polarization state, avoid polarization fading caused by the change of the input light polarization state, and significantly improve the stability and reliability of the system.

[0074] 2. The MZI structure of the present invention, compared with the control method based on an electrically feedback polarization controller, completes the polarization state optimization in one adjustment, without complex electrical feedback control, avoids the noise brought by electrical switching, and has lower insertion loss;

[0075] 3. The MZI structure of the present invention, compared with the polarization diversity scheme that requires a polarization beam splitter and multiple receivers, only requires ordinary single-mode fibers and one fiber polarization controller, greatly reducing the cost of the system. Description of the Drawings

[0076] Figure 1It is the block diagram of the MZI structure of the present invention that is not affected by the polarization state of the input light;

[0077] Figure 2 It is the flowchart of the MZI adjustment method of the present invention that is not affected by the polarization state of the input light;

[0078] Figure 3 It is the optical path diagram of the MZI structure adjustment process of the present invention that is not affected by the polarization state of the input light;

[0079] Figure 4 It is the Stokes parameters of the polarization state detected by the polarization analyzer in the embodiment of the present invention and its representation on the Poincaré sphere;

[0080] Figure 5 It is the amplitude change of the interference signal when adjusting the first polarization controller before adjusting the polarization rotation vector in the embodiment of the present invention;

[0081] Figure 6 It is the amplitude change of the interference signal when adjusting the first polarization controller after adjusting the polarization rotation vector in the embodiment of the present invention. Detailed implementation manners

[0082] In order to make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the application will be further elaborated in detail below with reference to the accompanying drawings. The described embodiments are only a part of the embodiments involved in the present invention. All non-innovative embodiments made by other researchers in the field based on this embodiment belong to the protection scope of the present invention. At the same time, for the step numbers in the embodiments of the present invention, they are only set for the convenience of elaboration and explanation, and no limitation is imposed on the order between the steps. The execution order of each step in the embodiment can be adaptively adjusted according to the understanding of those skilled in the art.

[0083] Embodiment 1

[0084] First, build a Mach-Zehnder interferometer according to the Figure 1 structure shown. The devices in the optical path include: the first coupler 1, the optical device X2, the first polarization controller 3, the optical device Y4, and the second coupler 5.

[0085] The optical signal enters the MZI through the incident end of the first coupler 1 and is split into two paths by the first coupler 1. The A1 path passes through the optical device X2 and the first polarization controller 3, and the A2 path passes through the optical device Y4, and finally is combined into one path and output by the second coupler 5.

[0086] Both the sensing optical fiber and the transmission optical fiber used in the optical path are non-polarization-maintaining single-mode optical fibers. In this embodiment, the optical device X2 is a delay optical fiber with a length of 2.5 meters, and the optical device Y4 is an acousto-optic modulator.

[0087] After the optical path is built, according toFigure 2 The process shown is referred to Figure 3 the optical path structure to measure and adjust the rotation matrix. The specific steps are as follows:

[0088] Step 1: As shown in (a) of Figure 3 , connect the second polarization controller 6 to the input end of the MZI structure, and fix the MZI structure in a damping box filled with high-density heat-insulating sponge to ensure that the system is protected from mechanical vibration and environmental temperature fluctuations.

[0089] Step 2: As shown in (b) of Figure 3 , disconnect the A1 path of the MZI and keep the A2 path connected.

[0090] Adjust the second polarization controller 6 to generate three different input polarization states, and use the polarization analyzer 7 to measure the input polarization state and the corresponding output polarization state, denoted as:

[0091]

[0092] The interface of the polarization analyzer, as shown in Figure 4 , the middle is the representation of the polarization state on the Poincaré sphere, and the S1, S2, and S3 values on the right are the Stokes parameters of the current light.

[0093] Take the input and output Stokes vectors as column vectors respectively and combine them into a matrix:

[0094]

[0095] First, calculate the covariance matrix H A2 :

[0096]

[0097] Perform singular value decomposition on the covariance matrix to obtain:

[0098]

[0099] Obtain the rotation matrix R A2 :

[0100]

[0101] Step 3: As shown in (c) of Figure 3 , disconnect the A2 path and connect the A1 path, and use the polarization analyzer 7 to record the polarization states of the input and output light of the MZI and the output light after the first polarization controller 3, denoted as:

[0102]

[0103] Take the input and output Stokes vectors as column vectors respectively and combine them into a matrix:

[0104]

[0105] Similar to Step 2, use the SVD method to fit the rotation matrices R of the first half and the second half of the A1 path A1前 and R A1后 :

[0106]

[0107] Step 4: Calculate the target rotation matrix R of the first polarization controller 3 when the two-channel rotation matrices are equal through the two-channel current rotation matrices 目标 :

[0108]

[0109] Calculate the equivalent rotation axis f of the Stokes space of the target rotation matrix 目标 and the equivalent rotation angle θ 目标 , and obtain:

[0110]

[0111] θ 目标 = 59.3081°

[0112] Define the rotation matrix R of the first polarization controller (3) PC :

[0113] R PC (θ1, θ2, θ3) = M QWP (θ3)M HWP (θ2)M QWP (θ1)

[0114] where θ1, θ2, and θ3 are the angles of the three fiber loops of the three-ring fiber polarization controller respectively, and M QWP (θ1), M QWP (θ2), M QWP (θ3) are the Mueller matrices of the first, second, and third fiber loops of the three-ring fiber polarization controller respectively, and their expressions are respectively:

[0115]

[0116] Use the least squares optimization method to find the angles of the three fiber loops of the first polarization controller 3 that satisfy the target rotation axis and rotation angle, and establish a multi-dimensional residual function:

[0117] F(θ1, θ2, θ3) = [Δf; Δθ]

[0118] where Δf = f PC (θ1, θ2, θ3) - f 目标is the residual between the Stokes space equivalent rotation axis of the first polarization controller 3 and the target equivalent rotation axis, Δθ = θ PC (θ1, θ2, θ3) - θ 目标 is the residual between the Stokes space equivalent rotation angle of the first polarization controller 3 and the target equivalent rotation angle.

[0119] Select the initial angles θ1 = 0°, θ2 = 0°, θ3 = 0°, set the tolerance ε < 1e - 6, and use the algorithm to iteratively update the angles until the residual norm is less than the tolerance, and the results are obtained:

[0120] θ1 = 26.2708°, θ2 = 22.5371°, θ3 = 1.6828°

[0121] Adjust the first polarization controller 3 according to the calculation results to make the polarization rotation transformation of the two paths of the MZI consistent.

[0122] Step Five: To reflect the adjustment effect, after the adjustment is completed, remove the polarization analyzer 7, connect a narrow linewidth light source 8 at the input end, and connect a photodetector 9 at the output end, as Figure 3 shown in (d) of.

[0123] Adjust the second polarization controller 6 to change the polarization state of the light input to the MZI, and record the amplitude changes of the interference signals output by the optical path before and after the adjustment respectively.

[0124] As Figure 5 and Figure 6 shown, without the rotation matrix adjustment, the change in the polarization state of the input light will cause a large fluctuation in the amplitude of the interference signal. After the polarization rotation vector adjustment, the range of the amplitude change of the interference signal is significantly reduced.

[0125] Step Six: As Figure 3 shown in (e) of, remove the narrow linewidth light source 8, the second polarization controller 6, and the photodetector 9 in the optical path, and restore the system to the normal working state.

[0126] In an embodiment of the present invention, an electronic device is further provided, including: one or more processors; a storage device on which one or more programs are stored; when the one or more programs are executed by the one or more processors, the one or more processors implement the MZI structure adjustment method not affected by the polarization state of the input light described in any of the above embodiments.

[0127] In an embodiment of the present invention, a computer - readable storage medium is further provided, on which a computer program is stored, and when the program is executed by a processor, the steps in any of the above - mentioned MZI structure adjustment methods not affected by the polarization state of the input light are implemented.

[0128] The above are only the preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. An MZI structure that is not affected by the polarization state of the input light, characterized in that: include: A first coupler (1), an optical device X (2), a first polarization controller (3), an optical device Y (4), and a second coupler (5); An optical signal enters the MZI structure through the incident end of a first coupler (1) and is divided into two optical signals A1 and A2 by the first coupler (1); the optical signal A1 passes through an optical device X (2) and a first polarization controller (3) in sequence and then enters the input end of a second coupler (5); the optical signal A2 passes through an optical device Y (4) and enters the input end of the second coupler (5); and the optical signals are combined into one output by the second coupler (5).

2. The MZI structure not affected by the polarization state of the input light according to claim 1, characterized in that: The sensing optical fiber and transmission optical fiber used in the MZI structure optical path are both common single-mode optical fibers; the optical device X (2) and the optical device Y (4) are single or serially combined delay optical fibers, frequency shifters, and optical amplifiers.

3. A method for adjusting an MZI structure that is not affected by the polarization state of the input light, applied to the MZI structure of claim 1, characterized in that: The steps include: S1, fixing the MZI structure in a heat-insulating and vibration-damping box, and connecting a second polarization controller (6) to the input end of the MZI structure; S2, disconnect the A1 optical signal of the MZI structure, adjust the second polarization controller (6), change the polarization state of the incident light, and record the Stokes vectors of the MZI input light and output light through a polarization analyzer (7); according to the combination of the Stokes vectors of the MZI input light and output light, fit the rotation matrix R of the A2 optical signal through the singular value decomposition method A2 ; S3, disconnecting the A2 optical signal, connecting the A1 optical signal, adjusting the second polarization controller (6), changing the polarization state of the incident light, and recording the Stokes vector of the MZI input light, output light, and output light after the first polarization controller (3) through a polarization analyzer (7); According to the Stokes vector combination of the MZI input light and the output light after the first polarization controller (3), the rotation matrix R of the light path of the A1 optical signal from the first coupler (1) to the first polarization controller (3) is fitted by the singular value decomposition method. A1前 ; According to the Stokes vector combination of the output light after the first polarization controller (3) and the output light of the MZI, the rotation matrix R of the A1 optical signal from the first polarization controller (3) to the second coupler (5) is fitted by the singular value decomposition method. A1后 ; S4, based on the obtained rotation matrix R A1前 , R A1后 and R A2 , solve the target rotation matrix R of the first polarization controller (3) 目标 , so that the A1 optical signal overall rotation matrix R ′ A1 With R A2 equal; Adjust the first polarization controller (3) until the Stokes space equivalent rotation axis f PC and the equivalent rotation angle θ PC With R 目标 The same makes the polarization rotation transformation of the two optical signals A1 and A2 consistent; S5, after the adjustment is completed, the second polarization controller (6) and the polarization analyzer (7) are removed, and the MZI structure is restored to a normal state.

4. The MZI structure adjustment method not affected by the polarization state of input light according to claim 3, characterized in that: In step S2, the Stokes space system describes the intensity and polarization characteristics of the light beam through the Stokes vector S: <h2 style=";text-align:left;direction:ltr">S = [S0,S1,S2,S3]<h2 style=";text-align:left;direction:ltr"> T Among them, S0 represents the total light intensity, the superscript T represents the transposition, S1, S2, and S3 represent the relative distribution of polarization states, and the rotation axis and rotation angle are fully described by S1, S2, and S3; The polarization device is described by the Mueller matrix M: Among them, m ij represents the matrix element of the Mueller matrix M, i=1,2,...,4, j=1,2,...,4; The effect of the device on the polarization state of light is regarded as the Stokes vector of light multiplied by the Mueller matrix of the device. For the device with lossless polarization conversion, the 3×3 Mueller matrix R is used. 3×3 To describe it, the specific form of the Mueller matrix is ​​as follows:

5. The MZI structure adjustment method not affected by the polarization state of input light according to claim 4, characterized in that: In step S2 and step S3, the light path rotation matrix R is fitted by the singular value decomposition method using the Stokes vector combination of the input light and the output light. The method includes the following sub-steps: S2.

1. Adjust the second polarization controller (6) to change the polarization state of the incident light, and measure the Stokes vectors of the three groups of MZI input light and output light through the polarization analyzer (7); the three groups of input light are respectively recorded as b1, b2 and b3, and the corresponding output light is respectively recorded as w1, w2 and w3. The measured Stokes vector combination of the input light and the output light of the optical path is: Among them, b ij represents the Stokes parameter of the input light, w ij represents the Stokes parameter of the output light; S2.

2. Take the Stokes vectors of the input light and the output light as column vectors, respectively, and construct matrices B and W: S2.

3. Calculate the covariance matrix H: H=WB T Perform singular value decomposition on the covariance matrix H and obtain: Among them, U and V svd is an orthogonal matrix, Σ is a diagonal matrix of singular values; The rotation matrix R is obtained as: R=V svd U T 。 6. The MZI structure adjustment method not affected by the polarization state of input light according to claim 3, characterized in that: The first polarization controller (3) and the second polarization controller (6) are both three-ring optical fiber polarization controllers. The three optical fiber rings of the first polarization controller (3) are adjusted to the same angle. The rotation matrix R of the three-ring optical fiber polarization controller is PC It is expressed as: R PC (θ1,θ2,θ3)=M QWP (θ3)M HWP (θ2)M QWP (θ1) Among them, M QWP (θ1), M QWP (θ2), M QWP (θ3) are the Mueller matrices of the first, second and third fiber rings of the three-ring fiber polarization controller, and θ1, θ2 and θ3 are the angles of the three fiber rings, respectively; Calculate the equivalent rotation angle θ in Stokes space PC and the equivalent rotation axis f PC : Among them, tr(R PC (θ1,θ2,θ3))=R 11 +R 22 +R 33 is the rotation matrix R PC The trace of R ij Represents R PC The matrix elements of .

7. The MZI structure adjustment method not affected by the polarization state of input light according to claim 6, characterized in that: Mueller matrix M QWP (θ1), M QWP (θ2), M QWP (θ3) are expressed as:

8. The MZI structure adjustment method not affected by the polarization state of input light according to claim 6, characterized in that: In step 4, adjusting the first polarization controller (3) includes the following sub-steps: S4.

1. Based on the fitted rotation matrix R A1前 , R A1后 and R A2 , calculate the rotation matrix R' of the A1 optical signal A1 With R A2 When they are equal, the target state of the first polarization controller (3) is: R′ A1 =R A1后 R 目标 R A1前 =R A2 Determine the target rotation matrix R 目标 : Decompose the target rotation matrix into the target Stokes space equivalent rotation angle θ 目标 and the equivalent rotation axis f 目标 : Among them, tr(R 目标 )=R 11 +R 22 +R 33 is the trace of the rotation matrix; S4.

2. By using the least square method, find the adjustment angles θ1, θ2 and θ3 of the three optical fiber rings of the first polarization controller (3), so that the Stokes space equivalent rotation axis and the equivalent rotation angle of the first polarization controller (3) after adjustment are consistent with the target; Create a multidimensional residual function: F(θ1,θ2,θ3)=[Δf;Δθ] Where Δf = f PC (θ1,θ2,θ3)-f 目标 is the residual between the Stokes space equivalent rotation axis of the first polarization controller (3) and the target equivalent rotation axis, Δθ=θ PC (θ1,θ2,θ3)-θ 目标 is the residual between the Stokes space equivalent rotation angle of the first polarization controller (3) and the target equivalent rotation angle; select a suitable initial angle and tolerance to minimize the residual norm Obtain the optimal θ1, θ2 and θ3; S4.

3. According to the calculated optimal angle, the three optical fiber rings of the first polarization controller (3) are adjusted to make the polarization rotation transformations of paths A1 and A2 consistent.

9. An electronic device, characterized in that: include: one or more processors; a storage device having one or more programs stored thereon; When the one or more programs are executed by the one or more processors, the one or more processors implement the MZI structure adjustment method that is not affected by the polarization state of the input light as claimed in any one of claims 3 to 8.

10. A computer-readable storage medium, characterized in that: A computer program is stored thereon, and when the program is executed by a processor, the steps in the MZI structure adjustment method that is not affected by the polarization state of the input light described in any one of claims 3 to 8 are implemented.

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