CN112485930A - Control method and system for realizing polarization stability - Google Patents
Control method and system for realizing polarization stability Download PDFInfo
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Abstract
The invention discloses a control method and a control system for realizing polarization stability, and belongs to the technical field of optical fiber communication and optical fiber sensing. The polarization state of the output light after passing through the polarization controller is quickly adjusted to be close to the arbitrarily specified target polarization state on the Poincare sphere through a quick positioning algorithm, and then the polarization state of the output light is further stabilized to be the target polarization state through a random gradient descent algorithm, so that the purpose that the arbitrary polarization state is stabilized to be the arbitrarily set target polarization state is achieved. The system is composed of an input end and an output end of two polarization analyzers, a calibrated polarization controller, a single chip microcomputer and the like, wherein the input polarization analyzer and the polarization controller which calibrates the relation between phase difference and voltage are used for rapid positioning, and meanwhile, the output polarization analyzer is combined with a random gradient descent algorithm to finally stabilize the output polarization state to a set value. The polarization stability control method of the invention gives consideration to the search speed and avoids local extreme values, and realizes the rapid and stable change of the polarization state to the intended target polarization state.
Description
Technical Field
The invention belongs to the technical field of optical fiber communication and optical fiber sensing, and particularly relates to a control method and a control system for realizing polarization stability.
Background
In the optical fiber communication system, due to the bending and extrusion of optical fibers and other factors in the optical fiber transmission process, the polarization state of light after transmission is dynamically and randomly changed, and the track of the polarization state of output light on the Poincar sphere is not a fixed point. For systems requiring stable polarization states, such as polarization multiplexing, coherent reception, polarization state quantum key distribution, etc., it is necessary to rapidly stabilize a randomly changing polarization state to a fixed polarization state, or to generate an output light with a stable polarization state, and the method is to realize polarization stabilization by continuously controlling and adjusting a Polarization Controller (PC).
At present, there are many schemes for realizing polarization stabilization, which are mainly divided into two categories, one is to set an objective function and optimize the objective function to control the PC and stabilize the polarization state by using a multidimensional optimization algorithm, such as a polarization stabilization control device and method (CN105629518A), and a particle swarm optimization algorithm used in the documents china OPTICS LETTERS COL 12(11), 110603(2014), and a genetic algorithm used in the documents Engineering Applications of aromatic intelligent significance Volume 25, Issue 4, (2012), and a gradient algorithm used in the method and device for improving the performance of the polarization controller (CN102221751A), which are disclosed in 11, 10 and 11 of 2014, 2012, but these optimization algorithms are difficult to consider the global search and the search speed: or the speed is slow to avoid falling into a local extreme value, or the speed is fast but easy to fall into a local optimum and a global optimum point is missed; the other method is to measure the polarization state of input light, calculate the control voltage of the polarization controller by combining the target polarization state, and directly convert the input light into the target polarization state. In addition, most polarization stabilization devices and methods can only stabilize the polarization state of any input light to a specific output light polarization state, not any output light polarization state. In many cases, the polarization state needs to be stabilized to any specified position on the Poincare sphere in practical application, and therefore, the practical application of the methods is limited.
Disclosure of Invention
The invention aims to combine the rapid positioning and the random gradient descent algorithm, rapidly convert any input light polarization state to the vicinity of a target polarization state by utilizing the rapid positioning without global search, further optimize the output light polarization state to the target polarization state by the random gradient descent algorithm, and give consideration to the search speed and avoid local extremum.
In order to achieve the above object, according to an aspect of the present invention, a control method for achieving polarization stabilization is provided, where an output light polarization state after an arbitrary input light polarization state passes through a polarization controller is rapidly adjusted to be near an arbitrary designated target polarization state on a poincare sphere through a rapid positioning algorithm, and then the output light polarization state is further stabilized to be a target polarization state by a random gradient descent algorithm, so as to achieve stabilization of the arbitrary polarization state to an arbitrarily set target polarization state, and the method specifically includes the following steps:
directly calculating the phase difference of the wave plate required to be applied by the polarization controller and the corresponding voltage value according to the input light and the target polarization state Stokes parameter;
applying the voltage value to a polarization controller to adjust the position of the polarization state of the output light on the Poincare sphere so that the included angle between the polarization state of the output light and the target polarization state on the Poincare sphere is smaller than a preset critical angle;
the polarization state of the output light is further adjusted by a random gradient descent algorithm to tend towards the target polarization state, thereby achieving polarization stabilization.
Preferably, the step of applying the voltage value to the polarization controller to adjust the position of the output light polarization state on the poincare sphere so that an included angle between the output light polarization state and the target polarization state on the poincare sphere is smaller than a preset critical angle includes the following specific steps:
according to the relative position of the input and the target polarization state on the Poincare sphere, distinguishing two situations of no blind area and blind area, the polarization controller only needs the front two-stage wave plate to change the phase difference or needs the front three-stage wave plate to change the phase difference, then the phase difference of the front two-stage wave plate or the front three-stage wave plate is calculated by adopting different formulas according to the input light and the target polarization state Stokes parameter, the voltage corresponding to the phase difference is applied to the calibrated polarization controller, the output light polarization state can be adjusted to be near the target polarization state through the adjustment of the front two-stage wave plate or the front three-stage wave plate of the polarization controller, and therefore the included angle of the light passing through the polarization controller is smaller than.
Preferably, the output light polarization state is further adjusted by a random gradient descent algorithm towards the target polarization state to achieve polarization stabilization, comprising the steps of:
the voltage of each wave plate in the polarization controller is adjusted in sequence according to a certain step length, the step length is in direct proportion to the included angle between the current output light polarization state and the target polarization state on the bonding ball, the voltage of one step length is increased or decreased for one wave plate every time, then the output light polarization state is measured, whether the voltage of one wavelength is increased or decreased for the wave plate is selected according to the situation that the included angle between the output light polarization state and the target polarization state is decreased, the same operation is performed on the next wave plate, and the three wave plates are adjusted in sequence in a circulating mode until the included angle between the output light polarization state and the target polarization state is smaller than a.
Preferably, the calibration process of the polarization controller is as follows:
calibrating the voltage on each wave plate of the polarization controller, and measuring the polarization state of output light by using a polarization analyzer;
and observing that the polarization state of the output light passes through a circular track on the Poincare ball in the process of gradually increasing the voltage, and corresponding the rotation angle of the polarization state to the voltage, thereby completing the calibration of the polarization controller.
Preferably, an included angle between the polarization state of the output light and the polarization state of the target on the bonded sphere is an included angle between a connecting line of the polarization state of the output light and the center of the bonded sphere and an included angle between the polarization state of the target and the connecting line of the center of the bonded sphere;
the step of calculating the included angle between the polarization state of the output light and the polarization state of the target on the Poincare sphere specifically comprises the following steps:
set the pair S of the target polarization state0Normalized Stokes parameter S1、S2、S3And calculating the included angle formula of the target polarization state and the input/output light polarization state on the Ponga sphere according to the normalized Stokes parameters of the target polarization state and the input/output light polarization state
θ＝acrcos(S1*S′1+S2*S′2+S3*S′3)
Wherein S1、S2、S3Normalized Stokes parameters, S ', to set target polarization states'1、S′2、S′3Normalized stokes parameters for the detected input/output light polarization states.
Preferably, the calculating an included angle between the polarization state of the output light and the polarization state of the target on the poincare sphere includes the following steps:
polarized light to be stabilized enters a front polarization analyzer, the front polarization analyzer obtains 4 groups of voltage values, and input light normalized Stokes parameters S 'are calculated through a measurement matrix of the front polarization analyzer'1、S′2、S′3；
Keeping the polarization controller unchanged, and measuring the polarization state of output light by a rear polarization analyzer at the output end of the polarization controller to obtain an output light Stokes parameter S ″1、S″2、S″3；
And calculating the included angle between the polarization state of the output light and the target polarization state through the included angle formula.
Preferably, the polarization controller is composed of five stages of equivalent phase difference adjustable angle fixed wave plates, the angle of each stage of wave plate is 0 °, 45 °, 0 °, 45 ° and 0 ° in sequence, the front three stage wave plate is used for controlling the polarization state of output light, and the rear two stage wave plate is used for returning the voltage of the front three stage wave plate to the intermediate voltage so as to continuously adjust the voltage when the voltage applied to the front three stage wave plate reaches the limit.
According to another aspect of the present invention, there is provided a control system for achieving polarization stabilization, the system comprising: the polarization analyzer comprises a front polarization analyzer, a rear polarization analyzer, a polarization controller, a driving circuit, a sampling circuit and a single chip microcomputer;
the output end of the preposed polarization analyzer is connected with the first input end of the singlechip through the sampling circuit; the output end of the rear polarization analyzer is connected to the second input end of the singlechip through the sampling circuit; the output end of the singlechip is connected with the input end of the polarization controller through the driving circuit;
the preposed polarization analyzer is used for detecting the polarization state of input light and outputting a four-path voltage signal of the polarization state of the input light;
the rear polarization analyzer is used for detecting the polarization state of the output light and outputting four-path voltage signals of the polarization state of the output light;
the sampling circuit is used for inputting digital signals after digital-to-analog conversion of four voltage signals output by the preposed polarization analyzer to the singlechip; the sampling circuit is also used for inputting digital signals after digital-to-analog conversion of four voltage signals output by the rear polarization analyzer to the singlechip;
the single chip microcomputer is used for receiving two paths of digital signals, performing matrix operation to obtain four Stokes parameters representing the polarization state, stabilizing the polarization state of output light to a target polarization state through a rapid positioning algorithm and a random gradient descent algorithm, and feeding back a control signal to the polarization controller through the driving circuit to realize stable control of the polarization state of incident light.
Preferably, the polarization controller is composed of five stages of equivalent phase difference adjustable angle fixed wave plates, the angle of each stage of wave plate is 0 °, 45 °, 0 °, 45 ° and 0 ° in sequence, the front three stage wave plate is used for controlling the polarization state of output light, and the rear two stage wave plate is used for returning the voltage of the front three stage wave plate to the intermediate voltage so as to continuously adjust the voltage when the voltage applied to the front three stage wave plate reaches the limit.
Generally, compared with the prior art, the technical scheme provided by the invention combines the rapid positioning and the random gradient descent algorithm, utilizes the rapid positioning to rapidly convert any input polarization state to the vicinity of the target polarization state, does not need global search, further optimizes the output polarization state to the target polarization state by the random gradient descent algorithm, gives consideration to the search speed and avoids local extreme values, can stabilize the input polarization state which is randomly and rapidly changed to the arbitrarily set target polarization state, has higher stabilization speed, and can be applied to various systems with high-speed polarization change.
Drawings
FIG. 1 is a schematic diagram of a polarization-stabilized control system of the present invention;
FIG. 2 is a schematic diagram of an angle between a target polarization state and an output light polarization state on a Poincar sphere according to the present invention;
FIG. 3 is a schematic diagram of the fast positioning algorithm of the present invention;
FIG. 4 is a trace plot of output polarization state on a Poincar sphere with polarization stabilization according to the present invention;
FIG. 5 is a flow chart of the polarization stabilization algorithm of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
The invention provides a control method for realizing polarization stability, which is characterized in that the polarization state of output light after the polarization state of any input light passes through a polarization controller is quickly adjusted to be near the polarization state of any appointed target on a Poincare sphere through a quick positioning algorithm, and then the polarization state of the output light is further stabilized to be the polarization state of the target through a random gradient descent algorithm so as to realize the stabilization of any polarization state to the polarization state of the target which is set arbitrarily, and the method specifically comprises the following steps:
directly calculating the phase difference of the wave plate required to be applied by the polarization controller and the corresponding voltage value according to the input light and the target polarization state Stokes parameter;
calculating an included angle between the polarization state of the output light and the target polarization state on the Poincar sphere according to the Stokes parameters of the input light and the output light and the preset Stokes parameter of the target polarization state;
applying the voltage value to a polarization controller to adjust the position of the polarization state of the output light on the Poincare sphere so that the included angle between the polarization state of the output light and the target polarization state on the Poincare sphere is smaller than a preset critical angle;
the polarization state of the output light is further adjusted by a random gradient descent algorithm to tend towards the target polarization state, thereby achieving polarization stabilization.
The core principle of the invention is that the fast positioning and the random gradient descent algorithm are combined, the fast positioning is utilized to fast convert the polarization state of any input light to the vicinity of the target polarization state, the global search is not needed, and then the random gradient descent algorithm further optimizes the polarization state of the output light to the target polarization state, the search speed is considered, and the local extreme value is avoided. The control method comprises the following steps:
the incident light polarization state is changed randomly and rapidly, the polarization state is detected through a polarization analyzer to obtain an input light Stokes parameter, then the output light is coupled to a rear polarization analyzer again through a calibrated polarization control device, the output light polarization state is detected to obtain an output light Stokes parameter, and an included angle is calculated between the output light Stokes parameter and a set target polarization state.
In the embodiment of the present invention, the included angle is set to 10 °, and other angles may be selected as the critical angle by an actual algorithm.
Further, if the included angle is greater than 10 °, calculating a wave plate phase difference of the polarization controller according to the input light and the target polarization state stokes parameter, and applying a voltage corresponding to the phase difference to the polarization controller; if the included angle is smaller than 10 degrees, entering a small-range random gradient descent algorithm, searching the optimal voltage value on each wave plate of the polarization controller by using the gradient algorithm, so that the included angle between the polarization state of the output light and the target polarization state is minimum, and finally realizing the polarization stabilization function.
Fig. 5 is a flowchart of the polarization stabilization algorithm of the present invention, as shown in fig. 5, the specific steps are:
s1, set the pair S of the target polarization state0Normalized Stokes parameter S1、S2、S3And calculating the included angle formula of the target polarization state and the input/output light polarization state on the Ponga sphere according to the normalized Stokes parameters of the target polarization state and the input/output light polarization state
θ＝acrcos(S1*S′1+S2*S′2+S3*S′3)。
Wherein S1、S2、S3Normalized Stokes parameters, S ', to set target polarization states'1、S′2、S′3Normalized stokes parameters for the detected input/output light polarization states.
Specifically, as shown in fig. 2, an included angle between the target polarization state and the output light polarization state on the poincare sphere is as follows: and the included angle between the connecting line of the polarization state of the output light and the center of the Bojia sphere and the included angle between the target polarization state and the connecting line of the center of the Bojia sphere. The angle θ is minimal when the output light polarization state coincides with the target polarization state.
S2, when the polarized light to be stabilized enters the system, firstly coupling part of the light guide front polarization analyzer 1, obtaining four groups of voltage values by the front polarization analyzer 1, and calculating the input light normalized Stokes parameter S 'by the measurement matrix of the polarization analyzer'1、S′2、S′3Then keeping the polarization controller unchanged, and measuring the polarization state of the output light by the polarization analyzer 2 at the output end to obtain the Stokes parameter S ″ of the output light1、S″2、S″3And calculating the included angle theta between the polarization state of the output light and the target polarization state by using an included angle formula.
S3, if theta is larger than 10 degrees, the distance between the polarization state of the output light and the target polarization state is judged to be large, the polarization state of the output light needs to be rapidly positioned and rapidly moved to the position near the target polarization state, and the normal work of a gradient algorithm is facilitated. The Stokes vectors of the input light polarization state and the target polarization state are known, and the required applied phase difference of each wave plate of the polarization controller is calculated by the following steps.
According to the relative positions of the input and target polarization states, as shown in fig. 3, two cases are distinguished:
(1) the target polarization state is not in the blind zone,
at the moment, the polarization state of the input light can be rotated to the target polarization state only by the first two fast axes pointing to the wave plates of 0 degree and 45 degrees;
(2) the polarization state of the target is in the blind area,
at this time, the target polarization state cannot be reached only by the first two wave plates, and a third wave plate with a fast axis pointing to 0 degree needs to be added.
Specifically, for case (1), as shown in FIG. 3, the trajectories of the 0 and 45 wave plates on the Poincare sphere are circles rotated around the S1 and S2 axes of the Poincare sphere, respectively, and the input light may be polarized SinTo the target polarization state SaimThe path of (A) is divided into two sections, S is firstly divided by a 0 DEG wave plateinRotate to D1And then D is converted by a 45-degree wave plate1Rotate to Saim，D1The normalized Stokes parameter of (A) can be calculated from the graph as
Then calculating D by the included angle formula1And SinAnd SaimThe included angle is the phase difference corresponding to the wave plates of 0 degree and 45 degrees;
to explain further, for case (2), as shown in FIG. 3, the input light polarization state SinTo the target polarization state SaimIs divided into three sections, and has two intermediate nodes D1And D2，D1And D2Respectively, as normalized Stokes parameters of
Then calculating D by the included angle formula1And Sin、D2And D1、D2And SaimThe included angle is the phase difference corresponding to the wave plates of 0 degree, 45 degrees and 0 degree.
When the phase difference required by each wave plate is calculated, the voltage value V1-V5 required to be applied by the polarization controller is obtained according to the calibrated relation between the voltage of the polarization controller and the phase difference. It should be noted that, when the voltage values of V4 and V5, i.e. the voltage values of the two latter wave plates, are zero, and corresponding voltages are applied to the polarization controller, due to other polarization errors that may exist in the calibrated polarization controller, the polarization state of the output light does not perfectly reach the target polarization state, but is close to the target polarization state, i.e. θ < 10 °.
And S4, if theta is less than 10 degrees, namely the polarization state of the output light is near the target polarization state, then entering a random gradient descent optimization process, and sequentially changing the voltage of the first three wave plates according to a certain step length.
Specifically, firstly, the wave plate 1 is adjusted, and the voltage of one step length is increased or decreased, so that the included angle between the polarization state of output light and the target polarization state is reduced; then adjusting the wave plate 2, increasing or decreasing the voltage of one step length, and reducing the included angle between the polarization state of the output light and the target polarization state; and finally, adjusting the wave plate 3, and increasing or decreasing the voltage of one step length to reduce the included angle between the polarization state of the output light and the target polarization state.
The step length is in direct proportion to the included angle theta, namely when the included angle theta is larger, the step length is larger, when the included angle theta is smaller, the step length is reduced so as to improve the precision, the process is continuously circulated until the included angle between the output light polarization state and the target polarization state is smaller than the threshold value, and the polarization stability is completed.
The trajectory of the output light polarization state onto the target polarization state on the poincare sphere is shown in fig. 4. And (4) keeping the operation of the algorithm, so that when the polarization state of the input light is randomly changed, the polarization state of the output light is always near the target polarization state, and the deviation is smaller than the threshold value.
Another embodiment of the present invention provides a control system for realizing polarization stabilization, as shown in fig. 1, including a front polarization analyzer, a rear polarization analyzer, a polarization controller, a driving circuit, a sampling circuit, and a single chip.
It should be noted that, in the present application, the front polarization analyzer is a polarization analyzer 1, the rear polarization analyzer is a polarization analyzer 2, and the polarization controller is a calibrated polarization controller.
Specifically, the output end of the polarization analyzer 1 is connected to the first output end of the single chip microcomputer through the sampling circuit, the output end of the polarization analyzer 2 is connected to the second input end of the single chip microcomputer through the sampling circuit, and the output end of the single chip microcomputer is connected to the input end of the polarization controller through the driving circuit.
The calibrated polarization controller is composed of five stages of equivalent phase difference adjustable angle fixed wave plates, the angle of each stage of wave plate is 0 degree, 45 degree, 0 degree, 45 degree and 0 degree, wherein the last two stages of wave plates are used for resetting, when the voltage applied to the current three stages of wave plates reaches the limit of 15V, the voltage of the current three stages of wave plates needs to be returned to the middle voltage so as to be convenient for continuing to adjust the voltage, namely the voltage of the wave plates is reset. At the moment, the voltage on the wave plate needing to be reset can be returned to the middle voltage under the condition of not changing the polarization state by the assistance of the last two stages of 45-degree and 0-degree wave plates.
The front third-stage wave plate is used for controlling the polarization state, the adjustable phase difference is controlled by the voltage applied to the wave plate, the voltage range is 0V-15V, the phase difference change of 0-2 pi can be realized, the voltage and phase difference change relation is calibrated, and the calibration process is as follows: the method comprises the steps of calibrating the relation between the voltage and the phase difference of each wave plate of the polarization controller respectively, calibrating the fifth wave plate to the first wave plate from back to front in sequence, changing the voltage on the wave plates of the polarization controller, measuring the output polarization state by using a polarization analyzer, observing that the output polarization state passes through a circular track on a Bojia ball when the output polarization state is increased along with the voltage from 0-15V, and corresponding the rotation angle of the polarization state, namely the phase difference generated by the wave plates, to the voltage, thereby completing the calibration of the polarization control.
The polarization analyzer 1 is configured to detect a polarization state of input light and output a four-way voltage signal of the polarization state of the output light. The polarization analyzer 2 is configured to detect a polarization state of the output light and output a four-way voltage signal of the polarization state of the output light.
The sampling circuit is used for inputting digital signals obtained by digital-to-analog conversion of the four voltage signals output by the polarization analyzer 1 to the single chip microcomputer, and the sampling circuit is also used for inputting digital signals obtained by digital-to-analog conversion of the four voltage signals output by the polarization analyzer 2 to the single chip microcomputer.
The singlechip is used for receiving two paths of digital signals and carrying out matrix operation to obtain four Stokes parameters S representing polarization states0、S1、S2、S3And stabilizing the polarization state of the output light to a target polarization state through a rapid positioning algorithm and a random gradient descent algorithm, and feeding back a control signal to the polarization controller through a driving circuit to realize stable control of the polarization state of the incident light.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (9)
1. A control method for realizing polarization stabilization is characterized by specifically comprising the following steps of:
directly calculating the phase difference of the wave plate required to be applied by the polarization controller and the corresponding voltage value according to the input light and the target polarization state Stokes parameter;
applying the voltage value to a polarization controller to adjust the position of the polarization state of the output light on the Poincare sphere so that the included angle between the polarization state of the output light and the target polarization state on the Poincare sphere is smaller than a preset critical angle;
the polarization state of the output light is further adjusted by a random gradient descent algorithm to tend towards the target polarization state, thereby achieving polarization stabilization.
2. The control method for realizing polarization stabilization according to claim 1, wherein the step of applying the voltage value to the polarization controller to adjust the position of the output light polarization state on the poincare sphere so that an included angle between the output light polarization state and the target polarization state on the poincare sphere is smaller than a preset critical angle includes the following specific steps:
according to the relative position of the input and the target polarization state on the Poincare sphere, distinguishing two situations of no blind area and blind area, the polarization controller only needs the front two-stage wave plate to change the phase difference or needs the front three-stage wave plate to change the phase difference, then the phase difference of the front two-stage wave plate or the front three-stage wave plate is calculated by adopting different formulas according to the input light and the target polarization state Stokes parameter, the voltage corresponding to the phase difference is applied to the calibrated polarization controller, the output light polarization state can be adjusted to be near the target polarization state through the adjustment of the front two-stage wave plate or the front three-stage wave plate of the polarization controller, and therefore the included angle of the light passing through the polarization controller is smaller than.
3. A control method for realizing polarization stabilization according to claim 1 or 2, wherein the polarization state of the output light is further adjusted to trend to the target polarization state by a random gradient descent algorithm, so as to realize polarization stabilization, and the method comprises the following steps:
the voltage of each wave plate in the polarization controller is adjusted in sequence according to a certain step length, the step length is in direct proportion to the included angle between the current output light polarization state and the target polarization state on the bonding ball, the voltage of one step length is increased or decreased for one wave plate every time, then the output light polarization state is measured, whether the voltage of one wavelength is increased or decreased for the wave plate is selected according to the situation that the included angle between the output light polarization state and the target polarization state is decreased, the same operation is performed on the next wave plate, and the three wave plates are adjusted in sequence in a circulating mode until the included angle between the output light polarization state and the target polarization state is smaller than a.
4. The control method for realizing polarization stability according to claim 2, wherein before directly calculating the phase difference of the wave plate required to be applied to the polarization controller and the corresponding voltage value by the input light and the stokes parameter of the target polarization state, the polarization controller needs to be calibrated, and the calibration process of the polarization controller is as follows:
calibrating the voltage on each wave plate of the polarization controller, and measuring the polarization state of output light by using a polarization analyzer;
and observing that the polarization state of the output light passes through a circular track on the Poincare ball in the process of gradually increasing the voltage, and corresponding the rotation angle of the polarization state to the voltage, thereby completing the calibration of the polarization controller.
5. The control method for realizing polarization stabilization according to any one of claims 1 to 4, wherein an included angle between the polarization state of the output light and the target polarization state on the Poincare sphere is an included angle between a connecting line of the polarization state of the output light and the center of the Poincare sphere and a connecting line of the target polarization state and the center of the Poincare sphere;
the step of calculating the included angle between the polarization state of the output light and the polarization state of the target on the Poincare sphere specifically comprises the following steps:
set the pair S of the target polarization state0Normalized Stokes parameter S1、S2、S3And calculating the included angle formula of the target polarization state and the input/output light polarization state on the Ponga sphere according to the normalized Stokes parameters of the target polarization state and the input/output light polarization state
θ＝acrcos(S1*S′1+S2*S′2+S3*S′3)
Wherein S1、S2、S3Normalized Stokes parameters, S ', to set target polarization states'1、S′2、S′3Normalized stokes parameters for the detected input/output light polarization states.
6. The control method according to claim 5, wherein the calculating an angle between the polarization state of the output light and the polarization state of the target on the Poincare sphere includes:
polarized light to be stabilized enters a front polarization analyzer, the front polarization analyzer obtains 4 groups of voltage values, and input light normalized Stokes parameters S 'are calculated through a measurement matrix of the front polarization analyzer'1、S′2、S′3；
Keeping the polarization controller unchanged, and measuring the polarization state of output light by a rear polarization analyzer at the output end of the polarization controller to obtain an output light Stokes parameter S ″1、S″2、S″3；
And calculating the included angle between the polarization state of the output light and the target polarization state through the included angle formula.
7. The control method according to claim 6, wherein the polarization controller comprises five stages of equivalent phase difference adjustable angle fixed wave plates, each stage of wave plates has an angle of 0 °, 45 °, 0 °, and the first three stage of wave plates are used for controlling the polarization state of output light, and the second two stage of wave plates are used for returning the voltage of the first three stage of wave plates to the intermediate voltage when the voltage applied to the first three stage of wave plates reaches the limit, so as to continuously adjust the voltage.
8. A control system for implementing the control method for polarization stabilization according to any one of claims 1 to 7, the system comprising: the polarization analyzer comprises a front polarization analyzer, a rear polarization analyzer, a polarization controller, a driving circuit, a sampling circuit and a single chip microcomputer;
the output end of the preposed polarization analyzer is connected with the first input end of the singlechip through the sampling circuit; the output end of the rear polarization analyzer is connected to the second input end of the singlechip through the sampling circuit; the output end of the singlechip is connected with the input end of the polarization controller through the driving circuit;
the preposed polarization analyzer is used for detecting the polarization state of input light and outputting four paths of voltage signals containing the polarization state information of the input light;
the rear polarization analyzer is used for detecting the polarization state of output light and outputting four voltage signals containing the polarization state information of the output light;
the sampling circuit is used for inputting digital signals after digital-to-analog conversion of four voltage signals output by the preposed polarization analyzer to the singlechip; the sampling circuit is also used for inputting digital signals after digital-to-analog conversion of four voltage signals output by the rear polarization analyzer to the singlechip;
the single chip microcomputer is used for receiving two paths of digital signals and carrying out matrix operation to obtain four Stokes parameters representing the polarization state, and the control signals are fed back to the polarization controller through the control method for realizing polarization stability in claim 1 to realize stable control of the polarization state of incident light.
9. The control system of claim 8, wherein the polarization controller comprises five stages of equivalent phase difference adjustable angle fixed wave plates, each stage of wave plates has an angle of 0 °, 45 °, 0 °, and the first three stage of wave plates are used for controlling the polarization state of output light, and the second two stage of wave plates are used for returning the voltage of the first three stage of wave plates to the intermediate voltage so as to continue to adjust the voltage when the voltage applied to the first three stage of wave plates reaches the limit.
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