MPI automatic control test system and method

Abstract

The application provides an MPI automatic control test system and method, which comprises the following steps: inputting an optical signal into an input interface of a test system, dividing the optical signal into a main path signal and a branch path signal through a 99:1 coupler; measuring the optical power of the main path signal and adjusting the polarization state of the main path signal; measuring the optical power of the branch path signal and adjusting the polarization state of the branch path signal; adding attenuation to the branch path signal with the adjusted polarization state according to the optical power of the main path signal, the polarization state of the branch path signal and the MPI size required to be tested; and coupling the main path signal with the adjusted polarization state and the branch path signal with the added attenuation through a 50:50 coupler. The application uses polarization maintaining devices, aligns two optical signals to the working axes (fast axis or slow axis) of the respective polarization maintaining devices through a polarization controller, and then uses a polarization maintaining coupler to couple the two optical signals, so that the purpose of aligning the polarization states of the two optical signals is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of MPI testing, in particular to an MPI automatic control testing system and method. BACKGROUND

[0002] In recent years, research on MPI has been growing, and many modeling, measurement and suppression methods have been proposed, but most of them are based on simulation level. The reason is that MPI in the actual system is difficult to accurately measure and calculate. In the existing optical communication network, due to the non-ideal nature of optical fiber, the phenomenon of multipath interference (MPI) will occur, and MPI will cause serious degradation of signal quality, so a series of MPI monitoring and suppression schemes have been proposed. In order to evaluate the effectiveness of these schemes, an experimental platform needs to be built to simulate the MPI phenomenon in the existing network. The influence of MPI on signal performance is related to polarization: when MPI and signal polarization are aligned, the signal degradation is the most serious. Therefore, in order to explore the size of the influence of MPI, it is often necessary to align the polarization of MPI and signal.

[0003] The paper entitled "Statistical method for multipath interference detection in IMDD optical links" by Absar Ulhassan, published in the journal of lightwave technology in July 2023, proposes a scheme in which an optical signal is divided into two signals by a 90:10 power divider. The two signals pass through a polarization controller and a variable optical attenuator, respectively, and then pass through a coupler. Finally, a polarizer is used. However, in this paper, the adjustment of the polarization of the two signals is manually controlled, and it cannot be completely guaranteed that the polarization of the two signals is aligned, so the above technical problems have not been completely solved.

[0004] In summary, there is still room for improvement in the efficiency and accuracy of testing MPI in the prior art, and there is a need for an MPI automatic control testing system and method that can automatically align the polarization and adjust the size of MPI. SUMMARY

[0005] In view of the defects in the prior art, the purpose of the present application is to provide an MPI automatic control testing system and method.

[0006] According to the MPI automatic control testing system provided by the present application, the first coupler (CP1), the first electrically controlled polarization controller (EPC1), the second coupler (CP2), the third coupler (CP3), the fourth coupler (CP4), the electrically controlled VOA, the first PD (PD1), the second PD (PD2), the FPGA and the second electrically controlled polarization controller (EPC2) are connected in series.

[0007] The optical signal is input from the input end of the first coupler, the first output end of the first coupler is connected with the optical fiber input end of the first electrically controlled polarization controller, the optical fiber output end of the first electrically controlled polarization controller is connected with the input end of the second coupler, the first output end of the second coupler is connected with the input end of the first PD, and the second output end of the second coupler is connected with the first input end of the fourth coupler;

[0008] The second output end of the first coupler is connected with the optical fiber input end of the second electrically controlled polarization controller, the optical fiber output end of the second electrically controlled polarization controller is connected with the input end of the third coupler, the first output end of the third coupler is connected with the input end of the second PD, the second output end of the third coupler is connected with the optical fiber input end of the electrically controlled VOA, the optical fiber output end of the electrically controlled VOA is connected with the second input end of the fourth coupler, and the output end of the fourth coupler outputs the optical signal.

[0009] The first pin, the second pin, the third pin, the fourth pin and the fifth pin of the FPGA are connected with the electrical signal input end of the first electrically controlled polarization controller, the electrical signal input end of the second electrically controlled polarization controller, the electrical signal output end of the first PD, the electrical signal output end of the second PD and the electrical signal input end of the electrically controlled VOA respectively.

[0010] Preferably, the first coupler, the second coupler, the third coupler and the fourth coupler are respectively a 99:1 coupler, a 90:10 coupler, a 50:50 coupler and a 50:50 coupler;

[0011] The first output end of the first coupler is a 99% corresponding output end, and the second output end is a 1% corresponding output end.

[0012] The first output end of the second coupler is a 10% corresponding output end, and the second output end is a 90% corresponding output end.

[0013] Preferably, the FPGA uses an MSP430F5529 32-bit floating-point processor.

[0014] Preferably, the electrically controlled VOA is an electrically controlled adjustable optical attenuator, which is used to control the intensity of the optical signal on the branch.

[0015] The first coupler, the second coupler, the third coupler and the fourth coupler are used to divide the optical signal into two optical signals according to a certain proportion, or to couple two optical signals into one signal.

[0016] The first electrically controlled polarization controller and the second electrically controlled polarization controller are used to align two signal lights to the working axes of respective polarization maintaining devices.

[0017] The first PD and the second PD are used for detecting power of the optical signal.

[0018] The FPGA controls the electrically-controlled polarization controller and the electrically-controlled adjustable optical attenuator through a built automatic control algorithm.

[0019] According to the MPI automatic control test method and the MPI automatic control test system, the test method comprises the following steps:

[0020] Step S1: inputting the optical signal to an input interface of the test system, and dividing the optical signal into a main path signal and a branch path signal through a 99:1 coupler;

[0021] Step S2: measuring the optical power of the main path signal and adjusting the polarization state of the main path signal;

[0022] Step S3: measuring the optical power of the branch path signal and adjusting the polarization state of the branch path signal;

[0023] Step S4: adding attenuation to the branch path signal with the adjusted polarization state according to the optical power of the main path signal, the polarization state of the branch path signal and the MPI size to be tested;

[0024] Step S5: coupling the main path signal with the adjusted polarization state and the branch path signal after attenuation through a 50:50 coupler.

[0025] Preferably, the adjustment of the polarization state of the main path signal comprises that the main path signal passes through the first electrically-controlled polarization controller, and then is divided into a light path to a power meter through a 90:10 polarization-maintaining coupler to measure the power, and then the FPGA controls the electrically-controlled polarization controller to adjust the polarization state of the main path signal according to the power size and the automatic control algorithm.

[0026] Preferably, the adjustment of the polarization state of the branch path signal comprises that the branch path signal passes through the second electrically-controlled polarization controller, and then is divided into a light path to a power meter through a 50:50 polarization-maintaining coupler to measure the power, and then the FPGA controls the electrically-controlled polarization controller to adjust the polarization state of the main path signal according to the power size and the automatic control algorithm.

[0027] Preferably, the step S4 adds attenuation to the branch path signal through the FPGA controlling the electrically-controlled adjustable optical attenuator.

[0028] Preferably, the automatic control algorithm comprises a PID algorithm and a scanning algorithm based on blind adjustment.

[0029] Preferably, the adjustment of the polarization state of the main path signal and the branch path signal through the electrically-controlled polarization controller comprises the following steps:

[0030] Rotating the 1 / 4 wave plate tilt angle in the electric control polarization controller, record the tilt angle corresponding to the maximum optical power, after the 1 / 4 wave plate scanning is completed, automatically return to the tilt angle corresponding to the maximum optical power, and the half wave plate is positioned to the tilt angle corresponding to the maximum optical power, so that the maximum optical power is positioned, and finally the optical power is close to the maximum optical power in the scanning process.

[0031] Compared with the prior art, the present application has the following beneficial effects:

[0032] 1、 the present application adopts polarization maintaining device, through polarization controller, two signal lights are aligned with the working axis (fast axis or slow axis) of each polarization maintaining device, then polarization maintaining coupler is used to couple two light signals, so that the purpose of aligning the polarization state of two light signals is achieved.

[0033] 2、 the present application inputs optical power into FPGA, then FPGA controls the electric control polarization controller and the electric control adjustable optical attenuator according to the designed automatic control algorithm, so that the automation of polarization alignment and MPI size adjustment is realized, and the efficiency and precision of MPI influence test are improved. BRIEF DESCRIPTION OF DRAWINGS

[0034] Other features, objects and advantages of the present application will become more apparent from the following detailed description of non-limiting embodiments with reference to the attached drawings:

[0035] Figure 1 It is a working principle diagram of the present application;

[0036] Figure 2 It is a structure diagram of the electric control polarization controller in the present application;

[0037] Figure 3 It is a simulink connection diagram of the PID control algorithm connecting the three-ring polarization controller and the polarization maintaining fiber in the present application;

[0038] Figure 4 It is a general experimental connection schematic diagram of the present application;

[0039] Figure 5 It is a software flowchart of the present application;

[0040] Figure 6 It is a polarization automatic alignment process diagram in the present application;

[0041] Figure 7 It is an anti-interference test result diagram after adding the PID algorithm in the present application;

[0042] Figure 8 It is a received current distribution diagram when the polarization of each branch is aligned and the MPI branch attenuation is-1.5dB in the present application;

[0043] Figure 9 The received current distribution diagram when the polarization of each branch is aligned and the MPI branch attenuation is -9.5dB in the application;

[0044] Figure 10 A three-ring polarization controller diagram in the application.

[0045] wherein, Figure 1 PC in the figure represents an electrically controlled three-ring polarization controller, the spiral at the bottom represents that the optical signal of the branch passes through more fiber paths than the main path above, and the dashed line between the PD and the FPGA represents the feedback signal of the optical power accessing the FPGA. DETAILED DESCRIPTION

[0046] The application will be described in detail below with specific embodiments. The following examples will help those skilled in the art to further understand the application, but do not limit the application in any form. It should be noted that for those skilled in the art, without departing from the concept of the application, a number of changes and improvements can be made. These all belong to the protection scope of the application.

[0047] According to the principle of MPI generation, the application divides the homologous optical signal into two paths, one of which transmits along a shorter fiber link to simulate the optical signal not disturbed by MPI, and the other uses a method of lengthening the fiber to simulate the MPI interference signal. Then the two signals are coupled to simulate the optical signal disturbed by MPI, wherein the intensity of the MPI branch optical signal is controlled by an optical attenuator.

[0048] According to the MPI automatic control test system provided by the application, the structure is as shown in Figure 1 The system mainly comprises a first coupler (CP1), a first electrically controlled polarization controller (EPC1), a second coupler (CP2), a third coupler (CP3), a fourth coupler (CP4), an electrically controlled VOA, a first PD (PD1), a second PD (PD2), a field programmable gate array FPGA (MSP430F5529 single-chip microcomputer), and a second electrically controlled polarization controller (EPC2). The first coupler, the second coupler, the third coupler, and the fourth coupler are respectively a 99:1 coupler, a 90:10 coupler, a 50:50 coupler, and a 50:50 coupler, wherein the first electrically controlled polarization controller and the second electrically controlled polarization controller are step motor structure diagrams, as shown in Figure 2 .

[0049] The input end of the first coupler is connected with the optical fiber input end of the first electrically controlled polarization controller, the optical fiber output end of the first electrically controlled polarization controller is connected with the input end of the second coupler, the first output end of the second coupler is connected with the input end of the first PD, and the second output end of the second coupler is connected with the first input end of the fourth coupler.

[0050] The second output end of the first coupler is connected with the optical fiber input end of the second electrically controlled polarization controller, the optical fiber output end of the second electrically controlled polarization controller is connected with the input end of the third coupler, the first output end of the third coupler is connected with the input end of the second PD, the second output end of the third coupler is connected with the optical fiber input end of the electrically controlled VOA, the optical fiber output end of the electrically controlled VOA is connected with the second input end of the fourth coupler, and the output end of the fourth coupler outputs the optical signal.

[0051] The first pin, the second pin, the third pin, the fourth pin and the fifth pin of the FPGA are connected with the electric signal input end of the first electrically controlled polarization controller, the electric signal input end of the second electrically controlled polarization controller, the electric signal output end of the first PD, the electric signal output end of the second PD and the electric signal input end of the electrically controlled VOA respectively.

[0052] The first output end of the first coupler is the 99% corresponding output end, and the second output end is the 1% corresponding output end.

[0053] The overall experimental connection schematic diagram of the application is shown in the figure. Figure 4 The AWG is an arbitrary waveform generator, the EA is a power amplifier, the MZM is a Mach-Zehnder optical modulator, the ELC is an ultra-narrow linewidth laser, the PC is a polarization controller, the SSMF is a standard single-mode optical fiber, and the DSO is a digital storage filter.

[0054] The FPGA used in the application is a MSP430F5529 32-bit floating-point processor, and the main frequency is as high as 150MHz.

[0055] According to the MPI automatic control test method provided by the application, the MPI automatic control test system is used, and the test method comprises the following steps:

[0056] In step S1, the optical signal is input to the input interface of the test system, and the optical signal is divided into a main path signal and a branch path signal through a 99:1 coupler.

[0057] Step S2: measuring the main path signal optical power, adjusting the main path signal polarization state. The step S2 comprises:

[0058] Step S2.1: the main path signal passes through the first electrically controlled polarization controller, and then is divided into one light by the 90:10 polarization maintaining coupler to measure the power on the power meter.

[0059] Step S2.2: the measured power is input to the FPGA, and then the FPGA controls the electrically controlled polarization controller to adjust the polarization state of the main path signal according to the power size and the automatic control algorithm.

[0060] Step S3: measuring the branch path signal optical power, adjusting the branch path signal polarization state. The step S3 comprises the following steps:

[0061] Step S3.1: the branch path signal passes through the second electrically controlled polarization controller, and then is divided into one light by the 50:50 polarization maintaining coupler to measure the power on the power meter.

[0062] Step S3.2: the measured power is input to the FPGA, and then the FPGA controls the electrically controlled polarization controller to adjust the polarization state of the branch path signal according to the power size and the automatic control algorithm.

[0063] Step S4: according to the main path signal optical power, the branch path signal polarization state and the required MPI size, adding attenuation to the branch path signal with the adjusted polarization state. After the branch path signal polarization state is adjusted, according to the main path signal power, the branch path signal power and the required MPI size, a certain attenuation is added to the branch path signal by the FPGA controlling the electrically controlled adjustable optical attenuator, and here only the MPI branch is added with attenuation.

[0064] Step S5: coupling the main path signal with the adjusted polarization state and the branch path signal after attenuation through the 50:50 coupler. The output signal of step S2 and the output signal of step S4 are coupled through the 50:50 coupler.

[0065] The automatic control algorithm used in the simulation of the application is the PID algorithm, and the automatic control algorithm used in the experiment is a scanning method based on "blind tuning". The difference from the general blind tuning method is that the general three-ring polarization controller has a simple structure as shown in Figure 10 The polarization controller is composed of a 1 / 4 wave plate, a half wave plate and a 1 / 4 wave plate in series. The application can complete polarization control by only using one half wave plate and one 1 / 4 wave plate of the polarization controller, that is, only Figure 10The working principle of the first two wave plates in the figure is that: after the polarization controller, a polarization maintaining fiber is connected, and theoretically, when the output optical power of the polarization maintaining fiber reaches the maximum, the polarization state of the light is linearly polarized light consistent with the polarization direction of the polarization maintaining fiber, that is, the present application converts any polarized light into linearly polarized light of a certain polarization direction through the polarization controller. According to the principle of the 1 / 4 wave plate, any polarized light can be converted into linearly polarized light after passing through the 1 / 4 wave plate at a suitable angle. According to the principle of the half wave plate, the half wave plate can change the polarization direction of the linearly polarized light while keeping the linearly polarized state. Therefore, only one half wave plate and one 1 / 4 wave plate can achieve the maximum output optical power of the polarization maintaining fiber. As shown in Figure 3 , Figure 3 The original signal in the figure refers to the optical signal incident to the polarization controller, which successively passes through the 1 / 2 wave plate and the 1 / 4 wave plate, and then passes through the polarization maintaining fiber. The optical power is obtained by taking the square and the envelope. The lower left part of the connection diagram is the PID module, wherein the input of the PID module is the optical power output by the polarization maintaining fiber, and the output is the tilt angle of the 1 / 2 wave plate.

[0066] The automatic control process is: first, rotate the tilt angle of the 1 / 4 wave plate, record the tilt angle corresponding to the maximum optical power, and then automatically return to the tilt angle corresponding to the maximum optical power after the 1 / 4 wave plate is scanned. Similarly, the half wave plate is positioned at the tilt angle corresponding to the maximum optical power, so as to realize the positioning of the maximum optical power. The output optical power of the polarization maintaining fiber during the scanning process is as shown in Figure 6 , and the final optical power is close to the maximum optical power during the scanning process. The process of scanning to the maximum positioning power is measured for many times, and the error between the final optical power and the maximum optical power during the scanning process is 0.867%. Compared with the three-ring simultaneous control, 1 / 3 of the time is saved.

[0067] The PID algorithm in the experiment is used to maintain the steady state, and the anti-interference test result is as shown in Figure 7 . First, rotate the tilt angle of the wave plate to make the optical power reach the preset value. During the steady state maintaining stage, the optical fiber line is disturbed twice, and the optical power can return to the preset value and stabilize in a period of time, which shows that the PID algorithm can make the optical power stable and has a certain anti-interference ability.

[0068] Further, as shown in Figure 5As shown, the software flow of the application is described as follows, wherein the left side is the main program, mainly responsible for the initialization of software and hardware, clock, AD, interruption setting, and the right side is the interruption program, mainly providing a time slice rotation signal for the main program, facilitating the scheduling between tasks. The main program includes: closing the watchdog, setting the GPIO configuration serial communication, then initializing the AD module, timer module, electric three-ring polarization controller, global variable, and waiting for interruption. The interruption program includes: firstly reading the AD data and converting it into optical power, setting to work in control mode, judging whether it is the traversal mode, if yes, executing the traversal program; if no, judging whether it is the maximum value mode, if yes, moving to the maximum value; if no, judging whether it is the control mode, if yes, performing PID control and then returning from interruption; if no, directly returning from interruption.

[0069] An important prerequisite for the application to realize the controllable MPI size is that the polarization directions of the MPI branch and the main path are aligned. Because only in the case of polarization alignment, the coupling of two optical signals is additive in the same direction, without considering the polarization direction of each path. At present, there are few works discussing the influence of polarization factor on MPI, but researchers have pointed out that the power cost of MPI always tends to converge to the worst case of polarization alignment of each reflection path and the main path. Researchers have also pointed out that the method of dealing with polarization in MPI research is to change the polarization state of each path by simulation or physical method, and to calculate the cost of MPI in the worst performance. These studies are sufficient to show that it is necessary to keep the polarization alignment of each path in the system for realizing the automatic control of MPI. Figure 8 As shown, when the polarization of each branch is aligned and the MPI branch attenuation is-1.5dB in the application, the highest amplitude level (the rightmost side) of the received current distribution shows a more "stout" and obvious overlap between adjacent distributions, which is a typical MPI interference characteristic. As shown, Figure 9 As shown, when the polarization of each branch is aligned and the MPI branch attenuation is-9.5dB in the application, the MPI characteristic of the received current distribution shown by the highest amplitude level is obviously reduced, because the MPI attenuation is larger and the signal strength of the MPI branch is smaller at this time, and the polarization of each branch is aligned. Figure 8 The comparison of the results shows that the MPI size control is realized.

[0070] The method for realizing the polarization alignment of the system of the application is to pass the optical signals of each branch through the electrically controlled three-ring polarization controller, and then connect the polarization maintaining fiber, constantly change the three-plate tilt angle of the three-ring polarization controller, and if the output optical signal of the polarization maintaining fiber reaches the maximum, it indicates that the polarization direction of the optical signal is consistent with the polarization maintaining fiber. If the optical power of the two optical signals both reaches the maximum, it is considered that the two optical signals are polarization aligned. Among them, the rotation of the wave plate of the polarization controller is completely realized by the automatic control of the single-chip microcomputer, and the system is a relatively independent automated product.

[0071] Those skilled in the art understand that, in addition to implementing the system provided by the present application and each device, module and unit thereof in the form of pure computer readable program code, the system provided by the present application and each device, module and unit thereof can also be implemented in the form of logic gates, switches, application specific integrated circuits, programmable logic controllers and embedded microcontrollers, etc. by logically programming the method steps to achieve the same functions. Therefore, the system provided by the present application and each device, module and unit thereof can be considered as a hardware component, and the devices, modules and units included therein for implementing various functions can also be considered as structures within the hardware component; the devices, modules and units for implementing various functions can also be considered as both software modules implementing methods and structures within hardware components.

[0072] The specific embodiments of the present application are described above. It needs to be understood that the present application is not limited to the specific embodiments described above, and various changes or modifications can be made by those skilled in the art within the scope of the claims, which does not affect the essential content of the present application. The embodiments of the present application and the features in the embodiments can be arbitrarily combined with each other without conflict.

Claims

1. An MPI automatic control test system, characterized in that, The application relates to an MPI automatic control test system. The light signal is input from an input end of a first coupler, a first output end of the first coupler is connected with a fiber input end of a first electrically-controlled polarization controller, a fiber output end of the first electrically-controlled polarization controller is connected with an input end of a second coupler, a first output end of the second coupler is connected with an input end of a first PD, and a second output end of the second coupler is connected with a first input end of a fourth coupler. A second output end of the first coupler is connected with a fiber input end of a second electrically-controlled polarization controller, a fiber output end of the second electrically-controlled polarization controller is connected with an input end of a third coupler, a first output end of the third coupler is connected with an input end of a second PD, a second output end of the third coupler is connected with a fiber input end of an electrically-controlled VOA, a fiber output end of the electrically-controlled VOA is connected with a second input end of the fourth coupler, and an output end of the fourth coupler outputs the light signal. First, second, third and fourth pins of the FPGA are connected with an electric signal input end of the first electrically-controlled polarization controller, an electric signal input end of the second electrically-controlled polarization controller, an electric signal output end of the first PD, an electric signal output end of the second PD and an electric signal input end of the electrically-controlled VOA respectively. The electrically-controlled VOA is an electrically-controlled adjustable optical attenuator used for controlling the intensity of the light signal on the branch. The first, second, third and fourth couplers are used for dividing the light signal into two light signals according to a certain ratio or coupling two light signals into one signal. The first and second electrically-controlled polarization controllers are used for aligning two signal lights to the working axes of respective polarization maintaining devices. The first and second PDs are used for detecting the power of the light signal. The FPGA controls the electrically-controlled polarization controllers and the electrically-controlled adjustable optical attenuator through an established automatic control algorithm. The first, second, third and fourth couplers are respectively 99:1 couplers, 90:10 couplers, 50:50 couplers and 50:50 couplers.

2. The MPI automated control test system of claim 1, wherein, The first output end of the first coupler is a 99% corresponding output end, and the second output end is a 1% corresponding output end. The first output end of the second coupler is a 10% corresponding output end, and the second output end is a 90% corresponding output end. The FPGA adopts an MSP430F5529 32-bit floating-point processor.

3. The MPI automated control test system of claim 1, wherein, The test method of the MPI automatic control test system comprises the following steps:

4. An MPI automatic control test method, characterized by, S1: inputting the light signal into an input interface of the test system, and dividing the light signal into a main path signal and a branch path signal through a 99:1 coupler; S2: measuring the light power of the main path signal and adjusting the polarization state of the main path signal; S3: measuring the light power of the branch path signal and adjusting the polarization state of the branch path signal. ​ Step S4: adding attenuation to the branch signal with adjusted polarization state according to the main signal optical power, the branch signal polarization state and the MPI size to be tested; Step S5: coupling the main signal with adjusted polarization state and the attenuated branch signal through a 50:50 coupler; controlling the electrically-controlled polarization controller to adjust the polarization states of the main signal and the branch signal, comprising: rotating the 1 / 4 wave plate tilt angle in the electrically-controlled polarization controller, recording the tilt angle corresponding to the maximum optical power, and automatically returning to the tilt angle corresponding to the maximum optical power after the 1 / 4 wave plate is scanned, and positioning the half wave plate to the tilt angle corresponding to the maximum optical power, so as to realize the positioning of the maximum optical power, and finally the optical power is close to the maximum optical power in the scanning process.

5. The MPI automated control testing method of claim 4, wherein, The adjustment of the polarization state of the main signal comprises that the main signal passes through the first electrically-controlled polarization controller and is divided into a branch light through a 90:10 polarization maintaining coupler to measure the power on the power meter, then the FPGA controls the electrically-controlled polarization controller to adjust the polarization state of the main signal according to the power size and the automatic control algorithm.

6. The MPI automated control testing method of claim 4, wherein, The adjustment of the polarization state of the branch signal comprises that the branch signal passes through the second electrically-controlled polarization controller and then is divided into a branch light through a 50:50 polarization maintaining coupler to measure the power on the power meter, then the FPGA controls the electrically-controlled polarization controller to adjust the polarization state of the main signal according to the power size and the automatic control algorithm.

7. The MPI automatic control test method of claim 4, wherein, In the step S4, the FPGA controls the electrically-controlled adjustable optical attenuator to add attenuation to the branch signal.

8. The MPI automated control testing method of claim 4, wherein, The automatic control algorithm comprises a PID algorithm and a scanning algorithm based on blind adjustment.

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