A method and system for measuring the photo-darkening effect of a double-clad gain fiber

Abstract

The application provides a kind of method and system for measuring the photo-darkening effect of double-clad gain fiber, relating to the field of special optical fiber.By obtaining the power loss data of double-clad gain fiber with different lengths under certain conditions, and building a model of photo-darkening effect, the power change of each fiber is processed, the data after eliminating the length influence is normalized, and a target function is set, then the model parameters are optimized to obtain the optimal data reference table of different fiber lengths and corresponding powers, the percentage change of the power of the measured fiber in the preset waveband before and after photo-darkening is calculated using the model, the measurement result is compared with the reference data, if the difference is less than the error threshold, it is considered as the effective measurement result of the measured fiber; The application has systematic steps, improves the accuracy of data processing, and thus improves the accuracy and reliability of measuring the photo-darkening effect of double-clad gain fiber.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of special optical fiber, in particular to a method and system for measuring the photo-darkening effect of double-clad gain fiber. BACKGROUND

[0002] The core of the double-clad gain fiber is doped with rare earth elements, and when the pump light is reflected in the inner cladding, it will pass through the core multiple times, so that the rare earth ions in the fiber core can fully absorb the pump light, thereby increasing the absorption rate of the pump light. Photo-darkening refers to the situation that the laser power of rare earth doped optical fiber decreases over time, and this phenomenon is common in gain fiber; photo-darkening will cause permanent damage to the gain fiber, which will reduce the service life of the fiber laser using the gain fiber as the gain medium. The development of high-quality double-clad gain fiber materials makes it possible to have high-power fiber lasers.

[0003] Double-clad gain fiber is an indispensable part of fiber laser or amplifier, and is one of the core devices of fiber laser, which can achieve a series of laser outputs in the visible, near-infrared to mid-infrared bands. In order to more effectively test and characterize the photo-darkening effect, J.J. Koponen et al. of the Finnish company Liekki company carried out a series of experiments. They used a 633nm wavelength light source to test the photo-darkening additional loss of ytterbium-doped fiber, and found that the additional loss of 633nm wavelength was 71 times that of the signal wavelength. According to the research of many domestic and foreign researchers, it is found that the repeatability of fiber core pump test is good, and it is very suitable for use as a measurement standard for photo-darkening. The cladding pump is more suitable for the study of photo-darkening of different particle number inversion levels. SUMMARY

[0004] The main purpose of the present application is to provide a method for measuring the photo-darkening effect of double-clad gain fiber, which has the advantages of simple optical path construction, simple operation steps, high stability of test optical path, short test period, high test efficiency and accurate test results.

[0005] To solve the above technical problems, the technical scheme adopted by the present application is as follows: a method for measuring the photo-darkening effect of double-clad gain fiber, comprising the following steps:

[0006] S1: obtaining and using a data set of different fiber lengths and corresponding power loss;

[0007] S2: calculating the power change of each fiber after eliminating the length effect, and then normalizing the data after eliminating the length effect, setting up a target function, and building a photo-darkening effect model, the formula is:

[0008] ;

[0009] wherein, and Pini and Pfin are initial power and final power, is an attenuation coefficient, is the length of the optical fiber;

[0010] S3: using a gradient descent algorithm to minimize the objective function to obtain an optimal data reference table of different optical fiber lengths and corresponding powers, i.e., a change table before and after attenuation;

[0011] S4: obtaining the optimal length of the optical fiber to be measured, denoted as L1; connecting the optical fiber to be measured with a length of L1 into the light-induced darkening effect model to obtain a measured power result, and obtaining the power test result again after a long time of pumping light; then calculating the power change percentage of the preset waveband of the test optical fiber before and after light-induced darkening;

[0012] S5: searching for the corresponding data in the data reference table in S3 and subtracting the measurement result in S4, if the difference is less than the error threshold, then it is the effective measurement result of the optical fiber to be measured. Then, according to the analysis and arrangement of S4, the power attenuation change graph of the optical fiber to be measured with time is obtained;

[0013] In the preferred scheme, in step S2, the relationship between the power loss and the length of the optical fiber is considered, and a linear regression is used to fit the relationship between the power loss and the length of the optical fiber, so as to eliminate the influence of the length of each optical fiber.

[0014] In the preferred scheme, in step S4, the power change percentage of the preset waveband of the test optical fiber before and after light-induced darkening is calculated, and the formula is:

[0015] ;

[0016] In the formula, A is the red light power before light-induced darkening, and B is the red light power obtained after light-induced darkening.

[0017] In the preferred scheme, the data set of different optical fiber lengths and corresponding power losses is obtained and utilized, including the following steps:

[0018] A plurality of optical fibers to be measured are sequentially connected into a test optical path, i.e., the two ends are respectively fused with a high-reflectivity grating and a low-reflectivity grating, the light in the light source is coupled into the optical fiber to be measured, a first pump light source is used for scanning test, the value of the power meter after stabilization is recorded and the first pump light source is turned off, the data is saved, and the data is denoted as A;

[0019] A second pump light source is turned on and lasts for a preset period of time, and the power meter records the power change curve in real time, the data is processed into time series data, and at the same time, the data is processed into a curve of the light-induced darkening additional loss of the second wavelength optical fiber with the change of pumping time, the second wavelength being the waveband length of the second pump light source;

[0020] Close the second pump light source, open the first pump light source, record the data after the power meter stabilizes, and close the first pump light source, save the data, and the data is recorded as B;

[0021] Wherein, after one optical fiber to be tested is tested, the test of the second optical fiber to be tested can be performed.

[0022] In the preferred embodiment, the data processing is a curve of the second wavelength fiber photo-darkening additional loss changing with pump time, and further comprises: arranging the collected time sequence data and corresponding power values, and comparing them with a standard time-power curve for consistency, and if within a preset error range, it is effective data.

[0023] In the preferred embodiment, judging that the power meter is stable, specifically: according to the real-time collected power, a power curve is drawn, and a 3δ principle is used for division.

[0024] In the preferred embodiment, the test optical fiber is fused by a 100P+ Fujikura fusion splicer.

[0025] A system for measuring the photo-darkening effect of a double-clad gain optical fiber, suitable for the method for measuring the photo-darkening effect of a double-clad gain optical fiber, comprising:

[0026] A data acquisition module for acquiring and utilizing data sets of different optical fiber lengths and corresponding power losses;

[0027] A model building module for calculating the power change of each optical fiber after eliminating the length effect, and then normalizing the data after eliminating the length effect, setting up a target function, and building a photo-darkening effect model, the formula being:

[0028] ;

[0029] In the formula, and are the initial power and the final power, is the attenuation coefficient, is the optical fiber length;

[0030] A data reference table module for minimizing the target function by using a gradient descent algorithm to obtain an optimal data reference table of different optical fiber lengths and corresponding powers;

[0031] An optical fiber test module for connecting the optical fiber to be tested with a length of L1 into the photo-darkening effect model to obtain the test result, i.e., calculating the power change percentage of the test optical fiber in the preset waveband before and after photo-darkening;

[0032] The test result module is used for finding corresponding data of the data reference table in S3 and subtracting the measurement result of S4, and if the difference is less than an error threshold, the effective measurement result of the to-be-measured optical fiber is obtained; then, the effective measurement result is analyzed and arranged according to S4 to obtain a power decay change graph of the to-be-measured optical fiber over time.

[0033] The application provides a method and system for measuring the photo-darkening effect of a double-clad gain optical fiber, power loss data of double-clad gain optical fibers with different lengths under specific conditions (such as the same pump power, working environment, etc.) are obtained, a mathematical model capable of describing the photo-darkening effect is built, the power change of each optical fiber is processed to eliminate the direct influence of the optical fiber length on the power loss, the data after eliminating the length influence is normalized, a target function is set, and model parameter optimization adjustment is performed to reduce the value of the target function, so as to obtain an optimal data reference table of different optical fiber lengths and corresponding powers, the change percentage of the power of a to-be-measured optical fiber in a preset waveband (such as a specific wavelength range) before and after photo-darkening is calculated by using the model, the measurement result is compared with the reference data, and if the difference is less than an error threshold, the measurement result of the to-be-measured optical fiber is regarded as effective. BRIEF DESCRIPTION OF DRAWINGS

[0034] The application will be further described below in combination with the drawings and embodiments:

[0035] Figure 1 is a test optical path diagram of the photo-darkening effect built by the application;

[0036] Figure 2 is a method flowchart of the photo-darkening effect of the application.

[0037] In the figure: light source 1; light source output optical fiber 4; WDM input optical fiber 3; WDM 4; 916nm pump 5; beam combiner 6; high-reflection grating 7; to-be-measured optical fiber 8; low-reflection grating 9; CPS 9; first filter 11; second filter 12; power meter 13. DETAILED DESCRIPTION

[0038] Embodiment 1

[0039] As shown in the figure, a method for measuring the photo-darkening effect of a double-clad gain optical fiber is proposed, which comprises the following steps: Figures 1-2

[0040] S1: Obtain and use a data set of different optical fiber lengths and corresponding power losses.

[0041] ​S2: Calculate the power change of each optical fiber after eliminating the length effect, then normalize the data after eliminating the length effect, set up a target function, build a photo darkening effect model, and the formula is:

[0042] ;

[0043] wherein, and are the initial power and the final power, is the attenuation coefficient, is the fiber length.

[0044] S3: Use the gradient descent algorithm to minimize the target function to obtain the optimal data reference table of different fiber lengths and corresponding powers.

[0045] S4: Connect the length L1 of the to-be-measured optical fiber to the photo darkening effect model to obtain the to-be-measured result, that is, calculate the power change percentage of the preset waveband of the test optical fiber before and after photo darkening.

[0046] S5: Find the corresponding data in the data reference table in S3, and subtract the measurement result in S4. If the difference is less than the error threshold, it is the effective measurement result of the to-be-measured optical fiber. Then, according to the analysis and arrangement of S4, the power attenuation change graph of the to-be-measured optical fiber with time is obtained.

[0047] In the above steps, the power loss data of double-clad gain optical fibers of different lengths under specific conditions (such as the same pump power, working environment, etc.) is obtained, a mathematical model capable of describing the photo darkening effect is built, the power change of each optical fiber is processed to eliminate the direct influence of the fiber length on the power loss, the data after eliminating the length effect is normalized, a target function is set, and the model parameter optimization adjustment is performed to reduce the value of the target function, so as to obtain the optimal data reference table of different fiber lengths and corresponding powers. The change percentage of the power of the to-be-measured optical fiber in the preset waveband (such as a specific wavelength range) before and after photo darkening is calculated using the model, the measurement result is compared with the reference data, and if the difference is less than the error threshold, it is considered as the effective measurement result of the to-be-measured optical fiber. The embodiment has systematic steps, improves the accuracy of data processing, and thus improves the accuracy and reliability of measuring the photo darkening effect of double-clad gain optical fibers.

[0048] In the embodiment, the initial length L1 of the to-be-measured gain optical fiber used in the test method of the photo darkening effect of the double-clad gain optical fiber is 5 m, and the error threshold can be set to be not greater than 0.03*reference data according to actual conditions, that is: .

[0049] In this embodiment, the first pump light source is a 976 nm pump light source, the second pump light source is a 633 nm wavelength pump light source, and the preset time period is 7200 seconds.

[0050] As shown in Figure 1 The 633 nm light source 1 used is a custom device using a THORLABS KLS635, a WDM, a (1+1)*1 combiner 6, a high reflection grating 7, a low reflection grating 9, and a CPS 9. Compared with the old aging test method, the test period is long and the efficiency is low. Compared with the spatial light path test method, the light path is complex and tedious to build, and the platform stability is required to be higher. The light path built is simple and easy to operate, the test period is short, and the efficiency is high. In the present application, the optical signal generated by the light source 1 is transmitted to the WDM 4 through the light source output optical fiber 4, then enters the measured optical fiber 8 through the combiner 6, the high reflection grating 7 and the low reflection grating 9 are used for reflecting and transmitting the optical signal respectively, the filters 11 and 12 are used to select specific wavelength light from the output signal for measurement, and finally the power meter 13 measures the power of the output optical signal to evaluate the performance of the measured optical fiber 8; the test method for the described double-clad gain fiber photo-darkening effect is all-fiber structure, and the test light path can be built by fiber fusion.

[0051] In the preferred scheme, in step S2, considering the relationship between the power loss and the length of the optical fiber, a linear regression is used to fit the relationship between the power loss and the length of the optical fiber, so as to eliminate the influence of the length of each optical fiber.

[0052] In the optical fiber communication system, as the length of the optical fiber increases, the attenuation of the optical signal in the transmission process will also increase, resulting in an increase in power loss. In this embodiment, a linear regression model is used. For each optical fiber, according to its length, the predicted power loss value is calculated using the linear regression model, the accuracy of the S4 measurement result is confirmed, and the power loss of the optical fiber due to the photo-darkening effect is estimated from the side, thereby providing a theoretical reference for the long-term life and reliability of the optical fiber.

[0053] In the preferred scheme, the data set of different optical fiber lengths and corresponding power losses is obtained and utilized, including the following steps:

[0054] A plurality of measured optical fibers are sequentially connected to the test light path, i.e. the two ends are fused with the high reflection grating and the low reflection grating respectively, the light in the light source is coupled into the measured optical fiber, the first pump light source is used for scanning test, the value of the power meter after stabilization is recorded and the first pump light source is turned off, the data is saved, and the data is recorded as A.

[0055] The second pump light source is turned on and lasts for a preset time period, and the power meter records the power change curve in real time. The data is processed as time series data, and at the same time, the data is processed as a curve of the second wavelength optical fiber photo-darkening additional loss changing with the pump time. The second wavelength is the wavelength length of the second pump light source.

[0056] Turn off the second pump light source, turn on the first pump light source, record the data after the power meter stabilizes, and turn off the first pump light source, save the data, and record the data as B.

[0057] Wherein, after the test of one optical fiber to be tested is completed, the test of the second optical fiber to be tested can be performed.

[0058] Specifically:

[0059] 1) Each time only one is connected, the length of the test fiber L1 is connected Figure 1 The light path is shown, that is, the two ends of the test fiber are respectively fused with the high reflection grating and the low reflection grating; first, turn on the 976nm pump light source (first pump light source), record the value after the power meter stabilizes, and the data is recorded as A; after the data is recorded, turn off the 976nm pump light source.

[0060] 2) Turn on the 633nm waveband light source (second pump light source), and the power meter records the power change curve in real time until 7200S, and then turn off the 633nm waveband light source; process the data as the percentage of power decrease caused by light-induced darkening with time; at the same time, process the data as the curve of the additional loss of the 633nm wavelength fiber light-induced darkening with pump time.

[0061] 3) After turning off the 633nm waveband light source, turn on the 976nm waveband light source, record the data after the power meter stabilizes, and record the data as B, and turn off the 976nm pump light source after the data is recorded.

[0062] 4) Calculate the percentage change of the power of the test fiber in the 976nm waveband before and after light-induced darkening.

[0063] In the preferred scheme, the percentage change of the power of the test fiber in the preset waveband before and after light-induced darkening is calculated, and the formula is:

[0064] ;

[0065] In the formula, A is the power before light-induced darkening, and B is the power obtained after light-induced darkening.

[0066] In the preferred scheme, the data processing into the curve of the additional loss of the second wavelength fiber light-induced darkening with pump time also includes: arranging the collected time sequence data and corresponding power values, and comparing them with the standard time power curve for consistency, if within the preset error range, it is effective data.

[0067] In this embodiment, the collated time series data and the corresponding power value are compared with the standard time-power curve for consistency. The standard time-power curve can be obtained based on previous experiments or theoretical models, which is used to describe the variation of the power of the optical fiber with time under certain conditions (such as pump power, working environment, etc.).

[0068] A preset error range is used to evaluate the consistency between the experimental data and the standard curve. The error range can be set according to experimental requirements, fiber characteristics, etc.

[0069] In the preferred embodiment, the power meter is judged to be stable, specifically: according to the real-time collected power, a power curve is drawn, and the 3δ principle is used for division.

[0070] In this embodiment, the real-time collected power data is associated with time, and a power curve with time is drawn, which intuitively shows the power change trend of the optical fiber under the action of the pump, such as the rise, stability or decline of the power, etc. The collected power data is statistically analyzed to calculate the mean (μ) and standard deviation (σ) of the power. According to the 3δ principle, the power data is divided into normal data and abnormal data: μ-3σ≤power≤μ+3σ. The data within this range is considered normal, reflecting the normal power change of the optical fiber under the action of the pump. The normal data is analyzed to extract useful information such as the rate of power change and the stable power value, so as to more effectively evaluate the photo-darkening effect of the double-clad gain optical fiber.

[0071] In the preferred embodiment, the test optical fiber is fused by a 100P+ Fujikura fusion splicer.

[0072] In order to describe the technical solutions of the present application more clearly and concisely, a specific optical path device is provided:

[0073] (1) A 633nm red light source, a 976nm pump source, a WDM, a (1+1)*1 combiner, a high-reflectivity grating, a low-reflectivity grating, a CPS, a 100P+ fusion splicer, a cutting knife and a power meter are used.

[0074] (2) The embodiment is used to measure the photo-darkening of Yb-doped double-clad optical fiber. The test optical fiber is a double-clad optical fiber produced by Nufern Company in the United States, with a core diameter of 20um, a cladding diameter of 400um, an octagonal cladding shape, a core numerical aperture of 0.065±0.005, a cladding numerical aperture of ≥0.46, and a test optical fiber length of 5m.

[0075] A specific implementation method is provided, which includes the following steps:

[0076] I. Optical path setup:

[0077] (1) 633nm light source and WDM connection: first, the jumper of the 633nm light source output end is stripped of the protective layer, and the bare optical fiber is exposed. Then, the bare optical fiber is cut using the Fujikura cutting knife, and the WDM input end is also cut using the Fujikura cutting knife. Then, the two cut optical fibers are fused and cured. After cutting the other input end optical fiber of the WDM, align the optical fiber end face with the blackbody absorption cavity. Simply put, fuse the optical fiber in Figure 1 with the optical fiber in Figure 4, and place the cut optical fiber in Figure 3 into the blackbody absorption cavity.

[0078] (2) WDM and (1+1)*1 combiner connection: fuse the output optical fiber in Figure 4 with the input optical fiber in Figure 6; fuse the pump source output optical fiber in Figure 5 with the input pump optical fiber in Figure 6.

[0079] (3) (1+1)*1 combiner and high reflection grating connection: fuse the output end in Figure 6 with the high reflection grating in Figure 7, and pay attention to the directionality of the high reflection grating.

[0080] (4) Low reflection grating and CPS connection: fuse Figure 9 with Figure 10, and pay attention to the directionality of the low reflection grating.

[0081] (5) Cut the other end of the CPS and align it with the filter. Place the power meter behind the filter. The filter and the CPS optical fiber end face form a 45° angle. The optical path is completed.

[0082] (6) The above fusions use Fujikura fusion machines and cutting knives. All the devices are placed on an optical water cooling platform, and the water temperature is set to 23°C.

[0083] II. Test steps of the photo-darkening effect of double-clad gain optical fiber

[0084] (1) First, cut the L1 length of the optical fiber to be tested, then connect the optical fiber to Figure 8, that is, fuse the two ends of the optical fiber to be tested with the high reflection grating and the low reflection grating respectively; first, turn on the 976nm pump source, record the stable value of the power meter, and the data is recorded as A; after the data is recorded, turn off the 976nm pump source.

[0085] (2) Turn on the 633nm waveband light source, and record the power change curve in real time. Turn off the 633nm waveband light source after 7200S. Process the data as a function of time, and the photo-darkening power drop percentage. At the same time, process the data as a function of pump time.

[0086] (3) After turning off the 633nm waveband light source, turn on the 976nm waveband light source, record the stable data of the power meter, and the data is recorded as B. After the data is recorded, turn off the 976nm pump source.

[0087] (4) Calculate the power change percentage of the test optical fiber in the 976nm waveband before and after light-induced darkening.

[0088] In use, first, in addition to the optical fiber to be tested, the remaining devices in the optical path are connected by optical fiber fusion, except for the filter; then the optical fiber to be tested is connected into the test optical path, the optical fiber to be tested is tested according to the operation steps, and after the test is completed, a red light attenuation curve and a 976nm power loss percentage are obtained.

[0089] The optical path used in this embodiment is easy to build, shorter than directly laser testing time, and can conveniently test the light-induced darkening of double-clad gain optical fiber, and more accurately test the long-term reliability of double-clad gain optical fiber and evaluate the service life.

[0090] Embodiment 2

[0091] In combination with Embodiment 1, a system for measuring the light-induced darkening effect of double-clad gain optical fiber is further illustrated, which is suitable for the method for measuring the light-induced darkening effect of double-clad gain optical fiber in Embodiment 1, and includes:

[0092] A data acquisition module is configured to acquire and utilize a data set of different optical fiber lengths and corresponding power losses.

[0093] A model building module is configured to calculate the power change of each optical fiber after eliminating the length influence, and then to normalize the data after eliminating the length influence, to set up a target function, and to build a light-induced darkening effect model, with the formula being:

[0094] ;

[0095] In the formula, and are initial power and final power, is an attenuation coefficient, is optical fiber length.

[0096] A data reference table module is configured to minimize the target function by using a gradient descent algorithm to obtain an optimal data reference table of different optical fiber lengths and corresponding powers.

[0097] An optical fiber testing module is configured to connect a length L1 optical fiber to be tested into the light-induced darkening effect model to obtain a test result, i.e., to calculate the power change percentage of the test optical fiber in a preset waveband before and after light-induced darkening.

[0098] A test result module is configured to find corresponding data in the data reference table in S3, and subtract the measurement result in S4, if the difference is less than an error threshold, then it is an effective measurement result of the optical fiber to be tested; and then the effective measurement result is analyzed and arranged according to S4 to obtain a power change curve over time of the optical fiber to be tested.

[0099] The above embodiments are only the preferred technical solutions of the present application, and should not be regarded as the limitation of the present application. The protection scope of the present application should be the technical solutions recited in the claims, including the equivalent replacement solutions of the technical features recited in the claims. That is, the equivalent replacement improvements within this range are also within the protection scope of the present application.

Claims

1. A method for measuring the photo-darkening effect of a double-clad gain fiber, characterized in that, Comprising the following steps: S1: Obtain and utilize the data set of different fiber lengths and corresponding power loss; S2: Calculate the power change of each fiber after eliminating the length effect, and then normalize the data after eliminating the length effect, set up a target function, build a photo darkening effect model, and the formula is: ； wherein and P0 is the initial power and P1 is the final power, a is the decay coefficient, L is the optical fiber length; S3: Adopt gradient descent algorithm to minimize the target function to obtain the optimal data reference table of different fiber lengths and corresponding power; S4: Connect the length L1 of the fiber to be measured into the photo darkening effect model to obtain the test result, that is, calculate the power change percentage of the preset waveband of the test fiber before and after photo darkening; S5: Find the corresponding data in the data reference table in S3, and subtract the measurement result in S4, if the difference is less than the error threshold, it is the effective measurement result of the fiber to be measured; then the effective measurement result is analyzed and arranged according to S4 to obtain the power decay change graph of the fiber to be measured over time; Obtain and utilize the data set of different fiber lengths and corresponding power loss, comprising the following steps: Connect a plurality of test fibers into the test optical path in turn, that is, the two ends are respectively fused with high and low reflection gratings, the light in the light source is coupled into the test fiber, the first pump light source is used for scanning test, the value of the power meter after stabilization is recorded and the first pump light source is turned off, the data is saved, and the data is recorded as A; Turn on the second pump light source and keep it on for a preset period of time, and the power meter records the power change curve in real time, and the data is processed into time sequence data, and at the same time, the data is processed into the curve of the additional loss of the second wavelength fiber photo darkening with the change of pump time, and the second wavelength is the waveband length of the second pump light source; Turn off the second pump light source and turn on the first pump light source, record the data of the power meter after stabilization, turn off the first pump light source, save the data, and record the data as B; Wherein, after the test of one test fiber is completed, the test of the second test fiber can be carried out.

2. The method for measuring photo-darkening effect of a double-clad gain fiber according to claim 1, wherein, In step S2, considering the relationship between the power loss and the length of the fiber, the relationship between the power loss and the length of the fiber is fitted by linear regression, so as to eliminate the length effect of each fiber.

3. The method for measuring photo-darkening effect of double-clad gain fiber according to claim 1, wherein, In step S4, the power change percentage of the preset waveband of the test fiber before and after photo darkening is calculated, and the formula is: ； In the formula, A is the red light power before photo darkening, and B is the red light power obtained after photo darkening.

4. The method for measuring photo-darkening effect of double-clad gain fiber according to claim 1, wherein, The data processing into the curve of the additional loss of the second wavelength fiber photo darkening with the change of pump time also includes: arranging the collected time sequence data and corresponding power values, and comparing them with the standard time power curve for consistency, if within the preset error range, it is effective data.

5. The method for measuring photo-darkening effect of double-clad gain fiber according to claim 1, wherein, Judging that the power meter is stable, specifically: according to the real-time collected power, a power curve is drawn, and the 3δ principle is adopted for division.

6. The method for measuring the photo-darkening effect of a double-clad gain fiber according to claim 1, wherein, The test fiber is fused by 100P+ Fujikura fusion splicer.

7. A system for measuring photo-darkening effects in a double-clad gain fiber, comprising: a light source; a double-clad gain fiber; a light detector; and a computer system. The method is suitable for measuring the photo darkening effect of the double-clad gain fiber, comprising: A data acquisition module for obtaining and utilizing the data set of different fiber lengths and corresponding power loss; The model building module is configured to calculate the power change of each optical fiber after eliminating the length effect, normalize the data after eliminating the length effect, set a target function, and build a photo darkening effect model, with the formula being: ； wherein and P0is the initial power and P1is the final power, is the decay coefficient, is the optical fiber length; The data reference table module is configured to minimize the target function by using a gradient descent algorithm to obtain an optimal data reference table of different optical fiber lengths and corresponding powers. The optical fiber testing module is configured to connect the optical fiber with a length of L1 to be tested into the photo darkening effect model to obtain a test result, i.e., to calculate the power change percentage of the preset waveband of the test optical fiber before and after photo darkening. The test result module is configured to find the corresponding data in the data reference table in S3 and subtract the measurement result in S4, and if the difference is less than an error threshold, the result is an effective measurement result of the test optical fiber; and then the effective measurement result is analyzed and arranged according to S4 to obtain a power decay change graph of the test optical fiber over time.

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