A method and system for evaluating performance of an energy delivery optical fiber in a gamma radiation environment

Abstract

The present application relates to a kind of gamma irradiation environment under the performance evaluation method and system of energy transmission fiber, irradiation induced attenuation test, high-power laser transmission test, electron paramagnetic resonance test and photoluminescence test are organically combined, and a set of highly generalization ability and general anti-radiation fiber engineering evaluation and selection guidance system are formed.By converting offline RIA result into equivalent additional insertion loss, and introducing correction term to establish irradiation output power prediction model, the power attenuation of fiber in running state can be quickly estimated.By introducing electron paramagnetic resonance and photoluminescence two complementary defect characterization means, the cause of fiber transmission performance degradation and heating enhancement after irradiation is explained from microcosmic level, the explainability of evaluation result is improved, and the integrity and reliability of irradiation transmission fiber performance degradation evaluation are fundamentally improved.

Description

Technical Field

[0001] This invention relates to the field of optical fiber performance research technology, specifically to a method and system for evaluating the performance of power transmission optical fibers under gamma irradiation. Background Technology

[0002] In high-irradiation scenarios such as nuclear facility operation, decommissioning, and spent fuel reprocessing, long-distance, maintainable, and highly integrated energy transmission and condition monitoring methods have always been key aspects of engineering implementation. Compared to traditional mechanical cutting and plasma cutting, kilowatt-level fiber lasers offer advantages such as high energy density, ease of remote operation, and strong adaptability to confined and narrow spaces, making them an important candidate technology in nuclear decommissioning and nuclear fuel reprocessing. However, during laser operation, the optical fiber is inevitably exposed to a complex and intense ionizing radiation field composed of gamma rays, X-rays, etc. The interaction between high-energy radiation and the fiber material induces topological reconstruction, atomic shifts, and the generation of a large number of electron-hole pairs in the amorphous quartz network, ultimately forming color centers and point defects with strong optical absorption activity within the material. This performance degradation induced by external high-energy radiation not only manifests as an exponential increase in fiber background transmission loss but also leads to spatial distortion of the macroscopic refractive index, material densification, and a precipitous drop in the optical damage threshold. Meanwhile, when high-power laser transmission and strong radiation field effects are nonlinearly superimposed in space and time inside the optical fiber, radiation-induced defects become strong absorption sources of laser energy, triggering localized and severe heat accumulation and thermal runaway, which in turn leads to carbonization of the fiber coating, melting of the cladding, or even catastrophic cracking of the end face.

[0003] Current research focuses on low-power signal links in communication bands or sensing applications, examining the impact of dB-level loss variations on link budget. However, kilowatt-level power transmission fibers face challenges related to thermal load, mode field distribution, end-face damage, and system stability. The evaluation metrics and failure modes differ significantly, making it impossible to simply extrapolate conclusions from communication fibers. Furthermore, research on power transmission fibers lacks a unified and verifiable bridge between macroscopic phenomena and microscopic defects, and clear evidence remains regarding which defect families contribute to the quantitative contribution of loss in the operating band. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a method and system for evaluating the performance of power-transmitting optical fibers under gamma irradiation. On one hand, it solves the problem that existing technologies struggle to provide a unified and quantitative evaluation of the performance degradation of power-transmitting optical fibers under high irradiation conditions. On the other hand, it provides a highly generalizable and universal radiation-resistant engineering evaluation and selection guidance system, improving the completeness and reliability of performance degradation assessment of power-transmitting optical fibers after irradiation.

[0005] To achieve the above objectives, in one aspect, the present invention provides a method for evaluating the performance of power-transmitting optical fibers under gamma irradiation, including radiation-induced attenuation testing and laser transmission testing of optical fiber samples before and after irradiation.

[0006] The average attenuation coefficient of the working band obtained from the radiative attenuation test is converted into the additional insertion loss over the actual sample length.

[0007] By conducting laser transmission tests on fiber optic samples before and after irradiation, a correction term is introduced to correct the additional insertion loss, thereby obtaining the effective insertion loss of the operating state that can truly represent the boundary conditions of high-power operation.

[0008] Based on the effective insertion loss in the operating state, a prediction model is established to predict the output power of the optical fiber after irradiation, thereby enabling a rapid estimation of the power attenuation of the optical fiber in the operating state.

[0009] Furthermore, in a specific embodiment, the method for evaluating the performance of power transmission optical fiber under γ-irradiation as described above involves performing radiation-induced attenuation tests on optical fiber samples before and after irradiation, extracting the average value of the characteristic attenuation window facing the high-power laser working band, obtaining the average attenuation coefficient of the working band, and multiplying the average attenuation coefficient of the working band by the length of the test section of the optical fiber sample to obtain the additional insertion loss.

[0010] Furthermore, in a specific embodiment, in the above-described method for evaluating the performance of power transmission optical fibers under γ-irradiation, the effective insertion loss in the operating state is equal to the difference between the additional insertion loss and the correction term.

[0011] Furthermore, in a specific embodiment, the method for evaluating the performance of power transmission optical fiber under γ-irradiation as described above involves applying the least squares method to fit and optimize the difference between the theoretically calculated additional insertion loss of the irradiated optical fiber sample at several pump levels and the actual additional insertion loss in the operating state, thereby obtaining the correction term.

[0012] The actual additional insertion loss in the operating state is calculated as follows:

[0013]

[0014] Where, ΔIL meas Add insertion loss to the actual operating state, P pre P represents the initial output power of the fiber sample before irradiation at a specific pump setting. post This represents the actual output power of the fiber optic sample after irradiation at a specific pump setting.

[0015] Furthermore, in a specific embodiment, the performance evaluation method for power transmission optical fibers under gamma irradiation as described above, wherein the prediction model for predicting the output power of the optical fiber after irradiation is as follows:

[0016]

[0017] Among them, P post, pred P is the predicted output power after irradiation. pre IL represents the initial output power of the fiber sample before irradiation at a specific pump level. eff This represents the effective insertion loss during operation.

[0018] Furthermore, in a specific embodiment, the method for evaluating the performance of power transmission optical fibers under γ-irradiation as described above also includes electron paramagnetic resonance testing of optical fiber samples before and after irradiation, extracting the peak position, line shape, and double integral area of ​​characteristic signals as semi-quantitative characterization parameters of paramagnetic defect concentration changes, using the double integral area as a paramagnetic defect index, and establishing a correlation with the average radiation-induced attenuation coefficient of the working band through linear fitting, which is used to explain the microscopic sources of macroscopic transmission degradation.

[0019] Furthermore, in a specific implementation, the method for evaluating the performance of power-transmitting optical fibers under gamma irradiation as described above also includes photoluminescence testing of fiber samples before and after irradiation, including excitation spectrum testing and emission spectrum testing. The emission spectrum is acquired under a fixed excitation wavelength, and the emission band is processed by Gaussian peak division to extract the peak position, peak area, and full width at half maximum (FWHM) parameters of each sub-peak. The peak area evolution law under different irradiation doses is used to determine the generation, transformation, and quenching process of optically active defect centers, providing an explanatory basis at the microscopic defect level.

[0020] On the other hand, a specific embodiment of the present invention provides a system for implementing the above-mentioned method for evaluating the performance of power transmission optical fibers under gamma irradiation, including an optical fiber sample group, a gamma irradiation unit, a radiation-induced attenuation testing unit, a laser transmission testing unit, and a data processing and evaluation unit.

[0021] The optical fiber sample group is fixed in a uniform manner and irradiated by a γ-irradiation unit.

[0022] The radiation-induced attenuation test unit includes a white light source, an input lens, an output connector, and a spectrometer. The white light source provides broadband incident light covering the test band. The incident light input is coupled into the optical fiber using a lens, and the optical fiber output is connected to the spectrometer through a connector to collect the transmission spectrum.

[0023] The laser transmission test unit includes a laser and a power meter. The laser is connected to the optical fiber input end, and the power meter is connected to the optical fiber output end.

[0024] The data processing and evaluation unit is used to process the test data, establish a prediction model for predicting the output power of the optical fiber after irradiation, and quickly estimate the power attenuation of the optical fiber under operating conditions.

[0025] Furthermore, in a specific implementation, in the above-described γ-irradiation environment power transmission fiber performance evaluation system, the fiber sample is fixed by a multi-turn coiling method to ensure that the geometric shape of the sample is consistent during the irradiation stage and the laser transmission stage, thereby reducing the impact of mechanical stress differences on the test results.

[0026] Furthermore, in a specific embodiment, the optical fiber performance evaluation system under gamma irradiation as described above, wherein the optical fiber samples are kept under the same ambient temperature, the same spatial orientation, and the same coiling state during the optical fiber irradiation process, so as to ensure the comparability between different samples or different dose groups.

[0027] Furthermore, in a specific implementation, the power transmission fiber performance evaluation system under gamma irradiation as described above involves numbering all samples before irradiation and dividing them into multiple batches according to the target cumulative dose, so as to ensure that samples at different dose points can be tested within the same time window as much as possible after irradiation.

[0028] Furthermore, in a specific embodiment, the optical fiber performance evaluation system under gamma irradiation as described above includes an infrared thermal imager in the laser transmission test unit to measure the temperature of the optical fiber sample during the laser transmission test.

[0029] Furthermore, in a specific embodiment, the power transmission fiber performance evaluation system under gamma irradiation as described above further includes an electron paramagnetic resonance (EPR) testing unit. An EPR spectrometer is used to measure the first differential spectrum of fiber samples before and after irradiation to obtain information on irradiation-induced paramagnetic defects. The data processing and evaluation unit extracts the peak position, line shape, and double integral area of ​​the characteristic signal as semi-quantitative characterization parameters for changes in paramagnetic defect concentration. The double integral area is used as a paramagnetic defect index, and a linear correlation is established with the average radiation-induced attenuation coefficient of the working band to explain the microscopic sources of macroscopic transmission degradation in the fiber.

[0030] Furthermore, in a specific embodiment, the optical fiber performance evaluation system under gamma irradiation as described above also includes a photoluminescence testing unit. A time-resolved fluorescence spectrometer is used to measure the steady-state photoluminescence of the optical fiber. The data processing and evaluation unit acquires the emission spectrum under a fixed excitation wavelength and performs Gaussian peak subdivision processing on the emission band. The peak position, peak area, and full width at half maximum (FWHM) parameters of each sub-peak are extracted. The peak area evolution law under different irradiation doses is used to determine the generation, transformation, and quenching process of optically active defect centers, providing an explanatory basis for the microscopic defect level of the optical fiber.

[0031] The beneficial effects of this invention are as follows:

[0032] (1) This invention proposes a comprehensive evaluation method for power-carrying multimode silica optical fibers under γ-irradiation, which organically combines irradiation-induced attenuation testing, high-power laser transmission testing, temperature response testing, electron paramagnetic resonance testing, and photoluminescence testing. This overcomes the problem in existing technologies that rely solely on single loss testing, single power testing, or single defect characterization methods, making it difficult to comprehensively evaluate the irradiation degradation behavior of power-carrying optical fibers. Through this comprehensive technical approach, multi-dimensional information such as additional loss in the operating band, output power attenuation, temperature rise enhancement, and defect evolution can be obtained simultaneously, thereby forming a continuous chain of evidence from macroscopic performance to microscopic mechanisms, improving the completeness and reliability of the performance degradation evaluation of power-carrying optical fibers after irradiation.

[0033] (2) This invention converts offline RIA results into equivalent additional insertion loss and further introduces a correction term to establish a post-irradiation output power prediction model. This allows for rapid estimation of fiber power attenuation under operating conditions without repeating a complete high-power operation test under every irradiation condition. This technique significantly improves the efficiency of performance evaluation of post-irradiation power-carrying fibers, reduces the cost and complexity of high-power testing, and has good engineering applicability. Under small sample conditions, the model achieves an average relative error of approximately 1% through leave-one-out cross-validation, and the coefficient of determination is greater than 0.999, indicating that this invention has high accuracy and robustness in output power prediction.

[0034] (3) This invention introduces two complementary defect characterization methods, electron paramagnetic resonance (EPR) and photoluminescence (PL), to establish a link between the accumulation of paramagnetic defects, changes in the optically active defect center, and loss in the operating band, decrease in output power, and increase in temperature rise. Through this technical solution, the reasons for the degradation of optical fiber transmission performance and the enhanced heating after irradiation can be explained at the microscopic level, thereby improving the interpretability of the evaluation results. Attached Figure Description

[0035] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a schematic diagram of the power transmission fiber performance evaluation system under γ-irradiation environment in a specific embodiment of the present invention.

[0037] Figure 2This is a schematic diagram of the radiation-induced attenuation (RIA) test unit in a specific embodiment of the present invention;

[0038] Figure 3 This is a schematic diagram of the laser transmission test unit in a specific embodiment of the present invention;

[0039] Figure 4 This is a comparison chart of the additional insertion loss and prediction of the optical fiber under different pump source settings in Embodiment 1 of the present invention.

[0040] Figure 5 This is a comparison chart of the measured and predicted output power of the optical fiber after irradiation in Embodiment 1 of the present invention;

[0041] Figure 6 The first derivative spectrum of the X-band EPR of the optical fiber before and after γ irradiation in Embodiment 2 of the present invention;

[0042] Figure 7 This is a linear fitting graph of the EPR double integral area and the 1080 nm RIA in Embodiment 2 of the present invention;

[0043] Figure 8 The PL emission spectrum (λex = 245 nm) under different irradiation doses in Example 2 of the present invention. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0045] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0046] The terms “comprising”, “including”, etc., as used herein indicate the presence of the steps, features, operations, or components, but do not preclude the addition of one or more other steps, features, operations, or components.

[0047] This invention relates to a method for evaluating the performance degradation and microscopic defects of energy-transmitting multimode silica optical fibers under gamma irradiation. To achieve this, it is necessary to preprocess and group the optical fiber samples first.

[0048] The fiber optic sample to be tested is cut to a predetermined length and fixed to the support frame in a uniform coiling manner. In some specific embodiments, the fiber optic sample is fixed using a multi-turn coiling method to ensure that the sample geometry is consistent during the irradiation and laser transmission stages, reducing the impact of mechanical stress differences on the test results. Furthermore, all samples are numbered before irradiation and divided into multiple batches according to the target cumulative dose to ensure that samples at different dose points can be subjected to subsequent testing within the same time window after irradiation, thereby reducing the impact of post-irradiation spontaneous annealing on the comparability of results.

[0049] When testing optical fiber samples, this invention requires performing radiation-induced attenuation (RIA), laser transmission, electron paramagnetic resonance (EPR), and photoluminescence (PL) tests on both unirradiated and irradiated samples. After completing the corresponding series of tests, the same group of samples is irradiated at a set dose point in a gamma irradiation device, and then the corresponding tests on the irradiated samples are performed.

[0050] The pretreated and grouped fiber optic samples were placed in a gamma irradiation device for total ionizing dose irradiation. The irradiation source was a gamma-ray field generated by a sealed cobalt-60 source. Multiple target total dose points were further set, such as 20 kGy, 50 kGy, and 100 kGy, with dose rates selected in the kGy / h range according to engineering simulation requirements. During irradiation, the samples were kept under the same ambient temperature, spatial orientation, and coiling state to ensure comparability between different samples or dose groups. After irradiation, the samples were stored in a light-protected, dry environment and subsequently characterized using subsequent experiments within a predetermined time window.

[0051] In some specific embodiments, the composition of the power transmission fiber performance evaluation system under γ-irradiation environment provided by the present invention is as follows: Figure 1 As shown, the system includes an optical fiber sample group, a gamma irradiation unit, a radiation-induced attenuation testing unit, a laser transmission testing unit, an electron paramagnetic resonance testing unit, a photoluminescence testing unit, and a data processing and evaluation unit. The entire system forms a highly generalizable and universal engineering evaluation and selection guidance system for radiation-resistant optical fibers.

[0052] First, in some specific embodiments, this invention provides a method for assessing the performance degradation of power transmission optical fibers under gamma irradiation and predicting output power, thereby addressing the problem that existing technologies struggle to provide a unified quantitative evaluation of the operating band loss, output power attenuation, and thermal risk of power transmission optical fibers under high radiation conditions. These specific embodiments creatively introduce a constant correction term that comprehensively characterizes the effects of photobleaching, thermal annealing, and the dynamic evolution of multimode distribution. They use offline test data to predict the effective insertion loss of actual optical fibers in high-power operating conditions, and the predicted mean relative error (MAPE) is strictly controlled to an extremely low level of one percent, providing a highly reliable lifetime early warning indicator for nuclear engineering.

[0053] In some specific embodiments, the method for evaluating the performance of power-transmitting optical fibers under gamma irradiation to address the above-mentioned problems includes radiation-induced attenuation testing and laser transmission testing of optical fiber samples before and after irradiation.

[0054] The average attenuation coefficient of the working band obtained from the radiative attenuation test is converted into the additional insertion loss over the actual sample length.

[0055] By conducting laser transmission tests on fiber optic samples before and after irradiation, a constant correction term is introduced to correct the additional insertion loss, thereby obtaining the effective insertion loss of the operating state that can truly represent the boundary conditions of high-power operation.

[0056] Based on the effective insertion loss in the operating state, a prediction model is established to predict the output power of the optical fiber after irradiation, thereby enabling a rapid estimation of the power attenuation of the optical fiber in the operating state.

[0057] In some specific embodiments, the system components for implementing the above method include: an optical fiber sample group, a gamma irradiation unit, a radiation-induced attenuation testing unit, a laser transmission testing unit, and a data processing and evaluation unit.

[0058] The optical fiber sample group is fixed in a uniform manner and irradiated by a γ-irradiation unit.

[0059] The radiation-induced attenuation test unit includes a white light source, an input lens, an output connector, and a spectrometer. The white light source provides broadband incident light covering the test band. The incident light input is coupled into the optical fiber using a lens, and the optical fiber output is connected to the spectrometer through a connector to collect the transmission spectrum.

[0060] The laser transmission test unit includes a laser and a power meter. The laser is connected to the optical fiber input end, and the power meter is connected to the optical fiber output end.

[0061] The data processing and evaluation unit is used to process the test data, establish a prediction model for predicting the output power of the optical fiber after irradiation, and quickly estimate the power attenuation of the optical fiber under operating conditions.

[0062] The following is a detailed description of each specific testing step.

[0063] Radiation-induced degradation (RIA) test:

[0064] Radiation-induced attenuation (RIA) testing is a crucial experimental method for evaluating changes in optical fiber transmission performance under ionizing radiation environments. The transmission loss of optical fibers primarily originates from inherent losses (such as scattering and absorption) and additional losses induced by external factors. When an optical fiber is exposed to ionizing radiation (such as gamma rays, X-rays, protons, neutrons, etc.), the fiber materials (quartz glass, coatings, dopants, etc.) absorb the radiation energy. Absorption centers are formed in the glass network of the fiber due to radiation dissociation or defects trapping electrons / holes, resulting in additional light absorption at specific wavelengths and a decrease in optical signal power—this is radiation-induced attenuation (RIA). RIA testing requires simulating the radiation environment and accurately measuring changes in optical loss.

[0065] In some specific implementations, the RIA test unit, such as Figure 2 As shown, the system consists of a white light source (halogen tungsten lamp), an input lens coupling, the fiber under test, an output connector coupling, and a YOKOGAWA AQ6370D spectrometer. The white light source provides broadband incident light covering the test wavelength range. The input is lens-coupled into the fiber, and the output is connected to the spectrometer via a connector to collect the transmission spectrum. Measurements were taken after the light source stabilized for half an hour. The spectrometer scanned wavelengths from 700 to 1500 nm with a resolution of 2 nm. The test method was the common truncation method, which measures the output power of the same fiber at different lengths. The absorption coefficient of the fiber is measured using the following formula:

[0066]

[0067] In the formula, α(λ) is the radiation-induced attenuation of an optical fiber of length L at wavelength λ, with units of dB·km. -1 P1(λ) is the output power measured at wavelength λ with an fiber length of L1; P2(λ) is the output power measured at wavelength λ with the fiber cut by L; L is the length of fiber cut off in both measurements. For each sample segment corresponding to a dose point, its intrinsic attenuation is measured before irradiation. For example, the output spectrum of a 30 m long sample is measured first, and then 2 m (L = 2 m) is cut off to measure the output spectrum of a 28 m long sample. After the corresponding total dose is irradiated in the γ irradiation unit, the fiber attenuation is measured again by cutting off 2 m on the same sample segment. Finally, the attenuation coefficient RIA of the fiber segment is obtained by subtracting the attenuation spectrum of the same sample after irradiation from that before irradiation. During the fiber RIA test, the coating layer is stripped at the input end and a small amount of refractive index matching oil (n≈1.44) is dripped to release the cladding mode.

[0068] Laser transmission test:

[0069] Before and after irradiation, high-power laser transmission tests were performed on the fiber optic samples, and the output power and temperature at key locations were recorded simultaneously. In some specific implementations, a stepped power increase method was used for testing: coupling and alignment were first completed at low power, and then the pump settings were gradually increased in fixed steps. The same test procedure was repeated for the irradiated samples to ensure consistency of test conditions before and after irradiation. Figure 3 As shown, the fiber optic laser transmission test experiment used an RFL-C6000X laser with a center wavelength of 1080±5 nm. The output power was read from a power meter probe connected to the fiber optic output segment. During the output power test, a FLIR infrared thermal imager was used for temperature measurement.

[0070] Additional insertion loss conversion for operating band:

[0071] The average attenuation coefficient of the operating band obtained from the radiative attenuation test is converted into the additional insertion loss over the actual sample length. Let the effective transmission length of the sample be L (in meters), then the additional insertion loss IL estimated by RIA is... RIA Calculate using the following formula:

[0072]

[0073] in, The average attenuation coefficient for the operating band is expressed in dB / km, IL. RIA The unit is dB. This step converts offline spectral loss parameters into length-dependent loss parameters for engineering applications, and is a key step in extrapolating material irradiation characterization results to actual transmission links.

[0074] Output power prediction:

[0075] In obtaining IL RIA Subsequently, to improve the accuracy of characterizing operational losses, an equivalent correction term ΔIL is introduced. corr This yields the operating state effective insertion loss IL, which truly represents the boundary conditions for high-power operation. eff :

[0076]

[0077] Where, ΔIL corr It can be obtained by least-squares fitting of the irradiated sample at several pump levels, and is used to compensate for the system difference between offline spectral measurements and actual losses during operation.

[0078] Specifically, the difference between the theoretically calculated additional insertion loss of the irradiated fiber sample at several pump levels and the actual additional insertion loss in operation is fitted and optimized using the least squares method to obtain the correction term.

[0079] The actual additional insertion loss in the operating state is calculated as follows:

[0080]

[0081] Where, ΔIL meas Add insertion loss to the actual operating state, P pre P represents the initial output power of the fiber sample before irradiation at a specific pump setting. post This represents the actual output power of the fiber optic sample after irradiation at a specific pump setting.

[0082] Furthermore, the predicted output power P after irradiation post,pred It can be obtained by the following formula:

[0083] .

[0084] The method described above converts offline RIA results into equivalent additional insertion loss and further introduces a correction term to establish a post-irradiation output power prediction model. This allows for rapid estimation of fiber power attenuation during operation without repeating complete high-power operation tests under every irradiation condition. This method significantly improves the efficiency of post-irradiation performance evaluation of power-carrying fibers, reduces high-power testing costs and complexity, and has good engineering applicability.

[0085] Furthermore, in some specific embodiments, this invention provides a highly generalizable and universal system for the engineering evaluation and selection of radiation resistance for power transmission fibers. This system eliminates the need for long-term deployment of kilowatt-level high-power laser testing systems in extremely expensive and dangerous high-radiation thermal chambers. It only requires extracting a small amount of safe and readily available offline low-power spectral data and a small number of benchmark test parameters to achieve high-confidence performance evaluation through cross-validation models.

[0086] Based on the above-mentioned radiation-induced attenuation (RIA) test and laser transmission test, this invention establishes a predictive model for predicting the output power of optical fiber after irradiation. At the same time, it combines electron paramagnetic resonance (EPR) test and photoluminescence (PL) test to form a continuous chain of evidence from macroscopic performance to microscopic mechanism, thereby improving the completeness and reliability of the performance degradation assessment of power transmission optical fiber after irradiation.

[0087] In some specific implementations, the performance evaluation system for power transmission optical fibers under gamma irradiation also includes an electron paramagnetic resonance (EPR) testing unit and a photoluminescence (PL) testing unit.

[0088] Electron paramagnetic resonance (EPR) testing:

[0089] Electron paramagnetic resonance (EPR) tests were performed on both unirradiated and irradiated samples to obtain information on irradiation-induced paramagnetic defects. X-band EPR testing was used to extract the peak position, line shape, and double integral area of ​​the characteristic signal as semi-quantitative characterization parameters of paramagnetic defect concentration changes. The EPR testing unit was performed using a JEOL JES-FA300 EPR instrument, measuring the first differential spectrum of the samples. As a specific test example, the microwave frequency of the room-temperature resonant cavity was 9.46 GHz, the central magnetic field was 340.0 mT, the microwave intensity was 1 mW, and the modulation frequency was 100 kHz. The scanning range was 100 G, and the scanning time was 30 seconds. The g-value was calculated using the following formula:

[0090]

[0091] Where h is Planck's constant, v is the microwave frequency, and μ is the microwave frequency. B For Bohr magneton, B res The resonant magnetic field strength is denoted by g. The g-factor is dimensionless and essentially reflects the proportional relationship between the resonant magnetic field strength and the microwave frequency, thus characterizing the location of magnetic field resonance.

[0092] All sample optical fibers were cut into bare fibers of approximately 5 cm in length after the organic coating was stripped away, and EPR experiments were performed. Ten fibers were used in each group. The double integral area S(D) of the EPR under different irradiation doses D was used as a paramagnetic defect index, and a correlation was established with the RIA coefficient of the working band of the radiation-induced attenuation test. The following relationship was established using linear fitting:

[0093]

[0094] Where d and c are fitting coefficients. This relationship can be used to link the degree of paramagnetic defect accumulation with the enhanced loss in the operating band, thus explaining the microscopic sources of macroscopic transmission degradation.

[0095] Photoluminescence (PL) spectroscopy testing:

[0096] Photoluminescence tests, including excitation and emission spectra, were performed on both unirradiated and irradiated samples to obtain information on changes in optically active centers such as oxygen vacancy-related defects. Emission spectra were acquired under a fixed excitation wavelength, and Gaussian peak subdivision was performed on the emission bands to extract the peak position, peak area, and full width at half maximum (FWHM) parameters of each sub-peak. The evolution of peak area under different doses was used to determine the generation, transformation, and quenching processes of optically active defect centers.

[0097] In some specific implementations, the photoluminescence testing unit uses an FLS920 time-resolved fluorescence spectrometer to measure steady-state photoluminescence (PL) of fiber optic samples before and after irradiation, completing the test at room temperature. As a specific test example, the excitation spectrum is scanned from 230 to 380 nm, and the emission spectrum is acquired at an excitation wavelength of 245 nm. The emission scan range is 300-700 nm with a step size of 1 nm, and the integration time for each wavelength point is 0.100 s. The slit bandwidths at the excitation and emission ends of the instrument are set to ExBW = 2 nm and EmBW = 5 nm, respectively, and the test temperature is 26.5 ℃. For each dose point, 0.3 m of uncoated bare fiber is used, cut into 1-3 cm segments, and laid in a single layer inside a quartz boat.

[0098] Based on the test and calculation results of each test unit of the above-mentioned performance evaluation system for power transmission optical fibers under gamma irradiation, a comprehensive evaluation of the performance degradation of the optical fiber under test in a gamma irradiation environment is conducted. The comprehensive evaluation includes at least one or more of the following:

[0099] 1. Irradiation-induced attenuation level in the operating band;

[0100] 2. Parameters of the dose-loss relationship model;

[0101] 3. Predicted output power after irradiation and prediction error;

[0102] 4. Degree of accumulation of paramagnetic defects;

[0103] 5. Characteristics of the generation, transformation and quenching of optically active defects.

[0104] Furthermore, the comparison results between optical fiber samples based on the above parameters can be used for screening, selection, and lifetime margin analysis of energy transmission optical fibers with different OH contents, different coating materials, different geometric parameters, or different preparation processes.

[0105] Example 1: An Example of Predicting Post-Irradiation Output Power Based on Offline RIA

[0106] By performing radiation-induced attenuation (RIA) tests on optical fibers before and after irradiation, the mean value of the characteristic attenuation window for high-power laser operating bands was extracted, and the laser operating window λ∈[1075,1085] nm was selected in the offline RIA spectrum RIA(λ).

[0107] Table 1. Mean and standard deviation of RIA of optical fiber in the 1080 ± 5 nm band

[0108]

[0109] Define the window average RIA as

[0110]

[0111] Where N is the number of sampling points in the interval [1075, 1085], RIA(λ) k ) represents the laser wavelength λ k The attenuation coefficient, expressed in dB / km, is used. This mean-smoothed value reflects the true uplift of the intrinsic macroscopic background absorption of the fiber material within the linewidth range of a Gaussian or super-Gaussian high-power laser. The theoretical additional insertion loss is derived from offline RIA. For a test fiber segment of length L (km), the additional insertion loss is obtained by offline RIA extrapolation using the following formula.

[0112]

[0113] In the formula, IL RIA The additional insertion loss represents the theoretical total loss of the optical fiber caused solely by the accumulation of static absorption defects, expressed in decibels (dB). Directly using this value for engineering evaluation represents the most conservative and systematically overestimated traditional calculation method in current technology.

[0114] This embodiment establishes a corrected model that can predict the output power in operation by conducting laser transmission tests on optical fibers before and after irradiation.

[0115] First, under extremely limited reference pump test conditions, the irradiated fiber was actually connected to a kilowatt-level laser test station to obtain data at N... p The initial ideal output power P of the optical fiber when it is not irradiated under a discretely set pump drive position. pre,i And the actual measured output power P after being irradiated with cumulative dose D. post,i (where i = 1, 2, ..., N) p Based on this limited set of measured power data ratios, the actual additional insertion loss ΔIL of the optical fiber under each specific pump level was calculated. meas

[0116]

[0117] Based on this, a constant correction term ΔIL is introduced. corr The physical meaning of this constant correction term lies in the fact that it equivalently represents the total amount of equivalent cancellation of various nonlinear physical mechanisms occurring inside the optical fiber during kilowatt-level laser transmission and associated local high temperatures, such as broadband optical bleaching accelerating defect annihilation, thermal annealing promoting lattice self-healing, and the re-evolution of energy mode distribution inside complex multimode optical waveguides.

[0118] By applying the least squares optimization theory, the above N pThe difference between the theoretically calculated additional insertion loss and the actual additional insertion loss in operation at each pump test point is used for global fitting optimization to derive the unique analytical solution for the constant correction term:

[0119]

[0120] Subsequently, by subtracting the offline theoretical calculation value from this constant correction term, the operating state effective insertion loss IL, which can truly represent the boundary conditions of high-power operation, is defined. eff :

[0121]

[0122] The IL eff This value is the sole core parameter used for engineering prediction of the output power after fiber optic irradiation, after eliminating systematic biases. Then, the operational output power is predicted using the model as follows:

[0123]

[0124] Among them, P post, pred P is the predicted output power after irradiation. pre IL represents the initial output power of the fiber sample before irradiation at a specific pump level. eff This represents the effective insertion loss during operation.

[0125] Figure 4 The figure shows the predicted loss level (IL) of the model. eff ).like Figure 4 As shown, the additional insertion loss of the optical fiber under different pump source settings (10%–90%) generally falls within the range of 0.024–0.190 dB, indicating that the additional insertion loss under operating conditions has a certain condition dependence but the overall range is limited. After introducing a constant term to correct the model, the effective insertion loss IL under operating conditions is obtained. eff It is 0.108 dB (solid red line), consistent with the mean of the measured ΔIL.

[0126] A comparison of power prediction curves with and without correction terms, for example Figure 5 As shown.

[0127] The output power P before irradiation pre As a reference input, the output power P after fiber irradiation was compared in the range of 0.37–3.10 kW. post The measured and predicted values. For example... Figure 5 As shown, the uncorrected RIA prediction (using only IL) RIA ==0.444 dB, corresponding to a fixed transmittance of approximately 0.903) given P postThe values ​​were significantly lower than the measured values ​​across the entire power range, demonstrating a conservative overestimation of operational losses by offline RIA extrapolation. After model correction (IL)... eff ==0.108 dB, corresponding to a transmittance of approximately 0.975), predicting P post The measured points almost perfectly coincide with the actual measurement points, significantly reducing systematic bias. This example demonstrates that the present invention can provide macroscopic degradation results after fiber optic irradiation.

[0128] Example 2: Microscopic Defect Correlation Based on Joint Characterization of EPR and PL

[0129] Electron paramagnetic resonance (EPR) and photoluminescence (PL) tests were performed on unirradiated samples and samples irradiated at 20 kGy, 50 kGy, and 100 kGy, respectively. Figure 6 As shown, the EPR test obtained the first derivative spectrum. After irradiation, the EPR of the sample showed a very sharp main signal. Through calibration and calculation, its g factor was determined to be g = 2.0006, which is a typical E′ color center signal. That is, the optical fiber was defected after radiation. The EPR test captured the characteristic signal of this defect, and the g value confirmed that this defect is the most representative E′ color center in the radiation damage of quartz optical fiber.

[0130] The target paramagnetic signal was processed by double integration to semi-quantitatively characterize the concentration of irradiation-induced paramagnetic defects. As shown in Table 2, the double integration area S increases monotonically with the dose, and the EPR signal at the center of E′ is observed to increase with the irradiation dose.

[0131] Table 2. Double integral area of ​​EPR derivative spectrum under different irradiation doses

[0132]

[0133] If a certain type of defect participates in the loss variation near 1080 nm, an approximately linear correlation will appear. Therefore, a linear fit is used for the double integral of the RIA coefficient and EPR derivative spectrum at 1080 nm:

[0134]

[0135] Where d and c are fitting coefficients. This relationship can be used to link the degree of paramagnetic defect accumulation with the enhancement of loss in the operating band.

[0136] like Figure 7 As shown, RIA 1080 (D) is positively correlated with S, and the accumulation of E′ center and the growth of near-infrared additional loss have a consistent evolutionary trend.

[0137] In PL testing, excitation and emission spectra of samples with different doses were collected. The emission spectrum was collected at an excitation wavelength of λex = 245 nm. For example... Figure 8 The PL emission spectra shown at different irradiation doses reveal that the E′ center-related EPR signal increases with increasing dose, while the ODC (oxygen defect center)-related PL signal exhibits a trend of first increasing and then decreasing. This indicates that under high-dose conditions, there exists a process of transformation from optically active ODC-related centers to paramagnetic, non-radiative dissipative centers. This embodiment provides an explanation at the microscopic defect level.

[0138] The comprehensive evaluation method and system for power transmission optical fibers under γ-irradiation proposed in this invention organically combines irradiation-induced attenuation testing, high-power laser transmission testing, temperature response testing, electron paramagnetic resonance testing, and photoluminescence testing to form a comprehensive technical route. This approach can simultaneously obtain multi-dimensional information such as additional loss in the operating band, output power attenuation, temperature rise enhancement, and defect evolution, thereby forming a continuous chain of evidence from macroscopic performance to microscopic mechanisms. This improves the completeness and reliability of the performance degradation evaluation of power transmission optical fibers after irradiation.

[0139] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. Thus, the invention also intends to include such variations and adaptations if they fall within the scope of the claims and their equivalents.

[0140] The above embodiments are merely illustrative examples of the present invention. The present invention may also be implemented in other specific ways or forms without departing from its spirit or essential characteristics. Therefore, the described embodiments should be considered illustrative rather than limiting in any respect. The scope of protection of the present invention should be defined by the claims, and any variations equivalent to the intent and scope of the claims should also be included within the scope of the present invention.

Claims

1. A method for evaluating the performance of power-transmitting optical fibers under gamma irradiation, characterized in that, This includes radiation-induced attenuation testing and laser transmission testing of fiber optic samples before and after irradiation. The average attenuation coefficient of the working band obtained from the radiative attenuation test is converted into the additional insertion loss over the actual sample length. By conducting laser transmission tests on fiber optic samples before and after irradiation, a correction term is introduced to correct the additional insertion loss, thus obtaining the effective insertion loss in the operating state. Based on the effective insertion loss in the operating state, a prediction model is established to predict the output power of the optical fiber after irradiation, thereby enabling a rapid estimation of the power attenuation of the optical fiber in the operating state.

2. The method for evaluating the performance of power-transmitting optical fibers under γ-irradiation environment as described in claim 1, characterized in that, Radiation-induced attenuation tests were performed on fiber samples before and after irradiation. The mean value of the characteristic attenuation window facing the high-power laser working band was extracted to obtain the average attenuation coefficient of the working band. The additional insertion loss was obtained by multiplying the average attenuation coefficient of the working band by the length of the test fiber sample.

3. The method for evaluating the performance of power-transmitting optical fibers under γ-irradiation environment as described in claim 1, characterized in that, The effective insertion loss in the operating state is equal to the difference between the additional insertion loss and the correction term.

4. The method for evaluating the performance of power-transmitting optical fibers under γ-irradiation environment as described in claim 1, characterized in that, The difference between the theoretically calculated additional insertion loss of the irradiated fiber sample at several pump levels and the actual additional insertion loss in operation is fitted and optimized using the least squares method to obtain the correction term.

5. The method for evaluating the performance of power-transmitting optical fibers under γ-irradiation environment as described in claim 4, characterized in that, The actual additional insertion loss in the operating state is calculated as follows: Where, ΔIL meas Add insertion loss to the actual operating state, P pre P represents the initial output power of the fiber sample before irradiation at a specific pump setting. post This represents the actual output power of the fiber optic sample after irradiation at a specific pump setting.

6. The method for evaluating the performance of power-transmitting optical fibers under γ-irradiation environment as described in claim 1, characterized in that, The prediction model used to predict the output power of the optical fiber after irradiation is as follows: Among them, P post, pred P is the predicted output power after irradiation. pre IL represents the initial output power of the fiber sample before irradiation at a specific pump level. eff This represents the effective insertion loss during operation.

7. The method for evaluating the performance of power-transmitting optical fibers under γ-irradiation environment as described in claim 1, characterized in that, It also includes electron paramagnetic resonance tests on fiber samples before and after irradiation, extracting the peak position, line shape, and double integral area of ​​characteristic signals as semi-quantitative characterization parameters of paramagnetic defect concentration; using the double integral area as a paramagnetic defect index, and establishing a correlation with the average radiation-induced attenuation coefficient of the working band through linear fitting, to explain the microscopic sources of macroscopic transmission degradation of optical fibers.

8. The method for evaluating the performance of power-transmitting optical fibers under γ-irradiation environment as described in claim 1 or 7, characterized in that, It also includes photoluminescence testing of fiber samples before and after irradiation, including excitation spectrum testing and emission spectrum testing. The emission spectrum is collected under a fixed excitation wavelength, and the emission band is processed by Gaussian peak division. The peak position, peak area and full width at half maximum (FWHM) parameters of each sub-peak are extracted. The peak area evolution law under different irradiation doses is used to determine the generation, transformation and quenching process of optically active defect centers, providing an explanatory basis for the microscopic defect level of optical fibers.

9. A system for implementing the method for evaluating the performance of power-transmitting optical fibers under γ-irradiation environment as described in claim 1, characterized in that, It includes an optical fiber sample group, a gamma irradiation unit, a radiation-induced attenuation testing unit, a laser transmission testing unit, and a data processing and evaluation unit; The optical fiber sample group is fixed in a uniform manner and irradiated by a γ-irradiation unit. The radiation-induced attenuation test unit includes a white light source, an input lens, an output connector, and a spectrometer. The white light source provides broadband incident light covering the test band. The incident light input is coupled into the optical fiber using a lens, and the optical fiber output is connected to the spectrometer through a connector to collect the transmission spectrum. The laser transmission test unit includes a laser and a power meter. The laser is connected to the optical fiber input end, and the power meter is connected to the optical fiber output end. The data processing and evaluation unit is used to process the test data, establish a prediction model for predicting the output power of the optical fiber after irradiation, and quickly estimate the power attenuation of the optical fiber under operating conditions.

10. The system as described in claim 9, characterized in that, The optical fiber sample is fixed by a multi-turn coiling method to ensure that the sample geometry is consistent during the irradiation and laser transmission stages, thereby reducing the impact of mechanical stress differences on the test results.

11. The system as described in claim 9, characterized in that, During fiber irradiation, fiber samples are kept under the same ambient temperature, spatial orientation, and coiling state to ensure comparability between different samples or different dose groups.

12. The system as described in claim 9, characterized in that, Before irradiation, all fiber optic samples were numbered and divided into multiple batches according to the target cumulative dose to ensure that samples at different dose points could be tested within the same time window as much as possible after irradiation.

13. The system as described in claim 9, characterized in that, The laser transmission test unit also includes an infrared thermal imager to measure the temperature of the optical fiber sample during the laser transmission test.

14. The system as described in claim 9, characterized in that, It also includes an electron paramagnetic resonance (EPR) testing unit, which uses an EPR spectrometer to measure the first differential spectrum of fiber samples before and after irradiation to obtain information on irradiation-induced paramagnetic defects. The data processing and evaluation unit extracts the peak position, line shape, and double integral area of ​​the characteristic signal as semi-quantitative characterization parameters of paramagnetic defect concentration. The double integral area is used as a paramagnetic defect index, and a correlation is established with the average radiation-induced attenuation coefficient of the working band through linear fitting to explain the microscopic sources of macroscopic transmission degradation of optical fibers.

15. The system as described in claim 9, characterized in that, It also includes a photoluminescence testing unit, which uses a time-resolved fluorescence spectrometer to measure steady-state photoluminescence of optical fiber. The data processing and evaluation unit collects the emission spectrum under a fixed excitation wavelength and performs Gaussian peak subdivision processing on the emission band, extracts the peak position, peak area and full width at half maximum (FWHM) parameters of each sub-peak, and uses the peak area evolution law under different irradiation doses to determine the generation, transformation and quenching process of optically active defect centers, providing an explanatory basis for the microscopic defect level of optical fiber.

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