Special fiber grating suitable for vehicle-mounted environment and preparation method thereof

Abstract

The application belongs to the technical field of fiber grating preparation, and provides a special fiber grating suitable for a vehicle-mounted environment and a preparation method thereof, which comprises the following steps: performing uniformity analysis on a grating period written by femtosecond laser, judging whether a grating period distortion phenomenon occurs, if the phenomenon occurs, performing construction and comparison of a writing data group about laser scanning speed and repetition frequency on normal grating periods and distorted grating periods, judging whether the root cause of the grating period distortion phenomenon is disconnection of the laser scanning speed and the repetition frequency, if yes, performing fluctuation analysis on the laser scanning speed and the repetition frequency, determining a priority adjustment object and a corresponding adjustment limit value or adjustment combination, and then implementing targeted adjustment, which can effectively solve the grating period distortion problem, realize the uniformity of the grating period, and guarantee the quality and stability of the femtosecond laser written grating.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of fiber grating preparation, and particularly relates to a special fiber grating suitable for a vehicle-mounted environment and a preparation method thereof. BACKGROUND

[0002] In a vehicle-mounted scenario, a vehicle operation will face complex and changeable environmental factors such as vibration, temperature fluctuation, impact and the like, and the fiber grating can be used to construct a vehicle-mounted state monitoring system due to its high sensitivity to physical parameters, but there are still many deficiencies in the preparation of the fiber grating, therefore, it is of great significance to research a special fiber grating suitable for a vehicle-mounted environment and a preparation method thereof.

[0003] In the technical field of femtosecond laser written gratings, the uniformity of grating periods is a key indicator to guarantee the performance of the grating. However, in the current femtosecond laser writing process, the problem of distortion of grating periods often occurs, and the uniformity of the periods is difficult to effectively guarantee, and there are often deviations of different degrees. The occurrence of this phenomenon is closely related to the insufficient collaborative control of key parameters such as laser scanning speed and repetition frequency. Due to insufficient understanding of the correlation and fluctuation characteristics of these parameters in the writing process, there is a lack of accurate adjustment basis and method, which leads to the inability to timely discover and solve the problem of parameter disconnection or improper matching, and further makes the quality stability of the grating poor, which is difficult to meet the strict requirements of high-precision application scenarios on the uniformity and consistency of grating periods, and seriously restricts the further development and application of femtosecond laser written grating technology.

[0004] Therefore, the application provides a special fiber grating suitable for a vehicle-mounted environment and a preparation method thereof. SUMMARY

[0005] In order to make up for the deficiencies of the prior art and solve at least one technical problem proposed in the background art.

[0006] The technical scheme adopted by the application to solve the technical problems is: a preparation method of a special fiber grating suitable for a vehicle-mounted environment, comprising the following steps:

[0007] Uniformity analysis is performed on the grating periods written by the femtosecond laser to determine whether the grating period distortion phenomenon occurs;

[0008] If the phenomenon occurs, a normal writing database and a distortion writing database are constructed by the laser scanning speed and the repetition frequency of the normal grating period and the distorted grating period, and by comparison and analysis, it is determined whether the root cause of the grating period distortion phenomenon is the disconnection of the laser scanning speed and the repetition frequency;

[0009] If yes, fluctuation analysis of the laser scanning speed and the repetition frequency is performed, if the fluctuation of the laser repetition frequency is higher than or equal to the fluctuation of the laser scanning speed, the laser repetition frequency is determined as the priority adjustment object, otherwise, the temperature peak under the combination of the laser repetition frequency and the laser scanning speed is analyzed to determine whether the priority adjustment object is the laser repetition frequency;

[0010] If the priority adjustment object is the laser repetition frequency, it is judged whether there is a linear mapping relationship between the laser repetition frequency and the temperature peak, if yes, the laser repetition frequency adjustment limit value is determined, otherwise, the adjustment combination database of the laser repetition frequency and the laser scanning speed is determined.

[0011] The laser repetition frequency is adjusted according to the laser repetition frequency adjustment limit value or the laser repetition frequency and the laser scanning speed are adjusted according to the adjustment combination database.

[0012] Further, the process of uniformity analysis of the grating period is:

[0013] The laser scanning speed and the laser repetition frequency of the femtosecond laser are obtained when the grating fringe is written, and the proportion is calculated to obtain the grating period;

[0014] All the written grating periods are obtained, and the grating period sequence is obtained by summarizing and integrating, the coefficient of variation of the grating period sequence is calculated, if the coefficient of variation is greater than or equal to the coefficient of variation threshold, it indicates that the grating period uniformity is low, and the grating period distortion phenomenon occurs.

[0015] Further, the acquisition method of the normal grating period and the distorted grating period is:

[0016] The grating period is compared with the ideal period range;

[0017] If the grating period is in the ideal period range, the grating period is marked as a normal grating period;

[0018] If the grating period is not in the ideal period range, the grating period is marked as a candidate distorted grating period;

[0019] Based on the candidate distorted grating period, the contribution degree of each candidate distorted grating period is calculated, wherein the contribution degree is the square value of the deviation of each candidate distorted grating period;

[0020] If the contribution degree is greater than or equal to the preset contribution degree, the candidate distorted grating period is marked as a distorted grating period.

[0021] Further, the construction process of the normal writing database and the distorted writing database is:

[0022] The laser scanning speed and the laser repetition frequency during writing of the normal grating period are integrated into a normal writing data group, and a normal writing database is obtained by summarizing;

[0023] The laser scanning speed and the laser repetition frequency during writing of the distorted grating period are integrated into a distorted writing data group, and a distorted writing database is obtained by summarizing;

[0024] The comparison and analysis process is as follows:

[0025] The normal writing database and the distorted writing database are compared to obtain a writing deviation value and a period deviation value;

[0026] The period deviation value and the writing deviation value are summed to obtain a writing dislocation value;

[0027] If the writing dislocation value is greater than or equal to a writing dislocation threshold value, it indicates that the root cause of the grating period distortion phenomenon is the dislocation of the laser scanning speed and the repetition frequency.

[0028] Further, the period deviation value is obtained in the following manner:

[0029] In the normal writing database, the proportion of the laser scanning speed and the laser repetition frequency in each normal writing data group is calculated and summed to obtain a normal grating period mean value; in the distorted writing database, the proportion of the laser scanning speed and the laser repetition frequency in each distorted writing data group is calculated and summed to obtain a distorted grating period mean value;

[0030] The absolute difference of the normal grating period mean value and the distorted grating period mean value is calculated to obtain the period deviation value;

[0031] The writing deviation value is the absolute deviation of the data correlation coefficients corresponding to the normal writing database and the distorted writing database.

[0032] Further, the fluctuation analysis process of the laser scanning speed and the laser repetition frequency is as follows:

[0033] The laser scanning speeds during writing of each grating period are summarized, and a coefficient of variation is calculated to obtain a speed coefficient of variation;

[0034] The laser repetition frequencies during writing of each grating period are summarized, and a coefficient of variation is calculated to obtain a frequency coefficient of variation;

[0035] If the frequency coefficient of variation is greater than or equal to the speed coefficient of variation, the laser repetition frequency is determined as the priority adjustment object.

[0036] Further, the fluctuation analysis process of the laser scanning speed and the laser repetition frequency further includes:

[0037] If the frequency variation coefficient is less than the speed variation coefficient, reanalysis is performed, specifically:

[0038] The normal grating period is averaged to obtain a normal grating period mean value, the laser repetition frequency at the time of writing all grating periods is averaged to obtain a laser repetition frequency mean value, and the product of the normal grating period mean value and the laser repetition frequency mean value is calculated to obtain a laser scanning speed mean value;

[0039] The laser repetition frequency mean value and the laser scanning speed mean value are used as a simulation parameter group, COMSOL software is used to simulate the writing of the fiber period according to the simulation parameter group, and after the simulation is completed, the temperature peak value is extracted according to the temperature field contour map;

[0040] If the temperature peak value is greater than or equal to the preset temperature threshold value of the fiber material, the laser repetition frequency is used as the priority adjustment object;

[0041] If the temperature peak value is less than the preset temperature threshold value of the fiber material, the temperature deviation between the temperature peak value and the preset temperature threshold value of the fiber material is calculated;

[0042] If the temperature deviation is less than the preset temperature deviation, the laser repetition frequency is used as the priority adjustment object.

[0043] Further, whether there is a linear mapping relationship between the laser repetition frequency and the temperature peak value is determined by fitting the temperature peak values under different laser repetition frequencies and judging the goodness of fit;

[0044] If there is, a fitting model obtained by fitting the temperature peak values under different laser repetition frequencies is obtained, the preset temperature threshold value is input into the fitting model, and the laser repetition frequency adjustment limit value is output;

[0045] If there is not, according to the simulation writing process of the fiber period, the simulation parameter groups with a temperature peak value less than the preset temperature threshold value are obtained, and all simulation parameter groups are summarized to obtain an adjustment combination database.

[0046] Further, the adjustment process is:

[0047] If there is a linear mapping relationship between the laser repetition frequency and the temperature peak value and it is a positive proportional relationship, during the grating period writing, if the grating period is not equal to the normal grating period, the laser repetition frequency is adjusted, and the laser repetition frequency cannot exceed the laser repetition frequency adjustment limit value, otherwise, if there is an inverse proportional relationship, the laser repetition frequency cannot be lower than the laser repetition frequency adjustment limit value;

[0048] If there is no linear mapping relationship between the laser repetition frequency and the temperature peak value, the laser repetition frequency and the laser scanning speed are adjusted according to the simulation parameter groups contained in the adjustment combination database.

[0049] A special fiber grating suitable for a vehicle-mounted environment is prepared by a special fiber grating preparation method suitable for a vehicle-mounted environment.

[0050] The beneficial effects of the present application are as follows: the uniformity of the femtosecond laser written grating period is analyzed to determine whether the grating period distortion phenomenon occurs, if it occurs, the normal grating period and the distorted grating period are constructed with respect to the writing data set of the laser scanning speed and the repetition frequency, respectively to obtain the normal writing database and the distorted writing database, the root cause of the grating period distortion phenomenon is determined by comparing and analyzing the normal writing database and the distorted writing database, if it is, the fluctuation analysis of the laser scanning speed and the repetition frequency is performed, if the laser repetition frequency fluctuation is higher than or equal to the laser scanning speed fluctuation, the laser repetition frequency is determined as the priority adjustment object, otherwise, the temperature peak under the combination of the laser repetition frequency and the laser scanning speed is analyzed to determine whether the laser repetition frequency is the priority adjustment object, if the priority adjustment object is the laser repetition frequency, it is determined whether there is a linear mapping relationship between the laser repetition frequency and the temperature peak, if there is, the laser repetition frequency adjustment limit value is determined, otherwise, the adjustment combination database of the laser repetition frequency and the laser scanning speed is determined, the laser repetition frequency is adjusted according to the laser repetition frequency adjustment limit value or the laser repetition frequency and the laser scanning speed are adjusted according to the adjustment combination database, the present application analyzes the uniformity of the femtosecond laser written grating period, combines the writing data comparison, fluctuation analysis and temperature peak correlation analysis of the laser scanning speed and the repetition frequency, determines the priority adjustment object and the corresponding adjustment limit value or adjustment combination, and then implements targeted adjustment, which can effectively solve the grating period distortion problem, realize the uniformity of the grating period, and guarantee the quality and stability of the femtosecond laser written grating. BRIEF DESCRIPTION OF DRAWINGS

[0051] The present application will be further described below with reference to the accompanying drawings.

[0052] Fig. 1 is a step flow chart of a special fiber grating preparation method suitable for a vehicle-mounted environment according to an embodiment of the present application;

[0053] Fig. 2 is a logic judgment schematic diagram of a special fiber grating preparation method suitable for a vehicle-mounted environment according to an embodiment of the present application. DETAILED DESCRIPTION

[0054] In order to make the technical means, creative features, purposes and effects realized by the present application easy to understand, the present application will be further described below with reference to the specific embodiments.

[0055] Embodiment 1: please refer to Figs. 1-2 As shown in the embodiment of the application, the method for preparing a special fiber grating suitable for a vehicle-mounted environment comprises the following steps:

[0056] Step one: uniformity analysis is performed on the grating period written by femtosecond laser to determine whether the grating period distortion phenomenon occurs;

[0057] In step one, femtosecond laser writing method is used to write the grating period, which does not need to load hydrogen, is resistant to high temperature (sapphire grating up to 1800℃), retains the mechanical strength of the coating, and is flexible in period adjustment. The vehicle-mounted environment needs to meet harsh conditions such as high temperature (such as brake disc temperature > 500℃), vibration, and electromagnetic interference. Therefore, femtosecond laser writing method is the best choice;

[0058] In step one, the process of uniformity analysis on the grating period written by femtosecond laser is as follows:

[0059] The laser scanning speed and laser repetition frequency of the femtosecond laser during grating fringe writing are obtained, and a proportional calculation is performed to obtain the grating period;

[0060] The calculation method of the grating period is: Λ=v / f, wherein Λ is the grating period, v is the laser scanning speed (instantaneous) during grating fringe writing, and f is the laser repetition frequency (instantaneous) during grating fringe writing;

[0061] All the written grating periods are obtained, and the grating period sequence is obtained by integration. The coefficient of variation of the grating period sequence is calculated, wherein the coefficient of variation is the ratio of the mean value to the standard deviation of the grating period sequence;

[0062] Preferably, the coefficient of variation is compared with the coefficient of variation threshold value;

[0063] If the coefficient of variation is greater than or equal to the coefficient of variation threshold value, it indicates that the grating period uniformity is low, and the grating period distortion phenomenon occurs;

[0064] If the coefficient of variation is less than the coefficient of variation threshold value, it indicates that the grating period uniformity is high, and the grating period distortion phenomenon does not occur;

[0065] Step two: if it occurs, the normal grating period and the distorted grating period are constructed in terms of the writing data group of the laser scanning speed and the repetition frequency to obtain the normal writing database and the distorted writing database, respectively. Through comparison and analysis of the normal writing database and the distorted writing database, it is determined whether the root cause of the grating period distortion phenomenon is the disconnection of the laser scanning speed and the repetition frequency;

[0066] In step two, if the grating distortion phenomenon occurs, the normal grating period and the distorted grating period are obtained in the following manner:

[0067] compare the grating period with the ideal period range;

[0068] if the grating period is in the ideal period range, mark the grating period as a normal grating period;

[0069] if the grating period is not in the ideal period range, mark the grating period as a candidate distorted grating period;

[0070] The construction of the ideal period range can be:

[0071] Based on the grating period sequence, the mean μ and the standard deviation σ of all grating periods in the grating period sequence are calculated, and the ideal period range is constructed based on the mean μ and the standard deviation σ of the grating period, that is: [μ-kσ, μ+kσ], wherein k is a coefficient, k takes a value of 2 or 3, for example, k takes a value of 2 in a high-precision scenario, and generally takes a value of 3;

[0072] Based on the candidate distorted grating period, the contribution degree of each candidate distorted grating period is calculated, wherein the contribution degree is the square value of the deviation of each candidate distorted grating period, and the calculation is as follows:

[0073] deviation square = (grating period - mean) 2 , wherein i represents the i-th candidate distorted grating period, and μ is the mean of all grating periods;

[0074] If the contribution degree is greater than or equal to the preset contribution degree, mark the candidate distorted grating period as a distorted grating period;

[0075] If the contribution degree is less than the preset contribution degree, do not perform any operation;

[0076] It can be understood that the contribution degree reflects the contribution degree of the distorted grating period to the non-uniformity (discreteness) of the grating period sequence, and the greater the contribution degree, the greater the distortion of the grating period and the higher the distortion;

[0077] In step two, the construction process of the normal writing database and the distorted writing database is:

[0078] Integrate the laser scanning speed and the laser repetition frequency when the normal grating period is written into a normal writing data group, and aggregate to obtain a normal writing database;

[0079] Integrate the laser scanning speed and the laser repetition frequency when the distorted grating period is written into a distorted writing data group, and aggregate to obtain a distorted writing database;

[0080] In step two, the comparison and analysis process is:

[0081] In the normal writing database, the ratio of the laser scanning speed and the laser repetition frequency (normal grating period) in each normal writing data group is calculated and summed to obtain the average of the normal grating period;

[0082] In the distortion writing database, the ratio of the laser scanning speed and the laser repetition frequency (distortion grating period) in each distortion writing data group is calculated and summed to obtain the average of the distortion grating period;

[0083] The absolute difference of the period of the average of the normal grating period and the average of the distortion grating period is calculated to obtain the period deviation value;

[0084] The data correlation coefficients of the normal writing database and the distortion writing database are calculated respectively, and the absolute difference is calculated to obtain the writing deviation value;

[0085] The calculation process of the data correlation coefficient is as follows:

[0086] Based on the normal writing database, the laser scanning speed of each writing data group in the normal writing database is integrated in time sequence as a laser scanning speed sequence, and the laser repetition frequency is integrated in time sequence as a laser repetition frequency sequence;

[0087] The Pearson correlation coefficient between the laser scanning speed sequence and the laser repetition frequency sequence is calculated by using the Pearson correlation coefficient method, that is, the data correlation coefficient of the normal writing database, wherein the data correlation coefficient of the distortion writing database is obtained by the same method as the data correlation coefficient of the normal writing database;

[0088] The period deviation value and the writing deviation value are summed to obtain the writing disconnection value;

[0089] In some embodiments, the writing disconnection value is compared with a writing disconnection threshold value;

[0090] If the writing disconnection value is greater than or equal to the writing disconnection threshold value, it indicates that the root cause of the grating period distortion phenomenon is the disconnection of the laser scanning speed and the repetition frequency;

[0091] If the writing disconnection value is less than the writing disconnection threshold value, it indicates that the root cause of the grating period distortion phenomenon is not the disconnection of the laser scanning speed and the repetition frequency, and then other causes are checked;

[0092] It can be understood that the laser scanning speed and the laser repetition frequency proportion consistency comparison (period deviation value) focuses on the macro overall feature: through the average deviation of the laser scanning speed and the laser repetition frequency of the normal and distorted periods, it is judged whether the average proportion of the two deviates significantly, which can quickly identify the overall proportion deviation problem (such as the overall laser scanning speed and the laser repetition frequency proportion is too large or too small), but cannot reflect the matching of the laser scanning speed and the laser repetition frequency in dynamic change (for example, even if the overall average deviation is small, there may be instantaneous disconnection of the laser scanning speed and the laser repetition frequency locally); the linear correlation comparison of the laser scanning speed and the laser repetition frequency focuses on the dynamic correlation feature: through the linear correlation strength of the laser scanning speed and the laser repetition frequency, it is judged whether the two keep synchronous change in the writing process (in the ideal state, the laser scanning speed and the laser repetition frequency fluctuate proportionally), which can capture local instantaneous disconnection (such as the laser scanning speed suddenly jumps while the laser repetition frequency is not synchronized, or vice versa), even if the overall laser scanning speed and the laser repetition frequency average deviation is not large, the dynamic matching failure can also be identified through the correlation decrease, and the combination of the two can cover the overall proportion deviation and local dynamic disconnection, effectively improve the analysis accuracy, and accurately judge the root cause of the grating period distortion;

[0093] Step three: if yes, then the fluctuation analysis of the laser scanning speed and the repetition frequency is performed, if the fluctuation of the laser repetition frequency is higher than or equal to the fluctuation of the laser scanning speed, then the laser repetition frequency is determined as the priority adjustment object, otherwise, the temperature peak under the combination of the laser repetition frequency and the laser scanning speed is analyzed to determine whether the laser repetition frequency is the priority adjustment object;

[0094] In step three, the fluctuation analysis process of the laser scanning speed and the laser repetition frequency is as follows:

[0095] The laser scanning speeds of all grating periods during writing are summarized, and the coefficient of variation is calculated to obtain the speed coefficient of variation;

[0096] The laser repetition frequencies of all grating periods during writing are summarized, and the coefficient of variation is calculated to obtain the frequency coefficient of variation;

[0097] If the frequency coefficient of variation is greater than or equal to the speed coefficient of variation, then the laser repetition frequency is determined as the priority adjustment object;

[0098] If the frequency coefficient of variation is less than the speed coefficient of variation, then further analysis is performed;

[0099] Among them, the reason for selecting the variation coefficient (the fluctuation is large) as the priority adjustment object is that:

[0100] Reason one: the essence of grating period distortion is the instability of the ratio of v and f (v / f), and this instability is often dominated by the dramatic fluctuation of one of the parameters (such as the instantaneous speed jump caused by mechanical vibration, or the high-frequency fluctuation of f due to the instability of the laser source). The parameter with greater fluctuation is the main contributor to the disconnection of the two, for example, if the fluctuation amplitude of v is 5 times that of f, then the fluctuation of v has a much greater impact on the stability of the v / f ratio than f. Prior to adjusting this parameter, the core cause of the distortion can be directly cut off, which is more targeted than blindly adjusting both parameters.

[0101] Reason two: adjusting parameters requires resource consumption (such as hardware debugging, control algorithm optimization, time cost, etc.), and the parameter with greater fluctuation has a higher disturbance weight on the v / f ratio: assuming that by adjusting the parameter with greater fluctuation, the standard deviation is reduced by 50%, the overall fluctuation of v / f can be reduced by 40%; while adjusting the parameter with less fluctuation, even if the standard deviation is also reduced by 50%, the overall fluctuation can only be reduced by 5%. Therefore, by prioritizing the adjustment of the parameter with greater fluctuation, the period uniformity can be significantly improved with less resource investment, which conforms to the principle of efficient optimization.

[0102] Reason three: the formation of a normal grating period depends on the strong linear correlation between v and f (such as a Pearson correlation coefficient close to 1), while the correlation is broken when the distortion occurs, and the parameter with greater fluctuation is the main contributor to the broken correlation. For example, if v suddenly jumps and f does not follow synchronously, it will directly cause the linear relationship between v and f to break. By prioritizing the adjustment of this parameter to make its fluctuation converge, the synchronization of the two can be restored faster, the v / f ratio can be stabilized again, and the grating period can return to the ideal range.

[0103] Reason four: in harsh environments such as vehicles, where there are high temperatures, vibrations, and electromagnetic interference, parameter fluctuations can be amplified (such as vibration causing unstable speed of the scanning mechanism, electromagnetic interference affecting the laser repetition frequency), and the parameter with greater fluctuation is often more sensitive to environmental interference. By prioritizing the adjustment, the anti-interference capability can be enhanced (such as upgrading the anti-vibration performance of the v driving motor, or optimizing the anti-electromagnetic interference design of the f laser source), which can improve the robustness of the system in complex environments from the source, and avoid repeated distortion.

[0104] Among them, the reanalysis process is:

[0105] The normal grating period is processed by averaging to obtain the normal grating period mean, the laser repetition frequency at the time of writing all grating periods is processed by averaging to obtain the laser repetition frequency mean, and the product of the normal grating period mean and the laser repetition frequency mean is calculated to obtain the laser scanning speed mean.

[0106] The laser repetition frequency mean and the laser scanning speed mean are used as the simulation parameter group.

[0107] The temperature field data includes the temperature values of the grid nodes, and the temperature field contour map is drawn according to MATLAB, Python (such as Matplotlib library) or Origin, the temperature peak value is extracted according to the temperature field contour map, and the temperature peak value is compared with the preset temperature threshold of the optical fiber material:

[0108] If the temperature peak value is greater than or equal to the preset temperature threshold of the optical fiber material, the laser repetition frequency is taken as the priority adjustment object, and the purpose is that although the fluctuation of the laser repetition frequency is small, under the current fluctuation, the temperature field caused by the laser repetition frequency does not meet the temperature requirement of the optical fiber material for optical fiber writing, and it is necessary to prioritize the adjustment of the laser repetition frequency;

[0109] If the temperature peak value is less than the preset temperature threshold of the optical fiber material, the temperature deviation of the temperature peak value and the preset temperature threshold of the optical fiber material is calculated;

[0110] If the temperature deviation is less than the preset temperature deviation, the laser repetition frequency is taken as the priority adjustment object, and the purpose is that since the temperature deviation is less than the preset temperature deviation, the temperature peak value is close to the preset temperature threshold of the optical fiber material, and therefore, the laser repetition frequency is taken as the priority adjustment object, which is beneficial to prevent the laser repetition frequency from causing the temperature peak value to exceed the preset temperature threshold of the optical fiber material in the future, and to ensure the quality of the optical fiber material;

[0111] If the temperature deviation is greater than or equal to the preset temperature deviation, the laser scanning speed is taken as the priority adjustment object;

[0112] Step four: if the priority adjustment object is the laser repetition frequency, it is judged whether there is a linear mapping relationship between the laser repetition frequency and the temperature peak value, if there is, the laser repetition frequency adjustment limit value is determined, otherwise, the adjustment combination database of the laser repetition frequency and the laser scanning speed is determined;

[0113] In step four, if the priority adjustment object is the laser repetition frequency, the process of judging whether there is a linear mapping relationship between the laser repetition frequency and the temperature peak value is as follows:

[0114] The temperature peak value under different laser repetition frequencies is obtained by simulating the writing of the optical fiber period under different laser repetition frequencies;

[0115] The simulation writing of the fiber period is as follows: according to different laser repetition frequencies and normal fiber periods, the laser scanning speeds corresponding to different laser repetition frequencies are calculated, and the simulation writing of the fiber period is performed according to different laser repetition frequencies and the corresponding laser scanning speeds. The simulation process has been described above, and will not be described here.

[0116] The temperature peaks under different laser repetition frequencies are fitted by using the least square method, and the goodness of fit is calculated.

[0117] If the goodness of fit is greater than or equal to the preset goodness of fit, it indicates that there is a linear mapping relationship between the laser repetition frequency and the temperature peak.

[0118] If the goodness of fit is less than the preset goodness of fit, it indicates that there is no linear mapping relationship between the laser repetition frequency and the temperature peak.

[0119] In step four, if it exists, the laser repetition frequency adjustment limit value is determined as follows:

[0120] The fitting model after fitting the temperature peaks under different laser repetition frequencies is obtained, the preset temperature threshold is input into the fitting model, and the laser repetition frequency adjustment limit value is output.

[0121] In step four, if it does not exist, the process of determining the adjustment combination database of the laser repetition frequency and the laser scanning speed is as follows:

[0122] According to the simulation writing process of the fiber period, the simulation parameter groups with the temperature peak less than the preset temperature threshold are obtained, and all the simulation parameter groups are summarized to obtain the adjustment combination database.

[0123] Step five: adjusting the laser repetition frequency according to the laser repetition frequency adjustment limit value or adjusting the laser repetition frequency and the laser scanning speed according to the adjustment combination database.

[0124] In step five, the process of adjusting the laser repetition frequency and the laser scanning speed is as follows:

[0125] If there is a linear mapping relationship between the laser repetition frequency and the temperature peak and it is a positive proportional relationship, when the grating period is written, if the grating period is not equal to the normal grating period, the laser repetition frequency is adjusted, and the laser repetition frequency cannot exceed the laser repetition frequency adjustment limit value, otherwise, if there is an inverse proportional relationship, the laser repetition frequency cannot be lower than the laser repetition frequency adjustment limit value.

[0126] If there is no linear mapping relationship between the laser repetition frequency and the temperature peak, the laser repetition frequency and the laser scanning speed are adjusted according to the simulation parameter groups contained in the adjustment combination database.

[0127] The technical scheme of the embodiment of the present application is: uniformity of a femtosecond laser written grating period is analyzed to determine whether a grating period distortion phenomenon occurs, if it occurs, a normal grating period and a distorted grating period are constructed in relation to laser scanning speed and repetition frequency writing data sets, respectively obtaining a normal writing database and a distorted writing database, through comparison and analysis of the normal writing database and the distorted writing database, it is determined whether the root cause of the grating period distortion phenomenon is the disconnection of the laser scanning speed and the repetition frequency, if it is, fluctuation analysis of the laser scanning speed and the repetition frequency is performed, if the laser repetition frequency fluctuation is higher than or equal to the laser scanning speed fluctuation, the laser repetition frequency is determined as the priority adjustment object, otherwise, temperature peaks under the combination of the laser repetition frequency and the laser scanning speed are analyzed to determine whether the priority adjustment object is the laser repetition frequency, if the priority adjustment object is the laser repetition frequency, it is determined whether there is a linear mapping relationship between the laser repetition frequency and the temperature peak, if there is, a laser repetition frequency adjustment limit value is determined, otherwise, an adjustment combination database of the laser repetition frequency and the laser scanning speed is determined, the laser repetition frequency is adjusted according to the laser repetition frequency adjustment limit value or the laser repetition frequency and the laser scanning speed are adjusted according to the adjustment combination database, the present application analyzes the uniformity of the femtosecond laser written grating period, combines the writing data comparison, fluctuation analysis and temperature peak correlation analysis of the laser scanning speed and the repetition frequency, determines the priority adjustment object and the corresponding adjustment limit value or adjustment combination, and then implements targeted adjustment, which can effectively solve the grating period distortion problem, realize the uniformity of the grating period, and ensure the quality and stability of the femtosecond laser written grating.

[0128] Embodiment 2: A special optical fiber grating suitable for a vehicle-mounted environment is prepared by the special optical fiber grating preparation method suitable for a vehicle-mounted environment described in Embodiment 1.

[0129] The basic principles, main features and advantages of the present application are shown and described above. Those skilled in the art should understand that the present application is not limited by the above embodiments, and the above embodiments and descriptions in the specification are only to illustrate the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the claimed present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for manufacturing a special fiber grating suitable for a vehicle-mounted environment, characterized in that: The method comprises the following steps: ​ uniformity analysis is performed on the grating period written by the femtosecond laser to determine whether the grating period distortion phenomenon occurs; if the grating period distortion phenomenon occurs, a normal writing database and a distortion writing database are constructed by using the laser scanning speed and the repetition frequency of the normal grating period and the distorted grating period, and the root cause of the grating period distortion phenomenon is determined by comparison and analysis; if the root cause is the disconnection of the laser scanning speed and the repetition frequency, fluctuation analysis is performed on the laser scanning speed and the repetition frequency, if the fluctuation of the laser repetition frequency is higher than or equal to the fluctuation of the laser scanning speed, the laser repetition frequency is determined as the priority adjustment object, otherwise, the temperature peak under the combination of the laser repetition frequency and the laser scanning speed is analyzed to determine whether the laser repetition frequency is the priority adjustment object; if the priority adjustment object is the laser repetition frequency, it is determined whether there is a linear mapping relationship between the laser repetition frequency and the temperature peak, if there is, the laser repetition frequency adjustment limit value is determined, otherwise, the adjustment combination database of the laser repetition frequency and the laser scanning speed is determined; the laser repetition frequency is adjusted according to the laser repetition frequency adjustment limit value or the laser repetition frequency and the laser scanning speed are adjusted according to the adjustment combination database; the fluctuation analysis process of the laser scanning speed and the laser repetition frequency comprises the following steps: the laser scanning speeds during the writing of the grating periods are summarized, and the coefficient of variation is calculated to obtain the speed variation coefficient; the laser repetition frequencies during the writing of the grating periods are summarized, and the coefficient of variation is calculated to obtain the frequency variation coefficient; if the frequency variation coefficient is greater than or equal to the speed variation coefficient, the laser repetition frequency is determined as the priority adjustment object; the fluctuation analysis process of the laser scanning speed and the laser repetition frequency further comprises the following steps: if the frequency variation coefficient is less than the speed variation coefficient, reanalysis is performed, specifically as follows: the normal grating periods are subjected to mean value processing to obtain the normal grating period mean value, the laser repetition frequencies during the writing of all the grating periods are subjected to mean value processing to obtain the laser repetition frequency mean value, the product of the normal grating period mean value and the laser repetition frequency mean value is calculated to obtain the laser scanning speed mean value; the laser repetition frequency mean value and the laser scanning speed mean value are used as a simulation parameter group, COMSOL software is used to simulate the writing of the fiber period according to the simulation parameter group, and after the simulation is completed, the temperature peak is extracted according to the temperature field contour map; if the temperature peak is greater than or equal to the preset temperature threshold of the fiber material, the laser repetition frequency is determined as the priority adjustment object; if the temperature peak is less than the preset temperature threshold of the fiber material, the temperature deviation between the temperature peak and the preset temperature threshold of the fiber material is calculated; if the temperature deviation is less than the preset temperature deviation, the laser repetition frequency is determined as the priority adjustment object.

2. The special fiber grating preparation method suitable for a vehicle-mounted environment according to claim 1, characterized in that: the process of uniformity analysis of the grating period comprises the following steps: the laser scanning speed and the laser repetition frequency of the femtosecond laser during the writing of the grating stripes are obtained, and proportional calculation is performed to obtain the grating period. All written grating periods are obtained, and a grating period sequence is obtained by integration. A coefficient of variation of the grating period sequence is calculated. If the coefficient of variation is greater than or equal to a coefficient of variation threshold, it is indicated that the grating period uniformity is low, and a grating period distortion phenomenon occurs.

3. The method according to claim 1, characterized in that: The normal grating period and the distorted grating period are obtained in the following way: The grating period is compared with the ideal period range; If the grating period is in the ideal period range, the grating period is marked as a normal grating period; If the grating period is not in the ideal period range, the grating period is marked as a candidate distorted grating period; Based on the candidate distorted grating period, a contribution degree of each candidate distorted grating period is calculated, wherein the contribution degree is a square value of the deviation of each candidate distorted grating period; If the contribution degree is greater than or equal to a preset contribution degree, the candidate distorted grating period is marked as a distorted grating period.

4. The method according to claim 3, characterized in that: The construction process of the normal writing database and the distorted writing database is as follows: The laser scanning speed and the laser repetition frequency when the normal grating period is written are integrated into a normal writing data group, and a normal writing database is obtained by integration; The laser scanning speed and the laser repetition frequency when the distorted grating period is written are integrated into a distorted writing data group, and a distorted writing database is obtained by integration; The comparison and analysis process is as follows: The normal writing database and the distorted writing database are compared to obtain a writing deviation value and a period deviation value; The period deviation value and the writing deviation value are summed to obtain a writing disconnection value; If the writing disconnection value is greater than or equal to a writing disconnection threshold, it is indicated that the root cause of the grating period distortion phenomenon is the disconnection of the laser scanning speed and the repetition frequency.

5. The method according to claim 4, characterized in that: The period deviation value is obtained in the following way: In the normal writing database, the proportion of the laser scanning speed and the laser repetition frequency in each normal writing data group is calculated and summed to obtain a normal grating period mean value; in the distorted writing database, the proportion of the laser scanning speed and the laser repetition frequency in each distorted writing data group is calculated and summed to obtain a distorted grating period mean value; The absolute difference value of the normal grating period mean value and the distorted grating period mean value is calculated to obtain the period deviation value; The writing deviation value is the absolute deviation of the data correlation coefficients corresponding to the normal writing database and the distorted writing database.

6. The method according to claim 1, characterized in that: Whether there is a linear mapping relationship between the laser repetition frequency and the temperature peak value is determined by fitting the temperature peak values under different laser repetition frequencies and judging the goodness of fit; If there is, a fitting model after fitting the temperature peak values under different laser repetition frequencies is obtained, a preset temperature threshold is input into the fitting model, and an adjustment limit value of the laser repetition frequency is output. If not, according to the simulation writing process of the fiber period, the simulation parameter groups with the temperature peak less than the preset temperature threshold are obtained, and all the simulation parameter groups are summarized to obtain an adjustment combination database.

7. The method according to claim 6, wherein the method is characterized in that: the adjustment process is: if there is a linear mapping relationship between the laser repetition frequency and the temperature peak and the relationship is positive, during the grating period writing, if the grating period is not equal to the normal grating period, the laser repetition frequency is adjusted, the laser repetition frequency cannot exceed the laser repetition frequency adjustment limit value, otherwise, if there is an inverse proportional relationship, the laser repetition frequency cannot be lower than the laser repetition frequency adjustment limit value; if there is no linear mapping relationship between the laser repetition frequency and the temperature peak, the laser repetition frequency and the laser scanning speed are adjusted according to the simulation parameter groups contained in the adjustment combination database.

8. A special fiber optic grating suitable for automotive environments, characterized in that: The special fiber grating is prepared by the method according to any one of claims 1-7.

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