A method and system for self-calibration based on sparse matching of tunable laser wavelengths

Abstract

The application provides a kind of based on tunable laser wavelength sparse matching self-calibration method and system, the method comprises: outputting multiple groups of different wavelength scanning laser according to preset timing scanning rule;Collect the reflected light intensity of each wavelength scanning laser by FBG;FBG reflected light intensity is normalized using the corresponding scanning laser original reference light intensity, and normalized reflected light intensity is obtained;Collect the etalon reflected light intensity of each wavelength scanning laser by fiber FP etalon;Real wavelength of each scanning point is calculated by combining etalon reflected light intensity, original reference light intensity;With the real wavelength of each scanning point, normalized reflected light intensity, the calibrated FBG reflection spectrum sampling point set is constructed and peak is fitted, and the actual center wavelength of FBG is obtained.The application realizes the real-time monitoring of tunable laser output wavelength and power, then carries out the joint correction of wavelength coordinate and power coordinate, and finally adopts non-uniform horizontal coordinate spectrum peak seeking algorithm to complete the real-time calibration of FBG sensing demodulation.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing technology, and in particular to a self-calibration method and system based on tunable laser wavelength sparse matching. Background Technology

[0002] During the on-orbit operation of spacecraft, real-time monitoring of structural temperature, strain, and vibration is crucial for ensuring their long-term safety. Traditional monitoring methods based on thermistors and strain gauges are limited by low channel capacity and weak electromagnetic interference resistance, and can no longer meet the requirements of high-capacity, high-speed, and high-precision structural health monitoring for aerospace equipment. Fiber Bragg grating sensing technology, with its advantages of multi-parameter monitoring capabilities, high measurement accuracy, and strong electromagnetic interference resistance, has become a new technology for addressing on-orbit monitoring needs and is currently the most promising solution for engineering applications. Among them, demodulation technology based on tunable laser diodes (TLDs) has advantages such as flexible wavelength scanning, high integration, and strong multi-channel multiplexing capabilities, and has great potential for achieving high-speed, high-capacity demodulation.

[0003] However, scanning laser demodulation technology still faces two challenges when applied to aerospace applications: firstly, the low output power of tunable semiconductor lasers limits the sensing channel capacity of demodulation systems; secondly, its wavelength tuning is susceptible to factors such as temperature drift, ionizing radiation, and device aging, leading to the accumulation of demodulation errors. Especially in long-term monitoring, traditional demodulation systems experience wavelength shifts due to environmental temperature fluctuations or device performance degradation, affecting measurement reliability. These issues restrict the engineering application of fiber optic sensing systems based on tunable semiconductor lasers in complex space environments.

[0004] Wavelength drift in semiconductor lasers caused by radiation is irreversible, and the complex composition of the on-orbit irradiation environment makes the wavelength drift pattern difficult to predict, thus making it impossible to compensate and correct it based on a specific model. Therefore, there is an urgent need to adopt a real-time calibration method for tunable laser wavelengths to dynamically compensate the demodulation system, thereby improving its measurement accuracy and reliability.

[0005] To address this issue, researchers have proposed various wavelength calibration schemes, primarily including temperature compensation methods based on reference FBGs, wavelength locking techniques using gas absorption cavities, and wavelength calibration methods employing FP etalons. However, these methods can only calibrate the overall drift characteristics of the demodulation system. For tunable laser demodulation systems with thousands of different wavelengths output in a time sequence, their demodulation performance depends on the wavelength stability of each output laser. Therefore, relying solely on overall calibration is insufficient to meet accuracy requirements, necessitating real-time compensation calibration for all output wavelengths. However, given the sheer number of wavelengths, there are currently no available reference components for individual calibration. Summary of the Invention

[0006] This invention proposes a self-calibration method and system based on tunable laser wavelength sparse matching to solve or partially solve the above-mentioned problems.

[0007] One aspect of the present invention provides a self-calibration method based on tunable laser wavelength sparse matching, the method comprising: outputting multiple sets of scanning lasers of different wavelengths according to a preset timing scanning pattern; Collect the reflected light intensity of the FBG for scanning laser at various wavelengths; The reflected light intensity of the FBG is normalized by using the original reference light intensity of the scanning laser corresponding to the same scanning point to obtain the normalized reflected light intensity of each scanning point. Synchronously acquire the intensity of etalon reflected light from the fiber optic FP etalon for each wavelength of scanning laser; By combining the reflected light intensity of the standard etalon and the original reference light intensity at each scanning point, the true wavelength of the scanning laser at each scanning point is calculated. Based on the true wavelength and normalized reflected light intensity of each scanning point, a set of calibrated FBG reflection spectrum sampling points is constructed. The peak is found by fitting the sampling point set to obtain the actual center wavelength of the FBG.

[0008] Furthermore, the step of outputting multiple sets of scanning lasers of different wavelengths according to a preset timing scanning pattern includes: Based on the wavelength range of the reference reflection peak of the fiber FP etalon, a preset timing scanning pattern is determined so that the nominal wavelength of the scanning laser at the same scanning point falls within the linear range of the edge of the corresponding reference reflection peak.

[0009] Furthermore, the calculation of the true wavelength of the scanning laser at each scanning point, by combining the reflected light intensity of the standard etalon and the original reference light intensity at each scanning point, includes: The reflection spectrum of the fiber FP etalon is pre-calibrated to determine the linear slope of the linear interval at the edge of each reference reflection peak; The scanning laser wavelength offset at the current scanning point is calculated using a wavelength offset calculation model, which is as follows: In the above formula, Let be the scanning laser wavelength offset at the i-th scanning point. Let be the intensity of the reflected light from the etalon at the i-th scan point. The initial reference light intensity of the etalon when there is no offset at the i-th scan point. The linear slope of the reference reflection peak of the pre-calibrated etalon; The true wavelength of the current scanning point is calculated by comparing the nominal wavelength of the same scanning point with the wavelength offset obtained from the solution.

[0010] Another aspect of the present invention provides a tunable laser wavelength sparse matching self-calibration system for performing the tunable laser wavelength sparse matching self-calibration system described above, the system comprising: A tunable laser is used to output multiple sets of scanning lasers of different wavelengths according to a preset timing scanning pattern. The first coupler has a beam splitting ratio of 2:1. It receives the scanning laser output from the tunable laser and splits it into two paths. One of the laser paths, which accounts for 1 part, is sent to the first circulator, and the other of the laser path, which accounts for 2 parts, is sent to the second coupler. The first circulator has an external FBG sensing grating connected to port 2 and a third photodetector connected to port 3. The third photodetector is used to collect the intensity of the light reflected by the FBG. The second coupler has a beam splitting ratio of 1:1. It receives the laser beam split from the first coupler and divides it into two paths. One path is directly connected to the first photodetector, which is used to collect the original reference light intensity of the scanning laser. The other path is sent to the second circulator. The second circulator has a 2-port connection to an optical fiber FP etalon and a 3-port connection to a second photodetector, which is used to collect the intensity of light reflected from the etalon. The signal processing control module is electrically connected to the first photodetector, the second photodetector, and the third photodetector, respectively, and is configured to execute the method described in claims 1 to 3 to complete light intensity normalization, wavelength offset calculation, spectral reconstruction, and peak fitting.

[0011] Furthermore, prior to performing the non-uniformity correction step, the method further includes: The transmission spectrum of the fiber optic FP etalon is collected, and the wavelength of each reference transmission peak and the fixed frequency interval between adjacent transmission peaks are determined based on the transmission spectrum. Based on the characteristic that the wavelength spacing of the etalon changes linearly with the band, the timing scanning law of the tunable laser is determined, and based on the timing scanning law, the sparse mapping matching between the scanning wavelength and the reference reflection peak of the etalon is completed.

[0012] Furthermore, the FBG sensing grating adopts a broadband FBG.

[0013] This invention proposes a self-calibration method and system based on tunable laser wavelength sparse matching. The method includes: outputting multiple sets of scanning lasers of different wavelengths according to a preset time-series scanning pattern; acquiring the reflected light intensity of the FBG (Fiber Optic Laser) at each wavelength scanning laser; normalizing the reflected light intensity of the FBG using the original reference light intensity of the scanning laser at the same scanning point to obtain the normalized reflected light intensity at each scanning point; synchronously acquiring the etalon reflected light intensity of the fiber optic FP (Fiber Optic Electrode) at each wavelength scanning laser; calculating the true wavelength of the scanning laser at each scanning point by combining the etalon reflected light intensity and the original reference light intensity; constructing a calibrated FBG reflection spectrum sampling point set based on the true wavelength and normalized reflected light intensity of each scanning point; fitting the sampling point set to find the peak to obtain the actual center wavelength of the FBG. This invention achieves real-time monitoring of the output wavelength and power of the tunable laser, then performs joint correction of wavelength and power coordinates, and finally uses a non-uniform abscissa spectral peak-finding algorithm to complete the real-time calibration of the FBG sensing demodulation.

[0014] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below. Attached Figure Description

[0015] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. In the drawings: Figure 1 This is a flowchart of a tunable laser wavelength sparse matching self-calibration method according to an embodiment of the present invention; Figure 2 This is a schematic diagram illustrating the calibration principle of the tunable laser wavelength sparse matching self-calibration method according to an embodiment of the present invention, wherein: Figure 2 (a) is a schematic diagram comparing the nominal value and the actual value of the scanning laser; Figure 2 (b) is the reflection spectrum of the wavelength etalon; Figure 2 (c) is the FBG reflection spectrum before wavelength calibration; Figure 2 (d) is the FBG reflection spectrum after wavelength calibration; Figure 3 This is a schematic diagram of the principle of tunable laser wavelength sparse matching self-calibration according to an embodiment of the present invention; Figure 4 This is a flowchart of the correction and compensation algorithm according to an embodiment of the present invention; Figure 5A schematic diagram of the system for acquiring the transmission spectrum of a standard etalon by a spectrometer, wherein: Figure 5 (a) is a schematic diagram of the testing device; Figure 5 (b) is the overall reflectance spectrum; Figure 5 (c) is a partial reflection spectrum; Figure 5 (d) represents the peak wavelength spacing; Figure 6 This is a structural diagram of the MG-Y laser drive control system; Figure 7 A comparison diagram of the laser output spectrum and the reflection spectrum of the standard etalon; Figure 8 The following are structural diagrams and physical images of the calibration system according to an embodiment of the present invention, wherein: Figure 8 (a) is a structural diagram of the calibration system; Figure 8 (b) is a physical diagram of the calibration system; Figure 9 For the demodulation and calibration system software interface; Figure 10 FBG spectrum acquired by the demodulation system; Figure 11 For the peak finding calculation results; Figure 12 This is an irradiation testing experimental setup; Figure 13 The result is calculated by the irradiation test demodulator. Detailed Implementation

[0016] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0017] Reference Figure 1 The self-calibration method based on tunable laser wavelength sparse matching provided by this invention specifically includes the following steps: S1. Output multiple sets of scanning lasers of different wavelengths according to the preset timing scanning pattern; In this embodiment, the scanning laser is output by a tunable laser, which scans cyclically from short wave to long wave along the wavelength band in a time sequence. Under normal operating conditions, the scanning laser is output at equal time intervals and equal nominal wavelength intervals.

[0018] Since this scheme requires matching and mapping all scanning wavelengths of the laser with the comb-shaped reference wavelength of the fiber FP etalon, this embodiment needs to output the scanning laser based on the preset timing scanning law of the wavelength interval of the etalon.

[0019] Furthermore, each scanning laser only has a theoretical nominal wavelength and nominal intensity. External environmental factors such as on-orbit irradiation and temperature disturbances can cause laser output drift: the actual wavelength and actual intensity of the laser corresponding to the same scanning time point will deviate from the nominal value, and the amount of wavelength and intensity drift at the same nominal scanning point at different times will vary. Specifically, as follows... Figure 2 As shown in (a), the horizontal axis represents the wavelength of each scanning point, and the vertical axis represents the light intensity of each scanning point. The gray arrows indicate the tunable laser output at equal intervals in the initial state, and the red arrows indicate the tunable laser after wavelength and light intensity fluctuations occur. This invention eliminates the demodulation error caused by this drift by performing real-time calibration of the true wavelength of each scanning point in subsequent steps.

[0020] S2. Collect the reflected light intensity of the FBG for each wavelength of scanning laser; In this embodiment, after the scanning laser is incident on the FBG sensing grating, the grating only reflects the incident laser with wavelengths matching its own resonance wavelength; lasers of other wavelengths are directly transmitted through the grating. By acquiring the FBG reflected light intensity signal corresponding to each time-series scanning point in real time using a photodetector, the original reflection spectrum of the FBG sensing grating can be completely acquired. Theoretically, environmental parameters such as the temperature and strain to be measured can be retrieved based on the central reflection wavelength of the FBG. However, as mentioned earlier, due to external disturbances such as irradiation and temperature, the true wavelength and true light intensity of the tunable laser output will deviate from the nominal value. If the center wavelength is directly calculated based on this uncalibrated original reflection spectrum, the obtained wavelength result will introduce significant measurement deviations, which cannot meet the requirements of high-precision demodulation on space.

[0021] S3. Normalize the reflected light intensity of the FBG using the original reference light intensity of the scanning laser corresponding to the same scanning point to obtain the normalized reflected light intensity of each scanning point. In this embodiment, the FBG reflected light intensity acquired under the same scanning sequence is divided by the synchronously measured original laser reference light intensity to complete the light intensity normalization calculation, and the normalized reflected light intensity corresponding to each scanning point is output. It should be noted that this scheme directly acquires the original laser reference light intensity in real time through an independent photodetector. Using this measured reference light intensity as the normalization benchmark, after normalization processing, the reflection spectrum amplitude error caused by the output light intensity drift at each scanning point of the laser can be completely eliminated, avoiding light intensity fluctuations interfering with subsequent peak finding accuracy. At this point, the normalized FBG reflection spectrum can be obtained, such as... Figure 2 As shown in (e).

[0022] S4. Synchronously acquire the intensity of reflected light from the fiber optic FP etalon for each wavelength scanning laser. In this embodiment, the fiber FP etalon has several reference reflection peaks with equal wavelength intervals; based on the mapping relationship between wavelength and reflected light intensity, the wavelength shift of the laser output can be monitored in real time by monitoring the change in reflected light power of the tunable laser incident on the etalon.

[0023] S5. By combining the reflected light intensity of the standard etalon and the original reference light intensity at each scanning point, the true wavelength of the scanning laser at each scanning point is calculated. S6. Based on the true wavelength and normalized reflected light intensity of each scanning point, construct a set of calibrated FBG reflection spectrum sampling points, fit the sampling point set to find the peak, and obtain the actual center wavelength of the FBG.

[0024] In embodiments of the present invention, such as Figure 2 As shown by the red curve in (c), a set of calibrated FBG reflection spectrum sampling points is constructed with the actual wavelength of each scanning point as the abscissa and the normalized reflected light intensity as the ordinate. The peak is found by fitting the sampling point set to obtain the actual center wavelength of the FBG.

[0025] The wavelength sparse matching FBG demodulation self-calibration method for tunable lasers provided in this invention can effectively eliminate measurement interference caused by wavelength drift and intensity drift of the output scanning laser of the tunable laser, achieving real-time, fast, and high-precision calibration of the FBG center wavelength. This scheme utilizes the linear mapping relationship of the reflection peak edge of the fiber FP etalon, eliminating the complex peak-finding calculation and relying on the intensity difference to quickly solve for the point-by-point wavelength drift. Simultaneous acquisition of the original reference intensity for normalization eliminates the interference of laser power fluctuations on the spectral amplitude, resulting in lower hardware costs. Furthermore, digital calibration is achieved solely through a back-end algorithm, requiring no modification to the laser hardware, making it highly versatile and capable of long-term stable adaptation to harsh conditions such as spaceborne irradiation and temperature fluctuations, significantly improving the FBG sensing demodulation accuracy.

[0026] Furthermore, in step S1, the step of outputting multiple sets of scanning lasers with different wavelengths according to a preset timing scanning rule includes: determining a preset timing scanning rule based on the wavelength range of the reference reflection peak of the fiber FP etalon, so that the nominal wavelength of the scanning laser at the same scanning point falls within the linear range of the edge of the corresponding reference reflection peak.

[0027] Reference Figure 2 (b) Figure 2 (c) Figure 2(b) Although the coordinate axes are not labeled, it can be determined from Figure 2 (a) that the horizontal axis is wavelength and the vertical axis is reflected light intensity. The green dashed line in the figure is the periodic comb-shaped reflection spectrum of the fiber FP etalon. Within the sloping regions on both sides of a single reflection peak, the wavelength and reflected light intensity show a stable linear correspondence. The gray vertical line represents the nominal reference wavelength of the laser under drift-free conditions, and the red vertical line represents the actual output wavelength of the laser after being shifted by external disturbances such as temperature and spatial irradiation. The black dots are the reflected light intensity sampling points collected by the photodetector when the corresponding wavelength is incident on the etalon reflection sloping side.

[0028] Within the region on either side of the peak of a single reference reflection peak in an optical fiber FP etalon, there exists a linear interval where the wavelength and reflected light intensity exhibit an approximately linear relationship. In this invention, when the scanning laser is set within this linear interval, even a small wavelength drift can result in a regular linear change in the reflected light intensity. Therefore, this scheme configures the nominal wavelength of the laser at each scanning point within this linear interval, providing a foundation for subsequently using a wavelength shift calculation model to solve for the wavelength drift.

[0029] Further, in step S5, the calculation of the true wavelength of the scanning laser at each scanning point by combining the reflected light intensity of the standard etalon and the original reference light intensity includes: S51. Pre-calibrate the reflection spectrum of the fiber FP etalon and determine the linear slope of the linear interval at the edge of each reference reflection peak; Before the formal demodulation work in this embodiment of the invention, ground calibration operation needs to be completed for the comb-shaped reflection spectrum of the fiber FP standard etalon shown by the green dashed line in the figure: select the linear slope interval of the reflection peak, use a high-precision light source for small step scanning, synchronously record the wavelength and the corresponding reflected light intensity, and obtain the fixed linear slope of the reflection peak edge through linear fitting. This slope will be stored in the system as a constant conversion coefficient to provide a reference parameter for subsequent real-time calculation of the wavelength drift of each scanning point.

[0030] S52. The scanning laser wavelength offset at the current scanning point is calculated using a wavelength offset calculation model. The wavelength offset calculation model is as follows: In the above formula, Let be the wavelength offset of the scanning laser at the i-th scanning point. Let be the intensity of the reflected light from the etalon at the i-th scan point. The initial reference light intensity of the etalon when there is no offset at the i-th scan point. The linear slope of the reference reflection peak of the pre-calibrated etalon; Specifically, in combination Figure 2 (b) and Figure 2(d) Under drift-free conditions, the laser is incident along the gray reference vertical line, corresponding to the reference light intensity. When the laser output wavelength shifts, the laser position shifts from the gray reference line to the red vertical line, and the sampling point moves up and down along the slope of the green reflection peak, and the collected reflected light intensity changes synchronously. That is, the standard etalon reflected light intensity obtained in actual measurement is the intersection of the red vertical line and the green dashed line in (d). Since the pre-calibrated intersection of the gray vertical and green vertical lines is known, the wavelength at the position of the gray vertical line is known, and the linear slope of the reference reflection peak is known, the difference between the wavelength at the red vertical line and the wavelength at the gray vertical line can be calculated based on the above wavelength shift calculation model.

[0031] S53. Calculate the true wavelength of the current scanning point based on the nominal scanning wavelength of the same scanning point and the wavelength offset obtained by the solution.

[0032] Furthermore, to implement the above theoretical method, this embodiment of the invention also provides a tunable laser wavelength sparse matching self-calibration system, referring to... Figure 3 The system includes: A tunable laser is used to output multiple sets of scanning lasers of different wavelengths according to a preset timing scanning pattern. The first coupler has a beam splitting ratio of 2:1. It receives the scanning laser output from the tunable laser and splits it into two paths. One of the laser paths, which accounts for 1 part, is sent to the first circulator, and the other of the laser path, which accounts for 2 parts, is sent to the second coupler. The first circulator has an external FBG sensing grating connected to port 2 and a third photodetector connected to port 3. The third photodetector (PD3 in figure 3) is used to collect the intensity of the FBG reflected light. The second coupler, with a beam splitting ratio of 1:1, receives the laser beam split from the first coupler and divides it into two paths; one path is directly connected to the first photodetector (attached). Figure 3 (PD1 in the image), the first photodetector is used to collect the original reference light intensity of the scanning laser; the other path is sent to the second circulator; The second circulator has a 2-port connection to an optical fiber FP etalon and a 3-port connection to a second photodetector (PD2 in Figure 3). The second photodetector is used to collect the intensity of the light reflected from the etalon.

[0033] In addition, embodiments of the present invention also include a signal processing control module, which is electrically connected to the first photodetector, the second photodetector, and the third photodetector respectively, and is configured to execute the above-mentioned self-calibration method to complete light intensity normalization, wavelength offset solution, spectral reconstruction, and peak finding.

[0034] Furthermore, referring to Figure 4 In this embodiment of the invention, the third photodetector acquires the FBG reflected light intensity at each scanning point, which can be expressed as: That is, the first i The FBG reflected light intensity at each scanning point, and the original reference light intensity of the scanning laser collected by the first photodetector, can be expressed as: That is, the first i The normalized reflected light intensity is obtained by dividing the original reference light intensity at each scan point by the original reference light intensity. I FRG ( j ).

[0035] Furthermore, the intensity of the light reflected from the etalon collected by the second photodetector is expressed as follows: Since the initial reference light intensity of the etalon is known, the wavelength offset Δ at the current scanning point can be calculated by combining the wavelength offset calculation model in the above method embodiment. λ(i Based on △ λ(i The sampling points of the FBG reflectance spectrum are corrected to obtain the corrected sampling point P. i ( λ i + △ λ(i ) ,I i ),in λ i For the first i The nominal wavelength of the scanning laser at each scanning point I i For the first i The normalized reflected light intensity at each scan point is then used to fit the peak and obtain the true center wavelength of the FBG. λ cal .

[0036] Furthermore, before performing the non-uniformity correction step, the method further includes: acquiring the transmission spectrum of the fiber FP etalon, calibrating the wavelength of each reference transmission peak and the fixed frequency interval between adjacent transmission peaks based on the transmission spectrum; determining the timing scanning law of the tunable laser based on the characteristic that the wavelength interval of the etalon changes linearly with the band, and completing the sparse mapping matching between the scanning wavelength and the reference reflection peak of the etalon based on the timing scanning law.

[0037] In practical applications, the number of scanning points for the original output wavelength of a tunable laser is much greater than the number of reference reflection peaks for an optical fiber FP etalon. Therefore, this embodiment of the invention performs sparse processing on the scanning wavelength sequence of the tunable laser based on the total number of reference reflection peaks, constructing a one-to-one sparse mapping relationship between scanning wavelength points and reference reflection peaks, so that each scanning laser wavelength after sparse screening matches a reference reflection peak of the optical fiber FP etalon; that is, the nominal wavelength of the scanning laser is set within the linear interval of the corresponding reference reflection peak. Only when the laser operates within this linear interval can a small wavelength drift cause a linear change in the intensity of the reflected light from the etalon, and then the wavelength drift amount at each scanning point can be solved using a wavelength shift calculation model.

[0038] Furthermore, in this embodiment, a broadband FBG is selected as the sensing grating. Specifically, this invention performs sparse processing on the original scanning wavelength sequence of the tunable laser, reducing the number of effective measurement points directly involved in wavelength calibration by an order of magnitude compared to conventional methods. If a narrow-spectrum FBG is used, the number of sampling points contained within the FBG reflection profile is too small, which reduces the stability of spectral fitting and peak finding, thus affecting demodulation accuracy. Using a broadband FBG allows more discrete wavelength sampling points to fall within the FBG reflection spectrum range under the same number of sampling points, obtaining sufficient in-peak sampling data and ensuring the fitting accuracy of the FBG center wavelength under sparse sampling conditions.

[0039] In one specific embodiment of the present invention, a 25 GHz fiber optic FP etalon is used, which provides 200 reference reflection peaks within a 40 nm bandwidth, with each reflection band having a bandwidth of approximately 16 pm. To achieve precise matching with the etalon, the present invention sparsely matches the conventional 2000 output wavelengths of a tunable laser to 200 output wavelength points, and calibrates them using a lookup table based on the transmission spectrum characteristics of the etalon to ensure that each output wavelength precisely corresponds to the reference reflection peak of the etalon. After processing by the aforementioned wavelength monitoring system, the 200 wavelengths after sparse matching can be used to correct the FBG peak finding calculation, thereby improving demodulation stability.

[0040] Furthermore, the temperature-compensated etalon exhibits excellent wavelength stability, meeting the requirements for long-term reliable operation under harsh environments. The etalon used in this invention is a 25 GHz temperature-insensitive fiber optic FP etalon developed by Guangzhou Aoxin Technology Co., Ltd., which exhibits a reference spectral stability better than ±1 pm within an ambient temperature range of 15 °C to 35 °C. Figure 5 (a) The transmission spectrum of a standard etalon acquired using a broadband light source and spectrometer. Overall, the spectrum exhibits a uniform comb-like distribution, with a frequency interval of 25 GHz between adjacent transmission peaks, corresponding to a wavelength interval of approximately 200 pm. This invention uses wavelength dimensions for description and calculation, and calculates the wavelength intervals corresponding to different bands, such as... Figure 5As shown in (b), the wavelength spacing increases linearly with increasing wavelength, from 194 pm to 205 pm. Therefore, when performing sparse matching of the output wavelength of a tunable laser, it is not possible to simply set an equal spacing of 200 pm. Instead, matching should be performed according to the above linear relationship to ensure that each output wavelength corresponds precisely to the reference reflection peak of the etalon.

[0041] Furthermore, the tunable laser used in this invention is the S7500 Modulated Grating Y-branch (MG-Y) laser manufactured by Finisar Corporation, USA. It belongs to a novel multi-electrode distributed Bragg reflector (DBR) tunable laser, possessing advantages such as continuous C-band tunability, nanosecond-level tuning speed, and high side-mode suppression ratio (>40 dB). Its die structure is as follows... Figure 6 As shown, the laser consists of six parts: a left grating reflector, a right grating reflector, a multimode interference (MMI) coupling region, a phase region, a gain region, and a semiconductor optical amplifier (SOA). The output wavelength of the laser is jointly controlled by the left and right grating reflectors and the phase region. The two grating reflectors generate comb-shaped reflection spectra with unequal spacing. By adjusting the parameters of the reflectors, the position of the overlapping peaks is controlled, ensuring that the reflected wavelength at a certain moment corresponds to the reflected wavelength of a pair of overlapping peaks. Then, the phase region controls the phase resonance condition of the output light to achieve fine-tuning of the wavelength, thereby obtaining output light of different wavelengths. Changing the injection current in the grating reflector and phase region of the laser causes a change in the free carrier concentration of the semiconductor material in that region, thereby changing the effective refractive index of the material and achieving tuning and control of the laser's output wavelength.

[0042] The driving system of the MG-Y laser consists of a host computer (PC), a serial port module, an FPGA main control unit, a multi-channel drive control link, and the MG-Y laser itself. The MG-Y laser integrates an SOA (Optical State Aspect), gain region, phase region, and MMI (Mechanical Management Interface). The PC sends control commands to the FPGA via the serial port module, and the FPGA outputs multiple control signals. Five of these signals drive adjustable voltage-controlled current sources via a digital-to-analog converter (DAC) to provide adjustable drive current to each control unit of the laser. Another FPGA control signal is sent to a temperature control module, which uses a thermoelectric cooler (TEC) to achieve constant temperature control of the optical chip. After the currents are regulated, the optical signals from each functional area of ​​the optical chip are combined via the MMI.

[0043] Furthermore, the MG-Y tunable semiconductor laser achieves continuous scanning of the output wavelength and stable control of optical power through the coordinated regulation of five driving currents. This invention pre-plans 200 target wavelength points based on an optical fiber FP etalon, with wavelength values ​​calculated according to the formula... (n=1, 2, 3, ..., 200) is set. Each target wavelength point is calibrated sequentially, and the corresponding five-channel drive current and actual output wavelength data are obtained. After data processing, a control lookup table containing 200 sets of current-wavelength mapping relationships is generated. This lookup table is then embedded in the FPGA to drive the laser to achieve wavelength scanning output.

[0044] Furthermore, this embodiment uses the high-resolution slow-scan mode of the spectrometer to acquire the spectral data of the output laser. The scanning frequency of the tunable laser is 200 Hz, and the spectrometer takes approximately 300 seconds to complete one C-band scan. The acquired laser spectrum is the cumulative average of hundreds of laser outputs, yielding an equivalent steady-state spectrum for accurate calculation of the center wavelength of the output laser. Based on the matching state between the measured center wavelength and the reflection band of the etalon, the lookup table can be further fine-tuned to achieve more accurate wavelength matching. Finally, based on... Figure 1 The calibration principle described above locks the laser output wavelength to the center of the etalon reflection band. Figure 7 The comparison results between the laser output spectrum and the etalon reflection spectrum are presented.

[0045] Furthermore, specific embodiments of the present invention are based on Figure 3 The system diagram shown includes a physical model, such as... Figure 8 As shown, three photodetectors (PD1~PD3) convert optical signals into voltage signals, which are then amplified by a transimpedance amplifier (TIA) and converted into digital signals by an analog-to-digital converter (ADC) before being sent to the FPGA for processing. Simultaneously, the control signals output by the FPGA are converted back into analog signals by a digital-to-analog converter (DAC) and fed back to the tunable semiconductor laser, achieving closed-loop control.

[0046] Furthermore, the host computer software LabVIEW is used to acquire and process digital signals. The software interface is as follows: Figure 9 As shown, the system can achieve real-time acquisition and display of the reference light intensity (PD1), the etalon calibration light intensity (PD2), and the FBG reflected light intensity (PD3, i.e., the reflection spectrum). Finally, the corrected spectrum is obtained through the calibration algorithm and displayed in real time. At the same time, the Gaussian fitting algorithm is used to perform peak finding calculation to achieve real-time display of the FBG center wavelength before and after calibration.

[0047] Furthermore, the calibrated FBG spectrum is as follows: Figure 10 As shown, the peak finding calculation results are as follows: Figure 11As shown. Given that the number of sampling points was reduced from 2000 to 200, in order to increase the number of sampling points for reconstructing the FBG spectrum, an FBG with a spectral width of 0.8 nm and a gate length of 2 mm was used for the experiment, and the stability of peak finding and demodulation was ±2 pm.

[0048] Furthermore, the present invention also conducted radiation tests on the above-mentioned adjustment system, using a test apparatus such as... Figure 12 As shown, the demodulator is mounted on an aluminum plate, positioned behind a rod-shaped cobalt source. The radiation dose rate is controlled by adjusting the distance between the demodulator and the cobalt source. The power supply for the demodulator is located behind the aluminum plate. The laser output from the demodulator is transmitted to the test room via a 30-meter optical fiber and connected to a reference grating (FBG) unaffected by radiation. This reference grating uses temperature-insensitive packaging, exhibiting a wavelength drift of less than 0.5 pm at room temperature, and can be used to calibrate the demodulation performance fluctuations of the demodulator after irradiation. Simultaneously, the demodulator is connected to a computer in the test room via a 30-meter signal line, and experimental data is stored and processed using LabVIEW-based real-time spectral acquisition and processing software.

[0049] The irradiation dose rate was set to 2 rad / s, and continuous irradiation lasted for 70 hours, resulting in a total dose of 504 krad. Figure 12 As shown, the variation of the center wavelength of the reference FBG with irradiation dose was recorded. The blue curve represents the measurement deviation of the uncalibrated FBG recorded by PD3. When the irradiation dose increases from 0 to 100 krad, ionizing radiation causes a rapid increase in the measurement deviation, which then levels off, with the overall measurement deviation exceeding 3.5 pm. The red curve represents the measurement deviation after calibration, showing a similar trend to the uncalibrated curve, but with a significantly reduced deviation to within 1.4 pm. Experimental results demonstrate that this real-time self-calibration method can effectively improve the measurement stability and sensing accuracy of the demodulator under irradiation conditions.

[0050] This paper addresses the issue of degraded demodulation stability caused by output wavelength and power fluctuations in spaceborne fiber optic sensing demodulation systems based on tunable semiconductor lasers (FSLs) under space irradiation conditions. A real-time self-calibration method based on FP etalon wavelength sparse matching is proposed and validated. This method utilizes a 25 GHz high-density etalon to provide 200 wavelength reference reflection points. By sparsely matching the 2000 output wavelengths of the MG-Y tunable laser to the etalon transmission peaks and combining differential monitoring of the reference light intensity and the etalon reflected light intensity, real-time capture of output wavelength drift and power fluctuations is achieved. Based on this, nonlinear corrections are performed on the equally spaced wavelength coordinates, and a non-uniform abscissa spectral peak-finding algorithm is used to complete real-time compensation for FBG sensing demodulation. Experimental results show that under a total gamma irradiation dose of 504 krad, the calibrated demodulation system exhibits a sensing wavelength drift of 1.5 pm, significantly better than the 3.5 pm of the uncalibrated system, demonstrating the effectiveness of this method in suppressing demodulation drift under irradiation conditions. This study provides a practical technical solution for high-reliability, high-precision long-term monitoring of aerospace fiber optic sensing systems in complex space radiation environments, which is of great significance for promoting the engineering application of fiber optic sensing technology in aerospace structural health monitoring.

[0051] The self-calibration method and system based on tunable laser wavelength sparse matching proposed in this invention have at least the following advantages: 1. By utilizing the linear characteristics of the reflection peak edge of the standard etalon, the wavelength shift can be quickly calculated through the intensity difference, avoiding complex peak finding calculations; combined with reference intensity normalization processing, the intensity error caused by laser power fluctuations and environmental disturbances can be effectively offset, ensuring the stability and reliability of spectral reconstruction and peak finding results.

[0052] 2. This invention corrects the non-uniformity of wavelength intervals as the band changes through offline calibration of standard etalon transmission spectra, abandons the traditional fixed equal interval matching method, accurately matches each scanning wavelength with the reference reflection peak, eliminates peak crossing and mismatch problems, and effectively improves the accuracy of wavelength calibration.

[0053] 3. This invention establishes a sparse mapping relationship between the laser scanning wavelength and the reference reflection peak of the etalon, performs sparse calibration on the high-density laser scanning sequence, and achieves full-band wavelength drift correction with a small number of reference peaks, which greatly reduces the amount of computation, improves the demodulation rate, adapts to high-speed scanning scenarios, simplifies the optical path configuration, and reduces hardware costs.

[0054] 4. To address the accuracy loss caused by sparse sampling, a broadband FBG is used to supplement the effective sampling points within the peaks, balancing low computational load with high-precision demodulation performance of ±2 pm. The entire solution is based on the algorithm and requires no hardware modification. Paired with a highly stable, temperature-insensitive etalon, it can adapt to harsh spaceborne conditions such as high and low temperatures and irradiation, ensuring high reliability during long-term operation.

[0055] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art and should not be interpreted in an idealized or overly formal sense unless specifically defined.

[0056] For the sake of simplicity, the method embodiments are described as a series of actions. However, those skilled in the art should understand that the embodiments of the present invention are not limited to the described order of actions, because according to the embodiments of the present invention, some steps can be performed in other orders or simultaneously. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions involved are not necessarily essential to the embodiments of the present invention.

[0057] Furthermore, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of the invention and form different embodiments. For example, any of the claimed embodiments can be used in any combination.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A self-calibration method based on sparse matching of tunable laser wavelengths, characterized in that, The method includes: Multiple sets of scanning lasers of different wavelengths are output according to a preset timing scanning pattern; Collect the reflected light intensity of the FBG for scanning laser at various wavelengths; The reflected light intensity of the FBG is normalized by using the original reference light intensity of the scanning laser corresponding to the same scanning point to obtain the normalized reflected light intensity of each scanning point. Synchronously acquire the intensity of etalon reflected light from the fiber optic FP etalon for each wavelength of scanning laser; By combining the reflected light intensity of the standard etalon and the original reference light intensity at each scanning point, the true wavelength of the scanning laser at each scanning point is calculated. Based on the true wavelength and normalized reflected light intensity of each scanning point, a set of calibrated FBG reflection spectrum sampling points is constructed. The peak is found by fitting the sampling point set to obtain the actual center wavelength of the FBG.

2. The method according to claim 1, characterized in that, The step of outputting multiple sets of scanning lasers of different wavelengths according to a preset timing scanning pattern includes: Based on the wavelength range of the reference reflection peak of the fiber FP etalon, a preset timing scanning pattern is determined so that the nominal wavelength of the scanning laser at the same scanning point falls within the linear range of the edge of the corresponding reference reflection peak.

3. The method according to claim 1, characterized in that, The true wavelength of the scanning laser at each scanning point is calculated by combining the reflected light intensity of the standard etalon and the original reference light intensity at each scanning point, including: The reflection spectrum of the fiber FP etalon is pre-calibrated to determine the linear slope of the linear interval at the edge of each reference reflection peak; The scanning laser wavelength offset at the current scanning point is calculated using a wavelength offset calculation model, which is as follows: In the above formula, Let be the scanning laser wavelength offset at the i-th scanning point. Let be the intensity of the reflected light from the etalon at the i-th scan point. The initial reference light intensity of the etalon when there is no offset at the i-th scan point. The linear slope of the reference reflection peak of the pre-calibrated etalon; The true wavelength of the current scanning point is calculated by comparing the nominal wavelength of the same scanning point with the wavelength offset obtained from the solution.

4. A self-calibration system based on tunable laser wavelength sparse matching, characterized in that, The system is used to perform the tunable laser wavelength sparse matching self-calibration method according to any one of claims 1-3, the system comprising: A tunable laser is used to output multiple sets of scanning lasers of different wavelengths according to a preset timing scanning pattern. The first coupler has a beam splitting ratio of 2:

1. It receives the scanning laser output from the tunable laser and splits it into two paths. One of the laser paths, which accounts for 1 part, is sent to the first circulator, and the other of the laser path, which accounts for 2 parts, is sent to the second coupler. The first circulator has an external FBG sensing grating connected to port 2 and a third photodetector connected to port 3. The third photodetector is used to collect the intensity of the light reflected by the FBG. The second coupler has a beam splitting ratio of 1:

1. It receives the laser beam split from the first coupler and divides it into two paths. One path is directly connected to the first photodetector, which is used to collect the original reference light intensity of the scanning laser. The other path is sent to the second circulator. The second circulator has a 2-port connection to an optical fiber FP etalon and a 3-port connection to a second photodetector, which is used to collect the intensity of light reflected from the etalon. The signal processing control module is electrically connected to the first photodetector, the second photodetector, and the third photodetector, respectively, and is configured to execute the method described in claims 1 to 3 to complete light intensity normalization, wavelength offset calculation, spectral reconstruction, and peak fitting.

5. The system according to claim 1, characterized in that, Prior to performing the non-uniformity correction step, the method further includes: The transmission spectrum of the fiber optic FP etalon is collected, and the wavelength of each reference transmission peak and the fixed frequency interval between adjacent transmission peaks are determined based on the transmission spectrum. Based on the characteristic that the wavelength spacing of the etalon changes linearly with the band, the timing scanning law of the tunable laser is determined, and based on the timing scanning law, the sparse mapping matching between the scanning wavelength and the reference reflection peak of the etalon is completed.

6. The system according to claim 5, characterized in that, The FBG sensing grating uses a broadband FBG.

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