A self-calibration function full spectrum analyzer and a calibration method thereof

Abstract

The present disclosure relates to a full-spectrum analyzer with self-calibration function and a calibration method thereof, and belongs to the technical field of optical fiber sensing demodulation. The demodulator realizes the integration of high-precision wavelength demodulation and online self-calibration function through the cooperative architecture of a scanning light source, a reference branch, a measurement branch and a self-calibration branch. The reference branch has a built-in standard as the wavelength reference core, and is assisted by active precision temperature control and anti-radiation reinforcement design. The measurement branch provides N acquisition channels and corresponding feedback channels, supporting multi-channel parallel sensing measurement. The self-calibration branch distributes the calibration light to the feedback channels of each measurement channel in the calibration state to realize real-time correction of the deviation of each channel. The present disclosure realizes online self-calibration, effectively compensates for channel drift, ensures long-term accuracy, and is suitable for extreme environments such as the nuclear industry.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic sensing demodulation technology, specifically relating to a full-spectrum analyzer with self-calibration function, and a calibration method for the demodulator, which is particularly suitable for high-precision fiber optic sensing signal demodulation in extreme environments with strong radiation and wide temperature variations, such as nuclear reactors, particle accelerators, and aerospace. Background Technology

[0002] Spectral demodulators, such as full-spectrum analyzers, are core devices in fiber optic sensing systems. Their function is to calculate the wavelength of the optical signal returned by the fiber optic sensor, thereby obtaining the measured physical quantity (such as strain, temperature, pressure, etc.). The measurement accuracy and long-term stability of the demodulator directly determine the performance of the entire fiber optic sensing system.

[0003] Existing full-spectrum analyzers suffer from the following major drawbacks: For example, temperature drift. The output characteristics of the etalon and other optical components inside the demodulator are highly sensitive to temperature. Changes in ambient temperature or the self-heating effect of internal components can cause wavelength measurements to drift, affecting demodulation accuracy. Although passive temperature compensation schemes exist, their effectiveness is limited and cannot meet the accuracy requirements at the PM level. Another example is multi-channel consistency issues. Full-spectrum analyzers typically contain multiple measurement channels. Differences in optical path and circuit parameters exist between different channels, and long-term acquisition can cause sampling delays and circuit drift, leading to poor measurement consistency across channels and deviations in demodulation results. Yet another example is radiation damage. In high-radiation environments such as the nuclear industry, gamma rays and neutron flux can cause permanent and irreversible damage to the etalon crystal and encapsulation materials (such as adhesives) inside the demodulator, causing etalon parameter drift and inaccurate demodulation references. Furthermore, there is a lack of self-calibration capabilities. Once put into use, existing demodulators cannot perform online calibration of their internal references and channel consistency. After long-term operation, the decline in accuracy cannot be corrected, severely impacting system reliability. In particular, maintenance is also difficult. In harsh environments such as those with nuclear radiation, the equipment is extremely difficult to maintain, and traditional demodulators are almost impossible to calibrate or replace on-site once their performance deteriorates.

[0004] Therefore, there is an urgent need for a new type of full-spectrum analyzer that can actively suppress temperature drift, resist radiation damage, and has online self-calibration capabilities.

[0005] It should be noted that the above introduction to the technical background is only for the purpose of providing a clear and complete explanation of the technical solutions of this application and facilitating understanding by those skilled in the art. It should not be assumed that these technical solutions are known to those skilled in the art simply because they have been described in the background section of this application. Summary of the Invention

[0006] The present invention aims to overcome the above-mentioned defects of existing full-spectrum analyzers and provide a novel full-spectrum analyzer and its calibration method that integrates active precision temperature control, system-level radiation hardening and optical path self-calibration functions.

[0007] In a first aspect of this disclosure, a self-calibrating full-spectrum analyzer is proposed, comprising: a scanning light source for generating scanning light; a reference branch configured to split the scanning light once or multiple times to obtain reference light, and generate corresponding calibration light based on the reference light; and a measurement branch configured to split the scanning light once or multiple times to obtain N measurement beams, where N is a positive integer; the N measurement beams are configured to be connected to corresponding sensors via corresponding N acquisition channels, and the N measurement beams are further configured to be connected to a photoelectric conversion and acquisition section via corresponding N feedback channels. The module is connected to a self-calibration branch, which is configured to receive the calibration light after it has been split, and to split the received calibration light into N calibration lights. The N calibration lights are configured to be connected to the measurement branch. When the full-spectrum analyzer is set to measurement mode, the connection between the self-calibration branch and the measurement branch is disconnected. When the full-spectrum analyzer is set to calibration mode, the connection between the measurement branch and the sensor is disconnected, and the self-calibration branch is configured to connect the N calibration lights to the photoelectric conversion and acquisition module through the corresponding N feedback channels.

[0008] Further, in some embodiments, the reference branch includes: a first coupler, the input of which is connected to the output of the scanning light source, for splitting the scanning light into reference light and measurement light; a second coupler, the input of which is connected to the reference light output of the first coupler; a etalon, the input of which is connected to one output of the second coupler; a third coupler, the input of which is connected to the output of the etalon; a first photodetector, connected to one output of the third coupler, forming a reference channel; a DWDM, the input of which is connected to the other output of the second coupler; and a second photodetector, connected to the output of the DWDM.

[0009] Furthermore, in some embodiments, the measurement branch includes: a first optical splitter, the input of which is connected to the measurement light output of the first coupler, for splitting the measurement light into N measurement beams; N fourth couplers, the input of each fourth coupler being connected to each output of the first optical splitter; N optical switches, the input of each optical switch being connected to one output of each of the fourth couplers, the output of each optical switch forming each of the acquisition channels; and N third photodetectors, each connected to the other output of each of the fourth couplers, forming each of the feedback channels.

[0010] Furthermore, in some embodiments, the self-calibration branch includes: a second optical splitter, the input of which is connected to another output of the third coupler, for splitting the calibration light into N calibration beams; the N outputs of the second optical splitter are respectively connected to the outputs of each of the optical switches, so that when the full-spectrum analyzer is in calibration state, the N calibration beams enter the corresponding third photodetector via the corresponding optical switch and the reflection end of the corresponding fourth coupler.

[0011] Furthermore, in some embodiments, the scanning light generated by the scanning light source is in the wavelength range of 1510~1590nm; the splitting ratio of the first coupler is 90:10; and both the first optical splitter and the second optical splitter are 1×N planar waveguide splitters.

[0012] Furthermore, in some embodiments, the full-spectrum analyzer with self-calibration function further includes a photoelectric conversion and signal amplification module, an AD analog-to-digital conversion and high-speed acquisition module, and a data processing module; the photoelectric conversion and signal amplification module is connected to the output terminal of each of the photodetectors, the AD analog-to-digital conversion and high-speed acquisition module is connected to the output terminal of the photoelectric conversion and signal amplification module, and the data processing module is connected to the output terminal of the AD analog-to-digital conversion and high-speed acquisition module.

[0013] In a second aspect of this disclosure, a self-calibration method for a full-spectrum analyzer as described in the first aspect is proposed, comprising the following steps: Step 1: The system enters calibration mode, disconnects the connection between the aforementioned measurement branch and the aforementioned sensor, and connects the self-calibration branch and the measurement branch, so that N calibration lights are connected to the photoelectric conversion and acquisition module through the corresponding N feedback channels; Step 2: Peak finding processing is performed on the calibration spectra of the reference channel and each measurement channel respectively to determine the position of the peak maximum value of each channel spectrum; Step 3: A preset number of data points are selected on both sides of the peak maximum value, and peak data fitting is performed. After fitting, the center wavelength value of each channel is calculated; Step 4: Steps 2 and 3 are repeated K times for a total of K times, and the average value of the center wavelength value of each channel is taken; Step 5: Based on the average value of the center wavelength of the reference channel, the offset of each measurement channel is calculated, and the offset is stored as a correction coefficient; Step 6: After calibration, the connection between the self-calibration branch and the measurement branch is disconnected, and the measurement branch is connected to the external sensor through each acquisition channel for normal detection; During normal measurement, the demodulation results of each measurement channel are corrected in real time according to the stored correction coefficient.

[0014] Further, in some embodiments, the formula for calculating the offset in step S5 is: Δλ_i = λ_ch_i - λ_ref, where λ_ref is the average center wavelength of the reference channel and λ_ch_i is the average center wavelength of the i-th measurement channel.

[0015] Furthermore, in some embodiments, after disconnecting the connection between the above-mentioned measurement branch and the above-mentioned sensor in step S1, the method further includes: confirming that each acquisition channel has been physically disconnected from the external sensor to ensure that the calibration optical path is not interfered with by the reflected light from the sensor end face.

[0016] Furthermore, in some embodiments, the fitting described in step S3 employs a Gaussian fitting or a Lorentz fitting method.

[0017] The beneficial effects of this disclosure are as follows: By dividing the functional architecture into reference, measurement, and self-calibration branches, clear decoupling and collaborative operation of optical path functions are achieved. Regarding self-calibration capabilities: through the switching between the built-in reference and self-calibration branches, the demodulator can perform online self-calibration at any time during use, effectively compensating for inter-channel deviations and circuit drift, ensuring long-term operational accuracy. Regarding ultra-high precision and stability: through TEC active temperature control, the standard etalon core is maintained at the zero-temperature drift point, achieving demodulation accuracy at the 1-2 pm level, with stability improved by 10-100 times compared to traditional solutions. Strong environmental adaptability: the radiation-hardened design enables it to withstand severe environmental temperature fluctuations, strong electromagnetic interference, and nuclear radiation environments, making it suitable for a wide range of applications. Attached Figure Description

[0018] The above and other features, advantages and aspects of the embodiments of this disclosure will become more apparent from the accompanying drawings and the following detailed description, wherein: Figure 1 A schematic diagram of the overall optical path structure of a self-calibrating full-spectrum analyzer according to an embodiment of the present disclosure is shown; Figure 2 A flowchart of a self-calibration method according to an embodiment of the present disclosure is shown; And in each of the accompanying figures, the same or corresponding reference numerals indicate the same or corresponding parts. Detailed Implementation

[0019] Embodiments of this disclosure will now be described in more detail with reference to the accompanying drawings. While some embodiments of this disclosure are shown in the drawings, it should be understood that this disclosure can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of this disclosure. It should be understood that the accompanying drawings and embodiments of this disclosure are for illustrative purposes only and are not intended to limit the scope of protection of this disclosure.

[0020] In the description of embodiments of this disclosure, the term "comprising" and similar terms should be understood as open-ended inclusion, i.e., "including but not limited to". The term "based on" should be understood as "at least partially based on". The term "one embodiment" or "the embodiment" should be understood as "at least one embodiment". The terms "first", "second", etc., may refer to different or the same objects. Other explicit and implicit definitions may also be included below.

[0021] The following description, in conjunction with the accompanying drawings, elaborates on exemplary embodiments of this disclosure.

[0022] Regarding the overall architecture of the full-spectrum analyzer. For example... Figure 1 As shown, this disclosure provides a full-spectrum analyzer with self-calibration function. Its overall architecture can be divided into three functional branches: reference branch, measurement branch and self-calibration branch. The dashed part is the main part of the self-calibration branch in the embodiment of this disclosure.

[0023] Specifically, in this illustrated embodiment, the scanning light source 1 generates scanning light in the wavelength range of 1510~1590nm. This scanning light is input to the reference branch and the measurement branch.

[0024] Regarding the reference branch, it should be understood that the reference branch is configured to split the scanning light into a reference light through one or more refractions, and generate a corresponding calibration light based on the reference light. Specifically, the scanning light is split into 10% reference light and 90% measurement light by a first coupler (90:10 coupler). The reference light is then split equally by a second coupler (50:50 coupler 1). One output of the second coupler is connected to the input of a etalon, and the output of the etalon is connected to the input of a third coupler (50:50 coupler 2). One output of the third coupler is connected to a first photodetector (PD0) for photoelectric conversion of the etalon's spectrum, and the other output is connected to a reference channel (REF CH0). The other output of the second coupler is connected to the input of a DWDM (Digital Wave Detector), which indicates the spectral band of the etalon. The output of the DWDM is connected to a second photodetector (PD1) for photoelectric conversion of the DWDM's spectrum. At this point, the reference branch generates calibration light (i.e., a comb-shaped spectral signal carrying wavelength reference information after being filtered by a standard etalon), and outputs it to the self-calibration branch through one of the output terminals of the third coupler.

[0025] Regarding the measurement branch, it should be understood that the measurement branch is configured to split the aforementioned scanning light one or more times to obtain N measurement beams. Specifically, 90% of the measurement light output of the first coupler (90:10 coupler) is connected to the input of the first optical splitter (illustrated as 1*16 PLC-1, which can be a 1×N planar waveguide splitter, where N is a positive integer, and in this embodiment N=16). The first optical splitter splits the measurement light into N measurement beams. Each output of the first optical splitter is connected to the input of N fourth couplers (50:50 couplers 3 to 18). One output of each fourth coupler is connected to the corresponding first optical switch 1 to N (it should be understood that the first optical switch is not shown, and it is connected to each sensor, which is not shown). The first optical switches 1 to N are connected to the corresponding external sensors via the corresponding acquisition channels CH1 to N. The other output end (reflection end) of each fourth coupler is connected to the corresponding third photodetector (PD2 to PD17) to form a feedback channel, which is used to feed back the measurement light or calibration light to the photoelectric conversion and acquisition module.

[0026] Regarding the self-calibration branch, it should be understood that the self-calibration branch is configured to receive the aforementioned calibration light (from the reference channel (REF CH0)) after splitting, and to split the received calibration light into N calibration beams. Specifically, the other output of the third coupler (50:50 coupler 2) is connected to the input of the second optical splitter (illustrated as 1*16 PLC-2, which can be a 1×N planar optical waveguide splitter; in this embodiment, N=16), for distributing the calibration light into N calibration beams. The N outputs of the second optical splitter are respectively connected to one end of the second optical switches 1 to N (as shown in the illustration, optical switches 1 to 16, while the other end of the second optical switches 1 to N is connected to a different path than the acquisition channels CH1-N, i.e., the second optical switches 1 to N can be connected to the corresponding fourth coupler via the channel).

[0027] It should be understood that when the full-spectrum analyzer is set to measurement mode, the connection between the self-calibration branch and the measurement branch is disconnected. Specifically, all of the second optical switches 1 to N shown in the figure are disconnected. At this time, each measurement channel is isolated from the internal self-calibration branch, and the external sensor is connected to the measurement branch through the acquisition channel (for example, via the closed first optical switches 1 to N), and the demodulator works normally.

[0028] Furthermore, when the aforementioned full-spectrum analyzer is set to calibration mode, the connection between the measurement branch and the aforementioned sensor is first disconnected (i.e., ensuring that no sensor is connected to the acquisition channels CH1 to N, for example, by disconnecting the first optical switches 1 to N), and then all the second optical switches 1 to N are closed. At this time, the N calibration lights from the self-calibration branch enter the corresponding third photodetectors (PD2 to PD17) through the corresponding optical switches and the reflection ends of the fourth couplers, thereby forming the spectral signal of the etalon in the feedback channel of each measurement channel, which is then acquired and processed by the photoelectric conversion and acquisition module. In this state, since the acquisition channels are disconnected from the sensors, the acquired signals come entirely from the calibration light and are not affected by the reflected light from the sensor end face.

[0029] Regarding sensor decoupling before calibration: The definition of calibration status explicitly requires disconnecting the sensor from the measurement branch first. If the sensor is still connected to the acquisition channel during calibration, the reflected light from the sensor end face will be superimposed on the calibration light, causing spectral distortion and resulting in an incorrect calibration reference. To address this, this disclosure adds a status feedback signal to the control circuit of the optical switch and adds a sensor connection detection step to the calibration process, ensuring that the system can only start the calibration process after confirming that each acquisition channel is physically disconnected from the sensor and all optical switches are in the closed state.

[0030] Furthermore, some embodiments further include the self-calibration method of the aforementioned self-calibrating full-spectrum analyzer. For example... Figure 2As shown, based on the above optical path architecture, this disclosure provides a self-calibration method, specifically including the following steps: Step S1: The system enters the calibration state. First, disconnect the connection between the above measurement branch and the above sensor (i.e., confirm that no external sensor is connected to each acquisition channel CH1-N). Then, connect the self-calibration branch to the measurement branch (i.e., close all second optical switches), so that the N calibration lights are connected to the photoelectric conversion and acquisition module through the corresponding N feedback channels, and acquire the calibration spectral data of each channel (including the feedback channels of the reference channel and the measurement channel). Step S2: Perform peak finding processing on the spectral data of each channel to determine the position of the peak maximum value. Step S3: Select M data points on both sides of the peak maximum value (M is a preset value, such as 10~20 points), and use Gaussian fitting or Lorentz fitting methods to fit the peak to obtain the accurate peak position, and calculate the center wavelength value accordingly. Step S4: Repeat steps two through three a total of K times (K is a preset value, e.g., 10-20 times) to obtain K center wavelength values ​​for each channel. Take the average value of each value and denote them as λ_ref (reference channel) and λ_ch_i (the i-th measurement channel). Step S5: Calculate the offset Δλ_i = λ_ch_i - λ_ref for the i-th measurement channel and store Δλ_i as the correction coefficient for that channel in the data processing module. Step S6: After calibration, disconnect the self-calibration branch from the measurement branch (i.e., disconnect all second optical switches and close all first optical switches), allowing the measurement branch to connect to external sensors through each acquisition channel for normal detection. In subsequent measurements, the data processing module subtracts Δλ_i from the demodulation result of the i-th measurement channel in real time, thereby correcting the channel deviation.

[0031] Furthermore, regarding error correction measures for error-prone aspects. During the implementation of this disclosure, the following error-prone aspects require special attention and corresponding error correction measures: (I) Sensor decoupling before calibration: The core requirement of calibration is to disconnect the connection between the sensor and the measurement branch. If the light switch is closed during calibration but the sensor is still connected to the acquisition channel, the reflected light from the sensor end face will be reflected by the fourth coupler into the third photodetector (PD2 to PD17), superimposed with the spectrum of the calibration light, causing spectral distortion and resulting in errors in peak finding and center wavelength calculation. To this end, this disclosure adds a status feedback signal to the control circuit of the light switch and adds a sensor connection detection module to ensure that the system can start the calibration process only after confirming that each acquisition channel has been physically disconnected from the sensor and all light switches are in the closed state. (II) Necessity of single-end single-point suspension fixation: The standard etalon core is fixed by single-end single-point glass solder suspension. If multi-point fixation or full contact fixation is used, thermal stress will cause micro-deformation of the core, changing the optical parameters. The single-end single-point structure of this disclosure effectively releases thermal stress and ensures the stability of the core's optical performance. (III) Glass solder instead of adhesive: In a nuclear radiation environment, organic adhesives will rapidly age and fail. This disclosure uses glass solder to fix the core, completely avoiding this problem. (IV) Soldering instead of adhesive bonding: The fiber optic collimator is soldered to the housing, eliminating the risk of collimator displacement caused by adhesive failure under radiation. (V) Inert gas sealing: The etalon is filled with high-purity nitrogen and sealed to prevent air from generating ionization products under radiation that corrode the optical components.

[0032] It should be understood that the above error correction measures significantly improve the reliability of the detuning instrument in harsh environments and the accuracy of calibration operations.

[0033] The above description is merely an optional embodiment of this disclosure and is not intended to limit this disclosure. Various modifications and variations can be made to this disclosure by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the scope of protection of this disclosure.

[0034] The various embodiments of this disclosure have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A full-spectrum analyzer with self-calibration function, characterized in that, include: A scanning light source, used to generate scanning light; The reference branch is configured to split the scanning light once or multiple times to obtain a reference light, and generate a corresponding calibration light based on the reference light; The measurement branch is configured to split the scanning light once or multiple times to obtain N measurement lights, where N is a positive integer. The N-channel measurement beams are configured to connect to the corresponding sensors via the corresponding N-channel acquisition channels, and the N-channel measurement beams are also configured to connect to the photoelectric conversion and acquisition module via the corresponding N-channel feedback channels. The self-calibration branch is configured to receive the calibrated light after it has been split, and to split the received calibrated light into N calibrated lights. The N-channel calibration beams are configured to connect to the measurement branch; When the full-spectrum analyzer is set to measurement mode, the connection between the self-calibration branch and the measurement branch is disconnected. When the full-spectrum analyzer is set to calibration mode, the connection between the measurement branch and the sensor is disconnected, and the self-calibration branch is configured to connect the N calibration beams to the photoelectric conversion and acquisition module through the corresponding N feedback channels.

2. The full-spectrum analyzer with self-calibration function according to claim 1, characterized in that, The reference branch includes: The first coupler, whose input end is connected to the output end of the scanning light source, is used to split the scanning light into reference light and measurement light; The second coupler has its input end connected to the reference light output end of the first coupler; A standard etalon, the input of which is connected to one output of the second coupler; A third coupler, the input of which is connected to the output of the etalon; The first photodetector is connected to one output terminal of the third coupler to form a reference channel; DWDM, whose input is connected to the other output of the second coupler; The second photodetector is connected to the output terminal of the DWDM.

3. The full-spectrum analyzer with self-calibration function according to claim 2, characterized in that, The measurement branch includes: The first optical splitter has its input end connected to the measurement light output end of the first coupler, and is used to split the measurement light into N measurement lights; N fourth couplers, with the input of each fourth coupler connected to the output of the first optical splitter respectively; N optical switches, each with its input terminal connected to one output terminal of the fourth coupler, and the output terminals of each optical switch forming the acquisition channel; N third photodetectors are respectively connected to the other output terminal of each of the fourth couplers to form each of the feedback channels.

4. The full-spectrum analyzer with self-calibration function according to claim 3, characterized in that, The self-calibration branch includes: The second optical splitter, whose input is connected to the other output of the third coupler, is used to split the calibration light into N calibration lights. The N output terminals of the second optical splitter are respectively connected to the output terminals of each optical switch, so that when the full spectrum analyzer is in calibration state, the N calibration beams enter the corresponding third photodetector via the corresponding optical switch and the reflection terminal of the corresponding fourth coupler.

5. The full-spectrum analyzer with self-calibration function according to claim 4, characterized in that, The scanning light generated by the scanning light source has a wavelength range of 1510~1590nm; the splitting ratio of the first coupler is 90:10; both the first optical splitter and the second optical splitter are 1×N planar optical waveguide splitters.

6. The full-spectrum analyzer with self-calibration function according to claim 4, characterized in that, It also includes a photoelectric conversion and signal amplification module, an AD analog-to-digital conversion and high-speed acquisition module, and a data processing module; the photoelectric conversion and signal amplification module is connected to the output terminal of each of the photodetectors, the AD analog-to-digital conversion and high-speed acquisition module is connected to the output terminal of the photoelectric conversion and signal amplification module, and the data processing module is connected to the output terminal of the AD analog-to-digital conversion and high-speed acquisition module.

7. A self-calibration method for a full-spectrum analyzer with self-calibration function as described in any one of claims 1 to 6, characterized in that, Includes the following steps: Step S1: The system enters the calibration state, disconnects the connection between the sensor and the measurement branch, and connects the self-calibration branch to the measurement branch, so that the N calibration lights are connected to the photoelectric conversion and acquisition module through the corresponding N feedback channels. Step S2: Perform peak finding processing on the calibration spectra of the reference channel and each measurement channel respectively to determine the position of the peak maximum value of each channel spectrum; Step S3: Select a preset number of data points on both sides of the maximum value of the peak, perform peak data fitting, and calculate the center wavelength value of each channel after fitting. Step S4: Repeat steps two and three for a total of K times, and take the average value of the center wavelength of each channel; Step S5: Using the average center wavelength of the reference channel as a benchmark, calculate the offset of each measurement channel and store the offset as a correction coefficient. Step S6: After calibration is completed, disconnect the self-calibration branch from the measurement branch, and allow the measurement branch to connect to the external sensor through each acquisition channel for normal detection. During normal measurements, the demodulation results of each measurement channel are corrected in real time based on the stored correction coefficients.

8. The self-calibration method according to claim 7, characterized in that, The formula for calculating the offset in step S5 is: Δλ_i = λ_ch_i - λ_ref, where λ_ref is the average center wavelength of the reference channel and λ_ch_i is the average center wavelength of the i-th measurement channel.

9. The self-calibration method according to claim 7, characterized in that, Step S1, after disconnecting the connection between the measurement branch and the sensor, also includes: confirming that each acquisition channel has been physically disconnected from the external sensor to ensure that the calibration optical path is not interfered with by the reflected light from the sensor end face.

10. The self-calibration method according to claim 7, characterized in that, The fitting in step S3 uses Gaussian fitting or Lorentz fitting methods.

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