A continuous high-precision wavelength calibration device and method for a frequency-swept laser

Abstract

The application belongs to the technical field of optical fiber sensing and optoelectronic measurement, and discloses a continuous high-precision wavelength calibration device and method for a frequency-swept laser. The device divides the optical signal output by the frequency-swept laser into three paths, and introduces the three paths into a frequency reference branch composed of an electro-optic modulator and a fiber ring resonator, an interference branch composed of a Mach-Zehnder interference branch, and a gas absorption cell, respectively. During calibration, the frequency reference generated by radio frequency modulation is combined with the instantaneous phase information of the interferometer, the free spectral range of the fiber ring resonator is calculated, and a continuous relative wavelength calibration curve is generated. Then, the absolute wavelength reference of the gas absorption cell is used for bias correction to obtain an absolute wavelength continuous calibration curve. The application realizes continuous and high-precision wavelength calibration in a wide range, and is suitable for technical fields such as optical fiber sensing, microcavity optical resonance sensing and optical fiber communication.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic sensing and optoelectronic measurement technology, specifically relating to a continuous high-precision wavelength calibration device and method for swept-frequency lasers. Background Technology

[0002] Sweep lasers enable continuous tuning of the output laser wavelength and possess excellent optical characteristics such as narrow linewidth and high spectral purity. They are now widely used in fiber optic sensing, microcavity optical resonant sensing, and fiber optic communication. In these systems, sweep lasers are typically used as wavelength measurement references. The system calculates environmental physical parameters such as temperature, strain, and pressure by analyzing the wavelength shift. Therefore, high-precision wavelength calibration of the sweep laser is crucial for ensuring the system's measurement performance. The accuracy and long-term stability of the wavelength calibration results directly determine the measurement accuracy and reliability of the entire sensing and communication equipment.

[0003] In the prior art, wavelength calibration schemes based on gas absorption cells have been reported, such as the pure gas absorption cell laser wavelength calibration method disclosed in Chinese patent document CN103411686A. This scheme utilizes the wavelength traceability and fixed wavelength value of characteristic absorption lines of gas molecules, using the gas absorption peak as an absolute wavelength reference to complete laser calibration. However, due to the limitations of gas molecule energy level transition characteristics, the wavelength intervals between gas characteristic absorption lines are relatively large, resulting in a sparse distribution of characteristic points available for calibration. For the intervals without absorption lines within the continuously tuned band of a swept-frequency laser, the real-time wavelength can only be estimated through interpolation algorithms using a limited number of calibration points. Interpolation calculations introduce significant systematic errors, making it difficult to meet the stringent calibration accuracy requirements of high-precision wavelength measurement scenarios.

[0004] To address the shortcomings of sparse calibration points and large interpolation errors, existing technologies have proposed combined calibration schemes, a typical example being the gas absorption cell combined with Fabry-Perot (FP) etalon wavelength calibration device and method disclosed in Chinese patent document CN105890779B. This scheme uses the gas absorption peak to provide an absolute wavelength reference, while simultaneously utilizing the equally spaced transmission resonant peaks output by the Fabry-Perot etalon to supplement a large number of intermediate calibration points between adjacent gas absorption calibration points. This shortens the interpolation interval, reduces wavelength errors caused by interpolation calculations, and effectively improves calibration accuracy at discrete points. However, the output signal of the Fabry-Perot etalon is only a discrete transmission peak, providing an effective wavelength reference only at each resonant peak position. There is still no reliable standard reference signal for the continuous wavelength interval between resonant peaks. This scheme can only achieve discrete wavelength point calibration and cannot meet the requirements for continuous high-precision calibration across the entire wavelength band under continuous wavelength tuning conditions of frequency-sweep lasers. Summary of the Invention

[0005] The purpose of this invention is to provide a continuous high-precision wavelength calibration device and method for swept-frequency lasers, which solves the problems of sparse calibration points, large interpolation errors, and the inability to perform continuous high-precision calibration of the entire band in existing swept-frequency laser wavelength calibration schemes, which can only achieve discrete point calibration.

[0006] This invention is achieved through the following technical solution: This invention discloses a continuous high-precision wavelength calibration device for a swept-frequency laser, comprising a beam splitter, a frequency reference branch, a Mach-Zehnder interferometer branch, a gas absorption cell, and a signal acquisition and processing module. A one-to-three beam splitter is used to split the continuous frequency-sweeping optical signal output by a frequency-sweeping laser into three optical signals, and output the three optical signals to the frequency reference branch, the Mach-Zehnder interferometer branch and the gas absorption cell, respectively. The frequency reference branch includes an electro-optic modulator and an optical fiber ring resonator connected in sequence. The electro-optic modulator is used to phase modulate the input optical signal to generate modulation sidebands with known frequency intervals. The optical fiber ring resonator is used to generate periodic resonance peaks on the optical frequency axis. The Mach-Zehnder interferometer branch includes a 1-to-2 beam splitter, a time-delay fiber, and a 2-to-2 beam splitter connected in sequence to generate interference signals; Gas absorption cells are used to provide absorption lines with a known and stable center wavelength; The signal acquisition and processing module includes a first photodetector, a second photodetector, a balanced photodetector, a digital acquisition card, and a signal processing module; the gas absorption cell is connected to the first photodetector, the fiber optic ring resonator is connected to the second photodetector, and the beam splitter is connected to the balanced photodetector; the first photodetector, the second photodetector, and the balanced photodetector are each connected to the signal processing module via the digital acquisition card.

[0007] Furthermore, the signal processing module is configured to: combine the instantaneous phase information of the periodic resonance peak generated by the frequency reference branch and the interference signal generated by the Mach-Zehnder interference branch to calculate the free spectral range of the fiber ring resonator and generate a continuous relative wavelength calibration curve; then, combine the absorption spectrum provided by the gas absorption cell to perform bias correction on the continuous relative wavelength calibration curve to obtain the absolute wavelength continuous calibration curve of the swept laser.

[0008] Furthermore, the input end of the one-to-three beam splitter is connected to the output end of the sweep laser, and the three output ends of the one-to-three beam splitter are respectively connected to the input end of the electro-optic modulator, the input end of the one-to-two beam splitter, and the input end of the gas absorption cell; The first output terminal of the 1-to-2 beam splitter is connected to the first input terminal of the 2-to-2 beam splitter via the delay fiber, the second output terminal of the 1-to-2 beam splitter is connected to the second input terminal of the 2-to-2 beam splitter, and the two output terminals of the 2-to-2 beam splitter are respectively connected to the two input terminals of the balanced photodetector. The output of the electro-optic modulator is connected to the input of the fiber optic ring resonator, the output of the fiber optic ring resonator is connected to the input of the second photodetector, and the output of the gas absorption cell is connected to the input of the first photodetector.

[0009] Furthermore, the delay fiber in the Mach-Zehnder interferometer branch is used to introduce optical path difference.

[0010] Furthermore, the signal processing module extracts instantaneous phase information from the interference signal using Hilbert transform or wavelet transform algorithms.

[0011] This invention also discloses a method for continuous high-precision wavelength calibration of a swept-frequency laser, comprising the following steps: The continuous sweeping optical signal output by the sweeping laser is divided into three paths; The first optical signal is phase-modulated to generate modulation sidebands with known frequency intervals, and then input into the fiber ring resonator to obtain resonant peak signals that are periodically distributed on the optical frequency axis, which serve as frequency scales. The second optical signal is input into the Mach-Zehnder interference branch, which consists of a 1-to-2 beam splitter, a time-delay fiber, and a 2-to-2 beam splitter, to obtain the interference signal. The third optical signal is input into the gas absorption cell to obtain a stable absorption spectral signal with a known center wavelength, which is used as an absolute wavelength reference. The optical signals of each branch are converted into electrical signals by the first photodetector, the second photodetector and the balanced photodetector. After being acquired by the digital acquisition card, the signals are processed by the signal processing module to obtain the absolute wavelength continuous calibration curve of the swept laser.

[0012] Furthermore, the processing procedure of the signal processing module includes: Extract instantaneous phase information from the interference signal; Based on the resonant peak signal and the instantaneous phase information, the free spectral range of the fiber ring resonator is calculated, and a continuous relative wavelength calibration curve is generated. The absorption spectral signal is used to perform bias correction on the continuous relative wavelength calibration curve to obtain the absolute wavelength continuous calibration curve of the swept laser.

[0013] Furthermore, when calculating the free spectral range of the fiber ring resonator, the resonance peak signal and the instantaneous phase information are used to compensate for the non-uniformity of the free spectral range of the fiber ring resonator caused by fiber dispersion.

[0014] Furthermore, when extracting instantaneous phase information from the interference signal, Hilbert transform or wavelet transform algorithms are used.

[0015] Furthermore, when using the absorption spectral line signal to perform offset correction on the continuous relative wavelength calibration curve, the wavelength corresponding to the absorption spectral line is used as the absolute reference to correct the overall offset of the relative wavelength calibration curve.

[0016] Compared with the prior art, the present invention has the following beneficial technical effects: This invention discloses a continuous high-precision wavelength calibration device for swept-frequency lasers. The continuously swept-frequency optical signal output from the laser is split into three paths using a 1-to-3 beam splitter. These paths are respectively introduced into a frequency reference branch composed of an electro-optic modulator and an optical fiber ring resonator, a Mach-Zehnder interferometer branch composed of a 1-to-2 beam splitter, a delay fiber, and a 2-to-2 beam splitter, and a gas absorption cell. A signal acquisition and processing module converts the optical signals from each branch into electrical signals for acquisition and processing, thus constructing a hardware platform capable of simultaneously acquiring a frequency reference signal, interferometric phase information, and an absolute wavelength reference. Combining the frequency reference generated by radio frequency modulation with the instantaneous phase information of the interferometer provides the basic architecture for subsequent continuous, high-precision wavelength calibration over a wide range, solving the problem that a single calibration method cannot simultaneously provide an absolute reference and continuous tracking.

[0017] Furthermore, the signal processing module is configured to calculate the free spectral range of the fiber optic ring resonator by combining the instantaneous phase information of the periodic resonance peak generated by the frequency reference branch and the interference signal generated by the Mach-Zehnder interference branch, and to generate a continuous relative wavelength calibration curve. Then, the absorption spectrum provided by the gas absorption cell is used to perform bias correction on the continuous relative wavelength calibration curve. This scheme fully utilizes the modulation sidebands with known frequency intervals generated by the electro-optic modulator to trace the frequency reference back to the RF reference, ensuring high accuracy and long-term stability of the frequency interval. Simultaneously, the instantaneous phase information of the interference branch is used to accurately compensate for the non-uniformity of the free spectral range of the fiber optic ring cavity caused by dispersion, achieving accurate calculation of the free spectral range of the reference cavity. Finally, bias correction is performed using the absolute wavelength reference of the gas absorption cell, making the calibration results traceable. These three elements work together to achieve the technical effect of continuous, high-precision wavelength calibration over a wide range.

[0018] Furthermore, the specific optical path connections and signal transmission paths between the swept laser, the 1-to-3 beam splitter, the electro-optic modulator, the fiber ring resonator, the 1-to-2 beam splitter, the time-delay fiber, the 2-to-2 beam splitter, the gas absorption cell, the first photodetector, the second photodetector, the balanced photodetector, the digital acquisition card, and the signal processing module are defined. This optical path structure ensures that the optical signal output from the swept laser can enter the frequency reference branch, the Mach-Zehnder interferometer branch, and the gas absorption cell respectively according to the predetermined three branches. Finally, the signal is converted into electrical signals by each photodetector and then aggregated by the digital acquisition card to the signal processing module. This provides stable and reliable hardware support for the signal processing module to jointly process the RF modulation frequency reference and the instantaneous phase information of the interferometer, ensuring a clear optical path and compact structure for the entire calibration device.

[0019] Furthermore, the delay fiber in the Mach-Zehnder interferometer branch is used to introduce the optical path difference. Since the phase change of the interference signal is proportional to the optical path difference, increasing the length of the delay fiber makes the phase response of the interference signal to changes in laser frequency more significant. This effectively reduces the frequency calculation error under the same photoelectric detection and quantization error conditions, improving the tracking accuracy and measurement reliability of the interferometer branch when the laser frequency changes continuously. This is an important guarantee for achieving high-precision continuous wavelength calibration.

[0020] Furthermore, the signal processing module is limited to extracting instantaneous phase information from the interference signal using either Hilbert transform or wavelet transform algorithms. Hilbert transform can analyze a real signal into a complex signal and accurately obtain its instantaneous phase, while wavelet transform can simultaneously analyze the signal in the time and frequency domains and effectively suppress noise interference. Both algorithms can stably and accurately extract instantaneous phase information from the interference signal, providing accurate phase data for subsequent calculations of the free spectral range of the fiber optic ring resonator using a frequency reference and for generating continuous relative wavelength calibration curves. This is a crucial step in achieving continuous wavelength tracking.

[0021] This invention also discloses a method for continuous high-precision wavelength calibration of swept-frequency lasers. The method involves splitting the optical signal output from the swept-frequency laser into three paths. The first path is phase-modulated and input into an optical fiber ring resonator to obtain the resonant peak signal, which serves as a frequency scale. The second path is input into a Mach-Zehnder interferometer branch to obtain the interference signal. The third path is input into a gas absorption cell to obtain the absorption spectral signal, which serves as the absolute wavelength reference. Photodetectors, digital acquisition cards, and signal processing modules then perform photoelectric conversion, acquisition, and processing to ultimately obtain the continuous absolute wavelength calibration curve of the swept-frequency laser. This method fully realizes the technical concept of combining the frequency reference generated by radio frequency modulation with the instantaneous phase information of the interferometer. It provides high-precision relative calibration through the frequency scale, continuous phase tracking through the interference signal, and an absolute wavelength reference through the absorption spectral line. The three signals are processed in parallel, complementing each other's advantages, effectively solving the problem that existing technologies can only achieve discrete point calibration and cannot achieve continuous high-precision calibration across the entire wavelength band.

[0022] Furthermore, the signal processing module's process is defined to include extracting instantaneous phase information from the interference signal, calculating the free spectral range of the fiber ring resonator based on the resonance peak signal and instantaneous phase information, generating a continuous relative wavelength calibration curve, and using the absorption spectral line signal to perform bias correction on the relative curve. This processing flow fully utilizes the known frequency interval generated by electro-optic modulation to trace the frequency reference back to the radio frequency reference to ensure accuracy and stability. At the same time, it uses the instantaneous phase information of the interference branch to accurately compensate for the non-uniformity of the free spectral range caused by fiber dispersion, achieving accurate calculation of the free spectral range of the reference cavity. The final generated absolute wavelength continuous calibration curve has both continuity and high precision characteristics, achieving the invention's objective of continuous, high-precision wavelength calibration over a wide range.

[0023] Furthermore, when calculating the free spectral range of the fiber optic ring resonator, the resonant peak signal and instantaneous phase information are used to compensate for the non-uniformity of the free spectral range caused by fiber dispersion. Since the free spectral range of the fiber optic ring resonator is not a constant value due to fiber dispersion, by introducing the instantaneous phase information of the interference branch to accurately correct the actual frequency interval at each resonant peak position, the nonlinear error caused by dispersion can be effectively eliminated. This makes the constructed frequency scale uniform and accurate across the entire wavelength range. This is a key technical means to achieve accurate calculation of the free spectral range of the reference cavity and a core link to achieve continuous high-precision wavelength calibration over a wide range.

[0024] Furthermore, when performing bias correction on continuous relative wavelength calibration curves based on absorption spectral signals, the wavelength corresponding to the absorption spectral line is used as the absolute reference to correct the overall offset of the relative wavelength calibration curve. Since both the interferometric branch and the frequency reference branch provide relative wavelength information, their calibration curves may have an overall offset. By using the absorption spectral line provided by the gas absorption cell, which has good wavelength traceability, a known center wavelength, and long-term stability, as the absolute reference for bias correction, it is possible to ensure that the final output absolute wavelength continuous calibration curve has traceability and long-term stability, meeting the stringent requirements for calibration accuracy in high-precision wavelength measurement scenarios, and completing a complete closed loop from relative calibration to absolute calibration. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the wavelength calibration device for a swept-frequency laser. The components include: 1. Sweeping laser; 2. One-to-three beam splitter; 3. One-to-two beam splitter; 4. Delay fiber; 5. Gas absorption cell; 6. Two-to-two beam splitter; 7. First photodetector; 8. Balanced photodetector; 9. Radio frequency source; 10. Electro-optic modulator; 11. Fiber optic ring resonator; 12. Second photodetector; 13. Digital acquisition card; 14. Signal processing module. Figure 2 This is a schematic diagram of the waveforms of the optical signals of each branch after processing in this invention; Figure 3 This is a schematic diagram of the free spectral range of the fiber optic ring cavity calculated in the experiment according to the present invention; Figure 4 This is a schematic diagram of the laser wavelength calibration results obtained in the experiment according to the present invention. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the present invention clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention; that is, the described embodiments are only a part of the embodiments of the present invention, and not all of them.

[0027] The components described and illustrated in the accompanying drawings and embodiments of this invention can be arranged and designed in various different configurations. Therefore, the detailed description of the embodiments of the invention provided in the following drawings is not intended to limit the scope of the claimed invention, but merely to illustrate one selected embodiment of the invention. All other embodiments obtained by those skilled in the art based on the accompanying drawings and embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0028] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0029] like Figure 1 As shown, the present invention discloses a continuous high-precision wavelength calibration device for a swept-frequency laser, comprising a swept-frequency laser 1, a one-to-three beam splitter 2, a one-to-two beam splitter 3, a delay fiber 4, a gas absorption cell 5, a two-to-two beam splitter 6, a first photodetector 7, a balanced photodetector 8, a radio frequency source 9, an electro-optic modulator 10, an optical fiber ring resonator 11, a second photodetector 12, a digital acquisition card 13, and a signal processing module 14.

[0030] The swept-frequency laser 1 outputs a continuous swept-frequency optical signal. The laser output is split into three optical signals by a 1-to-3 beam splitter 2, which are respectively introduced into a frequency reference branch composed of an electro-optic modulator 10 and an optical fiber ring resonator 11, a Mach-Zehnder interferometer branch composed of a 1-to-2 beam splitter 3, a delay fiber 4, and a 2-to-2 beam splitter 6, and a gas absorption cell 5. The frequency reference branch and the Mach-Zehnder interferometer branch are used for relative wavelength calibration, while the gas absorption cell 5 is used for absolute wavelength calibration. By combining the relative and absolute calibrations, the continuous wavelength calibration curve of the swept-frequency laser 1 can be obtained.

[0031] The structure and function of the three branches are described in detail below: Frequency Reference Branch: The optical signal enters the fiber optic ring resonator 11 after passing through the electro-optic modulator 10. As a typical optical resonant structure, the fiber optic ring resonator 11 can generate periodic resonance peaks on the optical frequency axis, but its free spectral range is affected by fiber dispersion and is not a constant value. To introduce a known frequency scale, the electro-optic modulator 10 is first used to phase-modulate the swept laser, generating symmetrically distributed modulation sidebands on both sides of the main mode. The frequency spacing between adjacent sidebands is determined by the modulation signal provided by the RF source 9, tracing the frequency reference back to the RF reference to ensure high accuracy and long-term stability of the frequency spacing. This step achieves a known frequency spacing, but the free spectral range of the fiber optic ring cavity remains unknown and needs to be calculated in conjunction with the instantaneous phase information of the Mach-Zehnder interferometer signal.

[0032] Mach-Zehnder Interference Branch: This branch consists of a 1-to-2 beam splitter 3, a delay fiber 4, and a 2-to-2 beam splitter 6. The delay fiber 4 introduces a larger optical path difference, making the phase change of the interference signal more significant, thereby reducing the impact of the total phase error on the frequency calculation result. The phase extraction of the interference signal can be performed using algorithms such as Hilbert transform and wavelet transform. The Mach-Zehnder interference branch mainly functions in two ways: first, by combining with an RF reference, it enables accurate determination of the free spectral range of the fiber ring cavity, thereby effectively compensating for the non-uniformity caused by fiber dispersion and constructing a high-precision frequency scale; second, it enables continuous tracking of laser frequency changes.

[0033] By leveraging the synergistic effect of the frequency reference of the fiber optic ring cavity and the phase tracking capability of the Mach-Zehnder interferometer branch, high-precision calibration of the relative wavelength of the sweep laser over a wide tuning range can be achieved.

[0034] The gas absorption cell 5 provides a known and stable absorption spectral signal with a center wavelength, which is used to establish an absolute wavelength reference. This is equivalent to biasing and correcting the continuous relative calibration curve, ensuring calibration accuracy and traceability.

[0035] The optical signals from the three branches are converted into electrical signals by the first photodetector 7, the second photodetector 12, and the balanced photodetector 8, respectively. After being acquired by the digital acquisition card 13, they are finally processed by the signal processing module 14 to obtain the absolute wavelength continuous calibration curve of the swept laser.

[0036] The optical signal transmission paths for each branch are as follows: The output of the swept laser 1 is connected to the input of the 1-to-3 beam splitter 2, which splits the optical signal into three paths. Its three outputs are respectively connected to the inputs of the electro-optic modulator 10, the 1-to-2 beam splitter 3, and the gas absorption cell 5. In the frequency reference branch, the output of the electro-optic modulator 10 is connected to the input of the fiber optic ring resonator 11, and the output of the fiber optic ring resonator 11 is connected to the input of the second photodetector 12. In the Mach-Zehnder interferometer branch, the 1-to-2 beam splitter 3 splits the input optical signal into two paths. Its first output is connected to the first input of the 2-to-2 beam splitter 6 via the delay fiber 4, and its second output is directly connected to the second input of the 2-to-2 beam splitter 6. The two outputs of the 2-to-2 beam splitter 6 are respectively connected to the two inputs of the balanced photodetector 8. The output of the gas absorption cell 5 is connected to the input of the first photodetector 7. The output terminals of the first photodetector 7, the second photodetector 12, and the balanced photodetector 8 are respectively connected to the input terminal of the digital acquisition card 13, and the output terminal of the digital acquisition card 13 is connected to the input terminal of the signal processing module 14.

[0037] During the continuous tuning of the frequency-sweeping laser, the digital acquisition card 13 synchronously acquires the output signals of the photodetectors from the three branches. After filtering, denoising, and normalization by the signal processing module 14, the waveforms of the three signals within the same frequency-sweeping time period are captured and superimposed for display, resulting in the following image. Figure 2 The diagram shows the waveforms of the optical signals from each branch after processing. Figure 2 The four curves in the image correspond to typical waveforms of the three branches during signal processing: the upper curve represents the transmission signal of the fiber optic ring cavity after electro-optic modulation, with modulation sidebands distributed on both sides of the main peak. The frequency interval between adjacent sidebands is determined by the RF source and is precisely known; the two middle curves represent the Mach-Zehnder interference signal and the instantaneous phase information extracted from this interference signal, respectively. The phase of the interference signal changes continuously with time, and the extracted instantaneous phase information is used to assist in calculating the free spectral range of the fiber optic ring cavity and continuously track the trend of laser wavelength changes; the lower curve represents the transmission spectrum signal of the gas absorption cell, where the peak position corresponds to the characteristic absorption spectral lines of gas molecules. Figure 2 It can be seen that the electro-optic modulated fiber ring cavity signal can provide a scale mark with known frequency intervals, the phase of the Mach-Zehnder interference signal and its extracted instantaneous phase information can continuously reflect the trajectory of laser frequency change, and the gas absorption peak signal can provide an absolute reference with a fixed wavelength position. The three signals each have their own advantages and complement each other, providing a data foundation for subsequent joint processing to achieve continuous high-precision calibration.

[0038] Figure 3 This is a schematic diagram of the free spectral range (FSR) of the fiber optic ring cavity calculated in the experiment according to the present invention. The signal processing module 14 first detects the positions of each resonant peak in the transmitted signal of the fiber optic ring cavity, and simultaneously extracts instantaneous phase information from the Mach-Zehnder interference signal using Hilbert transform; then, using the sideband frequency interval generated by electro-optic modulation as a known frequency scale, it calculates the actual frequency interval at each resonant peak position, i.e., the free spectral range (FSR); finally, it plots a curve with the scan time as the abscissa and the calculated FSR value as the ordinate, thus obtaining the free spectral range (FSR). Figure 3 .from Figure 3 It is clearly evident that, due to fiber dispersion, the free spectral range of the fiber ring cavity does not vary constantly with wavelength, but rather exhibits a certain trend. By combining instantaneous phase information, the actual FSR value at each resonant peak position can be accurately calculated. Figure 3 It is known that the free spectral range of an optical fiber ring cavity is not a fixed constant, and using the average value as a substitute will produce significant errors. This invention can indeed accurately calculate the free spectral range at each resonance peak, thereby effectively compensating for the dispersion effect, and verifying the effectiveness of this invention in constructing a high-precision frequency scale.

[0039] Signal processing module 14 Figure 3 The precise frequency intervals of each resonant peak in the fiber optic ring cavity, calculated in the standard, are used as the calibration reference. Combined with the continuous phase information provided by the Mach-Zehnder interferometry signal, phase interpolation is performed between adjacent resonant peaks to generate a continuous relative wavelength calibration curve covering the entire sweep range. Then, the positions of each absorption peak in the gas absorption peak signal are detected, and the overall offset of the relative wavelength calibration curve is corrected using the known center wavelength corresponding to the absorption peak as the absolute reference. Finally, a curve is plotted with the scan time as the abscissa and the calibrated absolute wavelength as the ordinate, resulting in the following... Figure 4 The diagram shows the wavelength calibration results of the swept-frequency laser. This invention can output a complete absolute wavelength continuous variation curve, achieving high-precision continuous calibration across the entire wavelength range. The calibration error at each absorption peak position is effectively corrected, verifying the feasibility and effectiveness of this invention in jointly processing the RF modulation frequency reference, the interferometer instantaneous phase tracking, and the absolute reference of the gas absorption cell.

[0040] The sweep laser wavelength calibration device of the present invention is implemented as follows: Before use, first check the connection status of the laser and each optical component, as well as the integrity of the optical path.

[0041] After the sweeping laser 1 is started, the output optical signal is split into three beams by a splitter 2 and enters the frequency reference branch, the Mach-Zehnder interferometer branch, and the gas absorption cell 5, respectively. The three optical signals are converted into electrical signals by the first photodetector 7, the second photodetector 12, and the balanced photodetector 8, which are then acquired by the digital acquisition card 13 and analyzed by the signal processing module 14. During the processing, the peak points of the fiber ring cavity signal and the gas absorption peak signal, as well as the instantaneous phase information of the Mach-Zehnder interferometer signal, can be extracted, thereby achieving continuous and high-precision calibration of the absolute wavelength of the sweeping laser.

[0042] The calibration system of this invention has a compact structure and a clear optical path, and can achieve the joint processing of absolute wavelength reference, relative frequency scale and instantaneous phase information, providing a reliable wavelength calibration method for high-precision optical measurements.

[0043] 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 it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the present invention.

Claims

1. A continuous high-precision wavelength calibration device for a swept-frequency laser, characterized in that, It includes a one-to-three beam splitter (2), a frequency reference branch, a Mach-Zehnder interferometer branch, a gas absorption cell (5), and a signal acquisition and processing module; The one-to-three beam splitter (2) is used to split the continuous sweeping optical signal output by the sweeping laser (1) into three optical signals, and output the three optical signals to the frequency reference branch, the Mach-Zehnder interference branch and the gas absorption cell (5) respectively. The frequency reference branch includes a connected electro-optic modulator (10) and an optical fiber ring resonator (11). The electro-optic modulator (10) is used to phase modulate the input optical signal to generate a modulation sideband with a known frequency interval. The optical fiber ring resonator (11) is used to generate periodic resonance peaks on the optical frequency axis. The Mach-Zehnder interferometer branch includes a 1-to-2 beam splitter (3), a time-delay fiber (4), and a 2-to-2 beam splitter (6) connected in sequence to generate an interference signal; The gas absorption cell (5) is used to provide a stable absorption spectrum with a known center wavelength; The signal acquisition and processing module includes a first photodetector (7), a second photodetector (12), a balanced photodetector (8), a digital acquisition card (13), and a signal processing module (14); the gas absorption cell (5) is connected to the first photodetector (7), the fiber optic ring resonator (11) is connected to the second photodetector (12), and the two-to-two beam splitter (6) is connected to the balanced photodetector (8); the first photodetector (7), the second photodetector (12), and the balanced photodetector (8) are respectively connected to the signal processing module (14) via the digital acquisition card (13).

2. The continuous high-precision wavelength calibration device for a swept-frequency laser according to claim 1, characterized in that, The signal processing module (14) is configured to: combine the instantaneous phase information of the periodic resonance peak generated by the frequency reference branch and the interference signal generated by the Mach-Zehnder interference branch to calculate the free spectral range of the fiber ring resonator (11) and generate a continuous relative wavelength calibration curve; then combine the absorption spectrum provided by the gas absorption cell (5) to perform bias correction on the continuous relative wavelength calibration curve to obtain the absolute wavelength continuous calibration curve of the swept laser.

3. The continuous high-precision wavelength calibration device for a swept-frequency laser according to claim 1, characterized in that, The input end of the one-to-three beam splitter (2) is connected to the output end of the sweep laser (1), and the three output ends of the one-to-three beam splitter (2) are respectively connected to the input end of the electro-optic modulator (10), the input end of the one-to-two beam splitter (3) and the input end of the gas absorption cell (5). The first output of the 1-to-2 beam splitter (3) is connected to the first input of the 2-to-2 beam splitter (6) via the delay fiber (4), the second output of the 1-to-2 beam splitter (3) is connected to the second input of the 2-to-2 beam splitter (6), and the two outputs of the 2-to-2 beam splitter (6) are respectively connected to the two inputs of the balanced photodetector (8). The output end of the electro-optic modulator (10) is connected to the input end of the fiber optic ring resonator (11), the output end of the fiber optic ring resonator (11) is connected to the input end of the second photodetector (12), and the output end of the gas absorption cell (5) is connected to the input end of the first photodetector (7).

4. The continuous high-precision wavelength calibration device for a swept-frequency laser according to claim 1, characterized in that, The delay fiber (4) in the Mach-Zehnder interference branch is used to introduce optical path difference.

5. The continuous high-precision wavelength calibration device for a swept-frequency laser according to claim 1, characterized in that, The signal processing module (14) extracts instantaneous phase information from the interference signal using Hilbert transform or wavelet transform algorithms.

6. A continuous high-precision wavelength calibration method for a swept-frequency laser based on the apparatus of any one of claims 1-5, characterized in that, Includes the following steps: The continuous sweeping optical signal output by the sweeping laser (1) is divided into three paths; The first optical signal is phase-modulated to generate a modulation sideband with a known frequency interval, and then input into the fiber ring resonator (11) to obtain a resonant peak signal that is periodically distributed on the optical frequency axis, which serves as a frequency scale. The second optical signal is input into the Mach-Zehnder interference branch consisting of a 1-to-2 beam splitter (3), a delay fiber (4), and a 2-to-2 beam splitter (6) to obtain the interference signal; The third optical signal is input into the gas absorption cell (5) to obtain a stable absorption spectral signal with a known center wavelength, which is used as an absolute wavelength reference. The optical signals of each branch are converted into electrical signals by the first photodetector (7), the second photodetector (12) and the balanced photodetector (8). After being acquired by the digital acquisition card (13), the signals are processed by the signal processing module (14) to obtain the absolute wavelength continuous calibration curve of the sweep laser.

7. The continuous high-precision wavelength calibration method for a swept-frequency laser according to claim 6, characterized in that, The processing procedure of the signal processing module (14) includes: Extract instantaneous phase information from the interference signal; Based on the resonant peak signal and the instantaneous phase information, the free spectral range of the fiber ring resonator (11) is calculated, and a continuous relative wavelength calibration curve is generated; The absorption spectral signal is used to perform bias correction on the continuous relative wavelength calibration curve to obtain the absolute wavelength continuous calibration curve of the swept laser.

8. A continuous high-precision wavelength calibration method for a swept-frequency laser according to claim 7, characterized in that, When calculating the free spectral range of the fiber ring resonator (11), the resonance peak signal and the instantaneous phase information are used to compensate for the non-uniformity of the free spectral range of the fiber ring resonator (11) caused by fiber dispersion.

9. A continuous high-precision wavelength calibration method for a swept-frequency laser according to claim 7, characterized in that, When extracting instantaneous phase information from the interference signal, Hilbert transform or wavelet transform algorithms are used.

10. A continuous high-precision wavelength calibration method for a swept-frequency laser according to claim 7, characterized in that, When using the absorption spectral line signal to perform offset correction on the continuous relative wavelength calibration curve, the wavelength corresponding to the absorption spectral line is used as the absolute reference to correct the overall offset of the relative wavelength calibration curve.

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