Laser dynamic linewidth characterization methods, systems, electronic devices, and media

Abstract

This invention discloses a method, system, electronic device, and medium for characterizing the dynamic linewidth of a laser. The method specifically includes: acquiring the interferometric beat frequency signal of the laser under test using an optical frequency domain reflection device, and converting the interferometric beat frequency signal into an optical time domain signal of the laser under test through resampling; performing a fast Fourier transform and frequency domain synthesis on the optical time domain signal to obtain the link response function; determining the edge position of the main reflection peak based on the envelope of the link response function and the first-order difference result of the envelope; and obtaining the dynamic linewidth characterization value of the laser under test based on the envelope amplitude difference between the edge positions on both sides of the main reflection peak. The method provided by this invention achieves effective characterization of the dynamic linewidth of a laser during high-speed frequency sweeping. This method overcomes the limitations of traditional methods that cannot be used for dynamic measurement, making it possible to accurately evaluate the dynamic linewidth, a key parameter affecting the signal-to-noise ratio and detection distance of laser measurement instruments.

Description

Technical Field

[0001] This invention relates to the field of optical measurement technology, and in particular to a method, system, electronic device, and medium for characterizing the dynamic linewidth of a laser. Background Technology

[0002] Tunable lasers, as core components of optical measurement and fiber optic sensing systems, have important applications in fiber optic communication and measurement technologies. Their frequency tuning performance directly affects the accuracy and stability of laser measurement instruments. For example, in instruments such as distributed fiber optic sensing (DFOS) and frequency modulated continuous wave (FMCW) lidar, the dynamic linewidth of the laser during rapid frequency sweep is a key parameter determining the system's signal-to-noise ratio and maximum detection distance.

[0003] Traditional methods for measuring the dynamic linewidth of lasers typically employ delayed self-heterodyne interferometry (DSHI) or spectrometer measurements. However, during actual operation, lasers exhibit a nonlinear response between the driving current and the laser frequency. Furthermore, at high tuning rates, lasers experience additional phase noise and transient frequency drift, resulting in a significantly wider dynamic linewidth than the steady-state linewidth. Therefore, these two methods are primarily suitable for measuring linewidth at static or slowly changing laser frequencies and cannot be used to characterize the dynamic linewidth of lasers during high-speed linear tuning. Summary of the Invention

[0004] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a method, system, electronic device, and medium for characterizing the dynamic linewidth of a laser, which can characterize the dynamic linewidth of a laser during high-speed linear tuning.

[0005] A method for characterizing the dynamic linewidth of a laser according to a first aspect embodiment of the present invention includes:

[0006] The interference beat frequency signal of the laser under test is obtained by an optical frequency domain reflection device, and the interference beat frequency signal is converted into the optical time domain signal of the laser under test by resampling.

[0007] The link response function is obtained by performing a fast Fourier transform and frequency domain synthesis on the optical time-domain signal.

[0008] Based on the envelope of the link response function and the first-order difference result of the envelope, the edge position of the main reflection peak is determined;

[0009] The dynamic linewidth characterization value of the laser under test is obtained based on the envelope amplitude difference at the edge positions on both sides of the main reflection peak.

[0010] The embodiments of the present invention have at least the following beneficial effects: The laser dynamic linewidth characterization method provided by the present invention obtains the interference beat frequency signal through the optical frequency domain reflection system and performs resampling, frequency domain transformation and synthesis, envelope and edge analysis in sequence, and finally extracts the envelope amplitude difference parameter reflecting the dynamic linewidth. This achieves indirect and effective characterization of the dynamic linewidth of the laser in high-speed frequency sweeping operation, and fundamentally overcomes the limitation that the traditional self-delay heterodyne interferometry or spectrometer method is only applicable to static or quasi-static measurements.

[0011] According to some embodiments of the present invention, the step of acquiring the interferometric beat frequency signal of the laser based on the optical frequency domain reflection device, and converting the interferometric beat frequency signal into the optical time domain signal of the laser under test by resampling, includes:

[0012] Based on the main interferometer of the optical frequency domain reflection device, the vertical polarization beat frequency signal and the horizontal polarization beat frequency signal of the laser under test are obtained;

[0013] Based on the auxiliary interferometer of the optical frequency domain reflection device, the beat frequency signal of the auxiliary branch of the laser under test is obtained;

[0014] Based on the auxiliary branch beat frequency signal, the vertical polarization beat frequency signal and the horizontal polarization beat frequency signal are resampled respectively to obtain the vertical time domain signal and the horizontal time domain signal of the laser under test.

[0015] According to some embodiments of the present invention, the step of resampling the vertically polarized beat frequency signal and the horizontally polarized beat frequency signal based on the auxiliary branch beat frequency signal includes:

[0016] Extract the instantaneous phase of the beat frequency signal of the auxiliary branch, and construct a linear time axis that is linearly related to the optical frequency based on the mapping relationship between the instantaneous phase and the original signal time axis;

[0017] The vertically polarized beat frequency signal and the horizontally polarized beat frequency signal are interpolated on the linear time axis to obtain the vertical time domain signal and the horizontal time domain signal.

[0018] According to some embodiments of the present invention, the step of performing a fast Fourier transform and frequency domain synthesis on the time-domain signal to obtain the link response function includes:

[0019] Perform Fast Fourier Transform on the vertical time domain signal and the horizontal time domain signal respectively to obtain the vertical frequency domain signal and the horizontal frequency domain signal;

[0020] The vertical frequency domain signal and the horizontal frequency domain signal are respectively subjected to point exponentiation processing to obtain the power spectra corresponding to the two vertical frequency domain signals and the horizontal frequency domain signals;

[0021] The two power spectra are combined and converted into a synthesized frequency domain signal, and the link response function is obtained based on the synthesized frequency domain signal.

[0022] According to some embodiments of the present invention, the step of determining the edge position of the main reflection peak based on the envelope of the link response function and the first-order difference result of the envelope includes:

[0023] Obtain all local maxima of the link response function, and obtain the upper envelope curve based on all the local maxima;

[0024] The upper envelope curve is iteratively smoothed to obtain a smoothed envelope curve;

[0025] Perform a first-order difference operation on the smooth envelope curve, and determine the edge position of the main reflection peak based on the position of the negative extremum in the first-order difference result.

[0026] A laser dynamic linewidth characterization system according to a second aspect embodiment of the present invention, the system being configured to perform the laser dynamic linewidth characterization method described in the above-described aspect embodiment; the system comprising:

[0027] Laser under test;

[0028] An optical frequency domain reflection device includes a first beam splitter, a main interferometer, and an auxiliary interferometer; the first beam splitter is used to receive the laser signal transmitted by the laser under test and transmit it to the main interferometer and the auxiliary interferometer respectively; the optical frequency domain reflection device is used to convert the laser signal output by the laser under test into an interferometric beat frequency signal;

[0029] A data acquisition card is used to acquire and transmit the interference beat frequency signal; the data acquisition card is also electrically connected to the laser under test.

[0030] A computer device is used to process the interferometric beat frequency signal to obtain dynamic linewidth characterization values.

[0031] According to some embodiments of the present invention, the main interferometer is provided with a second beam splitter, the input end of the second beam splitter being optically connected to the first output end of the first beam splitter; the first output end of the second beam splitter being optically connected to the input end of a circulator, and the second output end of the second beam splitter being optically connected to the first input end of a first coupler; the first output end of the circulator is connected to a main probe fiber, and the second output end of the circulator is optically connected to the second input end of the first coupler; the output end of the first coupler is connected to the optical paths of a first polarization beam splitter and a second polarization beam splitter respectively; the first polarization beam splitter is connected to the input end of a first balanced photodetector, and the second polarization beam splitter is connected to the input end of a second balanced photodetector; the output ends of the first balanced photodetector and the second balanced photodetector are electrically connected to the acquisition card respectively.

[0032] According to some embodiments of the present invention, the auxiliary interferometer is provided with a third beam splitter. The input end of the third beam splitter is connected to the second output end of the first beam splitter via an optical path. The first output end of the third beam splitter is connected to the auxiliary delay fiber via an optical path. The second output end of the third beam splitter is connected to the first input end of the second coupler via an optical path. The auxiliary delay fiber is also connected to the second input end of the second coupler via an optical path. The output end of the second coupler is connected to the input end of the third balanced photodetector via an optical path. The output end of the third balanced photodetector is electrically connected to the data acquisition card.

[0033] An electronic device according to a third aspect of the present invention includes a memory and a processor, the memory being used to store at least one program, and the processor being used to load the at least one program to execute the laser dynamic linewidth characterization method described in the above-described aspect embodiments.

[0034] A computer-readable storage medium according to a fourth aspect of the present invention includes a memory and a processor, the memory being configured to store at least one program, and the processor being configured to load the at least one program to perform the laser dynamic linewidth characterization method described in the above-described aspect embodiments.

[0035] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0036] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0037] Figure 1 This is a flowchart of a method for characterizing the dynamic linewidth of a laser according to an embodiment of the present invention;

[0038] Figure 2 This is a schematic diagram of the original interference beat frequency signal in an embodiment of the present invention;

[0039] Figure 3 This is a schematic diagram of the optical temporal domain signal after resampling according to an embodiment of the present invention;

[0040] Figure 4 This is a schematic diagram of the link response function according to an embodiment of the present invention;

[0041] Figure 5 This is a schematic diagram of the envelope of the link response function according to an embodiment of the present invention;

[0042] Figure 6 This is a schematic diagram of the first-order difference result of the envelope in an embodiment of the present invention;

[0043] Figure 7 This is a schematic diagram illustrating the relationship between the maximum measurement distance of the light source and the insertion loss in an embodiment of the present invention.

[0044] Figure 8 This is a structural diagram of a laser dynamic linewidth characterization system according to another embodiment of the present invention;

[0045] Figure 9 This is a structural diagram of an electronic device provided in another embodiment of the present invention.

[0046] Figure reference numerals: 1. Laser under test; 2. First beam splitter; 3. Third beam splitter; 4. Second beam splitter; 5. Auxiliary delay fiber; 6. Circulator; 7. Second coupler; 8. First coupler; 9. Main detection fiber; 10. Third balanced photodetector; 11. First polarization beam splitter; 12. Second polarization beam splitter; 13. First balanced photodetector; 14. Second balanced photodetector; 15. Data acquisition card; 16. Computer device; 17. Auxiliary interferometer; 18. Main interferometer. Detailed Implementation

[0047] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0048] In the description of this invention, "several" means one or more, "multiple" means two or more, "greater than," "less than," "exceeding," etc. are understood to exclude the stated number, and "above," "below," "within," etc. are understood to include the stated number. If "first," "second," etc. are used in the description, they are only for the purpose of distinguishing technical features and should not be construed as indicating or implying relative importance or implicitly indicating the number of indicated technical features or the order of the indicated technical features.

[0049] The concepts involved in this invention are explained below:

[0050] OFDR: Optical Frequency Domain Reflectometry, is an optical diagnostic technique based on the principle of linear frequency modulated laser interferometry and coherent detection. It achieves high-resolution, distributed measurement of fiber optic links by analyzing the frequency domain signal of backscattered Rayleigh light.

[0051] Please refer to Figures 1-7 , Figure 1 This is a flowchart illustrating a laser dynamic linewidth characterization method according to an embodiment of the present invention. This embodiment discloses a laser dynamic linewidth characterization method, which includes, but is not limited to, the following steps:

[0052] Step S100: Obtain the interference beat frequency signal of the laser under test 1 based on the optical frequency domain reflection device, and convert the interference beat frequency signal into the optical time domain signal of the laser under test 1 by resampling;

[0053] It should be noted that the laser under test 1 in this embodiment of the invention is a tunable laser. Step S100 involves interfering the swept-frequency output light of the laser under test 1 with the backscattered Rayleigh light generated by the optical fiber link in the optical frequency domain reflection device to obtain an interference beat frequency signal containing optical path difference information. The obtained interference beat frequency signal is referenced... Figure 2 By resampling the interferometric beat frequency signal to compensate for the phase noise introduced by the laser's frequency modulation nonlinearity, the original time-domain signal, which was uniformly sampled on the time axis but affected by frequency modulation distortion, is transformed into an equivalent time-domain signal uniformly distributed on the optical frequency axis. This provides a time-domain data foundation unaffected by frequency modulation distortion for subsequent dynamic linewidth extraction. The resampled optical time-domain signal serves as a reference. Figure 3 .

[0054] Step S200: Perform fast Fourier transform and frequency domain synthesis on the optical time-domain signal to obtain the link response function;

[0055] It should be noted that step S200 involves... Figure 3 The link amplitude response function obtained by performing Fast Fourier Transform and frequency domain synthesis on the optical time-domain signal shown is used to characterize the reflection or scattering intensity distribution at various spatial locations on the optical fiber link. This function lays the foundation for subsequent extraction of characteristic parameters characterizing the dynamic linewidth. The link response function after Fast Fourier Transform and frequency domain synthesis is shown below. Figure 4 .

[0056] Step S300: Based on the envelope of the link response function and the first-order difference result of the envelope, determine the edge position of the main reflection peak;

[0057] It should be noted that, referring to Figure 4 The dashed box A in the figure represents the main reflection peak of the link response function. This peak signal, with an amplitude significantly higher than the background noise, is formed in the link response function by the fiber end or a specific reflection event in the optical frequency domain reflection device. It can be used to analyze link loss and light source performance. (Refer to...) Figure 5 The envelope of the link response function refers to the contour of the amplitude of the complex signal in the frequency domain changing with frequency (corresponding to spatial location). The main function of extracting the envelope is to highlight the overall amplitude change trend of core events such as the main reflection peak, which facilitates subsequent location of the edge of the main reflection peak and calculation of the dynamic linewidth characterization value; refer to Figure 6 The first-order difference result of the envelope is as follows Figure 6 As shown, by finding the position of the minimum first-order difference value of the envelope, the location can be precisely determined. Figure 4 The corresponding position of the edge of the middle main reflection peak (i.e. Figure 4 (Middle circles B and C), thus providing precise geometric reference points for obtaining dynamic linewidth representation values.

[0058] Step S400: Based on the difference in envelope amplitude at the edge positions on both sides of the main reflection peak, obtain the dynamic linewidth characterization value of the laser under test 1.

[0059] It should be noted that there is an edge position on both sides of the main reflection peak. Step S400 of this embodiment of the invention obtains an insertion loss characterizing the coherence fading of the signal based on the difference in the envelope amplitude at the edge positions on both sides of the main reflection peak in the above-mentioned embodiment. The insertion loss obtained at this time is the dynamic linewidth characterization value of this embodiment of the invention.

[0060] Furthermore, the coherence distance of a tunable laser is affected by the dynamic linewidth of the laser, and the formula for the coherence distance of a tunable laser is:

[0061] ······①,

[0062] in, The physical length corresponding to the maximum optical path difference that allows light to maintain good coherence (produce stable interference) when propagating in a medium; is the speed of light in a vacuum; n is the refractive index of the propagation medium (in this embodiment, it is the refractive index of the fiber core in the OFDR system). Let be the instantaneous linewidth of the tunable laser during high-speed frequency sweep. From equation ①, we can see that the dynamic linewidth... The wider the coherence distance, the shorter the corresponding effective coherence length. The maximum measurement distance L of a tunable laser is limited by its coherence distance. Direct constraint: coherence distance The longer the fiber, the longer the maximum measurable distance L. When a laser is frequency-sweeping in an OFDR system, the closer the current fiber length is to its maximum measurable distance L, the greater the difference in envelope amplitude (i.e., insertion loss) at the edges of the main reflection peak. This increase in difference indicates a smoother edge to the main reflection peak, more significant signal broadening, and a wider dynamic linewidth of the laser. Therefore, by measuring multiple tunable lasers with different maximum measurable distances L while keeping the OFDR system and test fiber length constant, the insertion loss of each laser can be obtained, and its dynamic linewidth can be compared and characterized through the insertion loss.

[0063] It is understood that although the insertion loss obtained in the embodiments of the present invention is not an absolute frequency domain value of the linewidth and cannot be directly converted into the instantaneous linewidth (Hertz) of the tunable laser during operation, it can be effectively characterized through the following methods: for example, as a relative performance comparison parameter, the insertion loss of different lasers can be directly compared under the same test conditions; a larger value indicates a wider dynamic linewidth and poorer sweep frequency coherence; or as a trend-based quantitative indicator, by establishing its correlation with known performance parameters, the relative broadening of the dynamic linewidth and its changing trend with the operating state can be reflected. Figure 7 As shown, Figure 7 The horizontal axis in the figure represents the maximum measurement distance of the tunable laser. When the dynamic linewidth of the light source widens, causing its maximum measurable distance to shorten, the coherent fading degree obtained by this method also increases accordingly. The two show a consistent negative correlation trend, which verifies the effectiveness and rationality of this characterization parameter in reflecting the coherent performance of the laser.

[0064] It should be noted that in the above-mentioned embodiments, the length of the probe fiber in the OFDR system is less than the farthest measurement distance of all lasers. This is to ensure that all lasers under test can form a clear and stable main reflection peak interference signal at the end of the fiber, thereby establishing a consistent signal reference. This allows the system insertion loss obtained under the same test conditions to directly and fairly reflect the dynamic linewidth differences of each laser, rather than being limited by its ultimate detection capability.

[0065] It is understood that, compared with traditional fitting methods, the method adopted in this invention has the following significant advantages: model independence and high robustness. This method is a completely non-parametric model, does not depend on specific line type (such as Lorentz type) assumptions, and is insensitive to distortion or asymmetric morphology of the main reflection peak, thus exhibiting stronger robustness; accurate extraction of background trends. It can effectively extract and separate the background trend (envelope) of the main peak, while fitting methods often struggle to accurately characterize complex or irregular backgrounds; excellent numerical stability. The method process is highly deterministic, does not depend on initial parameter values, and does not exhibit iterative behavior. This method addresses local optima in optimization, demonstrating extremely stable and repeatable results. It exhibits strong noise resistance, being insensitive to noise and not amplifying it during envelope extraction, maintaining reliable performance even under low signal-to-noise ratio conditions. Furthermore, it boasts high efficiency and low computational complexity, with a time complexity of O(N), compared to fitting methods typically requiring O(N×k) (where k is the number of iterations, usually 5-20). It provides comprehensive background information, constructing realistic, continuous, and smooth background envelope curves, offering richer trend information, while fitting methods output only a limited number of parameters with limited information. In summary, this method outperforms traditional fitting methods in accuracy, stability, noise resistance, and computational efficiency, making it particularly suitable for dynamic linewidth representation scenarios requiring high robustness and processing speed.

[0066] Additionally, refer to Figure 1 , Figure 8 In step S100 of the above-described embodiments, the following steps are also included, but are not limited to:

[0067] Step S110: Based on the main interferometer 18 of the optical frequency domain reflection device, the vertical polarization beat frequency signal and the horizontal polarization beat frequency signal of the laser under test 1 are acquired.

[0068] Step S120: Based on the auxiliary interferometer 17 of the optical frequency domain reflection device, the beat frequency signal of the auxiliary branch of the laser under test 1 is acquired;

[0069] Step S130: Based on the auxiliary branch beat frequency signal, the vertical polarization beat frequency signal and the horizontal polarization beat frequency signal are resampled respectively to obtain the vertical time domain signal and the horizontal time domain signal of the laser under test 1.

[0070] It should be noted that the structures of the main interferometer 18 and the auxiliary interferometer 17 are as follows: Figure 8As shown. Step S110 simultaneously acquires two orthogonally polarized beat frequency signals: a vertically polarized beat frequency signal and a horizontally polarized beat frequency signal. This aims to overcome the signal fading problem caused by random polarization state changes in single-mode fiber. In an OFDR system, the polarization state of the backscattered Rayleigh light evolves randomly along the fiber. If only a single-path detection is used, its interference efficiency with the reference light will fluctuate drastically with the polarization state, leading to unstable amplitude or even complete fading of the link response function. By using polarization diversity reception, it can be ensured that at least one signal maintains effective interference under any polarization state, thereby improving system robustness and measurement reliability.

[0071] Additionally, refer to Figure 1 , Figure 3 In step S130 of the above-described embodiments, the following steps are also included, but are not limited to:

[0072] Step S131: Extract the instantaneous phase of the beat frequency signal of the auxiliary branch, and construct a linear time axis that is linearly related to the optical frequency based on the mapping relationship between the instantaneous phase and the time axis of the original signal.

[0073] Step S132: Interpolate the vertically polarized beat frequency signal and the horizontally polarized beat frequency signal on the linear time axis to obtain the vertical time domain signal and the horizontal time domain signal.

[0074] It should be noted that step S131 utilizes the instantaneous phase of the auxiliary branch signal to reflect the nonlinearity of the actual frequency sweep of the laser, and accordingly constructs a new time axis corresponding to the ideal linear frequency sweep, establishing a time-frequency linear mapping. Step S132, based on this linear time axis, resamples the two original polarized signals through interpolation to generate vertical and horizontal time-domain signals that are uniformly distributed on the optical frequency axis and have eliminated frequency modulation nonlinearity. These two steps work together to convert the original interference signal contaminated by frequency modulation distortion into a signal equivalent to that under ideal linear frequency modulation, as shown in the figure. Figure 3 As shown.

[0075] Additionally, refer to Figure 1 , Figure 4 In step S200 of the above-described embodiments, the following steps are also included, but are not limited to:

[0076] Step S210: Perform Fast Fourier Transform on the vertical time domain signal and the horizontal time domain signal respectively to obtain the vertical frequency domain signal and the horizontal frequency domain signal.

[0077] Step S220: Perform point exponentiation on the vertical frequency domain signal and the horizontal frequency domain signal respectively to obtain the power spectra of the two vertical frequency domain signals and the horizontal frequency domain signals.

[0078] Step S230: Combine the two power spectra and convert them into a combined frequency domain signal, and obtain the link response function based on the combined frequency domain signal.

[0079] It should be noted that steps S210 to S230 convert the polarization diversity time-domain signal into the link response function. Step S210 converts the two polarization time-domain signals to the frequency domain using a Fast Fourier Transform, mapping the time-domain interference information to the spectrum of the corresponding fiber spatial location. Step S220 performs a point power (modulus squared) operation on the two frequency-domain complex signals to convert the signals into a power spectrum. This eliminates the randomness of the complex phase and prepares the data for subsequent linear synthesis. Step S230 synthesizes the two power spectra. Its core purpose is to completely eliminate the deep polarization fading that may occur in a single signal through polarization diversity processing, ensuring that the final link response function has a stable and repeatable amplitude. In this embodiment of the invention, the power spectrum synthesis involves adding the two power spectra and taking the logarithm. The synthesized frequency-domain signal is as follows: Figure 4 As shown, this is the required link response function, whose amplitude envelope clearly characterizes the reflection or scattering intensity at each location on the fiber optic link.

[0080] Additionally, refer to Figures 4-6 In step S300 of the above-described embodiments, the following steps are also included, but are not limited to:

[0081] Step S310: Obtain all local maxima of the link response function, and obtain the upper envelope curve based on all local maxima;

[0082] Step S320: Iteratively smooth the upper envelope curve to obtain a smoothed envelope curve;

[0083] Step S330: Perform a first-order difference operation on the smooth envelope curve, and determine the edge position of the main reflection peak based on the position of the negative extremum in the first-order difference result.

[0084] It should be noted that steps S310 to S330 constitute the processing flow for accurately extracting the edge position of the main reflection peak from the link response function. Step S310 extracts all local maxima and constructs an upper envelope curve, aiming to separate the amplitude variation trend that clearly reflects the overall contour of the main reflection peak from the link response function, while initially suppressing the influence of local noise and fine structure. Step S320 further processes the upper envelope curve through iterative smoothing, the core purpose of which is to eliminate residual random fluctuations or minor fluctuations in the signal, thereby forming a smooth contour with significant "step" characteristics at the main reflection peak. This provides a stable and well-defined input for subsequent accurate detection of the edge position. Step S330 uses the first-order difference of the smoothed envelope curve to quantify its rate of change. By locating the negative extreme points in the difference result, the positions corresponding to the edges on both sides of the main reflection peak can be objectively and accurately identified.

[0085] Reference Figure 4In one embodiment of the present invention, the main peak is located at approximately 500m, then the flattened left envelope is 500m * 0.9 = 450m, and 500 * 1.1 = 550m. The frequency axis is calculated as follows:

[0086] f = ((0:N / 2-1)*(fs / N))······②,

[0087] In Equation ②, f is the frequency axis, N is the number of points of the input signal, fs is the sampling rate, and N can be calculated by multiplying the sampling rate by the acquisition time.

[0088] According to an embodiment of the second aspect of the present invention, referring to Figure 8 This invention provides a laser dynamic linewidth characterization system, which is used to perform the laser dynamic linewidth characterization method of the above-described embodiments; the system includes:

[0089] Laser under test 1;

[0090] The optical frequency domain reflection device includes a first beam splitter 2, a main interferometer 18, and an auxiliary interferometer 17; the first beam splitter 2 is used to receive the laser signal transmitted by the laser under test 1 and transmit it to the main interferometer 18 and the auxiliary interferometer 17 respectively; the optical frequency domain reflection device is used to convert the laser signal output by the laser under test 1 into an interference beat frequency signal;

[0091] Acquisition card 15 is used to acquire and transmit interference beat frequency signals; acquisition card 15 is also electrically connected to the laser under test 1;

[0092] Computer device 16 is used to process the interferometric beat frequency signal to obtain dynamic linewidth characterization values.

[0093] It should be noted that, when the system provided in this embodiment of the invention is working, the synchronous trigger signal of the tunable laser is transmitted to the external trigger input terminal of the acquisition card 15 as the external trigger signal of the acquisition card 15; the emitted light of the tunable laser enters through port a of the first beam splitter 2, and enters the main interferometer 18 and the auxiliary interferometer 17 of the optical frequency domain reflection device from ports b and c of the first beam splitter 2, respectively. The optical frequency domain reflection device converts the detected light signal into an interference beat frequency signal and transmits it to the acquisition card 15. The acquisition card 15 transmits the acquired analog electrical signal to the computer device 16. This invention, using an auxiliary interferometer 17 of the optical frequency domain reflector as a reference, collaboratively processes the original interferometric beat frequency signal acquired by the main interferometer 18, which includes polarization fading and frequency modulation nonlinear distortion. Finally, in the computer device 16, the dynamic linewidth characterization method for lasers provided in the above-described embodiments is used to quantify the dynamic phase noise level during the laser frequency sweep process using a relatively fixed value (i.e., insertion loss). This achieves an indirect, efficient, and systematic characterization of the laser's dynamic linewidth, allowing the dynamic linewidth of the tunable laser to be characterized before use, thereby determining the laser's quality parameters. This system requires only a single adjustment of the optical frequency domain reflector before measurement and only requires replacing the laser under test 1 during testing. This structure eliminates the need for a precision spectrometer or repeated replacement of the test fiber, providing an integrated and low-cost solution for evaluating and comparing the dynamic performance of lasers.

[0094] Additionally, refer to Figure 8 In the laser dynamic linewidth characterization system of the above-described embodiment, the optical frequency domain reflection device includes a main interferometer 18 equipped with a second beam splitter 4. The input end of the second beam splitter 4 is connected to the first output end of the first beam splitter 2 via an optical path. The first output end of the second beam splitter 4 is connected to the input end of the circulator 6 via an optical path, and the second output end of the second beam splitter 4 is connected to the first input end of the first coupler 8 via an optical path. The first output end of the circulator 6 is connected to a main probe fiber 9, and the second output end of the circulator 6 is connected to the second input end of the first coupler 8 via an optical path. The output end of the first coupler 8 is connected to the optical paths of the first polarization beam splitter 11 and the second polarization beam splitter 12, respectively. The first polarization beam splitter 11 is connected to the input end of the first balanced photodetector 13 via an optical path, and the second polarization beam splitter 12 is connected to the input end of the second balanced photodetector 14 via an optical path. The output ends of the first balanced photodetector 13 and the second balanced photodetector 14 are electrically connected to the acquisition card 15, respectively.

[0095] It should be noted that the laser signal emitted from port c of the first beam splitter 2 is received by port a of the second beam splitter 4. The second beam splitter 4 then transmits the acquired laser through ports b and c to ports a of the circulator 6 and the first coupler 8, respectively. The circulator 6 emits the received laser from port b, passes through the main probe fiber 9, generates backscattered Rayleigh light at the end of the main probe fiber 9, and enters port b of the circulator 6. It then exits from port c of the circulator 6 and enters port b of the first coupler 8. The first coupler 8 combines the light received from ports a and b and emits the combined beams at a 50:50 ratio to ports a of the first polarization beam splitter 11 and port a of the second polarization beam splitter 12, respectively. The light entering from port a of the first polarization beam splitter 11 is split into a first vertically polarized light and a first polarized light. Horizontally polarized light is generated, wherein the first vertically polarized light is output from port b of the first polarization beamsplitter 11 to the input of the first balanced photodetector 13, and the first horizontally polarized light is output from port c of the first polarization beamsplitter 11 to the input of the second balanced photodetector 14; light entering from port a of the second polarization beamsplitter 12 is split into second vertically polarized light and second horizontally polarized light, wherein the second vertically polarized light is output from port b of the first polarization beamsplitter 11 to the input of the first balanced photodetector 13, and the second horizontally polarized light is output from port c of the first polarization beamsplitter 11 to the input of the second balanced photodetector 14; the first balanced photodetector 13 and the second balanced photodetector 14 respectively convert the acquired beat frequency interference signals into electrical signals and transmit them to the acquisition card 15. In this process, the laser signal output by the tunable laser is converted into the interference beat frequency signals of the above-described embodiment, namely, the vertically polarized beat frequency signal and the horizontally polarized beat frequency signal.

[0096] Additionally, refer to Figure 8 In the laser dynamic linewidth characterization system of the above-described embodiment, the optical frequency domain reflection device includes an auxiliary interferometer 17 equipped with a third beam splitter 3. The input end of the third beam splitter 3 is optically connected to the second output end of the first beam splitter 2, the first output end of the third beam splitter 3 is optically connected to the auxiliary delay fiber 5, and the second output end of the third beam splitter 3 is optically connected to the first input end of the second coupler 7. The auxiliary delay fiber 5 is also optically connected to the second input end of the second coupler 7. The output end of the second coupler 7 is optically connected to the input end of the third balanced photodetector 10, and the output end of the third balanced photodetector 10 is electrically connected to the acquisition card 15.

[0097] It should be noted that the laser signal emitted from port b of the first beam splitter 2 is received by port a of the third beam splitter 3; the third beam splitter 3 transmits the laser signal through port b to port a of the auxiliary delay fiber 5, and through port c to port b of the second coupler 7; the auxiliary delay fiber 5 is used to obtain beat frequency signals with different optical paths of the interferometer arm and the reference arm. The main frequency of the beat frequency signal can be calculated from the tuning range, tuning rate and optical path difference between the two arms of the interferometer. Among them, the frequency range and tuning rate are inherent parameters of the laser and are known at the factory. Generally speaking, the optical path difference between the two arms of the interferometer is the length of the delay fiber on the interferometer; the auxiliary delay fiber 5 transmits the processed signal through port b to port a of the second coupler 7; the second coupler 7 combines the signals obtained from ports a and b in a 50:50 ratio and transmits them to the third balanced photodetector 10.

[0098] In some embodiments of the present invention, the first beam splitter 2, the second beam splitter 4, and the third beam splitter 3 are all 95:5 beam splitters. The first beam splitter 2 transmits 95% of the laser signal to the main interferometer 18 and transmits 5% of the laser signal to the auxiliary interferometer 17. The main detection fiber 9 and the auxiliary delay fiber 5 in the main interferometer 18 and the auxiliary interferometer 17 receive the 5% laser signal formed by the second beam splitter 4 and the third beam splitter 3. The first coupler 8 and the second coupler 7 are both 2×2 couplers. The 2×2 coupler can convert the laser signal into an interference beat frequency signal. The function of the first polarization beam splitter 11 and the second polarization beam splitter 12 is to decompose the incident light into two linearly polarized lights with orthogonal polarization directions, thereby eliminating the influence of polarization fading noise. The function of the first balanced photodetector 13, the second balanced photodetector 14, and the third balanced photodetector 10 is to convert the optical beat frequency signal into an electrical signal.

[0099] like Figure 9 As shown, Figure 9 This is a structural diagram of an electronic device provided in one embodiment of the present invention. The present invention also provides an electronic device, comprising:

[0100] The processor 801 can be implemented using a general-purpose central processing unit (CPU), microprocessor, application specific integrated circuit (ASIC), or one or more integrated circuits, and is used to execute relevant programs to implement the technical solutions provided in the embodiments of this application.

[0101] The memory 802 can be implemented as a read-only memory (ROM), static storage device, dynamic storage device, or random access memory (RAM). The memory 802 can store the operating system and other application programs. When the technical solutions provided in the embodiments of this specification are implemented through software or firmware, the relevant program code is stored in the memory 802 and is called and executed by the processor 801 to execute the laser dynamic linewidth characterization method of the embodiments of this application.

[0102] The 803 input / output interface is used to implement information input and output.

[0103] The communication interface 804 is used to enable communication and interaction between this device and other devices. Communication can be achieved through wired means (such as USB, network cable, etc.) or wireless means (such as mobile network, WIFI, Bluetooth, etc.).

[0104] Bus 805 transmits information between various components of the device (e.g., processor 801, memory 802, input / output interface 803, and communication interface 804);

[0105] The processor 801, memory 802, input / output interface 803, and communication interface 804 are connected to each other within the device via bus 805.

[0106] It should be noted that the electronic device in this embodiment of the invention is a computing device specifically capable of executing methods for characterizing the dynamic linewidth of a laser, such as a general-purpose computer, embedded processor, industrial control computer, or dedicated signal processing platform. This device executes the algorithm flow corresponding to each step of the above method by running instructions stored in its memory, including resampling the interferometric beat frequency signal input from the acquisition card, frequency domain transformation and synthesis, envelope extraction and differential operation, and finally outputting a dynamic linewidth characterization value (such as insertion loss).

[0107] Memory, as a non-transitory computer-readable storage medium, can be used to store non-transitory software programs and non-transitory computer-executable programs. Furthermore, memory may include high-speed random access memory, and may also include non-transitory memory, such as at least one disk storage device, flash memory device, or other non-transitory solid-state storage device. In some embodiments, memory may optionally include memory remotely located relative to the processor, and these remote memories can be connected to the processor via a network. Examples of such networks include, but are not limited to, the Internet, intranets, local area networks, mobile communication networks, and combinations thereof. The device embodiments described above are merely illustrative, and the units described as separate components may or may not be physically separate, and may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs.

[0108] It will be understood by those skilled in the art that all or some of the steps and systems in the methods disclosed above can be implemented as software, firmware, hardware, and suitable combinations thereof. Some or all of the physical components can be implemented as software executed by a processor, such as a central processing unit, digital signal processor, or microprocessor, or as hardware, or as an integrated circuit, such as an application-specific integrated circuit. Such software can be distributed on a computer-readable medium, which can include computer storage media (or non-transitory media) and communication media (or transient media). As is known to those skilled in the art, the term computer storage media includes volatile and non-volatile, removable and non-removable media implemented in any method or technology for storing information (such as computer-readable instructions, data structures, program modules, or other data). Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technologies, CD-ROM, digital versatile disc (DVD) or other optical disc storage, magnetic cartridges, magnetic tape, disk storage or other magnetic storage devices, or any other medium that can be used to store desired information and is accessible to a computer. Furthermore, as is known to those skilled in the art, communication media typically include computer-readable instructions, data structures, program modules, or other data in modulated data signals such as carrier waves or other transmission mechanisms, and may include any information delivery medium.

[0109] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for characterizing the dynamic linewidth of a laser, characterized in that, The method comprises the steps of: acquiring an interference beat frequency signal of a to-be-tested laser based on an optical frequency domain reflection device, and converting the interference beat frequency signal into a time domain signal of the to-be-tested laser through resampling; performing fast Fourier transform and frequency domain synthesis on the time domain signal to obtain a link response function; determining an edge position of a main reflection peak based on an envelope of the link response function and a first-order differential result of the envelope; obtaining a dynamic line width characteristic value of the to-be-tested laser based on an envelope amplitude difference of the edge position on both sides of the main reflection peak; The step of acquiring an interference beat frequency signal of a laser based on an optical frequency domain reflection device, and converting the interference beat frequency signal into a time domain signal of the to-be-tested laser, comprises the steps of: acquiring a vertical polarization beat frequency signal and a horizontal polarization beat frequency signal of the to-be-tested laser based on a main interferometer of the optical frequency domain reflection device; acquiring an auxiliary branch beat frequency signal of the to-be-tested laser based on an auxiliary interferometer of the optical frequency domain reflection device; resampling the vertical polarization beat frequency signal and the horizontal polarization beat frequency signal based on the auxiliary branch beat frequency signal to obtain a vertical time domain signal and a horizontal time domain signal of the to-be-tested laser; The step of performing fast Fourier transform and frequency domain synthesis on the time domain signal to obtain a link response function, comprises the steps of: performing fast Fourier transform on the vertical time domain signal and the horizontal time domain signal to obtain a vertical frequency domain signal and a horizontal frequency domain signal; performing modulus square calculation processing on the vertical frequency domain signal and the horizontal frequency domain signal to obtain power spectra corresponding to the vertical frequency domain signal and the horizontal frequency domain signal; combining the two power spectra and converting them into a combined frequency domain signal, and obtaining the link response function based on the combined frequency domain signal.

2. The method of claim 1, wherein, The step of resampling the vertical polarization beat frequency signal and the horizontal polarization beat frequency signal based on the auxiliary branch beat frequency signal, comprises the steps of: extracting an instantaneous phase of the auxiliary branch beat frequency signal, and constructing a linear time axis in linear relationship with an optical frequency based on a mapping relationship between the instantaneous phase and an original signal time axis; interpolating the vertical polarization beat frequency signal and the horizontal polarization beat frequency signal on the linear time axis to obtain the vertical time domain signal and the horizontal time domain signal.

3. The method of claim 1, wherein, The step of determining an edge position of a main reflection peak based on an envelope of a link response function and a first-order differential result of the envelope, comprises the steps of: acquiring all local maximum values of the link response function, and obtaining an upper envelope curve based on all the local maximum values; performing iterative smoothing processing on the upper envelope curve to obtain a smoothed envelope curve; performing first-order differential operation on the smoothed envelope curve, and determining the edge position of the main reflection peak according to the position of a negative extreme value in the first-order differential result.

4. A system for characterizing the dynamic linewidth of a laser, comprising: The system is used to perform the method for characterizing the dynamic line width of a laser according to any one of claims 1 to 3, and comprises: a to-be-tested laser; The optical frequency domain reflectometer comprises a first beam splitter, a main interferometer and an auxiliary interferometer; the first beam splitter is used for receiving a laser signal transmitted by the to-be-tested laser and transmitting the laser signal to the main interferometer and the auxiliary interferometer respectively; the optical frequency domain reflectometer is used for converting the laser signal output by the to-be-tested laser into an interference beat frequency signal; a collection card is used for acquiring and transmitting the interference beat frequency signal; the collection card is also electrically connected with the to-be-tested laser; a computer device is used for processing the interference beat frequency signal to obtain a dynamic line width representation value.

5. The system for characterizing the dynamic linewidth of a laser according to claim 4, wherein, The main interferometer is provided with a second beam splitter, an input end of the second beam splitter is optically connected with a first output end of the first beam splitter; a first output end of the second beam splitter is optically connected with an input end of a circulator, a second output end of the second beam splitter is optically connected with a first input end of a first coupler; a first output end of the circulator is optically connected with a main probe optical fiber, a second output end of the circulator is optically connected with a second input end of the first coupler; an output end of the first coupler is optically connected with a first polarization beam splitter and a second polarization beam splitter respectively; the first polarization beam splitter is optically connected with an input end of a first balanced photoelectric detector, the second polarization beam splitter is optically connected with an input end of a second balanced photoelectric detector; an output end of the first balanced photoelectric detector and an output end of the second balanced photoelectric detector are electrically connected with the collection card respectively.

6. The system for characterizing the dynamic linewidth of a laser of claim 4, wherein, The auxiliary interferometer is provided with a third beam splitter, an input end of the third beam splitter is optically connected with a second output end of the first beam splitter, a first output end of the third beam splitter is optically connected with an auxiliary delay optical fiber, a second output end of the third beam splitter is optically connected with a first input end of a second coupler; the auxiliary delay optical fiber is also optically connected with a second input end of the second coupler; an output end of the second coupler is optically connected with an input end of a third balanced photoelectric detector, an output end of the third balanced photoelectric detector is electrically connected with the collection card.

7. An electronic device, comprising: The computer readable storage medium stores computer executable instructions for causing a computer to execute the characterization method of the dynamic line width of the laser according to any one of claims 1 to 3.

8. A computer-readable storage medium, characterized in that, The computer readable storage medium stores computer executable instructions for causing a computer to execute the characterization method of the dynamic line width of the laser according to any one of claims 1 to 3.

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