A method and apparatus for detecting the linewidth of a narrow-linewidth laser.

Abstract

This invention discloses a method and apparatus for detecting the linewidth of a narrow-linewidth laser. The method includes acquiring data information pre-collected using a data acquisition card; preprocessing the data information using a cumulative averaging algorithm; performing a fast Fourier transform on the preprocessed time-domain data information; processing the data using a moving average algorithm; fitting the moving averaged data using an L-M algorithm; and detecting the linewidth of the fitted data using a time-delayed self-heterodyne method to calculate the laser linewidth data. This invention uses a time-delayed fiber beat frequency method to measure the linewidth of a narrow-linewidth laser, which greatly enhances the accuracy of laser linewidth measurement while reducing the number of components used. This method uses a data acquisition card for data acquisition, fast Fourier transform for analysis and processing, and moving average and L-M algorithms for data processing, reducing costs while accurately detecting narrower laser linewidths.

Description

Technical Field

[0001] This invention relates to a method and apparatus for detecting the linewidth of a narrow-linewidth laser, belonging to the field of laser technology. Background Technology

[0002] A laser is a device that emits laser light. Since the invention of the first microwave quantum amplifier in 1953, lasers have been applied in various industrial fields. Laser linewidth is a spectral characteristic of a laser; it is the frequency width corresponding to the point where the laser power function drops from its peak to halfway, i.e., the full width at half maximum (FWHM) of the linear function of the spectrum. Ideally, the linewidth of a single-mode laser is 0 nm, at which point the laser exhibits good coherence and monochromaticity. In practical applications, due to the presence of quantum coherence noise and incoherent spontaneous emission, the output laser has a certain linewidth.

[0003] Narrow-linewidth lasers (NLLs) are lasers that output a single longitudinal mode of intracavity vibration. Their characteristics include an extremely narrow linewidth in the laser spectrum and excellent coherence. NLLs are now widely used in optical communication, optical sensing, optical remote sensing, and high-precision spectroscopy, primarily due to their advantages such as narrow linewidth, low noise, and strong resistance to electromagnetic interference. The linewidth and phase noise parameters of a laser play a decisive role in the detection distance and accuracy of distributed fiber optic sensing systems, significantly impacting the quality and level of sensor detection. Therefore, accurate measurement and characterization of the linewidth are of great importance.

[0004] Laser linewidth measurement is also an important means of characterizing the properties of single-frequency narrow-linewidth lasers. In practice, laser performance is often judged based on the measured linewidth value. Therefore, achieving accurate measurement of laser linewidth, especially the accurate characterization and measurement of narrow-linewidth lasers, is particularly important. With the introduction of external cavity technology and the development of Q-switching and mode-locking techniques, the linewidths of narrow-linewidth lasers have now reached the kHz level, and some even reach several hertz. Accurate characterization of narrow-linewidth lasers is of great significance for studying their linewidth, noise, and coherence characteristics.

[0005] In recent years, with technological advancements, laser linewidth measurement has become possible through direct acquisition of the laser power spectrum function or calculation using phase noise information. However, as laser performance improves, laser linewidths are gradually narrowing. Existing methods such as spectrometer measurement and Fabry-Perot etalon interferometry are no longer sufficient for advanced laser linewidth detection. While the currently used beat frequency method can meet some of the current linewidth detection needs, it requires an expensive spectrometer (ESA) to display and save the laser linewidth. Furthermore, the laser emitted by the laser produces numerous spikes when displayed on the ESA, which can affect the accuracy of laser linewidth measurement. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method and apparatus for detecting the linewidth of narrow-linewidth lasers. This method employs a delayed fiber beat frequency method to measure the linewidth of narrow-linewidth lasers, significantly improving the accuracy of laser linewidth measurement while reducing the number of components used. The method uses a data acquisition card for data acquisition, Fast Fourier Transform (FFT) for analysis and processing, and employs moving average and LM algorithms to process the data, reducing costs while accurately detecting narrower laser linewidths.

[0007] To achieve the above objectives, the present invention is implemented using the following technical solution:

[0008] In a first aspect, the present invention provides a method for detecting the linewidth of a narrow-linewidth laser, comprising:

[0009] Acquire data information that has been collected in advance using a data acquisition card;

[0010] The data information is preprocessed using a cumulative averaging algorithm to obtain preprocessed time-domain data information.

[0011] The preprocessed time-domain data is subjected to a fast Fourier transform to convert the time-domain data into frequency-domain data.

[0012] The frequency domain data information is processed using a moving average algorithm to obtain the moving averaged data;

[0013] The LM algorithm is used to fit the moving average data to obtain the fitted data;

[0014] The fitted data is used to detect the linewidth using the time-delayed self-heterodyne method, and the laser linewidth data is calculated.

[0015] Furthermore, the data acquisition card uses a PICO acquisition card for data acquisition.

[0016] Furthermore, the parameter settings of the data acquisition card include sampling interval, sampling rate, and window function.

[0017] Furthermore, the data information is preprocessed using a cumulative averaging algorithm, including:

[0018] The data information is filtered using a cumulative averaging algorithm; noise is continuously filtered out as the number of accumulations increases, wherein the selection of the number of accumulations is in response to a manual selection signal.

[0019] Furthermore, the parameter settings for the Fast Fourier Transform include the number of sampling points and the sampling frequency.

[0020] Furthermore, the step of detecting the linewidth of the fitted data using the time-delayed self-heterodyne method and calculating the laser linewidth data includes:

[0021] The fitted data is input into a computer, and a Lorentz line-shaped spectrum is obtained on the computer using the time-delayed self-heterodyne method, wherein the full width at half maximum (FWHM) of the Lorentz line-shaped spectrum is the linewidth of the laser under test.

[0022] Secondly, the present invention provides a device for detecting the linewidth of a narrow-linewidth laser, comprising: a narrow-linewidth laser under test, an optical fiber coupler, a delay fiber, an optical fiber polarization scrambler, an erbium-doped fiber amplifier, an acousto-optic modulator, an optical fiber coupler, an optical fiber filter, a photodetector, and a data acquisition card; the narrow-linewidth laser under test is connected to the input end of the optical fiber coupler, the laser output from the optical fiber coupler is split into two paths, one path is connected to the input end of the delay fiber, and the other path is connected to the input end of the optical fiber coupler via the acousto-optic modulator; the optical fiber polarization scrambler is connected to the other input end of the delay fiber; the laser output from the optical fiber polarization scrambler is connected to the input end of the erbium-doped fiber amplifier; the output end of the erbium-doped fiber amplifier is connected to the input end of the optical fiber coupler; the output end of the optical fiber coupler is connected to the input end of the optical fiber filter; the output end of the optical fiber filter is connected to the input end of the photodetector; the photodetector performs coherent processing on the light input from the optical fiber filter, and then inputs it to the data acquisition card.

[0023] Thirdly, the present invention provides a detection device for a narrow linewidth laser linewidth detection apparatus, comprising:

[0024] The acquisition unit is used to acquire data information that has been collected in advance using a data acquisition card;

[0025] The preprocessing unit is used to preprocess the data information using a cumulative averaging algorithm to obtain preprocessed time-domain data information.

[0026] The conversion unit is used to perform a fast Fourier transform on the preprocessed time-domain data information to convert the time-domain data information into frequency-domain data information;

[0027] The processing unit is used to process the frequency domain data information using a moving average algorithm to obtain the moving averaged data;

[0028] The fitting unit is used to fit the moving average data using the LM algorithm to obtain the fitted data;

[0029] The calculation unit is used to detect the linewidth of the fitted data using the time-delayed autoheterodyne method and calculate the laser linewidth data.

[0030] Fourthly, the present invention provides a device for detecting the linewidth of a narrow linewidth laser, including a processor and a storage medium;

[0031] The storage medium is used to store instructions;

[0032] The processor is configured to operate according to the instructions to perform the steps of the method according to any of the preceding claims.

[0033] Fifthly, the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of any of the preceding methods.

[0034] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0035] This invention provides a method for detecting the linewidth of a narrow-linewidth laser. Compared with the method of directly processing data using a fiber optic spectrum analyzer, the laser signal curve processed is smoother. By rapidly acquiring laser signals multiple times and processing the data using FFT, and then using the moving average algorithm and LM algorithm to process multiple sets of data, the laser curve is made close to the Lorentz curve, overcoming the problems of signal glitches and inaccurate measurement results when using a fiber optic spectrum analyzer.

[0036] The narrow-linewidth laser linewidth detection device provided by this invention incorporates a filter to filter out background noise that affects the accuracy of system measurements. This device uses a data acquisition card instead of a traditional fiber optic spectrum analyzer. Compared to a traditional fiber optic spectrum analyzer, the data acquisition card can be controlled by a laptop computer and quickly collect multiple sets of data through software, thereby reducing detection time. At the same time, processing multiple sets of data can also improve detection stability, ultimately improving the detection accuracy of the device. Meanwhile, traditional fiber optic spectrum analyzers have the disadvantages of being expensive, bulky, and not easy to carry. This device uses a data acquisition card instead of a fiber optic spectrum analyzer, achieving modularity and enabling wide application in engineering fields.

[0037] This invention addresses the problems of low detection accuracy, long data collection time, and expensive and inconvenient experimental equipment when using the time-delay self-heterodyne method to detect laser linewidth. It proposes a signal processing method and improves the design of a corresponding linewidth detection experimental device. Existing methods for measuring the linewidth of narrow-linewidth lasers, such as dual-parameter linewidth measurement based on partially coherent optical interference, all require expensive and heavy fiber optic spectrum analyzers and involve a large amount of complex calculations. They are slow to detect and cannot be conveniently used for engineering measurements. This method and device overcome the above problems and can be applied to most engineering fields. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of processing frequency domain signals using a moving average algorithm, provided in an embodiment of the present invention.

[0039] Figure 2 This is a schematic diagram of the process of fitting moving average data using the LM algorithm according to an embodiment of the present invention;

[0040] Figure 3 This is the demodulated curve provided in this embodiment of the invention before using the moving average algorithm and the LM algorithm;

[0041] Figure 4 This is the demodulated curve obtained by using the moving average algorithm and the LM algorithm according to the embodiments of the present invention;

[0042] Figure 5 This is a schematic diagram of a narrow linewidth laser linewidth detection device provided in an embodiment of the present invention;

[0043] Figure 6 This is a flowchart of a method for detecting the linewidth of a narrow-linewidth laser provided in an embodiment of the present invention. Detailed Implementation

[0044] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0045] Example 1

[0046] like Figure 6 As shown in the figure, this embodiment introduces a method for detecting the linewidth of a narrow linewidth laser, including:

[0047] Acquire data information that has been collected in advance using a data acquisition card;

[0048] The data information is preprocessed using a cumulative averaging algorithm to obtain preprocessed time-domain data information.

[0049] The preprocessed time-domain data is subjected to a fast Fourier transform to convert the time-domain data into frequency-domain data.

[0050] The frequency domain data information is processed using a moving average algorithm to obtain the moving averaged data;

[0051] The LM algorithm is used to fit the moving average data to obtain the fitted data;

[0052] The fitted data is used to detect the linewidth using the time-delayed self-heterodyne method, and the laser linewidth data is calculated.

[0053] The method for detecting the linewidth of a narrow-linewidth laser provided in this embodiment involves the following steps in its application:

[0054] Step 1: After setting up the system equipment, conduct a linewidth measurement experiment on the laser. The data acquisition module uses PICO for data acquisition.

[0055] In this example, the data acquisition card's parameter settings include sampling interval: 800ps, sampling rate: 1.25GS / s, and window function: Hamming;

[0056] Step 2: Accumulate and average the data acquired by the data acquisition card to perform signal preprocessing;

[0057] Furthermore: the collected data is accumulated and averaged to perform signal preprocessing, including:

[0058] The laser emits laser light continuously over a period of time, causing the acquisition module to continuously collect signals. Before data processing, a cumulative averaging algorithm can be used for signal preprocessing. This can filter out most of the noise and effectively improve the information quality of the demodulated data, making the linewidth measurement of the narrowband laser more accurate. Although the cumulative averaging algorithm can continuously filter out noise and improve the signal-to-noise ratio (SNR) as the number of accumulations increases, the improvement in SNR becomes very slow after a certain number of accumulations. Therefore, the number of accumulations needs to be selected based on the actual situation. In this example, 100 sets of data were collected and averaged.

[0059] Step 3: Perform a Fast Fourier Transform (FFT) on the preprocessed time-domain data to transform the time-domain information into frequency-domain information;

[0060] In this example, the FFT parameters are set as follows: number of sampling points: 1,048,576, sampling frequency: 1.25 GHz;

[0061] Step 4: Process the frequency domain signal using a moving average algorithm to filter out noise as much as possible and obtain a smooth curve;

[0062] Furthermore, moving average and sliding window algorithms are applied to the frequency domain signal, such as... Figure 1 As shown;

[0063] The moving average method, also known as the moving average filtering method, mainly involves calculating the arithmetic mean of sampling points near a given point to obtain a smoothed value for that point. This algorithm can effectively filter out noise. In this example, the arithmetic mean of seven points near the given point will be calculated and then moved sequentially to obtain a smooth curve.

[0064] Step 5: Use the LM algorithm to fit the data after the moving average, with 10,000 iterations and an initial damping value of 0.01. The flowchart is as follows. Figure 2 As shown;

[0065] The LM algorithm introduces a damping factor into the Gauss-Newton method, eliminating its limitation of difficulty in selecting initial values ​​for the parameters to be estimated, while retaining its advantage of extracting the optimal solution. The core of the LM method's working mechanism is to obtain an iterative formula through linearization within a small range near each measured data point. The optimal solution for the parameters to be estimated can then be gradually obtained through iterative calculations.

[0066] Step Six: Calculate the laser linewidth data based on the linewidth detection using the time-delay self-heterodyne method; for example... Figure 3 , Figure 4 As shown;

[0067] The time-delay self-heterodyne method uses a modulation circuit or power supply to create a certain frequency difference between two beams of light passing through a coupler (in this device, an AOM generates a 200MHz upshift, so the center frequency of the laser is 200MHz). Therefore, the center frequency of the optical signal generated during the interference beat at the second coupler is not near zero frequency. This enhances the system's resistance to interference from the surrounding environment, thereby improving measurement accuracy and reducing system errors. When using the time-delay self-heterodyne method to detect linewidth, a Lorentz-shaped spectrum is obtained on a spectrum analyzer. The full width at half maximum (FWHM) of this spectrum is the linewidth of the laser under test. In practice, the -20dB linewidth of the Lorentz curve is typically read, and then the actual linewidth of the laser is calculated. The linewidth relationship is shown in Table 1.

[0068]

[0069] Where Δν is the laser linewidth;

[0070] Before using the moving average algorithm and the LM algorithm, the demodulated curve was not smooth enough, and the laser linewidth data could not be accurately calculated. After using the moving average algorithm, the curve became significantly smoother. According to the linewidth calculation formula of the delay self-heterodyne method, the laser linewidth is 14.63kHz, which is not much different from the standard linewidth of 15kHz, thus verifying the reliability of the proposed solution.

[0071] Example 2

[0072] like Figure 5As shown, this embodiment provides a device for detecting the linewidth of a narrow linewidth laser, including a narrow linewidth laser to be tested 1, a 50:50 fiber coupler 2, a delay fiber 3, a fiber polarization scrambler 4, an erbium-doped fiber amplifier (EDFA) 5, an acousto-optic modulator 6, a 50:50 fiber coupler 7, a fiber filter 8, a photodetector 9, and a data acquisition card 10. The narrow-linewidth laser under test 1 is connected to the input of a 50:50 fiber coupler 2. The laser output from the 50:50 fiber coupler is split into two paths. One path is connected to the input of a delay fiber 3, and the other path is connected to the input of a 50:50 fiber coupler 7 via an acousto-optic modulator 6. A fiber polarization scrambler 4 is connected to the other input of the delay fiber 3. The laser output from the fiber polarization scrambler is connected to the input of an erbium-doped fiber amplifier 5. The output of the erbium-doped fiber amplifier 5 is connected to the input of the 50:50 fiber coupler 7. The output of the 50:50 fiber coupler 7 is connected to the input of a fiber filter 8. The output of the fiber filter 8 is connected to the input of a photodetector 9. The photodetector 9 performs coherent processing on the light input from the fiber filter 8 and then inputs it to a data acquisition card 10.

[0073] Erbium-doped fiber amplifiers 5 and 11 are erbium-doped fiber amplifiers with a maximum signal gain of 47dB and a saturated output power of 17dBm.

[0074] Photodetector 9 is a photodetector with a 3dB detection bandwidth greater than 22GHz, a wavelength of 1550nm, and a maximum output power of 10mW.

[0075] Data acquisition card 10 is the PICO6000 series 8424E.

[0076] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A detection method of a detection device of a narrow-linewidth laser linewidth, characterized by, The detection device of the narrow-linewidth laser linewidth comprises: a to-be-detected narrow-linewidth laser, a fiber coupler, a delay fiber, a fiber polarization scrambling device, an erbium-doped fiber amplifier, an acousto-optic modulator, a fiber coupler, a fiber filter, a photodetector, and a data acquisition card; the to-be-detected narrow-linewidth laser is connected with an input end of the fiber coupler; laser output by the fiber coupler is divided into two paths, one of which is connected with an input end of the delay fiber, and the other of which is connected with an input end of the acousto-optic modulator through the fiber coupler; the fiber polarization scrambling device is connected with another input end of the delay fiber; laser output by the fiber polarization scrambling device is connected with an input end of the fiber erbium-doped fiber amplifier; an output end of the fiber erbium-doped fiber amplifier is connected with an input end of the fiber coupler; an output end of the fiber coupler is connected with an input end of the fiber filter; an output end of the fiber filter is connected with an input end of the photodetector; the photodetector coherently processes light input by the fiber filter, and then inputs a data acquisition card; The detection method comprises: acquiring data information collected in advance by using a data acquisition card; performing signal preprocessing on the data information by using an accumulative average algorithm to acquire time-domain data information after preprocessing; performing fast Fourier transform on the time-domain data information after preprocessing to convert the time-domain data information into frequency-domain data information; processing the frequency-domain data information by using a sliding average algorithm to obtain data after sliding average; fitting the data after sliding average by using an L-M algorithm to acquire data after fitting; detecting a linewidth by using a delay heterodyne method on the data after fitting to calculate laser linewidth data.

2. The detection method of the apparatus for detecting a narrow linewidth laser linewidth according to claim 1, characterized in that, The data acquisition card is a PICO acquisition card.

3. The detection method of the apparatus for detecting a narrow linewidth laser linewidth according to claim 1, characterized in that, Parameter setting of the data acquisition card comprises a sampling interval, a sampling rate, and a window function.

4. The detection method of the apparatus for detecting a narrow linewidth laser linewidth according to claim 1, characterized in that, The signal preprocessing on the data information by using the accumulative average algorithm comprises: filtering the data information by using the accumulative average algorithm; according to an increase in the number of accumulations, noise is filtered out constantly, wherein the number of accumulations is selected in response to manual selection of a signal.

5. The method of claim 1, wherein Parameter setting of the fast Fourier transform comprises a sampling point number and a sampling frequency.

6. The detection method of the apparatus for detecting a narrow linewidth laser linewidth according to claim 1, wherein, The detection of the linewidth by using the delay heterodyne method on the data after fitting to calculate the laser linewidth data comprises: inputting the data after fitting into a computer, and obtaining a Lorentz line spectrum on the computer by using the delay heterodyne method, wherein a full width at half maximum of the Lorentz line spectrum is the linewidth of the to-be-detected laser.

7. A detection device of a narrow-linewidth-laser-line-width detection device adapted to the detection method of the narrow-linewidth-laser-line-width detection device according to claim 1, characterized in that, comprise: an acquisition unit, configured to acquire data information collected in advance by using a data acquisition card; a preprocessing unit, configured to perform signal preprocessing on the data information by using an accumulative average algorithm to acquire time-domain data information after preprocessing; a conversion unit, configured to perform fast Fourier transform on the time-domain data information after preprocessing to convert the time-domain data information into frequency-domain data information; a processing unit, configured to process the frequency-domain data information by using a sliding average algorithm to obtain data after sliding average; a fitting unit, configured to fit the data after sliding average by using an L-M algorithm to acquire data after fitting; and A computing unit is configured to detect the line width of the fitted data by a time-delay heterodyne method to obtain the laser line width data.

8. An electronic device, comprising: The system comprises a processor and a storage medium. The storage medium is configured to store instructions. The processor is configured to operate according to the instructions to perform the steps of the method according to any one of claims 1-6.

9. A computer readable storage medium having stored thereon a computer program, characterized in that: The program, when executed by the processor, implements the steps of the method according to any one of claims 1-6.

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