CN115238231A - Method and device for detecting line width of narrow-line-width laser - Google Patents
Method and device for detecting line width of narrow-line-width laser Download PDFInfo
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Abstract
The invention discloses a method and a device for detecting the line width of a narrow-line-width laser, wherein the method comprises the steps of acquiring data information acquired by a data acquisition card in advance; preprocessing the data information by adopting an accumulation average algorithm; performing fast Fourier transform on the preprocessed time domain data information; processing by adopting a moving average algorithm; fitting the moving averaged data using an L-M algorithm; the fitted data is used for detecting the line width by a time delay self-heterodyne method, and the line width data of the laser is calculated; the method adopts a data acquisition card to acquire data, performs analysis processing through fast Fourier transform, and adopts a moving average algorithm and an L-M algorithm to process the data, thereby reducing the cost and simultaneously accurately detecting the narrower laser line width.
Description
Technical Field
The invention relates to a method and a device for detecting the line width of a narrow-line-width laser, belonging to the technical field of lasers.
Background
A laser is a device capable of emitting laser light, and since the first microwave quantum amplifier appeared in 1953, the laser has been used in various industrial fields. The laser linewidth is the spectral characteristic of the laser, and the laser linewidth is the frequency width corresponding to the laser power function when the peak value is reduced to a half, namely the full width at half maximum of the spectral linear function. The line width of the single mode laser is 0nm under the ideal state, and the laser has good coherence and monochromaticity. In practical application, due to existence of quantum coherent noise and incoherent spontaneous radiation, output laser has a certain line width.
The narrow linewidth laser outputs laser in a mode of vibrating a single longitudinal mode in a cavity, and is characterized in that the linewidth of a laser spectrum is very narrow, and the laser has excellent coherence characteristics. Narrow linewidth lasers have been widely used in the fields of optical communication, optical sensing, optical remote sensing, high-precision spectroscopy, etc., mainly due to the advantages of narrow linewidth, low noise, strong anti-electromagnetic interference capability, etc. The line width and phase noise parameters of the laser play a decisive role in the detection distance and detection precision of the distributed optical fiber sensing system, and have great influence on the detection quality and level of the sensor. Therefore, the method has great significance for accurate measurement and characterization of the line width.
Laser linewidth measurement is also an important means for characterizing the characteristics of a single-frequency narrow linewidth laser, and in actual operation, people often judge the performance of the laser according to the measured value of the linewidth of the laser, so that the realization of accurate measurement of the linewidth of the laser is particularly important for accurately characterizing and measuring the linewidth of the narrow linewidth laser. With the introduction of external cavity technology and the development of Q-switching and mode-locking technologies, the line width of the narrow-line-width laser has been developed to the kHz level, and some line widths even reach several Hertz. The precise characterization of the laser narrow linewidth has important significance for researching the characteristics of the narrow linewidth laser, such as linewidth, noise, coherence and the like.
With the progress of the technology in recent years, laser line width measurement can be directly obtained through a laser power spectrum function or calculated by utilizing phase noise information. However, with the improvement of the performance of the laser, the laser linewidth gradually narrows, the original methods such as a spectrometer measurement method and a fabry-perot etalon interference method cannot meet the requirement for line width detection of an advanced laser, while the beat frequency method mainly used at present can meet a part of the requirement for line width detection at present, but the beat frequency method needs to use an expensive frequency spectrum analyzer (ESA) to display and store the laser linewidth, and meanwhile, the laser emitted by the laser has more burrs when being displayed on the ESA, which affects the precision of line width detection of the laser.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provides a method and a device for detecting the line width of a narrow-line-width laser, wherein the line width of the narrow-line-width laser is measured by adopting a time-delay optical fiber beat frequency method, so that the accuracy of the line width measurement of the laser is greatly enhanced on the basis of reducing the use of devices; the method adopts a data acquisition card to acquire data, performs analysis processing through Fast Fourier Transform (FFT), and adopts a moving average algorithm and an L-M algorithm to process the data, thereby reducing the cost and accurately detecting the narrower laser line width.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a method for detecting a line width of a narrow-line-width laser, including:
acquiring data information acquired by a data acquisition card in advance;
performing signal preprocessing on the data information by adopting an accumulative average algorithm to obtain preprocessed time domain data information;
performing fast Fourier transform on the preprocessed time domain data information, and converting the time domain data information into frequency domain data information;
processing the frequency domain data information by adopting a moving average algorithm to obtain moving average data;
fitting the data subjected to the moving average by using an L-M algorithm to obtain fitted data;
and detecting the line width of the fitted data by a time delay self-heterodyne method, and calculating the line width data of the laser.
Furthermore, the data acquisition card adopts a PICO acquisition card for acquisition.
Further, the parameter setting of the data acquisition card includes sampling interval, sampling rate and window function.
Further, the signal preprocessing of the data information by using an accumulation average algorithm includes:
filtering the data information through an accumulation average algorithm; and continuously filtering the noise according to the increase of the accumulation times, wherein the selection of the accumulation times is selected in response to the manual selection signal.
Further, the parameter setting of the fast fourier transform includes a sampling point number and a sampling frequency.
Further, the step of detecting the line width of the fitted data by a time delay self-heterodyne method to calculate the line width data of the laser includes:
inputting the fitted data into a computer, and obtaining a Lorentz line type frequency spectrum on the computer by using a time delay self-heterodyne method, wherein the full width at half maximum of the Lorentz line type frequency spectrum is the line width of the laser to be measured.
In a second aspect, the present invention provides a device for detecting a line width of a narrow-line-width laser, including: the device comprises a narrow linewidth laser to be detected, an optical fiber coupler, a delay optical fiber, an optical fiber polarization scrambler, an erbium-doped optical fiber amplifier, an acoustic-optical modulator, an optical fiber coupler, an optical fiber filter, a photoelectric detector and a data acquisition card; the narrow linewidth laser to be detected is connected with the input end of an optical fiber coupler, the laser output by the optical fiber coupler is divided into two paths, wherein one path is connected with the input end of a delay optical fiber, the other path is connected with the input end of the optical fiber coupler through an acousto-optic modulator, an optical fiber polarization scrambler is connected with the other input end of the delay optical fiber, the laser output by the optical fiber polarization scrambler is connected with the input end of an optical fiber erbium-doped optical fiber amplifier, the output end of the optical fiber erbium-doped optical fiber amplifier is connected with the input end of the optical fiber coupler, the output end of the optical fiber coupler is connected with the input end of an optical fiber filter, the output end of the optical fiber filter is connected with the input end of a photoelectric detector, and the photoelectric detector performs coherent processing on the light input by the optical fiber filter and then inputs the light into a data acquisition card.
In a third aspect, the present invention provides a detection apparatus for detecting a line width of a narrow-line-width laser, including:
the acquisition unit is used for acquiring data information acquired by a data acquisition card in advance;
the preprocessing unit is used for preprocessing the data information by adopting an accumulative average algorithm to obtain preprocessed time domain data information;
the conversion unit is used for carrying out fast Fourier transform on the preprocessed time domain data information and converting the time domain data information into frequency domain data information;
the processing unit is used for processing the frequency domain data information by adopting a moving average algorithm to obtain moving average data;
the fitting unit is used for fitting the data subjected to the moving average by using an L-M algorithm to obtain the fitted data;
and the calculating unit is used for detecting the line width of the fitted data by a time delay self-heterodyne method and calculating the line width data of the laser.
In a fourth aspect, the present invention provides a device for detecting a line width of a narrow-line-width laser, including a processor and a storage medium;
the storage medium is used for storing instructions;
the processor is configured to operate in accordance with the instructions to perform the steps of the method according to any one of the preceding claims.
In a fifth aspect, the invention provides a computer-readable storage medium having stored thereon a computer program which, when executed by a processor, performs the steps of the method of any one of the preceding claims.
Compared with the prior art, the invention has the following beneficial effects:
compared with a laser signal curve processed by a method of directly processing data through an optical fiber spectrometer, the line width detection method of the narrow-line-width laser is smoother, the laser signal curve is made to be close to a Lorentz line shape by rapidly acquiring the laser signal for many times and processing the data through FFT (fast Fourier transform) and then processing a plurality of groups of data through a sliding average algorithm and an L-M (L-M) algorithm, and the problems of signal burr and inaccurate measurement result in the prior process of processing by using the optical fiber spectrometer are solved.
The filter is added in the detection device of the narrow linewidth laser linewidth, so that the background noise which can affect the system measurement accuracy is filtered, the device uses the data acquisition card to replace the traditional optical fiber spectrometer, compared with the traditional optical fiber spectrometer, the data acquisition card can be controlled by a notebook computer, and a plurality of groups of data are rapidly collected through software, so that the detection time is reduced, meanwhile, the detection stability can be improved by processing a plurality of groups of data, and finally, the detection accuracy of the device is improved.
The invention provides a signal processing method and improves and designs a set of corresponding line width detection experimental device based on the problems of low detection precision, long data collection time and expensive and not easy-to-carry experimental equipment when a time delay self-heterodyne method is used for detecting the line width of a laser, and other existing methods for measuring the line width of a narrow line width laser, such as double-parameter line width measurement based on partial coherent light interference, need to use an expensive and heavy optical fiber spectrometer, simultaneously need to carry out a large number of complex operations, cannot carry out convenient engineering measurement when the detection time is slow, and can be applied to most engineering fields.
Drawings
FIG. 1 is a schematic diagram of a frequency domain signal processing method using a moving average algorithm according to an embodiment of the present invention;
FIG. 2 is a schematic flow chart of fitting the moving average data by using the L-M algorithm according to the embodiment of the present invention;
FIG. 3 is a graph showing demodulation before the moving average algorithm and the L-M algorithm are applied according to the present invention;
FIG. 4 is a graph of demodulation after the moving average algorithm and the L-M algorithm are used according to the embodiment of the present invention;
FIG. 5 is a schematic diagram of a line width detection apparatus for a narrow line width laser according to an embodiment of the present invention;
fig. 6 is a flowchart of a method for detecting a line width of a narrow-line-width laser according to an embodiment of the present invention.
Detailed Description
The invention is further described below with reference to the accompanying drawings. The following examples are only for illustrating the technical solutions of the present invention more clearly, and the protection scope of the present invention is not limited thereby.
Example 1
As shown in fig. 6, the present embodiment introduces a method for detecting a line width of a narrow-line-width laser, including:
acquiring data information acquired by a data acquisition card in advance;
preprocessing the data information by adopting an accumulative average algorithm to obtain preprocessed time domain data information;
performing fast Fourier transform on the preprocessed time domain data information, and converting the time domain data information into frequency domain data information;
processing the frequency domain data information by adopting a moving average algorithm to obtain moving average data;
fitting the data subjected to the moving average by using an L-M algorithm to obtain fitted data;
and detecting the line width of the fitted data by a delay self-heterodyne method, and calculating the line width data of the laser.
The application process of the method for detecting the line width of the narrow-line-width laser device provided by the embodiment specifically relates to the following steps:
the method comprises the following steps: after system equipment is built, a line width measurement experiment is carried out on the laser, and a data acquisition module adopts a PICO (peripheral image sensor input) for acquisition;
in this example, the parameter settings of the data acquisition card include the sampling interval: 800ps, sampling rate: 1.25GS/s, window function: haiming;
step two: accumulating and averaging data information acquired by a data acquisition card, and performing signal preprocessing;
further: accumulating and averaging the collected data information, and performing signal preprocessing, wherein the signal preprocessing comprises the following steps:
the laser instrument can send laser in a period of time in succession, causes collection module to carry out signal acquisition constantly, before carrying out data processing, can adopt the average algorithm that adds up to do signal preprocessing, can filter most noise on the one hand, and on the other hand can effectively improve the data information after the demodulation for narrowband laser instrument linewidth measurement is more accurate. Although the accumulation average algorithm can continuously filter noise and improve the signal-to-noise ratio of a signal according to the increase of the accumulation times, when the accumulation times reach a certain degree, the signal-to-noise ratio is slowly improved, so that the selection of the accumulation times needs to be selected according to actual conditions. In this example, 100 sets of data were collected for cumulative averaging;
step three; performing Fast Fourier Transform (FFT) on the preprocessed time domain data, and converting time domain information into frequency domain information;
in this example, the FFT parameters include the number of samples: 1048576, sampling frequency: 1.25GHz;
step four: processing the frequency domain signal by adopting a moving average algorithm, and filtering noise as far as possible to obtain a smooth curve;
further, a moving average algorithm and a sliding window algorithm are applied to the frequency domain signal, as shown in fig. 1;
the moving average method is also called as a moving average filtering method, and the main idea is to take the arithmetic mean of the sampling points near the point as the smooth value of the point, and the algorithm can effectively filter the noise. In this example, the arithmetic mean of 7 points near the point will be calculated, and sliding will be performed in sequence to obtain a smooth curve;
step five: fitting the data after the moving average by using an L-M algorithm, wherein the iteration times are as follows: 10000. initial damping value: 0.01, the flow chart is shown in FIG. 2;
the L-M algorithm introduces a damping factor in the Gauss-Newton method, eliminates the limitation that the initial value of the parameter to be estimated is difficult to select, and simultaneously keeps the advantage of extracting the optimal solution. The core of the LM method working mechanism is that an iterative formula is obtained through linearization in a small range near each measured data, and the optimal solution of the parameter to be estimated can be obtained step by step through iterative operation.
Step six: detecting the line width according to a time delay self-heterodyne method, and calculating line width data of the laser; as shown in fig. 3 and 4;
the delay self-heterodyne method uses a modulation circuit or a power supply to make two beams of light passing through a coupler generate a certain frequency difference (the AOM is used by the device to generate an upward frequency of 200MHz, so the center frequency of the laser is 200 MHz), and the center frequency of an optical signal generated when the second coupler interferes with beat frequency is not near zero frequency, so that the anti-interference capability of the system to the surrounding environment is enhanced, the measurement accuracy is improved, and the system error is reduced. When the line width is detected by using a time delay self-heterodyne method, a Lorentz line type frequency spectrum is obtained on a frequency spectrograph, and the full width at half maximum of the frequency spectrum is the line width of the laser to be detected. In actual operation, the-20 dB linewidth of the lorentz curve is typically read and then calculated to obtain the actual linewidth of the laser. The line width relationship is shown in table 1.
Wherein, the delta nu is the line width of the laser;
before the sliding average algorithm and the L-M algorithm are adopted, the demodulated curve is not smooth enough, the line width data of the laser cannot be accurately calculated, after the sliding average algorithm is adopted, the curve becomes smoother obviously, the line width data is obtained according to a delay self-heterodyne line width calculation formula, the line width of the laser is 14.63kHz, the difference between the line width data and the standard line width 15kHz is small, and the reliability of the scheme is verified.
Example 2
As shown in fig. 5, the present embodiment provides a device for detecting a line width of a narrow line width laser, including a narrow line width laser 1 to be detected, 50:50 fiber coupler 2, delay fiber 3, fiber polarization scrambler 4, erbium-doped fiber amplifier (EDFA) 5, acousto-optic modulator 6, 50:50 an optical fiber coupler 7, an optical fiber filter 8, a photoelectric detector 9 and a data acquisition card 10. Narrow linewidth lasers 1 and 50 to be tested: 50 input ends of the optical fiber couplers 2 are connected, and 50: the laser output by the 50 optical fiber coupler is divided into two paths, wherein one path is connected with the input end of the delay optical fiber 3, and the other path is connected with the output end of the 50 optical fiber coupler through the acousto-optic modulator 6: 50, the input end of an optical fiber coupler 7 is connected, the optical fiber polarization scrambler 4 is connected with the other input end of the delay optical fiber 3, the laser output by the optical fiber polarization scrambler is connected with the input end of an optical fiber erbium-doped optical fiber amplifier 5, and the output end of the optical fiber erbium-doped optical fiber amplifier 5 is connected with a frequency converter 50:50, the input end of the optical fiber coupler 7 is connected, and the ratio of 50:50 the output end of the optical fiber coupler 7 is connected with the input end of the optical fiber filter 8, the output end of the optical fiber filter 8 is connected with the input end of the photoelectric detector 9, and the photoelectric detector 9 carries out coherent processing on the light input by the optical fiber filter 8 and then inputs the light into the data acquisition card 10.
The fiber erbium-doped fiber amplifier 5 and the fiber erbium-doped fiber amplifier 11 are fiber erbium-doped fiber amplifiers with maximum signal gain of 47dB and saturation output power of 17 dBm.
The photoelectric detector 9 is a photoelectric detector with a 3dB detection bandwidth larger than 22GHz, a wavelength of 1550nm and maximum output power of 10 mW.
The data acquisition card 10 is a PICO6000 series 8424E.
The above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, several modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.
Claims (10)
1. A detection method of a detection device for a narrow linewidth laser linewidth is characterized by comprising the following steps:
acquiring data information acquired by a data acquisition card in advance;
performing signal preprocessing on the data information by adopting an accumulative average algorithm to obtain preprocessed time domain data information;
performing fast Fourier transform on the preprocessed time domain data information, and converting the time domain data information into frequency domain data information;
processing the frequency domain data information by adopting a moving average algorithm to obtain moving average data;
fitting the data subjected to the moving average by using an L-M algorithm to obtain fitted data;
and detecting the line width of the fitted data by a delay self-heterodyne method, and calculating the line width data of the laser.
2. The detection method of the detection device of the line width of the narrow line width laser according to claim 1, characterized in that: and the data acquisition card adopts a PICO acquisition card for acquisition.
3. The detection method of the detection device of the narrow linewidth laser linewidth according to claim 1, characterized in that: the parameter setting of the data acquisition card comprises sampling interval, sampling rate and window function.
4. The detection method of the detection device of the narrow linewidth laser linewidth according to claim 1, characterized in that: performing signal preprocessing on the data information by adopting an accumulation average algorithm, wherein the signal preprocessing comprises the following steps of:
filtering the data information through an accumulation average algorithm; and continuously filtering the noise according to the increase of the accumulation times, wherein the selection of the accumulation times is selected in response to the manual selection signal.
5. The detection method of the detection device of the narrow linewidth laser linewidth according to claim 1, characterized in that: the parameter setting of the fast Fourier transform comprises the number of sampling points and the sampling frequency.
6. The detection method of the detection device of the narrow linewidth laser linewidth according to claim 1, characterized in that: the method for detecting the line width of the fitted data by a time delay self-heterodyne method and calculating the line width data of the laser comprises the following steps:
and inputting the fitted data into a computer, and obtaining a Lorentz line type frequency spectrum on the computer by using a delay self-heterodyne method, wherein the full width at half maximum of the Lorentz line type frequency spectrum is the line width of the measured laser.
7. A narrow linewidth laser linewidth detection device, comprising: the device comprises a narrow-linewidth laser to be detected, an optical fiber coupler, a delay optical fiber, an optical fiber polarization scrambler, an erbium-doped optical fiber amplifier, an acoustic-optical modulator, an optical fiber coupler, an optical fiber filter, a photoelectric detector and a data acquisition card; the narrow linewidth laser to be detected is connected with the input end of an optical fiber coupler, the laser output by the optical fiber coupler is divided into two paths, wherein one path is connected with the input end of a delay optical fiber, the other path is connected with the input end of the optical fiber coupler through an acousto-optic modulator, an optical fiber polarization scrambler is connected with the other input end of the delay optical fiber, the laser output by the optical fiber polarization scrambler is connected with the input end of an optical fiber erbium-doped optical fiber amplifier, the output end of the optical fiber erbium-doped optical fiber amplifier is connected with the input end of the optical fiber coupler, the output end of the optical fiber coupler is connected with the input end of an optical fiber filter, the output end of the optical fiber filter is connected with the input end of a photoelectric detector, and the photoelectric detector performs coherent processing on the light input by the optical fiber filter and then inputs the light into a data acquisition card.
8. A detection device for a line width of a narrow line width laser, comprising:
the acquisition unit is used for acquiring data information acquired by a data acquisition card in advance;
the preprocessing unit is used for preprocessing the data information by adopting an accumulative average algorithm to obtain preprocessed time domain data information;
the conversion unit is used for carrying out fast Fourier transform on the preprocessed time domain data information and converting the time domain data information into frequency domain data information;
the processing unit is used for processing the frequency domain data information by adopting a moving average algorithm to obtain moving average data;
the fitting unit is used for fitting the data subjected to the moving average by using an L-M algorithm to obtain the fitted data;
and the calculating unit is used for detecting the line width of the fitted data by a time delay self-heterodyne method and calculating the line width data of the laser.
9. The utility model provides a detection device of narrow linewidth laser instrument linewidth which characterized in that: comprising a processor and a storage medium;
the storage medium is used for storing instructions;
the processor is configured to operate in accordance with the instructions to perform the steps of the method according to any one of claims 1 to 6.
10. A computer-readable storage medium having stored thereon a computer program, characterized in that: the program when executed by a processor implements the steps of the method of any one of claims 1 to 6.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117073990A (en) * | 2023-10-16 | 2023-11-17 | 常州灵动芯光科技有限公司 | Linewidth testing system and method for narrow linewidth laser |
| CN117367751A (en) * | 2023-10-19 | 2024-01-09 | 中聚科技股份有限公司 | Performance detection method and device for ultra-pulse thulium-doped laser |
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117073990A (en) * | 2023-10-16 | 2023-11-17 | 常州灵动芯光科技有限公司 | Linewidth testing system and method for narrow linewidth laser |
| CN117073990B (en) * | 2023-10-16 | 2024-01-26 | 常州灵动芯光科技有限公司 | Linewidth testing system and method for narrow linewidth laser |
| CN117367751A (en) * | 2023-10-19 | 2024-01-09 | 中聚科技股份有限公司 | Performance detection method and device for ultra-pulse thulium-doped laser |
| CN117367751B (en) * | 2023-10-19 | 2024-05-10 | 中聚科技股份有限公司 | Performance detection method and device for ultra-pulse thulium-doped laser |
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