Laser linewidth measurement method and device based on digital decoherence

Abstract

The invention provides a laser linewidth measurement method and device based on digital decoherence, and is suitable for the technical field of laser linewidth analysis, and the method comprises the steps: dividing a to-be-measured laser source into first delay light and first reference light; performing digital de-coherence at least based on the first delay light and the first reference light to determine the frequency noise power spectral density of a to-be-measured laser corresponding to the to-be-measured laser source; and determining the laser line width of the to-be-measured laser according to the frequency noise power spectral density. The frequency noise power spectral density used for determining the laser line width is determined through digital decoherence, it is not required that the to-be-measured laser source and the auxiliary laser source have the same center wavelength, a complex physical optical fiber link is not needed so that introduction of a large amount of environmental noise can be avoided, and the flexibility, universality and precision of laser line width measurement can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of laser linewidth analysis, and particularly relates to a method and device for measuring laser linewidth based on digital decoherence. Background Art

[0002] The phase noise and linewidth of a laser are key parameters for measuring the frequency stability and phase noise characteristics of a laser, and are of great significance for high-precision laser measurement, optical communication, quantum technology and other fields. The traditional measurement methods for the phase noise and linewidth of a laser mainly include the beat frequency method and the delayed self-heterodyne method, etc.

[0003] However, when measuring a laser using the beat frequency method, it is necessary to use another one or more reference lasers, and it is required that the reference laser and the laser to be measured have the same central wavelength, which will result in poor flexibility and universality in measuring the laser linewidth by the beat frequency method.

[0004] When measuring a laser using the delayed self-heterodyne method, a large amount of environmental noise will be introduced by the optical fiber link used in the delay process, thus affecting the measurement accuracy of the laser linewidth. Summary of the Invention

[0005] In view of this, embodiments of the present invention provide a method and device for measuring laser linewidth based on digital decoherence to solve the problems of poor flexibility, poor universality and poor measurement accuracy existing in the traditional measurement methods of existing laser linewidth.

[0006] To achieve the above object, embodiments of the present invention provide the following technical solutions:

[0007] A first aspect of an embodiment of the present invention discloses a method for measuring laser linewidth based on digital decoherence, the method comprising:

[0008] Dividing a laser source to be measured into a first delayed light and a first reference light;

[0009] Performing digital decoherence at least based on the first delayed light and the first reference light to determine the frequency noise power spectral density of a laser to be measured corresponding to the laser source to be measured;

[0010] Determining the laser linewidth of the laser to be measured according to the frequency noise power spectral density.

[0011] Preferably, performing digital decoherence at least based on the first delayed light and the first reference light to determine the frequency noise power spectral density of a laser to be measured corresponding to the laser source to be measured, comprising:

[0012] Dividing an auxiliary laser source into a second delayed light and a second reference light;

[0013] Demodulate the first phase difference data of the laser source to be measured and the second phase difference data of the auxiliary laser source by using the first delay time, the first reference light, the second delay time, and the second reference light;

[0014] Based on the first phase difference data and the second phase difference data, eliminate the noise in the optical fiber link to obtain the third phase difference data;

[0015] Perform digital decoherence on the first phase difference data to obtain the fourth phase difference data, and perform digital decoherence on the third phase difference data to obtain the fifth phase difference data;

[0016] Use the fourth phase difference data and the fifth phase difference data to determine the frequency noise power spectrum density of the laser to be measured corresponding to the laser source to be measured.

[0017] Preferably, perform digital decoherence at least based on the first delay time and the first reference light to determine the frequency noise power spectrum density of the laser to be measured corresponding to the laser source to be measured, including:

[0018] Use the first delay time and the first reference light to demodulate the first phase difference data of the laser source to be measured;

[0019] Perform digital decoherence on the first phase difference data to obtain the fourth phase difference data;

[0020] Based on the fourth phase difference data, determine the frequency noise power spectrum density of the laser to be measured corresponding to the laser source to be measured.

[0021] Preferably, use the first delay time, the first reference light, the second delay time, and the second reference light to demodulate the first phase difference data of the laser source to be measured and the second phase difference data of the auxiliary laser source, including:

[0022] Summarize and transmit the first delay time and the second delay time to a delay optical fiber link and perform frequency shift to obtain a third delay time;

[0023] Summarize the third delay time and the first reference light and perform interference measurement to obtain a first interference signal, and summarize the third delay time and the second reference light and perform interference measurement to obtain a second interference signal;

[0024] Demodulate the first interference signal to obtain the first phase difference data, and demodulate the second interference signal to obtain the second phase difference data.

[0025] Preferably, use the first delay time and the first reference light to demodulate the first phase difference data of the laser source to be measured, including:

[0026] Transmit the first delayed light into a delay optical fiber link and perform frequency shifting to obtain a fourth delayed light;

[0027] Summarize the fourth delayed light and the first reference light and perform interference measurement through a photodetector to obtain a third interference signal;

[0028] Demodulate the third interference signal to obtain first phase difference data.

[0029] Preferably, perform digital decoherence on the first phase difference data to obtain fourth phase difference data, including:

[0030] Delay the first phase difference data by a specified time delay to form new phase difference data;

[0031] Compare the new phase difference data with the first phase difference data to obtain output phase difference data with 2 times the specified time delay;

[0032] Delay the new phase difference data by the specified time delay to update the new phase difference data;

[0033] Compare the updated new phase difference data with the output phase difference data with (i - 1) times the specified time delay to obtain output phase difference data with i times the specified time delay, where the initial value of i is 3;

[0034] Increase i by 1, return to execute the step of delaying the new phase difference data by the specified time delay to update the updated new phase difference data again until i is greater than m to obtain fourth phase difference data;

[0035] Wherein, the fourth phase difference data is: the output phase difference data with m times the specified time delay.

[0036] Preferably, use the fourth phase difference data and the fifth phase difference data to determine the frequency noise power spectral density of the laser to be measured corresponding to the laser source to be measured, including:

[0037] Calculate the cross power spectrum of the fourth phase difference data and the fifth phase difference data multiple times;

[0038] Average the cross power spectra obtained by multiple calculations to obtain the phase noise power spectral density of the laser to be measured corresponding to the laser source to be measured;

[0039] Use the phase noise power spectral density to determine the frequency noise power spectral density of the laser to be measured.

[0040] Preferably, determining the frequency noise power spectral density of the laser under test corresponding to the laser source to be tested based on the fourth phase difference data includes:

[0041] Performing a Fourier transform on the fourth phase difference data to obtain the phase noise power spectral density of the laser under test corresponding to the laser source to be tested;

[0042] Using the phase noise power spectral density to determine the frequency noise power spectral density of the laser under test.

[0043] Preferably, determining the laser linewidth of the laser under test according to the frequency noise power spectral density includes:

[0044] Performing a weighted integration on the frequency noise power spectral density using the β-line method, the direct integration method, or the piecewise integration method to determine the laser linewidth of the laser under test.

[0045] A second aspect of the embodiments of the present invention discloses a laser linewidth measurement device based on digital decoherence. The device includes:

[0046] A processing module for dividing the laser source to be tested into a first delayed light and a first reference light;

[0047] A decoherence module for performing digital decoherence based at least on the first delayed light and the first reference light to determine the frequency noise power spectral density of the laser under test corresponding to the laser source to be tested;

[0048] A determination module for determining the laser linewidth of the laser under test according to the frequency noise power spectral density.

[0049] Based on the above-mentioned laser linewidth measurement method and device provided by the embodiments of the present invention, the method is: dividing the laser source to be tested into a first delayed light and a first reference light; performing digital decoherence based at least on the first delayed light and the first reference light to determine the frequency noise power spectral density of the laser under test corresponding to the laser source to be tested; determining the laser linewidth of the laser under test according to the frequency noise power spectral density. By using digital decoherence to determine the frequency noise power spectral density for determining the laser linewidth, it is not required that the laser source to be tested and the auxiliary laser source have the same central wavelength, nor is it necessary to have a complex physical optical fiber link to avoid introducing a large amount of environmental noise, thereby improving the flexibility, universality, and accuracy of laser linewidth measurement. Description of the Drawings

[0050] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can also be obtained based on the provided drawings.

[0051] Figure 1 It is a schematic diagram of the principle architecture for obtaining the power spectral density based on digital decoherence provided by the embodiments of the present invention;

[0052] Figure 2 It is a flowchart of a method for measuring the laser linewidth based on digital decoherence provided by the embodiments of the present invention;

[0053] Figure 3 It is a flowchart of the first method for obtaining the frequency noise power spectral density provided by the embodiments of the present invention;

[0054] Figure 4 It is a flowchart of the second method for obtaining the frequency noise power spectral density provided by the embodiments of the present invention;

[0055] Figure 5 It is a flowchart of performing digital decoherence on the first phase difference data to obtain the fourth phase difference data provided by the embodiments of the present invention;

[0056] Figure 6 It is a schematic diagram of the structure of the hybrid triangular cap system provided by the embodiments of the present invention;

[0057] Figure 7 It is a block diagram of the structure of a laser linewidth measuring device based on digital decoherence provided by the embodiments of the present invention. Detailed implementation manners

[0058] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0059] In this application, the terms "comprising", "including" or any other variant thereof are intended to cover non-exclusive inclusion, such that a process, method, article or apparatus comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or apparatus. Without further limitation, an element qualified by the statement "comprising an..." does not exclude the presence of additional identical elements in the process, method, article or apparatus comprising the element.

[0060] The phase noise and linewidth of a laser are key parameters for measuring the frequency stability and phase noise characteristics of a laser, and are of great significance for high-precision laser measurement, optical communication, quantum technology and other fields. Phase noise refers to the fluctuation of the laser output phase, which is usually characterized by the power spectral density (including phase noise power spectral density and frequency noise power spectral density) in the frequency domain. Phase noise reflects the short-term random changes in the phase and frequency of the laser.

[0061] The linewidth is a parameter that describes the spectral width of the laser output. It is closely related to the phase noise of the laser. A laser with a narrow linewidth can provide higher frequency stability. High-precision measurement of phase noise and linewidth is crucial for the quality assessment of laser sources, especially in optical frequency atomic clocks, lidar and precision instruments.

[0062] The traditional measurement methods for the phase noise and linewidth of a laser mainly include direct spectrum analysis method, beat frequency method, delay self-heterodyne method, etc. The following will first briefly describe these traditional measurement methods.

[0063] The direct spectrum analysis method measures the linewidth by directly detecting the spectrum of the laser output signal. Specifically, the laser signal output by the laser is sent into a spectrum analyzer, which can display the frequency distribution of the laser signal. The linewidth refers to the width of the power distribution in the spectrum, usually expressed by the half-power point width (i.e., 3dB bandwidth) of the laser frequency. The direct spectrum analysis method can obtain the spectral morphology of the laser and is usually used to evaluate laser sources with relatively wide linewidths.

[0064] For the evaluation of narrow linewidth laser sources, it is generally achieved by the beat frequency method. Specifically, the laser to be measured is interferometrically measured with a reference laser that has a similar central wavelength and a consistent or more stable noise level, so as to obtain phase difference data or frequency offset. The principle is that two laser signals with similar central wavelengths will produce a low-frequency beat frequency signal after interference, and the frequency of this low-frequency beat frequency signal is equal to the difference between their frequencies. By detecting and analyzing the phase fluctuations of the beat frequency signal, the phase noise of the laser to be measured can be obtained, and further the linewidth of the laser to be measured can be obtained. When the reference laser is at the same level as the laser to be measured, the phase noise spectrum of the beat frequency signal is twice that of the phase noise spectrum of the laser to be measured; when the reference laser is better than the laser to be measured, the phase noise spectrum of the beat frequency signal is the phase noise spectrum of the laser to be measured. The beat frequency method has a relatively simple structure and is suitable for measuring lasers with extremely narrow linewidths.

[0065] The delayed self-heterodyne method is another commonly used method for measuring the laser phase noise spectrum. Its principle is similar to the beat frequency method, but it does not require an additional auxiliary laser source. In the delayed self-heterodyne method, the laser signal is split into two beams by an optical coupler. One of the beams is delayed by an optical fiber link beyond the coherence length and can be regarded as another reference light source that is incoherent with the original laser source. The delayed light and the non-delayed light interfere to produce a beat frequency signal. By detecting and analyzing the phase fluctuations of the beat frequency signal, the phase noise of the laser to be measured can be obtained, and further the linewidth of the laser to be measured can be obtained. At this time, the reference laser is at the same level as the laser to be measured, and the phase noise spectrum of the beat frequency signal is twice that of the phase noise spectrum of the laser to be measured. The delayed self-heterodyne method does not require an auxiliary laser source, reducing the complexity of the system, and is widely used in the evaluation of laser sources with linewidths of kHz and above.

[0066] The inventors have found through research that there are some limitations in the direct spectrum analysis method when measuring narrow linewidth lasers. Due to the limited frequency resolution of the spectrum analyzer, especially for lasers with very small frequency fluctuations, the limited resolution may not be sufficient to accurately measure the laser linewidth. Therefore, for narrow linewidth lasers, the beat frequency method or the delayed self-heterodyne method is generally used.

[0067] When using the beat frequency method to measure a laser, it often requires one or more additional reference lasers. In order to achieve the interferometric measurement between the reference laser and the laser to be measured, it is often required that the reference laser and the laser to be measured have the same central wavelength, and the linewidth of the reference laser is comparable to or better than that of the laser to be measured. In addition, due to the frequency drift of the laser itself, it is often difficult to perform long-term interferometric measurements with the beat frequency method. These factors limit the application of the beat frequency method in the evaluation of narrow linewidth lasers.

[0068] The delayed self-heterodyne method uses the delayed light of the laser itself as the reference light source, without the limitations of the beat frequency method. However, when measuring a laser with a linewidth on the order of Hz, the theoretical length of the delay fiber needs to reach 200,000 kilometers, which poses a huge challenge to the implementation of the physical system. In addition, during the delay process, a large amount of environmental noise will be introduced by the fiber optic link used, which limits the measurement accuracy of the delayed self-heterodyne method.

[0069] Generally speaking, the problems in the traditional measurement methods of laser phase noise and linewidth can be mainly divided into two categories. One category of problems is the excessive requirements for the reference source (beat frequency method), which makes the flexibility and universality of the measurement method poor; the other category of problems is that the physical system is complex, the measurement accuracy is insufficient, and it is vulnerable to noise interference (delayed self-heterodyne method), which makes the measurement method inapplicable to lasers with narrow linewidths on the order of Hz.

[0070] To solve the above problems, the embodiments of the present invention propose a method and device for measuring laser linewidth based on digital decoherence. By digital decoherence, the frequency noise power spectral density for determining the laser linewidth is obtained. It does not require the center wavelengths of the laser source to be measured and the auxiliary laser source to be the same, nor does it require a complex physical fiber optic link to avoid introducing a large amount of environmental noise, thereby improving the flexibility, universality, and accuracy of laser linewidth measurement.

[0071] That is to say, this solution does not require a reference laser with the same linewidth level and center wavelength as the laser source to be measured, nor does it require a complex physical system composed of an ultra-long fiber optic link, and it can measure the laser linewidth for a long time, improving the flexibility, universality, and accuracy of laser linewidth measurement.

[0072] It should be noted that the basic idea of the digital decoherence adopted in this solution is: using digital delay to replace the physical time delay of the fiber optic link, based on the delayed self-heterodyne detection of a short fiber optic link, using signal processing means to achieve the multiplication of the physical time delay, and finally obtaining the comparison measurement information of two incoherent light sources.

[0073] In the traditional measurement of the delayed self-heterodyne method, a fiber optic link longer than the coherence length of the laser source is required to make the delayed light and the reference light incoherent. Therefore, in theory, an evaluation of a laser source on the order of Hz requires a fiber optic link of more than 200,000 kilometers, which not only makes the physical system impossible to implement, but also introduces a large amount of environmental noise. The digital decoherence adopted in this solution can, on the basis of a short delay fiber optic, achieve the multiplication of the physical delay through digital delay.

[0074] To better understand the main content of this solution later, the basic principle of the digital decoherence adopted in this solution is briefly introduced here (taking the laser source to be measured as an example):

[0075] It should be noted that the laser source to be measured is divided into delayed light and reference light.

[0076] Step 1: Perform time-delay self-heterodyne interference measurement on the laser source to be measured, and set the time delay of the optical fiber link to (i.e., the specified time delay mentioned later, which is less than the coherence time of the laser source to be measured). Specifically, by using a short-time-delay self-heterodyne interference system, the interference signal of the delayed light and the reference light can be measured at the photodetector. After the interference measurement result (i.e., the measured interference signal) passes through radio frequency devices such as a low-noise radio frequency power amplifier (abbreviated as low-noise amplifier) and a filter, IQ demodulation can be performed to output the initial phase difference data between the delayed light and the reference light , where IQ represents in-phase and quadrature, and the specific content of the initial phase difference data is shown in formula (1).

[0077] (1);

[0078] In formula (1), is the fluctuation of the laser source phase with time, that is, the fluctuation of the reference light phase with time; t is the independent variable representing time; is the fluctuation of the delayed light phase with time. Compared with the reference light, the delayed light has a time delay of.

[0079] Step 2: Delay the obtained initial phase difference data by the specified time delay (i.e., delay ) to form new phase difference data ; Compare the new phase difference data with the initial phase difference data (the comparison process can be simply referred to as comparison measurement), and output the output phase difference data corresponding to the time delay of , that is, the output phase difference data has a 2-fold specified time delay.

[0080] It should be noted that from the content of the initial phase difference data and the new phase difference data formed in Step 2, and have the same part of " ". Therefore, comparing and can eliminate the phase noise , so as to output the output phase difference data corresponding to the time delay of . The specific content of the output phase difference data is shown in the following formula (2).

[0081] (2);

[0082] Step 3: Repeat the operation of the above Step 2 for each step after Step 3 until Step m.

[0083] For example, i represents the serial number of the step. At the i-th step, the phase difference data (at the 3rd step, i.e., i = 3, this item is ) the time delay specifies the time delay (i.e., the time delay ), forming new phase difference data (at the 3rd step, i.e., i = 3, this item is );

[0084] It should be noted that the output phase difference data obtained at the (i - 1)-th step (i.e., the previous step) is (at i = 3, this item is ).

[0085] Compare the new phase difference data with the output phase difference data obtained at the (i - 1)-th step , and it can be seen that and have the same part " ", so the phase noise can be eliminated, thereby outputting the output phase difference data corresponding to the time delay , and the specific content of the output phase difference data corresponding to the time delay and corresponding to the time delay is shown in the following formula (3). (3);

[0086] (3);

[0087] The above steps can accurately multiply the physical delay caused by the short optical fiber link through the digital system. By executing the above steps until the m-th step (until the i = m-th step is executed), the delay of the output phase difference data output extends from to .

[0088] It should be noted that the coherence time of the laser is determined by the nature of the laser source itself. If is greater than the coherence time of the laser source to be measured, digital decoherence can be achieved, that is, the ratio measurement result of the laser source to be measured itself ( ) and another beam of light obtained by delaying it beyond the coherence time ( ) can be obtained.

[0089] For example: When the laser source to be measured is a Hz-level laser, then >Digital decoherence can be achieved in >1 s; when the laser source to be measured is a sub-Hz laser, >10 s is sufficient to achieve digital decoherence. >10 s is sufficient to achieve digital decoherence.

[0090] Furthermore, performing a Fourier transform (FFT) on the obtained output phase difference data yields the power spectral density of the phase difference data (including the phase noise power spectral density and the frequency noise power spectral density). The specific content of the power spectral density of the phase difference data is shown in Equation (4).

[0091] (4);

[0092] In Equation (4), is the power spectral density of the phase difference data, with the independent variable being the frequency f, is the phase noise power spectral density of the reference light, is the time delay of the phase noise power spectral density of the delayed light, is the cross power spectrum of the reference light and the delayed light.

[0093] Since the reference light and the delayed light are from the same laser source and satisfy , where is the phase noise power spectral density of the laser source to be measured. Since the delay time exceeds the coherence time of the laser source to be measured, the reference light and the delayed light are incoherent at this time, that is, the cross power spectrum is randomly fluctuating and can be ignored during long-term measurements. Therefore, .

[0094] Based on the obtained power spectral density of the phase difference data, the phase noise power spectral density of the laser source to be measured can be solved. Furthermore, based on the frequency noise power spectral density of the laser source to be measured can be obtained , and the laser linewidth can be calculated according to the β-line method.

[0095] In practical applications, since the amount of data of the power spectral density in the full frequency domain is large, the Fourier transform is generally performed in segments by filtering and downsampling, so as to obtain the power spectral density in the high-frequency band, the middle-frequency band, and the low-frequency band respectively.

[0096] Generally speaking, the principle of obtaining the power spectral density based on digital decoherence is as Figure 1 shown, Figure 1 in which the "delayed self-heterodyne interference signal" is the interference signal of the delayed light and the reference light, the "short-delay phase difference data 0-1" is the initial phase difference data , and the "short-delay phase difference data 1-2" is the new phase difference data obtained after the time delay , "Short-delay phase difference data 2-3" is Time delay The newly obtained phase difference data , and so on.

[0097] Figure 1 In , "Long-delay phase difference data 0-2" is the output phase difference data , "Long-delay phase difference data 0-3" is the output phase difference data , and so on; the Fourier transform is performed in segments by filtering and downsampling to obtain the power spectral density in the high-frequency band, medium-frequency band, and low-frequency band respectively.

[0098] The above is an explanation of the principle of obtaining the power spectral density based on digital decoherence.

[0099] It should be noted that the fluctuation of the laser output frequency, i.e., the frequency noise of the laser source, and its frequency domain is the frequency noise power spectral density. The phase noise and frequency noise of the laser source can be obtained according to different measurement methods and can be converted into each other.

[0100] This solution measures the laser linewidth based on the "principle of obtaining the power spectral density based on digital decoherence" given above. See Figure 2 , which shows the flowchart of a laser linewidth measurement method based on digital decoherence provided by an embodiment of the present invention. Figure 2 It includes the following steps:

[0101] Step S201: Divide the laser source to be measured into a first delay light and a first reference light.

[0102] In the specific implementation of step S201, the laser source to be measured is divided into two paths, one path is the delay light, and the other path is the reference light. Among them, the delay light and the reference light separated from the laser source to be measured are called the first delay light and the first reference light.

[0103] Step S202: Perform digital decoherence based on at least the first delay light and the first reference light to determine the frequency noise power spectral density of the laser to be measured corresponding to the laser source to be measured.

[0104] In the specific implementation of step S202, digital decoherence is performed based on at least the first delay light and the first reference light to determine the frequency noise power spectral density of the laser to be measured corresponding to the laser source to be measured.

[0105] It should be noted that this solution provides two ways to obtain the frequency noise power spectral density, which are respectively called "the first way to obtain the frequency noise power spectral density" and "the second way to obtain the frequency noise power spectral density".

[0106] The "first method for obtaining the frequency noise power spectral density" requires starting an auxiliary laser source (which can also be called a reference laser source), while the "second method for obtaining the frequency noise power spectral density" does not require enabling the auxiliary laser source.

[0107] In practical applications, the "first method for obtaining the frequency noise power spectral density" or the "second method for obtaining the frequency noise power spectral density" can be selected according to the actual situation.

[0108] For example: when measuring a laser under test with a noise level better than the test environment, start the auxiliary laser source and use the "first method for obtaining the frequency noise power spectral density" to determine the frequency noise power spectral density of the laser under test.

[0109] Another example: when measuring a laser under test with a noise level worse than the test environment, do not start the auxiliary laser source and use the "second method for obtaining the frequency noise power spectral density" to determine the frequency noise power spectral density of the laser under test.

[0110] For the implementation process of the above "first method for obtaining the frequency noise power spectral density", it will be described in detail in the subsequent Figure 3 illustrated embodiments.

[0111] For the implementation process of the above "second method for obtaining the frequency noise power spectral density", it will be described in detail in the subsequent Figure 4 illustrated embodiments.

[0112] Step S203: Determine the laser linewidth of the laser under test according to the frequency noise power spectral density.

[0113] In the specific process of implementing step S203, after obtaining the frequency noise power spectral density of the laser under test, the β-line method, direct integration method, or piecewise integration method is used to perform weighted integration on the frequency noise power spectral density to determine the laser linewidth of the laser under test.

[0114] Specifically, weighted integration is performed on the frequency noise power spectral density of the laser under test to determine the laser linewidth of the laser under test. The weighted integration method can be the β-line method, direct integration method, piecewise integration method, etc.

[0115] In the embodiments of the present invention, digital decoherence is used to determine the frequency noise power spectral density for determining the laser linewidth, which does not require the center wavelengths of the laser under test and the auxiliary laser source to be the same, nor does it require a complex physical optical fiber link to avoid introducing a large amount of environmental noise, improving the flexibility, universality, and accuracy of laser linewidth measurement.

[0116] Regarding the above embodiments of the present invention Figure 2For the “first method for obtaining the frequency noise power spectrum density” involved in step S202, see Figure 3 , which shows a flow chart of a first method for obtaining frequency noise power spectrum density provided by an embodiment of the present invention, Figure 3 The steps include:

[0117] Step S301: dividing the auxiliary laser source into a second delay light and a second reference light.

[0118] In the process of implementing step S301, when measuring a laser to be tested whose noise level is better than that of the test environment, the auxiliary laser source is started and the auxiliary laser source is divided into two paths, one for delay light and the other for reference light, wherein the delay light and reference light separated by the auxiliary laser source are called second delay light and second reference light.

[0119] Step S302: using the first delayed light, the first reference light, the second delayed light and the second reference light, demodulate to obtain first phase difference data of the laser source to be measured and second phase difference data of the auxiliary laser source.

[0120] In the specific implementation of step S302, the first delayed light and the second delayed light are collectively transmitted to the delay optical fiber link and frequency-shifted to obtain the third delayed light.

[0121] The third delayed light and the first reference light are combined and interferometrically measured to obtain a first interference signal, and the third delayed light and the second reference light are combined and interferometrically measured to obtain a second interference signal.

[0122] The first interference signal is demodulated to obtain first phase difference data, and the second interference signal is demodulated to obtain second phase difference data.

[0123] Specifically, the first delayed light of the laser source to be measured and the second delayed light of the auxiliary laser source are aggregated together through a fiber coupler and transmitted to a delayed fiber link, and then frequency-shifted by an acousto-optic modulator to obtain a third delayed light.

[0124] The third delayed light is divided into two beams, which are respectively combined with the first reference light and the second reference light, and then interferometrically measured at the photodetector after passing through an optical filter. The power of the interference signal obtained by the interferometric measurement is amplified by a low-noise amplifier, and the excess noise is filtered out by a filter. Finally, a high-speed data acquisition card is used to acquire the first interference signal and the second interference signal.

[0125] The first interference signal and the second interference signal collected are respectively subjected to digital IQ demodulation to obtain the first phase difference data and the second phase difference data.

[0126] It should be noted that there is a deviation in the frequencies of the delayed light and the reference light (such as the third delayed light and the first reference light) participating in the interference. The function of the acousto-optic modulator is to shift the frequency of the light, which will cause a deviation in the frequencies of the delayed light and the reference light. The subsequent interference process on the photodetector is called heterodyne interference.

[0127] In some embodiments, the obtained first phase difference data and second phase difference data have a specified time delay (that is, they have ), and in the case of adopting "the first method of obtaining the frequency noise power spectral density", the specific content of the first phase difference data (denoted as at this time) is shown in formula (5), and the specific content of the second phase difference data (denoted as at this time) is shown in formula (6).

[0128] (5);

[0129] (6);

[0130] In formulas (5) and (6), is the first phase difference data (that is, the delayed self-heterodyne interference result of the laser source to be measured), is the second phase difference data (that is, the delayed self-heterodyne interference result of the auxiliary laser source); and are the link noises introduced by the fluctuations in the environment where the optical fiber link is located, is the wavelength of the auxiliary laser source, is the wavelength of the laser source to be measured, and n is the refractive index of the light transmitted in the optical fiber, is the fluctuation of the length of the optical fiber link over time.

[0131] It should be noted that the third delayed light is composed of two parts. One part is the result obtained after delaying the first delayed light, and the other part is the result obtained after delaying the second delayed light; when the third delayed light interferes with the first reference light, both of the aforementioned two parts of the third delayed light will interfere with the first reference light.

[0132] By filtering out other interference results through a path of radio frequency filter, only the interference result of "the first reference light" and the light obtained after delaying the "first delayed light" in the third delayed light is retained.

[0133] Similarly, by filtering out other interference results through another path of radio frequency filter, only the interference result of "the second reference light" and the light obtained after delaying the "second delayed light" in the third delayed light is retained.

[0134] In formulas (5) and (6), is the fluctuation of the phase of the laser source to be measured over time, i.e., the fluctuation of the phase of the first reference light over time; is the part of the third delayed light that is combined with the first reference light and corresponds to the first delayed light, and its phase fluctuation over time; is the fluctuation of the phase of the auxiliary laser source over time, i.e., the fluctuation of the phase of the second reference light over time; is the part of the third delayed light that is combined with the second reference light and corresponds to the second delayed light, and its phase fluctuation over time.

[0135] It should be noted that for a beam of laser, the magnitude of the fiber optic link noise it perceives is inversely proportional to the laser wavelength. Since both the auxiliary laser source and the laser source to be measured enter the same fiber optic link, the fiber optic link noise they sense is proportional to " the fluctuation of the length of the fiber optic link over time

[0136] Step S303: Based on the first phase difference data and the second phase difference data, eliminate the noise in the fiber optic link to obtain the third phase difference data.

[0137] In the specific process of implementing step S303, use the first phase difference data and the second phase difference data to eliminate the noise in the fiber optic link to obtain the third phase difference data .

[0138] Specifically, in the process of obtaining the first phase difference data and the second phase difference data above, the phase noises of the laser source to be measured and the auxiliary laser source are respectively coupled with the noise introduced by the fiber optic link. By effectively eliminating the noise in the fiber optic link, a measurement result (i.e., the third phase difference data) containing the phase noises of the laser source to be measured and the auxiliary laser source can be obtained. The specific content of the third phase difference data is shown in formula (7).

[0139] (7);

[0140] As can be seen from the content of formula (7) above, the third phase difference data has a specified time delay (i.e., has ).

[0141] Step S304: Perform digital decoherence on the first phase difference data to obtain the fourth phase difference data, and perform digital decoherence on the third phase difference data to obtain the fifth phase difference data.

[0142] In the specific process of implementing step S304, use the "principle of obtaining the power spectral density based on digital decoherence" given in the foregoing content to perform digital decoherence on the first phase difference data to obtain the fourth phase difference data (denoted as ), perform digital decoherence on the third phase difference data to obtain the fifth phase difference data .

[0143] It should be noted that in the case of adopting the "first method of obtaining the frequency noise power spectral density", the first phase difference data is equivalent to the "initial phase difference data" in the above-mentioned "principle of obtaining the power spectral density based on digital decoherence", and the fourth phase difference data is equivalent to the output phase difference data obtained in the m-th step (i = m) in the above-mentioned "principle of obtaining the power spectral density based on digital decoherence".

[0144] Similarly, the third phase difference data is equivalent to the "initial phase difference data" in the above-mentioned "principle of obtaining the power spectral density based on digital decoherence", and the fifth phase difference data is equivalent to the output phase difference data obtained in the m-th step (i = m) in the above-mentioned "principle of obtaining the power spectral density based on digital decoherence".

[0145] In the case of adopting the "first method of obtaining the frequency noise power spectral density", the specific content of the fourth phase difference data is shown in formula (8), and the specific content of the fifth phase difference data is shown in formula (9).

[0146] (8);

[0147] (9);

[0148] As can be seen from the content of formula (8) and formula (9), after digital decoherence, the time delay of the phase noise of the laser source extends from (specified time delay) to (m times the specified time delay), and the noise of the optical fiber link is expressed as , which is the result obtained after digital decoherence of the "link noise introduced due to the fluctuations in the environment where the optical fiber link is located " mentioned in the above formula (5).

[0149] In some embodiments, the fourth phase difference data and the fifth phase difference data have a time delay of m times the specified time delay, and the time delay of m times the specified time delay is greater than the coherence time of the laser to be measured.

[0150] Step S305: Use the fourth phase difference data and the fifth phase difference data to determine the frequency noise power spectral density of the laser to be measured corresponding to the laser source to be measured.

[0151] In the process of specifically implementing step S305, the cross-power spectra of the fourth phase difference data and the fifth phase difference data are calculated multiple times. The cross-power spectra obtained from the multiple calculations are averaged to obtain the phase noise power spectral density of the laser under test corresponding to the laser source to be measured. The frequency noise power spectral density of the laser under test is determined using the phase noise power spectral density.

[0152] Specifically, since the fourth phase difference data and the fifth phase difference data both contain the phase noise of the laser under test, by obtaining through multiple measurements and and calculating the cross-power spectrum between the two; averaging the cross-power spectra obtained from the multiple calculations can extract and the common-mode components in, that is, extract the phase noise power spectral density of the laser under test.

[0153] Among them, the specific operation process of "averaging the cross-power spectra obtained from the multiple calculations" is shown in formula (10).

[0154] (10);

[0155] In formula (10), refers to the average of K times, is and 's cross-power spectrum, is " " and " " (that is, the power spectral density of the phase difference data of the laser under test)'s cross-power spectrum, is " " and " " (that is, the power spectral density of the phase difference data of the laser under test)'s cross-power spectrum;

[0156] is the noise of the fiber optic link and " " (that is, the power spectral density of the phase difference data of the laser under test)'s cross-power spectrum, is the noise of the fiber optic link and " " (that is, the power spectral density of the phase difference data of the laser under test)'s cross-power spectrum. refers to 's specific multiple, which decreases as K increases.

[0157] It should be noted that when calculating the cross-power spectrum, when the two items participating in the calculation are the same, the result will be a positive real number, otherwise the result will be a random number. From the above explanation of formula (10), it can be seen that is a positive real number with a stable amplitude, and multiple averaging will not change 's magnitude.

[0158] Other than all other terms are random numbers, which will gradually decrease as the number of averaging increases, and the reduction ratio is times the original size. Therefore, the measurement result after multiple averaging of the cross-power spectrum is , where decreases as K increases until it is negligible; thus, the result obtained after multiple averaging is the power spectral density of the phase difference data of the laser under test , that is to say, the phase noise power spectral density of the laser under test is .

[0159] It should be noted that in the actual calculation of the cross-power spectrum, the higher the sampling rate, the higher the highest frequency of the obtained cross-power spectrum. However, when the sampling rate is too high, the requirements for system resources are higher. Therefore, usually, two groups of high-sampling-rate data and are first subjected to fast Fourier transform (FFT), and then the two Fourier transform results are conjugated and multiplied to obtain the cross-power spectrum in the high-frequency band; then the original data is downsampled and the same operation is performed to obtain the cross-power spectrum in the middle-frequency band, and so on to continuously obtain the cross-power spectrum in lower frequency bands.

[0160] After obtaining the phase noise power spectral density of the laser under test, the frequency noise power spectral density of the laser under test is calculated through " ", where f is the frequency (i.e., the independent variable of the power spectral density).

[0161] The above content in the embodiments of the present invention Figure 3 is the related description of "the first method for obtaining the frequency noise power spectral density". After determining the frequency noise power spectral density of the laser under test by using "the first method for obtaining the frequency noise power spectral density", the frequency noise power spectral density can be weighted and integrated by using the β-line method, the direct integration method or the piecewise integration method to determine the laser linewidth of the laser under test.

[0162] For example: According to the β-line method and the frequency noise power spectral density , the laser linewidth of the laser under test is determined.

[0163] It should be noted that the β-line method is a method for calculating the laser linewidth according to the frequency noise power spectral density. By drawing a β-line " ", retaining the at the frequency points of " ", and integrating the retained part, the laser linewidth can be calculated through the frequency noise power spectral density.

[0164] Regarding the above embodiments of the present invention Figure 2 Regarding the "second method for obtaining the frequency noise power spectral density" involved in step S202, refer to Figure 4 which shows a flowchart of the second method for obtaining the frequency noise power spectral density provided by the embodiments of the present invention. Figure 4 It includes the following steps:

[0165] Step S401: Using the first delayed light and the first reference light, demodulate to obtain the first phase difference data of the laser source to be measured.

[0166] In the specific process of implementing step S401, when measuring a laser to be measured with a noise level worse than the test environment, the auxiliary laser source is not started. The first delayed light is transmitted into the delay optical fiber link and frequency shifted to obtain the fourth delayed light. The fourth delayed light and the first reference light are aggregated and interferometrically measured through a photodetector to obtain the third interference signal. Demodulate the third interference signal to obtain the first phase difference data.

[0167] It should be noted that in the case of adopting the "second method for obtaining the frequency noise power spectral density", the first phase difference data is equivalent to the "initial phase difference data" in the above "principle of obtaining the power spectral density based on digital decoherence". ".

[0168] Step S402: Perform digital decoherence on the first phase difference data to obtain the fourth phase difference data.

[0169] In the specific process of implementing step S402, perform digital decoherence on the first phase difference data to obtain the fourth phase difference data. Among them, in the case of adopting the "second method for obtaining the frequency noise power spectral density", the fourth phase difference data is equivalent to the output phase difference data obtained in the m-th step (i = m) in the above "principle of obtaining the power spectral density based on digital decoherence".

[0170] Step S403: Determine the frequency noise power spectral density of the laser to be measured corresponding to the laser source to be measured based on the fourth phase difference data.

[0171] In the specific process of implementing step S403, after obtaining the fourth phase difference data, perform Fourier transform on the fourth phase difference data to obtain the phase noise power spectral density of the laser to be measured corresponding to the laser source to be measured. Use this phase noise power spectral density to determine the frequency noise power spectral density of the laser to be measured.

[0172] The above embodiments of the present invention Figure 4The content in is the related description about "the second method for obtaining the frequency noise power spectral density". After determining the frequency noise power spectral density of the laser under test by using "the second method for obtaining the frequency noise power spectral density", the frequency noise power spectral density can be weighted integrated by using the β-line method, the direct integration method or the segmented integration method, so as to determine the laser linewidth of the laser under test.

[0173] Regarding the above embodiments of the present invention Figure 3 in step S304, "performing digital decoherence on the first phase difference data to obtain the fourth phase difference data", and regarding the above embodiments of the present invention Figure 4 in step S402, "performing digital decoherence on the first phase difference data to obtain the fourth phase difference data", taking performing digital decoherence on the first phase difference data as an example, through Figure 5 to explain how to perform digital decoherence on the phase difference data.

[0174] Refer to Figure 5 , which shows the flowchart of performing digital decoherence on the first phase difference data to obtain the fourth phase difference data provided by the embodiments of the present invention, Figure 5 including the following steps:

[0175] Step S501: Delay the first phase difference data by a specified time delay to form new phase difference data.

[0176] In the process of specifically implementing step S501, using the "principle of obtaining the power spectral density based on digital decoherence" given in the foregoing content, taking the first phase difference data as the "initial phase difference data" to delay by a specified time delay ( ), to form new phase difference data.

[0177] Step S502: Compare the new phase difference data with the first phase difference data to obtain the output phase difference data with a 2-fold specified time delay.

[0178] In the process of specifically implementing step S502, compare the new phase difference data with the first phase difference data to obtain the output phase difference data with a 2-fold specified time delay.

[0179] Step S503: Delay the new phase difference data by a specified time delay to update the new phase difference data.

[0180] Step S504: Compare the updated new phase difference data with the output phase difference data with an (i - 1)-fold specified time delay to obtain the output phase difference data with an i-fold specified time delay, where the initial value of i is 3.

[0181] In the process of specifically implementing step S504, i starts from 3, and the updated new phase difference data is compared with the output phase difference data with an (i - 1)-fold specified time delay to obtain the output phase difference data with an i-fold specified time delay.

[0182] Step S505: Increase i by 1, and return to execute step S503 to update the updated new phase difference data again until i is greater than m to obtain the fourth phase difference data.

[0183] In the process of specifically implementing step S505, i = i + 1, and return to execute step S503 to update the updated new phase difference data again until i is greater than m to obtain the fourth phase difference data, and the fourth phase difference data is: the output phase difference data with an m-fold specified time delay.

[0184] It should be noted that "updating the updated new phase difference data again" specifically means: delaying the "updated new phase difference data" used before executing step S505 by the specified time delay again.

[0185] That is to say, when returning to execute step S503, the "updated new phase difference data" used in step S504 executed in the previous round will be delayed by the specified time delay again, and then step S504 of this round will be executed, and so on until i is greater than m to obtain the fourth phase difference data.

[0186] In other words, when returning to execute step S503, the "new phase difference data" in "delaying the new phase difference data by the specified time delay" mentioned in step S503 refers to the "updated new phase difference data" used in step S504 of the previous round.

[0187] It should be noted that for the execution principle of steps S501 to S505, reference can be made to the "principle of obtaining power spectral density based on digital decoherence" given in the foregoing content, which will not be elaborated here.

[0188] Furthermore, it should be noted that for the specific implementation method of performing digital decoherence on the third phase difference data to obtain the fifth phase difference data, reference can be made to the above Figure 5 content and the "principle of obtaining power spectral density based on digital decoherence" given in the foregoing content, which will not be elaborated here; the obtained fifth phase difference data is: the output phase difference data with an m-fold specified time delay.

[0189] The above is the related description of the laser linewidth measurement method based on digital decoherence given in this solution. In practical applications, in the case of adopting "the first method to obtain the frequency noise power spectral density", the "laser linewidth measurement method based on digital decoherence" can be realized by building a hybrid triangle-cap system.

[0190] For example Figure 6 Fig. shows a structural example of one of the hybrid triangle-cap systems provided by an embodiment of the present invention. Figure 6 The shown hybrid triangle-cap system is composed of an optical unit, a radio frequency unit, and a high-speed data processing unit.

[0191] Among them, the optical unit of the hybrid triangle-cap system mainly consists of an auxiliary laser source, a delay fiber, an acousto-optic modulator, a photodetector, a fiber filter ( Figure 6 abbreviated as optical filter in the text), and a fiber coupler. The optical unit can respectively implement the delay self-heterodyne interference measurement of the laser source to be measured and the delay self-heterodyne interference measurement of the auxiliary laser source. The auxiliary laser source does not require the same center wavelength as the laser source to be measured, nor does it require the same laser linewidth level as the laser source to be measured.

[0192] The radio frequency unit of the hybrid triangle-cap system consists of two groups of parallel low-noise radio frequency power amplifiers ( Figure 6 abbreviated as low-noise amplifiers in the text), radio frequency filters ( Figure 6 abbreviated as filters in the text), and a 4-channel high-speed data acquisition card. The radio frequency unit can amplify, filter, and perform high-speed acquisition on two groups of interference signals.

[0193] It should be noted that when the requirement for signal-to-noise ratio is extremely high or the quality of the laser source to be measured is extremely high, and it is necessary to suppress the noise of radio frequency devices, it can be considered that each group of low-noise radio frequency power amplifiers, radio frequency filters, and 4-channel high-speed data acquisition cards are composed of two sets of devices, that is, a total of four sets of instruments. At this time, the noise of radio frequency devices can be suppressed by a specified method.

[0194] The high-speed data processing unit of the hybrid triangle-cap system mainly includes an FPGA (Field Programmable Gate Array) high-speed processing board and a high-speed data memory. It can perform digital IQ demodulation on the sampled signal to obtain the initial phase difference data, and then perform digital decoherence on the initial phase difference data to obtain the output phase difference data (that is Figure 1(the long-delay difference data therein), further perform operations such as fast Fourier transform (FFT), filtering, and downsampling on the output phase difference data to obtain the phase noise power spectral density / frequency noise power spectral density of the laser, and finally calculate the laser linewidth. At the same time, the high-speed data memory stores effective data such as phase difference data and phase noise power spectral density / frequency noise power spectral density to meet other analysis requirements.

[0195] When using Figure 6 the shown hybrid triangular cap system to measure the laser linewidth, the first delayed light of the laser source to be measured and the second delayed light of the auxiliary laser source are aggregated together by an optical fiber coupler and transmitted into the delay optical fiber link, and then frequency-shifted by an acousto-optic modulator to obtain the third delayed light.

[0196] The third delayed light is divided into two beams. These two beams of the third delayed light are respectively aggregated with the first reference light and the second reference light through an optical fiber coupler, and after passing through an optical filter, interference measurement is performed at a photodetector. The power of the interference signal obtained by the interference measurement is amplified by a low-noise amplifier, and the excess noise is filtered by a filter. Finally, the first interference signal and the second interference signal are collected using a high-speed data acquisition card.

[0197] By respectively performing digital IQ demodulation on the collected first interference signal and second interference signal, the first phase difference data and the second phase difference data can be obtained. For the subsequent process of calculating the laser linewidth of the laser to be measured based on the first phase difference data and the second phase difference data, reference can be made to the relevant content in the above embodiments of the present invention Figure 3 and will not be elaborated here.

[0198] It should be noted that through the hybrid triangular cap system provided by the embodiments of the present invention, a combined result containing only the noise of any two of the three parts of the laser source to be measured, the auxiliary laser source, and the optical fiber link can be obtained.

[0199] Figure 6 The shown dual-laser structure is only one example of the hybrid triangular cap system given by the embodiments of the present invention. The key feature of the hybrid triangular cap system is that three independent units are formed by the laser source and the optical fiber link. Therefore, similar functions can also be realized using a single laser in cooperation with two different optical fiber links or three lasers, and various hybrid triangular cap systems will not be exemplified one by one here.

[0200] Based on the content of each of the above embodiments, the present solution can achieve the following beneficial effects:

[0201] 1. This scheme uses digital time delay to multiply the physical delay of the optical fiber link. Compared with the traditional time delay self-heterodyne method, this scheme does not require a complex physical optical fiber link. The digital time delay can multiply the delay introduced by the short optical fiber physical link, and ultimately achieve the decoherence of the laser source, thereby obtaining an accurate power spectral density.

[0202] 2. This solution does not require one or more auxiliary laser sources whose central wavelength is consistent with the laser source to be measured and whose line width is close to or better than the laser source to be measured. The laser source to be measured does not perform direct interference measurement with the auxiliary laser source, but each performs delayed self-heterodyne interference, which makes the selection of the auxiliary laser source more free, with almost no restrictions on the central wavelength and line width, and can also perform long-term continuous measurement without being affected by the frequency drift of the laser itself.

[0203] 3. The hybrid triangular hat system proposed in this scheme can be realized not only by one reference laser and one delay link, but also by two delay links or two reference lasers. The implementation method of the hybrid triangular hat system is more flexible. The hybrid triangular hat system can realize accurate measurement of the noise spectrum and line width of narrow linewidth laser.

[0204] Corresponding to the laser line width measurement method based on digital decoherence provided in the above embodiment of the present invention, see Figure 7 The embodiment of the present invention further provides a structural block diagram of a laser line width measurement device based on digital decoherence. The laser line width measurement device includes: a processing module 100, a decoherence module 200 and a determination module 300.

[0205] The processing module 100 is used to divide the laser source to be tested into a first delayed light and a first reference light.

[0206] The decoherence module 200 is used to perform digital decoherence based on at least the first delayed light and the first reference light to determine the frequency noise power spectrum density of the laser to be tested corresponding to the laser source to be tested.

[0207] The determination module 300 is used to determine the laser line width of the laser to be tested according to the frequency noise power spectrum density.

[0208] In some embodiments, the determination module 300 is specifically used to: perform weighted integration on the frequency noise power spectrum density by using a β-line method, a direct integration method or a piecewise integration method to determine the laser line width of the laser to be tested.

[0209] In the embodiment of the present invention, the frequency noise power spectral density used to determine the laser line width is determined by digital decoherence. It is not required that the laser source to be measured and the auxiliary laser source have the same central wavelength, and no complex physical optical fiber link is required to avoid introducing a large amount of environmental noise, thereby improving the flexibility, universality and accuracy of laser line width measurement.

[0210] Preferably, in combination with Figure 7 As shown in the content, the decoherence module 200 includes a partitioning sub-module, a first demodulation sub-module, an elimination sub-module, a first decoherence sub-module, and a first determination sub-module. The execution principles of each sub-module are as follows:

[0211] The partitioning sub-module is used to divide the auxiliary laser source into a second delayed light and a second reference light.

[0212] The first demodulation sub-module is used to demodulate the first phase difference data of the laser source to be measured and the second phase difference data of the auxiliary laser source by using the first delayed light, the first reference light, the second delayed light, and the second reference light.

[0213] In some embodiments, the first demodulation sub-module is specifically used to: aggregate and transmit the first delayed light and the second delayed light to a delay fiber optic link and perform frequency shift to obtain a third delayed light; aggregate the third delayed light and the first reference light and perform interference measurement to obtain a first interference signal, and aggregate the third delayed light and the second reference light and perform interference measurement to obtain a second interference signal; demodulate the first interference signal to obtain the first phase difference data, and demodulate the second interference signal to obtain the second phase difference data.

[0214] The elimination sub-module is used to eliminate the noise in the fiber optic link based on the first phase difference data and the second phase difference data to obtain the third phase difference data.

[0215] The first decoherence sub-module is used to perform digital decoherence on the first phase difference data to obtain the fourth phase difference data, and perform digital decoherence on the third phase difference data to obtain the fifth phase difference data.

[0216] The first determination sub-module is used to determine the frequency noise power spectral density of the laser to be measured corresponding to the laser source to be measured by using the fourth phase difference data and the fifth phase difference data.

[0217] In some embodiments, the first determination sub-module is specifically used to: calculate the cross power spectrum of the fourth phase difference data and the fifth phase difference data multiple times; average the cross power spectra obtained by multiple calculations to obtain the phase noise power spectral density of the laser to be measured corresponding to the laser source to be measured; use the phase noise power spectral density to determine the frequency noise power spectral density of the laser to be measured.

[0218] Preferably, in combination with Figure 7 As shown in the content, the decoherence module 200 includes a second demodulation sub-module, a second decoherence sub-module, and a second determination sub-module. The execution principles of each sub-module are as follows:

[0219] The second demodulation sub-module is used to demodulate the first phase difference data of the laser source to be measured by using the first delayed light and the first reference light.

[0220] In some embodiments, the second demodulation sub-module is specifically configured to: transmit the first delayed light into a delay optical fiber link and perform frequency shift to obtain the fourth delayed light; sum up the fourth delayed light and the first reference light and perform interference measurement through a photodetector to obtain the third interference signal; demodulate the third interference signal to obtain the first phase difference data.

[0221] The second decoherence sub-module is used to perform digital decoherence on the first phase difference data to obtain the fourth phase difference data.

[0222] The second determination sub-module is used to determine the frequency noise power spectral density of the laser to be measured corresponding to the laser source to be measured based on the fourth phase difference data.

[0223] In some embodiments, the second determination sub-module is specifically configured to: perform Fourier transform on the fourth phase difference data to obtain the phase noise power spectral density of the laser to be measured corresponding to the laser source to be measured; use the phase noise power spectral density to determine the frequency noise power spectral density of the laser to be measured.

[0224] Preferably, in some embodiments, the process of the first decoherence sub-module and the second decoherence sub-module performing digital decoherence on the first phase difference data to obtain the fourth phase difference data includes the following steps:

[0225] Delay the first phase difference data by a specified time delay to form new phase difference data;

[0226] Compare the new phase difference data with the first phase difference data to obtain the output phase difference data with a 2-fold specified time delay;

[0227] Delay the new phase difference data by a specified time delay to update the new phase difference data;

[0228] Compare the updated new phase difference data with the output phase difference data with an (i - 1)-fold specified time delay to obtain the output phase difference data with an i-fold specified time delay, where the initial value of i is 3;

[0229] Increase i by 1, and return to execute the step of "delay the new phase difference data by a specified time delay" to update the updated new phase difference data again until i is greater than m to obtain the fourth phase difference data;

[0230] Among them, the fourth phase difference data is: the output phase difference data with an m-fold specified time delay.

[0231] In summary, the embodiments of the present invention provide a method and device for measuring the laser linewidth based on digital decoherence. By using digital decoherence to determine the frequency noise power spectral density for determining the laser linewidth, it is not required that the laser source to be measured and the auxiliary laser source have the same central wavelength, nor is it necessary to use a complex physical optical fiber link to avoid introducing a large amount of environmental noise, thereby improving the flexibility, universality, and accuracy of laser linewidth measurement.

[0232] Each embodiment in this specification is described in a progressive manner. For the same or similar parts among the embodiments, reference can be made to each other. Each embodiment focuses on the differences from other embodiments. In particular, for a system or system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can refer to the partial description of the method embodiment. The systems and system embodiments described above are merely illustrative. The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed to multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. A person of ordinary skill in the art can understand and implement it without creative work.

[0233] Those skilled in the art can further realize that the units and algorithm steps of each example described in combination with the embodiments disclosed herein can be implemented by electronic hardware, computer software, or a combination of the two. To clearly illustrate the interchangeability of hardware and software, the components and steps of each example have been generally described according to their functions in the above description. Whether these functions are executed in a hardware or software manner depends on the specific application and design constraints of the technical solution. Skilled professionals can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of the present invention.

[0234] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A laser line width measurement method based on digital decoherence, characterized in that: The method comprises: The laser source to be measured is divided into a first delay light and a first reference light; Performing digital decoherence at least based on the first delayed light and the first reference light to determine the frequency noise power spectrum density of the laser to be measured corresponding to the laser source to be measured; The laser line width of the laser to be tested is determined according to the frequency noise power spectrum density.

2. The method according to claim 1, characterized in that At least based on the first delayed light and the first reference light, digital decoherence is performed to determine the frequency noise power spectrum density of the laser to be measured corresponding to the laser source to be measured, including: The auxiliary laser source is divided into a second delay light and a second reference light; Demodulating to obtain first phase difference data of the laser source to be measured and second phase difference data of the auxiliary laser source using the first delayed light, the first reference light, the second delayed light and the second reference light; Based on the first phase difference data and the second phase difference data, eliminating noise in the optical fiber link to obtain third phase difference data; Performing digital decoherence on the first phase difference data to obtain fourth phase difference data, and performing digital decoherence on the third phase difference data to obtain fifth phase difference data; The frequency noise power spectrum density of the laser to be tested corresponding to the laser source to be tested is determined by using the fourth phase difference data and the fifth phase difference data.

3. The method according to claim 1, characterized in that At least based on the first delayed light and the first reference light, digital decoherence is performed to determine the frequency noise power spectrum density of the laser to be measured corresponding to the laser source to be measured, including: Demodulating and obtaining first phase difference data of the laser source to be measured by using the first delayed light and the first reference light; Performing digital decoherence on the first phase difference data to obtain fourth phase difference data; The frequency noise power spectrum density of the laser to be measured corresponding to the laser source to be measured is determined based on the fourth phase difference data.

4. The method according to claim 2, characterized in that: Demodulating to obtain first phase difference data of the laser source to be measured and second phase difference data of the auxiliary laser source using the first delayed light, the first reference light, the second delayed light, and the second reference light includes: Transmitting the first delayed light and the second delayed light together into a delayed optical fiber link and performing frequency shifting to obtain a third delayed light; The third delayed light and the first reference light are combined and interferometrically measured to obtain a first interference signal, and the third delayed light and the second reference light are combined and interferometrically measured to obtain a second interference signal; The first interference signal is demodulated to obtain first phase difference data, and the second interference signal is demodulated to obtain second phase difference data.

5. The method according to claim 3, characterized in that: Demodulating and obtaining first phase difference data of the laser source to be measured by using the first delayed light and the first reference light includes: Transmitting the first delayed light into a delayed optical fiber link and performing frequency shifting to obtain a fourth delayed light; The fourth delayed light and the first reference light are combined and interferometrically measured by a photodetector to obtain a third interference signal; The third interference signal is demodulated to obtain first phase difference data.

6. The method according to any one of claims 2 to 5, characterized in that: Performing digital decoherence on the first phase difference data to obtain fourth phase difference data, comprising: Delaying the first phase difference data by a specified time delay to form new phase difference data; Comparing the new phase difference data with the first phase difference data to obtain output phase difference data having twice the specified time delay; Delaying the new phase difference data by the specified time delay to update the new phase difference data; Compare the updated new phase difference data with the output phase difference data having i-1 times the specified time delay to obtain the output phase difference data having i times the specified time delay, where the initial value of i is 3; i increases by 1, and returns to execute the step of delaying the new phase difference data by the specified time delay to update the updated new phase difference data again, until i is greater than m to obtain fourth phase difference data; The fourth phase difference data is: output phase difference data having m times the specified time delay.

7. The method according to claim 2, characterized in that: Determining the frequency noise power spectrum density of the laser to be tested corresponding to the laser source to be tested by using the fourth phase difference data and the fifth phase difference data includes: calculating a cross power spectrum of the fourth phase difference data and the fifth phase difference data for multiple times; Averaging the cross power spectra obtained by multiple calculations to obtain the phase noise power spectrum density of the laser to be tested corresponding to the laser source to be tested; The frequency noise power spectral density of the laser to be tested is determined by using the phase noise power spectral density.

8. The method according to claim 3, characterized in that Determining the frequency noise power spectrum density of the laser to be tested corresponding to the laser source to be tested based on the fourth phase difference data includes: Performing Fourier transformation on the fourth phase difference data to obtain a phase noise power spectrum density of the laser to be tested corresponding to the laser source to be tested; The frequency noise power spectral density of the laser to be tested is determined by using the phase noise power spectral density.

9. The method according to claim 1, characterized in that: Determining the laser line width of the laser to be tested according to the frequency noise power spectrum density includes: The frequency noise power spectrum density is weightedly integrated by using a β-line method, a direct integration method or a segmented integration method to determine the laser line width of the laser to be tested.

10. A laser line width measurement device based on digital decoherence, characterized in that: The device comprises: A processing module, used for dividing the laser source to be measured into a first delayed light and a first reference light; a decoherence module, configured to perform digital decoherence based at least on the first delayed light and the first reference light, so as to determine a frequency noise power spectrum density of the laser to be measured corresponding to the laser source to be measured; The determination module is used to determine the laser line width of the laser to be tested according to the frequency noise power spectrum density.

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