Laser linewidth measurement system and method based on short optical fiber circulation self-heterodyne method

Abstract

The invention provides a laser linewidth measurement system and method based on a short optical fiber circulation self-heterodyne method, and can be applied to the technical field of laser measurement. The system comprises a to-be-measured laser used for outputting a to-be-measured laser signal; the Y-shaped single-mode optical fiber beam splitter is used for dividing a laser signal to be measured into two paths; the acousto-optic modulator is used for moving the frequency of one path of laser signal to be measured by a fixed amount and outputting a first optical signal; the optical fiber cyclic delay loop is used for circularly delaying the other path of laser signal to be measured and outputting a second optical signal; the Y-type single-mode optical fiber coupler is used for carrying out interference on the first optical signal and the second optical signal and outputting a third optical signal; the adjustable optical fiber attenuator is used for attenuating the third optical signal to the response range of the photoelectric detector and outputting a fourth optical signal; the photoelectric detector is used for converting the fourth optical signal into an electric signal; and the signal processing module is used for obtaining the line width of the to-be-measured laser according to the electric signal. Interference signals of different orders can be sampled and analyzed at the same time.

Description

Technical Field

[0001] The present disclosure relates to the field of laser measurement, and in particular to a laser line width measurement system and method based on a short fiber cycle self-heterodyne method. Background Art

[0002] Lasers are now widely used in various fields due to their good coherence and monochromaticity. Among them, narrow linewidth lasers refer to lasers that output in the form of a single longitudinal mode of intracavity vibration. They are characterized by very narrow linewidth of the laser spectrum and excellent coherence characteristics. In many systems, the linewidth characteristics of the laser affect important indicators of the system, such as the detection distance, detection accuracy, detection sensitivity of the optical fiber sensing system, the quality of the signal in the communication system, etc. Therefore, the measurement of the laser linewidth is extremely important.

[0003] Traditional narrow linewidth laser linewidth measurement methods mainly include delayed non-zero self-heterodyne method and loop gain compensation delayed self-heterodyne method. The delayed non-zero self-heterodyne method requires hundreds of kilometers of delay optical fiber when measuring the laser linewidth of about 10kHz, which is not conducive to system integration and miniaturization. The loop gain compensation delayed self-heterodyne method does not require a long optical fiber length, but the obtained signal spectrum is separated, and the analysis of interference signals of different orders needs to be analyzed one by one. In addition, the detector sampling bandwidth and data acquisition bandwidth are positively correlated with the interference order, which has the disadvantages of long measurement time and high system cost. Summary of the invention

[0004] In view of the above problems, the present disclosure provides a laser linewidth measurement system and method based on a short fiber cycle self-heterodyne method.

[0005] According to a first aspect of the present disclosure, a laser linewidth measurement system based on a short fiber cycle self-heterodyne method is provided, comprising:

[0006] A laser to be tested, used for outputting a laser signal to be tested;

[0007] A Y-shaped single-mode optical fiber beam splitter is used to split the laser signal to be measured into two paths, and the two laser signals to be measured enter the acousto-optic modulator and the optical fiber cyclic delay loop respectively;

[0008] The acousto-optic modulator is used to shift the frequency of one of the two laser signals to be measured by a fixed amount and output a first optical signal;

[0009] The optical fiber cyclic delay loop is used to cyclically delay the other laser signal to be tested of the two laser signals to be tested, and output a second optical signal;

[0010] A Y-shaped single-mode optical fiber coupler, configured to interfere the first optical signal with the second optical signal and output a third optical signal;

[0011] an adjustable optical fiber attenuator, used to attenuate the third optical signal to within the response range of the photodetector and output a fourth optical signal;

[0012] The photodetector is used to convert the fourth optical signal into an electrical signal;

[0013] The signal processing module is used to obtain the line width of the laser to be tested according to the electrical signal.

[0014] According to an embodiment of the present disclosure, the optical fiber cyclic delay loop includes an X-type single-mode optical fiber coupler, a circulator, a delay optical fiber, and a Faraday rotation mirror;

[0015] The X-shaped single-mode optical fiber coupler is used to couple the other laser signal to be measured with the delayed signal output by the circulator, and output a coupled optical signal;

[0016] The circulator is used to output the coupled optical signal to the delay optical fiber;

[0017] The delay optical fiber is used to delay the coupled optical signal to obtain a delayed signal;

[0018] A Faraday reflector, used for reflecting the delayed signal to the circulator;

[0019] The circulator is also used to output the delayed signal to the X-type single-mode optical fiber coupler.

[0020] According to an embodiment of the present disclosure, the system further comprises an optical isolator disposed between the laser to be tested and the Y-shaped single-mode optical fiber beam splitter;

[0021] The optical isolator is used to prevent reflected light from entering the laser.

[0022] According to an embodiment of the present disclosure, the system further comprises an AOM driver connected to the AOM, the AOM driver being turned on at a low level;

[0023] The AOM driver is used to provide a driving signal for the AOM.

[0024] According to an embodiment of the present disclosure, obtaining the line width of the laser to be tested according to the electrical signal includes:

[0025] Performing a fast Fourier transform on the electrical signal to obtain a power spectral density;

[0026] The power spectral density is subjected to nonlinear fitting using a multi-order power spectral density hybrid equation to obtain a first-order optical fiber delay parameter;

[0027] Using the first-order fiber delay parameters, the amplitude-normalized multi-order power spectral density template is obtained;

[0028] Performing convolution analysis on the multi-order power spectrum density template and the power spectrum density to obtain power ratio information of the multi-order power spectrum density;

[0029] Obtaining a fixed attenuation ratio of the delay optical fiber through power proportion information of a multi-order power spectrum;

[0030] The fixed attenuation ratio of the delay optical fiber and the first-order optical fiber delay parameter are used to perform nonlinear fitting on the power spectrum density to obtain the line width of the laser to be measured.

[0031] According to an embodiment of the present disclosure, the frequency shift amount of the acousto-optic modulator is greater than or equal to 80 MHz.

[0032] According to an embodiment of the present disclosure, the time-delay optical fiber is a single-mode optical fiber or a polarization-maintaining optical fiber.

[0033] A second aspect of the present disclosure provides a laser linewidth measurement method based on a short fiber cycle self-heterodyne method, comprising:

[0034] Using the laser to be tested to output a laser signal to be tested;

[0035] The laser signal to be measured is divided into two paths by using a Y-shaped single-mode optical fiber beam splitter, and the two paths of laser signals to be measured enter the acousto-optic modulator and the optical fiber cyclic delay loop respectively;

[0036] Using the acousto-optic modulator to shift the frequency of one of the two laser signals to be measured by a fixed amount, and output a first optical signal;

[0037] Utilizing the optical fiber cyclic delay loop to cyclically delay another path of the two paths of laser signals to be measured, and outputting a second optical signal;

[0038] Using a Y-type single-mode optical fiber coupler to interfere the first optical signal with the second optical signal to output a third optical signal;

[0039] Attenuating the third optical signal to within the response range of the photodetector using an adjustable optical fiber attenuator, and outputting a fourth optical signal;

[0040] converting the fourth optical signal into an electrical signal using the photodetector;

[0041] The signal processing module is used to obtain the line width of the laser to be tested according to the electrical signal.

[0042] According to an embodiment of the present disclosure, the optical fiber cyclic delay loop includes an X-type single-mode optical fiber coupler, a circulator, a delay optical fiber and a Faraday rotation mirror, and the optical fiber cyclic delay loop is used to cyclically delay the other of the two laser signals to be measured, and outputting a second optical signal includes:

[0043] Using the X-shaped single-mode optical fiber coupler, the other path of the laser signal to be measured is coupled with the delayed signal output by the circulator to output a coupled optical signal, where the coupled optical signal is the second optical signal;

[0044] Outputting the coupled optical signal to the delay optical fiber using the circulator;

[0045] Delaying the coupled optical signal using the delay optical fiber to obtain a delayed signal;

[0046] Reflecting the delayed signal to the circulator using a Faraday reflector;

[0047] The circulator is used to output the delayed signal to the X-type single-mode optical fiber coupler.

[0048] According to an embodiment of the present disclosure, obtaining the line width of the laser to be tested according to the electrical signal includes:

[0049] Performing a fast Fourier transform on the electrical signal to obtain a power spectral density;

[0050] The power spectral density is subjected to nonlinear fitting using a multi-order power spectral density hybrid equation to obtain a first-order optical fiber delay parameter;

[0051] Using the first-order fiber delay parameters, the amplitude-normalized multi-order power spectral density template is obtained;

[0052] Performing convolution analysis on the multi-order power spectrum density template and the power spectrum density to obtain power ratio information of the multi-order power spectrum density;

[0053] Obtaining a fixed attenuation ratio of the delay optical fiber through power proportion information of a multi-order power spectrum;

[0054] The fixed attenuation ratio of the delay optical fiber and the first-order optical fiber delay parameter are used to perform nonlinear fitting on the power spectrum density to obtain the line width of the laser to be measured.

[0055] According to the laser linewidth measurement system and method based on the short fiber cycle self-heterodyne method provided by the present invention, by analyzing the mixed output spectrum, interference signals of different orders can be sampled and analyzed simultaneously, which has the characteristics of fast measurement time, low cost and large dynamic range. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] The above contents and other objects, features and advantages of the present disclosure will become more apparent through the following description of the embodiments of the present disclosure with reference to the accompanying drawings, in which:

[0057] Figure 1 The structure diagram of a laser line width measurement system based on a short fiber cycle self-heterodyne method according to an embodiment of the present disclosure is schematically shown;

[0058] Figure 2 A schematic diagram of the structure of another laser line width measurement system based on short fiber cycle self-heterodyne method according to an embodiment of the present disclosure is shown;

[0059] Figure 3 The flowchart of the laser line width measurement method based on the short fiber cycle self-heterodyne method according to the embodiment of the present disclosure is schematically shown;

[0060] Figure 4 A schematic diagram of multi-order power spectral density output of a laser linewidth measurement method based on a short fiber cycle self-heterodyne method provided by an embodiment of the present disclosure is schematically shown;

[0061] Figure 5 A schematic diagram of a hybrid power spectral density output of a laser linewidth measurement method based on a short fiber cycle self-heterodyne method provided by an embodiment of the present disclosure is schematically shown;

[0062] Figure 6 A schematic diagram of multi-order power spectral density output convolution analysis of a laser linewidth measurement method based on a short fiber cyclic self-heterodyne method provided by an embodiment of the present disclosure is schematically shown;

[0063] [Reference Signs]

[0064] 1-laser to be tested, 2-optical isolator, 3-Y-type single-mode fiber splitter, 4-acoustic-optic modulator driver, 5-acoustic-optic modulator, 6-X-type single-mode fiber coupler, 7-circulator, 8-single-mode fiber, 9-Faraday rotation mirror, 10-Y-type single-mode fiber coupler, 11-adjustable optical attenuator, 12-photodetector, 13-signal processing module, 20-optical fiber cyclic delay loop. DETAILED DESCRIPTION

[0065] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present disclosure. In the following detailed description, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of the embodiments of the present disclosure. However, it is apparent that one or more embodiments may also be implemented without these specific details. In addition, in the following description, descriptions of known structures and technologies are omitted to avoid unnecessary confusion of the concepts of the present disclosure.

[0066] The terms used herein are only for describing specific embodiments and are not intended to limit the present disclosure. The terms "comprise", "include", etc. used herein indicate the existence of the features, steps, operations and / or components, but do not exclude the existence or addition of one or more other features, steps, operations or components.

[0067] All terms (including technical and scientific terms) used herein have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification, and should not be interpreted in an idealized or overly rigid manner.

[0068] In the present disclosure, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or can communicate with each other; it can be a direct connection, or it can be indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present disclosure can be understood according to specific circumstances.

[0069] In the description of the present disclosure, it is necessary to understand that the terms "longitudinal", "length", "circumferential", "front", "rear", "left", "right", "top", "bottom", "inside", "outside", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present disclosure and simplifying the description, and do not indicate or imply that the subsystem or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present disclosure.

[0070] Throughout the drawings, the same elements are represented by the same or similar reference numerals. Conventional structures or configurations will be omitted when they may cause confusion in the understanding of the present disclosure. The shapes, sizes, and positional relationships of the components in the drawings do not reflect the actual size, proportion, and actual positional relationship. In addition, in the claims, any reference symbol between brackets shall not be construed as a limitation to the claims.

[0071] Similarly, in order to simplify the present disclosure and help understand one or more of the various disclosed aspects, in the above description of the exemplary embodiments of the present disclosure, the various features of the present disclosure are sometimes grouped together into a single embodiment, figure, or description thereof. The description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" and the like means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present disclosure. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0072] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the feature. In the description of the present disclosure, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0073] Figure 1 The structure of a laser linewidth measurement system based on a short fiber cycle self-heterodyne method according to an embodiment of the present disclosure is schematically shown.

[0074] like Figure 1 As shown, the laser linewidth measurement system based on the short fiber circulation self-heterodyne method includes: a laser to be measured 1, a Y-type single-mode fiber splitter 3, an acousto-optic modulator 5, an optical fiber circulation delay loop 20, a Y-type single-mode fiber coupler 10, an adjustable optical fiber attenuator 11, a photodetector 12 and a signal processing module 13.

[0075] The laser to be tested 1 outputs a laser signal to be tested.

[0076] The Y-shaped single-mode optical fiber beam splitter 3 is used to split the laser signal to be measured into two paths, and the two paths of laser signals to be measured enter the acousto-optic modulator 5 and the optical fiber cyclic delay loop 20 respectively.

[0077] The acousto-optic modulator 5 is used to shift the frequency of one of the two laser signals to be measured by a fixed amount and output a first optical signal.

[0078] The optical fiber cyclic delay loop 20 is used for cyclically delaying the other laser signal to be measured among the two laser signals to be measured, and outputting a second optical signal.

[0079] The Y-shaped single-mode optical fiber coupler 10 is used to interfere the first optical signal with the second optical signal and output a third optical signal.

[0080] The adjustable optical fiber attenuator 11 is used to attenuate the third optical signal to within the response range of the photodetector and output a fourth optical signal.

[0081] The photodetector 12 is used to convert the fourth optical signal into an electrical signal.

[0082] The signal processing module 13 is used to obtain the line width of the laser 1 to be tested according to the electrical signal.

[0083] In one embodiment, the frequency shift of the AOM 5 is greater than or equal to 80 MHz, for example, it can be 80 MHz, 200 MHz, etc.

[0084] Preferably, the splitting ratio of the Y-shaped single-mode optical fiber beam splitter 3 can be 10:90; 20:80; 30:70 or other different splitting ratios, which is not limited in the present disclosure.

[0085] In one embodiment, obtaining the line width of the laser to be tested based on the electrical signal includes: performing fast Fourier transform on the electrical signal to obtain power spectral density; performing nonlinear fitting on the power spectral density using a multi-order power spectral density hybrid equation to obtain a first-order fiber delay parameter; using the first-order fiber delay parameter to obtain an amplitude-normalized multi-order power spectral density template; performing convolution analysis on the multi-order power spectral density template and the power spectral density to obtain power share information of the multi-order power spectral density; obtaining a fixed attenuation ratio of the delay fiber through the power share information of the multi-order power spectrum; using the fixed attenuation ratio of the delay fiber and the first-order fiber delay parameter, performing nonlinear fitting on the power spectral density to obtain the line width of the laser to be tested.

[0086] Figure 2 The structure of a laser linewidth measurement system based on a short fiber cycle self-heterodyne method according to an embodiment of the present disclosure is schematically shown.

[0087] like Figure 2 As shown, the laser linewidth measurement system based on the short fiber circulation self-heterodyne method includes: a laser to be measured 1, an optical isolator 2, an X-type single-mode fiber splitter 3, an acousto-optic modulator driver 4, an acousto-optic modulator 5, an X-type single-mode fiber coupler 6, a circulator 7, a delay fiber 8, a Faraday rotation mirror 9, a Y-type single-mode fiber coupler 10, an adjustable fiber attenuator 11, a photodetector 12 and a signal processing module 13.

[0088] In this embodiment Figure 1The optical fiber cyclic delay loop 20 shown includes an X-type single-mode optical fiber coupler 6, a circulator 7, a delay optical fiber 8 and a Faraday rotating reflector 9. The X-type single-mode optical fiber coupler 6 is used to couple the other laser signal to be measured with the delay signal output by the circulator, and output a coupled optical signal. The circulator 7 is used to output the coupled optical signal to the delay optical fiber 8. The delay optical fiber 8 is used to delay the coupled optical signal to obtain a delayed signal. The Faraday reflector 9 is used to reflect the delayed signal to the circulator 7. The circulator 7 is also used to output the delayed signal to the X-type single-mode optical fiber coupler.

[0089] Optionally, an optical isolator is provided between the laser to be tested 1 and the Y-shaped single-mode optical fiber beam splitter 3 to prevent reflected light from entering the laser.

[0090] Optionally, the AOM driver 4 connected to the AOM 5 is turned on at a low level. The AOM driver 4 is used to provide a driving signal for the AOM 5.

[0091] Preferably, the splitting ratio of the X-shaped single-mode optical fiber coupler 6 can be 10:90; 20:80; 30:70, etc., and the present disclosure does not impose any limitation on this.

[0092] In one embodiment, the time-delay optical fiber is a single-mode optical fiber or a polarization-maintaining optical fiber.

[0093] Figure 3 The flowchart of the laser line width measurement method based on the short fiber cycle self-heterodyne method according to the embodiment of the present disclosure is schematically shown. Figure 4 A schematic diagram of multi-order power spectral density output of a laser linewidth measurement method based on a short fiber cycle self-heterodyne method provided by an embodiment of the present disclosure is schematically shown. Figure 5 A schematic diagram of a mixed power spectral density output of a laser linewidth measurement method based on a short fiber cycle self-heterodyne method provided in an embodiment of the present disclosure is schematically shown. Figure 6 A schematic diagram of multi-order power spectral density output convolution analysis of a laser linewidth measurement method based on a short fiber cycle self-heterodyne method provided by an embodiment of the present disclosure is schematically shown.

[0094] like Figure 3 As shown, the laser line width measurement method based on the short fiber cycle self-heterodyne method provided in this embodiment can be based on Figure 1 The provided laser linewidth measurement system based on the short fiber cycle self-heterodyne method is implemented. The laser linewidth measurement method based on the short fiber cycle self-heterodyne method includes operations S310 to S380.

[0095] In operation S310, a laser signal to be tested is outputted using a laser to be tested;

[0096] In operation S320, the laser signal to be measured is divided into two paths by using a Y-type single-mode optical fiber beam splitter, and the two paths of laser signals to be measured enter the acousto-optic modulator and the optical fiber cyclic delay loop respectively;

[0097] In operation S330, the frequency of one of the two laser signals to be measured is shifted by a fixed amount by using the acousto-optic modulator to output a first optical signal;

[0098] In operation S340, the optical fiber cyclic delay loop is used to cyclically delay the other laser signal to be tested of the two laser signals to be tested, and a second optical signal is output;

[0099] In operation S350, the first optical signal and the second optical signal are interfered with by using a Y-type single-mode optical fiber coupler to output a third optical signal;

[0100] In operation S360, the third optical signal is attenuated to within the response range of the photodetector by using an adjustable optical fiber attenuator, and a fourth optical signal is output;

[0101] In operation S370, the fourth optical signal is converted into an electrical signal using the photodetector;

[0102] In operation S380, a signal processing module is used to obtain the line width of the laser to be tested according to the electrical signal.

[0103] Optionally, the laser line width measurement method based on the short fiber cycle self-heterodyne method provided in this embodiment can be based on Figure 2 The provided laser line width measurement system based on the short fiber cyclic self-heterodyne method is implemented, the fiber cyclic delay loop includes an X-type single-mode fiber coupler, a circulator, a delay fiber and a Faraday rotation mirror, and the fiber cyclic delay loop is used to cyclically delay the other of the two laser signals to be measured, and the output of the second optical signal includes:

[0104] The X-shaped single-mode optical fiber coupler 6 is used to couple the other path of the laser signal to be measured with the delayed signal output by the circulator, and output a coupled optical signal, where the coupled optical signal is the second optical signal;

[0105] Outputting the coupled optical signal to the delay optical fiber using the circulator;

[0106] Delaying the coupled optical signal using the delay optical fiber to obtain a delayed signal;

[0107] Reflecting the delayed signal to the circulator using a Faraday reflector;

[0108] The circulator is used to output the delayed signal to the X-type single-mode optical fiber coupler.

[0109] Optionally, obtaining the line width of the laser to be tested based on the electrical signal includes: performing fast Fourier transform on the electrical signal to obtain power spectral density; performing nonlinear fitting on the power spectral density using a multi-order power spectral density hybrid equation to obtain a first-order fiber delay parameter; using the first-order fiber delay parameter to obtain an amplitude-normalized multi-order power spectral density template; performing convolution analysis on the multi-order power spectral density template and the power spectral density to obtain power share information of the multi-order power spectral density; obtaining a fixed attenuation ratio of the delay fiber through the power share information of the multi-order power spectrum; using the fixed attenuation ratio of the delay fiber and the first-order fiber delay parameter, performing nonlinear fitting on the power spectral density to obtain the line width of the laser to be tested.

[0110] It will be appreciated by those skilled in the art that the features described in the various embodiments and / or claims of the present disclosure may be combined and / or combined in a variety of ways, even if such combinations and / or combinations are not explicitly described in the present disclosure. In particular, the features described in the various embodiments and / or claims of the present disclosure may be combined and / or combined in a variety of ways without departing from the spirit and teachings of the present disclosure. All of these combinations and / or combinations fall within the scope of the present disclosure.

[0111] The embodiments of the present disclosure are described above. However, these embodiments are only for illustrative purposes and are not intended to limit the scope of the present disclosure. Although the embodiments are described above separately, this does not mean that the measures in the various embodiments cannot be used in combination to advantage. The scope of the present disclosure is defined by the attached claims and their equivalents. Without departing from the scope of the present disclosure, those skilled in the art may make a variety of substitutions and modifications, which should all fall within the scope of the present disclosure.

Claims

1. A laser line width measurement system based on short fiber cycle self-heterodyne method, characterized in that: include: A laser to be tested, used for outputting a laser signal to be tested; A Y-shaped single-mode optical fiber beam splitter is used to split the laser signal to be measured into two paths, and the two laser signals to be measured enter the acousto-optic modulator and the optical fiber cyclic delay loop respectively; The acousto-optic modulator is used to shift the frequency of one of the two laser signals to be measured by a fixed amount and output a first optical signal; The optical fiber cyclic delay loop is used to cyclically delay the other laser signal to be tested of the two laser signals to be tested, and output a second optical signal; A Y-shaped single-mode optical fiber coupler, configured to interfere the first optical signal with the second optical signal and output a third optical signal; an adjustable optical fiber attenuator, used to attenuate the third optical signal to within the response range of the photodetector and output a fourth optical signal; The photodetector is used to convert the fourth optical signal into an electrical signal; The signal processing module is used to obtain the line width of the laser to be tested according to the electrical signal.

2. The laser linewidth measurement system based on short fiber cycle self-heterodyne method according to claim 1, characterized in that: The optical fiber cyclic delay loop includes an X-shaped single-mode optical fiber coupler, a circulator, a delay optical fiber and a Faraday rotation mirror; The X-shaped single-mode optical fiber coupler is used to couple the other laser signal to be measured with the delayed signal output by the circulator, and output a coupled optical signal; The circulator is used to output the coupled optical signal to the delay optical fiber; The delay optical fiber is used to delay the coupled optical signal to obtain a delayed signal; A Faraday reflector, used for reflecting the delayed signal to the circulator; The circulator is also used to output the delayed signal to the X-type single-mode optical fiber coupler.

3. The laser linewidth measurement system based on short fiber cycle self-heterodyne method according to claim 1, characterized in that: The system further comprises an optical isolator arranged between the laser to be tested and the Y-shaped single-mode optical fiber beam splitter; The optical isolator is used to prevent reflected light from entering the laser.

4. The laser linewidth measurement system based on short fiber cycle self-heterodyne method according to claim 1, characterized in that: The system further comprises an AOM driver connected to the AOM, wherein the AOM driver is turned on at a low level; The AOM driver is used to provide a driving signal for the AOM.

5. The laser linewidth measurement system based on short fiber cycle self-heterodyne method according to claim 1, characterized in that: The obtaining the line width of the laser to be measured according to the electrical signal comprises: Performing a fast Fourier transform on the electrical signal to obtain a power spectral density; The power spectral density is subjected to nonlinear fitting using a multi-order power spectral density hybrid equation to obtain a first-order optical fiber delay parameter; Using the first-order fiber delay parameters, the amplitude-normalized multi-order power spectral density template is obtained; Performing convolution analysis on the multi-order power spectrum density template and the power spectrum density to obtain power ratio information of the multi-order power spectrum density; Obtaining a fixed attenuation ratio of the delay optical fiber through power proportion information of a multi-order power spectrum; The fixed attenuation ratio of the delay optical fiber and the first-order optical fiber delay parameter are used to perform nonlinear fitting on the power spectrum density to obtain the line width of the laser to be measured.

6. The laser linewidth measurement system based on short fiber cycle self-heterodyne method according to claim 1, characterized in that: The frequency shift amount of the acousto-optic modulator is greater than or equal to 80 MHz.

7. The laser linewidth measurement system based on short fiber cycle self-heterodyne method according to claim 2, characterized in that: The time-delay optical fiber is a single-mode optical fiber or a polarization-maintaining optical fiber.

8. A laser line width measurement method based on short fiber cycle self-heterodyne method, characterized in that: include: Using the laser to be tested to output a laser signal to be tested; The laser signal to be measured is divided into two paths by using a Y-shaped single-mode optical fiber beam splitter, and the two paths of laser signals to be measured enter the acousto-optic modulator and the optical fiber cyclic delay loop respectively; Using the acousto-optic modulator to shift the frequency of one of the two laser signals to be measured by a fixed amount, and output a first optical signal; Utilizing the optical fiber cyclic delay loop to cyclically delay another path of the two paths of laser signals to be measured, and outputting a second optical signal; Using a Y-type single-mode optical fiber coupler to interfere the first optical signal with the second optical signal to output a third optical signal; Attenuating the third optical signal to within the response range of the photodetector using an adjustable optical fiber attenuator, and outputting a fourth optical signal; converting the fourth optical signal into an electrical signal using the photodetector; The signal processing module is used to obtain the line width of the laser to be tested according to the electrical signal.

9. The laser line width measurement method based on short fiber cycle self-heterodyne method according to claim 8, characterized in that: The optical fiber cyclic delay loop includes an X-shaped single-mode optical fiber coupler, a circulator, a delay optical fiber and a Faraday rotation mirror. The optical fiber cyclic delay loop is used to cyclically delay the other laser signal to be measured among the two laser signals to be measured, and outputting a second optical signal includes: Using the X-shaped single-mode optical fiber coupler, the other path of the laser signal to be measured is coupled with the delayed signal output by the circulator to output a coupled optical signal, where the coupled optical signal is the second optical signal; Outputting the coupled optical signal to the delay optical fiber using the circulator; Delaying the coupled optical signal using the delay optical fiber to obtain a delayed signal; Reflecting the delayed signal to the circulator using a Faraday reflector; The circulator is used to output the delayed signal to the X-type single-mode optical fiber coupler.

10. The laser line width measurement method based on short fiber cycle self-heterodyne method according to claim 8, characterized in that: The obtaining the line width of the laser to be measured according to the electrical signal comprises: Performing a fast Fourier transform on the electrical signal to obtain a power spectral density; The power spectral density is subjected to nonlinear fitting using a multi-order power spectral density hybrid equation to obtain a first-order optical fiber delay parameter; Using the first-order fiber delay parameters, the amplitude-normalized multi-order power spectral density template is obtained; Performing convolution analysis on the multi-order power spectrum density template and the power spectrum density to obtain power ratio information of the multi-order power spectrum density; Obtaining a fixed attenuation ratio of the delay optical fiber through power proportion information of a multi-order power spectrum; The fixed attenuation ratio of the delay optical fiber and the first-order optical fiber delay parameter are used to perform nonlinear fitting on the power spectrum density to obtain the line width of the laser to be measured.

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