A dual-frequency fiber grating laser and Brillouin optical time domain reflectometer

Abstract

The present invention provides a dual-frequency fiber grating laser and a Brillouin optical time-domain reflectometer, comprising a dual-frequency laser cavity, a wavelength division multiplexer connected to the dual-frequency laser, and a polarization beam splitter and a pump source respectively connected to the wavelength division multiplexer, wherein the wavelength division multiplexer couples the pump laser output by the pump source to the dual-frequency laser cavity, and couples the orthogonal dual-polarization laser output by the dual-frequency laser cavity to the polarization beam splitter, and the polarization beam splitter separates the orthogonal dual-polarization laser and outputs two lasers with orthogonal polarization states. The beneficial effect of the present invention is that the pump wave light source and the eigenwave light source in the system of the Brillouin optical time-domain reflectometer are realized in one fiber grating laser, without the need for two independent lasers and a relatively expensive high-stability large-bandwidth optical phase-locked loop device, reducing the complexity of the light source in the Brillouin optical time-domain reflectometer system, improving the stability and reliability of the system, and reducing the cost of the light source in the Brillouin optical time-domain reflectometer system.

Description

Technical Field

[0001] The invention belongs to the technical field of optical fiber lasers, and in particular relates to a dual-frequency optical fiber grating laser and a Brillouin optical time domain reflectometer. Background Art

[0002] In the prior art, there are various structures of light sources in traditional Brillouin optical time-domain reflectometer (BOTDR) systems. One solution is that a pump wave light source and an eigenwave light source are generated by phase-locking two independent lasers, one of which is used as a pump wave and the other as an eigenwave, and the two lasers need to be phase-locked by a highly stable and large-bandwidth phase-locked loop device. The highly stable and large-bandwidth phase-locked loop device is expensive, and the light source structure of the Brillouin optical time-domain reflectometer (BOTDR) in this solution is complex, and the system stability of the Brillouin optical time-domain reflectometer (BOTDR) is not good. Another solution is to use a light source divided into two paths, one of which is used as a pump wave light source, and the other is processed as an eigenwave light source through a complex external modulation technology or a frequency conversion technology based on optical nonlinear principles. The optical complexity is high, so the BOTDR system is relatively large in volume and size. Summary of the invention

[0003] In view of the above problems, the present invention provides a dual-frequency fiber grating laser and a Brillouin optical time domain reflectometer to solve the above or other problems existing in the prior art.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is: a dual-frequency fiber grating laser, including a dual-frequency laser cavity, a wavelength division multiplexer connected to the dual-frequency laser, and a polarization beam splitter and a pump source respectively connected to the wavelength division multiplexer, the wavelength division multiplexer couples the pump laser output by the pump source to the dual-frequency laser cavity, and couples the orthogonal dual-polarization laser output by the dual-frequency laser cavity to the polarization beam splitter, the polarization beam splitter separates the orthogonal dual-polarization laser and outputs two lasers with orthogonal polarization states.

[0005] Furthermore, the dual-frequency laser cavity is an orthogonal dual-polarization fiber grating laser cavity.

[0006] Furthermore, the orthogonal dual-polarization fiber grating laser cavity is a distributed Bragg reflection cavity structure or a distributed Bragg feedback cavity structure.

[0007] Furthermore, the orthogonal dual-polarization fiber grating laser cavity is packaged in a constant temperature and vibration isolation manner.

[0008] Furthermore, the two laser beams with orthogonal polarization states output by the polarization beam splitter are laser beams in an s-polarization state and laser beams in a p-polarization state.

[0009] Furthermore, the frequency difference of the orthogonal dual-polarization lasers output by the dual-frequency laser cavity is adapted to the Brillouin frequency shift of the quartz optical fiber.

[0010] Furthermore, the wavelength division multiplexer is a dual-axis polarization-maintaining optical fiber passive device, and the pump source is a pump laser.

[0011] A Brillouin optical time domain reflectometer comprises the above-mentioned dual-frequency fiber grating laser, a pump wave transmission branch and an eigenwave transmission branch respectively connected to the dual-frequency fiber grating laser, an optical coupler and a photoelectric detection device, wherein the optical coupler is respectively connected to the pump wave transmission branch and the eigenwave transmission branch, and the optical coupler is connected to the photoelectric detection device, and of the two lasers with orthogonal polarization states output by the dual-frequency fiber grating laser, the laser with a high frequency enters the pump wave transmission branch for transmission and processing, and the laser with a low frequency enters the eigenwave transmission branch for transmission and processing, and the two processed lasers are output after interference by the optical coupler and received by the photoelectric detection device.

[0012] Furthermore, the pump wave transmission branch includes a first amplifier, a gain switch, a second amplifier, a circulator and a sensing optical fiber connected in sequence. The circulator is connected to an optical coupler. The high-frequency laser is amplified, modulated and amplified again by the first amplifier, the gain switch and the second amplifier in sequence, and then injected into the sensing optical fiber through the circulator. After the sensing optical fiber is excited, Brillouin scattered light is generated and enters the optical coupler through the circulator.

[0013] Furthermore, the eigenwave transmission branch includes a third amplifier, and the low-frequency laser enters the optical coupler after being amplified by the third amplifier.

[0014] Due to the adoption of the above technical solution, the dual-frequency fiber grating laser has a dual-frequency laser cavity and a pump source. After receiving the energy provided by the pump source, the dual-frequency fiber grating laser can output two single longitudinal mode lasers with orthogonal polarization states. The two single longitudinal mode lasers with orthogonal polarization states enter the polarization beam splitter through a wavelength division multiplexer, and are separated by the polarization beam splitter to output two polarization state lasers (s polarization state laser and p polarization state laser). The dual-frequency fiber grating laser is used as a light source in the optical path of the Brillouin optical time domain reflectometer, and only one light source is used to output two lasers with different frequencies. The two lasers with different frequencies are used as the pump wave and eigenwave of the Brillouin optical time domain reflectometer. The pump wave light source and the eigenwave light source in the optical time domain reflectometer system are realized in one fiber grating laser, eliminating the need for two independent lasers and a relatively expensive high-stability, large-bandwidth optical phase-locked loop device, external modulation devices or devices for nonlinear optical conversion optical paths, and complex modulation technology or optical nonlinear conversion technology, thereby reducing the complexity of the light source in the Brillouin optical time domain reflectometer system, improving the stability and reliability of the system, and reducing the cost of the light source in the Brillouin optical time domain reflectometer system. Moreover, the dual-frequency fiber grating laser is an all-fiber laser with a more compact size and smaller size, thereby making the size of the final Brillouin optical time domain reflectometer system instrument smaller. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a schematic structural diagram of a dual-frequency fiber grating laser according to an embodiment of the present invention;

[0016] Figure 2 It is a schematic structural diagram of a Brillouin optical time domain reflectometer according to an embodiment of the present invention.

[0017] In the figure: 1. dual-frequency laser cavity; 2. wavelength division multiplexer; 3. polarization beam splitter; 4. pump source; 5. constant temperature vibration isolation package; 6. first amplifier; 7. gain switch; 8. second amplifier; 9. circulator; 10. sensing fiber; 11. third amplifier; 12. optical coupler; 13. photoelectric detection device. DETAILED DESCRIPTION

[0018] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0019] Figure 1A structural schematic diagram of an embodiment of the present invention is shown. This embodiment relates to a dual-frequency fiber grating laser and a Brillouin optical time-domain reflectometer. The dual-frequency fiber grating laser serves as a light source in the optical path of the Brillouin optical time-domain reflectometer. The dual-frequency fiber grating laser outputs a pump wave and an eigenwave simultaneously, and does not require two independent lasers and a high-stability, wide-bandwidth optical phase-locked loop device, thereby reducing the cost of the light source of the Brillouin optical time-domain reflectometer, and also reducing the complexity of the light source of the Brillouin optical time-domain reflectometer, thereby improving the reliability of the Brillouin optical time-domain reflectometer system.

[0020] A dual-frequency fiber grating laser, such as Figure 1 As shown, it is applied in a Brillouin optical time domain reflectometer system and used as a light source in the optical path of the Brillouin optical time domain reflectometer system. The dual-frequency fiber grating laser comprises a dual-frequency laser cavity 1, a wavelength division multiplexer 2 connected to the dual-frequency laser cavity 1, and a polarization beam splitter 3 and a pump source 4 respectively connected to the wavelength division multiplexer 2, wherein the pump source 4 is used as a pump laser energy source of the dual-frequency fiber grating laser to supply pump laser energy, the wavelength division multiplexer 2 is used for laser transmission, the wavelength division multiplexer 2 couples the pump laser output by the pump source 4 to the dual-frequency laser cavity 1, and the dual-frequency laser cavity 1 outputs lasers of two frequencies after receiving the power of the pump laser, and the two lasers are orthogonal dual-polarization lasers, and the wavelength division multiplexer 2 couples the dual-frequency laser cavity 1 to the dual-frequency laser cavity 1. The output orthogonal dual-polarization laser is coupled to the polarization beam splitter 3, and the polarization beam splitter 3 separates the orthogonal dual-polarization laser and outputs two lasers with orthogonal polarization states. The frequencies of the two lasers with orthogonal polarization states are different, and they can be used as pump waves and eigenwaves of the Brillouin optical time-domain reflectometer. The output of the pump wave and the eigenwave in the Brillouin optical time-domain reflectometer system is realized in one laser, without the need for two independent lasers and a highly stable and wide-bandwidth optical phase-locked loop device, thereby reducing the complexity and cost of the light source in the Brillouin optical time-domain reflectometer system and improving the stability and reliability of the Brillouin optical time-domain reflectometer system.

[0021] Specifically, the pump source 4 outputs pump laser to the dual-frequency laser cavity 1, provides pump energy for the dual-frequency laser cavity 1, and enables the dual-frequency laser cavity 1 to output orthogonal dual-polarization laser. The pump source 4 is a pump laser, which uses a wavelength-band-cooled, wavelength-stable 974nm or 976nm laser, outputs pump laser power greater than 100mW, and the output pigtail is a 980nm single-mode optical fiber. The output pigtail of the pump laser is fused with the pump input end of the wavelength division multiplexer 2 to achieve the connection between the pump laser and the wavelength division multiplexer 2.

[0022] The above-mentioned dual-frequency laser cavity 1 is an orthogonal dual-polarization fiber grating laser cavity. After receiving the pump laser energy provided by the pump laser, the orthogonal dual-polarization fiber grating laser cavity outputs two single longitudinal mode lasers with orthogonal polarization states. The frequencies of the orthogonal dual-polarization lasers output by the dual-frequency laser cavity 1 are different. It is set that: the wavelengths of the two single longitudinal mode lasers with orthogonal polarization states output by the orthogonal dual-polarization fiber grating laser cavity are respectively and , then the corresponding frequencies of the two lasers are and , calculate the frequency difference of the two lasers according to the frequencies of the two lasers, and set: the frequency difference of the two single longitudinal mode lasers with orthogonal polarization states is ,but The frequency difference of the orthogonal dual-polarization lasers output by the dual-frequency laser cavity 1 is adapted to the Brillouin frequency shift of the quartz optical fiber. Near the Brillouin frequency shift of the quartz optical fiber, the Brillouin frequency shift of the quartz optical fiber is 11 GHz ± 500 MHz.

[0023] The output peak wavelength of the orthogonal dual-polarization fiber Bragg grating laser cavity can be any wavelength point in the range of 1528nm-1565nm, and the output laser power is above 50uW. The output tail fiber of the orthogonal dual-polarization fiber Bragg grating laser cavity is a polarization-maintaining fiber. The output tail fiber is fused with the common end fiber of the wavelength division multiplexer 2 to realize the connection between the orthogonal dual-polarization fiber Bragg grating laser cavity and the wavelength division multiplexer 2.

[0024] The dual-frequency fiber grating laser is an orthogonal dual-frequency laser, and the principle of the orthogonal dual-frequency laser is the same as that of an ordinary fiber grating laser. In some feasible embodiments, the above-mentioned orthogonal dual-polarization fiber grating laser cavity is a distributed Bragg reflection cavity structure or a distributed Bragg feedback cavity structure, and the intracavity gain fiber uses an active fiber doped with erbium or ytterbium and erbium as the gain medium, and a fiber Bragg grating is used as a cavity mirror. Since there is inherent birefringence in the gain fiber and the reflection grating, and the wavelength selection and light feedback are achieved by the same fiber grating, multi-mode oscillation can be eliminated, and it has a good single longitudinal mode output characteristic. The two modes in the laser cavity are two mutually orthogonal polarization states, and lasers of two orthogonal polarization states are output simultaneously. The laser wavelength varies with the refractive index of the birefringence, and the frequency difference of the two orthogonal polarization modes is different. It is set that: the birefringence coefficient of the fiber laser cavity is , then the frequency difference of the orthogonal dual-frequency laser is

[0025] .

[0026] Where c is the speed of light in a vacuum, n is the average refractive index of the optical fiber, and λ is the average wavelength.

[0027] It can be known from the above frequency difference calculation formula that the frequency difference of the dual-frequency laser output by the dual-frequency fiber grating laser depends on the birefringence coefficient of the fiber laser cavity.

[0028] The main difference between an orthogonal dual-frequency laser and an ordinary single-frequency fiber Bragg grating laser is that the laser cavity of the orthogonal dual-frequency laser needs special preparation and process control to ensure that it can output orthogonal dual-frequency lasers and the frequency difference of the dual-frequency lasers is controllable. The controllable birefringence formed in the orthogonal dual-polarization fiber Bragg grating laser cavity can be achieved by ultraviolet laser exposure, or by applying lateral stress to the laser cavity. By controlling the refractive index modulation depth in the two orthogonal directions of the fiber Bragg grating and the control of the birefringence of the active fiber, the frequency difference of the two orthogonal polarization modes output by the laser can be effectively controlled. The refractive index modulation depth in the two orthogonal directions of the fiber Bragg grating is controlled mainly by controlling the exposure amount of the prepared fiber Bragg grating during the preparation of the fiber Bragg grating by photolithography, so that the difference between the average refractive index in the direction of exposure of the fiber Bragg grating and the average refractive index perpendicular to the exposure direction can be controlled.

[0029] In some practicable embodiments, the orthogonal dual polarization fiber grating laser cavity is subjected to constant temperature and vibration isolation packaging 5, that is, a constant temperature and vibration isolation packaging 5 structure is provided on the orthogonal dual polarization fiber grating laser cavity, and the constant temperature and vibration isolation packaging 5 adopts a multi-layer vacuum chamber structure in structure, and the multi-layer vacuum chamber structure can isolate the influence of the external environment temperature and vibration sound on the orthogonal dual polarization fiber grating laser cavity, thereby ensuring the stability of the output laser frequency of the dual-frequency fiber grating laser. Specifically, when the orthogonal dual polarization fiber grating laser cavity is subjected to constant temperature and vibration isolation packaging, the constant temperature and vibration isolation packaging 5 adopts a multi-layer nested vacuum chamber packaging and a thermoelectric cooler to perform constant temperature control on the fiber FP cavity.

[0030] During the operation of the dual-frequency fiber Bragg grating laser, the constant temperature vibration isolation package 5 structure set on the orthogonal dual-polarization fiber Bragg grating laser cavity isolates the influence of the external environment temperature and vibration sound on the orthogonal dual-polarization fiber Bragg grating laser cavity, ensures the stability of the dual-frequency laser output by the orthogonal dual-frequency fiber Bragg grating laser, and makes the frequency difference of the two orthogonal polarization mode lasers output by the orthogonal dual-frequency fiber Bragg grating laser It is adapted to the Brillouin frequency shift of the quartz optical fiber and stabilized near the Brillouin frequency shift of the quartz optical fiber (approximately 11GHz±500MHz).

[0031] The wavelength division multiplexer 2 is used to couple the pump laser output by the pump laser to the orthogonal dual-polarization fiber grating laser cavity, and at the same time couple the orthogonal dual-frequency laser output from the orthogonal dual-polarization fiber grating laser cavity to the polarization beam splitter 3 and the subsequent optical path. The operating wavelength range of the pump laser input end of the wavelength division multiplexer 2 is 960nm-990nm, and the insertion loss does not exceed 0.5dB, that is, the insertion loss is controlled within 0.5dB, the pigtail type is 980nm single-mode fiber, and the port of the pump laser input end of the wavelength division multiplexer 2 is fused with the output pigtail of the pump laser.

[0032] The operating coverage wavelength range of the signal light end of the wavelength division multiplexer 2 is 1528nm-1565nm, and the insertion loss of the signal light end port does not exceed 0.5dB, that is, the insertion loss of the signal light end port is controlled within 0.5dB, the pigtail type of the signal light end is 1550nm polarization-maintaining optical fiber, and the signal light end port is fused with the input end of the polarization beam splitter 3.

[0033] The common end of the wavelength division multiplexer 2 has an operating wavelength range of 960nm-990nm and 1528nm-1565nm. The pigtail type of the common end port is a 1550nm polarization-maintaining pigtail, and the common end is fused with the output pigtail of the orthogonal dual-polarization fiber grating laser cavity.

[0034] In some feasible embodiments, preferably, the wavelength division multiplexer 2 is a dual-axis polarization-maintaining fiber passive device.

[0035] The above-mentioned polarization beam splitter 3 is used to separate the two orthogonal polarization states of single longitudinal mode lasers in the orthogonal dual polarization laser output by the orthogonal dual polarization fiber grating laser cavity. The optical fibers of the input port and the two output ports of the polarization beam splitter 3 are 1550nm polarization-maintaining optical fibers. The two output ports are the two output ends of the dual-frequency fiber grating laser. The two polarization states of the lasers output by the polarization beam splitter 3 are s-polarization state lasers and p-polarization state lasers, respectively. That is, the lasers output by the two output ports are orthogonally polarized lasers, wherein one port outputs s-polarization state lasers and the other port outputs p-polarization state lasers.

[0036] The insertion loss of the polarization beam splitter 3 does not exceed 1 dB, that is, the insertion loss is controlled within 1 dB. The input end of the polarization beam splitter 3 is fused with the signal light end of the wavelength division multiplexer 2, and the two output ends serve as output interfaces of the dual-frequency fiber grating laser.

[0037] The working process of the above-mentioned dual-frequency fiber grating laser is as follows: the pump source 4 (pump laser) outputs the pump laser, which is coupled into the orthogonal dual-polarization fiber grating laser cavity after passing through the wavelength division multiplexer 2. According to the birefringence effect in the orthogonal dual-polarization fiber grating laser cavity, the orthogonal dual-polarization fiber grating laser cavity outputs two orthogonal polarization mode lasers. After passing through the wavelength division multiplexer 2, the two orthogonal polarization mode lasers are transmitted to the input end of the polarization beam splitter 3. In the polarization beam splitter 3, the polarization beam splitter 3 separates the two orthogonal polarization mode lasers and outputs them from the two output ends of the polarization beam splitter 3 respectively, outputting two lasers with different frequencies.

[0038] A Brillouin optical time domain reflectometer, such as Figure 2 As shown, it includes the above-mentioned dual-frequency fiber grating laser, a pump wave transmission branch and an eigenwave transmission branch respectively connected to the dual-frequency fiber grating laser, an optical coupler 12 and a photoelectric detection device 13. The dual-frequency fiber grating laser serves as a light source in the optical path of the Brillouin optical time-domain reflectometer, and outputs two lasers with different frequencies for the Brillouin optical time-domain reflectometer, which are an eigenwave and a pump wave, respectively, so as to integrate the pump wave light source and the eigenwave light source in the prior art into one fiber grating laser, thereby reducing the complexity and cost of the light source of the Brillouin optical time-domain reflectometer; wherein the optical coupler 12 is respectively connected to the pump wave transmission branch and the eigenwave transmission branch, and the optical coupler 12 is connected to the photoelectric detection device 13, the pump wave transmission branch and the eigenwave transmission branch are used for the transmission of the two lasers output by the dual-frequency fiber grating laser, and of the two orthogonal polarization states of the laser output by the dual-frequency fiber grating laser, the laser with a higher frequency is used as the pump wave (with a frequency of ), the low frequency laser is used as the eigenwave (frequency is ), the high-frequency laser enters the pump wave transmission branch for transmission and processing, and the low-frequency laser enters the eigenwave transmission branch for transmission and processing. The two processed lasers are output after interference through the optical coupler 12 and are received by the photoelectric detection device 13.

[0039] The pump wave transmission branch includes a first amplifier 6, a gain switch 7, a second amplifier 8, a circulator 9 and a sensing optical fiber 10 connected in sequence. The circulator 9 is connected to an optical coupler 12. The high-frequency laser is amplified, modulated and amplified again by the first amplifier 6, the gain switch 7 and the second amplifier 8, and then injected into the sensing optical fiber 10 through the circulator 9. After the sensing optical fiber 10 is excited, the Brillouin scattered light generated by the sensor optical fiber 10 enters the optical coupler 12 through the circulator 9. The first amplifier 6 is set to perform a first amplification process on the high-frequency laser entering the pump wave transmission branch. The gain switch 7 is set to modulate the high-frequency laser after the first amplification process and modulate the high-frequency laser into a pulse light with a high extinction ratio. The second amplifier 8 is set to perform a second amplification process on the high-frequency laser after the modulation process. The sensing optical fiber 10 is set to generate Brillouin scattered light. The circulator 9 is set to inject the high-frequency laser after the second amplification process into the sensing optical fiber 10, and output the Brillouin scattered light generated after the sensor optical fiber 10 is excited to the optical coupler 12. Here, the frequency of the Brillouin scattered light excited by the pump wave is .

[0040] The first amplifier 6 and the second amplifier 8 are both erbium-doped fiber amplifiers, which are commercially available products and are selected according to actual needs. No specific requirements are made here.

[0041] The above-mentioned circulator 9 is a commercially available product, which is selected according to actual needs, and no specific requirements are made here.

[0042] The above-mentioned sensing optical fiber 10 is a commercially available product, which is selected according to actual needs, and no specific requirements are made here.

[0043] The above-mentioned eigenwave transmission branch includes a third amplifier 11. The low-frequency laser enters the optical coupler 12 after being amplified by the third amplifier 11. The third amplifier 11 is an erbium-doped fiber amplifier, which is a commercially available product and is selected according to actual needs. No specific requirements are made here.

[0044] The third amplifier 11 mentioned above is an erbium-doped fiber amplifier, which is a commercially available product and is selected according to actual needs. No specific requirements are made here.

[0045] The above-mentioned optical coupler 12 is a 2x2 optical coupler 12, which is a commercially available product. It is selected according to actual needs and no specific requirements are made here.

[0046] The above-mentioned photoelectric detection device 13 is a balanced photoelectric detector, which is a commercially available product and is selected according to actual needs. No specific requirements are made here.

[0047] The working process of the Brillouin optical time domain reflectometer is as follows: the dual-frequency fiber grating laser outputs two lasers with different frequencies, that is, the dual-frequency laser output by the dual-frequency fiber grating laser includes a high-frequency laser and a low-frequency laser, wherein the high-frequency laser is used as a pump wave ( ), the low frequency laser is used as the eigenwave ( ). The pump wave enters the first amplifier 6, is amplified by the first amplifier 6, and then enters the gain switch 7. It is modulated into a pulse light with a high extinction ratio by the gain switch 7. Then, the pulse light enters the second amplifier 8. After being amplified again by the second amplifier 8, it enters the circulator 9 from the port 1 of the circulator 9, and is injected into the sensing optical fiber 10 through the circulator 9. The Brillouin scattered light generated after the sensing optical fiber 10 is excited passes through the port 2 of the circulator 9, and then returns to the port 3 of the circulator 9, and enters the optical coupler 12 through the port 3 of the circulator 9; the eigenwave is amplified by the third amplifier 11 and enters the optical coupler 12. After the eigenwave interferes with the Brillouin scattered light returned from the port 3 of the circulator 9 in the 2x2 optical coupler 12, it is received by the photoelectric detection device 13.

[0048] Due to the adoption of the above technical solution, the dual-frequency fiber grating laser has a dual-frequency laser cavity and a pump source. After receiving the energy provided by the pump source, the dual-frequency fiber grating laser can output two single longitudinal mode lasers with orthogonal polarization states. The two single longitudinal mode lasers with orthogonal polarization states enter the polarization beam splitter through a wavelength division multiplexer, and are separated by the polarization beam splitter to output two polarization state lasers (s polarization state laser and p polarization state laser). The dual-frequency fiber grating laser is used as a light source in the optical path of the Brillouin optical time domain reflectometer, and only one light source is used to output two lasers with different frequencies. The two lasers with different frequencies are used as the pump wave and eigenwave of the Brillouin optical time domain reflectometer. The pump wave light source and the eigenwave light source in the optical time domain reflectometer system are realized in one fiber grating laser, eliminating the need for two independent lasers and a relatively expensive high-stability, large-bandwidth optical phase-locked loop device, external modulation devices or devices for nonlinear optical conversion optical paths, and complex modulation technology or optical nonlinear conversion technology, thereby reducing the complexity of the light source in the Brillouin optical time domain reflectometer system, improving the stability and reliability of the system, and reducing the cost of the light source in the Brillouin optical time domain reflectometer system. Moreover, the dual-frequency fiber grating laser is an all-fiber laser with a more compact size and smaller size, thereby making the size of the final Brillouin optical time domain reflectometer system instrument smaller.

[0049] The embodiments of the present invention are described in detail above, but the contents described are only preferred embodiments of the present invention and cannot be considered to limit the scope of implementation of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A Brillouin optical time domain reflectometer, characterized in that: It includes a dual-frequency fiber grating laser, a pump wave transmission branch and an eigenwave transmission branch respectively connected to the dual-frequency fiber grating laser, an optical coupler and a photoelectric detection device, wherein the optical coupler is respectively connected to the pump wave transmission branch and the eigenwave transmission branch, and the optical coupler is connected to the photoelectric detection device, and of the two lasers with orthogonal polarization states output by the dual-frequency fiber grating laser, the laser with a high frequency enters the pump wave transmission branch for transmission and processing, and the laser with a low frequency enters the eigenwave transmission branch for transmission and processing, and the two processed lasers are output after interference by the optical coupler and received by the photoelectric detection device; The dual-frequency fiber grating laser comprises a dual-frequency laser cavity, a wavelength division multiplexer connected to the dual-frequency laser, and a polarization beam splitter and a pump source respectively connected to the wavelength division multiplexer, wherein the wavelength division multiplexer couples the pump laser output by the pump source to the dual-frequency laser cavity, and couples the orthogonal dual-polarization laser output by the dual-frequency laser cavity to the polarization beam splitter, and the polarization beam splitter separates the orthogonal dual-polarization laser and outputs two lasers with orthogonal polarization states; The eigenwave transmission branch includes a third amplifier, and the low-frequency laser enters the optical coupler after being amplified by the third amplifier; The pump wave transmission branch includes a first amplifier, a gain switch, a second amplifier, a circulator and a sensing optical fiber connected in sequence, the circulator is connected to the optical coupler, the high-frequency laser is amplified, modulated and amplified again by the first amplifier, the gain switch and the second amplifier in sequence, and then injected into the sensing optical fiber through the circulator, and the sensing optical fiber is excited to generate Brillouin scattered light which enters the optical coupler through the circulator; The two laser beams with orthogonal polarization states output by the polarization beam splitter are respectively a laser beam in an s-polarization state and a laser beam in a p-polarization state; The frequency difference of the orthogonal dual-polarization lasers output by the dual-frequency laser cavity is adapted to the Brillouin frequency shift of the quartz optical fiber.

2. The Brillouin optical time domain reflectometer according to claim 1, characterized in that: The dual-frequency laser cavity is an orthogonal dual-polarization fiber grating laser cavity.

3. The Brillouin optical time domain reflectometer according to claim 2, characterized in that: The orthogonal dual-polarization fiber grating laser cavity is a distributed Bragg reflection cavity structure or a distributed Bragg feedback cavity structure.

4. The Brillouin optical time domain reflectometer according to claim 2 or 3, characterized in that: The orthogonal dual-polarization fiber grating laser cavity is packaged in a constant temperature and vibration isolation manner.

5. The Brillouin optical time domain reflectometer according to claim 4, characterized in that: The wavelength division multiplexer is a dual-axis polarization-maintaining optical fiber passive device, and the pump source is a pump laser.

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