U-band correlation optical time domain reflectometer based on random fiber laser

Abstract

The invention provides a U-band related optical time domain reflectometer based on a random fiber laser, which relates to the technical field of related optical time domain reflectometer and comprises a detection light source unit and a signal transmission and acquisition unit. A detection light source of the related optical time domain reflectometer is a 1.6 m random fiber laser with flexible output wavelength, the related optical time domain reflectometer specifically comprises a 1550 nm high-power pumping source, a point type feedback unit, a wavelength division multiplexer, an optical isolator and a passive optical fiber, and the point type feedback unit is a broadband point type feedback unit or a wavelength selection point type feedback unit; the signal transmission and acquisition unit comprises a second optical coupler, a circulator, a transmission optical fiber, a photoelectric detector, an avalanche photoelectric detector and an oscilloscope; according to the invention, the influence of the time delay effect on the system performance of the related optical time domain reflectometer can be avoided, and signal transmission and fault detection can be realized at the same time.

Description

Technical Field

[0001] The invention relates to the technical field of correlated optical time domain reflectometry, and in particular to a U-band correlated optical time domain reflectometer based on random fiber laser. Background Art

[0002] Correlated optical time-domain reflectometry is an optical time-domain reflectometry measurement method based on cross-correlation. Correlated optical time-domain reflectometry uses a continuous wave chaotic laser as a detection light source, which is injected into the optical fiber to be tested. When the chaotic light propagates in the optical fiber, backscattered light is generated. The backscattered light signal is cross-correlated with the originally emitted chaotic light. When there is a loss event such as a break in the link, a large reflection will be generated at this point, resulting in a high cross-correlation coefficient, which can then determine the location of the reflection event. The spatial distribution rate of the correlated optical time-domain reflectometer is independent of the distance and is only determined by the bandwidth of the chaotic light or the optical detection device. It can reach several centimeters in tens of kilometers of optical fiber. In addition to being applied to fault location, the dual-wavelength detection correlated optical time-domain reflectometer using wavelength-tunable chaotic light as the light source can also achieve high spatial distribution rate fiber Bragg grating sensing and positioning.

[0003] Lasers can be used as light sources for sensing systems. Generally, lasers are composed of working materials, resonant cavities, and pump sources. The working material is responsible for carrying a large number of atoms and molecules. With the help of the pump source, it can achieve particle number inversion, and then the stimulated radiation of particles can generate lasers. The existence of the resonant cavity can make the photons in the cavity have consistent frequency, phase, and running direction, so that the laser has good directionality and coherence. Random fiber lasers do not require the resonant cavity required in conventional fiber lasers, so they have lower requirements for the cavity, simpler structure, and more obvious advantages. Random fiber lasers are usually divided into three categories according to the gain type: fiber random lasers based on nonlinear gain, fiber random lasers based on rare earth doped ion gain, and fiber random lasers of mixed gain type. Among them, the gain in fiber random lasers based on nonlinear gain includes the gain generated by nonlinear effects such as Raman gain and Brillouin gain. Random Raman fiber lasers have the advantages of high output power and flexible wavelength conversion. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a U-band correlated optical time-domain reflectometer based on random fiber laser, which solves the problem of time delay effect caused by traditional semiconductor chaotic sources.

[0005] The technical solution of the present invention is as follows: A U-band correlated optical time-domain reflectometer based on random fiber laser, comprising a detection light source unit and a signal transmission and acquisition unit; The detection light source unit is a 1.6µm random fiber laser, including a 1550nm high-power pump source, a point feedback unit, a wavelength division multiplexer, an optical isolator and a passive optical fiber; the 1550nm high-power pump source is connected to one port of the wavelength division multiplexer, the point feedback unit is connected to another port of the wavelength division multiplexer, the common port of the wavelength division multiplexer is connected to the optical isolator, and the 1.6µm random fiber laser generated by laser in the passive optical fiber is used as the signal light of the correlated optical time domain reflectometer and is output from the output end of the optical isolator; The signal transmission and acquisition unit includes a second optical coupler, a circulator, a transmission optical fiber, a photodetector, an avalanche photodetector and an oscilloscope; the signal light output by the detection light source unit enters the second optical coupler, the splitting ratio of the second optical coupler is 9:1, wherein the 90% port transmits the signal light and is connected to the 1 port of the circulator, the 10% port transmits the reference light and is connected to the photodetector, the output end of the photodetector is connected to a channel of the oscilloscope, the signal light enters the transmission optical fiber through the 2 port of the circulator, the 3 port of the circulator is connected to the avalanche photodetector, and the output end of the avalanche photodetector is connected to another channel of the oscilloscope.

[0006] The passive optical fiber is a single-mode optical fiber or a dispersion-shifted optical fiber.

[0007] The detection distance range of the U-band correlated optical time domain reflectometer based on random fiber laser is 500-75000m.

[0008] The output power of the detection light source unit is 10-60mW.

[0009] The point feedback unit is a broadband point feedback unit or a wavelength selective point feedback unit; wherein the broadband point feedback unit is a first optical coupler with a splitting ratio of 1:1, and the wavelength selective point feedback unit is composed of a filter and a first optical coupler connected end to end.

[0010] When the point feedback unit of the detection light source unit is a wavelength selection point feedback unit, a fiber Bragg grating is connected to the tail end of the transmission optical fiber as a sensing element, and temperature and strain sensing is achieved by detecting changes in the mutual correlation coefficient caused by changes in the reflection intensity of the detection signal light.

[0011] The beneficial effects of adopting the above technical solution are: The present invention provides a U-band correlated optical time-domain reflectometer based on a random fiber laser. The present invention can achieve signal transmission and fault detection at the same time by designing a 1.6µm random fiber laser as a detection light source of the U-band correlated optical time-domain reflectometer. In addition, since the random fiber laser spectrum is modeless, a time delay effect can be avoided in the correlated optical time-domain reflectometer, which is beneficial to improving the positioning accuracy of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 Schematic diagram of a random fiber laser with a fixed wavelength in an embodiment of the present invention; Figure 2 Schematic diagram of a wavelength-tunable random fiber laser according to an embodiment of the present invention; Figure 3 Schematic diagram of a correlated optical time domain reflectometer based on a random fiber laser with a fixed wavelength in an embodiment of the present invention; Figure 4 Schematic diagram of a correlated optical time domain reflectometer based on a wavelength-tunable random fiber laser in an embodiment of the present invention; In the figure, 1-detection light source unit, 11-1550nm high power pump source, 13-wavelength division multiplexer, 14-passive optical fiber, 15-optical isolator, 2-second optical coupler, 3-circulator, 4-photodetector, 5-avalanche photodetector, 6-oscilloscope, 7-fiber Bragg grating, 8-transmission optical fiber, 121-broadband point feedback unit, 122-wavelength selection point feedback unit, 1211-first optical coupler, 1222-filter. DETAILED DESCRIPTION

[0013] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0014] A U-band correlated optical time domain reflectometer based on random fiber laser, comprising a detection light source unit 1 and a signal transmission and acquisition unit; The detection light source unit is a 1.6µm random fiber laser, including a 1550nm high-power pump source 11, a point feedback unit, a wavelength division multiplexer 13, a passive optical fiber 14 and an optical isolator 15; the 1550nm high-power pump source 11 is connected to one port of the wavelength division multiplexer 13, the point feedback unit is connected to another port of the wavelength division multiplexer 13, the common port of the wavelength division multiplexer 13 is connected to the optical isolator 15, and the 1.6µm random fiber laser generated by laser in the passive optical fiber 14 is output from the output end of the optical isolator as the signal light of the correlated optical time domain reflectometer; The signal transmission and acquisition unit includes a second optical coupler 2, a circulator 3, a transmission optical fiber 8, a photodetector 4, an avalanche photodetector 5 and an oscilloscope 6; the signal light output by the detection light source unit 1 enters the second optical coupler 2, the splitting ratio of the second optical coupler 2 is 9:1, wherein the 90% port transmits the signal light and is connected to the 1 port of the circulator 3, the 10% port transmits the reference light and is connected to the photodetector 4, the output end of the photodetector 4 is connected to a channel of the oscilloscope 6, the signal light is connected to the transmission optical fiber 8 through the 2 port of the circulator 3, the 3 port of the circulator 3 is connected to the avalanche photodetector 5, and the output end of the avalanche photodetector 5 is connected to another channel of the oscilloscope 6.

[0015] The passive optical fiber 14 is a single-mode optical fiber or a dispersion-shifted optical fiber.

[0016] The detection distance range of the U-band correlated optical time domain reflectometer based on random fiber laser is 500-75000m.

[0017] The output power of the detection light source unit is 10-60mW.

[0018] The point feedback unit is a broadband point feedback unit 121 or a wavelength selective point feedback unit 122, respectively. Figure 1 , Figure 2 As shown; wherein, the broadband point feedback unit 121 is composed of a first optical coupler 1211 with a splitting ratio of 1:1. Since the first optical coupler cannot change the wavelength of the output laser, it is a fixed wavelength, and the random fiber laser thus constructed is called a random fiber laser with a fixed wavelength; the wavelength selection point feedback unit 122 is composed of a filter 1222 and a first optical coupler 1211 connected end to end. The reflection wavelength of the point feedback unit is changed by changing the passing wavelength of the filter, so that the central wavelength of the laser output spectrum is changed, that is, the wavelength of the output laser can be adjusted by changing the filtering wavelength of the filter, which is called wavelength tunable. Therefore, the random fiber laser thus constructed is called a random fiber laser with adjustable wavelength, which can achieve dual-wavelength detection of the correlated optical time domain reflectometer.

[0019] The U-band correlated optical time-domain reflectometer based on random fiber laser can measure the change of reflectivity along the optical fiber. When the point feedback unit of the detection light source unit is a wavelength selection point feedback unit, the system can be used in conjunction with the fiber Bragg grating 7. By connecting the other end of the optical fiber to the fiber Bragg grating at the 2nd port of the circulator, the central wavelength of the fiber is sensitive to the external environment temperature and strain parameters, and the change of the mutual correlation coefficient caused by the change of the reflection intensity of the detection signal light is detected, thereby realizing temperature and strain sensing.

[0020] Example 1 Figure 3As shown, it is composed of a detection light source unit, a signal transmission and collection unit, wherein the point feedback unit in the detection light source unit 1 is a first optical coupler, such as Figure 1 As shown, the specific steps of system operation are: the 1550nm pump light generated by the 1550nm high-power pump source 11 enters the passive optical fiber 14 through the wavelength division multiplexer 13, and stimulates stimulated Raman scattering and Rayleigh scattering feedback in the passive optical fiber 14, and the backscattered light with changed wavelength propagates to the wavelength division multiplexer 13 again, and the light with a wavelength of 1.6µm can reach the first optical coupler 1211 through the wavelength division multiplexer 13, and the first optical coupler can provide broadband point feedback, and then the 1.6µm light enters the passive optical fiber 14 through the wavelength division multiplexer 13 again.

[0021] The above steps are performed continuously until a laser with good coherence and high energy is generated. The laser is generated in the passive optical fiber 14 and then output, and passes through the optical isolator 15 during the output process, which can prevent the subsequent system structure from affecting the random fiber laser.

[0022] The laser with a wavelength of 1.6µm enters the signal transmission and acquisition unit as a detection light source. It first passes through a second optical coupler 2, where the light is divided into two parts with a ratio of 1:9. 10% of the light is used as a reference light and then passes through the photodetector 4 to reach the oscilloscope 6. The remaining 90% of the light will pass through the circulator 3 and then propagate in the transmission optical fiber 8. When the optical signal encounters different medium interfaces (such as optical fiber sections), reflection will occur. The reflected light will pass through the circulator 3, the avalanche photodetector 5, and finally reach the oscilloscope 6. The reflected light signal and the reference light are cross-correlated. If the cross-correlation coefficient changes, it proves that the reflected light power has changed, that is, the optical fiber reflectivity has changed. Therefore, the system can lock the exact location of the fault by monitoring the change in reflectivity along the optical fiber. In this process, the circulator 3 can ensure that the returned light no longer enters the device before the circulator 3, and the avalanche photodetector 5 can amplify the reflected light signal so that even very weak light can be effectively detected.

[0023] Example 2 Figure 4 As shown, it is composed of a detection light source unit, a signal transmission and collection unit, wherein the point feedback unit in the detection light source unit is a combination of a first optical coupler and a filter, as shown in FIG. Figure 2As shown, the specific steps of system operation are: the 1550nm pump light generated by the 1550nm high-power pump source 11 enters the passive optical fiber 14 through the wavelength division multiplexer 13, and stimulates stimulated Raman scattering and Rayleigh scattering feedback in the passive optical fiber 14, and the backscattered light with changed wavelength propagates to the wavelength division multiplexer 13 again, and the light with a wavelength of 1.6µm can reach the wavelength selection point feedback unit 122 through the wavelength division multiplexer 13, where the first optical coupler can provide broadband point feedback, and the filter can screen out the optical signal with a specific wavelength and enter the passive optical fiber 14 again through the wavelength division multiplexer 13, so that the central wavelength of the laser output spectrum changes.

[0024] The above steps are performed continuously until a laser with good coherence, high energy and single wavelength is generated. The laser is generated in the passive optical fiber 14 and then output, and passes through the optical isolator 15 during the output process, which can prevent the subsequent system structure from affecting the random fiber laser.

[0025] The laser with a wavelength of 1.6µm enters the signal transmission and acquisition unit as a detection light source, and first passes through a second optical coupler 2, where the light is divided into two parts with a ratio of 1:9. 10% of the light is used as a reference light and then passes through the photodetector 4 to reach the oscilloscope 6. The remaining 90% of the light passes through the circulator 3 and enters the transmission optical fiber 8, and then is transmitted to the fiber Bragg grating 7 connected to the end of the transmission optical fiber 8. In this system, the temperature and strain sensing can be completed by monitoring the movement of the central wavelength of the fiber Bragg grating: the reflectivity of the fiber Bragg grating to two different wavelengths of detection light is related to its central wavelength. The greater the difference between the wavelength of the detection light and the central wavelength of the fiber Bragg grating, the smaller the reflectivity of the fiber Bragg grating to the detection light, and the smaller the intensity of the returned optical signal. The central wavelength of the fiber Bragg grating will change with the influence of external temperature and strain, resulting in a change in the reflectivity of the detection light, and then a change in the intensity of the returned light. By subtracting the mutual correlation coefficient of the return signal of the detection light of two different wavelengths from the reference light, the peak power difference of the mutual correlation coefficient of the two lights can be obtained. The peak power difference is linearly related to the central wavelength of the fiber Bragg grating, and the central wavelength of the fiber Bragg grating can be inferred from this. If the peak power difference calculated based on the two light intensities changes, the change in the central wavelength of the fiber Bragg grating can be obtained, and then the degree of change in the external environment can be determined. This part can be specifically expressed by the formula: Reflectivity of fiber Bragg grating to probe light The central wavelength of the fiber Bragg grating And its own wavelength The relationship is: , where B is the bandwidth of the fiber Bragg grating; Assume two different wavelengths λ1 and λ 2 The wavelength difference of the detection light is , then the signal intensity after being reflected by the fiber Bragg grating is and The central wavelength of the fiber Bragg grating and its own wavelength ( or ) is: , ; ∆λ is λ 1 and λ 2 The difference between the two light intensities can be obtained as follows:

[0026] In this process, the circulator 3 can ensure that the returned light no longer enters the device before the circulator 3, and the avalanche photodetector 5 can amplify the reflected light signal so that even very weak light can be effectively detected.

[0027] Since the wavelength of the optical signal of the related optical time domain reflectometer is in the U band and the wavelength is adjustable, the transmission of the optical signal with a wavelength in the C band can be achieved without interruption during use, so the invention can achieve fault monitoring and signal transmission at the same time.

[0028] The above description is only a preferred embodiment of the present disclosure and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in the embodiments of the present disclosure is not limited to the technical solutions formed by a specific combination of the above technical features, but should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the above inventive concept. For example, the above features are replaced with (but not limited to) technical features with similar functions disclosed in the embodiments of the present disclosure to form a technical solution.

Claims

1. A U-band correlated optical time-domain reflectometer based on random fiber laser, characterized in that: It includes a detection light source unit and a signal transmission and collection unit; The detection light source unit is a 1.6µm random fiber laser, including a 1550nm high-power pump source, a point feedback unit, a wavelength division multiplexer, an optical isolator and a passive optical fiber; the 1550nm high-power pump source is connected to one port of the wavelength division multiplexer, the point feedback unit is connected to another port of the wavelength division multiplexer, the common port of the wavelength division multiplexer is connected to the optical isolator, and the 1.6µm random fiber laser generated by laser in the passive optical fiber is used as the signal light of the correlated optical time domain reflectometer and is output from the output end of the optical isolator; The signal transmission and acquisition unit includes a second optical coupler, a circulator, a transmission optical fiber, a photodetector, an avalanche photodetector and an oscilloscope; the signal light output by the detection light source unit enters the second optical coupler, the splitting ratio of the second optical coupler is 9:1, wherein the 90% port transmits the signal light and is connected to the 1 port of the circulator, the 10% port transmits the reference light and is connected to the photodetector, the output end of the photodetector is connected to a channel of the oscilloscope, the signal light enters the transmission optical fiber through the 2 port of the circulator, the 3 port of the circulator is connected to the avalanche photodetector, and the output end of the avalanche photodetector is connected to another channel of the oscilloscope.

2. The U-band correlated optical time domain reflectometer based on random fiber laser according to claim 1, characterized in that: The passive optical fiber is a single-mode optical fiber or a dispersion-shifted optical fiber.

3. The U-band correlated optical time domain reflectometer based on random fiber laser according to claim 1, characterized in that: The detection distance range of the U-band correlated optical time domain reflectometer based on random fiber laser is 500-75000m.

4. The U-band correlated optical time domain reflectometer based on random fiber laser according to claim 1, characterized in that: The output power of the detection light source unit is 10-60mW.

5. The U-band correlated optical time domain reflectometer based on random fiber laser according to claim 1, characterized in that: The point feedback unit is a broadband point feedback unit or a wavelength selective point feedback unit; wherein the broadband point feedback unit is a first optical coupler with a splitting ratio of 1:1, and the wavelength selective point feedback unit is composed of a filter and a first optical coupler connected end to end.

6. The U-band correlated optical time domain reflectometer based on random fiber laser according to claim 5, characterized in that: When the point feedback unit of the detection light source unit is a wavelength selection point feedback unit, a fiber Bragg grating is connected to the tail end of the transmission optical fiber as a sensing element, and temperature and strain sensing is achieved by detecting changes in the mutual correlation coefficient caused by changes in the reflection intensity of the detection signal light.

Images