Double-pulse modulation long-distance distributed optical fiber temperature sensing system

Abstract

The invention relates to a double-pulse modulation long-distance distributed optical fiber temperature sensing system which comprises a laser, laser output by the laser is transmitted to a grating and a first-stage laser modulator through a beam splitter, laser output by the first-stage laser modulator is transmitted to one port of a circulator through a first laser amplifier, and laser output by the second-stage laser modulator is transmitted to the other port of the circulator through a second laser amplifier. A lower port of the circulator is connected with the sensing optical fiber, a second lower port of the circulator is connected with the input end of the second laser amplifier, the grating and the output end of the second laser amplifier are connected with the signal processing module, and a second-level laser modulator is further arranged between the first-level laser modulator and the first laser amplifier. The laser pulse width output by the first-stage laser modulator is larger than that output by the second-stage laser modulator, and the first-stage laser modulator has laser intensity gain of at least one decibel. The dipulse modulation long-distance distributed optical fiber temperature sensing system provided by the invention has a relatively long detection distance under the condition that the resolution ratio is not reduced.

Description

Technical Field

[0001] The present invention relates to a distributed optical fiber temperature sensing system, in particular to a dual-pulse modulation long-distance distributed optical fiber temperature sensing system. Background Art

[0002] The distributed fiber optic Brillouin temperature and strain monitoring system is based on BODTR (optical time domain reflectometry) technology. It detects stimulated Brillouin scattered light, identifies the spectrum at the optical cable location after photoelectric conversion, and uses a related demodulation algorithm to implement a real-time monitoring system for distributed optical cable temperature and micro-deformation.

[0003] In existing Brillouin temperature and strain monitoring equipment, the temperature monitoring technology is limited by the laser pulse energy, resulting in a short detection range of approximately 50 kilometers for a single channel and single optical fiber. To increase the detection range, the system needs to increase the laser pulse width to increase its output energy. This increases the detection range, but the increased laser pulse width reduces the system's sampling resolution, further reducing the system's detection resolution. Therefore, how to increase the detection range while maintaining the system's resolution has become a pressing technical challenge. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a dual-pulse modulation long-distance distributed optical fiber temperature sensing system with a long detection distance without reducing the resolution.

[0005] The dual-pulse modulation long-distance distributed optical fiber temperature sensing system of the present invention includes a laser, a first-level laser modulator, a first laser amplifier, and a circulator. The laser light output by the laser is transmitted to a grating and the first-level laser modulator respectively through a beam splitter. The laser light output by the first-level laser modulator is transmitted to one port of the circulator through the first laser amplifier. The next port of the circulator is connected to a sensing optical fiber, and the next port of the circulator is connected to the input end of a second laser amplifier. The output ends of the grating and the second laser amplifier are connected to a signal processing module. A second-level laser modulator is further provided between the first-level laser modulator and the first laser amplifier. The input end of the second-level laser modulator is connected to the output end of the first-level laser modulator, and the output end of the second-level laser modulator is connected to the input end of the first laser amplifier. The laser pulse width output by the first-level laser modulator is greater than the laser pulse width output by the second-level laser modulator, and the first-level laser modulator has a laser intensity gain of at least 1 decibel.

[0006] The advantage of this dual-pulse modulation long-distance distributed fiber optic temperature sensing system is that it outputs wide-pulse laser through a first-level laser modulator and performs intensity gain on the laser output by the laser. The amplified wide-pulse laser then outputs narrow-pulse laser through a second-level laser modulator, thereby forming a high-intensity narrow-pulse laser. In this way, the intensity of the laser output to the sensing optical fiber can be increased without reducing the system acquisition resolution, thereby greatly improving the effective detection distance of the sensing system.

[0007] Furthermore, in the dual-pulse modulation long-distance distributed optical fiber temperature sensing system of the present invention, a first wavelength division multiplexer is arranged between the circulator and the sensing optical fiber. The dual-pulse modulation long-distance distributed optical fiber temperature sensing system also includes a first pump source and a second pump source. The lasers output by the first pump source and the second pump source are transmitted to the first wavelength division multiplexer through the second wavelength division multiplexer, and are combined with the laser output by the circulator and then transmitted to the sensing optical fiber.

[0008] The setting of the first wavelength division multiplexer and the second wavelength division multiplexer realizes the combination of the three wavelengths of laser output by the laser, the first pump source, and the second pump source, thereby improving the signal intensity of Brillouin scattering in the second half of the sensing optical fiber, achieving the purpose of enhancing the signal and increasing the measurement length.

[0009] Furthermore, in the dual-pulse modulation long-distance distributed optical fiber temperature sensing system of the present invention, the laser wavelength output by the first pump source is 1450 nanometers, and the laser wavelength output by the second pump source is 1475 nanometers.

[0010] Furthermore, in the dual-pulse modulation long-distance distributed optical fiber temperature sensing system of the present invention, the laser output by the laser has a wavelength of 1550 nanometers.

[0011] Furthermore, in the dual-pulse modulation long-distance distributed optical fiber temperature sensing system of the present invention, the first laser amplifier and the second laser amplifier are both erbium-doped fiber amplifiers.

[0012] Furthermore, in the dual-pulse modulation long-distance distributed optical fiber temperature sensing system of the present invention, the first-level laser modulator is an electro-optical modulator, and the pulse width of its driving signal is 500-800 nanoseconds.

[0013] Furthermore, in the dual-pulse modulation long-distance distributed optical fiber temperature sensing system of the present invention, the secondary laser modulator is an acousto-optic modulator, and the pulse width of its driving signal is 4 to 20 nanoseconds.

[0014] Furthermore, in the dual-pulse modulation long-distance distributed optical fiber temperature sensing system of the present invention, the intensity gain of the input laser by the first-stage laser modulator is 2 decibels.

[0015] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement them in accordance with the contents of the specification, the embodiments of the present invention are described in detail below. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a structural block diagram of a dual-pulse modulation long-distance distributed optical fiber temperature sensing system according to Example 1.

[0017] Figure 2 This is a structural block diagram of a dual-pulse modulation long-distance distributed optical fiber temperature sensing system according to embodiment 2.

[0018] In the figure, there is a laser 1, a first-stage laser modulator 2, a first laser amplifier 3, a circulator 4, a grating 5, a sensing fiber 6, a second laser amplifier 7, a signal processing module 8, a second-stage laser modulator 9, a first wavelength division multiplexer 10, a first pump source 11, a second pump source 12, and a second wavelength division multiplexer 13. DETAILED DESCRIPTION

[0019] The following embodiments of the present invention are described in further detail with reference to 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.

[0020] Example 1: See Figure 1 The dual-pulse modulation long-distance distributed fiber optic temperature sensing system of this embodiment includes a laser 1, a first-level laser modulator 2, a first laser amplifier 3, and a circulator 4. The laser light output by the laser is transmitted to a grating 5 and a first-level laser modulator respectively through a beam splitter. The laser light output by the first-level laser modulator is transmitted to one port of the circulator through the first laser amplifier. The next port of the circulator is connected to a sensing optical fiber 6, and the next port of the circulator is connected to the input end of a second laser amplifier 7. The output ends of the grating and the second laser amplifier are connected to a signal processing module 8. A second-level laser modulator 9 is further provided between the first-level laser modulator and the first laser amplifier. The input end of the second-level laser modulator is connected to the output end of the first-level laser modulator, and the output end of the second-level laser modulator is connected to the input end of the first laser amplifier. The laser pulse width output by the first-level laser modulator is greater than the laser pulse width output by the second-level laser modulator, and the first-level laser modulator has a laser intensity gain of at least 1 decibel.

[0021] The advantage of this dual-pulse modulation long-distance distributed fiber optic temperature sensing system is that it outputs wide-pulse laser through a first-level laser modulator and performs intensity gain on the laser output by the laser. The amplified wide-pulse laser then outputs narrow-pulse laser through a second-level laser modulator, thereby forming a high-intensity narrow-pulse laser. In this way, the intensity of the laser output to the sensing optical fiber can be increased without reducing the system acquisition resolution, thereby greatly improving the effective detection distance of the sensing system.

[0022] The laser is used to generate laser light. In this embodiment, the laser outputs laser light with a wavelength of 1550 nanometers.

[0023] The beam splitter is used to output the laser light generated by the laser to the first-stage laser modulator and the grating respectively. The laser light input to the first-stage laser modulator is ultimately transmitted to the sensing fiber, thereby generating scattered light. The grating is used to generate an optical signal corresponding to the center of the Brillouin frequency shift, which is used to interfere with the backscattered light generated by the sensing fiber.

[0024] The primary laser modulator and the secondary laser modulator are used to perform two-stage modulation on the laser output by the laser to form a high-intensity, narrow-pulse-width laser.

[0025] The first laser amplifier is used to amplify the laser light output by the secondary laser modulator to ensure the laser intensity after long-distance transmission and the detection distance of the system.

[0026] The circulator is used to transmit the laser light output by the first laser amplifier to the sensing optical fiber, and transmit the scattered light signal generated by the sensing optical fiber to the second laser amplifier.

[0027] The second laser amplifier amplifies the scattered light signal output by the sensing optical fiber to ensure the sensitivity of subsequent signal detection.

[0028] In this embodiment, the first laser amplifier and the second laser amplifier are both erbium-doped fiber amplifiers.

[0029] The first-stage laser modulator is an electro-optic modulator, and the second-stage amplifier is an acousto-optic modulator.

[0030] The signal processing module is used to detect the scattered light of the sensing optical fiber. Specifically, the detection light output by the grating and the scattered light output by the second laser amplifier are coupled through a coupler and transmitted to the signal processing module. The signal processing module obtains the optical signal through the photodetector and transmits the detected optical signal to the spectrometer for analysis. The upper computer finally obtains the position and temperature of the sensing optical fiber corresponding to the scattered light by analyzing the optical signal spectrum. Its specific structure and principle are conventional technologies in this field and will not be repeated here.

[0031] Example 2: Reference Figure 2The dual-pulse modulation long-distance distributed optical fiber temperature sensing system of this embodiment adds the following technical content on the basis of the first embodiment. Specifically, a first wavelength division multiplexer 10 is arranged between the circulator and the sensing optical fiber. The dual-pulse modulation long-distance distributed optical fiber temperature sensing system also includes a first pump source 11 and a second pump source 12. The lasers output by the first pump source and the second pump source are transmitted to the first wavelength division multiplexer through the second wavelength division multiplexer 13, and are combined with the laser output by the circulator and then transmitted to the sensing optical fiber.

[0032] The setting of the first wavelength division multiplexer and the second wavelength division multiplexer realizes the combination of the three wavelengths of laser output by the laser, the first pump source, and the second pump source, thereby improving the signal intensity of Brillouin scattering in the second half of the sensing optical fiber, achieving the purpose of enhancing the signal and increasing the measurement length.

[0033] In actual applications, by combining the high-intensity narrow-pulse laser generated by the first-level laser modulator and the second-level laser modulator, the system can increase the temperature detection length of conventional Brillouin temperature and strain monitoring equipment from 50 km to 70 km. With the cost increased by less than 10%, the equipment performance is improved by 40%, thereby reducing the use cost of the equipment per unit distance to enable it to meet more usage scenarios.

[0034] During specific operation, the laser output by the laser is transmitted to the first-level amplifier and the grating respectively through the beam splitter. The first-level amplifier transmits the laser to the second-level amplifier, and then transmits the laser to one port of the circulator through the first laser amplifier. The laser transmitted to the circulator is transmitted to the first wavelength division multiplexer through the next port of the circulator. At the same time, the laser generated by the first pump source and the second pump source is combined through the second wavelength division multiplexer and transmitted to the first wavelength multiplexer. It is combined with the laser transmitted to the first wavelength division multiplexer by the circulator and output to the sensing optical fiber.

[0035] The Brillouin scattered light generated by the sensing optical fiber is transmitted back to the corresponding port of the circulator through the first combiner, and then transmitted to the second laser amplifier through its next port. The scattered light output by the second laser amplifier and the detection light output by the grating are coupled by a coupler and transmitted to the signal processing module, which then detects the scattered light and ultimately realizes the detection of temperature and distance.

[0036] In summary, the dual-pulse modulation long-distance distributed fiber optic temperature sensing system of this embodiment improves the system detection distance without reducing the sampling resolution. Through the two-stage modulation of the first-level laser modulator and the second-level laser modulator, the dual pump source enhanced signal of the first pump source and the second pump source increases the Brillouin temperature measurement detection distance from the conventional 50 km to 70 km, an increase of 40%, while the sampling accuracy remains unchanged.

[0037] Preferably, the laser wavelength output by the first pump source is 1450 nanometers, and the laser wavelength output by the second pump source is 1475 nanometers.

[0038] Preferably, the laser output by the laser has a wavelength of 1550 nanometers.

[0039] Preferably, the first laser amplifier and the second laser amplifier are both erbium-doped fiber amplifiers.

[0040] Preferably, the primary laser modulator is an electro-optical modulator, and the pulse width of its driving signal is 500-800 nanoseconds.

[0041] Preferably, the secondary laser modulator is an acousto-optic modulator, and the pulse width of its driving signal is 4 to 20 nanoseconds.

[0042] Preferably, the intensity gain of the input laser by the first-stage laser modulator is 2 decibels.

[0043] The above is only a preferred embodiment of the present invention, which is used to assist those skilled in the art to implement the corresponding technical solutions, and is not used to limit the scope of protection of the present invention, which is defined by the appended claims. It should be pointed out that for those skilled in the art, a number of equivalent improvements and variations can be made based on the technical solution of the present invention, and these improvements and variations should also be regarded as the scope of protection of the present invention. At the same time, it should be understood that although this specification is described in accordance with the above-mentioned embodiments, not every embodiment contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions of each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A dual-pulse modulation long-distance distributed optical fiber temperature sensing system, comprising a laser (1), a first-stage laser modulator (2), a first laser amplifier (3) and a circulator (4), wherein the laser output by the laser is transmitted to a grating (5) and a first-stage laser modulator respectively through a beam splitter, the laser output by the first-stage laser modulator is transmitted to one port of the circulator through the first laser amplifier, the next port of the circulator is connected to a sensing optical fiber (6), the next port of the circulator is connected to the input end of a second laser amplifier (7), the output ends of the grating and the second laser amplifier are connected to a signal processing module (8), and the system is characterized in that: A secondary laser modulator (9) is further provided between the primary laser modulator and the first laser amplifier, the input end of the secondary laser modulator being connected to the output end of the primary laser modulator, the output end of the secondary laser modulator being connected to the input end of the first laser amplifier, the laser pulse width output by the primary laser modulator being greater than the laser pulse width output by the secondary laser modulator, and the primary laser modulator having a laser intensity gain of at least 1 decibel.

2. The dual-pulse modulation long-distance distributed optical fiber temperature sensing system according to claim 1, characterized in that: A first wavelength division multiplexer (10) is provided between the circulator and the sensing optical fiber. The dual-pulse modulation long-distance distributed optical fiber temperature sensing system further comprises a first pump source (11) and a second pump source (12). The lasers output by the first pump source and the second pump source are transmitted to the first wavelength division multiplexer through the second wavelength division multiplexer (13), and are combined with the laser output by the circulator and then transmitted to the sensing optical fiber.

3. The dual-pulse modulation long-distance distributed optical fiber temperature sensing system according to claim 2, characterized in that: The laser wavelength output by the first pump source is 1450 nanometers, and the laser wavelength output by the second pump source is 1475 nanometers.

4. The dual-pulse modulation long-distance distributed optical fiber temperature sensing system according to claim 1, characterized in that: The laser output by the laser has a wavelength of 1550 nanometers.

5. The dual-pulse modulation long-distance distributed optical fiber temperature sensing system according to claim 1, characterized in that: The first laser amplifier and the second laser amplifier are both erbium-doped fiber amplifiers.

6. The dual-pulse modulation long-distance distributed optical fiber temperature sensing system according to claim 1, characterized in that: The primary laser modulator is an electro-optical modulator, and the pulse width of its driving signal is 500-800 nanoseconds.

7. The dual-pulse modulation long-distance distributed optical fiber temperature sensing system according to claim 1, characterized in that: The secondary laser modulator is an acousto-optic modulator, and the pulse width of its driving signal is 4 to 20 nanoseconds.

8. The dual-pulse modulation long-distance distributed optical fiber temperature sensing system according to claim 1, characterized in that: The intensity gain of the first-stage laser modulator to the input laser is 2 decibels.

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