CN107044862B - Hybrid fiber optic sensing system - Google Patents

Abstract

The invention discloses a hybrid optical fiber sensing system, and relates to the technical field of optical fiber sensing. The sensing system comprises a laser, an optical fiber coupler, a continuous detection optical path, a pumping pulse optical path, a sensing optical fiber, a second optical fiber circulator and a control system. The output end of the laser is divided into two paths after passing through the optical fiber coupler, the first path is connected with the input end of the continuous detection optical path, the second path is connected with the input end of the pumping pulse optical path, the output end of the continuous detection optical path is connected with one input end of the second optical fiber circulator through the sensing optical fiber, the output end of the pumping pulse optical path is connected with the other input end of the second optical fiber circulator, and the output end of the second optical fiber circulator is connected with the input end of the control system. The system has low cost, and can realize the static and dynamic simultaneous extraction of the whole and partial key strain/temperature information of the structure with larger range and higher space precision.

Description

Hybrid Fiber Sensing System

technical field

The invention relates to the technical field of optical fiber sensing, in particular to a hybrid optical fiber sensing system utilizing optical fiber grating reflection/transmission and optical fiber stimulated Brillouin scattering synchronous testing.

Background technique

Structural health monitoring can provide reliable data for performance evaluation, damage diagnosis and life prediction of structures during service, and can also provide important parameters for structure design, protection and theoretical research. Based on the technical advantages of optical fiber sensing, fiber Bragg grating sensing technology and sensing technology based on fiber Brillouin scattering have played an important role in the field of structural health monitoring. Especially in recent years, the sensing technology based on stimulated Brillouin scattering (BOTDA) has been greatly improved in terms of sensing range and spatial accuracy, and has obvious advantages over the sensing technology based on fiber optic spontaneous Brillouin scattering. Fiber Bragg grating sensing technology has the unique advantages of high precision, multiplexing and dynamic measurement, but it can only provide discrete spatial information. On the contrary, the sensing technology based on optical fiber Brillouin scattering can provide continuous information along the optical fiber within a range of hundreds of kilometers, but the accuracy is lower. How to integrate the two, give full play to the advantages of dual technologies, and simultaneously realize the overall information grasp of the structure and the monitoring of local key information is of great significance for structural health monitoring.

At present, researchers have carried out active research on this issue and achieved some research results. For example, the patent "Full-scale distributed and local high-precision collinear optical fiber sensing method" (application number: ZL200810064168.3) proposes to use optical switches or couplers to integrate BOTDA(R) and FBG demodulators to form a new Monitoring System. Patents "Based on Brillouin Optical Time Domain Reflective Optical Fiber Sensing and Fiber Bragg Grating Sensing Bottom Plate Stress Monitoring Device and Method" (Application No.: ZL201220426263.X) and "FBG-BOTDA Joint Sensor Detection Method for Pipe Piles Driven into Soil Layer "(Publication 201310397789.4) adopted a similar plan. Literature (Journal of Lightwave Technology, 2013, 31:1559-1565; Structural Health Monitoring, 2010, 9: 341-346; International Journal of Distributed Sensor Networks, 2012; Structural Control and HealthMonitoring, 2014, 21: 317 -330.) also The simultaneous application of two optical fiber sensing technologies to the monitoring of prestress loss in transmission lines, tunnels, FRP and concrete beams was reported respectively. The above schemes and applications, in essence, adopt the dual system of BOTDA(R) and FBG demodulator to realize single-fiber sharing. Among them, the optical switch solution cannot realize the simultaneous testing of the two. In the coupler scheme, BOTDR and FBG demodulator can be tested at the same time through a simple design, and the two will not cause mutual interference between optical signals; but during the simultaneous test of BOTDA and FBG, since BOTDA is a double-ended test It will enter the FBG demodulator, causing the signal-to-noise ratio of the demodulation system to decrease, and the peak finding is not accurate or even impossible to find the peak. The adoption of dual systems will lead to an increase in monitoring costs, and no real technical integration has been achieved. The patent "distributed optical fiber sensor for simultaneous monitoring of overall and local strain in engineering structures" (application number: 201110069430.5) adopts a single-system single-fiber technical solution, which makes the system compatible with fiber grating and Brillouin time-domain reflection technology, reducing system cost . This scheme can be used as a fusion of BOTDR technology based on single-ended measurement and FBG sensing technology. Compared with the sensing technology based on optical fiber stimulated Brillouin scattering, its sensing distance and spatial test accuracy are relatively limited.

Contents of the invention

The technical problem to be solved by the present invention is how to provide a hybrid optical fiber sensing system that can simultaneously acquire overall structural information of a larger range and higher spatial precision as well as static and dynamic information of local key positions.

In order to solve the above technical problems, the technical solution adopted by the present invention is: a hybrid optical fiber sensing system, characterized in that it includes a laser, an optical fiber coupler, a continuous detection optical path, a pump pulse optical path, a sensing optical fiber, a second optical fiber A circulator and a control system, the output end of the laser is divided into two paths through a fiber coupler, the first path is connected to the input end of the continuous detection optical path, and the second path is connected to the input end of the pump pulse optical path , the output end of the continuous detection optical path is connected to an input end of the second optical fiber circulator through the sensing fiber, and the output end of the pump pulse optical path is connected to the other input end of the second optical fiber circulator , the output end of the second optical fiber circulator is connected to the input end of the control system.

A further technical solution is that: the continuous detection optical path includes a second optical fiber polarization controller, a second photoelectric modulator, a first optical fiber circulator, a fiber grating, a second optical fiber amplifier and a polarization scrambler. One output end of the fiber coupler is connected to the input end of the second fiber polarization controller, the output end of the second fiber polarization controller is connected to the input end of the second photoelectric modulator, and the first The output end of the two photoelectric modulators is connected to an input end of the first optical fiber circulator, the fiber grating is connected to the other input end of the first optical fiber circulator, and the output end of the first optical fiber circulator connected to the input end of the second optical fiber amplifier, the output end of the second optical fiber amplifier is connected to the input end of the polarization scrambler, and the output end of the polarization scrambler is connected to one end of the sensing fiber.

A further technical solution is: the pump pulse optical path includes a first fiber polarization controller, a first electro-optic modulator, a third fiber polarization controller, a third electro-optic modulator, a pulse generator, and a first fiber amplifier, the An output end of the fiber coupler is connected to an input end of the first fiber polarization controller, an output end of the first fiber polarization controller is connected to an input end of the first electro-optic modulator, and the first The output end of the electro-optic modulator is connected to the input end of the third fiber polarizer, the output end of the third fiber polarizer is connected to an input end of the third electro-optic modulator, and the output of the pulse generator end is connected with the other input end of the third electro-optic modulator, the output end of the third electro-optic modulator is connected with the input end of the first optical fiber amplifier, and the output end of the first optical fiber amplifier is connected with the One input end of the second optical fiber circulator is connected.

A further technical solution is: the control system includes a third optical fiber circulator, an optical fiber F-P filter, a sawtooth wave generator, a first photodetector, a bandpass filter, a second photodetector, and a signal acquisition and controller, The output end of the second optical fiber circulator is connected to the input end of the third optical fiber circulator, an output end of the third optical fiber circulator is connected to an input end of the optical fiber F-P filter, and the sawtooth The output end of the wave generator is connected to the other input end of the optical fiber F-P filter, and the output end of the optical fiber F-P filter is connected to an input end of the signal acquisition and controller through the first photodetector , the other output end of the third optical fiber circulator is connected to the input end of the band-pass filter, and the output end of the band-pass filter is connected to the signal acquisition and controller via the second photodetector The other input terminal of the signal acquisition and controller is connected to the control terminal of the sawtooth wave generator.

A further technical solution is: a fiber grating array is arranged on the sensing optical fiber.

A further technical solution is: the fiber grating array includes more than two fiber gratings.

The beneficial effect produced by adopting the above technical scheme is that: the continuous detection optical path, the pump pulse optical path and the sensing fiber form a stimulated Brillouin scattering optical path based on double-ended measurement; meanwhile, the pump pulse optical path is The pulsed broadband light can be used as the main light source of the fiber grating array. When the optical power of the pump pulse optical path in certain bands is lower than the optical power of the continuous detection optical path, the continuous detection light provides a light source for the fiber grating array; The light source increases the system stability and expands the usage bandwidth of the fiber grating in the sensing fiber, thereby increasing the number of multiplexables.

The wavelength selection of the fiber grating array is performed by the rear optical fiber F-P filter, which avoids the light of the continuous detection optical path or the pump pulse optical path directly entering the first photodetector during the double-ended measurement process, resulting in a decrease in the signal-to-noise ratio or annihilation of the signal .

The transmitted light of the fiber grating array based on the continuous detection optical path and the reflected light of the fiber grating array based on the pump pulse optical path are coupled and enter the first photodetector at the same time. At this time, the signal acquisition and the controller have both the maximum light intensity detection and the minimum Two control modes for light intensity detection.

In summary, the sensing system can effectively reduce the system cost through the single-system single-fiber synchronous measurement of the fiber grating reflection/transmission and fiber stimulated Brillouin scattering signals. Through the optical system design, the static and dynamic simultaneous extraction of structural overall and local key strain/temperature information with a larger range and higher spatial precision can be achieved.

Description of drawings

Fig. 1 is the functional block diagram of hybrid optical fiber sensing system described in the embodiment of the present invention;

Among them: 1. Laser 2, fiber coupler 3, continuous detection optical path 31, second fiber polarization controller 32, second photoelectric modulator 33, first fiber circulator 34, fiber grating 35, second fiber amplifier 36, scrambler Polarizer 4, sensing fiber 41, fiber grating 5, pump pulse optical path 51, first fiber polarization controller 52, first electro-optic modulator 53, third fiber polarization controller 54, third electro-optic modulator 55, pulse Generator 56, first optical fiber amplifier 6, second optical fiber circulator 7, control system 71, third optical fiber circulator 72, optical fiber F-P filter 73, sawtooth wave generator 74, first photodetector 75, bandpass filter Device 76, second photodetector 77, signal acquisition and controller.

Detailed ways

The technical solutions in the embodiments of the present invention are clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

In the following description, a lot of specific details are set forth in order to fully understand the present invention, but the present invention can also be implemented in other ways different from those described here, and those skilled in the art can do it without departing from the meaning of the present invention. By analogy, the present invention is therefore not limited to the specific examples disclosed below.

As shown in Figure 1, the embodiment of the present invention discloses a hybrid optical fiber sensing system, including a laser 1, a fiber coupler 2, a continuous detection optical path 3, a sensing fiber 4, a pump pulse optical path 5, and a second optical fiber circulator 6 and control system 7. The output end of the laser 1 is divided into two paths through the fiber coupler 2, the first path is connected to the input end of the continuous detection optical path 3, and the second path is connected to the input end of the pump pulse optical path 5, so The output end of the continuous detection optical path 3 is connected to an input end of the second optical fiber circulator 6 through the sensing fiber 4, and the output end of the pump pulse optical path 5 is connected to the other input end of the second optical fiber circulator 6. The input end is connected, and the output end of the second optical fiber circulator 6 is connected with the input end of the control system 7 .

Preferably, the laser 1 is a narrow linewidth laser. The sensing fiber 4 is provided with a fiber grating array, and the fiber grating array includes more than two fiber gratings 41 .

Further, as shown in Figure 1, the continuous detection optical path includes a second fiber polarization controller 31, a second photoelectric modulator 32, a first fiber circulator 33, a fiber grating 34, a second fiber amplifier 35 and a polarization scrambler 36. An output end of the fiber coupler 2 is connected to the input end of the first fiber polarization controller 31, and an output end of the second fiber polarization controller 31 is connected to the input end of the second photoelectric modulator 32 , the output end of the second photoelectric modulator 32 is connected to an input end of the first optical fiber circulator 33, and the fiber grating 34 is connected to the other input end of the first optical fiber circulator 33, the The output end of the first optical fiber circulator 33 is connected with the input end of the second optical fiber amplifier 35, and the output end of the second optical fiber amplifier 35 is connected with the input end of the described polarization scrambler 36, and the described polarization scrambler 36 The output end of the sensor is connected with one end of the sensing fiber 4.

Further, as shown in FIG. 1 , the pump pulse optical circuit 5 includes a first fiber polarization controller 51, a first electro-optic modulator 52, a third fiber polarization controller 53, a third electro-optic modulator 54, and a pulse generator 55. The first optical fiber amplifier 56. An output end of the fiber coupler 2 is connected to an input end of the first fiber polarization controller 51, and an output end of the first fiber polarization controller 51 is connected to an input end of the first electro-optic modulator 52 connected, the output end of the first electro-optic modulator 52 is connected to the input end of the third fiber polarizer 53, and the output end of the third fiber polarizer 53 is connected to an input of the third electro-optic modulator 54 The output end of the pulse generator 55 is connected to the other input end of the third electro-optic modulator 54, and the output end of the third electro-optic modulator 54 is connected to the input end of the first optical fiber amplifier 56. The output end of the first optical fiber amplifier 56 is connected to an input end of the second optical fiber circulator 6 .

Further, as shown in Figure 1, the control system 7 includes a third optical fiber circulator 71, an optical fiber F-P filter 72, a sawtooth wave generator 73, a first photodetector 74, a filter 75, a second photodetector 76 and signal acquisition and controller 77. The output end of the second optical fiber circulator 6 is connected to the input end of the third optical fiber circulator 71, and an output end of the third optical fiber circulator 71 is connected to an input end of the optical fiber F-P filter 72 , the output end of the sawtooth wave generator 73 is connected to the other input end of the optical fiber F-P filter 72, and the output end of the optical fiber F-P filter 72 is connected to the signal acquisition via the first photodetector 74 It is connected with an input end of the controller 77, and the other output end of the third optical fiber circulator 71 is connected with the input end of the band-pass filter 75, and the output end of the band-pass filter 75 passes through the first The second photodetector 76 is connected to the other input end of the signal acquisition and controller 77 , and one control output end of the signal acquisition and controller 77 is connected to the control end of the sawtooth wave generator 73 .

The pump pulse optical path 5 provides pulsed broadband light, mainly covering the 1510 nm-1600 nm band, and can be used as the main light source of the fiber grating array 41; and in the 1460 nm-1510 nm band, the pump pulse optical path 5 The optical power is lower than the optical power of the continuous detection optical path 3. At this time, the continuous detection optical path provides the light source for the fiber grating array 41; the dual light sources increase the system stability and expand the use bandwidth of the optical fiber grating in the sensing fiber 4, thereby improving the optical power. Reusable quantity. At the same time, in order not to interfere with the detection of optical fiber stimulated Brillouin scattering signals, the wavelength of the fiber Bragg grating should avoid around 1550 nm; further, in order to obtain a better signal-to-noise ratio, the wavelength of the fiber Bragg grating should avoid the pump pulse optical path 5 and the optical power crossing point of the continuous detection optical path 3, comprehensively consider the 1460 nm-1515 nm band, 1525 nm-1545 nm, 1555 nm-1575 nm and 1585 nm-1600 nm.

The filter 75 is a bandpass filter, the bandwidth is preferably 1545 nm-1555 nm, and is used to introduce the reflected light and the transmitted light of the fiber grating array 41 into the optical fiber F-P filter 72 through an output end of the third optical fiber circulator 71 for wavelength Selection; the light passing through the bandpass filter 75 enters the second photodetector 76 as the detection end of stimulated Brillouin scattering.

The wavelength selection of the fiber grating array 41 is carried out by the post-installed fiber F-P filter 72, which prevents the light emitted by the continuous detection optical path 3 or the pump pulse optical path 5 from directly entering the first photodetector 74 during the double-ended measurement process, resulting in a decrease in the signal-to-noise ratio or The signal is obliterated.

The transmitted light of the fiber Bragg grating array 41 based on the continuous detection optical path 3 and the reflected light of the fiber Bragg grating array 41 based on the pumping pulse optical path 5 are coupled into the first photodetector 74 at the same time. At this time, the signal acquisition and the controller 77 have the maximum There are two control modes of light intensity detection and minimum light intensity detection, both of which guarantee a good signal-to-noise ratio.

Claims (6)

1. A hybrid optical fiber sensing system, characterized in that: comprising laser (1), fiber coupler (2), continuous detection optical path (3), sensing optical fiber (4), pumping pulse optical path (5), the first Two optical fiber circulators (6) and a control system (7), the output end of the laser (1) is divided into two paths after the fiber coupler (2), the first path is connected with the input of the continuous detection optical path (3) end connection, the second path is connected to the input end of the pump pulse optical path (5), and the continuous detection optical path includes a first fiber circulator (33) and a fiber grating (34), and the fiber grating (34) and The other input end of the first optical fiber circulator (33) is connected, the pump pulse optical path (5) includes a first optical fiber amplifier (56), and the output end of the continuous detection optical path (3) passes through the transmission Sensing optical fiber (4) is connected with an input end of second optical fiber circulator (6), and described sensing optical fiber (4) is provided with fiber grating array, and the output end of described pumping pulse light circuit (5) is connected with described Another input end of the second optical fiber circulator (6) is connected, and the output end of the second optical fiber circulator (6) is connected with the input end of the control system (7); The wavelength of the fiber Bragg grating is kept away from the vicinity of 1550nm, and at the same time avoids the vicinity of the intersection point of the optical power of the pump pulse optical path (5) and the continuous detection optical path (3); the wavelength of the fiber Bragg grating is 1525nm-1545nm and 1555nm-1575nm; Described control system (7) comprises the 3rd optical fiber circulator (71), optical fiber F-P filter (72) and band-pass filter (75), and described filter (75) is band-pass filter, and bandwidth is 1545nm- 1555nm, the output end of the second optical fiber circulator (6) is connected to the input end of the third optical fiber circulator (71), and an output end of the third optical fiber circulator (71) is connected to the optical fiber F-P One input end of the filter (72) is connected, and the other output end of the third optical fiber circulator (71) is connected with the input end of the bandpass filter (75). 2. hybrid optical fiber sensing system as claimed in claim 1, is characterized in that: described continuous detection optical path comprises the second optical fiber polarization controller (31), the second photoelectric modulator (32), the second optical fiber amplifier (35 ) and a polarization scrambler (36), an output end of the fiber coupler (2) is connected to the input end of the second fiber polarization controller (31), and the second fiber polarization controller (31) The output end is connected with the input end of the second photoelectric modulator (32), the output end of the second photoelectric modulator (32) is connected with an input end of the first optical fiber circulator (33), and the The output end of the first optical fiber circulator (33) is connected with the input end of the second optical fiber amplifier (35), and the output end of the second optical fiber amplifier (35) is connected with the input end of the described polarization scrambler (36). connected, the output end of the polarization scrambler (36) is connected with one end of the sensing fiber (4). 3. The hybrid optical fiber sensing system according to claim 1, characterized in that: the pump pulse optical path (5) comprises a first optical fiber polarization controller (51), a first electro-optic modulator (52), a third Fiber polarization controller (53), the third electro-optic modulator (54), pulse generator (55); an output end of the fiber coupler (2) and an input of the first fiber polarization controller (51) terminal connection, the output terminal of the first optical fiber polarization controller (51) is connected with an input terminal of the first electro-optic modulator (52), and the output terminal of the first electro-optic modulator (52) is connected with the The input end of the third optical fiber polarizer (53) is connected, the output end of the third optical fiber polarizer (53) is connected with an input end of the third electro-optic modulator (54), and the pulse generator (55 ) is connected to the other input of the third electro-optic modulator (54), and the output of the third electro-optic modulator (54) is connected to the input of the first optical fiber amplifier (56), The output end of the first optical fiber amplifier (56) is connected with an input end of the second optical fiber circulator 6. 4. The hybrid optical fiber sensing system as claimed in claim 1, characterized in that: said control system (7) (7) comprises a sawtooth wave generator (73), a first photodetector (74), a second photoelectric Detector (76) and signal acquisition and controller (77), the output end of described sawtooth wave generator (73) is connected with another input end of described optical fiber F-P filter (72), and described optical fiber F-P filter The output terminal of (72) is connected with an input terminal of described signal acquisition and controller (77) through described first photodetector (74), and the output terminal of described filter (75) is connected through described second photoelectric detector (74). The detector (76) is connected with the other input end of the signal acquisition and controller (77), and a control output end of the signal acquisition and controller (77) is connected with the control of the sawtooth wave generator (73). end connection. 5. The hybrid optical fiber sensing system according to claim 1, characterized in that the laser (1) is a narrow linewidth laser. 6. The hybrid fiber sensor system according to claim 5, characterized in that: the fiber grating array comprises more than two fiber gratings (41).