CN205120239U - Vibration detection device based on optical frequency domain reflectometer - Google Patents

Abstract

An optical frequency domain reflectometry based vibration detection apparatus, the apparatus comprising: modulation circuit, the optic fibre that awaits measuring, the narrow linewidth fiber laser that links to each other in proper order, two optical couplers, demodulation and data acquisition circuit, wherein: the modulation circuit is arranged between the two optical couplers in parallel, and the optical fiber to be tested is connected with the modulation circuit; the modulation circuit includes: the device comprises a signal generator, an erbium-doped fiber amplifier, an acousto-optic modulator and an optical circulator; the demodulation and data acquisition circuit includes: the device comprises an optical bridge, a data acquisition card, two analog-to-digital converters and two balanced photoelectric detectors connected in parallel, wherein: the input ends of the two parallel balanced photoelectric detectors are connected with the optical bridge, the output ends of the two parallel balanced photoelectric detectors are respectively connected with the input ends of the two analog-to-digital converters, and the output ends of the two analog-to-digital converters are connected with the data acquisition card; the utility model discloses combine optical frequency domain reflectometry technique to extract optical signal's phase information, realize the vibration detection of long distance high sensitivity.

Description

Vibration detection device based on optical frequency domain reflectometer

technical field

The utility model relates to a technology in the field of distributed optical fiber sensing, in particular to a vibration detection device based on an optical frequency domain reflectometer.

Background technique

In recent years, optical reflectometer technology has attracted increasing attention due to its ability to realize distributed measurements. Among them, the vibration detection technology based on light reflectometer has also been promoted. Most of the early vibration detection technologies were based on the Optical Time-Domain Reflectometer (OTDR) technology, and vibration detection was mostly based on intensity extraction to distinguish vibration signals. However, the spatial resolution of OTDR technology can only reach the meter level, which limits its application in vibration detection in some fields with high spatial resolution requirements. The intensity-based extraction can only demodulate the frequency domain and position of the vibration, but the vibration intensity cannot be reflected. In contrast, Optical Frequency‐Domain Reflectometer (OFDR) technology can achieve centimeter-level spatial resolution, but the detection distance is limited by the coherence length of the laser. When the measurement distance exceeds the coherence length, due to the phase noise of the laser impact, the spatial resolution and signal-to-noise ratio will drop sharply.

In order to improve the intensity sensitivity of vibration detection, improve the detection space resolution and detection distance, domestic and foreign scholars have proposed several improvement schemes based on OTDR and OFDR. For example, OFDR technology based on correlation processing (Z. Ding et al., "Long‐range vibration sensor based on correlation analysis of optical frequency‐domain reflectometry signals", OptExpress20, 28319‐28329 (2012)) can achieve vibration detection with high spatial resolution, but its detection distance cannot exceed the coherence length of the laser ; OTDR technology based on phase extraction (Z.Pan et al., "Phase-sensitive OTDR system based on digital coherent detection", Asia Communications and Photonics Conference and Exhibition, 2011) can obtain greater sensitivity, but its detection distance is limited by the signal-to-noise ratio and can only achieve a detection range of several kilometers.

After searching the prior art, it was found that the Chinese Patent Document No. CN101650197A, announced on February 17, 2010, discloses an optical frequency domain reflective optical fiber sensing system, the main structure includes a laser, a first optical fiber coupler, an optical circulator, a detection Optical fiber, second optical fiber coupler, photoelectric detection unit and spectrum analysis unit, the laser light emitted by the laser is divided into detection light and reference light by the first fiber coupler, the detection light is incident on the first port of the optical circulator, and transmitted from the second The port exits into the detection fiber, and the Rayleigh backscattered light generated in the detection fiber enters the second port of the optical circulator and exits from the third port, and the outgoing Rayleigh backscattered light and reference light enter the second fiber coupler and detected by the photoelectric detection unit, and the measured signal is input to the spectrum analysis unit.

Chinese patent document number CN103528666A, published on January 22, 2014, discloses a long-distance optical fiber vibration detection device and method based on Sagnac interference, including a light source, a photodetector, an optical circulator, a 2*2 coupler and an optical fiber delay fiber , the laser signal emitted by the light source passes through the optical circulator, enters the 2*2 coupler and is divided into two routes, one optical signal A, enters the optical fiber to be tested through the optical fiber delay fiber, and the Fresnel reflected optical signal returned at the end enters 2*2 coupler; the other optical signal B directly enters the optical fiber to be tested, and the Fresnel reflected optical signal returned at the end passes through the 2*2 coupler and enters the optical fiber delay fiber. 2*2 coupler; the optical signal interferes at the 2*2 coupler, and the interference signal passes through the optical circulator and is sensed by the photodetector. However, the above-mentioned technologies will generate insertion loss when the optical signal passes through the coupler and the optical circulator, and can only detect vibration, but cannot detect the vibration intensity.

Utility model content

Aiming at the above-mentioned deficiencies in the prior art, the utility model proposes a vibration detection device based on an optical frequency domain reflectometer, through the compensation of the erbium-doped optical fiber amplifier and the modulation of the acousto-optic modulator, the vibration signal is collected, and the balance photodetector And digital-to-analog converter to get all the information of the vibration signal, improve the detection distance and spatial resolution.

The utility model is achieved through the following technical solutions:

The utility model comprises: a modulation circuit, an optical fiber to be tested, a narrow-linewidth fiber laser connected in sequence, two optical couplers, a demodulation and data acquisition circuit, wherein the modulation circuit is arranged in parallel between the two optical couplers, and the The measuring fiber is connected to the modulation circuit.

The modulation circuit includes: a signal generator, an acousto-optic modulator connected in sequence, an erbium-doped fiber amplifier and an optical circulator, wherein the signal generator is connected with the acousto-optic modulator.

The demodulation and data acquisition circuit includes: an optical bridge, a data acquisition card, two analog-to-digital converters and two parallel balanced photodetectors, wherein: the input ends of the two parallel balanced photodetectors are connected to the optical bridge The output ends are respectively connected to the input ends of two analog-to-digital converters, and the output ends of the two analog-to-digital converters are connected to the data acquisition card.

technical effect

Compared with the prior art, the utility model compensates part of the insertion loss during the vibration detection process, and obtains the distance-time three-dimensional map and vibration intensity information of the vibration signal based on the phase extraction, and the detection distance reaches 40km.

Description of drawings

Fig. 1 is the utility model schematic diagram;

In the figure: 1 is a narrow linewidth fiber laser, 2a and 2b are optical couplers, 3 is an erbium-doped fiber amplifier, 4 is an acousto-optic modulator, 5 is an optical circulator, 6 is an optical fiber to be tested, and 7 is a signal generator , 8 is an optical bridge, 9 is a balanced photodetector, 10 is a digital-to-analog converter, 11 is a data acquisition card, A is a reference light, and B is a detection light;

Figure 2 is the experimental effect diagram of the superposition of 100 sets of data at 30km of the optical fiber to be tested;

In the figure: (a) is the intensity map, (b) is the phase map, (c) is the differential phase map, (d) is the reflection peak of a single connector;

Figure 3 is an experimental effect diagram at 40km of the optical fiber to be tested;

In the figure: (a) is the distance-time three-dimensional diagram based on phase detection, (b) is the time-phase curve of vibration region F based on phase detection, (c) is the distance-time three-dimensional diagram based on intensity detection, (d) is the time-phase curve based on the intensity detection of the vibration region F;

Figure 4 is an experimental effect diagram of an 800Hz vibration signal based on phase detection at 30km of the optical fiber to be tested;

In the figure: (a) is the distance-time three-dimensional map based on phase detection, and (b) is the time-phase curve of the vibration region.

Fig. 5 is an experimental effect diagram of vibration intensities of 0.08g, 0.12g, 0.16g and 0.2g respectively;

In the figure: (a) is the time-phase curve, (b) is the phase diagram.

detailed description

The following is a detailed description of the embodiments of the present utility model. This embodiment is implemented on the premise of the technical solution of the present utility model, and detailed implementation methods and specific operating procedures are provided, but the protection scope of the present utility model is not limited to the following the described embodiment.

Example 1

As shown in Figure 1, this embodiment includes: a modulation circuit, an optical fiber 6 to be tested, a narrow linewidth fiber laser 1 connected in sequence, two optical couplers 2a and 2b, a demodulation and data acquisition circuit, wherein: the modulation circuit is connected in parallel It is arranged between the two optical couplers 2a and 2b, and the optical fiber 6 to be tested is connected with the modulation circuit.

The optical couplers 2a and 2b are both 3dB, 50/50 optical couplers.

The optical fiber 6 to be tested is a 40km single-mode optical fiber (SMF).

The modulation circuit includes: a signal generator 7 , an acousto-optic modulator 4 connected in sequence, an erbium-doped fiber amplifier 3 and an optical circulator 5 , wherein: the signal generator 7 is connected with the acousto-optic modulator 4 .

The optical circulator 5 has three ports 5a, 5b and 5c.

The demodulation and data acquisition circuit includes: optical bridge 8, data acquisition card 11, two analog-to-digital converters 10 and two parallel balanced photodetectors 9, wherein: two parallel balanced photodetectors 9 The input end is connected to the optical bridge 8 , the output ends of the two balanced photodetectors 9 are respectively connected to the input ends of the two analog-to-digital converters 10 , and the output ends of the two analog-to-digital converters 10 are connected to the data acquisition card 11 .

The optical bridge 8 performs I/Q demodulation on the input optical signal to obtain the phase.

The data acquisition card 11 is an 8-bit data acquisition card.

This embodiment includes the following steps:

Step 1. During vibration detection, paste the PZT on the 30km and 40km of the optical fiber 6 to be tested, and the vibration signal is loaded on the PZT through the signal generator 7. The vibration intensity of the PZT is proportional to the loading voltage of the signal generator 7. At the same time, An accelerometer is attached to the PZT to detect the acceleration of the current vibration signal.

Step 2. The optical signal with a wavelength of 1550nm generated by the narrow linewidth fiber laser 1 is divided into two paths through the optical coupler 2a: reference light A and detection light B; the signal generator 7 synthesizes a 60MHz frequency modulation signal and modulates it through the acousto-optic modulator 4 On the probe light B entering the acousto-optic modulator 4; the modulated probe light B is amplified by the erbium-doped fiber amplifier 3 in turn, and the 5a port and 5b port of the optical circulator 5 are input into the optical fiber 6 to be tested, and the end of the optical fiber 6 to be tested is generated The Rayleigh backscattered light of the optical circulator 5 enters the optical circulator 5 from the 5b port of the optical circulator 5 and enters the optical coupler 2b through the 5c port; the Rayleigh backscattered light of the reference light A directly enters the optical coupler 2b and the probe light B Interference is performed; the two paths of light pass through the optical bridge 8 and are demodulated to form a phase difference.

Step 3, the reference light A and the detection light B that form the phase difference are sequentially converted into electrical signals by the balanced photodetector 9, and are converted into digital signals by the analog-to-digital converter 10 and collected by the data acquisition card 11, and the collected single frequency modulation The pulse and the signal to be measured are coherently processed to obtain a phase-based distance-time three-dimensional map, thereby obtaining the information of the vibration signal.

The pulse repetition frequency of the narrow linewidth fiber laser 1 is 2kHz.

The erbium-doped fiber amplifier 3 is used to compensate the insertion loss caused by modulation.

The frequency modulation time of the acousto-optic modulator 4 is 8 μs, the modulation bandwidth is 60 MHz, and the single-frequency signal rejection ratio is greater than 30 dB.

The frequency of the swept light output by the acousto-optic modulator 4 is 60 MHz, which corresponds to a theoretical spatial resolution of 1.6 m in OFDR.

The frequency sweep speed of the signal generator 7 is 7.5THz/s, and the frequency modulation range is 170-230MHz.

The phase difference between the reference light A and the probe light B passing through the optical bridge 8 is 90°±5°.

The bandwidth of the balanced photodetector 9 is 1.6 GHz.

The sampling rate of the data acquisition card 11 is 2GS/s.

The time-domain signal collected by the data acquisition card 11 can be transformed by Fourier to obtain the distributed backscattering signal of the optical fiber 6 to be tested.

As shown in Figure 2(a) and (c), at 30km away from the optical fiber 6 to be tested, when a vibration event occurs, as shown in A and D in the figure, the intensity pattern and differential phase pattern will diverge.

As shown in Figure 2(a)-(c), due to the mutual interference between the optical signals of different interference points, interference constructive or interference destructive, as shown in B, C and E in the figure, in the interference phase In the area of cancellation, the information obtained will be inaccurate due to the poor signal-to-noise ratio, resulting in a "dead zone".

As shown in FIG. 2( d ), it is a schematic diagram of a reflection peak of a connector in the optical fiber 6 to be tested. It can be obtained from the figure that its spatial resolution is 3.5 m.

As shown in Figure 3 (a), (b), at 40km of the optical fiber 6 to be tested, the vibration region F of the vibration signal of 200Hz and 0.08g can be detected based on phase extraction, as shown in Figure 3 (c), (d ), the same vibration event cannot be detected by intensity extraction; that is, phase-based detection has higher vibration intensity sensitivity than intensity-based detection.

As shown in Figure 5, there is a good linear relationship between the phase deviation caused by the vibration and the vibration intensity.

The frequency modulation time of the acousto-optic modulator 4 is 8 μs, and the influence of phase noise is small.

The detection range of this embodiment is 40km, and the sensitivity is 0.08g.

In this embodiment, while greatly reducing the phase noise, a vibration signal detection range of 40 km, a response frequency of 800 Hz and an intensity of 0.08 g is realized.

Claims (7)

1. the vibration detection device based on optical frequency domain reflectometer, it is characterized in that, comprise: modulation circuit, testing fiber, the narrow cable and wide optical fiber laser be connected successively, two photo-couplers, solution mediation data acquisition circuits, wherein: modulation circuit is arranged in parallel between two photo-couplers, and testing fiber is connected with modulation circuit.

2. the vibration detection device based on optical frequency domain reflectometer according to claim 1, it is characterized in that, described modulation circuit comprises: signal generator, the acousto-optic modulator, Erbium-Doped Fiber Amplifier and the optical circulator that are connected successively, wherein: signal generator is connected with acousto-optic modulator.

3. the vibration detection device based on optical frequency domain reflectometer according to claim 1, it is characterized in that, described solution is in harmonious proportion data acquisition circuit and comprises: light bridge, data collecting card, two analog to digital converters and two balance photodetectors in parallel, wherein: the input end of two balance photodetectors in parallel is connected with light bridge, output terminal is connected with the input end of two analog to digital converters respectively, and the output terminal of two analog to digital converters is connected with data collecting card.

4. the vibration detection device based on optical frequency domain reflectometer according to claim 1, is characterized in that, described photo-coupler is 50/50 photo-coupler.

5. the vibration detection device based on optical frequency domain reflectometer according to claim 1, is characterized in that, the exomonental frequency of described narrow cable and wide optical fiber laser is 2kHz.

6. the vibration detection device based on optical frequency domain reflectometer according to claim 2, is characterized in that, the frequency modulated time of described acousto-optic modulator is 8 μ s, and modulation band-width is 60MHz.

7. the vibration detection device based on optical frequency domain reflectometer according to claim 3, is characterized in that, the phase differential that described light bridge produces is 90 ° ± 5 °.