CN105067103B - Vibration detection device and its method based on optical frequency domain reflectometer - Google Patents

Abstract

A vibration detection device and method based on an optical frequency domain reflectometer, the device includes: a modulation module, an optical fiber to be tested, a narrow linewidth fiber laser connected in sequence, two optical couplers, a demodulation and data acquisition module, wherein The modulation module is arranged in parallel between two optical couplers, and the optical fiber to be tested is connected to the modulation module; the modulation module includes: a signal generator, an erbium-doped fiber amplifier, an acousto-optic modulator and an optical circulator; the demodulation and data acquisition module includes : Optical bridge, 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, and the output ends are respectively connected to two analog-digital The input ends of the converters are connected, and the output ends of the two analog-to-digital converters are connected with the data acquisition card; the invention combines the optical frequency domain reflectometer technology to extract the phase information of the optical signal to realize long-distance and high-sensitivity vibration detection.

Description

Vibration detection device and method based on optical frequency domain reflectometer

technical field

The invention relates to a technology in the field of distributed optical fiber sensing, in particular to a vibration detection device and method 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 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 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", Opt Express 20, 28319-28329 (2012)) can achieve high spatial resolution Vibration detection, 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 Greater sensitivity is obtained, 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 channels, 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, through the 2*2 coupler, enters the optical delay fiber, passes through the optical fiber once, and returns to 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.

Contents of the invention

Aiming at the above-mentioned deficiencies in the prior art, the present invention proposes a vibration detection device and method 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 of the photoelectric The detector and the digital-to-analog converter obtain all the information of the vibration signal, improving the detection distance and spatial resolution.

The present invention is achieved through the following technical solutions:

The invention relates to a vibration detection device based on an optical frequency domain reflectometer, comprising: a modulation module, an optical fiber to be tested, a narrow linewidth fiber laser connected in sequence, two optical couplers, a demodulation and data acquisition module, wherein: the modulation The module is arranged in parallel between two optical couplers, and the optical fiber to be tested is connected with the modulation module.

The modulation module 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 module 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.

The present invention relates to the vibration detection method of above-mentioned device, comprises the following steps:

Step 1. Attach the piezoelectric ceramic (PZT) to a point of the optical fiber to be tested, and the vibration signal is loaded onto the PZT through the signal generator. 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 generated by the narrow-linewidth fiber laser is divided into two paths through the optical coupler, and one path of detection light B passes through the acousto-optic modulator swept by the signal generator, the erbium-doped fiber amplifier, and the optical circulator to input the optical fiber to be tested. , the Rayleigh backscattered light generated at the end of the fiber to be tested enters the optical circulator and enters another optical coupler; the other reference light A directly enters the optical coupler and interferes with the Rayleigh backscattered light of the probe light B; The two paths of light after interference pass through the optical bridge and are demodulated to form a phase difference.

Step 3. The two optical signals forming the phase difference are sequentially converted into electrical signals through the balanced photodetector, converted into digital signals through the analog-to-digital converter, and then collected by the data acquisition card to obtain the information of the vibration signal.

technical effect

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

Description of drawings

Fig. 1 is a schematic diagram of the present invention;

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 embodiments of the present invention are described in detail below. This embodiment is implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operating procedures are provided, but the protection scope of the present invention is not limited to the following implementation example.

Example 1

As shown in Figure 1, this embodiment includes: a modulation module, 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 module, wherein: the modulation module 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 module.

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 module 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 to the acousto-optic modulator 4 .

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

Described demodulation and data acquisition module comprise: optical bridge 8, data acquisition card 11, two analog-to-digital converters 10 and two parallel balance photodetectors 9, wherein: the balance photodetector 9 of two parallel connections 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 converted into electrical signals by the balanced photodetector 9 in turn, 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 (6)

1. A kind of 1. vibration detection device based on optical frequency domain reflectometer, it is characterised in that including：Modulation module, testing fiber, according to Secondary connected narrow cable and wide optical fiber laser, two photo-couplers, demodulation data acquisition module, wherein：Modulation module parallel connection is set It is placed between two photo-couplers, testing fiber is connected with modulation module；

   Described modulation module includes：Signal generator, the acousto-optic modulator being sequentially connected, EDFA Erbium-Doped Fiber Amplifier and ring of light shape Device, wherein：Signal generator is connected with acousto-optic modulator；

   Described demodulation data acquisition module includes：Light bridge, data collecting card, two analog-digital converters and two are in parallel flat Weigh photodetector, wherein：The input of two balance photodetectors in parallel is connected with light bridge, output end respectively with two The input of analog-digital converter is connected, and the output end of two analog-digital converters is connected with data collecting card.
2. 2. vibration detection device according to claim 1, it is characterized in that, described photo-coupler is 50/50 photo-coupler.
3. 3. vibration detection device according to claim 1, it is characterized in that, the transmitting pulse of described narrow cable and wide optical fiber laser Frequency be 2kHz.
4. 4. vibration detection device according to claim 1, it is characterized in that, the frequency modulated time of described acousto-optic modulator is 8 μ S, modulation bandwidth 60MHz.
5. 5. vibration detection device according to claim 1, it is characterized in that, phase difference caused by described light bridge is 90 ° ± 5°。
6. A kind of 6. method for detecting vibration based on vibration detection device described in any of the above-described claim, it is characterised in that including Following steps：

   Step 1, PZT is attached to testing fiber a bit, vibration signal is loaded on PZT by signal generator, while in PZT On post accelerometer to detect the acceleration of current vibration signal；

   Optical signal is divided into two-way by photo-coupler caused by step 2, narrow cable and wide optical fiber laser, detects light B all the way and leads to successively Cross the acousto-optic modulator through signal generator frequency sweep, EDFA Erbium-Doped Fiber Amplifier, optical circulator input testing fiber, testing fiber end Rayleigh backscattering light caused by end enters optical circulator and inputs another photo-coupler；Another way reference light A is directly entered The photo-coupler is interfered with detecting light B rayleigh backscattering light；Two-way light after interference is formed by being demodulated after light bridge Phase difference；

   Step 3, the two ways of optical signals of formation phase difference pass sequentially through balance photodetector and are converted into electric signal, pass through modulus and turn Parallel operation is gathered after being changed into data signal by data collecting card, obtains vibration signal information.