CN113984181A

CN113984181A - Wavelength division multiplexing OTDR optical fiber vibration sensing device

Info

Publication number: CN113984181A
Application number: CN202111280037.0A
Authority: CN
Inventors: 岳耀笠; 唐超; 付益; 阳华; 王侠; 欧阳竑
Original assignee: CETC 34 Research Institute
Current assignee: CETC 34 Research Institute
Priority date: 2021-11-01
Filing date: 2021-11-01
Publication date: 2022-01-28

Abstract

The invention discloses a wavelength division multiplexing OTDR optical fiber vibration sensing device which is characterized by comprising a multi-wavelength laser pulse light source, a first wavelength division multiplexer, an OTDR optical transceiver and a sensing optical cable to be tested which are sequentially connected, wherein the output end of the OTDR optical transceiver is connected with a second wavelength division multiplexer, and the second wavelength division multiplexer is connected with a photoelectric sampling module. The device adopts an OTDR receiving and transmitting device with wavelength division multiplexing and time domain equal interval output, can realize that the distributed optical fiber vibration sensor based on the OTDR improves the sampling repetition frequency on the basis of not reducing the detection distance, and improves the phase demodulation working range of the distributed optical fiber vibration sensor.

Description

Wavelength division multiplexing OTDR optical fiber vibration sensing device

Technical Field

The invention relates to an optical fiber sensing technology, in particular to an OTDR optical fiber vibration sensing device of wavelength division multiplexing.

Background

Distributed optical fiber vibration sensing technologies such as an OTDR (phase-sensitive optical time domain reflectometer), a P-OTDR (polarized optical time domain reflectometer), a COTDR (coherent optical time domain reflectometer) and the like are based on an OTDR technology, are applied to the field of perimeter security and protection, and can greatly reduce the difficulty of security patrol. On the basis of improving the mode identification capability of the distributed optical fiber vibration sensor, the vibration signal amplitude on the sensing optical fiber is restored by adopting a phase demodulation technology, so that the mode identification efficiency can be greatly improved, and the false alarm rate of the system can be reduced. The phase demodulation is to sample the vibration signal by using the repetition frequency of the OTDR emission laser pulse as the sampling frequency, the interference signal caused by the vibration signal can be regarded as the superposition of a plurality of sine waves with different frequencies and amplitudes, according to the sampling theorem, the sampling frequency must be more than 2 times of the sine wave frequency of the maximum frequency, and the sampling frequency is usually 3-5 times of the sine wave frequency of the maximum frequency. The vibration signal is characterized in that the larger the mechanical vibration amplitude is, the higher the frequency of the coherent signal in the optical fiber is, and one mechanical wave period of the larger vibration signal can even generate more than 100 laser coherent periods, so that the phase demodulation of the vibration signal has requirements on the OTDR pulse repetition frequency, and the higher the laser repetition frequency is, the higher the mechanical frequency or the larger the mechanical amplitude of the vibration signal can be identified. For example, the OTDR system with 1kHz repetition frequency can support the maximum sine wave frequency of the demodulated vibration signal not greater than 500Hz, usually within 300Hz of the effective vibration signal frequency, when the mechanical wave amplitude is 20 pi (2 pi represents a backward rayleigh scattering phase change period caused by mechanical vibration), the 1kHz repetition frequency can only effectively demodulate the mechanical vibration signal with amplitude not greater than 20 pi within 30Hz, and meanwhile, the detection distance of the OTDR must not exceed the range of 20 pi

Wherein

For the OTDR pulse period, c is the vacuum speed of light, n is the refractive index of the fiber, and the use of high repetition frequency for OTDR means shortening of the detection distance. When the OTDR pulse repetition frequency is 10kHz, its maximum measurement distance is only 10 km.

Disclosure of Invention

The purpose of the invention is to

The distributed optical fiber vibration sensor such as OTDR, P-OTDR and the like has the contradiction of high repetition frequency and long-distance detection in phase demodulation application, and the wavelength division multiplexing OTDR optical fiber vibration sensing device is provided. The device can increase the laser wavelength and emit laser pulses at equal intervals on the basis of not reducing the detection distance, and respectively detect the sensing signals of all wavelengths at the receiving end by adopting de-wavelength division multiplexing, so that the sensing signals with high repetition frequency are not overlapped on the time domain, and the phase demodulation working range of the distributed optical fiber vibration sensor is improved.

The technical scheme for realizing the purpose of the invention is as follows:

a wavelength division multiplexing OTDR optical fiber vibration sensing device comprises a multi-wavelength laser pulse light source, a first wavelength division multiplexer, an OTDR optical transceiver, a sensing optical cable to be tested, and a second wavelength division multiplexer connected with the output end of the OTDR optical transceiver, wherein the multi-wavelength laser pulse light source is provided with a set of lasers, the photoelectric sampling module is provided with a set of detectors, the multi-wavelength laser pulse light source sequentially emits laser pulses at equal time intervals and is respectively connected with each port corresponding to the first wavelength division multiplexer, the first wavelength division multiplexer combines the multi-wavelength laser pulses into a whole and then is connected with the input end of the OTDR transceiver through a common port, the transmitting end of the OTDR transceiver is connected with a sensing optical cable, vibration signals on the sensing optical cable are transmitted back to the transmitting end of the OTDR transceiver and M paths of optical signals are output by the output end of the OTDR transceiver, m =1, 2, 4, and access the common end of M second wavelength division multiplexers, each second wavelength division multiplexer outputs vibration monitoring signals with different wavelengths by N wavelength division ends, and accesses the photoelectric sampling module, and the sensing detection digital signal with the sampling frequency of Nxf is synthesized and output by the photoelectric sampling module, wherein f is the repetition frequency of the laser pulse source, N is the wavelength number of the multi-wavelength laser pulse light source, N is a positive integer not less than 2, and the wavelength interval satisfies the isolation requirement of the first and second wavelength division multiplexers, and the N laser pulse light sources sequentially emit laser pulses at equal time intervals.

The common end of the first wavelength division multiplexer and the common end of the second wavelength division multiplexer are 1 optical fiber port, and 1 laser pulse signal with different wavelengths is respectively output or input by N wavelength division ends.

The OTDR optical transceiver is provided with 1 OTDR laser pulse input port, 1 sensing optical cable connection port, M sensing signal output ports, M =1, 2, 4, M sensing signal output ports are respectively connected with a common end of a second wavelength division multiplexer and wavelength division ends of the M second wavelength division multiplexers to respectively output N vibration monitoring signals with different wavelengths, and the vibration monitoring signals are respectively connected into different photoelectric sampling modules with M multiplied by N photoelectric detectors.

The device can adopt the emission laser pulse with increased laser wavelength and equal interval on the basis of not reducing the detection distance, and adopts the de-wavelength division multiplexing to respectively detect the sensing signals with various wavelengths at the receiving end, so that the sensing signals with high repetition frequency are not overlapped on the time domain, and the phase demodulation working range of the distributed optical fiber vibration sensor is improved.

Drawings

Fig. 1 is a schematic structural diagram of the embodiment.

Detailed Description

The invention will be further elucidated with reference to the drawings and examples, without however being limited thereto.

Example (b):

referring to fig. 1, an OTDR fiber vibration sensing apparatus of wavelength division multiplexing includes a multi-wavelength laser pulse light source, a first wavelength division multiplexer, an OTDR optical transceiver, a sensing optical cable to be measured, and a second wavelength division multiplexer connected to an output end of the OTDR optical transceiver, wherein the second wavelength division multiplexer is connected to an optical sampling module, the multi-wavelength laser pulse light source is provided with a set of lasers, the optical sampling module is provided with a set of detectors, the multi-wavelength laser pulse light source sequentially emits laser pulses at equal time intervals and is respectively connected to wavelength division ports corresponding to the first wavelength division multiplexer, the first wavelength division multiplexer combines the multi-wavelength laser pulses into one beam and connects the common port to an input end of the OTDR transceiver, an emitting end of the OTDR transceiver is connected to a sensing optical cable, a vibration signal on the sensing optical cable is transmitted back to the emitting end of the OTDR transceiver and 2 polarization diversity detection optical signals are output from the output end of the OTDR transceiver (at this time, m = 2), and access the common end of 2 second wavelength division multiplexers, each second wavelength division multiplexer outputs vibration monitoring signals with different wavelengths by 4 wavelength division ends, and enters the photoelectric sampling module, and the sensing detection digital signals with sampling frequency of 4 × 2kHz =4kHz are synthesized and output by the photoelectric sampling module, wherein 2kHz is the repetition frequency of the laser pulse source, 4 is the wavelength number of the multi-wavelength laser pulse light source, and the wavelength interval meets the isolation requirement of the first and second wavelength division multiplexers, and the 4 laser pulse light sources sequentially emit laser pulses in an equal time interval manner.

The common end of the first wavelength division multiplexer and the common end of the second wavelength division multiplexer are 1 optical fiber port, and 1 laser pulse signal with different wavelengths is respectively output or input by 4 wavelength division ends.

The OTDR optical transceiver is provided with 1 OTDR laser pulse input port, 1 sensing optical cable connection port and 2 sensing signal output ports and is used for outputting polarization diversity detection optical signals, and the 2 sensing signal output ports are respectively connected with a common end of a second wavelength division multiplexer and wavelength division ends of the 2 second wavelength division multiplexers and respectively output 4 paths of vibration monitoring signals with different wavelengths and are respectively connected into different photoelectric sampling modules with 8 photoelectric detectors.

Claims

1. A wavelength division multiplexing OTDR optical fiber vibration sensing device is characterized by comprising a multi-wavelength laser pulse light source, a first wavelength division multiplexer, an OTDR optical transceiver, a sensing optical cable to be tested and an output end of the OTDR optical transceiver which are connected in sequence, wherein the second wavelength division multiplexer is connected with an optoelectronic sampling module, the multi-wavelength laser pulse light source is provided with a group of lasers, the optoelectronic sampling module is provided with a group of detectors, the multi-wavelength laser pulse light source sequentially emits laser pulses in an equal time interval mode and is respectively connected with wavelength division ports corresponding to the first wavelength division multiplexer, the first wavelength division multiplexer synthesizes the multi-wavelength laser pulses into one beam and is connected with an input end of the OTDR transceiver through a common port, an emitting end of the OTDR transceiver is connected with a sensing optical cable, a vibration signal on the sensing optical cable is transmitted back to an emitting end of the OTDR transceiver and an output end of the OTDR transceiver outputs M optical signals, m =1, 2, 4, and access the common end of M second wavelength division multiplexers, each second wavelength division multiplexer outputs vibration monitoring signals with different wavelengths by N wavelength division ends, and accesses the photoelectric sampling module, and the sensing detection digital signal with the sampling frequency of Nxf is synthesized and output by the photoelectric sampling module, wherein f is the repetition frequency of the laser pulse source, N is the wavelength number of the multi-wavelength laser pulse light source, N is a positive integer not less than 2, and the wavelength interval satisfies the isolation requirement of the first and second wavelength division multiplexers, and the N laser pulse light sources sequentially emit laser pulses at equal time intervals.

2. A wavelength division multiplexed OTDR optical fiber vibration sensing device according to claim 1, wherein the common port of said first and second wavelength division multiplexers is 1 optical fiber port, and N wavelength division ports respectively output or input 1 laser pulse signal with different wavelengths.

3. The OTDR fiber vibration sensing device of claim 1, wherein said OTDR optical transceiver device has 1 OTDR laser pulse input port, 1 sensing optical cable connection port, M sensing signal output ports, M =1, 2, 4, where M sensing signal output ports are respectively connected to the common port of the second wavelength division multiplexer and the wavelength division ports of the M second wavelength division multiplexers to output N vibration monitoring signals with different wavelengths, and are respectively connected to different optical sampling modules with M × N photodetectors.