A Novel φ-otdr Detection Device Based on Fixed Reflection Point and Its Detection Method

Abstract

The invention discloses a novel [phi]-OTDR detection device based on fixed reflection points. The novel [phi]-OTDR detection device comprises a time delay generator, a laser, a pulse modulator, an erbium-doped optical fiber amplifier, an optical circulator, an optical fiber detection unit, a first coupler, a time delay optical fiber, a polarization controller, a second coupler, an avalanche photodetector and a signal collection card. The optical fiber detection unit comprises a plurality of optical fibers which are connected in sequence, and the fixed reflection points are respectively formed at the connection parts on two ends of each optical fiber. The invention further discloses a detection method of the novel [phi]-OTDR detection device based on the fixed reflection points. According to the invention, the vibration around the optical fiber detection unit is measured by the optical fiber detection unit, and the vibration position, the frequency and the amplitude are monitored in real time by means of three-port phase demodulation through a look-up table method; in addition, the optical fiber is divided into a plurality of segments by the optical fiber detection unit, the interference of the vibration event on one position to the whole optical fiber is avoided, and the system of the structure is easy to dismount and maintain.

Description

technical field [0001] The invention relates to the technical field of optical fiber sensing, in particular to a novel Φ-OTDR detection device based on fixed reflection points and a detection method thereof. Background technique [0002] Phase-sensitive optical time domain reflectometer (Φ-OTDR) vibration measurement has developed rapidly in the past ten years, and it has important application value in security monitoring of important places and health monitoring of major engineering structures. For example, the security monitoring of prison fences or national borders, and bridges, roads and buildings will inevitably be damaged with the increase in service life. The distributed vibration measurement system can be installed in security areas or on the surface of buildings for monitoring by Vibration caused by special events, so as to facilitate real-time monitoring or early detection of hidden dangers that may cause building accidents. [0003] Φ-OTDR can detect the position...

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Problems solved by technology

[0005] However, the currently commonly used Φ-OTDR also has obvious shortcomings. Most of them can only detect the location of the strain and extract its frequency domain information, and cannot quantitatively measure the strain value.

The main reason is that there is no definite, one-to-one correspondence between the optical signal obtained by the receiving end and the strain value loaded on the fiber, so the strain value loaded on the fiber cannot be calculated by the demodulation algorithm

A Masoudi and M Belal of the University of Southampton in the UK wrote "A distributed optical fiber dynamic strain sensor based on phase-OTDR" using a 3×3 coupler and a time-delay fiber for phase demodulation to achieve amplitude detection, but A positional vibration event is likely to cause interference on the entire section of optical fiber. If the optical fiber is damaged, it will be complicated to disassemble and repair the optical fiber; Zhu Fan and Zhang Yixin from the Optical Communication Engineering Research Center of Nanjing University et al. based on Ultra-weak Fiber Bragg Grating Array" uses Bragg grating reflection signals for phase demodulation, but it needs to control the frequency of the laser, the phase solution algorithm is relatively complicated, and the spatial resolution is low because of the need to use wide pulses; and Zhang Yixin , Zhang Xuping and others improved the method in the paper of Zhu Fan and Zhang Yixin in the patent "Phase-sensitive optical time domain reflection device and method based on fiber Bragg grating array" (patent number: CN201510389252.2), which can be used on the basis of quantitative analysis High spatial resolution is achieved on the surface, but in order to achieve high spatial resolution, the gratings used are relatively dense, which will increase the cost of detection, the complex process of installation and repair after damage is complicated, and the requirements for operators are high. Promote application

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