Low-Brillouin scattering threshold sensing fiber-based optical time domain reflectometer device and method

Abstract

A setting method of a low-Brillouin scattering threshold sensing fiber-based optical time domain reflectometer contains the following steps: an optical pulse signal generated by an optical pulse signal generation unit (100) passes through a scrambler (106) and then enters a first port of a circulator (107); the optical pulse signal enters a sensing fiber (108) from a second port of the circulator; backscattering light of pulse signal light in the sensing fiber (108) enters a filter unit (109) through a third port of the circulator; signal light outputted by the filter unit (109) and light outputted by a local oscillator unit (110) are coupled through a coupler (117); and the signal enters a detection and signal processing unit (118) for acquisition and processing of the signal. The sensing fiber of the Brillouin optical time domain reflectometer adopts a single-mode sensing fiber, and the sensing fiber is a sensing fiber composed of multiple different Brillouin frequency shifts.

Description

technical field [0001] The invention relates to an optical time domain reflectometer device based on a low Brillouin scattering threshold sensing fiber, and a method for increasing the Brillouin scattering threshold of an optical fiber, which is mainly used in long-distance continuous distributed Brillouin optical fiber transmission Sense and other technical fields. Background technique [0002] In continuous distributed optical fiber sensing, the Brillouin Optical Time Domain Reflectometer (BOTDR) based on spontaneous Brillouin scattering has a very important application in the diagnosis and monitoring of various structural safety. BOTDR mainly uses optical fiber In order to obtain the distribution of temperature and stress along the optical fiber, the linear relationship between the frequency shift of the spontaneous Burrillouin scattering spectrum and the temperature and stress of the optical fiber is obtained. Because the Brillouin OTDR uses spontaneous Brillouin scatte...

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Problems solved by technology

At the same time, for BOTDR, since the self-published Brillouin scattered light is relatively weak, and for the incident light of 1550nm in ordinary single-mode fiber, the Brillouin frequency shift is about 11GHz, so it is difficult to obtain Accurate Brillouin scattering signal, which brings a large measurement error

As the detector bandwidth increases, the greater the equivalent noise power value, the greater the minimum power that can be detected, which affects the temperature and strain resolution of the BOTDR system

In addition, the spatial resolution of the BOTDR system is limited by the detection pulse width and the bandwidth of the detector. To improve the spatial resolution, the detection pulse width must be reduced, and the bandwidth of the detector needs to be increased. The wider the detector bandwidth, the larger the space of the system. It is difficult to improve the resolution and temperature and strain resolution at the same time

Due to the limitation of the structure of ordinary single-mode fiber itself, the stimulated Brillouin threshold of ordinary single-mode fiber is low. When stimulated Brillouin scattering occurs, most of the incident light is converted into backscattered light, which is Affected the sensing distance

In order to increase the sensing distance, the power of the detection signal must be increased; and with the increase of the sensing distance, the threshold of stimulated Brillouin scattering is decreasing, and the stimulated Brillouin scattering is more likely to occur, which limits the Brillouin scattering in BOTDR. Sensing distance

The invention patent proposed by Lu Yuangang, authorization number: CN100504309C adopts the method of microwave source and electro-optical modulator to reduce the bandwidth of the detector, but it is difficult to detect in the microwave section 11GHz electronics, and

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