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...

AI Technical Summary

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 the price is very expensive

Some scholars have proposed a scheme to replace the microwave signal source in the coherent detection system. In 2007, J. Geng (J. Geng, S. Staines, M. Blake, and S. Jiang, "Distributed fiber temperature and strain sensor using coherent radio-frequency detection of spontaneous Brillouin scattering,"App.Opt.46,5928-5932,2007) reported a Brillouin time-domain reflectometer that does not require a microwave signal source, and its core is to use a Brillouin laser As a local oscillator, this method can reduce the bandwidth of the detector, but the system of the local oscillator is more complicated, and another high-precision microwave source and electro-optical modulator must be used. The precision of the microwave source and modulator limits the system performance, but also increases the cost of the system

D.Iida (D.Iida and F.Ito, "Cost-effective bandwidth-reduced Brillouin optical time domain reflectometry using a reference Brillouin scattering beam," App.Opt.48, 4302-4309, 2009) of NTT Corporation of Japan in 2009 Another Brillouin optical time-domain reflectometer that does not require a microwave source is reported, using the Brillouin scattered light generated by a fiber different from the sensing fiber as the local oscillator light, usually in the fiber Brillouin The linewidth of scattered light (about 30MHz) is several times wider than that of general DFB lasers (1-5MHz), and the measurement accuracy is affected by the wide linewidth of local oscillator light

The invention patent proposed by Zhang Xuping et al., authorization number: CN102393182A, the three-layer structure sensing fiber combined with the Brillouin optical time domain reflectometer of the Brillouin laser unit, which reduces the bandwidth of the detector, but the invention is not specified in the implementation process Sweep method

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