Narrow-bandwidth Brillouin optical timedomain reflectometer (OTDR) based on sensing optical fiber of three-layer structure

Abstract

The invention discloses a narrow-bandwidth Brillouin optical timedomain reflectometer (OTDR) based on a sensing optical fiber of a three-layer structure. The OTDR comprises a light pulse generating unit (200), wherein light pulses generated by the light pulse generating unit (200) enter into a first port of a circulator (207) after passing through a polarization scrambler (206), and enter into the sensing optical fiber (208) through a second port of the circulator; and backward scattered light of pulsed light in the sensing optical fiber (208) enter into a filter unit (209) through a third port of the circulator; light output by the filter unit and light output by a local oscillation light unit (210) are coupled into a detection and signal processing unit (217) through a coupler (216); and a pulse generator is used for driving a modulator to generate pulse and clock control. The sensing optical fiber in the OTDR can not only increase Brillouin threshold, but also reduce Brillouin frequency shift and bandwidth of a detector; and as a Brillouin ring-shaped cavity laser is designed to serve as local oscillation light concerned with detection, the bandwidth of the detector is greatly reduced, and the measuring accuracy of the Brillouin OTDR is improved.

Description

technical field [0001] The invention relates to a narrow-bandwidth Brillouin optical time-domain reflectometer based on a three-layer structure sensing optical fiber, which is mainly used in the technical field of optical fiber sensing networks. Background technique [0002] In the current distributed optical fiber sensing technology, the distributed optical fiber sensing technology based on Brillouin scattering can realize the continuous distributed measurement of the temperature and strain in the optical fiber, which can be applied to large buildings, highways, tunnels, bridges, large The monitoring and measurement of the health status of dams, communication optical cables, oil and gas pipelines, etc. has broad application prospects. Compared with other distributed optical fiber sensors, BOTDR based on self-published scattered optical time domain reflectometer has the advantages of single-ended sensing measurement and simultaneous sensing of temperature and strain. The in...

AI Technical Summary

Problems solved by technology

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

With the increase of the detector bandwidth, the larger the equivalent noise power value is, the larger the minimum power can be detected, which affects the temperature and strain resolution of the BOTDR system, and the price of the high-bandwidth detector is more expensive

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 et al., authorization number: CN100504309C uses a microwave source and an electro-optic modulator to reduce the bandwidth of the detector. However, it is difficult to detect electronically at 11 GHz in the microwave band, 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-optic 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

Images