Patent ID: 8988671
Filing Date: 2015-03-24
Classification: G01D,G01K,G01M

Abstract:
1. A Brillouin Optical Time-Domain Analyzer (BOTDA) system that combined optical pulse coding techniques and coherent detection, comprising: a narrow linewidth laser, a first polarization-maintaining coupler, a second polarization-maintaining coupler, a microwave generator, fiber under test (FUT), an optical circulator, a 3 dB coupler, a balance photodetector, a polarization scrambler (PS), an electrical spectrum analyzer and a digital signal processing unit; the output of the narrow linewidth laser is divided into two branches by the first polarization-maintaining coupler: a first branch CW light and a second branch CW light; characterized in that: the BOTDA system also comprises a frequency shifter, a first electro-optic modulators (EOM1), a pulse generator and a second electro-optic modulator (EOM2); wherein: the first branch CW light is used as the local oscillator light after shifted frequency f the second branch CW light is again separated into two branches by the second polarization-maintaining coupler (PMC2); the lower branch is modulated by the pulse generator to generate coded pump pulses via the first electro-optic modulator (EOM1); then generated coded pump pulses are directed into the first port of the optical circulator and input into the one end of the FUT through the second port of the optical circulator; in the upper branch, the probe signal light is generated after a frequency shifting f by the second electro-optic modulator (EOM2), operating in the suppressed carrier regime, controlled by the microwave generator; the generated probe signal light is two symmetrical sidebands; then the two sidebands are launched into the other end of the FUT, and then interact with the coded pump pulses through stimulated Brillouin scattering (SBS); the two interacted probe sidebands passing through the third port of the optical circulator are directed to the 3-dB coupler to mix with the OLO light, and then are detected by the balance photodetector (PD) (21); the output of the balance photodetector (PD) is observed and collected by the electrical spectrum analyzer (ESA), and the digital signal processing unit process the IF signals from the ESA to obtain the Brillouin gain spectrum and then makes the Lorentz fitting of the obtained spectrum to get the Brillouin frequency shift distribution; finally the distributed optical fiber temperature or strain sensing can be realized using the measured Brillouin frequency shift according to the relations of the Brillouin frequency shift with the temperature or strain.