Design and test of dual-channel light sources for distributed optical fiber sensing

For the purpose that a fiber sensor system of Brillouin optical time-domain analysis (BOTDA) needs two light sources of Brillouin frequency shift, a dual-channel light source system was proposed by employing Brillouin ring cavity frequency shift and electro-optic modulation. According to several parameters, pulse width, repetition frequency rate and step of frequency sweeping, the output light spectrum of dual-channel modulation was simulated. Based on field programmable gate array (FPGA) and direct digital synthesizer (DDS) chip, experimental system was setup and both pulse detect light and sweep frequency pulse light could be output from the setup. The minimum pulse width of the detection pulse was 10ns, and the sweep frequency range reached 0MHz~90MHz with a frequency sweep step of 30Hz and a time step of 1.6s. Experimental results show that the dual channel light source can meet the demands of general BOTDA systems, without the necessity of some high speed devices, such as high frequency microwave signal source. Signal acquisition modules can adopt regular photoelectric detectors below 100MHz so as to reduce the system cost.