Edge technique for the measurement of Brillouin frequency shift in optical fiber sensor

The measurement of Brillouin frequency shift in fiber sensor with edge technique is proposed. The relation between measurement accuracy of Brillouin frequency shift and signal to noise ratio (SNR) is analyzed. The edge technique is realized by choosing the frequency of electrical local oscillator and adopting lowpass filter (LPF). The system with edge technique measures the frequency shift by the edge signal rather than the maximum signal, because the edge signals are higher sensitive to the variation of frequency than the maximum signal. From the calculated results, the SNR required is 37 dB to achieve frequency shift resolution of 0.5 MHz by using double-edge technique, comparing with 65.1 dB in conventional detection system measuring the maximum signal, edge technique improves the measurement accuracy of Brillouin frequency shift greatly. In addition, by choosing the frequency of electrical local oscillator, the highest measurement accuracy of Brillouin frequency shift is achieved.