High performance interrogation of ultra-weak FBG array using double-pulse and heterodyne coherent detection

A high performance interrogation method for ultra-weak FBG (UWFBG) is proposed by using double-pulse and heterodyne coherent detection method. The disturbance of fiber is detected by resolving the phase of the heterodyne coherent signal. The double-pulse helps to locate the disturbance. With a differential method for the signals between different UWFBG pairs, the disturbance can be resolved precisely. In experiment, sinusoidal disturbance and triangle disturbance are demodulated quantitatively. The sensing frequency can be as low as 0.2Hz.