A novel Bragg grating sensor interrogation system utilizing a scanning filter, a Mach-Zehnder interferometer and a 3 x 3 coupler

This work describes a new technique for fibre Bragg grating (FBG) sensor in terrogation and multiplexing. The technique combines a scanning Fabry-Perot (SFP) bandpass filter used to wavelength-multiplex multiple gratings in a single fibre, and an unbalanced Mach-Zehnder fibre interferometer made with a 3 x 3 coupler to detect strain-induced wavelength shifts. A passive tech nique for interferometer drift compensation using non-sensing FBGs is inclu ded in the system. A prototype complete system interrogates four gratings i n a single fibre at a Nyquist sampling rate up to 10 kHz, with a noise floo r measured near 4 n is an element of Hz(-1/2) above 0.1 Hz. The inclusion o f the interferometer drift compensation technique is shown to make quasi-st atic measurements feasible.