Demodulation system for phase-locked fiber grating sensors based on XPM

The XPM technique is applied to the demodulation system for fiber grating sensor. According to XPM principle, the intensity of accessorial light can be altered by feedback control and the phase of the light signal from the M-Z interferometer can be modulated in a phase-locked way, thus the system phasic-difference can be locked at the point of the highest sensitivity. The method resolves the precision non-linearity of interferometric demodulation, the limit of very small range for demodulating, the non-linearity of the demodulating sensitivity, the affect of backlight and undercurrent pair in the demodulating circuit, the delay-effect by PZT tune and the error from the machine. The measurement precision of temperature can reach 0.1°C in this system, and the uncertainty is 0.3°C.