Multipoint Fiber Bragg Grating Sensing Using Two-Photon Absorption Process in Silicon Avalanche Photodiode

We propose a multipoint fiber Bragg grating (FBG) sensing system that measures both spectral change of FBGs and precise distance to them by using intensity-modulated light and two-photon absorption process in a silicon avalanche photodiode. We experimentally confirm the principle using five cascaded FBGs with almost the same Bragg wavelength. The optical path length difference and the reflection spectrum for each FBG are successfully measured at the same time. The relative uncertainty of path length measurement is in the order of 10-4.