High-speed optical wavelength interrogator using a PLC-type optical filter for fiber Bragg grating sensors

Abstract

We study a new sensing system for health monitoring of aircraft structures made of composite materials. This sensing system is composed of fiber Bragg grating (FBG) sensors and a piezoelectric transducer (PZT). The FBG sensors receive elastic wave generated by the PZT. For high-frequency vibration monitoring, or acoustic emission (AE) detection, we have developed high-speed optical wavelength interrogator for FBG sensors. In this FBG interrogator, we used an optical filter which converts wavelength shift of the reflected light from the FBG into the output optical power change. This system is suitable for high-speed wavelength detection because there is no mechanical moving part. We studied two types of optical filter. One is a Mach-Zender interferometer and the other is an arrayed waveguide grating (AWG). Both of them were fabricated using silica-based planar lightwave circuit (PLC) technology. The optical filters based on the PLC technology have the advantage in integration of optical components. By combining the FBG interrogator using the AWG optical filter with the PZT actuator, we succeeded to detect elastic wave propagating in the CFRP laminated plate. As a result, we found that this FBG/PZT hybrid sensing system is very promising for detection of internal defects in composite materials.