Abstract

A vibration measurement system is proposed that uses a combination of a fiber Bragg grating (FBG) built-in cantilever (referred to as sensor FBG hereinafter) with an asymmetrical cross section and a referenced FBG with pre-controllable reflected light spectrum (referred to as demodulation FBG hereinafter) based on a revised method of grating matching. One side of the cladding on the sensor FBG was etched to within 11 pm of the core and the opposite no-etched side was coated with a material to absorb laser light. When a low-frequency mechanical vibration was applied to the always vibrating sensor FBG that was driven by photothermal energy, the composite vibration waveform included both frequency components of photothermal vibration and mechanical vibration could be optically detected.

© 2018 The Author(s)