A thin foil optical strain gage based on silicon-on-insulator microresonators

We present a novel type of optical strain gage. The strain gage consists of a thin polyimide foil with an integrated optical circuit. The strain sensing elements are optical microresonators. The optical response to strain of these microresonators is a wavelength shift of the resonance wavelength. The optical circuit includes several of these resonators to measure strain in different directions. The strain sensor is read-out using a single-mode optical fiber. Because the different microresonators in the optical circuit have different resonance wavelengths, they can be read out using the same fiber. Our strain sensor is some kind of a cross between electrical resistance foil gages and fiber Bragg grating (FBG) sensors. It is a thin foil device, with a thickness of a few tens of micrometers, but it is an optical device and can be read out in a similar way as FBG sensors. We present the working principle, fabrication and first experimental results.