Temperature Insensitive Fiber Optic Interferometric Sensor

We present a Michelson-type fiber-optic interferometric displacement sensor that is insensitive to temperature variations. A fused biconical tapered coupler was built and cleaved immediately after the coupled length. The cleaved coupler was fixed with epoxy in a cylindrical glass tube and polished until two cores, very close to each other, could be observed. The end of one core was selectively coated using an aluminium deposition process, and was used as part of the reference arm; the other core was used as the sensing arm. Displacements of a vibrating reflective surface were measured for frequencies ranging from dc to 100 kIIz and extremely stable output signals, devoid of thermal drifts, were observed over sustained periods of time.