Geometrical modulation-based interferometry for displacement sensing using optically coupled suspended waveguides

A geometrical modulation-based interferometry (GMI) for a displacement sensor is presented. The implementation of the GMI is based on the suspended optical waveguide displacement sensors (SOWDSs) technology. The interferometry effect of the GMI results from light propagating in geometrically modulated and mutually coupled suspended waveguides with an in-plane degree of freedom. The building block of the suspended waveguides is a single-crystal silicon (SCS) beam with superficial layers comprising a 0.6-/spl mu/m-thick SiO/sub 2/, 0.4-/spl mu/m-thick Si/sub 3/N/sub 4/, and 0.6-/spl mu/m-thick SiO/sub 2/. The SCS beam is fabricated with a cross section of 1.6 /spl mu/m/spl times/10 /spl mu/m and may guide light with wavelength in the 1.3-1.5-/spl mu/m range. The first SiO/sub 2/ layer serves as a buffer layer that allows light with wavelength in the 0.6-0.9-/spl mu/m range to be guided in the Si/sub 3/N/sub 4/ layer. This paper discusses the theoretical consideration and the characterizations of a GMI displacement sensor.