Displacement sensing using geometrical modulation in reflection mode (GM-RM) of coupled optical waveguides

An optical displacement sensing method for micro-electro-mechanical systems (MEMS) is presented. The concept uses the displacement of micromachined structure to modulate the optical coupling between two waveguides fabricated next to the structure. The waveguides are based on suspended optical waveguide displacement sensors (SOWDS) technology and are fabricated in parallel with the suspended structure using the single crystal reactive ion etching and metalization (SCREAM) process. The building block of the waveguides is a single crystal silicon (SCS) beam with superficial top layers comprising 0.6 m thick , 0.4 m thick and 0.6 m thick . The SCS beam is fabricated with a cross section of and may guide light with wavelength in the 1.3-1.5 m range. The first layer serves as a buffer layer that allows light with wavelength in the 0.6-0.9 m range to be guided in the layer. This paper discusses the response of the sensor to acoustical pulse excitation. The sensing concept is considered for displacement sensing both for sensors (acoustical, vibrational, flow, thermal etc), and as an independent displacement sensing means for actuators.