Optical MEMS pressure and vibration sensors using integrated optical ring resonators

In this paper we propose and analyse novel optical MEMS based pressure and vibration sensors utilising integrated optical ring resonators. The wavelength shift of light propagating in the resonator, located over the micro-mechanical structure, due to stress induced refractive change because of applied pressure or vibration, provides the desired sensor output. In the case of pressure sensor, as the circular diaphragm deflects due to the differential pressure, stress induced refractive index change in the waveguide lead to change in the wavelength shift providing the measure of pressure. For 1mm radius circular diaphragm with 65mum thickness, wavelength shift of 0.78 pm/kPa is obtained with a pressure range of 300 kPa. In the case of vibration sensor, the straight portion a race track resonator is located at the foot of a cantilever beam with proof mass. As the beam deflects due to vibration, stress induced refractive change in the waveguide located over the beam lead to the wavelength shift providing the measure of vibration. A wavelength shift of 3.19 pm/g in the range of 280 g for a cantilever beam of 1750 mum times 450 mum times 20 mum has been obtained. Since the wavelength of operation is around 1.55 mum, hybrid integration of source and detector is possible on the same substrate Also it is less amenable to noise as wavelength shift provides the sensor signal. This type of sensors can be used for precession instrumentation, aerospace application and other harsh environments with suitable design