Fabrication of a silicon Mach-Zehnder interferometer for mechanical measurands

We present an integrated Si micromechanical Mach-Zehnder interferometer based on the ARROW structure. The interferometer has its reference arm supported by the Si substrate and the sensing arm is suspended over a cavity realized using Si surface micromachining techniques. An applied pressure causes deflection of the suspended arm resulting in optical path elongation and hence in an optical phase shift with respect to the reference. The design of the interferometer was based on simulations of the photonic transport in the ARROW for the different geometric parameters. Silicon integrated circuit technology was employed for the interferometer fabrication i.e. low temperature CVD oxide for the core and second cladding and LPCVD poly for the first cladding layer. Prior to surface micromachining, the composite waveguide structure was annealed so as to minimize the residual stress and hence the sag in the free standing sensing arm.