Mechanical considerations in the design of a micromechanical tuneable InP-based WDM filter

A FVDM photodetector for fiberoptic communication systems using a wavelengt hs around 1.55 mu m has earlier been proposed as a tuneable Fabry-Perot int erferometer micromachined on InP and integrated with a photodiode, The inte rferometer consists of a mirror suspended on beams and is tuned by electros tatic attraction. The size of the mirror is 30 mu m x 30 mu m. In order to maintain the filter performance, the mirror must be kept so fiat that the m aximum bending deflection of the mirror surface is below 1 nm. Four alterna tive filter geometries are considered. A mathematical model describing the influence of system parameters, including tuning voltage and the sizes of t he filter components, is developed. The upper and lower bounds of the natur al frequency of mechanical vibrations are also calculated analytically. Wit h finite-element analysis (FEA) the response to electrostatic actuation is calculated and the flatness of the mirror surface during tuning and at chan ged ambient temperature conditions is investigated. The dynamic behavior is also studied using modal analysis. The results of the analytic and FEA mod eling are compared and found to agree.