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

A FVDM photodetector for fiberoptic communication systems using a wavelengths around 1.55 mu m has earlier been proposed as a tuneable Fabry-Perot interferometer micromachined on InP and integrated with a photodiode, The interferometer consists of a mirror suspended on beams and is tuned by electrostatic 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 maximum bending deflection of the mirror surface is below 1 nm. Four alternative filter geometries are considered. A mathematical model describing the influence of system parameters, including tuning voltage and the sizes of the filter components, is developed. The upper and lower bounds of the natural frequency of mechanical vibrations are also calculated analytically. With finite-element analysis (FEA) the response to electrostatic actuation is calculated and the flatness of the mirror surface during tuning and at changed ambient temperature conditions is investigated. The dynamic behavior is also studied using modal analysis. The results of the analytic and FEA modeling are compared and found to agree.