Silicon Fabry-Perot filter for WDM systems channels monitoring

A simple and low-cost solution for tracking the frequency of WDM channels, based on the thermo-optic tuning of single-cavity Fabry-Perot silicon optical filters, is presented. High finesse and narrow bandwidth are obtained thanks to coating stacks deposited by e-beam evaporation on both facets of a previously thinned and polished silicon wafer. The filter, in a first prototypal version, resolves up to seven 50-GHz-spaced channels, at wavelengths around 1550 nm, with a crosstalk of -10 dB.