Simple and low-cost silicon Fabry-Perot filter for WDM channel monitoring

We propose a simple and low-cost solution for tracking the frequency of WDM channels, based on the thermo-optic tuning of Fabry-Perot silicon optical filters. The fabricated structures exhibit, due to a suitable coating stack on both cavity sides, high finesse and narrow bandwidth. Moreover, the free spectral range is large compared to the channel spacing, allowing the monitoring of one carrier frequency at a time. By means of a heater we change the cavity refractive index and move the transmission peaks, thus scanning the WDM frequency set. In particular, in a preliminary prototype realized by using a 100-/spl mu/m-long silicon cavity we demonstrate the possibility to resolve up to seven 50-GHz-spaced channels, with a crosstalk of -10 dB, at wavelengths around 1550 nm. More channels are easily resolvable by using shorter cavities.