This paper presents, for the first time, a micromachined in-plane tunable optical filter (TOF) using thermo-optic effect for wavelength division multiplexed telecommunication. The TOFs are comprised of a Fabry-Perot silicon optical resonator formed between two distributed Bragg reflectors with high-reflectance based on silicon/air-gap pairs. The whole device was vertically fabricated using silicon deep reactive ion etching (DRIE). And input/output optical fibers were easily aligned along with the TOF structure on the substrate by exploiting in-plane fiber alignment.
Tunability of the TOFs is experimentally achieved through thermal modulation of optical path length by heating the silicon resonator. As an input voltage increases, a notch of reflectance spectrum shifts to a longer wavelength with a tuning range of 9 nm and 3dB bandwidth of 2nm. The temperature of a silicon resonator was estimated to be about 93°C for the tuning range.