Athermal evanescent wave filter based on slab waveguide coupled silica microfiber

Thermal instability of optical devices based on evanescent wave coupling between an optical fiber and a slab waveguide has been a serious problem for their sensing and telecommunication applications and thermal compensation is highly necessary. In this paper, a passive thermal compensation approach is proposed and an inherently temperature insensitive evanescent wave filter based on slab waveguide coupled silica microfiber was demonstrated by both theoretical analysis and experiments. It was theoretically illustrated that the thermal properties of the proposed filter could be effectively suppressed by optimizing its geometry parameters. Fabricated from a 2.32 mu m-diameter microfiber and embedded in Teflon with negative thermo-optic coefficient, the temperature sensitivity of the filter was compensated to be as low as 3.3 pm/degrees C, almost thirty times less than the filter without the embedding layer. These results are very encouraging toward the development of thermal stable slab coupled fiber devices.