An all-dielectric tunable optical filter based on the thermo-optic effect
Journal of Optics A: Pure and Applied Optics, Volume 6, Number 6

A MEMS based, thermally tunable optical filter, hybridly assembled with a fibre based input/output, is presented. The filter is based on a Fabry–Perot interferometer employing a silicon cavity and silicon based dielectric Bragg reflectors and is fabricated as a free-standing membrane. The filter membrane is fixed to the substrate through micromachined suspension arms, which act as a thermal isolation. Wavelength tuning is achieved through thermal modulation of the cavity's optical thickness using thin film resistors. The filter characteristics measured were a full width at half-maximum value (FWHM) of 1.19 nm at a wavelength of 1530 nm and a finesse exceeding 1000. The tuning efficiency of a single-cavity filter with Bragg mirrors based on silicon nitride and silicon dioxide was measured to be 51.9 pm K−1. Measurements of static and transient electrothermal behaviour were performed on filter membranes, resulting in maximum temperatures of 700 °C and thermal time constants of 5.14 ms. The assembly technique relied on the alignment of optical fibres with the filter array using a novel silicon optical bench approach.