Design and Fabrication of Double-Cavity Tunable Filter Using Micromachined Structure

We propose a micromachined tunable optical filter with a double-cavity structure, which exhibits a sharper and flatter filter response than a conventional single-cavity filter, resulting in lower interchannel crosstalk and lower insertion loss. The possibility of using widely tunable filters in 200-GHz-spacing wavelength-division-multiplexing (WDM) systems is presented. In addition, a lower tuning voltage can be achieved with thinner movable cantilevers. We have fabricated a double-cavity filter with 7.5-pair top, 23.5-pair middle and 3.5-pair bottom GaAs/GaAlAs multilayer mirrors. The filter provides a better shape factor of reflection spectra of 0.41 than a single-cavity filter.