Design, Fabrication, and Characterization of Tunable Micromachined Filter with Double-Cavity Structure

In this study, we demonstrated micromachined double-cavity optical filters with a narrow 3 dB bandwidth of similar to 0.7 nm in reflection spectra. These double-cavity filters exhibited a sharper and flatter response than conventional single-cavity filters, resulting in a lower crosstalk. We were able to reduce filter bandwidth by increasing the number of distributed Bragg reflector (DBR) layers to be 18.5, 45.5, and 16.5 pairs of GaAs/AlGaAs layers at the top, in the middle, and at the bottom of the filters, respectively. The thermal wavelength tuning of the filters was demonstrated with the aid of thermal strain in movable cantilevers. For the heating of the p-n junction in the cantilevers, the filters exhibited a continuous tuning range of similar to 7 nm with an applied voltage of 15 V. The temperature dependence of filter wavelength was experimentally investigated using an external heater, which the filters showed a linear temperature sensitivity. In addition, the extinction ratios of reflection spectra were maintained at similar to 12 dB over the entire tuning range.