Micromachined Tunable Filters Using Stress Control of Multilayer Semiconductor Mirrors

摘要

We proposed and demonstrated a micromachined filter with stress control, which gives us novel functions including temperature insensitive operation, thermal wavelength tuning, wavelength trimming and 2-D multi-wavelength integration. In this paper, we present the design and the fabrication of micromachined thermally tunable filters with a low tuning voltage. In our micromachined filter, an air gap is formed between GaAlAs/GaAs DBRs with an upper DBR mirror freely suspended above the substrate by a cantilever structure. A novelty in our devices is to add a GaAs or GaAlAs thermal strain control layer on the upper DBR. We can freely control the temperature dependence of the proposed MEMS based resonant cavity. Either temperature insensitive operation or wide wavelength tuning induced by temperature change can be realized. Also, we fabricated a micromachined thermally tunable filter with a heating element. There are two electrodes integrated on the top p-type doped strain control layer of this filter for heating the cantilever. When a voltage is applied between the two electrodes resulting in heating, the micromachined cantilever moves due to thermal strain. The proposed structure enables thermal wavelength tuning either for red shift or blue shift. The amount of wavelength tuning is controlled by the length and the thermal capacity of the cantilever. We can expect a lower tuning voltage than that of a conventional electrostatic force tuning scheme. We measured the reflection spectra of fabricated filters with changing an applied voltage between two electrodes. We achieved wavelength tuning of 50 nm at an applied voltage of 6V.