142nm electrostatically actuated tuning using surface-micromachined vertical air-cavity wavelength-selective elements for applications in 1.55μm VCSEL's

Surface-micromachined 1.55mum vertical-resonator-based devices, capable of wide, continuous, monotonic and kink-free tuning are designed, technologically implemented and characterized. Tuning is achieved by mechanically actuating one or several membranes in a vertical resonator including two ultra-highly reflective DBR mirrors. The tuning is controlled by a, single parameter (actuation voltage). The two different layers composing the mirrors reveal a very strong refractive index contrast. Filters including InP/air-gap DBR's (3.5 periods) using GaInAs sacrificial layers reveal a continuous tuning of >9% of the absolute wavelength. Varying a reverse voltage (U=0 .. -3.2V) between the membranes, a tuning range up to 142nm was obtained by electrostatic actuation. The correlation of the wavelength and the applied voltage is accurately reproducible without any hysteresis. Appropriate miniaturization is shown to increase the mechanical stability and the effectiveness of spectral tuning by electrostatic actuation since the relative significance of the fundamental physical forces can be varied considerably by appropriate scaling. Model calculations are performed for symmetric and asymmetric optical filter structures, varying layer thickness and compositions. Finally the filter results are used to design micromachined tunable air-gap VCSEL's. Theoretical model calculations demonstrate very wide spectral tuning by micromachined actuation of air-gap VCSEL resonators.