Thermal and Optical Characterization of Silicon-Based Tunable Optical Thin-Film Filters

In this paper, we report on the successful fabrication and comprehensive optical and electrothermal characterization of a silicon-based tunable optical filter. Of particular interest here are the static and transient electrothermal characteristics of the filter membrane. The filter is configured as a Fabry-Perot resonator with dielectric Bragg reflectors and is fabricated as a stress-compensated multilayer of dielectric thin-films. Tunability is achieved by changing the refractive index of the solid-state cavity material through thermal modulation, accomplished by Joule heating in metal thin-film resistors. The filter layers are configured as a membrane to provide good thermal isolation and its electrothermal behavior was characterized in steady-state and dynamically. A maximum stable temperature difference of 450 K and a heating efficiency of 13.4 K mW^-1 were measured with a thermal time constant for the filter hotplate of 3 ms. The filter´s spectral width is 0.28 nm at a wavelength of 1550 nm and through thermal modulation it was possible to shift the filter peak over more than 29 nm.