Mechanically switchable photonic crystal structures based on coupled photonic crystal slabs

Using both analytic theory, and first-principles finite-difference time-domain simulations, we introduce several novel mechanically tunable photonic crystal structures consisting of coupled photonic crystal slabs. These structures exploit guided resonance effects which give rise to strong variation of transmission for normally incident light. First, when the two slabs are separated apart by a few wavelengths, such a coupled slab structure behaves as a miniaturized Fabry-Perot cavity with two photonic crystal slabs acting as highly reflecting mirrors. Therefore, the transmission through the structure is highly sensitive to the spacing between the slabs. Second, when the two slabs are in proximity to each other, the evanescent tails of the resonance start to overlap. Exploiting the evanescent tunneling, we introduce a new type of optical all-pass filter. The filter exhibits near complete transmission for both on and off resonant frequencies, and yet generates large resonant group delay. Thus, we expect the coupled photonic crystal slab structures to play important roles in micro-mechanically tunable optical sensors and filters.