Nanowire-based tunable photonic crystals

Photonic crystals, materials with periodically varying refractive indices, show exciting optical properties that enable many technological applications. Conventional photonic crystals have optical properties that are determined at the time of fabrication and the ability to tune them is quite limited, particularly at visible frequencies. We investigate theoretically the possibility to use nanowires or nanotubes as the building block for tunable two-dimensional photonic crystals. Tunability is achieved by fabricating flexible nanowires in a periodic pattern and actuating them electrostatically. This changes the lattice basis, which in turn modifies the optical properties of the photonic crystal. We use a finite-difference time-domain method to model photonic crystals with changeable bases. We show that the optical transmission through a two-dimensional photonic crystal with only a few rows of nanowires in the light propagating direction can be electrostatically tuned from over 90% transmission to less than 10%. We demonstrate that tunability is maintained in realistic three-dimensional experimental geometries. Finally, we analyse the performance of the photonic crystals in terms of actuation voltages and tuning speeds, and conclude that the response time of a tunable carbon-nanofibre-based photonic crystal lies in the microsecond range.