Design of two-dimensional tunable photonic crystals with multiple functionalities.

Negative refraction is an interesting phenomenon which can provide sub-wavelength imaging and a novel way to control the propagation path of photons. Photonic crystals have been intensively researched to achieve negative refraction. In this article, we present design and simulations of a new two-dimensional tunable photonic crystal obtained using the plane wave expansion method. The newly designed photonic crystals exhibit tunability among positive, zero, and negative refractions, when liquid crystals infiltrated in the structures are electrically tuned. The equifrequency surface diagrams of the designed photonic crystal unveil the refraction direction of photons in the structures. The tunability is further confirmed using the finite-difference time-domain simulation.