Tunable superlensing by a mechanically controlled photonic crystal

We investigated negative refraction and subwavelength imaging by a mechanically tunable photonic crystal (PC) slab. A honeycomb-structured PC composed of a silicon-polyimide membrane was used because it exhibits isotropic negative refraction within the second photonic band. Using the finite-difference time-domain (FDTD) method, we demonstrated focusing properties of the PC lenses at various frequencies and mechanical stresses. Analyses based on a ray optics model and equifrequency surface also confirmed the behavior observed by the FDTD simulations. These results suggested a mechanically tunable superlens, whose achievable frequency bandwidth was 12.9% of the center frequency for a mechanical stress of ±10%.