Mechanically Tunable Negative-Index Photonic Crystal Lens

We report the microelectromechanical systems (MEMS)-enabled mechanically tunable negative-index photonic crystal lens, which was comprised of 2-D photonic crystal and symmetrical electro-thermal actuators. The 2-D photonic crystal was made of a honeycomb lattice of silicon rods embedded in an SU-8 membrane. A silicon input waveguide and deflection block were also fabricated for light in-coupling and monitoring of focused spot size, respectively. When actuated, the electro-thermal actuators stretched the photonic crystal and consequently modified the photonic band structure. This, in turn, modified the focal length of the photonic crystal lens. The fabricated device was fully characterized using a tunable laser and an infrared camera while being actuated with a constant current source. The intensity and lateral spot size observed at the deflection block gradually increased as the applied current increased from 0 to 0.3 A. The observed behavior was in excellent agreement with finite-difference time-domain (FDTD) simulations, confirming the mechanical tuning of negative-index imaging.