Simulation of Ultrafast GaN/AlN Intersubband Optical Switches

A one-dimensional finite-difference time-domain (FDTD) simulator for ultrafast optical switches based on intersubband transition (ISBT) in GaN/AIN waveguide is described. Influences of the inhomogeneous broadening and the 2D mode profile have been taken into consideration. The ultrafast optical response (τ ∼ 185 fs) measured in a GaN/AIN waveguide was successfully reproduced by the simulator. At present, however, the saturation characteristics of the fabricated device are mainly limited by the excess TM loss caused by the dislocation in MBE-grown nitride layers. When the dislocation density is reduced and the structure is optimized, the switching pulse energy will be improved to about 10 pJ. Further reduction (∼ 1 pJ) will be possible when low-loss submicron waveguides with spot-size converters are developed.