The authors experimentally demonstrate the controllability of the defe
ct mode in a submillimetre three-dimensional silicon photonic crystal.
The resonant mode at 253 GHz is created inside the forbidden gap by i
nserting interstitial defects. The transmission level of the mode is m
odulated externally by more than 8 dB with a 330 mW laser illumination
. Transmission spectra are confirmed by numerical simulations.