Imaging of photonic crystal cavity mode via refractive index sensing

Silicon (Si) based integrated Photonic Crystal (PhC) cavities show great promise for biosensing applications, owing to their high Quality (Q) factor, low mode volume and compatibility with Complementary metal–oxide–semiconductor (CMOS) fabrication. We present the development of a new experimental technique to experimentally determine the sensing properties of PhC cavity mode. It makes use of a silica nano-tip fiber that moves in the near field of the PhC cavity and of a high numerical microscope objective that collects the field radiated out-of plane from the cavity. Measuring the intensity fluctuations that are induced by the nano tip via local perturbation of the refractive index allows us to map the intensity profile of the cavity mode.