High- $Q$ and High-Sensitivity One-Dimensional Photonic Crystal Slot Nanobeam Cavity Sensors

We present and theoretically investigate an optical sensor based on a one-dimensional photonic crystal slot nanobeam cavity. The cavity possesses a high calculated Q-factor of 174000 and an ultra-small effective mode volume of ~0.0236 (λ/n)
³
at a resonant wavelength of 1535 nm. Using a slot nanobeam structure, we can strongly confine the resonant-mode field in the air slot region, and thus, the spatial overlap and interaction of light field and detected analytes can be greatly enhanced. An estimated sensitivity as high as 851 nm/refractive index unit is achieved. Due to the high Q and high sensitivity of the cavity, the figure of merit for sensing is very high at 96465. These are the best results for optical sensors based on photonic crystal cavities featuring both a high sensitivity and a high Q-factor to the best of our knowledge. In addition, the total size for the sensing part of the sensor is only 20 × 2 μm
²
.