Numerical design of a silicon nitride nanobeam cavity for biochemical sensing

Abstract

The field of integrated photonics has experienced rapid growth in the past few decades. Sensors based on photonic crystal (PhC) nanobeam cavities are of great interest due to their size , sensing capabilities, and possible applications such as biochemical sensing. Silicon Nitride (SiN) platforms are competitive option against its counterpart Silicon due to the cost of material, no loss due to Two-Photon Absorption (TPA) or Free Carrier Absorption (FCA), and wide transparency window in both visible and near-infrared regions of the spectrum. Nevertheless, SiN presents low refractive index contrasts, which makes it challenging to achieve optical field confinement inside the cavity. Previous work have proven that slow light waveguides can compensate the low refractive index (RI) contrast in order to obtain high $\mathcal{Q}$ cavities. This thesis presents a design of a slow light PhC nanobeam cavitiy based on SiN working at near-infrared range. A numerical analysis was performed using a high-Q deterministic design. The proposed nanobeam cavity consists of a slow-light PhC waveguide bounded by two Bragg mirrors. For biochemical sensing purposes, the cavity is designed such that the optical mode supported has most of the field in the medium around it, thereby increasing the light-matter interaction between the cavity mode and the analyte. The sensing performance of the structure was studied by RI sensing analysis. The cavity designs presents a Q factor up to $\sim1.2\times10^{4}$ at a wavelength $\sim$ 900 nm. The bulk sensitivity and FOM were found at 215 nm/RIU and 2843, respectively.