Silicon On-chip 1D Photonic Crystal Nanobeam Bandgap Filter Integrated with Nanobeam Cavity for Accurate Refractive Index Sensing

Abstract

A novel method for integration of high-performance 1-D photonic crystal nanobeam bandgap filter (1-D PC-NBF) and high-sensitivity 1-D PC nanobeam cavity sensor (1-D PC-NCS) is proposed on a monolithic silicon chip. The 1-D PC-NBF consists of a simple 1-D PC nanobeam waveguide, in which the bulk air-hole grating radii are kept the same. The 1-D PC-NCS consists of a common 1-D PC nanobeam cavity, in which the air-hole grating radius is parabolically tapered from center to end. By using the 3-D finite-difference time-domain (3-D-FDTD) method, the proposed 1-D PC-NBF with an effective low-pass bandgap ranging from 1533 to 1785 nm (with width > 250 nm) is demonstrated, where the resonant wavelengths lying in the bandgap are not guided. Then, by connecting an additional 1-D PC-NBF to a 1-D PC-NCS in series, a transmission spectrum only containing the specific fundamental mode of the 1-D PC nanobeam cavity for sensing purposes is created, while the other high-order modes are filtered out. Moreover, the additional 1-D PC-NBF has no influence on the properties (e.g., $Q$-factor, resonance position, and sensitivity) of the fundamental resonant mode of 1-D PC-NCS. In particular, the footprint of the proposed 1-D PC nanobeam integrated sensor is ultracompact around $0.7\ \mu\text{m}\times 10\ \mu\text{m}$, which is improved more than three orders of magnitude compared with the integrated sensor devices based on 2-D PC. Thus, the method presented here is promising to build highly parallel integrated sensor arrays for lab-on-a-chip applications and accurate detections.