High-Q and high-sensitivity width-modulated photonic crystal single nanobeam air-mode cavity for refractive index sensing

TLDR

The air‑mode cavity localizes light strongly in the low‑index region, enabling substantial overlap with analytes. We propose a novel optical sensor based on a one‑dimensional photonic crystal single nanobeam air‑mode cavity. The sensor’s performance is theoretically studied by introducing a quadratically modulated width tapering, yielding a waveguide‑coupled 1D‑PhC SNAC with a calculated Q of 5.16×10⁶ and an effective mode volume of 2.18(λ/n)³. The resulting device achieves a refractive‑index sensitivity of 537.8 nm/RIU, represents the first PhC single‑nanobeam geometry with both high Q and high sensitivity, and offers a platform for ultracompact lab‑on‑a‑chip multiplexed sensing.

Abstract

We propose a novel optical sensor based on a one-dimensional (1D) photonic crystal (PhC) single nanobeam air-mode cavity (SNAC). The performance of the device is investigated theoretically. By introducing a quadratically modulated width tapering structure, a waveguide-coupled 1D-PhC SNAC with a calculated high quality factor of 5.16×10(6) and an effective mode volume of V(eff)∼2.18(λ/n(si))(3) can be achieved. For the air mode mentioned above, the light field can be strongly localized inside the air region (low index) and overlaps sufficiently with the analytes. Thus, the suggested PhC SNAC can be used for high-sensitivity refractive index sensing with an estimated high sensitivity of 537.8 nm/RIU. To the best of our knowledge, this is the first PhC single nanobeam geometry that features both high Q-factors and high sensitivity, and is potentially an ideal platform for realizing ultracompact lab-on-a-chip applications with dense arrays of functionalized spots for multiplexed sensing.