Coherent cavity coupling in O-band silicon photonic sensors for water environment detection.

Authors

Bartosz Janaszek, Marcin Kieliszczyk, Muhammad Ali Butt

Published in

Scientific reports. May 19, 2026. Epub May 19, 2026.

Abstract

Silicon photonic refractive index sensors based on optical resonators offer high sensitivity and compact integration; however, their performance is fundamentally limited by resonance linewidth and spectral resolution. In this work, we propose and numerically investigate a silicon-on-insulator (SOI) refractive index sensor based on a coherently coupled dual-cavity architecture, designed to achieve linewidth narrowing and enhanced sensing performance. The device consists of two loop resonators interconnected via a directional coupler and side-coupled to a bus waveguide, enabling controlled coherent interference and extended photon lifetime. The novelty of the design lies in using the directional-coupler-mediated interaction between two loop cavities to favor a dominant coupled supermode while suppressing parasitic multi-interference features. A comprehensive parametric optimization of the coupling length, inter-resonator gap, bus-cavity gap, and resonator radius is performed using finite-element simulations. The results show that under optimal coupling conditions, the structure supports a dominant supermode with suppressed multi-interference effects, leading to a significantly reduced resonance linewidth and improved spectral purity. As a result, the proposed sensor achieves a high refractive index sensitivity of 304.02 nm/RIU, a quality factor of approximately 2.2 × 10⁴, and a limit of detection as low as 1.64 × 10^- 4 RIU, corresponding to sub-ppm-level sensing performance. Compared to conventional single-ring and other coupled-resonator configurations, the proposed architecture provides a favorable trade-off between sensitivity, limit of detection, and fabrication complexity relative to slot or SWG-based designs. Moreover, operation in the O-band offers distinct advantages for sensing in aqueous environments. The presented approach demonstrates an effective strategy for engineering narrow-linewidth resonances in silicon photonics and provides a promising route toward high-resolution SOI sensing devices compatible with established CMOS fabrication workflows, for chemical and biological applications.

PMID:
42156956
Bibliographic data and abstract were imported from PubMed on 20 May 2026.

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