This research proposes extending paper-clip spiral waveguide designs to mid-infrared silicon photonics for chemical sensing applications. The study presents a novel suspended silicon architecture employing broadened Archimedean spirals with subwavelength grating metamaterial cladding to overcome limitations of conventional SOI platforms at wavelengths beyond 3.6 µm. Theoretical analysis predicts propagation losses below 0.5 dB/cm at 3.8 µm with evanescent field ratios exceeding 35%, representing a 2–3× improvement over conventional racetrack resonators. The work establishes a complete fabrication protocol and experimental validation plan for chip-scale sensors targeting parts-per-billion detection limits.
Key findings
Extension of paper-clip spiral waveguides from telecom delay lines to MIR evanescent field absorption spectroscopy enables ultra-long optical paths in compact footprints.
Theoretical modeling predicts propagation losses below 0.5 dB/cm at 3.8 µm with evanescent field ratios exceeding 35% using suspended silicon with SWG cladding.
Broadened Archimedean spiral geometries with Euler bends minimize radiation losses compared to conventional circular resonators while maintaining broadband operation.
The architecture targets 2–3× improvement in sensitivity over racetrack resonators for detecting methane at 3.31 µm and carbon dioxide at 4.26 µm.
Critical fabrication challenges include DRIE etching, membrane release, and mitigation of sidewall roughness scattering and thermal drift.
Limitations & open questions
Operation limited to 3–5 µm atmospheric window due to silicon absorption at longer wavelengths.
Fabrication complexity involving deep reactive ion etching and suspended membrane release introduces risk of structural failure.
Sensitivity dependent on mitigation of sidewall roughness scattering and thermal drift effects.