Waveguide-Integrated Mid-Infrared Plasmonics with High-Efficiency Coupling for Ultracompact Surface-Enhanced Infrared Absorption Spectroscopy

TL;DR

This paper demonstrates the design and simulation of waveguide-integrated plasmonic structures in the mid-infrared for highly efficient, compact surface-enhanced infrared absorption spectroscopy, enabling on-chip molecular sensing.

Contribution

It introduces novel mid-IR plasmonic structures integrated with silicon waveguides for enhanced SEIRA, extending plasmonics into the mid-infrared range.

Findings

Achieved up to 80% resonance dip in arrays

Single resonator resonance dip up to 40%

Simulated effective SEIRA signals for molecular layers

Abstract

Waveguide-integrated plasmonics is a growing field with many innovative concepts and demonstrated devices in the visible and near-infrared. Here, we extend this body of work to the mid-infrared for the application of surface-enhanced infrared absorption (SEIRA), a spectroscopic method to probe molecular vibrations in small volumes and thin films. Built atop a silicon-on-insulator (SOI) waveguide platform, two key plasmonic structures useful for SEIRA are examined using computational modeling: gold nanorods and coaxial nanoapertures. We find resonance dips of 80% in near diffraction-limited areas due to arrays of our structures and up to 40% from a single resonator. Each of the structures are evaluated using the simulated SEIRA signal from poly(methyl methacrylate) and an octadecanethiol self-assembled monolayer. The platforms we present allow for a compact, on-chip SEIRA sensing system with highly efficient waveguide coupling in the mid-IR.