Waveguide-integrated mid-infrared plasmonics with high-efficiency coupling for ultracompact surface-enhanced infrared...

Area of Science:

• Plasmonics and Nanophotonics
• Mid-Infrared Spectroscopy
• Chemical Sensing

Background:

• Waveguide-integrated plasmonics has shown promise in visible and near-infrared regions.
• Surface-enhanced infrared absorption (SEIRA) spectroscopy enables sensitive detection of molecular vibrations.
• Extending SEIRA to the mid-infrared (mid-IR) is crucial for analyzing a wide range of molecular fingerprints.

Purpose of the Study:

• To develop and evaluate waveguide-integrated plasmonic structures for mid-IR SEIRA.
• To investigate the performance of gold nanorods and coaxial nanoapertures on a silicon-on-insulator platform.
• To demonstrate compact, on-chip SEIRA sensing with efficient waveguide coupling in the mid-IR.

Main Methods:

• Computational modeling of plasmonic structures (gold nanorods, coaxial nanoapertures) on a silicon-on-insulator (SOI) waveguide.
• Simulation of SEIRA signals using poly(methyl methacrylate) and an octadecanethiol self-assembled monolayer.
• Analysis of optical resonance dips and field enhancement in near diffraction-limited areas.

Main Results:

• Achieved resonance dips up to 90% from arrays of plasmonic structures.
• Demonstrated resonance dips up to 50% from single resonators.
• Validated the simulated SEIRA signal for common organic molecules.

Conclusions:

• The proposed waveguide-integrated plasmonic platforms are effective for mid-IR SEIRA.
• These platforms enable compact, on-chip SEIRA sensing systems with high waveguide coupling efficiency.
• The developed structures show significant potential for sensitive molecular vibrational analysis in the mid-IR.