Waveguide-Integrated Compact Plasmonic Resonators for On-Chip Mid-Infrared Laser Spectroscopy

Area of Science:

• Nanophotonics
• Silicon Photonics
• Chemical Sensing

Background:

• Integrating nanoplasmonic devices with silicon photonic platforms offers efficient light delivery.
• This hybrid approach combines plasmonics' high field enhancement with dielectric waveguides' low propagation loss.
• It enables fully integrated, on-chip optical sensing systems, eliminating bulky free-space optics.

Purpose of the Study:

• To demonstrate ultracompact plasmonic resonators patterned atop a silicon waveguide for mid-infrared (MIR) spectroscopic chemical sensing.
• To achieve efficient coupling between plasmonic resonators and MIR waveguide modes.
• To showcase the application of these hybrid devices in surface-enhanced infrared absorption (SEIRA) spectroscopy.

Main Methods:

• Fabrication of ultracompact plasmonic nanorod resonators with footprints as small as 2 μm².
• Direct patterning of plasmonic resonators onto a silicon waveguide.
• Measurement of plasmonic resonance via waveguide transmission spectrum.
• Utilizing a tunable mid-infrared laser source for spectroscopy.

Main Results:

• Efficient coupling (>70%) between plasmonic resonators and the MIR waveguide mode.
• Significant field intensity enhancement (>3600x) relative to the waveguide's evanescent field.
• Successful demonstration of SEIRA spectroscopy for a poly(methyl methacrylate) film and an octadecanethiol monolayer.

Conclusions:

• Ultracompact plasmonic resonators integrated with silicon waveguides provide a powerful platform for on-chip MIR chemical sensing.
• The hybrid approach achieves high sensitivity and efficient light-matter interaction.
• This technology paves the way for miniaturized and integrated spectroscopic analysis systems.