Ultra-compact broadband terahertz spectroscopy sensor enabled by resonant-gradient metasurface

Area of Science:

• Optics and Photonics
• Materials Science
• Spectroscopy

Background:

• Metasurfaces offer advanced optical functionalities by engineering resonances.
• Current metasurface designs face limitations in continuous spectral mapping due to discrete sampling.
• Terahertz (THz) spectroscopy demands enhanced broadband spectral information for sensing and detection.

Purpose of the Study:

• To present an integrated terahertz plasmonic gradient micro-photonic approach for encoding broadband spectra.
• To enable continuous space-to-spectrum mapping for molecular fingerprint observation.
• To overcome the limitations of discrete spectral sampling in current metasurface designs.

Main Methods:

• Utilized smooth variations in metasurface unit cells to create a gradient photonic structure.
• Engineered extraordinary density of resonances and excited bound states in the continuum (BICs).
• Developed a compact device (400 × 125 μm²) for THz spectral encoding.

Main Results:

• Achieved continuous spectral mapping over a 0.9 THz width with only 19 modes.
• Demonstrated real-time, label-free identification of multiple analytes.
• Showcased enhanced vibrational fingerprint detection without complex scanning.

Conclusions:

• The developed approach advances portable THz spectroscopy with compact size and broad capabilities.
• Offers adjustable resolution for enhanced molecular fingerprinting.
• Paves the way for next-generation sensing and detection technologies.