Boosting local field enhancement by on-chip nanofocusing and impedance-matched plasmonic antennas

TL;DR

This paper demonstrates on-chip nanofocusing combined with impedance-matched plasmonic antennas at telecom wavelengths, achieving significant local field enhancement for applications in sensing and spectroscopy.

Contribution

It introduces a novel on-chip nanofocusing and antenna excitation method, with experimental validation showing a field enhancement of up to 12000 times.

Findings

Achieved field enhancement up to ~12000 times

Distributed enhanced field over 30x30x10 nm^3 gap

Demonstrated efficient excitation of dipole and quadrupole modes

Abstract

Strongly confined surface plasmon-polariton modes can be used for efficiently delivering the electromagnetic energy to nano-sized volumes by reducing the cross sections of propagating modes far beyond the diffraction limit, i.e., by nanofocusing. This process results in significant local-field enhancement that can advantageously be exploited in modern optical nanotechnologies, including signal processing, biochemical sensing, imaging and spectroscopy. Here, we propose, analyze, and experimentally demonstrate on-chip nanofocusing followed by impedance-matched nanowire antenna excitation in the end-fire geometry at telecom wavelengths. Numerical and experimental evidences of the efficient excitation of dipole and quadrupole (dark) antenna modes are provided, revealing underlying physical mechanisms and analogies with the operation of plane-wave Fabry-P\'erot interferometers. The unique combination of efficient nanofocusing and nanoantenna resonant excitation realized in our experiments offers a major boost to the field intensity enhancement up to $\sim 12000$, with the enhanced field being evenly distributed over the gap volume of $30\times 30\times 10\ {\rm nm}^3$, and promises thereby a variety of useful on-chip functionalities within sensing, nonlinear spectroscopy and signal processing.