Plasmonic tuning of nano-antennas for super-gain light amplification

Abstract

Nanoscale conductive materials are often used for inducing localized free electron oscillations known as plasmons . This is due to their high electronic excitability under optical irradiation owing to their super-small volume. Recently, plasmons have been of interest for enhancing the gain-bandwidth product of optical amplifiers. There are currently two well-established mechanisms for light amplification. The first one is via stimulated emission of radiation (lasers) using a given energy source and often an optical feedback mechanism. The second one is based on the nonlinear coupling of a low-intensity input wave and a high-intensity pump wave for energy exchange (parametric amplifiers). Both techniques have shortcomings. Lasers have a small operation bandwidth and offer a limited gain, but require moderate energy pumping to operate. Whereas optical parametric amplifiers (OPAs) offer a high operation bandwidth along with a much higher optical gain, with the drawback of requiring intense pumping to be functional. The aim of this paper is to introduce a technique that combines the advantages and eliminates the drawbacks of both techniques in the nanoscale to allow for a better amplification performance in integrated optical devices. This is achieved by inducing a plasmonic chirp in conductive nanomaterials a.k.a nano-antennas, which enables the confinement of an enormous electric energy density that can be coupled to an input beam for amplification. Using the Finite Difference Time Domain numerical-method with the material parameters of well-known semiconductors, intramaterial condensation of electric energy density is observed in semiconductor nano-antennas for certain plasmonic chirp-frequencies which enables broadband high-gain optical amplification based on free-electron oscillations that is promising for small-scale optical devices requiring a high gain-bandwidth product. The results are in good agreement with semiempirical data.

Keywords

• optical amplification
• nano-antenna
• plasmon
• lasers
• semiconductors
• high energy density