Hyperbolic carbon nanoforest for phase matching of ordinary and backward electromagnetic waves: second harmonic generation

TL;DR

This paper demonstrates how engineered hyperbolic metamaterials made of carbon nanotubes can enable phase matching and efficient second harmonic generation involving backward electromagnetic waves, with potential applications in nonlinear photonics.

Contribution

It introduces a novel hyperbolic carbon nanotube-based metamaterial design that supports co-propagating and contra-propagating modes for enhanced nonlinear optical processes.

Findings

Successful phase matching of backward and forward waves in the metamaterial.

Enhanced second harmonic generation efficiency demonstrated numerically.

Reversal of wave propagation direction achieved in the THz regime.

Abstract

We show that deliberately engineered dispersive metamaterial slab can enable the co-existence and phase matching of contra-propagating ordinary fundamental and extraordinary backward second harmonic surface electromagnetic modes. Energy flux and phase velocity are contra-directed in the backward waves which is the phenomenon that gives rise to unique nonlinear optical propagation processes. We show that frequencies, phase, and group velocities, as well as nanowaveguide losses inherent to the electromagnetic modes supported by such metamaterial, can be tailored to maximize conversion of frequencies and to reverse propagation direction of the generated wave. Such a possibility, which is of paramount importance for nonlinear photonics, is proved with a numerical model of the hyperbolic metamaterial made of carbon nanotubes standing on the metal surface. Extraordinary properties of the backward-wave second harmonic generation in the reflection direction and of the corresponding frequency doubling metareflector in the THz are investigated with a focus on the pulsed regime.