Exceptional Point Generated Robust Asymmetric High-Order Harmonics

TL;DR

This paper introduces a metallic-silicon waveguide system leveraging exceptional points and Jordan form Hamiltonians to achieve robust, unidirectional high-order harmonic generation that is resilient to geometrical imperfections.

Contribution

It proposes a novel waveguide design with complex optical potential modulation that enables unidirectional harmonic generation at exceptional points, independent of geometrical imperfections.

Findings

Unidirectional high harmonic generation at specific waveguide lengths.

Harmonic phase becomes independent of coupling.

Fundamental mode remains reciprocal despite non-reciprocal harmonic generation.

Abstract

We propose a metallic-silicon system with a complex optical potential modulated along the length of the waveguide for a robust higher harmonic generation. For right moving fields when the strength of non-Hermiticity becomes equal to the real part of the optical potential, the dynamical equations associated with modal field amplitudes in our proposed system are described by a Jordan form Hamiltonian. This ultimately will allow for a unidirectional higher frequency generation which always has a maximum value for a specific length of the waveguide irrespective of the geometrical imperfections in the design of the waveguide. Furthermore, the phase of the generated higher harmonic mode becomes independent of the coupling between the fundamental frequency and higher harmonic one. Unlike other proposed spatiotemporal modulated systems when the system has a Jordan form Hamiltonian, the fundamental mode remains reciprocal while the harmonic generation is non-reciprocal. Consequently, while the proposed device cannot be used as an optical isolator it can be used for many other devices such as laser cavities, interferometry, and holographic processes.