Nonreciprocal second harmonic generation in a magnetoelectric material

TL;DR

This paper demonstrates a highly efficient nonreciprocal second harmonic generation in a magnetoelectric material, leveraging interference between magnetic and electric dipole processes, with potential applications in integrated photonic devices.

Contribution

It introduces a novel nonreciprocal SHG mechanism in CuB2O4, achieving near 100% transmission change with small magnetic fields, advancing nonlinear optical nonreciprocity.

Findings

Almost 100% SHG transmission change with 10 mT magnetic field reversal

Resonant magnetic-dipole transition enhances nonreciprocity

Interference between magnetic and electric dipole SHG processes

Abstract

Nonreciprocal devices that allow the light propagation in only one direction are indispensable in photonic circuits and emerging quantum technologies. Contemporary optical isolators and circulators, however, require large size or strong magnetic fields because of the general weakness of magnetic light-matter interactions, which hinders their integration into photonic circuits. Aiming at stronger magneto-optical couplings, a promising approach is to utilize nonlinear optical processes. Here, we demonstrate nonreciprocal magnetoelectric second harmonic generation (SHG) in CuB2O4. SHG transmission changes by almost 100% in a magnetic-field reversal of just 10 mT. The observed nonreciprocity results from an interference between the magnetic-dipole- and electric-dipole-type SHG. Even though the former is usually notoriously smaller than the latter, it is found that a resonantly enhanced magnetic-dipole-transition has a comparable amplitude as non-resonant electric-dipole-transition, leading to the near-perfect nonreciprocity. This mechanism could form one of the fundamental bases of nonreciprocity in multiferroics, which is transferable to a plethora of magnetoelectric systems to realize future nonreciprocal and nonlinear-optical devices.