Enhanced Interband Optical Nonlinearities from Coupled Quantum Wells

TL;DR

This paper demonstrates a novel class of engineered nonlinear materials using coupled quantum wells that exhibit significantly enhanced second order susceptibility, enabling efficient nonlinear optical processes for quantum information applications.

Contribution

First experimental realization of designer nonlinear materials leveraging interband transitions in asymmetric quantum well structures to achieve high $$ susceptibility.

Findings

Observed strong second harmonic generation enhancement at 1550 nm

Extracted $$ values up to 2750 pm/V, surpassing bulk GaAs

Validated experimental results with quantum mechanical calculations

Abstract

The recent, rapid advances in nonlinear chipscale nanophotonics in the visible and near-infrared have been largely driven by manipulating the local dielectric environment proximate to decades-old workhorse bulk nonlinear optical materials, rather than increasing the inherent strength of their nonlinear response. While proposed decades ago, we demonstrate the first experimental realization of a new class of designer nonlinear materials that leverage the interband optical transition in asymmetric structures to provide strong second order susceptibility, $\chi^{(2)}$. Using simple AlGaAs/GaAs coupled quantum wells operating in the near-infrared as a prototype, we observed strong second harmonic generation enhancement of 1550 nm to 775 nm over bulk controls. Extracted $\chi^{(2)}$ values were as high as 2750 pm/V, which is $>$7x that of bulk GaAs. Furthermore, measured susceptibilities agreed well with quantum mechanical calculations of $\chi^{(2)}$ using layer profiles extracted from electron microscopy. Growth interruptions were employed to improve interfacial abruptness in response to electron microscopy characterization, resulting in increased $\chi^{(2)}$ toward the simulation predictions for ideal heterointerfaces. More complex layer designs showed predicted $\chi^{(2)}$ up to 7 nm/V. Such materials are anticipated to find myriad applications, including entangled photon generation at telecommunications wavelengths for chipscale quantum information processing.