Enhanced interband optical nonlinearities from coupled quantum wells

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, to our knowledge, 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, &\#x3C7;(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&\#x2013;775&\#x00A0;nm over bulk controls. Extracted &\#x3C7;(2) values were as high as 2750&\#x00A0;pm/V, which is >7&\#xD7; that of bulk GaAs. Furthermore, measured susceptibilities agreed well with quantum mechanical calculations of &\#x3C7;(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 &\#x3C7;(2) toward the simulation predictions for ideal heterointerfaces. More complex layer designs showed predicted &\#x3C7;(2) up to 7&\#x00A0;nm/V. Such materials are anticipated to find myriad applications, including entangled photon generation at telecommunications wavelengths for chipscale quantum information processing.