Cryogenic second harmonic generation in periodically-poled lithium niobate waveguides

Abstract

Prospective integrated quantum optical technologies will combine nonlinear optics and components requiring cryogenic operating temperatures. Despite the prevalence of integrated platforms exploiting χ (2) -nonlinearities for quantum optics, for example used for quantum state generation and frequency conversion, their material properties at low temperatures are largely unstudied. Here, we demonstrate the first second harmonic generation in a fiber-coupled lithium niobate waveguide at temperatures down to 4.4 K. We observe a reproducible shift in the phase-matched pump wavelength within the telecom band, in addition to transient discontinuities while temperature cycling. Our results establish lithium niobate as a versatile nonlinear photonic integration platform compatible with cryogenic quantum technologies.

Efficient Type II Second Harmonic Generation in an Indium Gallium Phosphide on insulator wire waveguide aligned with a crystallographic axis

“…The large intrinsic nonlinearity in addition to the high-index contrast of sub-wavelength structures leads to very large effective nonlinearities. Different schemes for phase matching have been proposed and implemented [7,8,9]. Type I modal phase matching, consisting in engineering the waveguide cross section such that a pump mode and a SH higherorder mode propagate at the same phase velocity, is attractive because standard waveguiding structures can be used.…”