Group index matched frequency conversion in lithium niobate on insulator waveguides

TL;DR

This paper demonstrates the design and fabrication of lithium niobate on insulator waveguides with engineered group indices, enabling efficient on-chip frequency conversion and photon-pair generation for quantum technologies.

Contribution

It introduces a method for group index engineering in LNOI waveguides and experimentally realizes group index matched nonlinear frequency conversion processes.

Findings

Successful demonstration of group index matched sum-frequency generation

Experimental realization of photon-pair creation via SPDC in LNOI

Numerical analysis of cladding effects on dispersion properties

Abstract

Sources of spectrally engineered photonic states are a key resource in several quantum technologies. Of particular importance are the so-called factorizable biphoton states which possess no spectral entanglement and hence, are ideal for heralded generation of high-purity single photons. An essential prerequisite for generating these states through nonlinear frequency conversion is the control over the group indices of the photonic modes of the source. Here, we show that thin-film lithium niobate on insulator (LNOI) is an excellent platform for this purpose. We design and fabricate periodically poled ridge waveguides in LNOI to demonstrate group index engineering of its guided photonic modes and harness this control to experimentally realize on-chip group index matched type-II sum-frequency generation (SFG) and photon-pair creation through spontaneous parametric down-conversion (SPDC). Also, we numerically study the role of the top cladding layer in tuning the dispersion properties of the ridge waveguide structures and reveal a distinctive difference between the air and silica-clad designs which are currently among the two most common device cladding configurations in LNOI. We expect that these results will be relevant for various classical and quantum applications where dispersion control is crucial in tailoring the nonlinear response of the LNOI-based devices.