Quadratic Supercontinuum Generation from UV to Mid-IR in Lithium Niobate Nanophotonics

TL;DR

This paper demonstrates a novel quadratic supercontinuum generation technique in lithium niobate nanophotonic waveguides, achieving broad spectral coverage from UV to mid-IR with high energy efficiency through dispersion engineering and quasi-phase matching.

Contribution

It introduces a new dispersion engineering principle and experimentally demonstrates highly efficient quadratic supercontinuum generation in integrated lithium niobate waveguides, surpassing previous methods.

Findings

Achieved multi-octave supercontinuum with femtojoule pump energy

Extended spectral coverage into mid-IR from 350 nm to 5000 nm

Demonstrated energy-efficient difference-frequency generation

Abstract

Supercontinuum light sources are widely used for applications ranging from imaging to sensing and frequency comb stabilization. The most common mechanisms for their generation rely on cubic nonlinearities, for instance in crystals, optical fibers, and integrated photonics. However, quadratic supercontinuum generation (QSCG) offers potential for enhanced energy efficiency and broader spectral coverage because of the typically much stronger nonlinearity and ability to achieve both coherent up- and down-conversion via three-wave mixing processes. Despite such potentials, demonstrations of QSCG in integrated photonic waveguides have been sparse and have barely surpassed their cubic counterparts in terms of spectral coverage and energy-efficiency. Here, we introduce a new dispersion engineering principle and experimentally demonstrate purely quadratic supercontinuum generation in lithium niobate nano-waveguides substantially outperforming previous demonstrations in integrated photonics. In one device, by engineering a near-zero dispersion profile and using a single poling period for quasi-phase matched saturated second-harmonic generation, we achieve robust and energy efficient multi-octave QSCG with only femtojoules of pump pulse energy. In another device, we use a flat dispersion profile with two distant zero crossings of group velocity dispersion (GVD) to achieve broadband difference-frequency generation (DFG) for extending the spectral coverage further into the mid-IR and cover the entire transparency window of lithium niobate from 350 nm to 5000 nm. Our results showcase how DFG-assisted QSCG can access hard-to-access spectral regions in an energy-efficient fashion by properly utilizing dispersion engineering and quasi-phase matching.