Kavli Affiliate: Alireza Marandi
| First 5 Authors: Selina Zhou, Selina Zhou, , ,
| Summary:
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.
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