2.7‐Octave Supercontinuum Generation Spanning from Ultraviolet to Near‐Infrared in Thin‐Film Lithium Niobate Waveguides

Supercontinuum generation (SCG) with spectral coverage across the full visible and ultraviolet (UV) ranges is crucial for numerous quantum computing and atomic systems. Here, such ultrabroad‐bandwidth SCG is demonstrated in low‐loss thin‐film lithium niobate (TFLN) nanophotonic waveguides fabricated by photolithography‐assisted chemo‐mechanical etching (PLACE) technique, without additionally introducing complex periodic poling. The MgO‐doped waveguides are designed to exhibit anomalous dispersion in the telecom band by tailoring the waveguide thickness, simultaneously enabling dispersive wave emergence, second harmonic, and third harmonic generation to broaden the spectrum. Thanks to the utilization of the strong χ (2) and χ (3) nonlinear processes in the fabricated low‐loss (≈3 dB m −1 ) waveguide, the SCG with a −80‐dB spectral bandwidth as large as 2.7 octaves spanning from 330 to 2250 nm is observed by pumping the waveguide with a 1550‐nm femtosecond pulsed laser with 0.687 nJ, agreeing well with numerical simulation. Meanwhile, the SCG sustains its stable spectral envelope for a long period of time thanks to the mitigation of the photorefractive effect of lithium niobate by doping of MgO. And theoretical simulation is carried out to verify the coherence of the fundamental and second harmonic waves.