2.7-octave supercontinuum generation spanning from ultraviolet to near-infrared in thin-film lithium niobate waveguides

TL;DR

This paper demonstrates ultrabroadband supercontinuum generation spanning ultraviolet to near-infrared in thin-film lithium niobate waveguides, utilizing dispersion management and nonlinear processes without periodic poling, achieving a record spectral coverage.

Contribution

The work introduces a novel approach to supercontinuum generation in thin-film lithium niobate waveguides with dispersion engineering and MgO doping, achieving record spectral coverage without periodic poling.

Findings

Achieved 2.7-octave supercontinuum from 330 nm to 2250 nm.

Demonstrated effective dispersion management and nonlinear processes in TFLN waveguides.

Fabricated low-loss, MgO-doped TFLN waveguides with photolithography and chemo-mechanical etching.

Abstract

Supercontinuum generation (SCG) with spectral coverage across the full visible and ultraviolet (UV) ranges is crucial for optical clocks, quantum computing and sensing. However, achieving such SCG in nanophotonic platforms is challenging due to the difficulties in spectrum broadening. Here, Such ultrabroad-bandwidth SCG was demonstrated in thin-film lithium niobate (TFLN) nanophotonic waveguides by dispersion management, without periodic poling for spectral broadening. Anomalous-dispersion waveguides were designed in the telecom band, simultaneously enabling dispersive wave emergence, modal-matched second harmonic generation, and third harmonic generation for spectrum broadening. Moreover, MgO was intentionally doped to mitigate the photorefractive effect of lithium niobate, which frequently results in un-sustained spectrum broadening and in turn limits the accessible SCG coverage. By leveraging photolithography assisted chemo-mechanical etching, low-loss MgO doped TFLN nanophotonic waveguides were fabricated. As a result, thanks to the utilization of the strong second-order and third-order nonlinear processes, gap-free 2.7-octave SCG spanning from 330 nm to 2250 nm was observed by pumping the waveguide with a 1550-nm femtosecond pulsed laser with 0.687 nJ, agreeing well with numerical simulation. This spectral coverage represents the state of the art in TFLN platforms without fine microdomains, and even close to the record in sophisticated chirped periodically poled TFLN waveguides.