Generation of multiple user-defined dispersive waves in a silicon nitride waveguide

Abstract

The quest for a wide and bright supercontinuum source has received significant attention, addressing pivotal challenges in ultra-fast spectroscopy, imaging, and frequency metrology. Among the diverse optical nonlinear mechanisms steering supercontinuum generation, dispersive waves emerge as crucial contributors, providing heightened spectral intensity, wavelength tunability, and superior temporal coherence. Nevertheless, their generation is tightly bound by waveguide geometry, limiting both their numbers and the wavelengths at which they manifest. In this paper, we demonstrate the controlled generation of multiple dispersive waves in fundamental optical transverse mode by leveraging quasi phase-matching in an integrated silicon nitride (Si3N4) waveguide. This approach involves modulating the group velocity dispersion through varying the width of the Si3N4 waveguide crossing anomalous and normal dispersion, which facilitates the creation of diverse dispersive waves in fundamental transverse electromagnetic (TE) polarization at multiple phase-matched wavelengths. A wide nonlinear optical spectral broadening surpassing conventional approaches is achieved with good temporal and spatial coherence. Remarkably, the generation of the multiple dispersive waves and the supercontinuum is achieved by a 190-fs pulse duration pump with peak power as low as 110 W (24 pJ). This work offers flexibility to manipulate dispersive waves in an integrated platform beyond current dispersion engineering. It represents a significant step forward in developing an integrated broadband source with a user-defined spectral shape, accomplished with minimal pump power requirements.