On-chip octave-spanning flat supercontinuum in all-normal-dispersion silicon nitride waveguides

Abstract

On-chip supercontinuum generators have emerged as an attractive optical source with small size, broad spectrum and high power efficiency. Nevertheless, there has long been a trade-off between spectral uniformity and bandwidth. We propose a novel silicon nitride waveguide with flat saddle-shaped all-normal dispersion, particularly for enhancing the nonlinear interactions over a wide band. By launching a 250-fs 30-kW input pulse, an ultra-flat (-6 dB) octave-spanning supercontinuum extending from 638 nm to 1477 nm can be generated. We analyze the performance of the supercontinuum generator in terms of spectral flatness and bandwidth under different input pulse conditions. Thanks to mature dispersion engineering, the pump wavelength can be flexibly selected within the flat dispersion region. The generated supercontinuum, therefore, can be applied to different spectral regions by shifting the center wavelength.