Exploring the polarization dependence of supercontinuum generation in silicon-nitride waveguides

The broad coherent spectra obtained by supercontinuum generation (SCG) are of significant importance for applications in, e.g., spectroscopy and precision metrology. Of particular interest is SCG using integrated optical waveguides fabricated from stoichiometric silicon nitride (Si3N4), which has provided the broadest supercontinuum, so far, on a chip [1]. Although SCG in silicon-nitride waveguides is extensively studied, it is limited to input beams polarized to excite either the fundamental (quasi) TE- or TM-mode of these waveguides.
Here, we explore the dependence of SCG in silicon-nitride waveguides on varying polarization directions of the pump and varying birefringence of the waveguide cross-section, both experimentally and numerically. Applying pump light polarized to excite the TE and TM modes simultaneously, we find that the generated SC spectrum becomes much broader than the spectra from the separately excited TE- and TM-modes.
[1] J. P. Epping et al., "On-chip visible-to-infrared supercontinuum generation with more than 495 THz spectral bandwidth", Opt. Express 23, 19596 (2015).