  Dispersion engineering in silicon nitride (SiX NY ) waveguides is
investigated through the optimization of the waveguide transversal dimensions
and refractive indices in a multi-cladding arrangement. Ultra-flat dispersion
of -84.0 +/- 0.5 ps/nm/km between 1700 and 2440 nm and 1.5 +/- 3 ps/nm/km
between 1670 and 2500 nm is numerically demonstrated. It is shown that typical
refractive index fluctuations as well as dimension fluctuations during the
fabrication of the SiX NY waveguides are a limitation for obtaining ultra-flat
dispersion profiles. Single- and multi-cladding waveguides are fabricated and
their dispersion profiles measured (over nearly 1000 nm) using a low-coherence
frequency domain interferometric technique. By appropriate thickness
optimization, the zero-dispersion wavelength is tuned over a large spectral
range in both single-cladding waveguides and multi-cladding waveguides with
small refractive index contrast (3 %). A flat dispersion profile with 3.2
ps/nm/km variation over 500 nm is obtained in a multi-cladding waveguide
fabricated with a refractive index contrast of 37 %. Finally, we generate a
nearly three-octave supercontinuum in this dispersion flattened multi-cladding
SiX NY waveguide.
