  Designing integrated photonics, especially to leverage Kerr-nonlinear optics,
requires accurate and precise knowledge of refractive index across the visible
to infrared spectral ranges. Tantala (Ta_2O_5) is an emerging material platform
for integrated photonics and nanophotonics that offers broadband ultralow loss,
moderately high nonlinearity, and advantages for scalable and heterogeneous
integration. We present refractive-index measurements on a thin film of
tantala, and we explore the efficacy of this data for group-velocity dispersion
(GVD) engineering with waveguide and ring-resonator devices. In particular, the
observed spectral extent of supercontinuum generation in fabricated waveguides,
and the wavelength dependence of free spectral range (FSR) in optical
resonators provide a sensitive test of our integrated-photonics design process.
Our work opens up new design possibilities with tantala, including with
octave-spanning soliton microcombs.
