Silicon nitride (SixNy) waveguides constitute a technology platform to realize optical signal processing based on the nonlinear Kerr effect. Varying the stoichiometry of the core (i.e., x and y in silicon nitride) provides an additional degree of freedom for engineering the waveguide properties, such as nonlinear Kerr parameter and dispersion. We demonstrate low-stress high-confinement silicon-rich nitride waveguides with flat and anomalous dispersion over the entire C and L optical wavelength transmission bands for optical signal processing based on cross-phase modulation. The waveguides do not show any nonlinear loss for a measured optical input intensity of up to 1.5 × 109 W/cm2. In particular, we achieve wavelength conversion of 10 Gb/s signals across the C band; XPM broadening is also observed in the O band. In addition, we highlight the use of SixNy waveguides for nonlinear microwave photonics. Specifically, we demonstrate radio-frequency spectral monitoring of optical signals with a bandwidth of hundreds of gigahertz.