  Nonlinear photonic chips are capable of generating and processing signals
all-optically with performance far superior to that possible electronically -
particularly with respect to speed. Although silicon has been the leading
platform for nonlinear optics, its high two-photon absorption at
telecommunications wavelengths poses a fundamental limitation. We review recent
progress in CMOS-compatible platforms for nonlinear optics, focusing on Hydex
glass and silicon nitride and briefly discuss the promising new platform of
amorphous silicon. These material systems have opened up many new capabilities
such as on-chip optical frequency comb generation, ultrafast optical pulse
generation and measurement. We highlight their potential future impact as well
as the challenges to achieving practical solutions for many key applications.
