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