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-on-insulator has been the leading platform for nonlinear optics, its high two-photon absorption at telecommunications wavelengths poses a fundamental limitation that is an intrinsic property of silicon's bandstructure. We review recent progress in new non-silicon 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.
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