  Integrated optical isolators have been a longstanding challenge for photonic
integrated circuits (PIC). An ideal integrated optical isolator for PIC should
be made by a monolithic process, have a small footprint, exhibit broadband and
polarization-diverse operation, and be compatible with multiple materials
platforms. Despite significant progress, the optical isolators reported so far
do not meet all these requirements. In this article we present monolithically
integrated broadband magneto-optical isolators on silicon and silicon nitride
(SiN) platforms operating for both TE and TM modes with record high
performances, fulfilling all the essential characteristics for PIC
applications. In particular, we demonstrate fully-TE broadband isolators by
depositing high quality magneto-optical garnet thin films on the sidewalls of
Si and SiN waveguides, a critical result for applications in TE-polarized
on-chip lasers and amplifiers. This work demonstrates monolithic integration of
high performance optical isolators on chip for polarization-diverse silicon
photonic systems, enabling new pathways to impart nonreciprocal photonic
functionality to a variety of integrated photonic devices.
