AbstractSilicon photonics has been established as a mature and promising technology for
optoelectronic integrated circuits, mostly based on the silicon-on-insulator
(SOI) waveguide platform. However, not all optical functionalities can be
satisfactorily achieved merely based on silicon, in general, and on the SOI
platform, in particular. Long-known shortcomings of silicon-based integrated
photonics are optical absorption (in the telecommunication wavelengths) and
feasibility of electrically-injected lasers (at least at room temperature). More
recently, high two-photon and free-carrier absorptions required at high optical
intensities for third-order optical nonlinear effects, inherent lack of
second-order optical nonlinearity, low extinction ratio of modulators based on
the free-carrier plasma effect, and the loss of the buried oxide layer of the
SOI waveguides at mid-infrared wavelengths have been recognized as other
shortcomings. Accordingly, several novel waveguide platforms have been
developing to address these shortcomings of the SOI platform. Most of these
emerging platforms are based on heterogeneous integration of other material
systems on silicon substrates, and in some cases silicon is integrated on other
substrates. Germanium and its binary alloys with silicon, III–V compound
semiconductors, silicon nitride, tantalum pentoxide and other high-index
dielectric or glass materials, as well as lithium niobate are some of the
materials heterogeneously integrated on silicon substrates. The materials are
typically integrated by a variety of epitaxial growth, bonding, ion implantation
and slicing, etch back, spin-on-glass or other techniques. These wide range of
efforts are reviewed here holistically to stress that there is no pure silicon
or even group IV photonics per se. Rather, the future of the
field of integrated photonics appears to be one of heterogenization, where a
variety of different materials and waveguide platforms will be used for
different purposes with the common feature of integrating them on a single
substrate, most notably silicon.
Novel Polarization Rotators for Silicon Photonic Integrated Circuits