  Optical isolators are indispensable components of optical networks.
Magneto-optic isolators have excellent operating characteristics, including
low-to-no power consumption, but are not well suited for on-chip integration.
The technique of temporal modulation of dielectric constant offers an
alternative way to achieve isolation without magnetic field but is not without
its own drawbacks. In this work I examine diverse methods of optical isolation
via temporal modulation and show that independent on whether modulation is
achieved by carrier injection, Pockels and acousto-optic effects, or any other
conceivable method, there is essentially the same set of constraints on
footprint, modulation frequency, and, most important, on power consumption
required to achieve full isolation without excessive insertion loss. This power
is estimated to be on the order of at least a hundred of milliwatts and whether
this requirement is acceptable will depend on ongoing progress of both
magneto-optic and time modulated integrated technologies.
