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. Temporal modulation of the dielectric constant
offers an alternative way to achieve isolation without a 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 of whether modulation is achieved by carrier injection,
Pockels and acousto-optic effects, or any other 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. With materials that are widely used
today and in the near future, this power is estimated to be on the
order of at least 100 mW, and whether this requirement is acceptable
will depend on the ongoing progress of both magneto-optic and time-modulated
integrated technologies.