Exceptional point magneto-optic isolators.

We show that operating magneto-optic coupled ring isolators near an exceptional point (EP) fundamentally improves their tradeoff between isolation bandwidth and insertion loss. In analogy to EP sensors, operating a coupled ring isolator at an EP causes its isolation bandwidth to depend on the square root of the nonreciprocal phase shift (NRPS) instead of the usual linear dependence, thereby enhancing the bandwidth when the NRPS is small. In cases of practical interest, this behavior enables more than a 50% increase in 20 dB isolation bandwidth at 3 dB insertion loss for a given pair of rings. The advantage of EP operation grows in the vicinity of magneto-optic material resonances and should extend to other types of on-chip isolators that rely on similarly weak nonreciprocal perturbations.