Angular-Momentum-Biased Nanorings To Realize Magnetic-Free Integrated Optical Isolation

We present the concept and practical design of nonreciprocal optical nanodevices that do not require magnetic materials or bias, but instead are based on a fully integrated nanophotonic ring resonator spatiotemporally modulated to impart angular momentum bias that, according to the Onsager-Casimir principle, can break time-reversal symmetry. On the basis of this idea, we discuss optimal designs for compact optical isolators exhibiting arbitrarily large isolation and low transmission loss, achieved by properly selecting the quality factor of the nanoring, the amount of angular momentum bias, and the gaps between ring and channel/drop waveguides. A practical implementation based on stepwise modulation and pin junctions is explored, showing strong nonreciprocal response in a simple, integrated design. These findings can enable the realization of on-chip, fully integrable nonreciprocal optical nanocomponents as a new paradigm in all-optical communication systems.