Optical isolators based on nonreciprocal four-wave mixing

17 pages, 6 figures
In this work we propose and theoretically characterize optical isolators consisting of an all-dielectric and non-magnetic resonator featuring an intensity-dependent refractive index and a strong coherent field propagating in a single direction. Such devices can be straightforwardly realized in state-of-the-art integrated photonics platforms. The mechanism underlying optical isolation is based on the breaking of optical reciprocity induced by the asymmetric action of four-wave mixing processes coupling a strong propagating pump field with co-propagating signal/idler modes but not with reverse-propagating ones. Taking advantage of a close analogy with fluids of light, our proposed isolation mechanism is physically understood in terms of the Bogoliubov dispersion of collective excitations on top of the strong pump beam. A few most relevant set-ups realizing our proposal are specifically investigated, such as a coherently illuminated passive ring resonator and unidirectionally lasing ring or Taiji resonators.
We acknowledge financial support from the European Union FET-Open grant “MIR-BOSE” (No. 737017), from the H2020-FETFLAG-2018-2020 project “PhoQuS” (No. 820392), from the Provincia Autonoma di Trento, and from the Q@TN initiative. A.M. acknowledges financial support from the Comunidad de Madrid via Proyecto Sinérgico CAM 2020 Y2020/TCS-6545 (NanoQuCo-CM).