Compact optical circulator based on a uniformly magnetized ring cavity

► We present the design principles of a new class of compact magneto-optical circulators. ► The circulators consist of a multiring cavity butt-coupled to rib waveguides. ► We show how to maximize the magneto-optical effect in a uniformly magnetized cavity. ► We explore circulator operation in the presence of direct-pathway waveguide coupling. ► This coupling is shown to produce non-reciprocal Fano resonances in transmittance spectra.