Rotating optical microcavities with broken chiral symmetry.

We demonstrate in open microcavities with broken chiral symmetry that quasidegenerate pairs of copropagating-wave resonances are transformed by rotation to counterpropagating ones, leading to a striking change of emission directions. The rotation-induced relative change in output intensity increases exponentially with cavity size, in contrast to the linear scaling of the Sagnac effect. By tuning the degree of spatial chirality with cavity shape, we are able to maximize the emission sensitivity to rotation without spoiling the quality factor.