  We present the geometric optics expansion for circularly polarized
gravitational waves on a curved spacetime background, to subleading order. We
call spin optics to the subleading order geometric optics expansion, which
involves modifying the standard eikonal function by including a specially
chosen helicity-dependent correction. We show that the techniques developed for
the propagation of electromagnetic waves can also be applied to gravitational
waves in the limit of spin optics. However, one needs to account for the
difference in the photon and graviton helicity, which we do here.
