  Nonreciprocal optical devices have broad applications in light manipulations
for communications and sensing. Non-magnetic mechanisms of optical
nonreciprocity are highly desired for high-frequency on-chip applications.
Here, we investigate the nonreciprocal properties of light propagation in a
dielectric waveguide induced by a subwavelength spinning cylinder. We find that
the chiral modes of the cylinder can give rise to unidirectional coupling with
the waveguide via the transverse spin-orbit interaction, leading to different
transmissions for guided wave propagating in opposite directions and thus
optical isolation. We reveal the dependence of the nonreciprocal properties on
various system parameters including mode order, spinning speed, and coupling
distance. The results show that higher-order chiral modes and larger spinning
speed generally give rise to stronger nonreciprocity, and there exists an
optimal cylinder-waveguide coupling distance where the optical isolation
reaches the maximum. Our work contributes to the understanding of
nonreciprocity in subwavelength moving structures and can find applications in
integrated photonic circuits, topological photonics, and novel metasurfaces.
