  We theoretically propose a method of rectifying spin current with a
linearly-polarized electromagnetic wave in inversion-asymmetric magnetic
insulators. To demonstrate the proposal, we consider quantum spin chains as a
simple example; these models are mapped to fermion (spinon) models via
Jordan-Wigner transformation. Using a nonlinear response theory, we find that a
dc spin current is generated by the linearly-polarized waves. The spin current
shows rich anisotropic behavior depending on the direction of the
electromagnetic wave. This is a manifestation of the rich interplay between
spins and the waves; inverse Dzyaloshinskii-Moriya, Zeeman, and
magnetostriction couplings lead to different behaviors of the spin current. The
resultant spin current is insensitive to the relaxation time of spinons, a
property of which potentially benefits a long-distance propagation of the spin
current. An estimate of the required electromagnetic wave is given.
