  Rodriguez-Fortuno et al. (19 April 2013, p. 330) reported the unidirectional
excitation of electromagnetic guided modes via the oblique illumination of a
circularly polarized light. This comment points out that the same scheme was
addressed in our a-year-ahead paper and that magnetic dipoles play a key role
in the unidirectional excitation which was neglected in Rodriguez-Fortuno et
al.'s report.
