  The purpose of this comment is first to correct a misapprehension of the role
played by composite wave diffraction on surface-wave generation at
subwavelength structures and second to point out that periodic Bloch structures
are unnecessary for the efficient production of the surface plasmon polariton
(SPP) guided mode either as traveling or standing waves. Guided surface waves
originate from simple slit or groove edges illuminated under normal incidence,
and one-dimensional (1-D) surface cavities from these standing waves are easily
realized.
