  Here I investigate both numerically and experimentally, the polarization
conversion capabilities of a rectangular array of holes with two unequal
orthogonal periodicities. We show that it is possible to tune the periodicities
in such a way that the transmitted light is circularly polarized for a
nominated wavelength, Lambda-CPL, when the structure is illuminated with
appropriately oriented linearly polarized light at normal incidence. A device
was fabricated and experiments confirmed that a degree of circular polarization
of 0.89 could be achieved at the resonant wavelength.
