A birefringent device of substantially uniform thickness less than about 10 microns,
and being suitable for operating in a wavelength range about a central wavelength
is disclosed. The device includes a base substrate, a layer of periodic index regions
of alternating refractive indices applied to a first surface of the base substrate,
and a cap substrate located substantially adjacent to the layer distal to the base
substrate. The layer of periodic index regions has a periodicity of less than the
central wavelength. The device being suitable to produce an arbitrary phase retardation
between 0 and 2 phase.