Diffractive surface relief elements for use in the infrared: waveguide structures as reflection holograms

Waveguide structure in this context means metallic coated gratings which have periods smaller than the wavelength of the incident light. The grooves of these subwavelength gratings can be regarded as waveguides. Since the phase velocity depends on the groove width of the waveguide, the phase of the reflected light is a function of the duty cycle. By adding waveguides with different duty cycles together, binary lattices can be made which approximate nearly every arbitrary continuous phase function. Examples of these waveguide structures are the so-called artificial dielectrics which act as beam deflector, cylindrical Fresnel zone mirror and Fresnel zone mirror. These elements are presented in this paper.