A study of LC-based sub-wavelength diffractive optical element structures for optical cross-connect applications

Two novel concepts of liquid crystal (LC) diffractive structures are introduced and analyzed. Both structures are aimed at overcoming the Fringing Field effect in thin LC cells while allowing sufficiently large phase dynamic range to be attained. The first Structure is a combination of a Sub-wavelength Metal Grating Configuration, combined with a built-in Reflective. Blazed Grating structure and a uniform thickness LC Cell. The reflective blazed grating, provides a periodic, linear phase modulation, while the metal-strip Sub-wavelength grating, acts as a polarization- sensitive transparent multi-electrode element. The thin liquid crystal layer provides the spatially -varying dynamic phase profile. It is shown, that this structure allows a triple- beam deflection operation. A diffraction analysis based on the LC director simulation shows a diffraction efficiency, of over 66% in all three diffraction angles. A detailed High-spatial resolution analysis of the Fringing field effect on the LC alignment for this structure is described. The second configuration is based on a built-in blazed diffractive grating, composed of two optical substrates with different refractive indices and a uniform-thickness LC layer, enclosed in a Fabry-Perot Cavity. It is shown that this structure which overcomes the difficulties of LC alignment and fringing field effects in Hybrid, Blazed LC-Glass structures, allows a dynamic switching of a Laser beam with a diffraction efficiency exceeding 75%.