Multistage Optical Interconnects for Parallel Access Optical Shared Memories

We have completed a network design study that identified the Dilated Benes network routing algorithm as the most compatible with this technology and that quantified the importance of BCGH performance in attaining large (>or = 1024 node) networks. We therefore placed more emphasis on achieving high efficiency and contrast ratio BCGH. The diffraction efficiency of the original binary phase LiNbO3 element was increased from 6% to 60% by going to four phase level design, and transmission through uncoated elements was increased from 51% to >99% by antireflection coating. A contrast ratio between orthogonal polarizations of 160:1 was demonstrated with 60% diffraction efficiency. As a subsystem demonstration, we used two BCGH and a liquid crystal polarization rotator to create a 2x2 optical node that combined both routing and switching. We demonstrated switching contrast ratio of better than 50:1, and also used a high speed diode to show 20 MHz data modulation. We conclude that polarization-selective holographic optical elements with transmission and diffraction efficiencies approaching 100% require only fabrication refinements, and that such elements can become a key component of future optical systems, including a high bandwidth multistage interconnection network using polarization switching.