OPTICAL DESIGN FOR LARGE-SCALE FREE-SPACE OPTICAL SWITCHING MODULES

To achieve large-scale and compact free-space optical switching networ ks, highly efficient coupling between input and output fiber arrays an d low-loss beam propagation for a long-span are required. In the casca ded optical beam-shifter module using liquid-crystal devices, beam exp ansion due to optical diffraction limits the scale of the switching ne twork. A microlens configuration consisting of collimating lenses and relay lenses with a long focal length is proposed for long-span beam p ropagation. This lens configuration can reduce the limitation on the s cale of switching network. It is shown that a large-scale and compact optical switching network can be constructed. The relationship between the aperture size to determine the physical size of an optical switch and the focal lengths for the required lens system also are shown. A long focal-length microlens fabricated using the sputter-liftoff metho d was shown to be very useful for long-span beam propagation.