An at least 3-port optical circulator has first group of optical components, and a second group of optical components, the first group being separated from the second group by an optical distance "1". Each group of optical components has a divider and combiner for dividing an input beam into two beams...http://www.google.es/patents/US5991076?utm_source=gb-gplus-sharePatente US5991076 - Optical circulator
