An optical isolator of reduced insertion loss and fabrication cost which comprises a nonreciprocal optically active element, such as a Faraday rotator, for 45.degree. rotation of polarization, a pair of lenses arranged on the opposite sides of the optically active element and a pair of birefringent crystal...http://www.google.es/patents/US4375910?utm_source=gb-gplus-sharePatente US4375910 - Optical isolator
