Compact Faraday optical isolators are unidirectional light valves, available with a 2 or 4 mm clear aperture, in 532, 638, 650, and 785 nm wavelengths with optional waveplates. They have >33 dB isolation and >95% transmission. The devices contain optically contacted polarizing beamsplitter cubes.
Newport (MKS Instruments)
Irvine, CA