The 3 or 4 port Fiber optic Circulator is a compact, high performance light wave component that transmits the incoming signal from port 1 to port 2, and another incoming signal from port 2 to port 3 simultaneously. Thorlabs' Optical Circulators are non-reciprocating, one-directional, three port devices which are great for bidirectional propagation of light in a single fiber. 1) The Maximum IL is under all states of polarization and within full operating temperature and wavelength ranges as specified. 2) Parameters do not include connectors.