81 dB), broadband (at least 50 GHz bandwidth) and high-extinction (up to 27 dB) circulators, based on Mach-Zehnder interferometers including so-called fiber null-couplers. Thorlabs' Single Mode (SM) Optic Circulators are non-reciprocating, one directional, three-port devices that are used in a wide range of optical setups and for numerous applications. The ABSTRACT optical circulator is one of the key devices in the optical add-drop modules (OADMs) used in wavelength-division multiplexing (WDM) technology, which finds applications in large-capacity long-haul telecommunications systems. It provides low insertion loss, broad band high isolation, low PDL, excellent temperature stability and optical path epoxy free. This means that if light enters port 1 it is emitted from port 2, but if some of the emitted light is reflected back to the circulator, it does not come out of port 1 but.
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