Here, we present a solution to this issue by realizing low-loss (0. 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. The latter are directional couplers, whose splitting-ratio. R. A low-loss optical cir-culator has been developed to. 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. Our SM optical circulators have a center wavelength of 1064, 1310 (O-Band), or 1550 nm (C-Band).