The wavelengths range from 1540 nm to 1560 nm. Low return losses are necessary for correct operation. The operational bandwidth of such circulators is tied to the bandwidth of the directional waveguide coupler and has the potential for simultaneous broadband operation and small device footprint. Thorlabs also offers Polarization-Maintaining (PM) Fiber Optical Circulators. 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. 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.
