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This is in contrast to its coupler counterpart, which can have losses in excess of 3 dB for 50:50 signal-splitter configurations. 1).Īnother useful feature is the low pass-through insertion loss of a circulator, typically less than 1 dB for a three-port device. For example, an optical circulator has the means to discriminate inbound and outbound signal paths on Port 2 in such a way that inbound signals are routed to the Port 3 interface and outbound signals are routed from the Port 1 interface without interference (see Fig. One of the most useful features of an optical circulator is its ability to perform a beamsplitter function on a full-duplex optical signal. In fact, circulators are available for all standard wavelengths and can be polarization insensitive or polarization maintaining. Models are also available having different grades of isolation. Models of circulators are available with three, four, or more port constructions. The required number of ports, operating wavelength, polarization sensitivity, port isolation, and mechanical packaging are variables that must be considered when selecting a circulator for optimum system performance. Optical circulators are available in a variety of configurations and performance options. Today, optical circulators continue to gain popularity for a broad array of applications, including optical amplifiers, optical add and drop systems, dense wavelength-division multiplexing (DWDM) networks, optical time domain reflectometers (OTDRs), and instrumentation. While the earliest theoretical work on optical circulators began at that time, integrated products were not adequately commercialized until recently. Microwave circulators have been widely used to separate full-duplex signals in radio communication and radar systems since their commercial introduction in the early 1960s. Second, optical circulators have high adjacent port isolation and eliminate the need for external isolators.Īs with many lightwave devices, analogous origins of optical devices can be found in the microwave domain. First, optical circulators are low-loss devices, unlike splitters that incrementally add 3-dB losses for each device used. Several performance advantages of optical circulators make them indispensable for routing bidirectional optical traffic.