Optical communications systems typically use separate fibers to transmit information in each direction. These bidirectional communications systems are commonly called duplex systems because fibers are installed in pairs with one fiber to transmit in each direction. To support these duplex communications systems, the fiber-optic cabling infrastructure must provide correct signal polarity so that the transmitter on one end of the channel will connect to the receiver on the other end. Maintaining the correct transmit-to-receive polarity throughout the cabling system is critical for system operation.
The increasing use of optical connectivity in data communications networks (particularly in areas of highly concentrated equipment, such as data centers) has driven the need for more compact forms of connectivity. One way our industry has responded is by deploying ribbon-based (MTP/MPO) connectors into these dense installations. MTP connectors commonly bring 12 or 24 fibers together in the same footprint as a single SC connector. However, the density advantages of the MTP cause a significant change in the way signal polarity is maintained.
TIA TR-42.8 has addressed this issue by publishing TIA 568B.1-7. This addendum to TIA-568B.1 defines cabling methods to maintain signal polarity when using ribbon connectors. The document defines three cabling topologies, which include legacy and new, best-of-breed methods.
In addition to supporting duplex systems, two of these cabling methods will enable the use of parallel optics. Parallel optics applications utilize a transmitter with a group of sources on one end of the system and a receiver with a group of detectors on the other end. Information is transmitted on several fibers in parallel, at a much higher data rate than is possible with serial transmission.
Matt Brown is product manager for fiber apparatus with CommScope Enterprise Solutions. He has authored a number of national standards, including 568B.1-7, and contributes to several committees within the TIA and IEC. He can be reached at firstname.lastname@example.org.