Time Division Multiplexers (TDM)

Time division multiplexers (TDM) share transmission time on an information channel among many data sources. One of the key choices in choosing time division multiplexers is the selection of the transfer mode that will be used. Synchronous transfer mode is a communications mode in which data signals are sent at precise intervals that are regulated by a system clock. Additional start and stop pulses are not required. Asynchronous transfer mode (ATM) is a connection-oriented protocol that uses very short, fixed-length (53 bytes) packets called cells to carry voice, data, and video signals. By using a standard cell size, ATM can use software for data switching. Consequently, ATM can route and switch traffic at higher speeds. An asynchronous/synchronous time division multiplexer is capable of both asynchronous and synchronous transfer modes.

There are three cable choices for time division multiplexers (TDM). Single-mode optical fiber cable allows only one mode to propagate. The fiber has a very small core diameter of approximately 8 µm. It permits signal transmission at extremely high bandwidths and allows very long transmission distances. Multimode fiber optic cable supports the propagation of multiple modes. Multimode fiber may have a typical core diameter of 50 to 100 µm with a refractive index that is graded or stepped. It allows the use of inexpensive LED light sources. Connector alignment and coupling is less critical than with single mode fiber. Distances of transmission and transmission bandwidth are also less than with single mode fiber due to dispersion. Single-mode/multimode time division multiplexers can be used with both single mode and multimode cable types.

Performance specifications for time division multiplexers (TDM) include number of channels, maximum data rate, wavelength range, operating voltage, optical output, electrical output, data transmission type, and data interface. Additional features may also be available.

Many types of connectors are used with time division multiplexers (TDM). Biconic connectors have precision-tapered ends for low insertion loss. D4 and FC connectors are durable, zirconia-ceramic ferrules with a keyed body for repeatability. FC connectors are used primarily with single-mode fibers, but are also used in telephone systems, instruments, and high-speed communication links. Designed for use in FDDI networks, FDDI connectors are 2.5 mm ferrules that include a fixed shroud. ESCON connectors have the same measurements, but use an adjustable shroud. LC connectors are high-precision, zirconia-ceramic ferrules that feature an RJ-45 push-pull housing and latching. MT-RJ connectors hold two fibers with a ferrule that is smaller than the one used in MTP connectors, devices that are threaded and well-suited for high-density applications. ST connectors are easy-to-assemble devices that feature a bayonet mounting system. They are used with both single-mode and multi-mode fibers in communications applications. SMA connectors include a low-cost, multi-mode coupling that is suitable for military applications. Loop back connectors are used to test transceiver systems.

• Dense Wavelength Division Multiplexer (DWDM)
  Dense wavelength division multiplexers (DWDM) use an optical (analog) multiplexing technique to increase the carrying capacity of a fiber network beyond what can be achieved with time division...
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