Wavelength Division Multiplexers (WDM)

Wavelength division multiplexers (WDM) are passive devices that combine light signals with different wavelengths, coming from different fibers, onto a single fiber. They include dense wavelength division multiplexers (DWDM), devices that use optical (analog) multiplexing techniques to increase the carrying capacity of fiber networks beyond levels that can be accomplished via time division multiplexing (TDM). With DWDM, different wavelengths of light can transmit multiple streams of information along a single fiber with minimal interference. Typically, four or more wavelengths in the 15nn nm erbium-doped fiber amplifier (EDFA) region are multiplexed. Most DWDM systems for long-distance transmissions offer 16 to 40 wavelengths at 2.5 Gbps (OC-48 SONET or STM-16 SDH), or 10 Gbps (OC-192 SONET or STM-64 SDH) per wavelength. They are deployed as point-to-point, static overlays for TDM networks and represent a precursor to optical networking. In reducing the cost of transport, dense wavelength division multiplexers require fewer electrical generators and share a single optical amplifier over multiple signals.  

Specifications for wavelength division multiplexers (WDM) include cable type, wavelength range, bandwidth, channel spacing, number of channels, insertion loss, polarization dependent loss, and isolation. Single mode fibers allow one mode to propagate. Multimode fibers support the propagation of multiple modes. Channel spacing is the center-to-center difference in frequency between neighboring channels. Two hundred GHz corresponds to .4 nm spacing, 100 GHz corresponds to .2 nm spacing, and 50 GHz corresponds to .1 nm spacing. Insertion loss is the attenuation caused by the insertion of wavelength division multiplexers (WDM) in an optical transmission system.  Polarization dependent loss is the maximum deviation in insertion loss across all input polarization states. Isolation is a measure of light at an undesired wavelength at any given point. Some wavelength division multiplexers (WDM) are rack-mountable or offer the adding or dropping of channels during operation. Others include light emitting diode (LED) indicators for monitoring power or synchronization. Operating temperature and operating humidity are additional considerations when selecting wavelength division multiplexers (WDM).  

Wavelength division multiplexers (WDM) use many types of connectors. FC and D4 connectors are durable, zirconia-ceramic ferrules with a keyed body for repeatability. MU connectors are 1.25 mm ferrules designed for high-speed data communications, voice networks, telecommunications, and dense wave division multiplexing (DWDM). FDDI connectors, 2.5 mm ferrules with a fixed shroud, are used in fiber distributed data interface (FDDI) applications. ESCON connectors, 2.55 mm ferrules with an adjustable shroud, are used in enterprise system connection (ESCON) applications. 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. SC and ST connectors are easy-to-assemble and feature a bayonet mounting system. SMA connectors include a low-cost, multi-mode coupling that is suitable for military applications. Biconic connectors have precision-tapered ends for low insertion loss. Loopback connectors are used to test transceiver systems.

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