Planar Lightwave Circuit

The planar lightwave circuit or PLC is a type of optical splitter/combiner in which the waveguide or the medium used to split the optical signal is fabricated using a silcon dioxide chip. The manufacture of PLC splitters involves a lithographic process similar to that used in the manufacture of silicon computer chips. PLC splitters provide the most uniformity between fiber outputs (the downstream fibers) with respect to the amount of optical loss measured on each fiber. This is particulary important when the design of the PON begins to approach the maximum optical loss allowable in a particular PON distribution network. PLC splitters also are very compact relative to other splitter types so service providers can more easily integrate them into existing DSLAM cabinets and other existing outside plant enclosures if necessary. While PLC splitters are typically more costly to deploy than other splitter types, the performance characteristics inherent in the PLC splitter make it the least sensitive to wide temperature variations and therefore more suitable for more extreme outdoor environments.

Fused Biconical Taper

Another type of passive optical splitter is known as the Fused Biconical Taper or FBT splitter. The FBT splitter is manufactured by thermally fusing two overlapping fibers together under tension. The resulting fusion splice creates a two by two splitter. Typically, one of these splitters is trimmed off and the result is a single fiber subtending to two fibers. These two fiber outputs can then be fused to additional one by two splitters until the desired number of splits is achieved. Although a near perfect FBT splitter will achieve close to a 3dbm loss per split just as the PLC splitter, the optical loss measured across FBT output fibers is typically less uniform. Consequently, FBT splitters must be deployed where extreme temperature variations or other environmental factors are not likely to cause the optics connected at the ends of the fiber to drift from their optimum wavelength specifications. Like PLC splitters, FBT splitters are available in a variety of configurations including small to large split ratios and special purpose splitters like a 2x32 splitter. Their lower cost makes them particularly suitable for passive optical LAN (POL) deployments since a POL does not typically deploy splitters in outdoor environments.