<title>Expanded Beam Directional Couplers For LAN</title>

For LAN systems using a loop or ring topology, two types of directional couplers are required for signal transfer between fibers-eauiport and tapoff. The former divides light equally into its output ports, while a tapoff coupler divides light asymetrically into its output ports. In a system where fiber splicing, connectors, and serialized {daisy-chained) couplers play a significant role, the type of couplers utilized before and after these optical components determines the system performance. Figure 1 illustrates a ring data bus employing a three port tapoff coupler and a four port directional coupler. Two technologies are used to perform the reauired couplingfused hiconical taper and expanded beam. Key optical coupler parameters affecting system performance are fiber to fiber compatibility, output port power uniformity, output port model distribution, and environmental ruggedness. An expanded beam directional coupler is the preferred choice when these parameters are important. This presentation will focus on the optical roperties and performance for three port and four port euuiport and tapoff directional couplers utilizing GRIN microlenses.