Fiber-Optic Couplers

Figure 6-9.—Basic ferrule connector design. Butt-jointed connectors and expanded-beam connectors are the two basic types of fiber-optic connectors. Fiber-optic butt-jointed connectors align and bring the prepared ends of two fibers into close contact. The end faces of some butt-jointed connectors touch, but others do not. depending upon the connector design. Types of butt-jointed connectors include cylindrical ferrule and biconical connectors. Figure 6-9 shows a basic ferrule design. Fiber-optic expanded- beam connectors use two lenses to first expand and then refocus the light from the transmitting fiber into the receiving fiber. Single fiber butt-jointed and expanded- beam connectors normally consist of two plugs and an adapter (coupling device) (fig. 6-10). Expanded-beam connector shown in figure 6-11 uses two lenses to expand and then refocus the light from the transmitting fiber into the receiving fiber. Expanded-beam connectors are normally plug-adapter- plug type connections Fiber separation and lateral misalignment are less critical in expanded-beam coupling than in butt-jointing. The same amount of fiber separation and lateral misalignment in expanded- beam coupling produces a lower coupling loss than in butt-jointing; however, angular misalignment is more critical. The same amount of angular misalignment in expanded-beam coupling produces a higher loss than in butt-jointing. Also, expanded-beam connectors are much harder to produce. Resent applications for expanded-beam connectors include multifiber connections, edge connections for printed circuit boards, and other applications. FIBER-OPTIC COUPLERS Some fiber-optic data links require more than simple point-to-point connections. These data links may be of a much more complex design that requires multiport or other types of connections. In many cases, these types of systems require fiber-optic components that can redistribute (combine or split) optical signals throughout the system. One type of fiber-optic component that allows for the redistribution of optical signals is a fiber-optic coupler. A fiber-optic coupler is a device that can distribute the optical signal (power) from one fiber among two or more fibers. Also, a fiber-optic coupler Figure 6-10.—Plug-adapter-plug configuration. 6-10