intensity of incident optical radiation. The relationship between the input optical radiation and the output electrical current is given by the detector responsivity.

FIBER-OPTIC SYSTEM TOPOLOGY

Most of the discussion on fiber-optic data links provided earlier in this chapter and in the CE Basic TRAMAN refers to simple point-to-point links. A point-to-point fiber-optic data link consists of an optical transmitter, an optical fiber, and an optical receiver. In addition. any splices or connectors used to join individual optical fiber sections to each other and to the transmitter and the receiver are included. Figure 6-3 provides a schematic diagram of a point-to-point fiber-optic data link.

A common fiber-optic application is the full duplex link. This link consists of two simple point-to- point links. The links transmit in opposite directions between the equipment. This application may be configured using only one fiber. If configured with one fiber. fiber-optic splitters are used at each end to couple the transmit signal onto the fiber and receive signals to the detector.

All fiber-optic systems are simply sets of point-to- point fiber-optic links. Different system topologies arise from the different ways that point-to-point fiber- optic links can be connected between equipment. The term topology, as used here, refers to the configuration of various types of equipment and the fiber--optic components interconnecting them. This equipment may be computers, workstations, consoles, or other equipment. Point-to-point links are connected to produce systems with linear bus, ring, star, or tree topologies. Point-to-point fiber-optic links are the basic building block of all fiber-optic systems.

SYSTEM INSTALLATION

The Navy has a standard to provide detailed information and guidance to personnel concerned with the installation of fiber-optic cables and cable plants. The fiber-optic cable plant consists of all the fiber- optic cables and the fiber-optic interconnection equipment, including connectors, splices, and interconnection boxes. The fiber-optic cable and cable plant installation standard consists of the following:

Detailed methods for cable storage and handling, end sealing, repair, and splicing

Detailed methods for fiber-optic equipment installation and cable entrance to equipment

Detailed methods to install fiber-optic cables in cableways

Detailed methods for installing fiber-optic connectors and other interconnections, such as splices

Detailed methods for testing fiber-optic cable plants before, during, and after installation and repair

There are other standards that discuss fiber-optic system installation. Many of these standards incor- porate procedures for repair, maintenance, and testing. The techniques developed for installing fiber-optic hardware are not much different than for installing hardware for copper-based systems: however. the primary precautions that need to be emphasized when installing fiber-optic systems are as follows:

Optical fibers or cables should never be bent at a radius of curvature less than a certain value, called the minimum bend radius. Bending an optical fiber or cable at a radius smaller than the minimum bend radius causes signal loss.

Fiber-optic cables should never be pulled tight or fastened over or through sharp comers or cutting edges. Extremely sharp bends increase the fiber loss and may lead to fiber breakage.

Fiber-optic connectors should always be cleaned before mating. Dirt in a fiber-optic connection will significantly increase the connection loss and may damage the connector.

Precautions must be taken so the cable does not become kinked or crushed during installation of the

Figure 6-3. - A schematic diagram of a point-to-point fiber-optic data link. 6-4