The function of the fiber is to carry, or guide, the between a transmitter and a receiver with minimum signal distortion and power loss. With this function, the pulse dispersion and attenuation rate becomes important performance parameters. Worldwide, all data communication fibers are glass fibers with a glass diameter of 125 microns (approximately 0.005”). These small glass fibers cannot be used without protection.
The cable is the package that provides this protection. The cable protects the fiber during both installation and uses. The cable protects the fiber from degradation of optical and mechanical properties as long as the cable is used within the limits for which it has been designed. These limits include installation limits and environmental limits. The network designer defines both types of limits. However, the installer controls the condition imposed on the cable during installation. Therefore, the installer must be aware of the installation specifications of the cables he is installing.
The light travels in the central region of the fiber. This region, with a diameter of one half to one twelfth the diameter of the glass, is small enough to require precise alignment whenever light travels enters or leaves a fiber. Connections, either connectors and or splices, provide precise alignment to minimize power loss along the link. By minimizing power loss, the connections contribute to adequate power level at the receiver.
Jointly, the transmitter and receiver are called optoelectronics. The transmitter converts an electrical signal to an optical signal. The receiver performs the reverse conversion. The function of both devices is conversion with maximum signal accuracy. In digital systems, this accuracy specification is the ‘bit error rate’ (BER). The BER is the ratio of error bits to total bits. In a fiber data network, each end of each link contains a transmitter and a receiver. This combination is known as a ‘transceiver’.
While the fiber, cable, connection and optoelectronics allow the link to function optically, these components require protection to provide reliable operations. The function of hardware is provision of reliability to the networks.
Hardware includes all products other than passive devices and those addressed. Hardware products include conduit, inner duct, enclosures, splice trays, splice covers, cable hangers, pedestals, cable raceways and cable trays.
Passive devices are couplers, splitters, wavelength division multiplexers and de-multiplexers, rotary joints, optical amplifiers, fiber switches and rotators. Passive devices are used in some networks, such as CATV, those based on 10BASE-FP, and fiber-to-the –home (FTTH) networks. These devices manipulate light as light. They do not require conversion of the optical signal into an electrical signal in order to perform this manipulation.
While passive devices simplify networks design and can reduce network cost, they have a price: optical power loss that can be significant. As an example of this loss, consider a 32 port optical splitter: the power drop from input to output port is 16 – 17 dB. In contrast, the maximum power loss allowed between some data communication transmitters and receivers is between 2.38dB and 19dB.
From the installer’s perspectives, the passive device creates power loss and a potential for reflectance. These two characteristics will be of concern to the installer.
