 optical signal. electromagnetic wave a continuum of oscillating electric and mag- netic fields moving in a straight line at a constant velocity. electrovolt energy gained by an electron that passes across a positive voltage of one volt. fiber mile the length of fiber conduit times the number of strands in a conduit. fiber-optic modem the use of an LED or laser and photodetector in a common housing to provide electrical-to-optical and optical-to- electrical conversion. forward bias the application of a positive voltage across an appropri- ately doped p-n semiconductor. frequency the number of periodic oscillations or waves that occur per unit time. frequency division multiplexing an analog technology in which the bandwidth of a transmission medium is subdivided by frequency. frequency spectrum another name for the electromagnetic radia- tion spectrum. Fresnel reflection loss the reflection of light back towards the trans- mitter due to an air gap between connectors. gain the amount by which the intensity of light is increased in a laser diode by amplification. Glossary gamma rays radiation with the highest frequency and shortest wave- length. glass fiber a cable with a glass core and glass cladding. graded-index fiber a fiber whose refractive index gradually dimin- ishes from the center of the core outward towards the cladding. heterojunction a crystal placed between two dissimilar semiconduc- tors that confines light to the region of a p-n junction in a semicon- ductor. horizontal cabling cabling between a telecommunications outlet in a work area and the horizontal cross-connect. incoherent light that radiates in all directions. index of refraction the ratio of the velocity of light in a vacuum to that in a material. infrared waves above the microwave region but below visible light. insertion loss a loss of optical power at a connector measured in dB. jacket a coating applied over the cladding of a fiber that represents the outer layer of the cable. laser a device that generates coherent light. light-emitting di