glass core and a plastic coating. power budget the difference in dB between transmitted optical power and receiver sensitivity. quantum efficiency the ratio of the number of emitted photons to the number of electrons that cross the p-n junction of a semiconductor. radio waves waves that have the longest wavelength and lowest fre- quencies of all waves within the frequency spectrum. Raman effect amplification that occurs when a large continuous- wave laser is co-launched at a lower wavelength than the signal to be amplified. Glossary Rayleigh scattering a phenomenon recognized by Lord Rayleigh that notes that short wavelengths scatter more strongly than longer wavelengths. scattering the spreading of optical pulses as photons collide with impurities in a fiber. section under SONET a section is a transmission path between two repeaters. self-phase modulation the broadening of light pulses as they flow down a river. Shannon's Law a formula that defines the maximum bit rate on a channel in terms of bandwidth and the signal-to-noise ratio. shell the area of an atom where electrons circulate. signal-to-noise ratio the ratio of signal power divided by noise power on a transmission medium. single mode a flow of light that lacks refraction, resulting in pulses traveling the fiber in one mode. step-index fiber a fiber which has an abrupt change in the index of refraction going from the core to the cladding. tempest electronic emissions generated by equipment. total internal reflection the refraction of a beam of light SO that virtually 100 percent remains in a medium. traverse burning the rotation of a large glass tube over a heat source while passing a series of gases through the tube. tunable laser a laser capable of transmitting multiple bands of light through a single strand of optical fiber. ultraviolet radiation in the electromagnetic spectrum above visible light. valance band the outer shell of an atom. vertical-cavity laser a laser formed by the vertical stacking of mirrors. visible light wavelengths between 400 an