r. The laser beam is fired into the modulator, which splits the beam into two parallel beams, each with half the amplitude of the original. One of the beams passes through a slice of lithium niobate, which, when a volt- age is applied to the crystal, refracts the light and causes the beam to become out fo phase with the other beam. When the beams are joined together at the other end of the modulator, they cancel each other out, resulting in an OFF condition or 0 data bit. When the voltage is removed from the lithium niobate, the beams remain in phase with each other and combine to produce a beam with the same amplitude as in the origi- nal beam. This signifies a "1" data bit. Because it is possible to apply remove a voltage to or from a lithium niobate crystal faster than switch- ing a laser on and off, this type of modulator offers the potential to break the present speed barrier for transmitting over optical fiber. Distance also limits the speed of transmission over an optical fiber. Because transmission distance is a function of the optical transmitter and type of optical fiber, we will postpone a discussion of the con- straints associated with transmission distance to Chapters 3 and 4. Team-Fly® CHAPTER Understanding Optical Fiber Chapter Three The goal of this chapter is to explain the production, operation, and uti- lization of optical fiber. In SO doing we will describe how light travels down an optical fiber, discuss the different types of fiber available for different applications, and examine several parameters that govern the ability to transmit information in the form of light efficiently and effec- tively through an optical fiber. Evolution Although we associate the transmission of light within an optical fiber as a modern element of science, the concepts behind the technology date to the nineteenth century. During the mid-1800s the physicist John Tyndall showed that light could be bent around a corner while it trav- eled through a stream of pouring water. During 1880, Alexander Gra- ham Bell, who we