TABLE OF CONTENTS The two types of signals carried by optical fibers, analog and digital, have significantly different baseband (i.e., electrical) formats and spectra. The term baseband as used here refers to the signal prior to modulation on the optical source. In Figure 7 1, the baseband signal is input to the optical transmitter and output from the receiver. A baseband signal can be complete unto itself. It can also be obtained through combining or multiplexing other signals of lesser bandwidth/speed into a wider bandwidth signal. A video signal is complete but is still a combination of independent signals conveying the luminance, color, and sound information. An analog signal represents the originating electrical information in as exact a form as possible. Another way to think of an analog signal is that it is not a series of pulses. A digital signal is just that, on the other hand. It originates as either the output of a computing activity or as an encoded signal that began in analog format. Our voices begin in analog format, for example, but are transmitted in digital format. The longer distance portions of the national telecommunications network are almost 100 percent digital at this time.
The electrical format of these baseband signals is not of great interest for the discussion here. The spectral content, on the other hand, is important to optical transmission, since it dictates the required bandwidths and performance of components in the optical transmission path. Table 7 1...
