arge fleets of trucks/cars/aircraft). 2.3.4 Fiber-optic Links Fiber-optic cable is a revolution in connecting transmitters to receivers. It seems possible to support incredible-and I do mean incredible-rates of information along this cable. Using fiber-optic cable, it appears that we can support 1014 bits/s, at the very least. Right now, we don't know how to send information at this high a rate (although we're moving in that direction)-we also don't have that much information to send yet! In a fiber-optic cable system, you have an information signal, which is an incom- ing electrical signal. To use a fiber-optic cable, you have to turn this electrical signal into light. Figure 2.18 shows how you might do this at the transmitter side, using a device called an emitter. The emitter might be, for example, a LED (light-emitting diode) or an FP (Farby Parot) laser diode. Chapter Two Incoming information Original information on electrical signal Cladding on electrical signal Emitter Detector Light Outgoing information signal on a light wave Figure 2.18 Fiber-optic link The fiber-optic cable, which you can also see in Figure 2.18, is made up of two parts: a core and a cladding. The light travels down the core. It remains in the core and never leaves it (never entering the cladding). This is because the two materials chosen for core and cladding are carefully selected to ensure that total internal refrac- tion occurs-that means that as light enters the boundary between core and cladding, it is bent in such a way that it remains in the core. (For more on this, check out a physics book.) At the receiver side, the light signal, which has made it through the fiber-optic cable, must be returned to an electrical signal. That job is done using a detector, as seen in Figure 2.17. The detector might be, for example, a PIN diode or an APD (avalanche photo diode). The light sent down the fiber-optic cable corresponds to an electromagnetic wave with a frequency in the range of 1014 to 1015 Hz. As mentioned already, the system appears