The function of the receiver is to accept low level power from the detector and convert it into a
high voltage output. There are many ways to accomplish this. The figure on the left shows a
detector current producing a voltage drop across a load resistance. The voltage drop is directed
into amplifier. An output voltage representative of the transmitted signal is the result. Other
electronics maybe added to the circuitry to maintain adequate response. A gain control may be
used in the front end to vary the impedance of the receiver.
It is reasonably priced. The APD is more expensive than the PIN diode since it provides greater
receiver sensitivity. The APD also requires an auxiliary power supply.
So far, fiber optics has only played a small role in practical Local Area Networks. Many papers
have been published in scholarly journals describing experimental fiber optic LANs. A few
companies even offer commercial ones, but the few that have been installed are only a small
fraction of LANs in use. Local Area Networks themselves are not as widespread one might
think. This material has been used in few practical LANs but has been tested in many laboratory
LANs.
This will be changing. Most present terminals and personal computer require only modest
transmission rates, which often can be sent over telephone lines. Current LANs operate at speeds
about 10Mbits/s, at which there is little benefit from using them (except in some special cases).
Future devices will require faster data transmission to allow better quality graphics, faster access
to databases and more efficient sharing of information. The need for faster transmission will
accelerate the development of LANs and their use of them. To get a good understanding of fiber
optics in networks, we will have to see how fiber optics can improve the capability of present
and the next generation LANs being developed around fiber optics. Interest in higher speed
transmission could motivate uses of fiber optics in networks.