Optical transmitters and receivers
The role of the receiver is to convert the optical signal back to the original electrical signal, thereby recovering the data sent by the transmitter. This chapter discusses optical transmitters and receivers and introduces their various components. The purpose of an optical source is to convert electrical signals to light waves. Optical detection is the function of the optical receiver that is unique to optical communication systems. An optical detector does the opposite of what the optical source does; it converts the normally weak optical input signal into a current output. Optical detectors are usually photodiodes that are photoelectric devices. There are two types of photodiodes: positive-intrinsic-negative (PIN) photodiode and avalanche photodiode (APD). A way of improving receiver sensitivity is to use an (APD), which provides current amplification within itself before the circuitry of the following amplifier. The primary purpose of an optical receiver is to detect the light incident on it and to convert it to an electrical signal.