An electrical-to-optical converter (E/O) is a device that converts electrical signals into optical signals, usually by using a laser diode. It is commonly used in fiber optic communication systems to transmit and receive data. This device usually consists of a photodetector. nal into a corresponding light signal that can be injected into the fiber. The light emitter is an important element because it is often the most costly element in the system, and its characteris ics often strongly influence the final performance limits of a given link.