Light-emitting diodes (LEDs) and laser diodes are the most commonly used optical transmitters. Light-emitting diodes (LEDs) and laser diodes are semiconductor devices. There is a major difference between light-emitting diodes (LEDs) and laser diodes and that is that Light-emitting diodes or the LEDs have the power to produce incoherent light. On the other hand laser diodes have the power to produce coherent light. These semi conductors devices or transmitters are designed to be compact for the optical communications so that they are efficient and reliable. They work in optimal wavelength range and high frequencies. These devices are used commonly today for the transmission of data and voice.