Optoelectronics

Optoelectronic devices convert back and forth between electrical and optical signals. Due to the prevalence of CMOS devices, both analog and digital signals are most easily processed and stored in electronic form. However, optical signals provide distinct advantages for high-speed and long-distance transmission.
There are two key technologies for converting electrical signals to optical: light-emitting diodes (LEDs) and lasers. LEDs use current flowing through a PN junction to emit photons. This junction can be engineered to produce any desired spectrum of light. LEDs can be manufactured relatively cheaply and also small in size. Lasers also convert electricity into visible light, but can produce a coherent, more spectrally pure, and more powerful light source. Lasers require more electrical power than LEDs. A laser diode is a device that has qualities of both a laser and an LED. Converting optical signals into electrical signals is accomplished via a photodiode or photovoltaic cell.
Many optoelectronic systems mimic their purely electronic counterparts. There are optoelectronic switches, transceivers, and multiplexers. They perform the same basic functions but have either optical inputs, outputs, or both. These optoelectronic systems are comprised of LEDs, lasers, laser diodes, and photodetectors. The logical operation and storage is always performed by electronics however.