An optical computer is a computer that uses bound electrons in isolating crystals instead of free electrons in transistors for compu­tation. Its digital signals are modulated onto a carrier wave in the visible region. No modulator or demodulator exists, because the base band of­fers only 10 GHz bandwidth whereas the visible band offers to THz. It is similar to performing digital computation by a radio.

A more practical limit is the crystal. Cur­rent crystals need light with 1 GW/cm2 inten­sity. And as a typical die (in microelectronics) is about 1 cm2, and some absorption takes place, this means kilowatts of power consumption, which only allows pulsed operation, but nanotubes may reduce this in the future.

The speed of computers has now become a pressing problem as electronic circuits reach their miniaturization limit. The rapid growth of the Internet, expanding at almost 15% per month, de­mands faster speeds and larger bandwidths than electronic circuits can provide. Electronic switch­ing limits network speeds to about 50 Gigabits per second (1 Gigabit (Gb) is 109, or 1 billion bits).

Optical data processing can perform sev­eral operations simultaneously (in parallel) much faster and easier than electronics. This “parallel­ism” when associated with fast switching speeds would result in staggering computational power. For example, a calculation that might take a con­ventional electronic computer more than eleven years to complete could be performed by an opti­cal computer in a single hour.