Photonic computing

Today's computers use the movement of electrons in-and-out of transistors to do logic. Photonic computing is intended to use photons or light particles, produced by lasers, in place of electrons. Compared to electrons, photons are much faster – light travels about 30 cm, or one foot, in a nanosecond – and have a higher bandwidth.

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Computers work with binary, on or off, states. A completely optical computer requires that one light beam can turn another on and off. This was first achieved with the photonic transistor, invented in 1989 at the Rocky Mountain Research Center. This demonstration eventually created a growing interest in making photonic logic componentry utilizing light interference.

Light interference is very frequency sensitive. This means that a narrow band of photon frequencies can be used to represent one bit in a binary number. Many of today's electronic computers use 64 or 128 bit-position logic. The visible light spectrum alone could enable 35 billion bit positions.

Recent research shows promise in temporarily trapping light in crystals. Trapping light is seen as a necessary element in replacing electron storage for computer logic.

While photonic computing is still seen as impractical by many, research is being pushed along by strong market forces already implementing networking and, thus, creating opportunities. Recent years have seen the development of new conducting polymers which create transistor-like switches that are smaller, and 1,000 times faster, than silicon transistors.

Optical switches switch optical wavelengths. Optical switching, while not all-optical, has already become important in networking environments. 100 terabit-per-second data-handling is expected within the decade. Existing technologies include:

• Micro-electro-mechanical systems, or MEMS, which use tiny mechanical parts such as mirrors.
• Thermo-optics technology, derived from ink-jet technology, creates bubbles to deflect light.
• Liquid crystal switching changes (e.g., by filtering and rotating) the polarization states of the light.

Photonic logic

Photonic logic is the use of photons (light) in logic gates (AND, NAND, OR, NOR, XOR, XNOR). Photonic logic refers to the usage of light (photons) to form logic gates. Switching is obtained using nonlinear optical effects when two or more signals are combined.

Resonators are especially useful in photonic logic, since they allow a build-up of energy from constructive interference, thus enhancing optical nonlinear effects.

Other approaches currently being investigated include photonic logic at a molecular level, using photoluminescent chemicals.

See also

• Photonics
• Optical computer

References

• Ibrahim TA, Amarnath K, Kuo LC, Grover R, Van V, Ho PT. Photonic logic NOR gate based on two symmetric microring resonators. Opt Lett. 2004 Dec 1;29(23):2779-81.
• Biancardo M et al. A potential and ion switched molecular photonic logic gate, Chem. Commun., 2005, (31), 3918-3920