Friday, February 20, 2009

Optical Computer

In most modern computers, electrons travel between transistor switches on metal wires or traces to gather, process and store information. The optical computers of the future will instead use photons traveling on optical fibers or thin films to perform these functions. But entirely optical computer systems are still far into the future. Right now scientists are focusing on developing hybrids by combining electronics with photonics. Electro-optic hybrids were first made possible around 1978, when researchers realized that photons could respond to electrons through certain media such as lithium niobate (LiNbO3). To make the thin polymer films for electro-optic applications, NASA scientists dissolve a monomer (the building block of a polymer) in an organic solvent. This solution is then put into a growth cell with a quartz window. An ultraviolet lamp shining through this window creates a chemical reaction, causing a thin polymer film to deposit on the quartz.



An ultraviolet lamp causes the entire quartz surface to become coated, but shining a laser through the quartz can cause the polymer to deposit in specific patterns. Because a laser is a thin beam of focused light, it can be used to draw exact lines. A laser beam's focus can be as small as a micron-sized spot (1 micron is 1-millionth of a meter, or 1/25,000 of an inch), so scientists can deposit the organic materials on the quartz in very sophisticated patterns. By painting with light, scientists can create optical circuits that may one day replace the electronics currently used in computers.



NASA scientists are making these organic thin films on the Space Shuttle to overcome problems caused by convection. Convection is a circular motion in air or in a liquid created from uneven heating. On Earth's surface, when a gas or liquid is heated it expands, becoming lighter and less dense. This lighter material rises, mixing with cooler and denser material from above. Such turbulence occurs in the world's weather patterns or even in a pot of water boiling on the stove.



Convection creates difficulties when trying to create a uniform film. A UV lamp or laser light will raise the temperature of the film solution, causing the hotter solution to rise. Aggregates of solid polymers often form in the solution, and convective flows that develop in the solution can carry these aggregates to the surface of the quartz. Because aggregates on optical films can cause light to scatter, the goal is to make the films as smooth and uniform as possible.

No comments:

Post a Comment