Taking a Practical Step Forward in Optical Computing Using Slow Light: Photonic Crystals Offer a Slow Light Solution for Optical Computing
Previously published on Apr 13, 2011
Quantum computing is the Mount Everest of the information technology revolution. What approach succeeds will almost assuredly utilize optical components. With the limits of traditional electronics threatening to halt progress, alternatives, such as optical computing, will be needed in the not so distant future. One major hurdle for the development of such optical systems has been the need to convert between optical and electronic signals. Because time spent converting optical data into an electronic format takes longer than simply using the traditional medium, the concept is impractical in many respects. On the other hand, an almost paradoxical concept known as slow light offers a way around this barrier with a very practical solution.
It is a fundamental law of the universe that light can only exist at the speed of light. That is, photons must always move at approximately 300 million meters per second.
Looking closely at this law reveals a rather obvious loophole. Light waves passing through almost any given medium usually take longer to propagate through said medium than they would free space, because the light is bent along a lengthier path due to the internal properties of the medium. In other words, photons will continue to move at light speed, but it takes them longer to navigate through an object rather than simply moving within a vacuum at light speed, i.e. light goes slower. Consequently, given the proper medium, light could be slowed to a crawl, or even stopped.
It is how much a medium bends light that determines the "speed" of light and this property classically depends upon a material's index of refraction. A material with a high enough index of refraction, therefore, could be used to slow light. While the first demonstration of slow light in 1999, which yielded a speed around 17 meters per second, utilized a Bose-Einstein Condensate, which is a low-temperature state of matter where the atoms lose their individual characteristics and act almost as a single particle, one alternative approach is to utilize the many emerging manmade meta-materials that exhibit extreme properties, including super high indexes of refraction. On the other hand, researchers at the University of Sydney in New South Wales looked at advances in photonic crystals to suggest an even easier, more dynamic alternative.
Photonic crystals are a rapidly advancing technology first developed in the 1990's. By engineering regular structures in an optical material, light will respond to the pattern as though it is passing through a crystal. Giving researchers far greater control over light, photonic crystals can be used to slow light to variable speeds at continually shrinking costs with greater precision and less bulk. In fact, Professor Benjamin Eggleton's research group has already demonstrated an approach using a photonic crystal structure engineered by a University of St. Andrews team led by Professor Thomas F. Krauss for use over a broad bandwidth yields a sixteen fold increase in processing speeds over a traditional silicon chip, or 640 gigabits a second.
As such, it is obvious the next step forward is hybrid systems using photonic crystal chips. The key to processing and transmitting data stems from the ability to control how information flows. Light can get information to where it needs to go rather quickly, but the information must be stored until it can be used. Optical buffering as the "old fashion" approach relies on costly conversions between optical and electronic signals, so slowing light is a better option. If light is slowed or stopped until it is needed, a hybrid optical-electronic system would be extremely practical with results instantly surpassing the capacity of electronic devices. Consequently, we may soon see a major advancement in the telecommunications industry, followed by a renewed revolution in all computing technologies.
Thanks to initiatives for promoting civil investments in solar energy, LED lighting, national security and so on, technologies based on research from the fields of optics have known great progress in recent years. Just as the fruits of this research finally start to ripen, however, public support is drying up due to budget battles in Europe and the United States. Meanwhile, private funding can often be very selective to our civilization's detriment as entrepreneurs only want to invest in products that guarantee them a return, especially in the current environment where high return, low cost business deals can be exploited by the investment community. The US was already significantly behind in providing funds for research while even less funding is certain to retard progress just as we are the verge of major advances on a number of fronts.
With relatively low-cost experimental needs, the optical sciences offer solutions for everything from national and energy security to pharmaceutical and agricultural applications. Breakthroughs like slow light, meta-materials, photonic crystals, and quantum dots, which are essentially "traps" for photons and other particles, came about due to somewhat basic theories of some very complex subjects and scientists simply questioning. Not only do these discoveries and more have a myriad of potential applications, the costs associated with these technologies fall as we see progress while the benefits and profits begin to amass. Pursuing related research has already revealed some very meaningful discoveries and opportunities, but our society must be more aggressive in our pursuit of the basic research required to realize current and future gains.