Processing at the Speed of Light

Consider this. An optical computer in a single hour can carry out an operation that would take a conventional electronic computer more than eleven years! Mind-boggling?

While traditional electronic computers can do only one thing at a time, optical computers can compute in parallel. They can be both thousands of times more powerful than traditional computers, and tremendously energy-efficient. This is because light, or photons, is more westernized as compared to electrons. Light beams can run close to each other, and even criss-cross each other’s path, with no cross-talk. And massive space reduction can be achieved by placing virtually unlimited optical paths in a limited space.

When associated with fast switching speeds, this ability of an optical computer to do tasks in parallel can result in staggering computational power?

Moreover, traveling at 186,000 miles per hour the fastest thing known to man light can tremendously reduce inter- and intra-chip communication time, pushing up processor speeds. Issues like those of bus speeds could become a thing of the past, as light has the potential of providing all the bandwidth that we need. Optics has already had a revolutionizing effect on networking using with fiber optics.

This is just the tip of the iceberg. Electronic switching limits network speeds to about 50 Gbps. What we need however is terabit speeds (never satisfied are we?). Fraser, Abdeldayer, and teams of NASA have built all-optical logic gate circuits switching at gigabit and terabit rates, besides nanosecond and Picosecond all-optical switches.

The Fourier transform (which is extremely important in signal analysis) has a major role to play in optical computers. In optical systems data is conveyed by the modulation of a cross-section of a light beam, usually by some sort of a transparency. In this the transmitted beam may also suffer a phase change. Now to carry out an operation, say subtraction, two light beams having different amplitudes (hence representing different numbers), and having a 180-degree phase difference are combined. The amplitudes cancel, thus giving us the final result.

The use of beam splitters and transparencies allows us to perform arithmetic operations on a continuous feed of data in parallel. The capability to carry out unlimited fan addition is one of the strongest points of optical computing. Optical computing can also be used to find solutions of partial differential equations where accuracy is not much of a concern and analytical solutions not possible.

The heart of any modern electronic circuit is the transistor. To carry out processing using optics we need a similar device. A transphasor is the electronic equivalent of a transistor. Other important non linear devices are the Fabry-Perot resonator, interference filter bistable device, Hybrid resonator based bistable device and of course the SEED (Self electro-optical Device).

Logic gates are primarily implemented by three methods laser logic gates, threshold logic and shadow casting. Out of these shadow casting is optically very simple with no lenses or non-linear devices being required.

Optical computers also offer the possibility of dynamic reconfiguration if spatial light modulators control the optical inter- connection pattern. The reconfiguration pattern may be changed real time.

Time Travel?

Researchers have recently found that under certain conditions, when a pulse of light is passed through a gas filled chamber, the pulse emerges at the other end even before it has entered the chamber. Effectively, it travels through time and space time travel, if you wish. This really isn t as weird or impossible as it sounds. It s just one of the offshoots of Einstein s theory of relativity. Hence, with light reaching its destination even before it has really started its journey, the possibilities opened up for computer speed are obvious. This phenomenon doesn t just offer possibilities for staggering processing speeds, but also for networking. We can already see the benefits of fiber-optic technology. Just imagine what could be achieved if light could travel from one end of the fiber to another, faster than it currently does.

In optical computing, post-processing also plays a major role requiring a lot of computing power. The usual correlation process requires a Fourier transform, multiplication by a matched filter and an inverse Fourier transform. Research has found that greater flexibility and S/N ratio may be achieved if the first Fourier transform is performed optically and the second using a digital electronic computer.