Tech Page: Let There Be Light

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FIG. 1: IBM researchers have developed the world''s fastest optical transceiver, which can handle up to 160 Gbps of data in a very small package.
Photo: Courtesy IBM

Most people mark the birth of modern electronics with the invention of the transistor in 1947. This device single-handedly overcame the limitations of vacuum tubes, especially in terms of size, heat dissipation, and reliability, leading the way to supercomputers, personal computers, and a vast assortment of electronic musical tools in the last 60 years.

Today, electronic technology is starting to reach the limits of its capabilities, and many labs are working on a new technology called photonics with the potential to far exceed these limits. Whereas electronics is concerned with manipulating streams of electrons, photonics deals with light, which consists of a stream of photons.

Photonic computing offers many advantages over its electronic counterpart. For one thing, light can be switched on and off much faster than electricity, allowing far higher digital data rates. In addition, light is much more energy efficient and less prone to pulse degradation, especially over long distances. Finally, crosstalk is eliminated because there are no electromagnetic fields arising from different current paths to interact with each other.

However, these advantages do not come cheap. Ironically, the lack of interaction between photons means that the technology to manipulate them is more sophisticated than its electronic equivalent. And photonics is in its infancy, with critical breakthroughs appearing only in the last few years.

One vital field of research is the development of nonlinear optical materials, which change their optical properties depending on the light that enters them. One of the most important nonlinear effects is photorefraction, in which the intensity of the incoming light changes the refractive index of the material. This changes the angle at which the light is bent as it passes through the material, suggesting the possibility of superfast, multistate optical switches.

Another critical area of development is holographic memory, which stores data as interference patterns in a block of photosensitive material. A laser beam is split into two identical beams, one of which is modulated in a way that corresponds to the data to be stored. When the two beams meet within the storage material, the resulting interference pattern is recorded. This process can be repeated at different angles, yielding a data density up to tens of terabits per cubic centimeter.

Then there's the interface that sends and receives data between digital devices via optical networking. IBM recently demonstrated the world's fastest optical transceiver, which can send and receive data at 160 gigabits per second, eight times faster than currently available optical components. According to the company, this is fast enough to download a typical high-definition, feature-length movie in 1 second instead of the hours it takes today.

“The explosion in the amount of data being transferred when downloading movies, TV shows, music, and photos is creating demand for greater bandwidth and higher speeds in connectivity,” says Dr. T. C. Chen, vice president of science and technology for IBM Research. “Greater use of optical communications is needed to address this issue. We believe our optical transceiver technology may provide the answer.”

Even better, the new transceiver measures only 3.25 mm by 5.25 mm (see Fig. 1), allowing it to be incorporated into small devices. The IBM researchers combined current CMOS technology with optical components made of more-exotic materials, such as indium phosphide and gallium arsenide. This approach makes it easier to integrate optical communication into existing electronic circuits. Such an integrated approach may well lead to the first applications of photonics in the music industry, where terabytes of storage and gigahertz of bandwidth would not be wasted.