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Device could vastly improve fiber optic comminucations

A multidisciplinary research effort at MIT has resulted in a device that may improve the efficiency and information-carrying capacity of fiber optic communication systems by a hundredfold.

Researchers from the Departments of Materials Science and Engineering, Physics, and Electrical Engineering and Computer Science have designed, manufactured and tested a photonic band gap (PBG) microcavity resonator that operates at optical wavelengths (1.3-1.7 micrometers). This is the first device of this type ever made. Its sub-micrometer dimensions (minimum feature size is 0.1 micrometer) also make it smaller than any previously designed optical waveguide by a factor of 100.

A presentation of the work is scheduled for the Conference on Lasers and Electro Optics on May 22.

The small size and high resolution of the optical PBG resonator provide a means for increasing the information-carrying capacity of an optical fiber into the terahertz range. "That is the Holy Grail of telecommunications system design," said Professor Lionel Kimerling, one of the project supervisors and director of the Materials Processing Center. "Such a bandwidth could provide almost unlimited information to end users, putting the world immediately at their fingertips."

To date, PBG resonators have only been designed for use at microwave wavelengths (1-100 millimeters) and frequencies in the gigahertz range.

The materials and manufacturing technique used are already common to integrated circuit technology in the fabrication of microchips. This means that these devices can be constructed right on a microchip for direct interfacing with other electronic devices, further increasing information processing speeds and lowering signal loss.

In the case of telecommunications systems, they can also take advantage of the existing network of underground fiber optic cables. Previously, each optical fiber transmitted one signal. These PBG structures act as gratings (filters) for the control of light. They do this by separating light into different color bands, or "channels." With MIT's optical PBG resonator, more than 100 channels of different information could be piped simultaneously down a single optical fiber.

In addition, where the optical PBG microcavity resonator is used for light-emission applications instead of signal transmission and filtering, it can provide the capability for the development of microlasers and microLEDs.

James Foresi, a graduate student in materials science and engineering under the direction of Professor Kimerling, was involved in all stages of the project. Other collaborators included research scientist Pierre Villeneuve and graduate student Shan Hui Fan, both in the Department of Physics under Professor John Joannopoulos; research staff member Juan Ferrara under the direction of Professor Hank Smith in the Department of Electrical Engineering and Computer Science (EECS), and research staff members Erik Thoen and Gunther Steinmeyer in Professor Eric Ippen's laboratory in EECS.

Funding was provided by MIT's National Science Foundation Materials Research Science and Engineering Center (NSF-MRSEC), the Defense Advanced Research Projects Agency (DARPA) and the Air Force Office of Scientific Research (AFOSR).

A patent for the design was submitted in 1994 by researchers in the physics department and is awaiting approval.

A version of this article appeared in MIT Tech Talk on May 14, 1997.

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