New Semiconductor Materials Yield Broadband Amplifier Fiber

Kathleen G. Tatterson

SYRACUSE, N.Y. -- A new fabrication technique has created cylindrical optical fibers that promise to enable small broadband optical amplifiers for use in communications networks, according to university researchers who have created the technology under sponsorship by the US Air Force.

Doping cadmium/tellurium- or cadmium/sulfur-core fiber with cadmium/ sulfur/selenide (CdSSe) produces a fiber that can absorb and amplify light better than existing technologies, say scientists from Syracuse University, the University of Connecticut and the Photonics Center at the Air Force's Rome Laboratories.

The main advantage of these new fibers over traditional rare-earth-doped glass fiber light amplifiers (e.g., erbium-doped fiber amplifiers) is their broad wavelength range, said the project leader, Phil-ipp Kornreich of Syracuse University's electrical engineering and computer science department. "Er-doped amplifiers are very restrictive as to the wavelengths at which one can operate, which makes them very expensive," he explained. Commercially available Er-doped fibers are not tunable at all, whereas the semiconductor cylinder fibers are tunable from 100 to 120 nm. Their range can vary between 862 and 6200 µm, depending on the semiconductor.

Kornreich added that because the semiconductor cylinder fiber light amplifiers have more electron states available per unit length of fiber, they can be made much shorter (between 5 and 10 mm) than Er-doped amplifiers, which are 2 to 20 m long with the same amplification capabilities.

In a vacuum

The fibers are made by depositing the doped semiconductor compound onto a 1- to 2-mm glass rod in a vacuum chamber. The coated rod is inserted into a glass tube, which is then closed at one end and drawn to a diameter of 8 µm.

Eric Donkor of the University of Connecticut's electrical engineering department said that it is now possible to vary the absorption edge from the visible to the infrared. For the fibers in which the nanoparticles of compounds such as CdSSe are incorporated into the core, less light is lost than in the fiber currently available commercially. Donkor is scheduled to present these findings at the IEEE/LEOS meeting in Boston later this month.

The Air Force plans to use the new technology for ultrafast switching in fiber optic networks, optical amplification and the design of fiber polarizers. The researchers are refining their initial experiments by employing new equipment and plan to demonstrate a more advanced example of the technology by next year.