Towards 10 Gigabits Per Second: Lehigh Group Reports Best Threshold Values For Near-infrared Range Lasers

Nelson Tansu, 26, an assistant professor of electrical and computerengineering at Lehigh, and Luke J. Mawst, associate professor ofelectrical computer engineering at Wisconsin, have reported the best threshold values to date for near-infrared-range (with an emission wavelength of 1300-nm), indium-gallium-arsenide-nitride (InGaAsN) lasers that emit from a quantum well.

The researchers published their findings in two recent issues of Applied Physics Letters (APL) - on July 7 and Sept. 29.

Tansu's group also reported the best threshold values yet for near-infrared-range quantum-well (QW) lasers operating under continuous-wave conditions at temperatures up to 100 degrees C.

The first APL article was titled "High-performance and high-temperature continuous-wave-operation 1300-nm InGaAsN quantum well lasers by organometallic vapor phase epitaxy."

The goal of Tansu's work is to use metal organic chemical vapor deposition (MOCVD) to develop lasers and advanced compound semiconductor nanostructures for optoelectronic devices. He also seeks to combine these semiconductor nanostructures with photonic crystals (artificial structures with periodicity of certain optical properties) to make novel optoelectronic devices. His work has applications in optical communications, mid-infrared devices, free-space communications, visible light sources, information sciences, and biochemical detection.

The criteria for high-performance lasers, says Tansu, include low operating current, high efficiency, the ability to operate at high speeds at a range of temperatures (from room temperature to 100 degrees C.), and the ability to operate at high temperatures without the need for costly additional electronics to maintain thermal stability.

One type of laser with which Tansu works is high-performance VCSELs, or vertical cavity surface-emitting lasers, which are cheap to produce and operate at a low current. VCSELs are used in short-haul communications systems, which operate with an 850-nm wavelength, allow a transmission range of about 200-500 meters and are typically found in university campuses, offices, residential complexes and similar venues.

The accomplishments by Tansu's group have the potential to lead to the production of low-cost and high-performance 1300-nm VCSELs, capable of a transmission rate of 10 gigabytes per second. Tansu's group is one of the first to realize high-performance near-infrared range InGaAsN quantum wells by using MOCVD technology, which is the technology of choice to produce VCSELs in manufacturing. Near-infrared range lasers, which operate with a 1300-nm wavelength, allow a transmission range of 20 to 100 kilometers and are also called metropolitan optical networks because they can connect cities that are in close proximity.

The group achieved its breakthrough using InGaAsN, a new lasing material also known as dilute-nitride, on a gallium-arsenide substrate, instead of the conventional approach based on indium-phosphide technology.

"Using dilute-nitride grown on a gallium-arsenide base," says Tansu, "it is much easier to make the high-performance reflectors that are critical to achieving high-performance VCSELs. We accomplished this by using MOCVD, which is also known as MOVPE [Metal-Organic Vapor Phase Epitaxy]."

Tansu's works represent the first realization of MOCVD-grown high-performance 1300-nm dilute-nitride lasers under continuous-wave (CW) operations rather than pulsed conditions, and with a better performance than that achieved with molecular beam epitaxy. (A German research group previously demonstrated that type of high-performance laser with molecular beam epitaxy.) CW is a virtual prerequisite for lasers to be used in real-world applications; pulsed conditions are typically used in the early stages of experimentation.

The lasers in Tansu's system emit from a 6-nm-thick quantum well that is grown on a dilute-nitride semiconductor nanostructure layer using a strained-compensated technique.

In all, Tansu has published 11 journal and conference papers since he joined the Lehigh faculty on July 1.

The other articles have appeared in several APLs, IEEE's Journal of Quantum Electronics, IEEE's Journal of Selected Topics in Quantum Electronics, the Proceedings of the 16th IEEE Laser and Electro Optics Society Annual Meeting (2003), and other journals and conference proceedings. Tansu has also been invited to write a review paper on the physics and devices of dilute nitride lasers for an issue of the IOP's Journal of Physics: Condensed Matter Physics in 2004.

On Oct. 10, Tansu was featured in the cover article of GATRA, the second-most widely circulated weekly news magazine in Indonesia (population 250 million), where Tansu was born and raised. The article described five Indonesians who are employed as university professors outside Indonesia.