Source: Lehigh University
Towards 10 Gigabits Per Second: Lehigh Group Reports Best Threshold Values
For Near-infrared Range Lasers
High-performance, vertical cavity surface-emitting lasers (VCSELs) produced
with vapor deposition and capable of operating with a 1300-nm wavelength
have moved a step closer to reality thanks to research at Lehigh University
and the University of Wisconsin-Madison.
Nelson Tansu, 26, an assistant professor of electrical and computer
engineering at Lehigh, and Luke J. Mawst, associate professor of electrical
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
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
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.
Do Wah Ditty
"Our country puts $1 billion a year up to help feed the hungry. And we're by
far the most generous nation in the world when it comes to that, and I'm
proud to report that. This isn't a contest of who's the most generous. I'm
just telling you as an aside. We're generous. We shouldn't be bragging about
it. But we are. We're very generous."
- Washinton D.C., July 16, 2003