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Transistor laser functions as non-linear
electronic switch, processor
James E.
Kloeppel, Physical Sciences Editor
217-244-1073; kloeppel@uiuc.edu
2/6/06
 |
Click
photo to enlarge |
University
of Illinois photo |
| The
transistor invented by Milton Feng, left, and Nick
Holonyak has now been found to possess fundamental
non-linear characteristics that are new to a transistor
and permit its use as a dual-input, dual-output, high-frequency
signal processor. |
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CHAMPAIGN, Ill.
— The transistor laser invented by scientists at the University
of Illinois at Urbana-Champaign has now been found to possess fundamental
non-linear characteristics that are new to a transistor and permit its
use as a dual-input, dual-output, high-frequency signal processor.
“We have hit upon something surprisingly fundamental and rich
in possibilities,” said Nick Holonyak Jr., a John Bardeen Chair
Professor of Electrical and Computer
Engineering and Physics at Illinois. “We have at once a new form of transistor and a new
form of laser.”
By modifying the base region with quantum wells and resonator configurations,
Holonyak, electrical and computer engineering professor Milton Feng,
and their colleagues have shifted the transistor operation from spontaneous
emission to stimulated emission. The altered recombination process of
the transistor changes the device characteristics, giving near laser
threshold a fundamental and potentially useful non-linearity. The scientists
describe their work in the Feb. 6 issue of the journal Applied Physics
Letters.
“Transistors have never done this before,” said Holonyak,
who also is a professor in the university’s Center for Advanced
Study, one of the highest forms of campus recognition. “Operating
as a new form of transistor, the transistor laser offers new signal
mixing and switching capabilities.”
The transistor laser combines the functionality of both a transistor
and a laser by converting electrical input signals into two output signals,
one electrical and one optical.
 |
Click
photo to enlarge |
Credit: Milton
Feng and Nick Holonyak |
| Scanning
electron microscope image of a dual-input heterojunction
bipolar transistor laser (HBTL) on a Cu heat sink
acting as frequency mixer for up and down conversion.
The image shows a cleaved, front to back, segment
of the laser crystal with emitter (E), base (B), and
collector (C) metallization as shown. The laser output
is shown schematically as hV and the electrical output
as Vout. Both output signals produce integer multiples
(mixing) of the input signals at frequencies mf1 +nf2. |
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“Using separate
base inputs, we can apply two independent signals to the active region
of the transistor laser,” said Feng, the Holonyak Chair Professor
of Electrical and Computer Engineering at Illinois.
“We can mix them, manipulate them, so that we get out an electrical
signal which is some multiple of the first input plus some multiple
of the second input,” Feng said. “We also get out an optical
signal, which is modulated by some multiple of the first input plus
some multiple of the second input.”
As proof of concept, the researchers demonstrated the operation of a
transistor laser as a non-linear microwave mixing device and signal
processor using a single emitter and a twin-contact base. Two signals,
one at 2.0 gigahertz and one at 2.1 gigahertz, were mixed. Both electrical
and optical output signals were obtained at mixing frequencies from
0.1 gigahertz to 8.4 gigahertz.
The data make it clear that stimulated recombination in a transistor,
besides its implications for another form of laser with modulation speed
potentially as high as that of a transistor, is the basis for a useful
non-linear element, a different form of electronic switch and processor,
the researchers said.
The transistor laser also raises the possibility of replacing wiring
between components at the chip- or board-level with optical interconnects,
thus offering more flexibility and capability in electronic-photonic
integrated circuits.
“It’s too early to tell where all of this will go,”
Holonyak said. “We’re still studying the physics and device
properties of the transistor laser. We’re a long way from the
end.”
Co-authors of the paper with Feng and Holonyak are postdoctoral research
associates Gabriel Walter and Richard Chan, and graduate student Adam
James. The Defense Advanced Research Projects Agency funded the work.
To
reach Nick Holonyak, call 217-333-4149.
To reach Milton Feng, call 217-333-8080; e-mail: mfeng@uiuc.edu.
