Electrical engineers build ‘No-waste’ laser
11 Feb Science Daily
A team of University of California, San Diego researchers has built
the smallest room-temperature nanolaser to date, as well as an even more
startling device: a highly efficient, “thresholdless” laser that funnels
all its photons into lasing, without any waste.
The two new lasers require very low power to operate, an important
breakthrough since lasers usually require greater and greater “pump
power” to begin lasing as they shrink to nano sizes.
The small size and extremely low power of these nanolasers could make
them very useful components for future optical circuits packed on to
tiny computer chips, Mercedeh Khajavikhan and her UC San Diego Jacobs
School of Engineering colleagues report in the Feb. 9 issue of the
journal Nature.
They suggest that the thresholdless laser may also help researchers
as they develop new metamaterials, artificially structured materials
that are already being studied for applications from super-lenses that
can be used to see individual viruses or DNA molecules to “cloaking”
devices that bend light around an object to make it appear invisible.
All lasers require a certain amount of “pump power” from an outside
source to begin emitting a coherent beam of light or “lasing,” explained
Yeshaiahu (Shaya) Fainman, a professor in the Department of Electrical
and Computer Engineering at UC San Diego and co-author of the new study.
A laser’s threshold is the point where this coherent output is greater
than any spontaneous emission produced.
The smaller a laser is, the greater the pump power needed to reach
the point of lasing. To overcome this problem, the UC San Diego
researchers developed a design for the new lasers that uses quantum
electrodynamic effects in coaxial nanocavities to alleviate the
threshold constraint.
Like a coaxial cable hooked up to a television (only at a much
smaller scale), the laser cavity consists of a metal rod enclosed by a
ring of metal coated, quantum wells of semiconductor material.
Khajavikhan and the rest of the team built the thresholdless laser by
modifying the geometry of this cavity.
The new design also allowed them to build the smallest
room-temperature, continuous wave laser to date. The new
room-temperature nanoscale coaxial laser is more than an order of
magnitude smaller than their previous record smallest nanolaser
published in Nature Photonics less than two years ago.
The whole device is almost half a micron in diameter by comparison,
the period at the end of this sentence is nearly 600 microns wide.
These highly efficient lasers would be useful in augmenting future
computing chips with optical communications, where the lasers are used
to establish communication links between distant points on the chip.
Only a small amount of pump power would be required to reach lasing,
reducing the number of photons needed to transmit information, said
Fainman.
The nanolaser designs appear to be scalable meaning that they could
be shrunk to even smaller sizes an extremely important feature that
makes it possible to harvest laser light from even smaller nanoscale
structures, the researchers note.
This feature eventually could make them useful for creating and
analyzing metamaterials with structures smaller than the wavelength of
light currently emitted by the lasers.
Fainman said other applications for the new lasers could include tiny
biochemical sensors or high resolution displays, but the researchers are
still working out the theory behind how these tiny lasers operate.
They would also like to find a way to pump the lasers electrically
instead of optically. Coauthors for the Nature study, “Thresholdless
Nanoscale Coaxial Lasers,” include Mercedeh Khajavikhan, Aleksandar
Simic, Michael Kats, Jin Hyoung Lee, Boris Slutsky, Amit Mizrahi,
Vitaliy Lomakin, and Yeshaiahu Fainman in the Department of Electrical
and Computer Engineering at the UC San Diego Jacobs School of
Engineering. The nanolasers are fabricated at the university’s NANO3
facility.
The research was funded by the Defense Advanced Research Projects
Agency, the National Science Foundation, the NSF Center for Integrated
Access Networks (CIAN), the Cymer Corporation and the U.S. Army Research
Office.
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