(Space Daily Via
Thomson Dialog NewsEdge) The laser uses only a microwatt of
power, one of the smallest operating powers ever achieved.
This nanolaser design should be useful in future miniaturized
circuits containing optical devices. The researchers present
their nanolaser in the latest issue of Optics Express, an
open-access journal published by the Optical Society of
America.
The laser is made of a semiconductor material known as
gallium indium arsenide phosphate (GaInAsP). The laser's small
size and efficiency were made possible by employing a design,
first demonstrated at the California Institute of Technology
in 1999, known as a photonic-crystal laser. In this design,
researchers drill a repeating pattern of holes through the
laser material. This pattern is called a photonic
crystal.
The researchers deliberately introduced an
irregularity, or defect, into the crystal pattern, for example
by slightly shifting the positions of two holes. Together, the
photonic crystal pattern and the defect prevent light waves of
most colors (frequencies) from existing in the structure, with
the exception of a small band of frequencies that can exist in
the region near the defect.
By operating at room temperature and in a mode where laser
light is emitted continuously, the new nanolaser from Yokohama
National University distinguishes itself from previous
designs. For a laser device that depends on the delicate
effects of quantum mechanics, the random noise associated with
even a moderately warm environment usually overwhelms the
process of producing laser light.
Yet this laser
operates at room temperature. It also produces a continuous
output of light, rather than a series of pulses. This
desirable continuous operation is more difficult to achieve
because it requires careful management of the device's power
consumption and heat dissipation.
According to Yokohama
researcher Toshihiko Baba, the new nanolaser can be operated
in two modes depending what kind of Q value is chosen. Q
refers to quality factor, the ability for an oscillating
system to continue before running out of energy. A common
example of an oscillating system would be a tuning
fork.
The higher its Q value, the longer it will ring
after being struck. Lasers are oscillating systems because
they produce light waves that repeatedly bounce back and forth
inside the device to build up a beam. Nanolasers operated in a
high-Q mode (20,000) will be useful for optical devices in
tiny chips (optical integrated circuits). In a moderate-Q
(1500) configuration the nanolaser needs only an extremely
small amount of external power to bring the device to the
threshold of producing laser light. In this near-thresholdless
operation, the same technology will permit the emission of
very low light levels, even single photons.
Copyright
2007 Space Daily, Distributed by United Press International
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