2007-06-21
High-performing Room-temperature Nanolaser Uses
Honeycomb-like Photonic
Crystal |
Scientists at Yokohama
National University in Japan have built a highly efficient
room-temperature nanometer-scale laser that produces stable,
continuous streams of near-infrared laser light. The overall device
has a width of several microns (millionths of a meter), while the
part of the device that actually produces laser light has dimensions
at the nanometer scale in all directions.
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 Optics Express.
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.
Article: Kengo Nozaki, Shota Kita, and Toshihiko Baba, "Room
temperature continuous wave operation and controlled spontaneous
emission in ultrasmall photonic crystal nanolaser," Optics Express,
Vol. 15, Issue 12, pp. 7506-7514
Note: This story has been adapted from a news release issued by
Optical Society of America.
High-performing Room-temperature Nanolaser Uses Honeycomb-like
Photonic Crystal
