Quantum dot lasers -- 1 dot makes all the difference

April 12, 2007
Quantum dot lasers -- 1 dot makes all the difference
Microdisk lasers used in experiments by NIST, Stanford University and Northwestern University are made by layering indium arsenide on top of gallium arsenide and etching out disks about 1.8 micrometers across on pillars of gallium arsenide. Scanning tunneling microscope image (inset) shows some of the approximately 130 "quantum dot" islands of indium arsenide in each disk. Credit: NIST

Physicists at the National Institute of Standards and Technology and Stanford and Northwestern Universities have built micrometer-sized solid-state lasers in which a single quantum dot can play a dominant role in the device’s performance. Correctly tuned, these microlasers switch on at energies in the sub-microwatt range. These highly efficient optical devices could one day produce the ultimate low-power laser for telecommunications, optical computing and optical standards.

How small can a laser get? The typical laser has a vast number of emitters—electronic transitions in an extended crystal, for example—confined within an optical cavity. Light trapped and reflecting back and forth in the cavity triggers the cascade of coherent, laser light. But about a decade ago, researchers made the first quantum dot laser.

Quantum dots are nanoscale regions in a crystal structure that can trap electrons and “holes,” the charge carriers that transport current in a semiconductor. When a trapped electron-hole pair recombines, light of a specific frequency is emitted. Quantum-dot lasers have attracted attention as possible embedded communications devices not only for their small size, but because they switch on with far less power then even the solid-state lasers used in DVD players.

In recent experiments*, the NIST-Stanford-Northwestern team made “microdisk” lasers by layering indium arsenide on top of gallium arsenide. The mismatch between the different-sized atomic lattices forms indium arsenide islands, about 25 nanometers across, that act as quantum dots. The physicists then etched out disks, 1.8 micrometers across and containing about 130 quantum dots, sitting atop gallium arsenide pillars.

The disks are sized to create a “whispering gallery” effect in which infrared light at about 900 nanometers circulates around the disk’s rim. That resonant region contains about 60 quantum dots, and can act as a laser. It can be stimulated by using light at a non-resonant frequency to trigger emission of light. But the quantum dots are not all identical. Variations from one dot to another mean that their emission frequencies are slightly different, and also change slightly with temperature as they expand or contract. At any one time, the researchers report, at most one quantum dot—and quite possibly none—has its characteristic frequency matching that of the optical resonance.

Nevertheless, as they varied a disk’s temperature from less than 10K to 50K, the researchers always observed laser emission, although they needed to supply different amounts of energy to turn it on. At all temperatures, they say, some quantum dots have frequencies close enough to the disk’s resonance that laser action will happen. But at certain temperatures, the frequency of a single dot coincided exactly with the disk’s resonance, and laser emission then needed only the smallest stimulation. It’s not quite a single-dot laser, but it’s a case where one quantum dot effectively runs the show.

Citation: Z.G. Xie, S. Götzinger, W. Fang, H. Cao and G.S. Solomon. Influence of a single quantum dot state on the characteristics of a microdisk laser. Physical Review Letters, 98, 117401 (2007).

Source: NIST

Explore further: Bringing the chaos in light sources under control

Related Stories

Bringing the chaos in light sources under control

November 18, 2015

Noise is an issue in optical telecommunications. And findings means of controlling noise is key to physicists investigating light-emitting diodes or lasers. Now, an Italo-Iraqi team has worked on a particular type of light ...

Photons open the gateway for quantum networks

October 23, 2015

There is tremendous potential for new information technology based on light (photons). Photons (light particles) are very well suited for carrying information and quantum technology based on photons—called quantum photonics, ...

A resonator for electrons

October 13, 2015

Resonators are an important tool in physics. The curved mirrors inside the resonators usually focus light waves that act, for instance, on atoms. Physicists at ETH Zurich have now managed to build a resonator for electrons ...

Novel quantum dot laser paves the way for lower-cost photonics

March 3, 2014

With the explosive growth of bandwidth demand in telecommunications networks, experts are continually seeking new ways to transmit increasingly large amounts of data in the quickest and cheapest ways possible. Photonic devices—which ...

Recommended for you

Test racetrack dipole magnet produces record 16 tesla field

November 30, 2015

A new world record has been broken by the CERN magnet group when their racetrack test magnet produced a 16.2 tesla (16.2T) peak field – nearly twice that produced by the current LHC dipoles and the highest ever for a dipole ...

Turbulence in bacterial cultures

November 30, 2015

Turbulent flows surround us, from complex cloud formations to rapidly flowing rivers. Populations of motile bacteria in liquid media can also exhibit patterns of collective motion that resemble turbulent flows, provided the ...

CERN collides heavy nuclei at new record high energy

November 25, 2015

The world's most powerful accelerator, the 27 km long Large Hadron Collider (LHC) operating at CERN in Geneva established collisions between lead nuclei, this morning, at the highest energies ever. The LHC has been colliding ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.