Quantum Hard Drive

Telecommunications Wavelength Quantum Dot Laser Grown On Silicon

A new generation of high speed, silicon-based information technology has been brought a step closer by researchers in the Department of Electronic and Electrical Engineering at UCL and the London Centre for Nanotechnology.

The team's research, published in Nature Photonics journal, provides the first demonstration of an electrically driven, quantum dot laser grown directly on a silicon substrate (Si) with a wavelength (1300-nm) suitable for use in telecommunications.

Silicon is the most widely used material for the fabrication of active devices in electronics. However, the nature of its atomic structure makes it extremely hard to realise an efficient light source in this material.

As the speed and complexity of silicon electronics increases, it is becoming harder to interconnect large information processing systems using conventional copper electrical interconnects. For this reason the field of silicon photonics (the development of optical interconnects for use with silicon electronics) is becoming increasingly important.

The ideal light source for silicon photonics would be a semiconductor laser, for high efficiency, direct interfacing with silicon drive electronics and high-speed data modulation capability. To date, the most promising approach to a light source for silicon photonics has been the use of wafer bonding to join compound semiconductor laser materials from which lasers can be made to a silicon substrate.

Direct growth of compound semiconductor laser material on silicon would be an attractive route to full integration for silicon photonics. However, the large differences in crystal lattice constant between silicon and compound semiconductors cause dislocations in the crystal structure that result in low efficiency and short operating lifetime for semiconductor lasers.

The UCL group has overcome these difficulties by developing special layers which prevent these dislocations from reaching the laser layer together with a quantum dot laser gain layer. This has enabled them to demonstrate an electrically pumped 1,300 nm wavelength laser by direct epitaxial growth on silicon. In a recent paper in Optics Express (Vol. 19 Issue 12, pp.11381-11386 (2011)) they report an optical output power of over 15 mW per facet at room temperature.

In related work the group, working with device fabrication colleagues at the EPSRC National Centre for III-V Technologies, have demonstrated the first quantum dot laser on a germanium (Ge) substrate by direct epitaxial growth. The laser, reported in Nature Photonics, (DOI: 10.1038/NPHOTON.2011.120, 12 June 2011) is capable of continuous operation at temperatures up to 70 deg. C and has a continuous output power of over 25 mW per facet.

What The Heck is A Quantum Hard Drive? » Geeky Gadgets

Before we explain the socks out of this emerging new technology allow us a moment’s digression for a short message. The short message is “Warning: Prolific use of the word quantum is sprinkled among the sentences below.”

It all begins with the so far too-difficult-to-define quantum information, which the California Institute of Technology has found a way to transmit via quantum hard drives. The value of this breakthrough is it can overhaul optical based data storage that’s still in vogue among hard drives today.

For extra meat, here are a few technical chunks lifted from the original text:

“…the concept could be applied to more parallel transfers in future quantum drivess, with the number being virtually unlimited. The concept is based on electromagnetic transparency that absorbs four quantum channels and slows down the light to zero for storage.

Lasers were used to cool the four quantum memories, each made up of one million cesium atoms that are magnetically separated by one millimeter. The technique was first achieved by Caltech five years ago, but was limited to two ensembles. The Institute has now applied it theoretically to unlimited nodes and made a computer possible.”

For a more comprehensive review of this new field, we suggest a hearty perusal of the source article, itself only a click away. Enjoy!

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