New anti-laser tech paves way for optical computing

Yale University scientists have built what they call the first anti-laser, a device that can cancel out beams of light generated by a laser.

Such a device could be an integral element in optical computers, a long promised successor to today's computers that would use light instead of electrons to process information.

While scientists have long known of different ways to absorb light, this work is unique in that it can absorb light of a particular wavelength, the researchers claim.

"After some research, we found that several physicists had hinted at the concept in books and scientific papers, but no one had ever developed the idea," said Yale University physicist A. Douglas Stone, who along with fellow researcher Hui Cao led a team of researchers to build the anti-laser. The device was based on the theoretical work Stone published last summer. A summary of their work appears in the Feb. 18 issue of Science.

Lasers, short for Light Amplification by Stimulated Emission of Radiation, generate coherent light, which is to say a stream of light photons that all have the same frequency, amplitude and wave pattern.

The researchers built what they call a Coherent Perfect Absorber (CPA), a silicon wafer that traps and dissipates incoming coherent light of a predefined wavelength. In other words, just as a laser generates coherent light, the CPA absorbs coherent light. The light's energy is dissipated as heat.

Such an anti-laser switch could help solve one of the toughest challenges in building an optical computer, namely the management and manipulation of the light used to encode information. For instance, a CPA could be used in an optical switch, one that would absorb light of a particular wavelength while letting light with other wavelengths pass. It could also be used to detect incoming light, or as a waveguide to direct beams of light along certain routes.

That could lead to optical switches replacing transistors in future computers. Optical computers could potentially be much more powerful than today's computers, given that the size of components could be shrunk beyond the limits of today's electron-based technologies.

As with any prototype, the CPA has some limitations, which the researchers feel can be overcome with more work. The current CPA absorbs 99.4 of all light it receives, but they would like to get that number up to 99.999%. Also, the current CPA is one centimeter wide, which they say can be shrunk to a much more compact six microns.

Joab Jackson covers enterprise software and general technology breaking news for The IDG News Service. Follow Joab on Twitter at @Joab_Jackson. Joab's e-mail address is

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