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Destructive interference could enable new optical applications

Researchers at MIT say they have discovered a new way to trap light. Rather than use mirrors or photonic crystals, the MIT approach uses waves with the same wavelength, but exactly with opposite phases. While one particular frequency is trapped, light of all other wavelengths can pass freely.

"For many optical devices you want to build," says Professor Marin Soljacic, "including lasers, solar cells and fibre optics, you need a way to confine light." While this has most often been accomplished using mirrors of various kinds, in all cases the passage of light is blocked. MIT's new approach sees light of a particular wavelength blocked by destructive interference from other waves that are precisely out of phase. "It's a very different way of confining light," Prof Soljacic says.

Possible applications could include large area lasers and chemical or biological sensors.

The research team points out that, in mathematical terms, the new phenomenon — where one frequency of light is trapped while other nearby frequencies are not — is an example of an 'embedded eigenvalue'. This had been described as a theoretical possibility by computer pioneer John von Neumann in 1929. While physicists have since been interested in the possibility of such an effect, nobody had previously seen this phenomenon in practice, except for special cases involving symmetry.

Graham Pitcher

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MIT News Office

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