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Light propagation on a chip like shopping before christmas

Posted October 30, 2012

(a) Light traveling through the periodic medium. (b) Light becoming trapped inside the medium at the encircled area. Credit: University of Twente

High frequency electromagnetic waves such as light are quite hard to deal with, when trying to perfect light-based data or energy transmission/processing technologies. This is particularly obvious in nanoscale structures, like modern signal processing microchips or waveguides. Even the smallest internal structure disorder inside the waveguide results in so-called “light entrapment” effect.

It is important to measure the magnitude of these distortions of passing light, so that physicists would be able to determine the exact nature of imperfections in an integrated waveguides. So how scientists are able to accomplish this?

It turns out that light propagates in an integrated waveguide like people shopping on a busy day before Christmas. “Passing through a shopping street can be tedious, especially on a busy day just before Christmas. With a steady pace you can make it through in a reasonable time, but the slower you walk, the higher the chance that you are diverted by not-to-miss offers.” MESA+ researcher Pepijn Pinkse explains that this example illustrates what happens when light propagates in a nanostructure.

Under normal conditions the propagation of light is strongly affected by the periodic order of the nanostructure. Energy gaps emerge where light is not allowed to propagate as a result of interference. The boundary between an energy gap and energies where light can still propagate is called the band edge. Light near the band edge travels at a lower velocity. Slowly propagating light enhances the sensitivity of nanoscale sensors and is of interest for controlling optical information. However, even the smallest amount of disorder in a structure, which is fundamentally unavoidable, significantly alters the transport of light near the band edge. Up till now, it has been a major challenge to directly measure this effect.

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