Breakthrough: World's smallest photon in a dielectric material
Until recently, it was widely believed among physicists that it was impossible to compress light below the so-called diffraction limit, except when using metal nanoparticles, which unfortunately also absorb light. It therefore seemed impossible to compress light strongly in dielectric materials such as silicon, which are key materials in information technologies and come with the important advantage that they do not absorb light. Interestingly, it was shown theoretically already in 2006 that the diffraction limit also does not apply to dielectrics. Still, no one has succeeded in showing this in the real world, simply because it requires such advanced nanotechnology that no one has been able to build the necessary dielectric nanostructures until now.
A research team from DTU has successfully designed and built a structure, a so-called dielectric nanocavity, which concentrates light in a volume 12 times below the diffraction limit. The result is ground-breaking in optical research and has just been published in Nature Communications.
“Although computer calculations show that you can concentrate light at an infinitely small point, this only applies in theory. The actual results are limited by how small details can be made, for example, on a microchip,” says Marcus Albrechtsen, PhD-student at DTU Electro and first author of the new article.
“We programmed our knowledge of real photonic nanotechnology and its current limitations into a computer. Then we asked the computer to find a pattern that collects the photons in an unprecedentedly small area — in an optical nanocavity — which we were also able to build in the laboratory.”
Optical nanocavities are structures specially designed to retain light so that it does not propagate as we are used to but is thrown back and forth as if you put two mirrors facing each other. The closer you place the mirrors to each other, the more intense the light between the mirrors becomes. For this experiment, the researchers have designed a so-called bowtie structure, which is particularly effective at squeezing the photons together due to its special shape.
Interdisciplinary efforts and excellent methods
The nanocavity is made of silicon, the dielectric material on which most advanced modern technology is based. The material for the nanocavity was developed in cleanroom laboratories at DTU, and the patterns on which the cavity is based are optimized and designed using a unique method for topology optimization developed at DTU. Initially developed to design bridges and aircraft wings, it is now also used for nanophotonic structures. More