Light Transmitted Through Nanocable

Boston College scientists (L-R) Krzysztof Kempa, Michael Naughton, Jakub Rybczynski and Zhifeng Ren have transmitted visible light through a "nanocoax" cable they developed that is hundreds of times thinner than a human hair [photo courtsey: Boston College]

A team of scientists from Boston College have created the first nanoscale coaxial cables that can transmit visible light. Operating much like the coaxial cables used to distribute television and radio signals, these cables can transmit light with wavelengths nearly 4 times their 200 nm diameter. This discovery defies a key principle that says light cannot pass through a hole much smaller than its wavelength.

This achievement is built upon thir earlier (year 2004) invention of a microscopic antenna that captures visible light in much the same way radio antennae capture radio waves. This time they developed a "nanocoax" -- a carbon nanotube-based coaxial cable with a diameter of about 300 nm (a human hair is several hunderd times wider). The nanocoax is designed in a way such that the center wire protruded at one end, forming a light antenna. The other end was blunt, allowing measurement of the light received by the antenna and transmitted through the medium. The researchers were able to transmit both red and green light into the nanocoax and out the other end, indicating that the cable can carry a broad spectrum of visible light.

Their coaxial cable is based around a carbon nanotube, which forms the central conductor and is surrounded by a concentric ring of transparent aluminium oxide -- which acts as the dielectric layer – and finally a concentric conducting metal ring that acts as the outer conductor. This structure is able to enclose energy and let the cable transmit electromagnetic signals with wavelengths much larger than the diameter of the cable itself.

The researchers claim that the ability to control light over sub-wavelength distances could lead to better optical microscopes, smaller computer chips and more efficient solar panels. It may open the door to a wide array of new technologies, from high-efficiency, inexpensive solar cells to microscopic light-based switching devices for use in optical computing. The technology could even be used to help some blind people see through the creation of artificial retinas.

Reference: "Subwavelength waveguide for visible light",
Appl. Phys. Lett. 90, 021104 (January 8th issue, 2007) Link to Abstract
Authors: J. Rybczynski, K. Kempa, A. Herczynski, Y. Wang, M. J. Naughton, and Z. F. Ren of Dept of Physics, Boston College, MA; Z. P. Huang and D. Cai of NanoLab Inc., Newton, MA; M. Giersig of Center of Advanced European Studies and Research (CAESAR), Bonn, Germany.