Visible Light Goes through Miniature Cable

The discovery defies a key principle that holds that light cannot pass through a hole much smaller than its wavelength. In fact, the team forced visible light, which has a wavelength of between 380 to 750 nanometers, to travel down a cable whose diameter is smaller than even the low end of that range.

The advance builds upon the researchers' earlier invention of a microscopic antenna that captures visible light in much the same way radio antennae capture radio waves. This time, the physicists designed and fabricated a tiny version of the coaxial cable.

"Our coax works just like the one in your house, except now for visible light," says Jakub Rybczynski, a research scientist in the Boston College Physics Department and the lead author of the APL article.

Coaxial cables are typically made up of a core wire surrounded by a layer of insulation, which in turn is surrounded by another metal sheath. This structure encloses energy and lets the cable transmit electromagnetic signals with wavelengths much larger than the diameter of the cable itself.

With this design in mind, the physicists developed what they called a "nanocoax" – a carbon nanotube-based coaxial cable with a diameter of about 300 nanometers.

The physicists designed their nanocoax so that the center wire protruded at one end, forming a light antenna. The other end was blunt, allowing the scientists to measure 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.; Source: Boston College