Tiny optical cable comes to light

Physicists at BostonCollege have beamed visible light through the narrowest nanoscopic cable to date, an achievement they anticipate will lead to advances in solar power and optical computing.

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

The researchers said their achievement opens 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. It could even be used to help some blind people see.

The advance builds upon the researchers’ 2004 invention of a microscopic antenna that captures visible light in much the same way radio antennae capture radio. This time they have designed and fabricated a tiny version of a coaxial cable.

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.

The physicists developed what they called a ‘nanocoax,’ a carbon nanotube-based coaxial cable with a diameter of about 300 nanometres.

They designed it so that the centre wire protruded at one end, forming a light antenna. The other end was blunt, allowing them to measure the light received by the antenna and transmitted through the medium.

They 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.