EMERGING AND NANOTECHNOLOGIES
Nano-Sized Coaxial Cable Transmits Visible Light
To fabricate a nanosized coaxial cable researchers took a carbon nanotube (a), coated it with aluminum oxide (b), and then coated that with chromium (c).
Coaxial cables have been at the forefront of telecommunications applications for decades. Thanks to a team of researchers from Boston College (Chestnut Hill, MA; www.bc.edu), nano-sized versions of these common cables could soon be making electromagnetic waves in the medical device industry as well.
Coaxial cables are typically configured with one wire inside of another, separated by an insulator. Dubbed a nanocoax by the research team, their tiny cable is designed with the same configuration as the common coax, though scaled down 10,000 times. Measuring about 300 nm in diameter, the miniscule cable consists of an inner wire of a carbon nanotube and an outer wire of chromium, with aluminum oxide serving as an insulator.
“That configuration of one wire inside of another is well known for being very efficient in transmitting electromagnetic energy, electromagnetic waves,” says Michael Naughton, physics department chair at the college and one of the researchers involved in the project. “Light is just another part of the electromagnetic spectrum.”
Coaxial cables are recognized for their ability to transmit wavelengths significantly larger in size than their own diameter. Taking this into consideration, the researchers significantly scaled the cable down and disproved a common scientific principle that light could not pass through a hole much smaller than its wavelength, which typically measures between 300 and 800 nm, according to Naughton.
Naughton notes that light will, in fact, go in a traditional coax if a person takes a flashlight and shines it into the cable, for example. However, the light won’t travel very far. The nanocoax, on the other hand, was able to successfully transmit red and green light from one end to the other. This feat was made possible by a length of carbon nanotube protruding from one end of the cable that acts as a light antenna.
“Because it has all the properties of the familiar and conventional coax, it functions just like one. [Light] can’t go kilometers or even meters or millimeters, but it can go many tens of wavelengths down the pipe; I suspect it could even go 100 µm,” Naughton says. “We’re not going to run it between buildings, but for possible manipulation of light on the nanoscale, it’s a huge distance in order to do something functional.”
In addition to potential applications in solar power energy efficiency and optical computing, the nanocoax could have significant ramifications in the medical industry. Naughton suggests that the cable could be used in retinal implants for patients suffering from the eye disease macular degeneration or for detecting single molecules of pathogens in the body.
“It could be a significant improvement over anything that’s out there now, including implantable telescopes or other implantable devices that receive light from a camera and send electrical signals,” says Naughton. “No wires [would be necessary]; a little chip would function on its own.”
Naughton’s coinventors of the cable include BC faculty members Kris Kempa and Zhifeng Ren, as well as postdoctoral fellow Jakub Rybczynski. The researchers recently published their findings in the January 8, 2007, issue of the journal Applied Physics Letters.