PORTLAND, Ore. A nanowire manufacturing
method has yielded 50-nm optical cables &3151; one-thousandth the thickness of a human hair by drawing a millimeter-sized silica wire across a sapphire
Since the nanowire's 50-nm diameter is as much as
one-third the size of the wavelength of light going through it, light spirals around the outside of the fiber (rather
than inside it) with minimal signal loss.
"This new method of manufacturing subwavelength-diameter silica wires, in concert with the research group's ongoing efforts in micromachining,
may lead to a further reduction of the size of optical and photonic devices," said Julie Chen, program director in National Science Foundation's Nanomanufacturing
program.Chen was referring to a Harvard University research group led by Eric Mazur and Limin
Tong (also of Zhejiang University in China), along with colleagues from Tohoku University in Japan.
The group reported improving upon previous attempts by others to stretch silicon into nanowire by wrapping it around a sapphire taper and holding it over a flame at 1,700 degrees C. The resulting 50-nm wire had a very smooth surface and uniform composition.
When connected to communications lasers with wavelengths as much as three times longer than the nanowires are thick, the nanowires carried light on the outside of the cable instead of inside. Like a linked-chain downspout that guides water along its outside, the nanowires appear to transport light similarly.
Subwavelength nanowires carry light by virtue of
evanescent waves that envelop the slender filament, incidentally enabling the beam to be diverted by merely touching it to another nanowire.
In tests, the silica material remained
atomically smooth and uniform in diameter, enabling the laser beam to remain coherent while being transmitted around the outside of the nanowires.
Mazur and Tong's wires were as long as 2 cm, giving them an aspect ratio of 1 to 40,000. The group also reported
that the nanowires were resilient and flexible, easily curling into sub-100 micron loops.
Communications using the nanowires could vastly reduce the space needed for optical cables. As is, the nanowire may be useable in implanted medical devices that use nanoscale lasers, for medical laser microsurgery and in ultra-sensitive single-molecule sensors to detect toxins before they reach harmful levels.
"Broader applications for short-pulse laser research include microsurgery such as laser-eye surgery and dermatology, and studies of neurons in microscopic nematodes," NSF's Chen said.