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Nanowires offer low-loss connection

17 Dec 2003

Super smooth silica nanowire could be the way to wire optical circuits of the future.

Low-loss silica nanowires that can guide light around tight corners have been fabricated by a team from the US, China and Japan. The researchers from Harvard University, Zhejiang University and Tohoku University say that their wires are promising for building future microphotonic devices. (Nature 426 816)

Eric Mazur’s group at Harvard transforms silica optical fiber into a nanowire by a two-stage drawing method. First a flame heated fiber is drawn into a 1 micron wide wire. This is then wound around a heated sapphire taper to create wires as small as 50 nm in diameter and up to several tens of millimeters long.

Although silica nanowires with diameters ranging from ten to several hundred nanometres have been made in the past by other methods, their optical performance has been limited. This is largely due to the roughness of the wires’ sidewalls and undesirable fluctuations in their width.

In contrast, the latest design of wire reported in this week’s Nature is very smooth and offers an optical loss of less than 0.1 dB/mm for either visible and infrared light.

They are also very strong and flexible. For example, the team has twisted them together and tied them into knots and a 280 nm wide wire was bent into a radius of 2.7 micron without breaking. Fracture tests show that wires have a typical tensile strength of 5.5 GPa.

As a result, the wires could be ideal for making low-loss tight bends on some kind of miniature optical circuit. Calculations suggest that a 450 nm diameter wire could route red light around a 90 deg bend (5 micron radius) with a bending loss of just 0.3 dB.

“The wire is very promising in many areas, where larger-width optical waveguides are currently used, such as microphotonic devices for optical communication and optical sensing,” explained Limin Tong who is currently working in Mazur’s group. “Our nanowires could lead to smaller device sizes and or higher performance.”

Oliver Graydon is editor of Optics.org and Opto & Laser Europe magazine.

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