Harvard Researchers Create High Performance Optical Nanowires
Jordan Richman, 2/25/04
Using a $20 Bunsen burner and some silica optical fiber (little pieces of glass), Dr. Limin Tong, a visiting professor at Harvard from China, describes in a recent paper published in the December 18 issue of the journal Nature, how he was able to make a 50 nanometer, high performance light transmitting nanowire. First he heats the fiber and draws it out to a 1 micron wide wire. He then winds the wire around a the tip of a heated sapphire needle. Since sapphire is such a good conductor of heat, its heat softens the glass fiber evenly as Dr. Tong draws out the fiber down the shaft of the sapphire needle.
"If you pull fast, it is very thin," said Dr. Tong. He found that if he pulled more slowly he could produce a thicker wire.
Dr. Eric Mazur who led the Harvard optical nanowire research team pointed out that while much thinner nanowires have been produced in the past by other scientists none of them had the even diameters or smoothness exhibited by Dr. Tong's nanowires. The sidewall of the earlier wires were rough and there were unwanted variations in their width. The wires produced by Tong and Mazur are very smooth and offer much less optical loss for either visible and infrared light.
"These wires show surface smoothness at the atomic level, along with uniformity of diameter," Dr. Mazur said.
Even though Tong's and Mazur's optical nanowires are much thinner than even the wavelengths of their transported light, they are still able to guide a light beam with a high degree of accuracy and a minimum of optical signal loss. When light passes through a conventional fiber optic it flows through it like water in a garden hose. Nanowires do not hold the light. They act instead like guide rails for light waves which are much wider than the nanowires. The light surrounds the tiny nanowire as evanescent waves. "Evanescent coupling" occurs when two of the wires touch. Unlike fiber optics where the light is fixed within the filament, coupling causes an exchange of light waves when two of the wires touch. Larger evanescent fields can be produced by varying combinations of nanowires which may applied for the production of smaller and more effective sensor technology. For many sensor devices, especially in medicine, size is of critical importance. Sensors could detect many toxins, for example, at once and with greater precision and accuracy with these new smaller diameter nanowires packed into the same area of a sensor.
Despite their width of only 50 nanometers, these new nanowires are still barely visible since they have a 2 centimeter length. They are able to curl into tiny light conducting loops with remarkable tensile strength. They are as much as five times stronger than spider silk. Their resiliency and flexibility, along with their beadlike structure, have been cited as qualities that may make them play a role in the manufacture of new electronic chips that use on and off optical signals. Reducing the size of the nanowires diameter to less than 50 nanometers probably would not increase their effectiveness in transporting light waves, but the flexibility of Tong/Mazur nanowires introduces many new options in modern electronic engineering. The nanowires can be tied into tiny knots making the alignment of optical components much easier to accomplish.
"It's like the old TV's, where we used to have flexible wires to go from one board to another, " said Dr. Richard Osgood, a professor of electrical engineering and applied physics at Columbia University. "You don't have to get everything exactly aligned to close things."
Dr. Mazur points out that these nanowires are not the same as conventional fiber optic cables that circumnavigate the globe but could be used for distances that range at about an inch. They would be useful for devices that use fiber optics and light signals as low-loss interfaces which would provide further compact design and speed for those processors. Fiber optic cables, which are about the size of a human hair, combine phone messages and then have to separate them. The combiners are called multiplexers and the signal separators are demultiplexers. The new nanowires may one day become part of these processing modes in telecommunications.
End
Notes for Amy Perry
1) Tong, Mazur, and Osgood quotes are all from the NYT's clipping you sent. There is an inked in date at the bottom of the clipping: NYT G8 1/29/04 and the authors E-mail: Eisenberg:nytimes.com (Anne Eisenberg)
For the lead illustration I recommend the one showing Tong's fabrication of his nanowire using the sapphire taper and Bunsen burner since it is not the smallness of the width that was his innovation but the refinement of the nanowires smoothness of surface and and even diameter that he accomplished with his Bunsen burner and sapphire needle.
Showing the nanowire on top of a human hair and the nanowire tied as a knot making a loop are other illustrations that could be used.
Jordan Richman, 2/25/04
Using a $20 Bunsen burner and some silica optical fiber (little pieces of glass), Dr. Limin Tong, a visiting professor at Harvard from China, describes in a recent paper published in the December 18 issue of the journal Nature, how he was able to make a 50 nanometer, high performance light transmitting nanowire. First he heats the fiber and draws it out to a 1 micron wide wire. He then winds the wire around a the tip of a heated sapphire needle. Since sapphire is such a good conductor of heat, its heat softens the glass fiber evenly as Dr. Tong draws out the fiber down the shaft of the sapphire needle.
"If you pull fast, it is very thin," said Dr. Tong. He found that if he pulled more slowly he could produce a thicker wire.
Dr. Eric Mazur who led the Harvard optical nanowire research team pointed out that while much thinner nanowires have been produced in the past by other scientists none of them had the even diameters or smoothness exhibited by Dr. Tong's nanowires. The sidewall of the earlier wires were rough and there were unwanted variations in their width. The wires produced by Tong and Mazur are very smooth and offer much less optical loss for either visible and infrared light.
"These wires show surface smoothness at the atomic level, along with uniformity of diameter," Dr. Mazur said.
Even though Tong's and Mazur's optical nanowires are much thinner than even the wavelengths of their transported light, they are still able to guide a light beam with a high degree of accuracy and a minimum of optical signal loss. When light passes through a conventional fiber optic it flows through it like water in a garden hose. Nanowires do not hold the light. They act instead like guide rails for light waves which are much wider than the nanowires. The light surrounds the tiny nanowire as evanescent waves. "Evanescent coupling" occurs when two of the wires touch. Unlike fiber optics where the light is fixed within the filament, coupling causes an exchange of light waves when two of the wires touch. Larger evanescent fields can be produced by varying combinations of nanowires which may applied for the production of smaller and more effective sensor technology. For many sensor devices, especially in medicine, size is of critical importance. Sensors could detect many toxins, for example, at once and with greater precision and accuracy with these new smaller diameter nanowires packed into the same area of a sensor.
Despite their width of only 50 nanometers, these new nanowires are still barely visible since they have a 2 centimeter length. They are able to curl into tiny light conducting loops with remarkable tensile strength. They are as much as five times stronger than spider silk. Their resiliency and flexibility, along with their beadlike structure, have been cited as qualities that may make them play a role in the manufacture of new electronic chips that use on and off optical signals. Reducing the size of the nanowires diameter to less than 50 nanometers probably would not increase their effectiveness in transporting light waves, but the flexibility of Tong/Mazur nanowires introduces many new options in modern electronic engineering. The nanowires can be tied into tiny knots making the alignment of optical components much easier to accomplish.
"It's like the old TV's, where we used to have flexible wires to go from one board to another, " said Dr. Richard Osgood, a professor of electrical engineering and applied physics at Columbia University. "You don't have to get everything exactly aligned to close things."
Dr. Mazur points out that these nanowires are not the same as conventional fiber optic cables that circumnavigate the globe but could be used for distances that range at about an inch. They would be useful for devices that use fiber optics and light signals as low-loss interfaces which would provide further compact design and speed for those processors. Fiber optic cables, which are about the size of a human hair, combine phone messages and then have to separate them. The combiners are called multiplexers and the signal separators are demultiplexers. The new nanowires may one day become part of these processing modes in telecommunications.
End
Notes for Amy Perry
1) Tong, Mazur, and Osgood quotes are all from the NYT's clipping you sent. There is an inked in date at the bottom of the clipping: NYT G8 1/29/04 and the authors E-mail: Eisenberg:nytimes.com (Anne Eisenberg)
For the lead illustration I recommend the one showing Tong's fabrication of his nanowire using the sapphire taper and Bunsen burner since it is not the smallness of the width that was his innovation but the refinement of the nanowires smoothness of surface and and even diameter that he accomplished with his Bunsen burner and sapphire needle.
Showing the nanowire on top of a human hair and the nanowire tied as a knot making a loop are other illustrations that could be used.
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