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Intellect

‘Light pipes’ help BYU engineers use a microchip to detect gas vapors

A Brigham Young University professor and his research collaborators have created a portable laboratory the size of a microchip that uses light to detect gases.

Electrical engineering professor Aaron Hawkins, his student research assistants, and colleagues at the University of California-Santa Cruz achieved the advance by focusing light through special tubes tiny enough for use on the scarce silicon real estate. Light normally disperses in all directions from its source. But these "light pipes" are specially designed to focus intense beams of light on a small number of atoms inside.

The BYU team's light pipes have a leg up on more common light "waveguides" like fiber optics, which are solid. Their hollow waveguides can contain gases or fluids; therefore, they can use light to identify substances by the wavelengths of light they reflect, a process called atomic spectroscopy. All on a chip the size of a fingernail.

"We've taken what is typically done on a lab bench and tried to shrink all of that to a little chip," said Hawkins, who reported his findings in the new issue of the journal Nature Photonics. "You could use the optical phenomenon produced in a portable setting for a variety of applications."

Those applications - someday - could include sensors that alert users to dangerous gases or gauges to measure air quality. Other applications of this process include highly secure quantum communications and advances in atomic clocks, which are useful for global positioning satellite systems and cell phone networks.

Hawkins and UC-Santa Cruz professor Holger Schmidt have been working together on the application of these hollow waveguides to optical problems for about four years. Their work is funded by the Defense Advanced Research Projects Agency and the National Science Foundation.

"This is the first paper that shows how we can combine optical waveguiding and integrated optics with atomic spectroscopy -- nobody has done that before," Schmidt said. Speaking of his BYU collaborators, he added: "We have very complimentary skills and facilities. We've had a long track record of a very successful collaboration."

Hawkins was assisted by his graduate student Donald Conkey, who is a coauthor on the new paper, in the delicate maneuverings required to create the device at such a small size. They built the chip in BYU's dust-free "clean room," then faced the challenge posed by the nature of the gas that was to be tested inside. Rubidium vapor degrades when exposed to oxygen, which meant that it had to be inserted into the small and fragile chips inside a sealed container called a glove box.

"It was easy to conceive, but doing it was very difficult," Hawkins said. "Sticking rubidium, which is extremely reactive to water and oxygen, into tiny on-chip reservoirs and then getting it to fill up the open tubes was the hard part."

After the chip was built and rubidium successfully added, the device was sent to the team at UC-Santa Cruz for testing.

Looking forward, the research team is also collaborating on projects involving liquid in small waveguides, funded by the National Institutes of Health. This work is aimed at looking for viruses in biological fluids, which could lead to medical testing of blood and saliva. Results from these liquid-filled waveguides were recently published in Applied Physics Letters.

Hawkins summed up the contributions of the research team by noting they are fulfilling a common engineering goal - to take something useful and make it smaller.

"This approach brings what others are doing in the lab closer to mass production," he said. "We are taking cutting edge science and transitioning it into something we could conceivably see in a product."

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