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Posted: August 2, 2007

Optical breakthrough makes Lab-on-a-Chip possible

(Nanowerk News) Georgia Tech researchers have found a way to shrink all the sensing power of sophisticated biosensors -- such as sensors that can detect trace amounts of a chemical in a water supply or a substance in your blood -- onto a single microchip.
This scanning electron microscopy image details a portion of the photonic crystal structure used for wavelength demutiplexing. A periodic array of holes with a 220 nanometer radius is etched through the top silicon layer of a silicon-on-insulator wafer. (Source: Georgia Tech)
"We believe we have developed the most compact WD that has been reported to date," said Ali Adibi, a professor in Georgia Tech's School of Electrical and Computer Engineering and the lead researcher on the project. "If you want to have many optical functions on a single micro- or nano-sized chip, you have to be able to practically integrate all those functions in the smallest amount of space possible. Our WD solves many problems associated with combining delicate optical functions in such a small space."
The Georgia Tech team was able to shrink its WD by combining into one crystal three unique properties of photonics crystals -- the superprism effect (separating wavelengths much more finely than a regular prism), negative diffraction or focusing (reversing the expansion of the light beam and focusing it back to its original size after interacting with the material being analyzed) and negative refraction (filtering wanted and unwanted wavelengths).
"This project really demonstrates the importance of dispersion engineering in photonic crystals -- and it's all done by changing the geometry of some holes you etch in the silicon. It's very simple and it allows you to combine properties into one material that you never could before," Adibi said.
Despite the more advanced capabilities of the photonic crystals used in Georgia Tech's WD, they are no more complex or difficult to manufacture than conventional photonic crystals, Adibi added.
The result is a WD that is less than a millimeter in all dimensions rather than the several centimeters of other currently available WDs. Furthermore, Georgia Tech's WD can be integrated for several other functionalities on a single chip for signal processing, communications, or sensing and lab on-a-chip applications.
Source: Georgia Tech
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