Photonic crystals pave way for lab-onna-chip

Clever stuff

Researchers at Georgia Tech have made a breakthrough in optical technology by shrinking a key sensor component to less than a millimetre in all directions.

The work paves the way for integrating sophisticated bio-sensors onto so-called lab-on-a-chip devices that could be used for roadside drugs testing, on the spot environmental testing, running blood tests in remote areas, and so on.

The breakthrough has been to shrink a device called a wavelength demultiplier (WD) by radically redesigning photonic crystals. These are highly periodic structures etched in silicon that allow extremely fine control of light.

When space is an issue, as it can be in compact communications, signal processing, optical sensors, and multiple wavelengths of light are combined. To get the information back out, they need to be separated when they reach their destinations, the researchers explain. This is where the WD comes in: it sorts the various signals out at the end.

By redrawing the mask for the photonic crystal, the team has been able to combine three functions: superprisming, focusing, and filtering. The design also eliminates problems of wavelength interference, which means that although the crystal is tiny, it will work at very high resolutions - between 64 and 100 microns.

Ali Adibi, a professor in Georgia Tech's School of Electrical and Computer Engineering and the lead researcher on the project, says the design eliminates many of the problems associated with "combining delicate optical functions in such a small space".

"This project really demonstrates the importance of dispersion engineering in photonic crystals. 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."

The new design should not be any more expensive or difficult to manufacture, Adibi said. ®

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