On-chip spectral sensor for everyday applications

April 05, 2019 //By Rich Pell
On-chip spectral sensor for everyday applications
Engineers at the University of Wisconsin-Madison have developed a spectrometer - an instrument used to separate and measure spectral (light) components of a substance or object - that is so small that they say it could be integrated with the camera of a typical smartphone without sacrificing accuracy.

Often used to detect dangerous chemicals based on a unique "fingerprint" of absorbed and emitted light, spectrometers have traditionally been both bulky and expensive, preventing their use outside the lab. Now, say the researchers, their miniaturized on-chip spectrometer has significant potential for portable applications such as consumer electronics, health care, and manufacturing.

"This is a compact, single-shot spectrometer that offers high resolution with low fabrication costs," says Zhu Wang, one of the electrical engineers that created the device.

The device uses arrays of photodetectors, each of which has a unique responsivity with rich spectral features. The spectrometer is completely complementary metal–oxide–semiconductor (CMOS) compatible and can be mass produced at low cost.

The spectrometer measures just 200 micrometers on each side (roughly one-20th the area of a ballpoint pen tip), and say the researchers, is delicate enough to lie directly on a sensor from a typical digital camera. To achieve the small size, the researchers based their device on specially designed materials that forced incoming light to bounce back and forth several times before reaching the sensor - elongating the path along which light traveled without adding bulk, and boosting the device's resolution.

The device is also capable of hyperspectral imaging, which collects information about each individual pixel in an image in order to identify materials or detect specific objects amidst a complicated background. Hyperspectral sensing, for example, could be used to detect seams of valuable minerals within rock faces or to identify specific plants in a highly vegetated area.

Looking ahead, the researchers hope to boost the device's spectral resolution as well as the clarity and crispness of the images it captures, potentially paving the way for even more enhanced sensors. For more, see " Single-shot on-chip spectral sensors based on photonic crystal slabs ."

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