Engineers at UC Davis have developed a tiny "spectrometer on a chip" that could miniaturize devices for medical, agricultural and environmental sensing with visible and infrared light. 

A spectrometer analyzes chemical mixtures based on the spectrum of light (including infrared light) they reflect. Spectral sensing can be used, for example, to diagnose disease, assess the health of crops in a field, or measure soil quality. 

Conventional spectrometers use gratings or prisms to separate light into its wavelengths, making them inherently bulky. Another approach is to use electronic sensors to detect different wavelengths directly. 

The team led by Professor Saif Islam in the UC Davis Department of Electrical and Computer Engineering has now developed a spectrometer chip less than half a square millimeter in size. 

"We wanted to take this power [of a spectrometer] out of the lab and put it in your pocket," said postdoctoral scientist Ahasan Ahamed, first author of the paper about the work published in Advanced Photonics. 

The new chip uses sixteen silicon photodetectors, each sensitive to a different wavelength of light. The detectors are treated to make them sensitive to near-infrared wavelengths. The detectors are integrated with a neural network that compares the light with thousands of examples to analyze samples. 

"We are paving the way for a future where your watch or phone doesn’t just take pictures [but] analyzes the chemistry of the world around you," Islam said.