Tiny sensor could turn a smartphone into a spectrometer

Researchers have demonstrated a spectrometer that is orders of magnitude smaller than current technologies and can accurately measure wavelengths of light from ultraviolet to the near-infrared. The technology makes it possible to create hand-held spectroscopy devices and holds promise for the development of devices that incorporate an array of the new sensors to serve as next-generation imaging spectrometers.

“Spectrometers are critical tools for helping us understand the chemical and physical properties of various materials based on how light changes when it interacts with those materials,” said Brendan O’Connor, corresponding author of a paper on the work, and a professor of mechanical and aerospace engineering at North Carolina State University. “They are used in applications that range from manufacturing to biomedical diagnostics. However, the smallest spectrometers on the market are still fairly bulky. We’ve created a spectrometer that operates quickly, at low voltage, and that is sensitive to a wide spectrum of light,” O’Connor said.

“Our demonstration prototype is only a few square millimetres in size — it could fit on your phone. You could make it as small as a pixel, if you wanted to.”

The technology makes use of a tiny photodetector capable of sensing wavelengths of light after the light interacts with a target material. By applying different voltages to the photodetector, you can manipulate which wavelengths of light the photodetector is most sensitive to.

“If you rapidly apply a range of voltages to the photodetector, and measure all of the wavelengths of light being captured at each voltage, you have enough data that a simple computational program can recreate an accurate signature of the light that is passing through or reflecting off of the target material,” O’Connor said. “The range of voltages is less than one volt, and the entire process can take place in less than a millisecond.”

Previous attempts to create miniaturised photodetectors have relied on complex optics, used high voltages, or have not been as sensitive to such a broad range of wavelengths.

In proof-of-concept testing, the researchers found their pixel-sized spectrometer was as accurate as a conventional spectrometer and had sensitivity comparable to commercial photodetection devices.

“In the long term, our goal is to bring spectrometers to the consumer market,” O’Connor said. “The size and energy demand of the technology make it feasible to incorporate into a smartphone, and we think this makes some exciting applications possible. From a research standpoint, this also paves the way for improved access to imaging spectroscopy, microscopic spectroscopy and other applications that would be useful in the lab.”

The research findings have been published in the journal Device.

Image credit: Brendan O'Connor, NC State University.