Researchers have successfully 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," says 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 says. "Our demonstration prototype is only a few square millimeters 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 says. "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 miniaturized 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 says. "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 paper, "Single pixel spectrometer based on a bias-tunable tandem organic photodetector," is published in the journal Device. First author of the paper is Harry Schrickx, a former Ph.D. student at NC State. The paper was co-authored by Abdullah Al Shafe, a former Ph.D. student at NC State; Caleb Moore, a former undergraduate at NC State; Yusen Pei, a Ph.D. student at NC State; Franky So, the Walter and Ida Freeman Distinguished Professor of Materials Science and Engineering at NC State; and Michael Kudenov, the John and Catherine Amein Family Distinguished Professor of Electrical and Computer Engineering at NC State.
The work was done with support from the National Science Foundation under grants 1809753 and 2324190, and from the Office of Naval Research under grant N000142412101.
