A collection of mini-spectrometer chips are arrayed on a tray after being made through conventional chip-making processes. [Image from MIT]
Spectrometers distinguish different wavelengths of light and can be used to figure out the chemical composition of everything from laboratory materials to distant starts. The devices are typically large in size and price, with six-figure price tags, according to the researchers.
The MIT researchers suggest that the new approach to making spectrometers on a chip could give advantages in performance, size, weight and power consumption compared to spectrometers currently on the market.
There have been other attempts at making chip-based spectrometers, but the researchers say there is one main challenge. The device’s ability to spread light based on its wavelength is dependent on the size of the device.
“If you make it smaller, the performance degrades,” Juejun Hu, associate professor of materials science and engineering and one of the researchers on the project, said in a press release.
There is another type of spectrometer that uses a mathematical approach known as a Fourier transform. That device is also limited by its size. High-performance devices need a long, tunable optical path length, which has made miniaturized spectrometers, less efficient than bench top ones.
The MIT researched used a different method. Their system is based on optical switches that can flip a beam of light between different optical pathways, which can also be different lengths. The electronic optical switches eliminate the need to use movable mirrors and can easily made using standard chip-making technology.
“There’s a huge benefit in terms of robustness. You could drop it off the table without causing any damage,” Derek Kita, a doctoral student and researcher on the project, said.
Path lengths in power-of-two increments can be combined in a number of ways to copy an exponential number of discrete lenses which could then lead to a spectral resolution that increases with the number of on-chip optical switches. The researchers compare it to a balance scale that can measure a broad range of weights by combining a smaller number of standard weights.
The researchers built the device with an industry-standard semiconductor manufacturing service. The device had six sequential switches to produce 64 spectral channels. It also had built-in processing capability to control the device and process its output. Using this manufacturing method allowed to to expand to 10 switches, making the resolution rise to 1,024 channels. The device is developed as a plug-and-play unit that can be easily integrated with existing optical networks.
Machine-learning techniques also helped reconstruct detailed spear from a limited number of channels. The new MIT-developed method detected both broad and narrow spectral peaks.
The researchers suggest the new type of spectrometers could be used in sensing devices, material analysis systems, optical coherent tomography in medical imaging and monitoring the performance of optical networks.
“[This work] is a very interesting approach, as it enables realizing a high-resolution spectrometer on a small footprint. This new device enables applications such as on-chip spectroscopic sensors, which is a hot research topic,” Gunther Roelkens, a professor at Ghent University in Belgium, said. “The challenge for future research will be to extend the wavelength coverage while maintaining the same resolution. Also, addressing different wavelength bands will enable many new applications.”
The research was published in the journal Nature Communications and was supported by the National Science Foundation, MIT SENSE.nano, the U.S. Department of Energy and the Saks Kavanaugh Foundation.
