The chemical composition of an array of materials is commonly determined by spectrometers, large expensive devices that identify different wavelengths of light. Miniature spectrometers that are just as accurate but less costly might be realized with new chip technology developed at MIT.
Past efforts to design chip-based spectrometers have encountered a size constraint, as an instrument’s ability to spread out light based on wavelength and conventional optics is dependent on the device’s size. Performance degrades with diminishing size of the equipment. Inferior performance also marks spectrometers based on the Fourier transform approach.
The MIT design eliminates moving parts and is based on optical switches, which can instantly flip a beam of 
The fully packaged, plug-and-play digital Fourier transform instrument. Source: MITlight between different optical pathways that can be of different lengths. The electronic optical switches obviate the need for movable mirrors, which are required in current instruments, and can easily be fabricated using standard chip-making technology.
Path lengths in power-of-two increments are used and can be combined in different ways to replicate an exponential number of discrete lengths and result in a potential spectral resolution that increases exponentially with the number of on-chip optical switches.
An industry-standard semiconductor manufacturing service was contracted to build a device with six sequential switches, producing 64 spectral channels, with built-in processing capability to control the device and process its output. By expanding to 10 switches, the resolution would jump to 1,024 channels. The tool was designed as a plug-and-play unit that could be easily integrated with existing optical networks.
New machine-learning techniques were also applied to reconstruct detailed spectra from a limited number of channels. The method works well to detect both broad and narrow spectral peaks, and system performance was shown to match calculations.
Potential applications in sensing devices, materials analysis systems, optical coherent tomography in medical imaging and monitoring the performance of optical networks are identified. The new approach to making spectrometers on a chip could provide major advantages in performance, size, weight and power consumption, compared to current instruments.
The research is published in Nature Communications.
