Spectrometry: Miniaturising near-infrared devices

The development of compact, handheld devices to measure spectra in the near-infrared (NIR) wavelength range would have a wide range of applications, including medical diagnostics and self-monitoring of blood glucose levels.

Many spectrometers are designed with gratings incorporated - this allows the device to detect different wavelengths of incident light separately and provides a more detailed sample analysis. However, grating-based micro-spectrometers require an optical path of a certain length to ensure good resolution, therefore placing limitations on shrinking the size of the device.

Now, Tetsuo Kan at the University of Electro-Communications in Tokyo and co-workers have developed a micro-spectrometer capable of detecting NIR spectra using a Schottky photodetector and a gold-based grating, the combination of which means a lengthy optical path is unnecessary.

Their design makes use of the phenomenon known as 'surface plasmon resonance' (SPR) - the oscillation of electrons on a surface where negative and positive permittivity materials meet, following stimulation by incident light. The team placed the gold grating directly onto the surface of a photodetector made from a silicon substrate (see image). The photodetector uses the resulting SPR created on the surface of the gold to generate a photocurrent.

When different wavelengths of light hit the device, the angle of the SPR changes. By converting the different photocurrents back into their corresponding light wavelengths, the team could differentiate between different wavelengths of light at high resolution. The new micro-spectrometer performed comparably to a commercial spectrometer when tested with NIR light. Crucially, the design is also compatible with semiconductor fabrication.

Reference

Chen, W., Kan, T., Ajiki, Y., Matsumoto, K., & Shimoyama, I. NIR spectrometer using a Schottky photodetector enhanced by grating-based SPR. Optics Express 24 (22) (2016) doi: 10.1364/OE.24.025797

Associate Professor:

Tetsuo, KAN (Ph.D. from the University of Tokyo 2006/03)

Current research areas:

MEMS(Micro Electro Mechanical Systems)

Current research subjects:

Plasmonic and metamaterial MEMS devices

Personal website

http://www.ms.mi.uec.ac.jp/