Chinese scholars and overseas collaborators have made progress in the research of on-chip ultra-miniature spectrometers

Figure Research on ultra-miniature electrical tuning spectrometer: (a) schematic diagram of the device and band structure of the ultra-miniature spectrometer; (b) Study on the delocalization of heavy metal atoms to enhance the interlayer exciton light absorption; (c) Infrared photoelectric response characteristics of devices with adjustable electric field; (d) The working principle and mechanism of the spectrometer; (e) Single-pixel scanning active imaging photographs; (f) Reconstructed spectral information for the position of point A at (e) and comparison with conventional spectrometer measurements

With the support of the National Natural Science Foundation of China (grant number: 61922005, U1930105), Professor Zhang Yongzhe's team at Beijing University of Technology and Professor Duan Pinfeng's team at UCLA jointly researched and made progress
in the research of ultra-miniature spectrometers on a chip 。 The research results were published in Nature Communications under the title "Electrically tunable two-dimensional heterojunctions for miniaturized near-infrared spectrometers.
" Links to papers: https://doi.
org/10.
1038/s41467-022-32306-z
.

Spectrometer is one of the basic instruments and equipment for scientific research and industrial production in modern society, which can identify and analyze
substances through spectral measurement.
The spectroscopic instruments currently in use are usually used in many industries
by a mechanical unit to achieve frequency spectroscopic function, and then use detector devices for intensity measurement, and finally achieve spectral measurement in the form of interconnection.
However, under such a modular combination working mechanism, the entire system often has problems such as large size, heavy weight and high cost, and cannot realize the growing demand
for in-situ, handheld, and on-chip integrated spectral measurement.
Therefore, the development of new miniaturized spectrometers has become a research direction
that urgently needs breakthroughs in the field.

In response to these current conditions and problems, the joint team developed an ultra-miniature electrical tuning on-chip near-infrared spectrometer with a feature size of less than 10 μm (Figure A).

The spectral measurement function is realized only by a single electrically tunable van der Waals heterojunction photodetector
.
The researchers exemplarily selected ReS 2/_{WSe 2} heterojunctions with near-infrared band response for development and demonstration
.
The van der Waals heterojunction is a Type II.
band structure with interlayer exciton transition tunability
.
In view of the difficulty in converting and extracting optical response signals caused by the spatial separation and low overlap of the interlayer exciton wave function, the researchers proposed a new idea of delocalization of heavy metal atoms to enhance the transition dipole moment of interlayer excitons, and then increased the light absorption capacity based on interlayer excitons by nearly 2 times (Figure B).

Through the combination of theory and experiment, the regulation of exciton transition energy between van der Waals heterojunctions was studied, and the infrared response characteristics (1.
15~1.
47 μm) with adjustable response cut-off wavelength of the device were realized (Figure C).

Combined with the electrically tunable infrared response characteristics of the device, the team proposed the working principle of the device for spectrometer (Figure D), and used the mathematical idea of regression reconstruction to realize the demonstration of spectral measurement and imaging in the near-infrared band, and the reconstructed spectral information was highly consistent with the results measured by traditional commercial benchtop spectrometers (Figures e and F).

The research results of this project provide a potential solution for
the miniaturization of spectrometers.