  Miniaturized on-chip spectrometers with small footprints, lightweight, and
low cost are in great demand for portable optical sensing, lab-on-chip systems,
and so on. Such miniaturized spectrometers are usually based on engineered
spectral response units and then reconstruct unknown spectra with algorithms.
However, due to the limited footprints of computational on-chip spectrometers,
the recovered spectral resolution is limited by the number of integrated
spectral response units/filters. Thus, it is challenging to improve the
spectral resolution without increasing the number of used filters. Here we
present a computational on-chip spectrometer using electrochromic filters that
can be electrochemically modulated to increase the efficient sampling number
for higher spectral resolution. These filters are directly integrated on top of
the photodetector pixels, and the spectral modulation of the filters results
from redox reactions during the dual injection of ions and electrons into the
electrochromic material. We experimentally demonstrate that the spectral
resolution of the proposed spectrometer can be effectively improved as the
number of applied voltages increases. The average difference of the peak
wavelengths between the reconstructed and the reference spectra decreases from
14.48 nm to 2.57 nm. We also demonstrate the proposed spectrometer can be
worked with only four or two filter units, assisted by electrochromic
modulation. This strategy suggests a new way to enhance the performance of
miniaturized spectrometers with tunable spectral filters for high resolution,
low-cost, and portable spectral sensing, and would also inspire the exploration
of other stimulus responses such as photochromic and force-chromic, etc, on
computational spectrometers.
