  Integrated spectrometers hold great promise for in-situ, in vitro, and even
in vivo near-infrared (NIR) sensing applications. However, practical NIR
applications require fine resolution, high accuracy, and mostly importantly,
ultra-wide observation window that spans multiple overtone regions, for
capturing spectral fingerprints. In this paper, we present an integrated
reconstructive spectrometer utilizing dispersion-engineered ring resonators,
achieving an over 520 nm operational bandwidth together with a superior
resolution of less than 8 pm. This translates into an over 65,000
bandwidth-to-resolution ratio that represents a significant record breakthrough
for miniaturized spectrometers. Moreover, we showcase a packaged spectrometer
chip with auxiliary electronics, creating a fully functional NIR spectroscopic
sensor. Various bandwidth-demanding NIR sensing applications are examined,
including the classification of different types of solid substances and the
concentration test of aqueous and organic solutions, all achieving
approximately 100% accuracy. Specifically, we test the sensor's detection limit
using glucose solutions and successfully identify concentrations as low as 0.1%
(i.e. 100 mg/dL), which matches that of the commercial benchtop counterparts
and sets up a new benchmark for miniaturized spectroscopic sensors.
