  Sensing platforms based upon photonic integrated circuits have shown
considerable promise; however, they require corresponding advancements in
integrated optical readout technologies. Here, we present an on-chip
spectrometer that leverages an integrated thin-film lithium niobate modulator
to produce a frequency-agile electro-optic frequency comb for interrogating
chip-scale temperature and acceleration sensors. The chirped comb process
allows for ultralow radiofrequency drive voltages, which are as much as seven
orders of magnitude less than the lowest found in the literature and are
generated using a chip-scale, microcontroller-driven direct digital
synthesizer. The on-chip comb spectrometer is able to simultaneously
interrogate both an on-chip temperature sensor and an off-chip, microfabricated
optomechanical accelerometer with cutting-edge sensitivities of $\approx 5\
{\mu} \mathrm{K} \cdot \mathrm{Hz}^{-1/2}$ and $\approx 130\ \mu \mathrm{m}
\cdot \mathrm{s}^{-2} \cdot \mathrm{Hz}^{-1/2}$, respectively. This platform is
compatible with a broad range of existing photonic integrated circuit
technologies, where its combination of frequency agility and ultralow
radiofrequency power requirements are expected to have applications in fields
such as quantum science and optical computing.
