Ultra‐Broadband Spectral Reconstruction Using Cooperative Tuning in a Dual‐Resonator Chip‐Scale Spectrometer

ABSTRACT This work presents a high‐performance on‐chip reconstructive spectrometer with an ultrabroad bandwidth, realized using a co‐designed dual‐resonator structure comprising an optimized radius microdisk resonator (MDR) and a compact double‐spiral (DS) waveguide. The closely spaced waveguides in the DS structure induce frequent evanescent coupling, leading to pronounced phase mismatch that significantly differentiates the signature patterns associated with distinct wavelength components. Furthermore, the excitation of bidirectional propagation modes effectively extends the optical path length, further enhancing spectral distinguishability. The use of an optimized radius MDR considerably improves thermal tuning efficiency and mitigates the limitation imposed by the low thermo–optic coefficient of the silicon nitride () platform, enabling low‐power operation without compromising performance. The resulting spectrometer achieves a spectral resolution of 0.08 nm across a 150 nm bandwidth within a compact footprint, representing a notable advance in high‐performance on‐chip spectroscopic sensing.