An efficient mid-infrared computational spectrometer based on synergistic microcavity-coupled photonic crystal waveguides.

The mid-infrared spectral region holds substantial promise for telecommunications, chemical sensing, and biomedical diagnostics applications. These fields increasingly demand high-resolution, miniaturized, and portable spectrometers. Leveraging recent advances in silicon photonics and computational reconstruction techniques, on-chip spectrometers offer a compact and lightweight solution. This paper presents a distinctive photonic spectrometer prototype based on microcavity-coupled photonic crystal waveguide (MPCW) architecture, operating at the mid-infrared region. The device achieves uniquely defined spectral responses by synergistically integrating non-uniform microcavity resonances with sharp photonics crystal band edges. Benefiting from the slow-light effect, titanium microheaters provide efficient thermal tuning, facilitating further precise spectral response control. The alternating optimization approach for spectral reconstruction eliminates the need for exhaustive parameter searches and substantially alleviates the computational burden. Thus, our MPCW spectrometer can retrieve an unknown spectrum with a resolution of 0.5 nm over a 100 nm bandwidth within several seconds, demonstrating high performance and robustness. Furthermore, the scalable nature of photonic crystal designs permits straightforward adaptation to other wavelength regimes by tailoring the MPCW dimensions.