Long-wave infrared frequency comb generator for chemical agent and explosive precursor detection

We present the design and numerical characterization of a CMOS-compatible silicon-in-zinc selenide (Si–ZnSe) micro-ring resonator for soliton frequency comb generation in the long-wave infrared (LWIR) band. The proposed device is engineered to operate within the 9.5–12 µm range, corresponding to the molecular fingerprint region of chemical warfare agents, explosive precursors, and emerging opioid analogs. By leveraging the high nonlinear refractive index of silicon and the low optical absorption of ZnSe, the structure achieves strong field confinement and efficient Kerr nonlinear interactions while mitigating mid-IR loss mechanisms. Using a mixed-field finite-difference solver, we extract the effective indices and compute the integrated dispersion, demonstrating an exceptionally flat profile below 150 MHz integrated dispersion across the entire spectral window. The micro-ring exhibits a free spectral range of approximately 60 GHz, matching the detection bandwidth of high-speed photodiodes. We further solve the normalized Lugiato–Lefever equation using a symmetric split-step Fourier method to model soliton dynamics within the resonator. Simulation results confirm the generation of stable dissipative Kerr solitons with a broadband comb spectrum exhibiting slow spectral roll-off, indicating strong nonlinear coupling and low phase mismatch. The resulting frequency comb spans multiple micrometers in the LWIR, enabling simultaneous multi-species detection. This integrated platform offers compactness, scalability, and compatibility with existing semiconductor manufacturing processes. The combination of wide spectral coverage, high sensitivity, and CMOS compatibility positions this technology as a promising foundation for portable, fielddeployable spectroscopic systems capable of real-time identification of hazardous chemicals, explosive precursors, and fentanyl-like opioids in complex environments.