Artificial photonic bandgap waveguides for on-chip optical gas sensing

Abstract On-chip optical gas sensors have garnered increasing attention for environmental monitoring, industrial process control, and medical diagnostics due to their high reliability, excellent scalability, compact footprints, and compatibility with large-scale integration. However, achieving strong light–gas interaction in a compact device remains a critical challenge. Artificial photonic bandgap (PBG) waveguides offer a powerful strategy to tackle this problem by enabling precise tailoring of modal confinement, dispersion, evanescent field, and topologically robust transport through engineered waveguide microstructures. This review provides a comprehensive overview of recent advances in on-chip gas sensors utilizing artificial PBG waveguides. We begin by outlining the fundamental principles and key performance metrics of on-chip gas sensing, including refractive-index sensing, infrared (IR) absorption spectroscopy, Raman spectroscopy, and photothermal spectroscopy. We then summarize four types of artificial PBG platforms: subwavelength grating, hyperuniform disordered solids, photonic crystal, and topological photonic crystal waveguides. We highlight their working mechanisms, typical device implementations, and performance-footprint trade-offs. Particular emphasis is placed on how these platforms balance optical confinement, gas overlap factors, light–matter interaction enhancement, optical losses, fabrication tolerance, and transport robustness. Finally, we discuss future trends in system-level integration, spectral extension into the mid-IR molecular fingerprint region, intelligent signal processing, and practical applications in optical sensing. By linking on-chip optical-field-manipulation approaches with device- or system-level optimization strategies, this review aims to provide a structured framework to advance compact, robust, and high-performance integrated photonic gas sensors.