Applications of Photonic Crystals in Gas Sensors: A Review

Photonic crystals (PhCs) are artificially structured optical media in which a periodic variation of refractive index controls the propagation of electromagnetic waves. Their photonic band gaps, defect modes, high-quality resonances, slow-light regimes, and strong field confinement make them attractive platforms for compact and highly sensitive gas sensors. This review summarizes the main mechanisms by which photonic crystals improve gas detection, with emphasis on absorption spectroscopy, refractive-index sensing, photonic-crystal waveguides, slotted structures, photonic-crystal fibers (PCFs), hollow-core PCFs (HC-PCFs), resonant cavities, and plasmonic or functional-material-assisted devices. The review also discusses representative applications for methane, hydrogen, carbon dioxide, carbon monoxide, hydrogen sulfide, ammonia, and multicomponent gases. Particular attention is given to slow-light enhancement, which increases the effective interaction between light and gas molecules without requiring a physically long gas cell. PCFs provide an additional advantage because their microstructured cladding can simultaneously guide light, admit gas into the sensing region, and create large evanescent-field overlap. Recent developments involving metal–organic frameworks (MOFs), surface-plasmon effects, Vernier configurations, and integrated group-IV photonics indicate a pathway toward smaller, more selective, and more intelligent sensors. Nevertheless, practical deployment remains limited by gas diffusion, temperature and humidity cross-sensitivity, fabrication tolerances, optical coupling losses, packaging, and the trade-off between sensitivity and dynamic range. Future progress is expected from hybrid materials, mid-infrared operation, CMOS-compatible fabrication, machine-learning-assisted spectral analysis, and integration of photonic, microfluidic, and electronic functions on a single platform.

کلیدواژه ها:

photonic crystal ، gas sensor ، photonic crystal fiber ، hollow-core fiber ، slow light ، absorption spectroscopy ، methane ، hydrogen ، optical sensing