Multi-component gas sensing based on slotted photonic crystal waveguide with liquid infiltration

A high sensitive multi-component gas sensing system was proposed, in which the slotted photonic crystal waveguide (SPCW) was used as the gas cell and the fiber Fabry–Perot (FFP) was adopted as the wavelength filter. By choosing the refractive index that infiltrated in the first and second rows of air holes adjacent to the slot respectively, the working wavelength of SPCW could be tuned to matches with one absorption line of the measured gas, thus, the system could detect different kinds of gases selectively. Meanwhile, a very high group index of 150 with flat bandwidth could be achieved and the electric field enhancement factor would reach to 12. Combined with the wavelength modulation techniques (WMS) for signal processing, the minimum detection limit of 1.56 ppm was achieved.