A 2D slotted photonic crystal cavity-based optical methane sensor with increased selectivity

In this work, a slotted photonic crystal cavity (PCC) based optical sensor is proposed for the detection of methane gas. The proposed cavity is made of two slots and central holes in the middle row of the photonic crystal structure (PCS). Cryptophane E is used as a sensitive material to detect methane gas. By combining the high resonant nature of the structure and adsorbing phenomenon of cryptophane E, one can increase the sensitivity and selectivity of structure together. The variation in the concentration of methane is able to alter the index of refraction of cryptophane E infiltrated in slots and holes at centre of structure, and thus able to alter the position of the resonant wavelength. The sensitivity obtained from this structure is 614 nm/RIU with a quality factor of 14,717. In addition, the proposed methane sensor only responds to methane gas and avoid interruption by any other gases which in turn enhance the measurement accuracy.