Measurement of methane concentration with cryptophane E infiltrated photonic crystal microcavity

A miniaturized, high-sensitive, and high-precision gas sensor for the measurement of methane concentration was realized in a cryptophane E infiltrated photonic crystal (PC) microcavity, by combing selective adsorption property of cryptophane E to methane and excellent resonant property of PC microcavity. The concentration variation of methane would change the refractive index (RI) of cryptophane E that infiltrated in defected holes of PC microcavity, and then induce a shift in resonant wavelength, allowing precision measurement of methane concentration. Simulation results of PC microcavity showed that the RI sensitivity of 363.8 nm/RIU, quality factor of 12,923, and transmission of 0.9122 could be obtained by increasing the radii of defected holes, which does not require sophisticate geometrical adjustment and high-precision requirement for fabrication. However, its resonant property is comparable to other subtle-tuned PC microcavities. Besides, the designed methane sensor is only in response to methane, which can prevent the interrupt of other gases and enhance the measurement accuracy. Benefiting from the high RI sensitivity and high quality factor of the microcavity, a theoretical detection limit of 697.35 ppm for methane sensing can be achieved.