Sensing Gases by the Pole Effect of Parity-Time Symmetric Coupled Resonators

The pole is the unique phenomena in the paritytime (PT) symmetry structure. To explore the application of the pole effect, a PT-symmetry resonator coupling system is designed as a gas sensor. The large transmittance and reflectance near the pole are found extraordinary sensitive to the refractive index of the polluted air in the system. Through measuring the reflectance, the refractive index of the polluted air and the concentration of gas in the air can be detected. The sensor has an extraordinary sensitivity in detecting the gases with low concentration. The maximum sensitivities ΔR/R for the methane, acetylene, and ethane are 0.112, 0.190, and 0.282, respectively. The limitation of detectable concentration change is 1/1500 for methane with the photodetector that can sense the relative change rate of the reflectance of 10-3.