Multi-coupling gap system modeling for methane detection using hollow-core photonic bandgap fibers

Hollow-core photonic bandgap fibers (HC-PBFs) have been recently demonstrated as a powerful technology in the field of gas sensing. The long interaction path lengths achievable with these fibers are advantageous for the detection of weakly absorbing gases such as methane. However, using long path lengths yield to very high insertion times of the gas into the fiber. In this paper, an alternative configuration based on a multi-coupling gap HC-PBF system to detect methane is proposed to overcome this problem. For this purpose, a conventional configuration using one long piece of HC-PBF is compared to this novel configuration, which uses four shorter pieces of HC-PBF with the same overall length as the first configuration. The experimental results are validated theoretically modeling the normalized pressure inside the fiber. A very good correlation between the experimental data and the theoretical fit is obtained, demonstrating the feasibility of the system proposed.