Coexistence of transmission mechanisms for independent multi-parameter sensing in a silica capillary-based cascaded structure

The coexistence of transmission mechanisms, including Fabry-Perot (FP), Mach-Zehnder (MZ), and anti-resonant (AR), is demonstrated via a silica capillary-based cascaded structure. The analysis for MZ shows that one pathway is formed by the beam refracted into the silica capillary cladding from the air core, rather than being transmitted into the cladding directly at the splicing interface. Using the ray optics method, the two coexistence conditions are derived for FP and MZ, and for FP, MZ and AR, respectively. The existence percentages of the three mechanisms can be obtained using the fast Fourier transform. Finally, the coexistence of multiple transmission mechanisms is applied for independent multi-parameter sensing with the FP-based temperature sensitivity of 10.0 pm/°C and AR-based strain sensitivity of 1.33 nm/N. The third mechanism MZ interference can assist in verifying changes in both the temperature and axial strain. This shows the possibility to optimize the transmission spectra for independent multi-parameter sensing by tailoring the existence percentages of different mechanisms.