Pd-Ag film coated cascaded long period gratings for hydrogen gas sensing

A Mach-Zehnder-like interferometer based on cascaded long period gratings with palladium silver (Pd-Ag) film coating is developed for monitoring the hydrogen concentration. The visibility of fringes is measured using Fourier analysis. The basic theory was given and preliminary experiment had been proved that this sensor can used to monitor the hydrogen concentration. The sensor showed a good response.