Pd/Au nanofilms based tilted fiber Bragg grating hydrogen sensor

A tilted fiber Bragg grating (TFBG) hydrogen sensor based on Pd/Au composite nanofilms was proposed. Pd and Au films with thickness of 25 nm and 35 nm were deposited on the surface of TFBG by magnetron sputtering method. Pd is a face centered cubic structure, which is capable of adsorbing hydrogen atoms. Accordingly, the effective refractive index of Pd/Au composite film changes with the variations of hydrogen concentrations, which will change the intensities of cladding modes resonant wavelength in TFBG transmission spectrum. The experimental results illustrated that when the hydrogen concentration changes by 1.02%, the intensity of cladding mode resonant wavelength (1558.4 nm for instance) decreases by 1.628 dB, and the hydrogen concentration sensitivity of 1.597 dB/% was obtained, which is almost 16 times higher than that of the current similar hydrogen sensor. The average response and recovery time were 37 s and 49 s, respectively. In addition, the proposed sensor can be made inherently temperature-insensitive by referencing all wavelengths to the wavelength of the core mode resonance of the grating, which is isolated from the fiber surroundings.