Hydrogen Detection Using Polarization Diversity via a Subwavelength Fiber Aperture

A photonic hydrogen gas sensor is fabricated by etching a subwavelength aperture into an optically thick palladium film deposited on the facet of an optical fiber. Upon adsorption of hydrogen onto the palladium surface, the complex refractive index of the film will change, altering the transmission through the aperture. Due to the plasmonic resonances and enhanced transmission of the C aperture, its response to hydrogen is several times larger than that of a plain film or a nonresonant aperture. Furthermore, the asymmetry of the aperture produces a different hydrogen response for the two polarizations. This leads to different sensitivities to hydrogen. By measuring the polarization-dependent loss (PDL), we can accurately quantify the hydrogen concentration since common-mode noise is eliminated.