Abstract

Hydrogen used as a propellant for spacecraft and as an alternate fuel for automotive use is potentially dangerous when leaking from storage tanks, fuel cells, supply lines, valves, or engines. Thus, small, rugged sensors are needed that can be distributed in multitudes at critical locations of a hydrogen based combustion or rocket engine. Such sensors ought to be easily connected with a central monitor. Planar and strip optical waveguides with fiber optic links meet these requirements in principle. We investigated the feasibility and sensitivity of detecting hydrogen by its interaction with a metal cladding on a dielectric waveguide. Planar dielectric waveguides of various oxides deposited by using a reactive low voltage ion plating process, and of spin coated polyimide on thermally oxidized silicon wafers as substrates were used, with a thin top layer of palladium as the hydrogen sensitive cladding. We used prism couplers for initial experiments to determine the sensitivity of the palladium cladding with respect to the change of its optical constants upon exposure to various concentrations of hydrogen in air. Grating couplers and integrated optical Mach–Zehnder interferometer configurations were studied for suitability in practical sensor applications.

© 1993 Optical Society of America