Hetero-core fiber optic surface plasmon resonance sensor based on Au/Ta₂O₅/Pd multi-layer films for hydrogen sensing

In this paper, we describe a novel fiber optic surface plasmon resonance (SPR) hydrogen sensor based on hetero-core structured fiber optics with multi-layer films of gold (Au), tantalum pentaoxide (Ta 2 O 5 ) and palladim (Pd) uniformly coated onto a cylindrical cladding surface. The hetero-core fiber sensor has a simple structure with easy fabricationwhich has no need of cladding removal. In addition, the cladding surface could work as a sensing region because the transmitted light is largely leaked into cladding layer owing to the core diameter mismatch between the transmission and inserted fibers. Due to the uniform cylindrical coating SPR resonant curves have been obtained for the cases of 0 and 4% hydrogen with a SPR resonant wavelength shift of 28nm at a concentration of 4% hydrogen in nitrogen for the case of the coating films consisted of 25nm Au/60nm Ta 2 O 5 60/5nm Pd. Sensing properties in terms of response time and sensitivity on hydrogen detection have been experimentally obtained with changing Pd layer thickness in the light intensity-based experiment with an LED operation at 850 nm. It is indicated that a transmitted loss change of approximately 0.23 dB is produced with a response time of 15 sec. for a hydrogen concentration change of 4%, in the case of Au 25 nm, Ta 2 O 5 60nm and Pd 3 nm. The experimental results have revealed that the proposed hydrogen sensor could detect hydrogen concentration with realizing a high sensitivity and as a fast response time as a previously reported sensor.