Theoretical investigation into the optimisation of an optical fibre surface plasmon resonance hydrogen sensor based on a PdY alloy

We propose a novel optical fibre surface plasmon resonance hydrogen sensor which utilises a sensing multilayer capped with an alloy of Pd and Y as the hydrogen sensitive layer. The PdY alloy mitigates transition of the Pd crystalline lattice from the → β phase during hydrogen absorption (Liu et al 2012 Rev. Sci. Instrum. 83 1-5) reducing mechanical stress on the sensing film during operation and prolonging the lifetime of the device. We theoretically investigate the performance of the sensor in terms of sensitivity and detection accuracy, finding a trade-off between the two. Therefore, a figure of merit (FOM) which encompasses both these parameters is introduced. We determine the dimensions of the multilayer which give optimum sensing performance. The optimal sensor demonstrated a FOM of 0.063 and had an Ag thickness of 50.5 nm and a SiO₂ thickness of 72 nm. This sensor demonstrated a sensitivity of 17.64 nm to 4% hydrogen and a detection accuracy of 0.014 and operated at a spectral centre of 528.87 nm. In a practical application, the optimum sensing performance is also dependent on the spectrum of the light source used. For the first time, we show how the optimum dimensions of the multilayer are influenced by the spectral centre of the light source and we present these optimal dimensions for a wavelength range encompassing the visible to near-IR spectrum.