Hydrogen Sensing Using Palladium Coated Long Period Gratings

Research output: ThesisDoctoral Thesis


The use of palladium coated optical fibres contaning an in-fibre long period grating (LPG) structure for the sensing of low concentrations of hydrogen has been investigated. Previous proof of principle experiments were refined and extended, demonstrating sensitivities of up to 90 pm for 1% hydrogen at an operating temperature of 70ºC.

Characterisation of the Pd deposition technique (RF sputter coating) including XPS and SEM analysis to investigate surface roughness and contamination were carried out and are discussed. These measurements were prompted by the need to characterise and eliminate sensor drift associated with delamination of the sensor layer.

Particular care was taken to characterise the optical properties of Pd thin films, both in the presence of hydrogen and without, through ellipsometry and surface plasmon resonance, since values gained from the literature showed wide variations. The results presneted in this thesis differ from published Pd refractive indices but are specific for the conditions used in this work.

Techniques to directly measure the refractive index profile within the core of an LPG were investigated and a possible solution is presented.

Theoretical models to calculate the transmission spectrum of an LPG, both with and without a Pd Layer are presented, discussed and the implications due to the poor characterisation of the LPG are considered.

The potential use of higher order double caldding modes (with up to 20 times the sensitivity of the lower mode orders) as a sensing regime is investigated and the practical limitations discussed
Original languageEnglish
Awarding Institution
  • Heriot-Watt University
  • Maier, Robert Raimund, Supervisor
  • Barton, James, Supervisor
Thesis sponsors
Award date19 Jun 2012
Publication statusPublished - 2012


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