We present a detailed numerical analysis that describes the influence of palladium (Pd) layer thickness on the spectral characteristics of long period fiber gratings (LPFGs) and their response to the uptake of hydrogen. The investigation is carried out with a view of determining an optimal layer thickness to design high sensitivity LPFG based hydrogen sensors. Coupled differential equations for a four layer waveguide structure have been solved using matrix method considering a layer of Pd with finite thickness on the cladding. Response of higher order cladding modes of the Pd-coated LPFG at turn-around-point (TAP) and also at mode transition could be computed. It has been shown that if properly designed, the resonant wavelength of a desired mode may shift by about 20 nm for 1% uptake of hydrogen. There is good match between simulations and experiments for LPFGs with coupling to higher order cladding modes.
|Number of pages||8|
|Journal||Journal of Lightwave Technology|
|Publication status||Published - 1 Nov 2016|
- Long period fiber grating
- turn-around-point grating
- mode transition
- palladium coatings
- hydrogen detection.