Design of Palladium Coated Long Period Fiber Grating for Hydrogen Sensing

Nandini Basumallick, Palas Biswas, Richard Carter, Robert Raimund Maier, Sankhyabrata Bandyopadhyay, Kamal Dasgupta, Somnath Bandyopdhayay

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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.
Original languageEnglish
Pages (from-to)4912-4919
Number of pages8
JournalJournal of Lightwave Technology
Issue number21
Publication statusPublished - 1 Nov 2016


  • Long period fiber grating
  • turn-around-point grating
  • mode transition
  • palladium coatings
  • hydrogen detection.


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