Tilted Fibre Bragg Grating sensors. Application in monitoring of the chemical fabrication of nanometer metal films

An accurate and efficient sensing platform based on a tilted fibre Bragg gratings (TFBG) sensor, in particular concerning the monitoring of the chemical fabrication of nanometer metal films is presented.;In presented work the TFBG is used to monitor the fabrication of the nanoscale metal layers on the outside of the fibre cladding, that will eventually be used for sensing by metal-coated fibres. The sensor calibration is done by relating the fabricated metal film thickness, measured by Atomic Force Microscopy, to the spectral response of the sensor. Measurements using linearly polarized were determined to be crucial for the accurate monitoring of gold coatings with thicknesses ranging from1 to 50 nm.;The developed sensing platform is capable of acquiring the optical response of the sensor at 50 different states of linearly polarized light, within a 10 second interval. Changes in metal film thickness as small as 1 nm were detected during the real-time monitoring of an electroless metal plating process.;This possibility opens the way of creating TFBG-based surface plasmon resonance sensors, where the thickness of the metal coating is precisely tuned to obtain the plasmon resonance in the working range of the TFBG sensor.;TFBGs have grating planes that are tilted relative to the fiber's transverse axis thereby causing the excitation of several tens of cladding mode resonances, each uniquely addressed by its wavelength. The large differential sensitivity of the core and cladding modes to various perturbations allows the development of very accurate fiber sensors with a unique set of advantages and wide operating range.;In order to get a physical insight into the processes occurring in the sensor, a numerical method was developed for a fast and accurate solution to the sensor's electromagnetic field structure problem, and a mode coupling technique was introduced for the theoretical prediction of the sensor's spectral response.