Fabrication tolerances in long-period fiber grating refractometric sensors

Abstract

This work focuses on the results and analyses performed on long-period optical-fiber gratings (LPFG) designed for use as refractometric sensors. The study was conducted with non-uniform LPFG specially designed for refractometric applications. First, LPFG transmission spectra were calculated for nominal period, propagation constant of the cladding mode and phase shift between the adjacent LPFG sections. Then, a random variation of the above parameters was introduced and the effect of this variation on the transmission spectrum of the LPFG, with the external refractive index as parameter, was evaluated. Finally, a change in the resonant wavelength against the external refractive index was investigated under random variation of parameters. We have found that in some long-period fiber grating refractometric sensors fabrication tolerances should as stringent as 0.2 % of nominal parameter. The methodology of tolerance analysis and quantitative data obtained in this work might be useful in establishing tolerances for fabrication parameters of longperiod fiber grating refractometric sensors.