Thickness influence on the polarization dependency of tilted fiber Bragg gratings coated by zinc oxide thin films

Tilted fiber Bragg gratings (TFBGs) transmitted amplitude spectra intrinsically depend on light polarization, leading to the existence of two peak families separated by a few picometers to a few tens of picometers for the s and p-polarized light states. In this paper, we demonstrate that, thanks to a dense thin film with high refractive index (Zinc oxide) deposited around TFBGs, the polarization dependency can be drastically enhanced, resulting in a wavelength separation of up to 550 picometers between the two orthogonal resonance peak families. This results in two important assets: the sensitivity is extended to surrounding refractive index (SRI) values above 1.45 while the strong polarization dependency makes the demodulation process easier with differential SRI sensitivities between the two modes families.