Fabrication and performance characteristics of optical fiber gratings for sensing applications

Optical fiber gratings, often classified as short-period and long-period fiber gratings according to the magnitude of the period of refractive index modulation along the propagation axis, are increasingly becoming essential components in optical fiber sensors. In this paper, we discuss fabrication techniques and various performance characteristics of the optical fiber gratings employed in the sensor head. Optical fiber gratings can be fabricated using UV lasers based on the photosensitivity effect, CO₂ laser or electric arc to induce surface deformation and/or stress relaxation, etc. Change of the spectral characteristics of short-period fiber gratings occurs mainly due to variation of the sub-μm grating period. Peak wavelength shift due to environmental change and chirp-induced effects like dual peak separation can be effectively utilized for sensing applications. We also discuss control of the temperature sensitivity, dual peak separation, and reduction of the polarization-dependent loss (PDL) of long-period fiber gratings and their application to sensing of various physical quantities.