Point-by-Point Induced High Birefringence Polymer Optical Fiber Bragg Grating for Strain Measurement

Abstract

In this paper, the first- and fourth-order fiber Bragg grating (FBG)-based axial strain sensors are proposed. The FBGs are inscribed in step-index polymer optical fibers (POFs) (TOPAS core and ZEONEX cladding) via the point-by-point (PbP) direct-writing technique. A first-order FBG with a single peak is obtained with a pulse fluence of 7.16 J/cm2, showing a strain sensitivity of 1.17 pm/με. After that, a fourth-order FBG with seven peaks is obtained with a pulse fluence of 1.81 J/cm2 with a strain sensitivity between 1.249 pm/με and 1.296 pm/με. With a higher fluence of 2.41 J/cm2, a second fourth-order FBG with five peaks is obtained, each of which is split into two peaks due to high birefringence (Hi-Bi) of ~5.4 × 10−4. The two split peaks present a strain sensitivity of ~1.44 pm/με and ~1.55 pm/με, respectively. The peak difference corresponding to Hi-Bi presents a strain sensitivity of ~0.11 pm/με and could potentially be used for simultaneous dual-parameter measurement, such as temperature and strain.