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

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/cm(2), showing a strain sensitivity of 1.17 pm/mu epsilon. After that, a fourth-order FBG with seven peaks is obtained with a pulse fluence of 1.81 J/cm(2) with a strain sensitivity between 1.249 pm/mu epsilon and 1.296 pm/mu epsilon. With a higher fluence of 2.41 J/cm(2), 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 similar to 5.4 x 10(-4). The two split peaks present a strain sensitivity of similar to 1.44 pm/mu epsilon and similar to 1.55 pm/mu epsilon, respectively. The peak difference corresponding to Hi-Bi presents a strain sensitivity of similar to 0.11 pm/mu epsilon and could potentially be used for simultaneous dual-parameter measurement, such as temperature and strain.