Effects of Ge concentration, boron co-doping, and hydrogenation on fiber Bragg grating characteristics

Strain Measurement on Cracks Using Fiber Bragg Gratings for Use in Aircraft Composite Skin Repairs

“…where λ 0 and λ 1 are the initial and final inscription wavelengths and Λis the grating period. In an older work, we used telecom SM fibers, with 5% and special 20% germanium and germanium-boron co-doped fibers (Ge-Bo), with and without hydrogen loading to benchmark their photosensitivity by inscribing and testing a number of different FBGs [19]. It was established that the high germanium and boron co-doped fibers (20% Ge) had the highest photosensitivity, producing grating with peak refractive index modulation ∆n of about 3.5 × 10 −3 .…”

“…Furthermore, a multiple fiber array grating consisting of an array of five short FBGs, each 1.2 mm long, with separation of 2.5 mm from each other, was also embedded in the composite, about 3.5 mm from the edge of the patch, shown as c in Figure 3. It should be noted that the inscription of such short multiple FBGs, with a combined length of 16 mm, was only made possible by the use of the very photosensitive hydro-boron fiber and protocol, shown in Figure 1 and in [19]. The choice of the FBGs locations was determined by stress analysis, which determined that the maximum force exerted on the composite patch was at the outer section of the coupon above the crack.…”

Femtosecond-Pulsed Laser Written and Etched Fiber Bragg Gratings for Fiber-Optical Biosensing

“…The highest photosensitivity can be obtained by germanium-doped fibers. Other post-fabrication techniques such as hydrogen loading, flame brushing, or boron co-doping can also increase the photosensitivity, however, for some techniques it works only transiently [ 12 , 14 , 15 , 16 ]. A further limitation of the phase mask technique is that only a single Bragg grating period can be obtained from a given phase mask and more complex grating structures would require more complex, expensive phase masks.…”