Turnaround-Point Long-Period Fiber Gratings (TAP-LPGs) as High-Radiation-Dose Sensors

This letter reports the application of turnaround-point (TAP) long-period gratings (LPGs) for radiation dosimetry. The LPGs were realized using the CO2 laser-writing technique. After a Co-60 gamma dose of 6 kGy, the TAP-LPGs show a radiation-induced shift of more than 35 nm for each of the dual resonance dips, which is the highest shift reported to date for any type of fiber gratings. These LPGs can therefore be used as radiation sensors down to doses of a few Gy with modest wavelength-resolving instrumentation. The LPGs show significant sensitivity of wavelength shifts up to 80 nm for a dose of 65 kGy. We attribute the very high radiation sensitivity to near-TAP operation and doping of Boron in the fiber. This should open up applications of LPGs to radiation dosimetry.