High Radiation Sensitivity of Chiral Long Period Gratings

Abstract

The radiation sensitivity of chiral long period gratings was investigated for the first time. After a Co-60 gamma dose of 100 kGy they show radiation-induced changes of their transmission dip wavelength of up to 10 nm, which is 100 to 1000 times higher than the radiation-induced wavelength shift of different fiber Bragg grating types. They can therefore be used as radiation sensors down to doses of 10 Gy or even below, but not for accurate dose measurements since the size of the wavelength shift after a certain dose still depends on the radiation dose rate. Chiral gratings made of eight single mode fiber types with differences of their radiation-induced attenuation of several orders of magnitude were investigated in order to look for a correlation between dip wavelength shift and fiber attenuation. However, the dip wavelength curves do not show exactly the same order as the fiber attenuation curves. A theory that can exactly predict all properties of the chiral gratings might enable us to specify from our results an optimized fiber for the production of gratings that can also be used for radiation dosimetry.

Radiation and taper tuning of Long Period Grating for high sensitivity strain measurement

“…We have used Gamma radiation exposure and slight tapering of fiber with CO 2 laser as the tools for tuning near TAP LPG. Wavelength shift of ±35nm was observed for gamma radiation exposure of 6kGy which is higher than the wavelength shift reported in [8]. Simulation of PMC for increased and decreased value of core refractive index showed that the gamma radiation exposure is effectively increasing the core refractive index by an order of 10 -5 -10 -4 , which is significant for a near TAP-LPG.…”

“…It has been reported that certain Fiber Bragg gratings (FBGs) can be used for radiation dose sensing [7]. Chiral LPG has shown 10 nm shift for 100 kGy dose of gamma radiation [8]. Cladding etching has been earlier used for resonance peak positioning in LPG [9].…”

Chiral fiber sensors for harsh environments

“…2,3,5) and of the most sensitive ones (nos. 4,6,7,8) differed by more a factor of 100. Fibers that show higher attenuation at 1550 nm also show higher RIA down to UV wavelengths.…”

“…An overview of manufacturers, dimensions, and core and cladding dopant concentrations in these fibers is given in Table I 7 . The core of the Nufern 1 fiber is highly doped with P, whereas the cores of the Nufern fibers 2 and 3 are doped with rare earth elements.…”

“…The second grating of fibers 1, 4, 6, 7, and 8 was also irradiated with a dose rate of only 0.1 Gy/s up to a dose of 20 kGy in order to examine whether the radiation-induced wavelength shift of the transmission dip is independent of the dose rate and does not depend on the time to reach respective dose values. 7 This is a precondition for a sensor to be suitable for radiation dosimetry. The aluminum plate was placed in a climate chamber in order to measure the temperature sensitivity of the CLPGs.…”