[3] [3] Liu Y, Zhang L, Bennion I. Fibre optic load sensors with high transverse strain sensitivity based on longperiod gratings in B/Ge co-doped fibre. Electronics Lett,1999,35(8): 661～662

[4] [4] Rao Y J, Wang Y P, Ran Z L, et al. Novel fiber-optic sensors based on long-period fiber gratings written by high-frequency CO2 laser pulses. J of Lightwave Technology, 2003,21(5): 1320～1327

[5] [5] Wagreich R B, Atia W A, Singh H, et al. Effects of diametric load on fibre Bragg gratings fabricated in low birefringent fibre. Electronics Lett, 1996,32(13): 1223～1224

[6] [6] Calero J, Wu S P, Pope C, et al. Theory and experiments on birefringent optical fibers embedded in concrete structures. J of Lightwave Technology, 1994,12(6): 1081～1091

[7] [7] VanWiggeren G D, Gaylord T K, Davis D D, et al. Axial rotation dependence of resonances in curved CO2-laser-induced long-period fibre gratings. Electronics Lett, 2000,36(16): 1354～1355

[8] [8] Ryu S H, Park Y, Oh S T, et al. Effect of asymmetric stress relaxation on the polarization-dependent transmission characteristics of a CO2 laser-written longperiod fiber grating. Opt Lett, 2003,28(3): 155～157