Broadening Adjustable Range on Post-Fabrication Resonance Wavelength Trimming of Long-Period Fiber Gratings and the Mechanisms of Resonance Wavelength Shifts

The adjustable range on post-fabrication resonance wavelength trimming of long-period fiber gratings was broadened toward the blue side, and the mechanisms of the resonance wavelength shifts caused by heating were investigated. It can be concluded that the glass structure relaxes more slowly than the residual stress with decreasing heating temperature and the blue shift caused by the residual stress relaxation appears more strongly at the early stage of heating. The blue shift of 41 nm was obtained by heating a long-period grating at 600 degrees C for 3500 minutes. The changes of the index difference inducing the wavelength shifts of 41 nm and 35 nm were estimated at about -1.2 x 10(-4) and +1.0 x 10(-4) by numerical analysis, respectively.