Expanding Blue Shift on Post-Fabrication Resonance Wavelength Adjustment of Long-Period Fiber Gratings by Heating

摘要

The adjustable range of resonance wavelengths of long-period fiber gratings was broadened toward the blue wavelength side by heating. The mechanisms of the blue and red wavelength shifts were investigated. It becomes clear 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 large blue shift of a resonance wavelength, 41 nm, was obtained by heating a long-period grating at 600 ℃ for 3500 minutes. The core index reduction inducing the blue shift was estimated at about 10~(-4) by numerical analysis.