Fiber Bragg gratings with enhanced thermal stability by residual stress relaxation.

Fiber Bragg gratings with greatly enhanced thermal stability have been fabricated by the use of femtosecond laser pulse irradiation on optical fibers with relaxed residual stress, through using high temperature annealing treatment. The grating reflectivity and resonant wavelength can be maintained for periods up to 20 hours using isothermal measurements and temperatures up to 1200 degrees C. No hysteresis was observed in the wavelength response when the gratings were annealed and the temperature cycled repeatedly between room temperature and 1200 degrees C.