436 Measurement and Characterization of Gratings 25 years at 300 K. The relationship between the time of annealing and the anneal temperature shows that annealing at 480 K for 1 min is equivalent to 25 years at 300 K. In order to ensure that the grating meets the specification for the application, this initial "burning-in" phase must be taken into account, since there is a reduction in the refractive index modulation. REFERENCES [1] V. Mizrahi, J.E. Sipe, Optical properties of photosensitive fiber phase gratings, J. Light- wave Technol. 11 (10) (1993) 1513­1517. [2] R. Kashyap, P.F. McKee, D.J. Armes, M. Shabeer, D.C. Cotter, Measurement of ultra- steep edge, high rejection fibre Bragg grating filters, Electron. Lett. 31 (15) (1995) 1282­1283. [3] J. Martin, J. Lauzon, S. Thibault, F. Ouellette, Novel writing technique of long highly reflective in fiber gratings and investigation of the linearly chirped component, post-deadline paper PD29-1, in: Proc. Conference on Optical Fiber Communications, OFC '94, 1994, p. 138. [4] R. Kashyap, M. de Lathouwer, P. Emplit, M. Haelterman, R.J. Campbell, D.J. Armes, Dark soliton generation using a fibre Bragg grating, 9­11 September. Photosensitivity and Quadratic Nonlinearity in Glass Waveguides: Fundamentals and Applications, OSA Annual Meeting, Oregon, 1995. [5] A. Carballar, M.A. Muriel, Phase reconstruction from the reflectivity in fiber Bragg