Multivariate identification of low-loss sampled fiber Bragg gratings by downhill simplex method

The use of the downhill simplex method is proposed for multivariate identification of phase difference and reflectivity of low-loss sampled fiber Bragg gratings (SFBGs). Phase differences between two FBGs, which are determined by optical lengths between two adjacent FBGs, are the most important parameter in SFBG fabrication. The frequency of phase difference estimation error within 0.05p has been achieved to 78 % with small calculation amount. Low-loss SFBGs with 0.1π of phase error were fabricated by using the proposed identification method.