Reconstruction of parameters of an optical fiber from the transmission spectrum of long-period gratings induced in this fiber

An optimization technique is developed to determine parameters of a fiber from the transmission spectrum of long-period gratings written in this fiber and to identify the type of the cladding modes exited by the gratings. The technique is based on fitting the experimental dependence of resonance wavelengths on grating period or cladding radius by theoretical calculation. The resolutions that can be achieved by this method are 10 nm in the core radius, 100 nm in the cladding radius, and 10−5 in the refractive index.