We study, for the first time, the refractive index profile of a highly reflecting fiber Bragg grating with a reflectivity of 99.91%, by combining measurements from both sides of the grating and using an inverse scattering algorithm. Fiber gratings are important elements in optical communication systems. In practice, gratings do not have an ideal structure and may limit the performance of the overall system. Therefore, it is important to find new methods to study the refractive index structure of gratings in order to improve the manufacture process of the gratings. High reflection gratings are often needed in optical communication systems in order to decrease loss, The structure of gratings with a small or a moderate reflection coefficient can be studied by measuring the complex reflection spectrum of the grating, and analyzing the result using Fourier or Gabor transforms [1,2]. Such measurement techniques cannot be used to interrogate gratings with high reflectivity (>60%) since: (a) the measured complex reflection spectrum does not give directly the grating structure; (b) the forward propagating wave strongly attenuates along the grating, preventing the reconstruction of the region close to the output end of the grating; (c) the measurement becomes sensitive to noise and to performance of the optical spectrum analyzer used in the experimental setup when the grating is interrogated by a low-coherence spectral interferometry technique.
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