In this area, fiber gratings are being used in filtering devices for multiplexing/demultiplexing in WDM systems, gain equal-izers for Erbium-doped fiber amplifiers (EDFAs), and in the external cavity lasers, used to stabilize light-source wavelength. This paper introduces the basic theory of optical fiber gratings and describes manufacturing techniques. It also summa-rizes developmental results with. Superstructure fiber Bragg gratings (SSFBG), in which the amplitude and phase in grating corrugation are controlled, can realize versatile functions for DWDM systems. We review our technique to fabri-cate densely-spaced SSFBG, multiple phase-shift (MPS) technique. For short periods of the index modulation, the disorder in index of refraction perturbation induces the light reflection in a limited.
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