"In this work some phenomena that occur during the propagation of pulse light in nonlinear optical loop mirror are studied. The study is based on a wavelength-tunable Sagnac birefringence filter. Theoretical and experimental studies were performed. The device is a Sagnac interferometer including a symmetric fiber coupler and a length of high birefringence fiber in the loop while a wave retarder is inserted at each end of the birefringence fiber for absolute wavelength tinning. We demonstrated experimentally using this Sagnac interferometer a simple configuration to perform wavelength-tuning and multi wavelength operation in a fiber ring laser that is composed of an Erbium-doped fiber and includes a fiber optic Sagnac interferometer as spectral filter. On the other hand we propose an analyze numerically a novel dispersion-imbalanced nonlinear optical loop mirror (NOLM) scheme allowing simulations compression and amplitude noise reduction of chirped ultra-short pulse signal. The fiber distributed GiresTournois etalon (DGTE) was made of two uniform fiber Bragg gratings inserted asymmetrically in the loop, and both are used for dispersion imbalance the NOLM and compress the pulses. The results show that the output pulses are accompanied by side lobes, which originate from the non-uniformity of the DGTE dispersion spectrum. The parameters had been considered in accordance with the available commercially optical fibers data."