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Optimal design of Er3+-doped amplifier for soliton optical fiber communications

Erbium doped fiber amplifiers are often used in all-optical networks. When the optical network uses linear regime of the pulse propagation, the goal of design optimization is gain flattening. This work presents the results of the study of nonlinear regime of propagation in optical fiber amplifier when pulses can propagate in soliton regime. Due to their remarkable stability and distortionless the solitons can be used as information bits in long-distance and high-bit-rate optical fiber communication systems. To compensate the strong attenuation suffered by soliton that has passed a long distance between neighboring reshaping points, one should apply a strong amplification. However, the soliton strongly amplified by the device with flattened gain is not longer a soliton, but a lump, the decay of which produces much radiation and, perhaps additional solitons. We developed new method that enabled us to choose the spatial dependence of the gain coefficient so that the amplified solitary wave remains an exact soliton at each point of fiber amplifier. The theory of optimal control of distributed media is applied for optimization of soliton propagation in nonlinear media. The goal of optimization is to eliminate nonsoliton radiation. An analytical solution of the optimal control problem is obtained.