Discrete-eigenvalue multiplexing for soliton fiber-optic communication links

Background and Objectives: The nonlinear Fourier transform gives a powerful tool to analyze fiber-optics solitons. The solitons are described by a discrete set of eigenvalues of two coupled differential equations, which gives the nonlinear Fourier transform. Using the discrete eigenvalues for optical signal coding can increase the signal-to-noise ratio and reduce the effect of fiber nonlinearity. In the present paper an all-fiber-optics method is proposed to modulate the discrete eigenvalues. When the information is transmitted using optical solitons, the channel coding can be realized by changing the discrete eigenvalues which are calculated by means of the nonlinear Fourier transform. A modification of optical solitons and discrete eigenvalues in special optical fibers is considered. Materials and Methods: The interaction of optical solitons in a fiber with a periodic change in the dispersion was analyzed. Numerical simulations based on the nonlinear Schrödinger equation with variable coefficients were used. The discrete eigenvalues were calculated using methods of the inverse scattering problem. Results: A multiplexing scheme for fiber-optic transmission lines has been proposed. Conclusion: It is shown that the discrete soliton spectrum can be controlledby using a dispersion oscillating fiber. After propagation in a fiber with a periodic change of the dispersion, two interacting solitons change their complex eigenvalues. The magnitude and sign of the change depends on the distances between the solitons and on the modulation period of the fiber. The usage of the dispersion oscillating fiber allows one to create soliton pairs with a unique discrete eigenvalues. This phenomenon can be used to encode a signal by applying all-optical methods.