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.