The article examines the development of methods of one to increase the spectral efficiency of the fiber optic systems of transmission. The essence of the method is shown with the use of alphabet as signals with peak modulation and frequency manipulation. On the receiving side, such signals are distinguished by successive application of selective operations on the frequency subcarrier and spectral analysis of the low-frequency envelope of the signal. A short optical pulse with duration of 3-10 ps with a given shape of the low-frequency envelope is formed on the transmitting side. In order to form such a pulse the method of approximation of a given function with a weighted sum of short pulses of duration about 100 fs is used. With such short functions, it is proposed to use laser pulses in the mode-locking mode. Such pulses have a sufficiently short duration and are approximately Gaussian. To form the output signal, a single laser pulse is divided into several directions (about 100). Further in each direction, the pulse is amplified (or attenuated) in accordance with the necessary amplitude of the readout. In each direction the pulse is then delayed by the necessary time in the delay line. The output signals from the delay lines are summed and transmitted to the input of the trunk optical fiber. It is shown that this method can be implemented using existing technologies. As a problematic part the creation of a system of delay lines with slightly different delay time is considered. The time difference step is approximately 100 fs. As a method of manufacturing such systems of delay lines, it is proposed to use optical fibers of the same length with a slightly different composition of alloying additives. This method allows regulating the difference in group velocities (group refractive indices) with sufficient accuracy and provides the necessary accuracy of the delay step of the initial pulse. The performed calculations show that the use of the proposed methods makes it possible to substantially increase the throughput of fiber-optic transmission systems using modern technologies for manufacturing optical components.