We propose a new approach to simulating fiber-optic communication lines (FOCLs) using an amplifier model as a section of active fiber with saturated gain and a nonuniform spectrum, and report the development of an algorithm for constructing a train of dissipative solitons with a phase-shift keying (PSK) modulation format for transmitting data over FOCLs. By establishing periodic dynamics of the parameters of carrier pulses in the amplification section, it is possible to transmit signals over long distances without reducing efficiency. The stability of this approach to adding amplifier noise is demonstrated.

We report an efficient noniterative numerical algorithm for solving a system of linearly coupled nonlinear Schrödinger equations (NLSE) describing the propagation of light pulses in multicore optical fibers, with optical losses and saturated gain taken into account. The method can also be used in the case of a single scalar NLSE. The proposed algorithm is based on the split-step Fourier method and has the second order of accuracy in the evolutionary variable and the exponential order of accuracy in time. To solve the system of coupled NLSEs, we propose to approximate the matrix exponential using the Pade approximation.

The general characteristics of an optical signal as a result of generation in a resonator can be described using a dynamic model based on the complex cubic Ginzburg–Landau equation, which takes into account the saturated gain and dissipative terms responsible for the distributed action of various intracavity devices. The paper proposes two new effective modifications of the split-step Fourier method for a numerical solution to equations of this type. The first algorithm is based on the application of a new way of separating physical processes affecting the optical signal during propagation in a fiber, which made it possible to express the action of both nonlinear and dispersive spatial steps by explicit analytical expressions. The second proposed method enabled significant improvement in the accuracy of calculations due to including energy evolution in the coefficients of the equation. Numerical experiments have shown that the new schemes can produce the second order of approximation with respect to the evolutionary variable in contrast to the classical scheme that provides only the first order of approximation.

We propose a theoretical approach to study the multicore fiber propagation dynamics of optical pulses near a stationary solution known as “light bullet”. A system of coupled non-conservative nonlinear Schrödinger equations is used as a mathematical model. An approximate analytical stationary solution for this system of equations is found and studied.

We present a new way to handle dual-polarization signal processing in fiber-optic networks. It combines chromatic dispersion compensation (CDC) with sliding window techniques to make processing signals more precise and effective. The nonlinear Fourier transform (NFT) is a key tool used here to manage chromatic dispersion and the Kerr effect, which are crucial for transmitting signals over long distances.

We investigate linear and nonlinear modes of parity-time (PT)-symmetric multicore fibers with a twist of peripheral cores with gain and loss around the lossless central core. We determine the spectral properties of such a light guiding system and demonstrate that the presence of the lossless central core combined with the fiber twist may significantly change the supermode structure, as well as the PT-symmetry breaking threshold of the multicore fiber with gain and loss. We also construct stationary nonlinear modes of the fiber and verify their stability.

Linear and nonlinear modes of PT-symmetric multicore fibers twisted around the central axis are studied. We determine the spectral properties of such systems and show that the presence of a central core and twist can significantly change the mode structure, as well as the PT-symmetry breaking threshold. We also construct stationary nonlinear modes and investigate their stability.

We propose the new, to the best of our knowledge, distributed mathematical model of dissipative soliton evolution in ultra-long fiber lasers. The model is based on a modified Ginzburg–Landau equation, has a stable analytical solution, and takes into account the saturated gain and saturable absorption. The analytical results show a good accordance with the results of numerical simulation of ultra-long ring cavity fiber lasers. The results may be applied to the analysis of a wide range of fiber laser systems.

We demonstrate numerically and analytically that the twisting of the 7-core hexagonal fiber leads to an increase in the efficiency of pulse combining and to a reduction of the distance along the fiber to the combining point.

A novel practical method for electronic triggering of essentially different pulsed regimes in fiber cavity lasers is introduced. The method relies on electronic control of complementary transmission characteristics of a fiber-coupled LiNbO 3 waveguide electro-optic switch (WEOS) which plays the role of the variable output coupler in a fiber cavity. The method was studied using a testbed laser configuration comprised of a semiconductor optical amplifier (SOA) and an all-fiber cavity. Modulation of the WEOS-based output coupling in the fast gain recovery configuration allowed not only high-quality mode locking and harmonic mode-locking at certain pulse repetition rates determined by the cavity round trip time, but it also allowed nanosecond pulsed output of the same quality to be yielded by cavity dumping at widely and continuously tunable repetition rate (ranging from kHz to MHz). Thus, WEOS-based electronically variable output coupling allows uniquely high flexibility for lasing regimes and characteristics within a single all-fiber cavity configuration.

We demonstrated how the nonlinear Fourier transform based on the Zakharov-Shabat spectral problem can be used to characterise coherent structures in dissipative systems. We consider as a particular, albeit important practical example model equation that is widely used to analyse laser radiation and demonstrate that dissipative solitons can be described by a limited number of degrees of freedom { discrete eigenvalues. Our approach can be applied for signal processing in a number of optical systems, from lasers to micro-resonators.

We present the theoretical analysis of fiber lasers with cavity dumping with the small number of active fiber cells inside the cavity in order to find the optimal gain efficiency in such systems.

A two-level iterative algorithm for finding stationary solutions of coupled nonlinear Schrödinger equations describing the propagation dynamics of an electromagnetic pulse in multimode and multicore optical fibers of various structures was developed and tested. Using as an example the proposed analytical soliton solution which is localized in space and time, test calculations were performed, and the convergence of the algorithm was demonstrated.