Train Of Optical Solitons Research Articles

Femtosecond laser inscriptions in Kerr nonlinear transparent media: dynamics in the presence of K-photon absorptions, radiative recombinations and electron diffusions

Femtosecond lasers interacting with Kerr nonlinear optical materials, propagate in form of filaments due to the balance of beam diffraction by self-focusing induced by the Kerr nonlinearity. Femtosecond laser filamentation is a universal phenomenon that belongs to a general class of processes proper to ultrashort lasers processing systems, associated with the competition between nonlinearity and dispersion also known to promote optical solitons. The present work considers a model describing femtosecond laser inscriptions in a transparent medium with Kerr nonlinearity. Upon inscription, the laser stores energy in the optical material which induces an electron plasma. The model consists of a cubic complex Ginzburg-Landau equation, in which an additional K-order nonlinear term takes into account K-photon absorption processes. The complex Ginzburg-Landau equation is coupled to a time first-order nonlinear ordinary differential equation, accounting for time evolution of the plasma density. The main objective of the study is to examine effects of the competition between multi-photon absorptions, radiative recombination and electron diffusion processes, on temporal profiles of the laser amplitude as well as of the plasma density. From numerical simulations, it is found that when the photon number (i.e. K) contributing to multiphoton ionization is large enough, taking the electron diffusion processes into account favours periodic structures in temporal profiles both of the laser and the plasma density. The pulse repetition rate in the optical soliton train is increased with increase of the electron diffusion coefficient, while the plasma density is a train of multi-periodic anharmonic wave patterns.

Soliton radiation beat analysis of optical pulses generated from two continuous-wave lasers.

We propose a fibre-based approach for generation of optical frequency combs (OFCs) with the aim of calibration of astronomical spectrographs in the low and medium-resolution range. This approach includes two steps: in the first step, an appropriate state of optical pulses is generated and subsequently moulded in the second step delivering the desired OFC. More precisely, the first step is realised by injection of two continuous-wave (CW) lasers into a conventional single-mode fibre, whereas the second step generates a broad OFC by using the optical solitons generated in step one as initial condition. We investigate the conversion of a bichromatic input wave produced by two initial CW lasers into a train of optical solitons, which happens in the fibre used as step one. Especially, we are interested in the soliton content of the pulses created in this fibre. For that, we study different initial conditions (a single cosine-hump, an Akhmediev breather, and a deeply modulated bichromatic wave) by means of soliton radiation beat analysis and compare the results to draw conclusion about the soliton content of the state generated in the first step. In case of a deeply modulated bichromatic wave, we observed the formation of a collective soliton crystal for low input powers and the appearance of separated solitons for high input powers. An intermediate state showing the features of both, the soliton crystal and the separated solitons, turned out to be most suitable for the generation of OFC for the purpose of calibration of astronomical spectrographs.

Generation of Solitons and Train of Soliton Pulses in Three Level Λ-Type Cold Atom Electromagnetically Induced Transparency System

We point out that a train of optical solitons can be generated in a cold-atom system by modulational instability (MI). By numerical simulation, we not only prove that the MI analysis of equations of motion for the atomic-state amplitudes and probe field can be replaced with that of one nonlinear Schrodinger equation, but also give the similarities and differences in the generation of the soliton wave train between the original Maxwell–Schrodinger equations and the nonlinear Schrodinger equation. Through the numerical simulation of the original equation of motion, we found that the generation of a single soliton or a couple of solitons can be achieved by adjusting the initial pulse amplitude, and propose a quantitative relationship. These results are different from those in previous reports, which mainly focus on the kind of nonlinear pulse that can propagate stably in an electromagnetically induced transparency (EIT) medium. The merits and shortages of our scheme are also shown by comparing what with a fi...

Electrostriction temporal shift of laser pulses in optical fibres

A model is proposed which describes the electrostriction temporal shift of laser pulses in their high-frequency train propagating in an optical fibre. The validity of the model is confirmed by good agreement of its predictions with the results of studies of relative temporal shifts in the high-frequency train of optical solitons known from the literature. The model predicts the possibility of a substantial reduction of temporal shifts in the data pulse train in fibreoptic links composed of fibres with different signs of dispersion. For comparatively low pulse repetition rates (less than 500 MHz), the oscillating dependence of the relative temporal shift of pulses on the data transmission rate is found.

Random evolution and coherence degradation of a high-order optical soliton train in the presence of noise

The intrinsic evolution of a high-order soliton described by the nonlinear Schrödinger equation is initiated by a self-four-wave mixing effect (or modulational instability) and recurs neatly every soliton period. We show that when there is noise such as amplified spontaneous emission, however, a high-order soliton evolves randomly and independently and is distorted because the evolution is initiated by noise. Thus the time and the frequency coherence of a soliton pulse train are both greatly degraded.

Generation of a train of soliton pulses by induced modulational instability in optical fibers

The modulational instability of a cw optical signal in a glass fiber combined with an externally applied amplitude modulation can be utilized to produce a train of optical solitons with a wide range of pulse width (50-1 psec) and repetition period ( less, similar250 psec).