Comprehensive research on self phase modulation based optical delay systems

This paper comprehensively investigates the properties of self phase modulation based optical delay systems consisting of dispersion compensation fibre and highly nonlinear fibres. It researches into the impacts of power level launched into highly nonlinear fibres, conversion wavelength, dispersion slope, modulation format and optical filter bandwidth on the overall performance of optical delay systems. The results reveal that, if the power launched into highly nonlinear fibres is fixed, the time delay generally varies linearly with the conversion wavelength, but jumps intermittently at some conversion wavelengths. However, the time delay varies semi-periodically with the power launched into highly nonlinear fibres. The dispersion slope of highly nonlinear fibres has significant influence on the time delay, especially for the negative dispersion slope. The time delay differs with modulation formats due to the different combined interaction of nonlinearity and dispersion in fibres. The bandwidth of the optical filters also greatly affects the time delay because it determines the bandwidth of the passed signal in the self phase modulation based time delay systems. The output signal quality of the overall time delay systems depends on the conversion wavelength and input power level. The optimisation of the power level and conversion wavelength to provide the best output signal quality is made at the end of this paper.

Self-phase modulation via similariton solutions of the perturbed NLSE Modulation instability and induced self-steepening

The perturbed nonlinear Schrodinger equation(PNLSE)describes the pulse propagation in optical fibers,which results from the interaction of the higher-order dispersion effect,self-steepening(SS)and self-phase modulation(SPM).The challenge between these aforementioned phenomena may lead to a dominant one among them.It is worth noticing that the study of modulation instability(MI)leads to the inspection of dominant phenomena(DPh).Indeed,the MI triggers when the coefficient of DPh exceeds a critical value and it may occur that the interaction leads to wave compression.The PNLSE is currently studied in the literature,mainly on finding traveling wave solutions.Here,we are concerned with analyzing the similarity solutions of the PNLSE.The exact solutions are obtained via introducing similarity transformations and by using the extended unified method.The solutions are evaluated numerically and they are shown graphically.It is observed that the intensity of the pulses exhibits self steepening which progresses to shock soliton in ultrashort time(or near t=0).Also,it is found that the real part of the solution exhibits self-phase modulation in time.The study of(MI)determines the critical value for the coefficients of SS,SPM,or high dispersivity to occur.

Linear and nonlinear propagation characteristics of multi-Gaussian laser beams

Theoretical investigation on the propagation characteristics of a new class of laser beams known as multi Gaussian(M.G)laser beams has been presented.To investigate the linear characteristics,propagation of the laser beam in vacuum has been considered.Whereas,the nonlinear characteristics have been investigated in plasmas.Optical nonlinearity of the plasma has been modeled by relativistic mass nonlinearity of the plasma electrons in the field of laser beam.Formulation is based on finding the semi analytical solution of the wave equation for the slowly varying envelope of the laser beam.Particularly,the dynamical evolutions of the beam width and longitudinal phase of the laser beam have been investigated in detail.

Performance limit of a multi-frequency probe based coherent optical time domain reflectometry caused by nonlinear effects

The nonlinear effects that limit the performance of the multi-frequency probe（MFP）based coherent optical time domain reflectometry（C-OTDR）are investigated.Based on theoretical analysis and experimental results,compared with conventional C-OTDR,when the probe pulse has power gradient within the pulse width,self-phase modulation（SPM）and cross-phase modulation（XPM）are strengthened in the new C-OTDR scheme.The generation of four-wave mixing（FWM）is dependent on SPM and XPM,and with modulation frequency of phase modulator higher than 40 MHz,the stimulated Brillouin scattering（SBS） threshold can be enhanced by more than 5 dB,which benefits the maximum dynamic range of the MFP C-OTDR.

Supercontinuum generation at 1.55 μm in an all-normal dispersion photonic crystal fiber with high-repetition-rate picosecond pulses

We demonstrate the generation of supercontinuum(SC) spectrum covering S+C+L band of optical communication by injecting 1.4 ps optical pulses with center wavelength of 1552 nm and repetition rate of 10 GHz into an all-normal dispersion photonic crystal fiber(PCF) with length of 80 m. The experimental results are in good agreement with the numerical simulations, which are used to illustrate the SC generation dynamics by self-phase modulation and optical wave breaking(WB).

Influence of group-delay ripple on timing jitter induced by SPM and IXPM in systems with dispersion compensated by CFBG

An analytical expression was proposed to analyze the influence of group-delay ripple （GDR） on timing jitter induced by self-phase modulation （SPM） and intra-channel cross-phase modulation （IXPM） in pseudolinear transmission systems when dispersion was compensated by chirped fiber Bragg grating （CFBG）. Effects of ripple amplitude, period, and phase on timing jitter were discussed by theoretical and numerical analysis in detail. The results show that the influence of GDR on timing jitter changes linearly with the amplitude of GDR and whether it decreases or increases the timing jitter relies on the ripple period and ripple phase. Timing jitter induced by SPM and IXPM could be suppressed totally by adjusting the relative phase between the center frequency of the pulse and the ripples.

Multi-pulse operation of a Kerr-lens mode-locked femtosecond laser

Our experimental results show that the presence of a proper amount of negative group velocity dispersion is essential to multi-pulse operation of a Kerr-lens mode-locked femtosecond laser. We demonstrate that the pulse separations and the number of pulses contained within a cavity round trip are strongly dependent on the initial perturbations. The results allow us to get a better understanding on the influences of the convoluted self-phase modulation and intra-cavity dispersions on the stable multi-pulse oscillation in a Kerr-lens mode-locked femtosecond laser.