Michail P. Fedoruk

Reduced-power optical solitons in fiber lines with short-scale dispersion management

We examine the properties of dispersion-managed (DM) solitons in fiber lines with dispersion-compensation period L much shorter than amplification distance Z(a) . DM solitons in systems with short-scale dispersion compensation have reduced power compared with DM solitons in previously studied regimes with L>/=Z(a) power (for the same local and average dispersion and the same pulse width). As a result, chirped DM soliton transmission with reasonably low power can be realized with shorter pulses when DM solitons in systems with large L/Z(a) ratios have energies that are too high to be used in practice.

Sub-critical regime of femtosecond inscription

We apply well known nonlinear diffraction theory governing focusing of a powerful light beam of arbitrary shape in medium with Kerr nonlinearity to the analysis of femtosecond (fs) laser processing of dielectric in sub-critical (input power less than the critical power of self-focusing) regime. Simple analytical expressions are derived for the input beam power and spatial focusing parameter (numerical aperture) that are required for achieving an inscription threshold. Application of non-Gaussian laser beams for better controlled fs inscription at higher powers is also discussed.

Modulation instability in high power laser amplifiers

The modulation instability (MI) is one of the main factors responsible for the degradation of beam quality in high-power laser systems. The so-called B-integral restriction is commonly used as the criteria for MI control in passive optics devices. For amplifiers the adiabatic model, assuming locally the Bespalov-Talanov expression for MI growth, is commonly used to estimate the destructive impact of the instability. We present here the exact solution of MI development in amplifiers. We determine the parameters which control the effect of MI in amplifiers and calculate the MI growth rate as a function of those parameters. The safety range of operational parameters is presented. The results of the exact calculations are compared with the adiabatic model, and the range of validity of the latest is determined. We demonstrate that for practical situations the adiabatic approximation noticeably overestimates MI. The additional margin of laser system design is quantified.

Dispersion-management in fiber communication lines using Raman amplification

We propose a dispersion management scheme combined with Raman amplification that supports strongly confined optical pulses with potential applications in ultra-high speed single-channel optical communication systems.

On the theory of the modulation instability in optical fiber amplifiers

The modulation instability (MI) in optical fiber amplifiers and lasers with anomalous dispersion leads to cw radiation breakup. This can be both a detrimental effect limiting the performance of amplifiers and an underlying physical mechanism in the operation of MI-based devices. Here we revisit the analytical theory of MI in fiber optical amplifiers. The results of the exact theory are compared with the previously used adiabatic approximation model, and the range of applicability of the latter is determined.

Direct modeling of error statistics at 40 Gbit/s rate in SMF/DCF link with strong bit overlapping

Through extensive direct modeling we determine exponential tails of the probability density functions for marks/spaces and quantify patterning effect in the error statistics for SMF/DCF transmission at 40 Gbit/s. Simple derived analytical approximations for the PDF tails enable us to accurately predict the error rate.

Magic dispersion maps for multichannel soliton transmission

Using asymptotic theory and a momentum method, we have identified a family of dispersion management schemes that are advantageous for massive multichannel soliton transmission. For the practical case of two-step dispersion maps, special schemes are found that have optimal launch point locations (where no pulse prechirping is needed) that are independent of the fibers dispersion. Despite the variation of dispersion with respect to carrier wavelength due to the fibers dispersion slope, the transmission in several different channels can be optimized simultaneously using the same optimal launch point. Theoretical predictions are verified by direct numerical simulations.

Optimal power budget in quasi-linear dispersion-managed fiber links

We have developed a theory of power budget optimization in dispersion-managed cascaded optical amplifier systems. It can be used for a variety of systems and can be easily generalized for more complex configurations. Applying our general results to a specific configuration we analyzed a novel design of the transmission system with periodically imbalanced in-line amplification.

Adaptive Pulse Shaping Through BER Feedback

We propose a simplified approach to optical signal pre-distortion based on adaptive pulse shaping through unconventional use of a MZ modulator. The scheme allows natural tailoring of transmitted pulses by optimising the received pulse.

Patterning of Errors in 40 Gbit/s WDM RZ-DBPSK SMF/DCF Optical Transmission System

Through extensive direct modelling we quantify patterning effects in a WDM RZ-DBPSK fibre link at 40 Gbit/s channel rate. We demonstrate BER improvement through skewed channel pre-encoding reducing the occurrence of the most dangerous triplets.