Analysis and minimization of cross phase modulation in semiconductor optical amplifiers for multichannel WDM optical communication systems

A theoretical model for crosstalk in multichannel wavelength division multiplexing communication systems due to cross phase saturation in semiconductor optical amplifier structure is developed. This theoretical model is used to analyze the impact of the cross phase noise on the performance of semiconductor optical amplifiers in saturation region for WDM communication system by using differential phase shift modulation format. It is shown that by increasing the carrier life time, width and thickness while reducing the confinement factor, differential gain and bias current in the SOA structure mitigates the cross talk due to cross phase saturation. The impact of penalty and cross phase noise imposed on multichannel WDM links have been investigated for different parameters of the SOA with the variation in transmission distance. With the slight increase in differential gain of 200.2 × 10⁻¹⁸ cm² and confinement factor 0.41, the maximum transmission distance observed is 5220 km with good quality and nil power penalty for 10 × 40 Gb/s soliton RZ-DPSK WDM signals for the first time.     

The Vlasov equation and the Hamiltonian mean-field model

We show that the quasi-stationary states of homogeneous (zero magnetization) states observed in the N-particle dynamics of the Hamiltonian mean-field (HMF) model are nothing but Vlasov stable homogeneous states. There is an infinity of Vlasov stable homogeneous states corresponding to different initial momentum distributions. Tsallis q-exponentials in momentum, homogeneous in angle, distribution functions are possible, however, they are not special in any respect, among an infinity of others. All Vlasov stable homogeneous states lose their stability because of finite N effects and, after a relaxation time diverging with a power-law of the number of particles, the system converges to the Boltzmann–Gibbs equilibrium.     

Boson-like quantum dynamics of association in ultracold Fermi gases

We study the collective association dynamics of a cold Fermi gas of 2N atoms in M atomic modes into a single molecular bosonic mode. When the atomic translational motion is slow compared to the atom-molecule conversion rate, the many-body fermionic problem for 2^M amplitudes is effectively reduced to a dynamical system of min{N, M} + 1 amplitudes, making the solution no more complex than the solution of a two-mode Bose-Einstein condensate and allowing realistic calculations with up to 10⁴ particles. The many-body dynamics is shown to be formally similar to the dynamics of the bosonic system under the mapping of boson particles to fermion holes, producing collective enhancement effects due to many-particle constructive interference.     

The analysis of the error statistics in a 5 × 40 Gbit/s fibre link with hybrid amplification

We quantify the error statistics and patterning effects in a 5 × 40 Gbit/s WDM RZ-OOK SMF/DCF fibre link using hybrid Raman/EDFA amplification. By extensive use of a numerical model, we determine how the error statistics change with the transmission distance. This knowledge is used as a basis for a constrained coding technique in order to improve the transmission error rate. We propose an adaptive constrained code for mitigation of the patterning effects and demonstrate that this approach can substantially reduce the bit error rate (BER) even for very large values of the channel BER (BER > 10^− 1). The proposed technique can be used in combination with forward error correction schemes (FEC) to extend the range of channel BERs that an FEC scheme is effective over.     

Crostalk in WDM SCM Systems due to SRS

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Performance improvement for N × 80-Gb/s WDM transmission link with optimized alternate polarization

In this paper, it is shown that at a high bit rate of 80-Gb/s alternate polarization of adjacent bits in a Wavelength Division Multiplexed (WDM) transmission link improves the system performance in terms of improved Q factor and minimum bit error rate (BER). Alternate Polarization Return to Zero (al-PRZ) further suppresses the non-linear effects at higher power levels of 25 dBm per channel and also improves the transmission length to 640 km for a N × 80-Gb/s WDM system and hence results in an improvement of BER to 10⁻²⁰.     

Analytical investigations on crosstalk in fiber Raman amplification for WDM systems

In this paper, the analytical investigations for the crosstalk in fiber amplification for WDM channels have been reported. The crosstalk between WDM channels with external Raman amplification including second-order dispersion terms has been investigated. It has been shown that the higher-order dispersion severely degrades the performance of optical communication systems. To ensure small crosstalk, the signal gain and the injected pump power should be limited to the value well below the threshold of Raman amplification. Analytical formula for signal interference ratio (SIR) and gain in fiber Raman amplifier including the impact of second-order dispersion terms for WDM systems has been derived at different wavelengths. It has also been shown that there is increase in crosstalk due to second-order dispersion.     

Antikaon production in nucleon- nucleon reactions near threshold

The antikaon production cross section from nucleon-nucleon reactions near threshold is studied in a meson exchange model. We include both pion and kaon exchange, but neglect the interference between the amplitudes. In case of pion exchange the antikaon production cross section can be expressed in terms of the antikaon production cross section from a pion-nucleon interaction, which we take from the experimental data if available. Otherwise, a K* -resonance exchange model is introduced to relate the different reaction cross sections. In case of kaon exchange the antikaon production cross section is related to the elastic KN and K?N cross sections, which are again taken from experimental measurements. We find that the one-meson exchange model gives a satisfactory fit to the available data for the NN → NN KK? cross section at high energies. We compare our predictions for the cross section near threshold with an earlier empirical parameterization and that from phase space models.     

Single-pion production in antiproton-proton interactions

Single-pion production in $\text{p}\text{p}$ interactions at 9.1 GeV/c is analysed and cross sections are given. The p_lab dependence of the isospin amplitudes is determined by a fit to the world data. The data are also compared with the predictions of a reggeized Deck model. The results and the $\text{N}\text{π}\text{N}$ amplitudes are compared with the results at other energies and with the corresponding NπN amplitudes.     

Evolution of cooperation in well-mixed N-person snowdrift games

We study the time evolution of cooperation in a recently proposed N-person evolutionary snowdrift game, by focusing on the details of the evolutionary dynamics. It is found that the analytic solution for the equilibrium fraction of cooperators as given previously by the replicator dynamics stems from a balance between the terms: the cost to contribute to a common task and the risk in refusing to participate in a common task. Analytic expressions for these two terms are given, and their magnitudes are studied over the whole range of parameter space. Away from equilibrium, it is the imbalance between these terms that drives the system to equilibrium. A continuous time first-order differential equation for the degree of cooperation is derived, for arbitrary interacting group size N and cost-to-benefit ratio. Analytic solutions to the time evolution of cooperation for the cases of N=2 and N=3 are obtained, with results in good agreement with those obtained by numerical simulations. For arbitrary N, numerical solutions to the equation give the time evolution of cooperation, with the long time limit giving the equilibrium fraction of cooperators.     

Modify SRS-induced crosstalk with variety of fiber in SCM–WDM transmission links

In this paper, the SRS-induced crosstalk has been evaluated in a SCM–WDM communication links at different modulation frequencies and transmission lengths for variety of fiber. Results show that SRS-induced crosstalk dominates at low frequency. As the dispersion and effective area of fiber (A_eff) decreases, initially the crosstalk remains high and then it decreases with increase in modulation frequency. The present work shows that out of five different types of fiber, standard single mode fiber (SMF) has minimum crosstalk (−78 to −38) dB, (−55 to −33) dB and (−46 to −34) dB at modulation frequencies, transmission lengths and optical powers. Dispersion compensation fiber (DCF) has maximum crosstalk (−60 to −12) dB, (−37 to −12) dB and (−27 to −12) dB at modulation frequencies and transmission lengths.     

Log-normal distribution of pulse amplitudes due to Raman cross talk in wavelength division multiplexing soliton transmission

The effect of delayed Raman response on soliton collisions in wavelength division multiplexing (WDM) transmission systems is investigated. Taking into account the stochastic nature of pulse sequences in different frequency channels and the Raman-induced cross talk, it is shown that the soliton amplitude is a random variable with a log-normal distribution. Moreover, the Raman-induced self-frequency shift and cross-frequency shift are also random variables with log-normal-like distributions. These results imply that fluctuations in soliton amplitude and frequency induced by soliton collisions in the presence of delayed Raman response play an important role in massive WDM transmission.     

A scalable hybrid WDM/OCDMA-PON based on wavelength-locked RSOA technology

A novel architecture of hybrid WDM/OCDMA-PON employing two wavelength bands for two different groups of ONUs is proposed. OCDMA is overlayed on WDM channel in a single network and the total capacity of WDM/OCDMA-PON becomes 2m times larger than the traditional WDM-PON. Meanwhile, a C + L band ultra-broadband light source is used for upstream transmission, which can be seen as a cost-effective manner in FTTH. In simulation system, 1.25 Gb/s downstream and upstream data based on the architecture are transmitted with good performance. And the crosstalk penalties from adjacent code channels (at the same wavelength) are found to be little in upstream and downstream transmissions.     

Quark models and polarized electroproduction of the Roper resonance

We calculate the recoil polarization observables for neutral pion electroproduction on the proton. In particular, for theN(938)→N ^*(1440) transition, we study these observables for several quark models of the resonant amplitudes. We find that the polarization response functions, unlike the unpolarized cross section, have encouragingly large sensitivity to the presence of the Roper. Furthermore, these observables can clearly reveal the presence of a longitudinal coupling.     

A new determination of the πN coupling constantf 2

The coupling constantf ² has been determined from forward dispersion relations for theπN helicity flip and no-flip amplitudes, using the recent information on total cross sections, phase shifts and charge exchange forward cross sections. The calculation gives also the values of the amplitudes and the first derivative at the crossing symmetry point.     

An approximate method for calculating scattering and absorption of light by fractal aggregates

A simplified version of the coupled dipole method (CDM) is proposed which allows one to reduce the initial system of 3N×3N equations to a simpler system of N×N equations. The method neglects depolarization effects in the interaction of dipoles but, unlike the mean field approximation, it takes into account local fluctuations of the scalar amplitudes of the excited dipole moments. Simple analytic solutions are obtained for integrated cross sections averaged over aggregate orientations. It is shown by the example of ballistic fractal aggregates that this method provides the accuracy close to that of a standard CDM, being substantially less time-consuming. In the case of biospheres, the approximate method is compared with the exact results of the multipole expansion.     

Amplitudes of multichannel scattering on the barrier with a constant height in the scattering direction

The immersing method is applied to solve the N-channel scattering problem. In particular, we consider the particle scattering on a multidimensional potential barrier, which is constant in the scattering direction and arbitrary in the lateral direction. For this case the scattering amplitudes t _m and r _m (m = 1, 2, …, N) are determined. Transition from the obtained formulas to the case of thin potential is performed. For this case analytical expressions of transmission amplitudes t _m and reflection amplitudes r _m are obtained. We show that the product of transmission and reflection amplitudes in the channel m does not depend on the scattering channel. It is assumed that the scattering particle falls on the potential with the longitudinal wave vector k _l corresponding to the channel l.     

The NN cross sections and resonances

The N$\text{N}$ amplitudes for J ? 2 are calculated using Bryan-Phillips non static OBEP and treating annihilation in the framework of a many channel N/D-formalism. For the first time all poles are found simultaneously with cross sections, reasonably well reproduced by adjusting only the coupling of the annihilation channel. The resonances have large widths and partial wave cross sections do not show any structure, suggesting that the recently found N$\text{N}$ resonances, both narrow and wide, are not of quasi nuclear origin.     

Amplitudes of multichannel scattering on a two-dimensional potential barrier with constant height

The immersing method is applied to solve the N-channel scattering problem for concrete potential. In particular, we consider the particle scattering on a two-dimensional potential barrier, which is constant in the scattering direction and arbitrary in the cross-section direction. For this case the scattering amplitudes t _m and r _m (1,2, m= ...,N) are determined. A transition from the obtained formulas to the case of ?-potential is performed. For this case transmission amplitudes t _m and reflection amplitudes r _m are obtained. It is also shown that the product of transmission and reflection amplitudes along the channel m does not depend on the scattering channel.     

Non-equilibrium processes in heavy-ion collisions at relativistic energies

We use transport theory to describe the inclusive cross sections for protons and pions produced in collisions between two identical heavy ions at an energy of 800 MeV per particle. In addition to the nucleonic we take the Δ-degree of freedom into account. Thus we consider a two-component system whose distributions in transverse momentum and rapidity we describe by two coupled Fokker-Planck equations. These transport equations contain the one-nucleon knock-out process as initial condition. In the limit of large interaction times they lead to thermal equilibrium (fireball) distributions. For light nuclei the interaction time is not large enough for equilibrium to be reached. A recent experiment for two colliding carbon nuclei at 800 MeV per nucleon shows evidence of nonequilibrium effects. We compare our calculations with experimental data for ¹²C on ¹²C and Ne on NaF at 800 MeV/N.