Power pre-emphasis for suppression of FWM in coherent optical OFDM transmission

Four-wave-mixing (FWM) due to the fiber nonlinearity is a major limiting factor in coherent optical OFDM transmission. We propose to apply power pre-emphasis, i.e. to allocate the transmitted power nonuniformly among subcarriers in order to suppress the FWM impairment. The proposed technique was numerically investigated for both single channel 15.6 Gbs CO-OFDM transmissions and 7-channel WDM transmissions, showing that up to 1 dB improvement in the system's Qfactor can be achieved without considering sophisticated power loading algorithms developed for wireless communications

Oscillating tails of dispersion-managed soliton

Oscillating tails of dispersion-managed optical fiber system are studied for strong dispersion map in the framework of path-averaged Gabitov-Turitsyn equation. The small parameter of the analytical theory is the inverse time. An exponential decay in time of soliton tails envelope is consistent with nonlocal nonlinearity of Gabitov-Turitsyn equation, and the fast oscillations are described by a quadratic law. The pre-exponential modification factor is the linear function of time for zero average dispersion and cubic function for nonzero average dispersion.Comment: 6 pages, 4 figures; submitted to Jounal of the Optical Society of America

Simultaneous imaging of diesel spray atomisation and evaporation processes in a single-cylinder CR diesel engine

This document is the Accepted Manuscript version of the following article: Mohammad Reza Herfatmanesh, Mohammadreza Anbari Attar, and Hua Zhao, ‘Simultaneous imaging of diesel spray atomisation and evaporation processes in a single-cylinder CR diesel engine’, Experimental Thermal and Fluid Science, Vol. 50, pp. 10-20, October 2013. © 2013 Elsevier Inc. This manuscript version is made available under the terms of the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/. The Version of Record is available online at DOI: https://doi.org/10.1016/j.expthermflusci.2013.04.019 :In direct injection diesel engines, combustion and formation of pollutants are directly influenced by the spatial and temporal distributions of the injected fuel. In this study mixture formation during the pre-combustion phase of a diesel engine was investigated using the laser-induced exciplex fluorescence (LIEF) technique. The main purpose of this investigation was to develop an experimental setup capable of providing the full-field view of both liquid and vapour phases of evaporating diesel sprays during the fuel injection process inside the combustion chamber of a diesel engine with optical access. An expanded laser beam was employed for full combustion chamber visualisation. In this study two model fuels were tested; one consisted of 89% decane, 10% α-methyl-naphthalene and 1% TMPD and the other 88% decane, 10% α-methyl-naphthalene and 2% TMPD. The spray atomisation and evaporation processes during the pre-combustion phase of a diesel engine were measured at an injection pressure of 1200 bar and the engine speed of 1500 rpm. The results demonstrated the capability of the full-field LIEF technique in simultaneous imaging of liquid fraction and fuel vapour distribution during high pressure fuel injection process. It also highlighted the effect of dopant concentration on the fluorescence intensity of liquid and vapour signals. The exciplex system containing 1% TMPD produced better visualisation of the liquid phase, though the crosstalk in the vapour phase precluded accurate detection of the vapour phase signal. In contrast, the exciplex system containing 2% TMPD resulted in satisfactory visualisation of the vapour phase; however the intensity of the liquid phase was compromised as a result. This was presumed to be mainly due to the spectral shift of the exciplex species and/or TMPD decomposition at elevated temperatures and pressures.Peer reviewedFinal Accepted Versio

On non-local variational problems with lack of compactness related to non-linear optics

We give a simple proof of existence of solutions of the dispersion manage- ment and diffraction management equations for zero average dispersion, respectively diffraction. These solutions are found as maximizers of non-linear and non-local vari- ational problems which are invariant under a large non-compact group. Our proof of existence of maximizer is rather direct and avoids the use of Lions' concentration compactness argument or Ekeland's variational principle.Comment: 30 page

Deterministic Raman crosstalk effects in amplified wavelength division multiplexing transmission

We study the deterministic effects of Raman-induced crosstalk in amplified wavelength division multiplexing (WDM) optical fiber transmission lines. We show that the dynamics of pulse amplitudes in an N-channel transmission system is described by an N-dimensional predator-prey model. We find the equilibrium states with non-zero amplitudes and prove their stability by obtaining the Lyapunov function. The stability is independent of the exact details of the approximation for the Raman gain curve. Furthermore, we investigate the impact of cross phase modulation and Raman self and cross frequency shifts on the dynamics and establish the stability of the equilibrium state with respect to these perturbations. Our results provide a quantitative explanation for the robustness of differential-phase-shift-keyed WDM transmission against Raman crosstalk effects.Comment: 34 pages and 12 figures. Revised paper. Submitted to Optics Communication

Supply-Power-Constrained Cable Capacity Maximization Using Multi-Layer Neural Networks

We experimentally solve the problem of maximizing capacity under a total supply power constraint in a massively parallel submarine cable context, i.e., for a spatially uncoupled system in which fiber Kerr nonlinearity is not a dominant limitation. By using multi-layer neural networks trained with extensive measurement data acquired from a 12-span 744-km optical fiber link as an accurate digital twin of the true optical system, we experimentally maximize fiber capacity with respect to the transmit signal's spectral power distribution based on a gradient-descent algorithm. By observing convergence to approximately the same maximum capacity and power distribution for almost arbitrary initial conditions, we conjecture that the capacity surface is a concave function of the transmit signal power distribution. We then demonstrate that eliminating gain flattening filters (GFFs) from the optical amplifiers results in substantial capacity gains per Watt of electrical supply power compared to a conventional system that contains GFFs.Comment: arXiv admin note: text overlap with arXiv:1910.0205

Remote (250 km) Fiber Bragg Grating Multiplexing System

We propose and demonstrate two ultra-long range fiber Bragg grating (FBG) sensor interrogation systems. In the first approach four FBGs are located 200 km from the monitoring station and a signal to noise ratio of 20 dB is obtained. The second improved version is able to detect the four multiplexed FBGs placed 250 km away, offering a signal to noise ratio of 6–8 dB. Consequently, this last system represents the longest range FBG sensor system reported so far that includes fiber sensor multiplexing capability. Both simple systems are based on a wavelength swept laser to scan the reflection spectra of the FBGs, and they are composed by two identical-lengths optical paths: the first one intended to launch the amplified laser signal by means of Raman amplification and the other one is employed to guide the reflection signal to the reception system

Exact two-particle eigenstates in partially reduced QED

We consider a reformulation of QED in which covariant Green functions are used to solve for the electromagnetic field in terms of the fermion fields. It is shown that exact few-fermion eigenstates of the resulting Hamiltonian can be obtained in the canonical equal-time formalism for the case where there are no free photons. These eigenstates lead to two- and three-body Dirac-like equations with electromagnetic interactions. Perturbative and some numerical solutions of the two-body equations are presented for positronium and muonium-like systems, for various strengths of the coupling.Comment: 33 pages, LaTex 2.09, 4 figures in EPS forma

Temperature-dependent cross sections for meson-meson nonresonant reactions in hadronic matter

We present a potential of which the short-distance part is given by one gluon exchange plus perturbative one- and two-loop corrections and of which the large-distance part exhibits a temperature-dependent constant value. The Schrodinger equation with this temperature-dependent potential yields a temperature dependence of the mesonic quark-antiquark relative-motion wave function and of meson masses. The temperature dependence of the potential, the wave function and the meson masses brings about temperature dependence of cross sections for the nonresonant reactions pi pi -> rho rho for I=2, KK -> K* K* for I=1, KK* -> K* K* for I=1, pi K -> rho K* for I=3/2, pi K* -> rho K* for I=3/2, rho K -> rho K* for I=3/2 and pi K* -> rho K for I=3/2. As the temperature increases, the rise or fall of peak cross sections is determined by the increased radii of initial mesons, the loosened bound states of final mesons, and the total-mass difference of the initial and final mesons. The temperature-dependent cross sections and meson masses are parametrized.Comment: 42 pages with 10 figure