Dispersion Management Technique Research Articles

Overcoming Fiber Nonlinear Effects in Large Capacity Optical Transmission Systems

We have tackled the technical challenge of how to mitigate fiber nonlinearity effects in our high-speed optical communication systems. Over the last decade, we have improved the tolerance to nonlinearity by 30 dB by developing numerous technologies that can be categorized into four types:(1) new design of optical fibers to reduce nonlinearity, (2) transmission and signal amplification technologies that reduce signal power level without optical SNR degradation, (3) dispersion management techniques to reduce the nonlinear interactions, and (4) new modulation formats and forward-error-correction techniques. We believe that a deeper understanding of fiber nonlinearity effects will make it possible to realize more cost effective and transparent optical networks in the near future.

Controllability of Solitons Propagating in Optical Fiber Transmission System

We review theoretical studies on transmission control and dispersion management techniques which have introduced in optical soliton communication systems to increase the bit rate and extend the transmission distance. A systematic procedure to synthesize a control system is presented and the ability to reduce the timing jitter arising from the amplifier noise is compared for several control systems. The dispersion-managed(DM) soliton solution is also presented.

On the characteristics of an optical pulse propagation in an inhomogeneous fibre and dispersion management

Properties of an optical pulse propagating in an optical fibre whose refractive index is inhomogeneous in the transverse direction are studied. A variational technique has been used to study the change in an initially chirped Gaussian pulse with a ‘sech’ type amplitude. The nonlinear ordinary differential equations so generated are studied numerically to analyze their stability properties in several physical situations. In the second part of the paper, we discuss how the technique of dispersion management can be applied to the problem. The space variation of amplitude, chirp, etc. are obtained numerically and it is found that their behaviours are sensitive to the sign of ‘ s’, the coefficient of inhomogeneity, when dispersion management is there and also on the amplification distance Z a.

Dispersion management for atomic matter waves.

We demonstrate the control of the dispersion of matter wave packets utilizing periodic potentials. This is analogous to the technique of dispersion management known in photon optics. Matter wave packets are realized by Bose-Einstein condensates of 87Rb in an optical dipole potential acting as a one-dimensional waveguide. A weak optical lattice is used to control the dispersion relation of the matter waves during the propagation of the wave packets. The dynamics are observed in position space and interpreted using the concept of effective mass. By switching from positive to negative effective mass, the dynamics can be reversed. The breakdown of the approximation of constant, as well as experimental signatures of an infinite effective mass are studied.

Long-haul 40 Gb/s DWDM transmission with aggregate capacities exceeding 1 Tb/s

We present an experimental investigation of 40 Gb/s transmission technology aimed at an aggregate capacity exceeding 1 Tb/s over multithousand kilometer transmission distances. These studies have been performed using a variety of dispersion management and modulation techniques. The transmission distances investigated range from a minimum of 2000 km, which is considered a regional undersea cable distance, up to a transatlantic distance of 6200 km. Our regional distance experiments were performed using both slope-matched and conventional dispersion maps where the accumulated dispersion becomes large for the edge channels. Dispersion map studies showed that slope-matched fiber performs better than nonslope-matched fiber (NZDSF) beyond 2000 km due to its larger effective area and lower accumulated dispersion slope. The demonstration of 38/spl times/40 Gb/s over 6200 km was the first transoceanic length experiment using 40 Gb/s DWDM channels. This was achieved with a relatively simple amplifier chain that uses only C-band EDFAs. Modulation format studies showed that RZ performs better over transoceanic distance, carrier-suppressed RZ performs better with nonslope-matched fiber at a distance of 2055 km, and prefiltered carrier-suppressed RZ is more suited for higher spectral efficiency. Experimental techniques for high bit-rate experiments are presented.

Long-haul WDM transmission with 20 Gbit/s data channels using Raman-assisted optical amplification

The impact of Raman amplification on the optical and electrical signal-to-noise ratios of a high-speed signal (20 Gbit/s) is discussed. Combining Raman amplification with wideband higher-order fibre dispersion management technique yields successful long-haul Tbit/s-capacity wavelength-division multiplexed transmission based on the use of high-speed data channels.

Stabilizing effects of dispersion management

A cubic nonlinear Schrödinger equation (NLS) with periodically varying dispersion coefficient, as it arises in the context of fiber-optics communication, is considered. For sufficiently strong variation, corresponding to the so-called strong dispersion management regime, the equation possesses pulse-like solutions which evolve nearly periodically. This phenomenon is explained by constructing ground states for the averaged variational principle and justifying the averaging procedure. Furthermore, it is shown that in certain critical cases (e.g. quintic nonlinearity in one dimension and cubic nonlinearity in two dimensions) the dispersion management technique stabilizes the pulses which otherwise would be unstable. This observation seems to be new and is reminiscent of the well-known Kapitza’s effect of stabilizing the inverted pendulum by rapidly moving its pivot.

High Bit Rate OTDM-Transmission on Standard Fibre

Summary In this paper we describe experimental and numerical studies on high bit rate, single span transmission system over a length of 160 km without amplifiers in the link (unrepeatered). From these studies we revealed that the tolerance of the residual dispersion is very restrictive. Proper dispersion management and PMD compensation techniques are important topics in these and future systems.

Long-haul 16 x 10 Gb/s WDM transmission experiment using higher order fiber dispersion management technique

We propose a dispersion management scheme for long-haul wavelength-division-multiplexed (WDM) transmission systems that considers not only second-, but also third-order dispersion using transmission fibers with opposite dispersion signs; it eliminates waveform distortion due to the existence of third-order dispersion with reducing interchannel interaction caused by fiber nonlinearity. With this technique, WDM transmission with a total capacity of 160 Gb/s is demonstrated over 9412 km.

Terminal dispersion management for 8×10 Gbit/s long-haul transmission over nonzero dispersion-shifted fibre

The design of terminal dispersion management in 8×10 Gbit/s long-haul transmission system over nonzero dispersion-shifted fibre is presented in this paper through simulation. Wide-range dispersion management for all channels can be realised by terminal dispersion management technique. The optimal precompensation ratio is almost kept constant at 65% for a wide range of span numbers N and nonlinearity factor γP while the total compensation ratio (always <1) slightly decreases for higher N and γP. The eye-opening penalty of a 6×80 km system with γP=0.007/km can be less than 0.8 dB for a total compensation ratio in the range 60–85%.

Quarter Tbit/s (25 × 10 Gbit/s) over 9288km WDMtransmission experiment using nonlinearsupported RZ pulse in higher order dispersionmanaged line

It is experimentally shown that RZ pulse transmission without significant spectral broadening over a wide wavelength range is possible in higher order dispersion managed fibre spans. The use of this technique, together with wideband fibre dispersion and optical passband management techniques, yields long-distance WDM transmission with the largest capacity of 25 × 10 Gbit/s over 9000 km.

Optimal dispersion management for a wavelength division multiplexed optical soliton transmission system

Soliton's frequency shift arising from the pulse collision between wavelength division multiplexed (WDM) channels in an optical transmission line may be reduced by dispersion management technique. The reduction mechanism is due to a cancellation between the shifts in normal and anomalous dispersion fibers. With a proper management of the dispersion, the effect of lumped amplifiers on the frequency shift may also be canceled out. In this paper, we give a detailed analysis of the frequency shift in dispersion managed systems, and explain the reduction mechanism of the shift. We then propose optimal dispersion management schemes by means of minimizing the frequency shift. We also present a statistical analysis of the collision induced timing jitter for a two-channel WDM system.

Analytical performance evaluation of nonreturn-to-zero transmission systems operating in normally dispersive nonlinear fibers

An analytical theory for the evaluation of the performance of a nonreturn-to-zero (NRZ) transmission system operating in weakly normally dispersive nonlinear fibers is presented. Explicit expressions are given to compute an estimate of the transmission bit error rate, and those are compared with results obtained through numerical simulations. A good agreement is found, both for systems having fibers with a constant dispersion value, and for systems encompassing dispersion management technique.

160 Gb/s in 28-nm WDM transmission over 238 km of DSF with standard fiber compensation

160 Gb/s (8/spl times/20 Gb/s PRBS NRZ channels) have been transmitted on a 28-nm optical bandwidth over three DSF amplifier spans for a total distance of 238 km. The dispersion management technique, based upon the use of standard fiber, includes both partial in-line compensation and individual channel compensation at the output of the receiver demultiplexer.

Modulational instabilities in fibers with periodic dispersion management

We analytically and numerically analyze the occurrence of modulational instability in fibers with periodic changes in the group-velocity dispersion. For small variations, a set of resonances occurs in the gain spectrum. However, large dispersion variations eliminate these resonances and restrict the bandwidth of the fundamental gain spectrum. This research has been motivated by the adoption of dispersion management techniques in long-haul optical communications.

Performance evaluation of very long span direct detection intensity and polarization modulated systems

In this paper long distances very high capacity NRZ optical transmission systems adopting direct detection are considered in links with a low average chromatic dispersion. Particular attention is devoted to polarization modulated (PM-DD) systems. Polarization modulated systems results to he more degraded with respect to intensity modulated (IM-DD) systems by the light depolarization induced by the interplay among the Kerr effect, the ASE noise of the optical amplifiers and the polarization mode dispersion. The light depolarization is particularly strong in conditions of large spectral broadening that are met when the chromatic dispersion value is maintained very low along the link. On the other hand the use of a fluctuating chromatic dispersion with a mean value equal to zero, whereas the local dispersion is different from zero, shows the double advantage to reduce the chromatic dispersion impairments and to limit the spectral broadening. The advantages offered by this dispersion management technique have been already shown in several experiments for IM-DD systems: in this work we show that this technique is very important also for PM-DD systems since the limitation in the spectral broadening reduces the light depolarization. We show that adopting a suitable dispersion management and an opportune preamplifier optical filter transmissions at 5 Gb/s can be attained in transoceanic links by means of FM-DD systems.

Comparison of the performance of optically amplified transmission systems

In this paper, we show a comparison among the performance of single- and multichannel optical systems considering NRZ and soliton signals. The results have been obtained by means of numerical simulations, taking into consideration the chromatic dispersion, the Kerr nonlinearity, the fiber loss, and the ASE noise of the optical amplifiers. The performance of IM-DD and coherent asynchronous ASK systems have been evaluated in terms of the Q factor. We have considered the propagation in links encompassing conventional step-index fibers, DS fibers and in links with two different dispersion management techniques in which the chromatic dispersion is varied along the propagation distance both in randomly and in deterministically way. The effects of the in-line filtering process are mainly investigated in soliton propagation.

Modeling of four-wave mixing and gain peaking in amplified WDM optical communication systems and networks

A theoretical model is presented for analyzing the propagation of densely spaced WDM optical signals through a cascade of erbium-doped fiber amplifiers and single-mode optical fibers with nonuniform chromatic dispersion. By combining a numerical solution for the EDFA and an analytical expression for FWM components generated through the cascade, the model allows a realistic system analysis which includes gain peaking effect, amplified spontaneous emission accumulation and the effect of dispersion management on the four-wave mixing efficiency. The FWM power distribution at the end of the multi-amplifier transmission link is computed taking into account the phase relation between FWM light amplitudes generated within different sections of the link. The transmission of many WDM channels, evenly spaced around 1547.5 nm, has been analyzed for various dispersion management techniques and propagation distances. Numerical results point out the importance of such a model for a realistic design of WDM optical communication systems and networks. A proper choice of chromatic dispersion, amplifier characteristics, span length, input signal powers and wavelengths, combined with the use of gain equalizing filters, allows to maximize the transmission distance ensuring acceptable signal-to-noise ratio (SNR) and limited SNR variation among channels.

2.5 Gbit/s-9720 km, 10 Gbit/s-6480 km transmissioninthe FSA commercial system with 90 km spaced opticalamplifier repeaters and dispersion-managed cables

The authors report 2.5 and 10 Gbit/s transoceanic distance transmission in a commercial FSA optical amplifier system which has 90 km repeater spacing. The unique fibre dispersion management technique and amplifier passband management scheme used in the system are successfully demonstrated. The SNR improvement achieved with polarisation scrambling is also reported.

Light depolarisation in long fibre links

Light depolarisation in nonsoliton long-haul fibre links is studied. If dispersive effects are absent, the degree of polarisation can be calculated analytically, while in the presence of dispersive effects a numerical analysis is used. Results show how a dispersion management technique enables maintainance of a high degree of polarisation in transoceanic distances.