Soliton Transmission Research Articles

An historical review of application of optical solitons for high speed communications.

The history of application of optical solitons for high speed communications presents an interesting example of how an abstract mathematical concept has been put into practical use. The historical development introduced in this manuscript is divided into five stages: (1) historical background and the discovery of the optical soliton, (2) the idea and demonstration of all optical soliton transmission systems, (3) identification of possible problems, (4) demonstration of soliton control and (5) discovery of dispersion managed optical solitons (DMS). Although there are many interesting related subjects such as modulational instability, dark solitons, and spatial solitons, the manuscript focuses only on the subject of primarily theoretical developments of soliton based communications in fibers. (c) 2000 American Institute of Physics.

Tolerance of dispersion-managed soliton transmission to the shape of the input pulses

We showed that long-distance transmission is affected by the source pulse tails. Fast tail dropoff dramatically improves the transmission. We found that the tails must be at least 20 dB down 50 ps from the peak in order to successfully transmit signals over 20 000 km at 20 Gbit/s with anomalous path average dispersion. While tails that are 15 dB down 50 ps from the peak are sufficient to transmit data at 10 Gbit/s over 20 000 km with anomalous path average dispersion, the tails must be down at least 25 dB 50 ps from the peak to transmit data with slightly normal path average dispersion.

Stabilized scheme for dispersion management

We introduce a model in which completely stable propagation of dispersion-managed (DM) solitons is provided by periodic coupling of the system fiber’s core to short segments of a parallel lossy core. Considering the model in the distributed approximation, we identified a vast stability domain in its parameter space. We also obtained a set of DM-strength–power characteristics for stable solitons at fixed values of the DM period. We found that, as for the filtered single-core DM model, stable transmission of the solitons is possible at virtually all the values of the DM strength, whereas the normalized peak power of the pulse must exceed a certain minimum value. Close to this minimum, we found a stable transmission regime with moderate values of the DM strength, S∼3, and a DM period of approximately 1.5–2 soliton periods (defined as for the homogeneous fiber), which may be promising for reducing soliton–soliton interactions. We also found cases in which the soliton transmission remained stable in the corresponding strongly discrete (lumped) model as well as at normal average dispersion.

Feasibility of densely dispersion managed soliton transmission at 160 Gb/s

We numerically demonstrate 160 Gb/s densely dispersion-managed soliton transmission in a single channel over 2000 km in the dispersion-flattened fibers in the presence of polarization mode dispersion and of large variation in group-velocity dispersion. The best performance is achieved by a proper design of the dispersion profile with possible minimum average dispersion, so that the soliton interactions are minimized.

Stable transmission of solitons in the region of normal dispersion

We study in detail stability of exact chirped solitary-pulse solutions in a model in which stabilization of the pulses is achieved by means of short segments of an extra lossy core, which is parallel coupled to the main one. We demonstrate that, in the model’s three-dimensional parameter space, there is a vast region in which the pulses are fully stable, for both signs of the group-velocity dispersion. These results open the way to a stable transmission of solitary optical pulses in the normal-dispersion region and thus to an essential expansion of the bandwidth offered by the nonlinear optical fibers for telecommunications in the return-to-zero regime. In the cases in which the pulses are unstable, we study the development of the instability, which may end by either blowing up or decaying to zero. In the case when the pulses are stable, we also simulate interactions between them, concluding that they always eventually merge into one pulse.

Dispersion Managed Solitons: The Key to Terabit Per Second Optical Fiber Communication Systems

Dispersion managed solitons, now being developed by a number of different groups, can resolve the technical problems that in the past have prevented the use of the soliton transmission format in optical fiber communication systems. Given the rapid progress being made by researchers, within two years an Internet backbone powered by these inherently stable and robust nonlinear optical pulses will be a reality.

Nonlinear Gain Control of Dispersion-Managed Soliton Amplitude and Collisions

The stabilizing action of nonlinear gain on dispersion-managed soliton transmissions is investigated. By means of a proper combination of nonlinear gain and filtering, the background and amplitude instability introduced by lumped guiding filters can be controlled. Indeed, radiative background that may not be separated from the signal when the average dispersion is close to zero is shown to be suppressed. Taking advantage of the large tolerance with respect to input energy variations, dispersion-managed solitons are found to be stable after collisions among different frequencies when supported by the same nonlinear gain element for all channels. This demonstrates the feasibility of nonlinear gain for wavelength-division-multiplexed transmissions and may open up the possibility of high-speed soliton transmission with large tolerance with respect to power fluctuations and densely packed wavelength channels.

1 ps pulse generation from a harmonically mode-locked erbium-doped fiber ring laser and its application to optical communication systems

This paper describes a very simple and stable harmonically mode-locked erbium-doped fiber ring laser that produces high-peak-power, 1 ps transform-limited sech2 optical pulses at 1564 nm at a repetition rate of 1 GHz. This very short pulse duration is attributed to the insertion of a comb generator in the modulation scheme. The temporal and spectral characteristics of the pulses are studied. Soliton transmission over 40 km of standard nondispersion-shifted single-mode fiber is demonstrated using this laser. ©2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 24: 285–287, 2000.

Ultrahigh-speed long-distance TDM and WDM soliton transmission technologies

Recent progress on time-division multiplexed (TDM) and wavelength-division multiplexed (WDM) soliton transmission is described, in which dispersion management (DM) plays an important role in increasing the power margin and the dispersion tolerance. The characteristics of the DM soliton are compared with those of return-to-zero (RZ) and nonreturn-to-zero (NRZ) pulses. With a small dispersion swing, the system can still be described as an average soliton with a nonlinear Schrodinger equation (NLSE), whereas with a large dispersion swing, the soliton-like steady-state pulse becomes a chirped Gaussian pulse, in which the master equation is closer to a linear Schrodinger equation (LSE) with a parabolic potential well. An in-line modulation scheme up to 80 Gb/s per channel and its two-channel WDM transmission over 10000 km are described. A 640-Gb/s (40 Gb/s/spl times/16 channels) WDM soliton transmission over 1000 km is also reported with a DM single-mode fiber, without the use of in-line modulation. Finally, dark soliton transmission at 10 Gb/s over 1000 km is described as a different nonlinear pulse application.

"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 fiber's dispersion. Despite the variation of dispersion with respect to carrier wavelength due to the fiber's 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.

Supermode stabilized coupled-cavity 5- and 10-GHz mode-locked Ti:Er:LiNbO/sub 3/ waveguide lasers

By coupling the active laser cavity to a passive low-finesse Fabry-Perot resonator, supermode stabilization of mode-locked Ti:Er:LiNbO/sub 3/ waveguide lasers for 5- and 10-GHz pulse repetition rates with side mode suppression ratios of 60 and 55 dB has been achieved. The 10-GHz source emits pulses with a pulsewidth of 5.7 ps and a time-bandwidth product lower than 0.52 within an RF frequency tuning range of 3.2 MHz. The 5-GHz source has been used in a 2/spl times/5 Gbit/s soliton transmitter. In a back-to-back measurement, a Q-factor of 25.1 dB has been obtained. In soliton transmission experiments over 160 km on a step-index fiber, an extrapolated bit error rate of 6/spl middot/10/sup -17/ has been measured. The passive cavity can serve also as a pulse repetition rate multiplier. Pulse repetition rate multiplication from 2.5 to 10 GHz has been demonstrated.

Tuning of in-line filter position for dispersion-managed soliton transmission

We optimise the positioning of guiding filters in a fiber-optic transmission system with periodic dispersion compensation. It is shown that stabilization of pulse energy fluctuations and interaction reduction for adjacent pulses that propagate in the same channel may be achieved whenever the filters are placed at optimal points within the map.

Influence of Stochastic High-Order Perturbations on Soliton Transmission System

The influence of stochastic high-order perturbations on soliton transmission system is studied by self-companying operator method. Arrival time jitters variation induced by stochastic third-order dispersion is approximately proportional to three powers of transmission distance, that by stochastic nonlinear dispersion and self-steeping are approximately proportional to the transmission distance.

Time Jitters Caused by Randomly Varying Birefringence in Soliton Transmission System

Soliton propagation in fiber with randomly varying birefringence is studied by using self-companying operator method. It is shown that randomly varying birefringence leads to time jitters increasing with transmission distance, and disrupts the stability of soliton transmission. The fluctuation of time jitters is stochastic, and nonlinear gain is introduced to remove the influence.

Stable filter control of wavelength division multiplexed soliton systems

In wavelength division multiplexing (WDM) soliton transmission systems with frequency filter control, the growth of spontaneous emission from amplifiers due to excess gain near the central region of the filter is suppressed due to the spectral diffusion caused by cross-phase modulation by solitons in other WDM channels. It is numerically demonstrated that, for a canonical case of the map strength S of /spl sim/5, if there are six or more channels, then the spectral diffusion is sufficient to suppress the growth and stable filter control is achieved without sliding, phase and/or amplitude modulation.

640 Gbit/s (40 Gbit/s × 16 channel) dispersion-managed DWDM soliton transmission over 1000 km with spectral efficiency of 0.4 bit/Hz

The results from a 640 Gbit/s (40 Gbit/s/spl times/16 channel) dense WDM soliton transmission experiment over 1000 km with the use of a dispersion-managed transmission line are reported. The spectral efficiency was as high as 0.4 bit/Hz. The transmission line comprised conventional 1.3 /spl mu/m singlemode fibres and dispersion compensating fibres with dispersion slope compensation and a repeater span of 50 km.

Long-distance transmission of bandwidth-managed solitons in fibres with alternating dispersion

It is shown that bandwidth management in dispersion-alternating fibres allows noise accumulation in spaces to be suppressed and signal pulses, bandwidth-managed solitons (BMS), to be stably propagated over ultra-long distances. Both the amplitude and timing jitter of the signal pulses are greatly reduced by using BMS while the transmission distance is dramatically increased.

The Application of Mode-Locked Laser Technologies to Long Distance Transmission and Control of Soliton

The control scheme of long distance optical transmission is treated based on conception of mode-locked Laser cavity in this paper. The general mode-locking equation of fiber ring soliton Laser is first constructed, then we give the general perturbed nonlinear schrodinger equation, and finally the transmission and control equations of optical soliton communication systems with various different configurations, respectively, are obtained.

Stabilizing the Pereira-Stenflo Solitons in Nonlinear Optical Fibers

We study in detail stability of exact chirped solitary-pulse solutions in a model of a filtered nonlinear optical fiber, in which stabilization of the pulses is achieved by means of an extra lossy core, parallel-coupled to the main one. We demonstrate that, in the model's three-dimensional parameter space, there is a vast region where the pulses are fully stable, for both signs of the group-velocity dispersion. These results open way to a stable transmission of optical solitons in the normal-dispersion region and, thus, to an essential expansion of the bandwidth offered by the nonlinear optical fibers for telecommunications. In the cases when the pulses are unstable, we study the development of the instability, which may end up by either a blowup or decay to zero

Limitations of Soliton Transmission in a Cascaded Optical Amplifier System

The performance limitations of a soliton transmission link imposed by accumulated optical, amplifiers spontaneous emission (ASE) noise is presented. An analytical approach is developed to determine the impact of accumulated ASE-noise, dispersion, and nonlinearity on soliton propagation. The results are evaluated by computer simulation using beam propagation method for a dispersion shifted fiber. The amplified ASE noise is modelled as a zero mean Gaussian random process and the effects of ASE, dispersion and self-phase modulation are presented in terms of the signal to noise ratio at the output of the receiver filter for several values of the soliton peak power levels. The results show that the output soliton pulse is highly degraded due to the combined influence of ASE, SPM and dispersion and there is a drastic reduction in the output signal to noise ratio when the soliton pulse width is of the order of 20 ps or less with a peak power of the order of 5 mW or more.