High Bit-rate Systems Research Articles

Study on soliton phase characteristics in 100 Gbps single‐channel telecommunication system

SummaryHere, we demonstrate the peculiar particle nature of soliton pulses with relative to phase, where the adjacent soliton pulses in a sequence attract and repel each other periodically for in‐phase and out‐of‐phase arrangement, respectively. This effect of soliton's interaction and repulsion is studied analytically by using perturbation theory approach. The study of soliton pair characteristics are mainly noted for different relative spacing (qo) between them and for different phase of launched soliton pulses. Following the analytical studies, we analyzed the effect in a 100 Gbps, single channel and uncompensated telecommunication system for different phased soliton sequences. Such that, the performance of the telecommunication system is characterized in terms of Q‐factor (Q) and bit‐error rate to realize the influence of phase on soliton pulses. The system was studied for 1 collision length (LD) of 123.36 km. It is seen that, for 100 Gbps system implemented with standard single mode telecom fiber, with soliton spaced at qo = 5.28, the in‐phase pulses interacted at 61.68 km, which has resulted in Q = 0 (bit‐error rate = 1). It is realized that for small‐phase introduction on soliton pulses, the system yielded fair Q demonstrating the non‐interaction at the Ip as the pulses deviate with respect to increasing phase values. But, it is also shown that large phase between pulses introduces more deviation, which results in overlapping of deviated pulses with adjacent pulses in sequence resulting in degradation of high bitrate system performance.

The Development of PMD and its Compensation Method

With the quickly development of fiber communication, PMD(Polarization mode dispersion) has became one of the key factor which limit high-bit rate system performance. In 1986, C.D.Poole[1] and other people found that if do not consider loss of SOP, two upright PSP will change along certain length SMF. In 1987, D.Andresciani and N.S.Bergano validate the theory of C.D.Poole each either. Late ninety of last century, statistical theory forming[2]. In the paper, we discuss the study of PMD, including statistics of PMD, measure technology, the affect of system by PMD, and PMD Compensation Method.

Evaluation of nonlinear phase noise in DPSK transmission for different link designs

We analyzed the impact of nonlinear phase noise caused by Gorden-Mollenauer effect in single-channel return-tozero differential phase-shift-keying (RZ-DPSK) transmission in dependence of system bit rates, dispersion compensation schemes and different fiber types. The investigation is reported by simulating RZ-DPSK signals for 3200 km, taking into account penalties in Q-factor induced by nonlinear phase noise. From these simulation results, higher bitrate systems, system with pre-compensation schemes and system using stand single mode fiber transmission are more robust against nonlinear phase noise. Furthermore, by looking into the standard deviation of the signal intensity and phase for all sampling points within one-bit duration, we observed that optical noise can be washed out from the bit center during propagation.

A novel bit-error indicating scheme using only one judge threshold

A novel all-optical bit-error indicating scheme based on self-phase modulation and band-pass filtering is proposed. In this scheme, the amplified original bit stream propagates through a high-nonlinear fiber where self-phase modulation occurs, and then passes through a band-pass filter to be converted to a bit-error indicating signal. In the bit-error indicating signal, the error bit has the highest peak power, and the “1” and “0” bits have lower ones. At the same time, the bit-error indicating signal is synchronous with the delayed original bit stream. Therefore, the position of the error bit in the original bit stream can be identified by setting only one judge threshold in the bit error indicating signal. The performance of this scheme has been demonstrated for an 80 Gb/s bit-stream with return-to-zero format by simulation. The results show that the proposed scheme can be used for the all-optical bit-error indicating of the super high bit-rate systems with the return-to-zero format.

An all-optical bit-error indicating scheme based on self-phase modulation and filtering

In this paper, a novel all-optical bit-error indicating scheme is numerically studied. The bit-error indicating function is achieved by two all-optical processing stages. Firstly, the amplified original bit stream propagates through a high-nonlinear fiber and experiences self-phase modulation which causes intensity-dependent spectrum broadening and split. And then, the bit stream output from the high-nonlinear fiber is filtered by a band-pass filter with the same central wavelength as the original bit stream to generate an error bit indicating signal. The error bit indicating signal, in which only the “Error” bits have the highest peak power, is synchronous with the delayed original bit stream. Therefore, the position of the “Error” bits in the original bit stream can be identified by setting only one judge threshold in the error bit indicating signal. The scheme is demonstrated for an 80 Gb/s bit stream with return-to-zero format by simulation. The results show that the scheme can be used for the all-optical bit-error indicating of the super high bit-rate systems using the return-to-zero format which is favored in the optical time division multiplexing transmission systems.

Numerical analysis of four-wave-mixing based multichannel wavelength conversion techniques in fibers

We numerically investigate four-wave-mixing (FWM) based multichannel wavelength conversion for amplitude-modulated signals, phase-modulated signals, together with mixed amplitude and phase modulated signals. This paper also discusses the influence of stimulated Brillouin scattering (SBS) effects on high-efficiency FWM-based wavelength conversion applications. Our simulation results show that DPSK signals are more suitable for FWM-based multichannel wavelength conversion because the OOK signals will suffer from the inevitable data-pattern-dependent pump depletion. In future applications, when the modulation format is partially upgraded from OOK to DPSK, the influence of OOK signals on the updated DPSK signals must be considered when using multichannel wavelength conversion. This influence becomes severe with the increase of OOK channel number. It can be concluded that DPSK signals are more appropriate for both transmission and multichannel wavelength conversion, especially in long haul and high bit-rate system.

In-Service Dispersion Monitoring in 32>tex<$times$>/tex<10.7 Gbps WDM Transmission System Over Transatlantic Distance Using Optical Frequency-Modulation Method

We develop an in-service dispersion monitoring technique based on the optical frequency modulation (FM) method and examine its applicability to wavelength division multiplexing (WDM) long-haul transmission systems. This method is insensitive to the group-delay drift induced by environmental perturbations and can measure the dispersion value with its sign (normal or anomalous) accurately only from the received signal light. These features are very attractive for the application in ultralong-haul transmission systems. We implement the in-service dispersion monitor in a 32 /spl times/ 10.7 Gbit/s WDM transmission system. Accurate dispersion monitoring at a transmission distance of 5950 km is achieved without any bit error rate (BER) penalty. Also, we discuss the applicability of the optical FM method to higher bit-rate systems from the experimental result.

A complex baseband platform for spatial-temporal mobile radio channel simulations

Joint spatial-temporal signal processing has been recognized as the key to reducing the effects of the intersymbol and cochannel interference seen in very high bit-rate mobile radio communications systems. Developing hardware simulators that can simulate mobile radio propagation scenarios in time and space domains is essential for evaluating the real-time performance of spatial-temporal signal processing schemes. This paper outlines a complex baseband platform developed for spatial-temporal mobile radio channel simulations. The platform consists of a complex baseband fading/array response simulator, a digital signal processor (DSP) board, and a general-purpose parameter estimator that uses systolic array implementation of the recursive least square (RLS) algorithm. Results of experiments conducted using the developed platform are presented to confirm the proper operation of the system.

Correction to "integrated tunable fiber gratings for dispersion management in high-bit rate systems"

Correction to "integrated tunable fiber gratings for dispersion management in high-bit rate systems"

Integrated tunable fiber gratings for dispersion management in high-bit rate systems

Dispersion management is becoming paramount in high-speed wavelength-division-multiplexed lightwave systems, that operate at per-channel rates of 40 Gb/s and higher. The dispersion tolerances, in these systems, are small enough that sources of dispersion variation, that are negligible in slower systems, become critically important to network performance. At these high-bit rates, active dispersion compensation modules may be required to respond dynamically to changes occurring in the network, such as variations in the per-channel power, reconfigurations of the channel's path that are caused by add-drop operations, and environmental changes, such as changes in ambient temperature. We present a comprehensive discussion of an emerging tunable dispersion compensating device, based on thermally actuated fiber gratings. These per-channel devices rely on a distributed on-fiber thin film heater, deposited onto the outer surface of a fiber Bragg grating. Current flowing through the thin film generates resistive heating at rates that are governed by the thickness profile of the metal film. A chirp in the grating is obtained by using a thin-film, whose thickness varies with position along the length of the grating in a prescribed manner; the chirp rate is adjusted by varying the applied current. The paper reviews some of the basic characteristics of these devices and their implementation, in a range of different applications, including the mitigation of power penalties associated with optical power variations. We present detailed analysis of the impact of group-delay ripple and polarization-mode dispersion on systems performance, and present results from systems experiments, that demonstrate the performance of these devices at bit rates of 10, 20, 40 and 160 Gb/s. We also discuss advantages and disadvantages of this technology, and compare to other devices.

Statistical Modeling of RMS-Delay Spread Based on Three Dominant Propagation Paths

Two analytical models for the parameter of rms delay spread are presented for a three-path radio environment. The reasons that led to the development of these models are: (i) the fact that the assumption of the existence of two paths in the radio channel did not seem to be enough for the description of all cases, (ii) simulation results showed that in most cases there are significant differences between the Cumulative Distribution Functions (CDFs) of rms-delay spread obtained for a two-path and a three-path radio environment. On the contrary, the CDFs obtained for L = 3, 4, 5 and 10 (L is the number of paths) are similar, and (iii) experimental results in indoor environment showed that in most cases there are 3 dominant paths in the radio channel. Probability Density Functions of the resulting rms delay spread are plotted for different values of the parameters of the models and compared with simulation results. In order to examine the validity of the models, measurements have been conducted in National Technical University of Athens while others have been obtained from the literature and compared with theoretical results. In all cases, the X-square criterion showed that the match between experimental and theoretical results is very good. These models, therefore, can be used for the design of high bit-rate systems that will operate without problems resulting from intersymbol interference.

An analytical statistical model for the RMS delay spread parameter in millimeter frequencies

A new statistical model for rms delay spread is presented. The model has been developed under the assumption of the existence of two paths (two-path model). It is assumed that the amplitude of each path follows the so-called log-Student distribution with one degree of freedom, while the differential propagation delay of the two paths follows the uniform distribution. The parameters involved with the model are mz and sz the mean and standard deviation of the ratio of the two paths’ amplitudes. Theoretical curves for τrms as well as for the mean and standard deviation of τrms are plotted for different values of mz and sz. These curves are extremely useful for the choice of the parameters of the model for different cases. In order to examine the validity of the new model, measurements from the literature have been collected and compared with the theoretical results. In all cases a very good agreement, according to the X-square criterion, between theoretical and experimental curves has been observed. As a result, the new model can be used by system engineers for the development of wireless high bit-rate digital systems that will not suffer from intersymbol interference.

Timing jitter of ultrashort solitons in high-speed communication systemsII Control of jitter by periodic optical phase conjugation

We consider the use of periodic optical phase conjugation for reducing the timing jitter in high-speed fiber-optic communication systems employing ultrashort solitons (width <10 ps) in dispersion-decreasing fibers. Using adiabatic perturbation theory, we derive analytically an expression for the trajectory of a periodically conjugated ultrashort soliton in a communication link after including the effect of amplifier noise and use it to derive the timing jitter in the soliton arrival time at the end of a transmission line. The analysis takes into account not only the group-velocity dispersion but also the Raman effect and the third-order dispersion. We show that the timing jitter can be minimized by using an optimized amplifier spacing (∼65–80 km) for a specific value of average fiber dispersion. The use of shorter amplifier spacings increases timing jitter because of third-order dispersion while for larger amplifier spacings the increased jitter originates from the Raman effect. For high-bit rate systems considered in this paper the Gordon–Haus contribution to the timing jitter is negligible. Under optimized conditions, nearly error-free transmission can be realized at a bit rate of ∼100 Gb/s over a distance of 1200 km even in the absence of optical filters. We discuss the role of optical filters for improving system performance and the impact of fiber-dispersion fluctuations on the periodic filtering of ultrashort solitons.

Electro-optic modulation by electron transfer in multiple InGaAsP/InP barrier, reservoir, and quantum well structures

Recently, a novel optical modulator heterostructure has been introduced based on voltage controlled electron transfer from a reservoir to a closely spaced quantum well. It has proven to exhibit large absorptive and refractive modulation at high speed and low power dissipation. In order to achieve monolithic integration with the existing high quality InGaAsP/InP lasers for high bit-rate systems, it is crucial to implement such devices within the same material system. In this letter, we demonstrate for the first time, InGaAsP/InP electron-transfer modulators grown using metalorganic vapor phase epitaxy.

Statistical dispersion budgeting method for single-mode fiber transmission systems

A statistical dispersion budgeting method for spliced single-mode fiber transmission spans is proposed. The method aids in the design of fiber spans in high bit-rate (>1 Gb/s) systems. Intended for spans containing many splices, the method yields, in theory, greater span lengths than those calculated with the traditional worst-case dispersion budgeting method.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Modulation-induced spectral penalties in high bit-rate single-mode systems

Measurements of spectral penalty in a fully regenerated system and time-resolved spectra are described. Computer simulations to predict the spectral penalty due to modulation-induced wavelength shifts alone are also presented.