Comparison of span configurations of Raman-amplifieddispersion-managed fibers

We evaluate the performance of dispersion-managed fiber transmission systems employing distributed Raman amplification with 50- and 100-km span length for three different span configurations. The evaluation considers the optical signal-to-noise ratio and the nonlinear phase shift as a measure for the impact of nonlinear effects. The simulation results indicate that a 100-km-long span with the dispersion compensating fiber placed in the span center achieves the best tradeoff between optical signal-to-noise degradation and nonlinear effects     

Impact of dispersion fluctuations on 40-Gb/s dispersion-managed lightwave systems

We study numerically the impact of random dispersion fluctuations on the performance of 40-Gb/s dispersion-managed lightwave systems designed using either the chirped return-to-zero or the soliton format and employing backward-pumped distributed Raman amplification. We consider two-section dispersion maps with /spl beta//sub 2/=/spl plusmn/4 and /spl plusmn/8 ps/sup 2//km and show that the Q parameter decreases rapidly in both cases as the nonlinear effects become stronger. The impact of dispersion fluctuations can be reduced by lowering the average input power, but the system length is then limited by amplifier noise.     

Optimum space-time processors with dispersive interference: unifiedanalysis and required filter span

We consider optimum space-time equalizers with unknown dispersive interference, consisting of a linear equalizer that both spatially and temporally whitens the interference and noise, followed by a decision-feedback equalizer or maximum-likelihood sequence estimator. We first present a unified analysis of the optimum space-time equalizer, and then show that, for typical fading channels with a given signal-to-noise ratio (SNR), near-optimum performance can be achieved with a finite-length equalizer. Expressions are given for the required filter span as a function of the dispersion length, number of cochannel interferers, number of antennas, and SNR, which are useful in the design of practical near-optimum space-time equalizers     

色散管理传输系统中克尔效应对偏振模色散的补偿研究

光纤的随机双折射效应可导致脉冲无规展宽即偏振模色散(PMD)。在零路径色散管理孤子传输系统中，二阶色散和三阶色散效应均被完全补偿，克尔效应成为一种有害因素会使脉冲变窄，但是当光纤的随机双折射被考虑时，克尔效应正好与PMD相互抵消，使光脉冲准稳定传输，不同的光纤偏振模色散参数分别对应不同的最佳系统功率。此外，如果考虑不同偏振方向的损耗差异，则即使在最佳匹配条件下，微小的偏振损耗差异也可产生很大的脉宽波动。因此，偏振相关损耗是影响脉冲传输质量的相当重要的因素，不论在理论计算还是在工程设计中都应当认真考虑。     

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.     

Experimental quantification of soliton robustness to polarizationmode dispersion in conventional and dispersion-managed systems

We have experimentally quantified the soliton robustness to polarization mode dispersion (PMD) in both conventional and dispersion-managed (DM) soliton systems. Long-term measurements were performed in a computer-controlled system where the PMD characteristics varied randomly with time. Apart from the PMD itself, the performance of both systems depends on the average dispersion while the performance of the DM system also depends on the dispersion map strength. The results show that the robustness can be even more pronounced for DM systems with relatively small dispersion map strengths (0相似文献   

Pulse broadening factor as a criterion to assess nonlinear penalty of 40-Gbit/s RZ-DQPSK signals in dynamic transparent optical networks

The real-time scheduling and routing in dynamic transparent optical networks requires fast and accurate evaluation of transmission penalty caused by nonlinear kerr effects with different dispersion maps. However, the conventional method using nonlinear phase shift can only be applied to assess the nonlinear penalty with optimized dispersion maps. In this paper, we introduce pulse broadening factor into the approach and propose a novel method to accurately evaluate nonlinear penalty and numerically investigate the feasibility of our novel method in 40-Gb/s Return-to-Zero Differential Quadrature Phase-Shift Keying (RZ-DQPSK) systems. Simulation results show that our approach can achieve good evaluation performance even with non-optimized dispersion maps.     

DDF色散值的阶梯曲线近似在色散管理系统中的应用

针对色散管理系统中色散渐减光纤(DDF)制造工艺复杂的缺点,设计一种色散渐减光纤的替代色散管理链路.利用两种正负色散光纤,通过设计正负色散光纤的长度来调整各个色散管理周期的平均色散值,使相邻放大器中光纤链路的色散值呈阶梯曲线状递减,从而近似代替色散渐减光纤平衡减弱的非线性效应.数值模拟结果表明色散渐减光纤的阶梯曲线近似对40Gbit/s的光传输系统性能有很大的提高作用.     

Optimum near-far resistance for dual-rate DS/CDMA signals: randomsignature sequence analysis

Optimum near-far resistance is studied for synchronous dual-rate DS/CDMA systems. Three multirate access schemes are considered: multicode (MC) access where high-rate users multiplex their data bits onto multiple codes and form a single-rate system; variable spreading length (VSL) access where the spreading lengths of signature sequences are inversely proportional to users' data rates; and variable chipping rate (VCR) access where the chipping rates of the signature sequences are proportional to users' data rates. In order to remove the influence of signature sequences in the comparison of the three schemes, random signature sequences are assumed. Optimum mar-far resistance is then averaged over all possible realizations. Two types of code sets are considered for the VSL system: general random codes and random repetition codes. Bounds and approximations are provided for the average optimum near-far resistance. Analytical results show that the performance depends on the access schemes and the data rate of the users. The results for the VSL scheme with general random codes are extended for performance evaluation of systems with signature sequences which span many symbol intervals     

Dispersion statistics in concatenated single-mode fibers

Dispersion measurement data from two sets of fiber cable lengths were employed to determine the histograms of slope and wavelength of zero chromatic-dispersion in concatenated single-mode fibers. We use a Monte-Carlo technique under two concatenating scenarios, depending on whether those fibers being concatenated are or are not manufactured by the same process. Results show that the variances of slope and wavelength of zero dispersion are inversely proportional to the numberNof fiber cable lengths being concatenated. The average and standard deviation of zero-chromatic dispersion wavelength changes less than 0.005 percent or 1 percent, respectively, when the actual dispersion slopes of individual fiber lengths being concatenated are replaced by random quantities distributed with uniformity within 0.08-0.1 ps/km . nm².     

Sensitivity of double-gate and FinFETDevices to process variations

We investigate the manufacturability of 20-nm double-gate and FinFET devices in integrated circuits by projecting process tolerances. Two important factors affecting the sensitivity of device electrical parameters to physical variations were quantitatively considered. The quantum effect was computed using the density gradient method and the sensitivity of threshold voltage to random dopant fluctuation was studied by Monte Carlo simulation. Our results show the 3/spl sigma/ value of V/sub T/ variation caused by discrete impurity fluctuation can be greater than 100%. Thus, engineering the work function of gate materials and maintaining a nearly intrinsic channel is more desirable. Based on a design with an intrinsic channel and ideal gate work function, we analyzed the sensitivity of device electrical parameters to several important physical fluctuations such as the variations in gate length, body thickness, and gate dielectric thickness. We found that quantum effects have great impact on the performance of devices. As a result, the device electrical behavior is sensitive to small variations of body thickness. The effect dominates over the effects produced by other physical fluctuations. To achieve a relative variation of electrical parameters comparable to present practice in industry, we face a challenge of fin width control (less than /spl sim/1 nm 3/spl sigma/ value of variation) for the 20-nm FinFET devices. The constraint of the gate length variation is about 10/spl sim/15%. We estimate a tolerance of 1/spl sim/2 /spl Aring/ 3/spl sigma/ value of oxide thickness variation and up to 30% front-back oxide thickness mismatch.     

Performance evaluation of very long span direct detection intensityand 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     

Dispersion-Managed Solitons and Optimization of the Dispersion Management

We overview recent progress in dispersion-managed (DM) fiber optic communications. Wavelength-division-multiplexing transmission of a DM soliton (or more general return-to-zero (RZ) formatted data) is an attractive way to realize middle- and long-distance ultra-high-capacity fiber communication systems. We present a theory of the DM optical soliton and a simple basic theory of the general DM RZ transmission. Two ordinary differential equations for the root-mean-square pulse width and chirp (momentum equations) describe the fast (during compensation period) evolution of the DM pulse. Applying chirped Gauss–Hermite orthogonal functions we derive a path-averaged propagation equation governing both the shape of the DM soliton and the slow (average) evolution of any chirped DM pulse. We describe the breathing dynamics of the self-similar core and oscillating tails of the DM optical pulse propagating in a fiber line with an arbitrary dispersion map. Based on the developed theory we describe the basic system principles, the design, and the optimization rules for DM fiber links. We demonstrate how to determine the energy enhancement of the DM soliton and optimal (chirp-free) points for launching of the signal, and how to evaluate the characteristics of a carrier signal for specific system parameters. DM solitons in systems with in-line filtering and Bragg gratings are also studied. Analytical results are illustrated by numerical simulations for a number of specific dispersion maps actively used in practice.     

Optimum Receiver Filters for Optical Fiber Systems With Polarization Mode Dispersion

We use a semi-analytical receiver model combined with importance sampling applied to first-order polarization-mode dispersion (PMD) to show that the performance of optical fiber systems whose optical and electrical receiver filter bandwidths are optimized for polarization-mode dispersion in practical on-off-keyed systems is equivalent to the performance of the same systems in which the receiver filters are optimized for operation in the absence of PMD. We also observed an increase in the sensitivity of the performance with respect to variations in the receiver filter bandwidths in the return-to-zero format in systems with PMD when compared with PMD-free operation.      

波分复用系统中色散管理孤子相互作用诱导时间移动的分析

研究了波分复用 (WDM)弱色散管理系统中 ,孤子碰撞诱导的孤子到达时间的移动 ;以及波分复用强色散管理系统中 ,利用变分原理分析了孤子相互作用引起的时移、啁啾、时间位置和孤子频率等的演化。研究表明 ,弱和强色散管理中 ,在光纤的路径平均色散接近于零时 ,孤子碰撞引起的时间移动很小     

Investigation of Multilevel Phase and Amplitude Modulation Formats in Combination With Polarization Multiplexing up to 240 Gb/s

We present experimental investigations of the receiver sensitivity and dispersion tolerance of multilevel optical communication systems with a symbol rate of 40 Gbaud. Four- and eight-level communication is obtained by combining binary amplitude modulation with either binary or quadrature differential phase modulation. We experimentally compare the dispersion tolerance, and show that multilevel modulation formats offer much better dispersion tolerance compared to binary formats. By combining multilevel modulation with polarization multiplexing, bit rates up to 240 Gb/s were obtained. We demonstrate transmission over 50-km fiber span with no power penalty for a pseudorandom binary sequence length of$2^7-1$bits.     

Four-wave mixing penalties in long-haul WDM transmission links

We show computationally and experimentally that large resonances in signal variance due to four-wave mixing can occur in wavelength-division-multiplexed transmission systems. These resonances are the result of periodic amplifier spacing and distribution in dispersions and lengths of the fiber spans     

软辫线长度对主动和被动屏蔽效能的影响

针对软辫线长度所带来的电磁兼容问题,给出被动屏蔽效能和主动屏蔽效能的定义,并利用被动屏蔽效能和主动屏蔽效能对软辫线效应进行了评价。仿真实验及理论计算结果表明：随着软辫线长度的变化,被动屏蔽效能和主动屏蔽效能变化的趋势相同,但数值差别很大,不能等效使用。     

System penalty effects caused by spectral variations and chromatic dispersion in single-mode fiber-optic systems

Optical submarine systems are now being planned, and because of the need for high levels of confidence in such systems, all aspects that affect performance need detailed investigation. Of particular importance are penalties that may arise from spectral effects. A theoretical and practical examination has been made of the relationship between source spectrum and system performance in the presence of chromatic dispersion. Equipment is described which provides an automatic record of the power budget penalty resulting from spectral variations for all temperatures in the operating range. Significant differences are found, even between lasers of the same type. The nature of the corresponding spectral differences is studied, and evidence is presented to show that both random and regular variations exert appreciable effects.     

Average dispersion decreasing densely dispersion-managed fiber transmission systems

The authors propose an average dispersion decreasing densely dispersion-managed (A4DM) fiber line, which can substantially improve the performance of high-speed optical transmission systems. They show that the A4DM fiber lines have many advantages over densely dispersion-managed fiber lines.