Noise analysis of photonic packet synchronizer

This paper investigates and analyzes the in-band crosstalk generated in the photonic packet synchronizer that consists of a sequence of optical fiber delay lines and 2 /spl times/ 2 optical switches. This paper shows that the second-order in-band crosstalk is dominant and its contribution is proportional to the square of the number of delay lines. It is found that coherent, partially coherent, and incoherent in-band crosstalk may coexist at the output of the synchronizer, causing the power penalty to vary with the delay time of the main signal. A close-form formula is derived for the mean and variance of the beating noise between the main signal and a crosstalk element. The power penalty caused by the in-band crosstalk is further numerically studied and a guideline for the requirement of the optical switches used in the synchronizer is provided.     

Analysis of signal distortion and crosstalk penalties induced by optical filters in optical networks

The design of optical communication networks with network switching elements operating in the optical domain requires careful system analysis and potentially stringent component requirements. We consider here network elements such as transparent optical cross-connects that demultiplex WDM signals, optically switch individual channels, and then multiplex the wavelengths together again before transmission into the next span. Network element optical impairments that can significantly degrade signal quality are in-band (same wavelength) crosstalk and signal distortion from filter concatenation effects. We examine tradeoffs between accumulated crosstalk and filter distortion in the context of the optical filters used in the network elements and demonstrate the balance that must be struck in the design of the filters and network system. As an example, we study a 10-Gb/s network with 50-GHz channel spacing, examining both nonreturn-to-zero (NRZ) and return-to-zero (RZ) modulation formats. In both cases, we find optimal filter bandwidths that minimize the total signal degradation measured in terms of Q penalty, including filter misalignment statistics and signal laser frequency offset. A model is developed to treat the statistical nature of filter misalignment and its effect on filter-generated in-band crosstalk. The optical node penalties suffered by RZ signals can be significantly higher than that of NRZ signals and must be considered when estimating overall system reach.     

OSNR Penalty Imposed by Linear In-Band Crosstalk Caused by Interburst Residual Power in Multipoint-To-Point Networks

We present an analysis of linear in-band crosstalk in high split long reach wavelength/time-division-multiplexing passive optical networks (WDM-TDM PONs). In this letter, a mathematical model is deducted for the first time to calculate optical signal-to-noise ratio penalties due to in-band crosstalk in multipoint-to-point networks. The network performance can be perturbed by in-band crosstalk caused by power leakages from burst-mode optical network units (ONUs) in off-state. Our study results show that the leaked powers in upstream ONU transmitters can have an impact on the achievable split factor of WDM-TDM PONs. Furthermore, the performance limitations caused by aggregated interburst residual power are discussed.     

Modeling of in-band crosstalk in WDM optical networks

In this paper, we analyze three different simulation models which allow the impact of in-band crosstalk on the transmission performances of wavelength division multiplexing (WDM) optical networks to be evaluated: an accurate simulation (AS), a Gaussian correlated noise (GCN) model, and a Gaussian white noise (GWN) model. In the AS, an interfering channel is generated at each node and added to the signal after an optical filtering. The final result must be averaged with respect to the message transmitted on the interfering channels and to the phases of the optical carriers. In the GCN the crosstalk term is modeled as a Gaussian correlated noise, whose spectrum coincides with that of the interfering channel. This model can be further simplified if the noise is also assumed uncorrelated (GWN approximation). The results obtained by these simulation models are also compared with those produced by an analytical model allowing to evaluate the in-band crosstalk penalty     

Performance analysis of differential-phase-shift-keying optical receivers in the presence of in-band crosstalk noise

In-band crosstalk can pose important limitations in an all-optical wavelength-division-multiplexed (WDM) network. Recent studies have demonstrated that differential phase shift keying (DPSK), can tolerate higher in-band crosstalk-noise levels compared to amplitude shift keying (ASK). In this paper, the performance of a DPSK receiver, limited by in-band crosstalk noise, is studied theoretically. The model takes into account both the in-band crosstalk noise as well as the amplified-spontaneous-emission (ASE) noise of the optical amplifiers. The model is based on the evaluation of the moment-generating function (MGF) of the decision variable through which, the error probability (EP) can be calculated by applying the saddle point approximation. This provides a rigorous model for the evaluation of the EP of a DPSK receiver in the presence of ASE and in-band crosstalk noises. In the absence of the ASE noise, a closed-form formula for the EP is also given that is useful for estimating the error floor set by the in-band crosstalk noise.     

Application of the saddle point method for the evaluation of crosstalk implications in an arrayed-waveguide grating interconnection

The effect of in-band crosstalk can pose severe limitations in an optical network. In this paper, the implications of in-band crosstalk induced by an arrayed-waveguide grating (AWG) router in a passive N/spl times/N optical interconnection are analyzed with non-Gaussian statistics using a numerical model. The model is based on the saddle point approximation and takes into account fluctuations of the transfer function's sidelobes induced by the phase errors in the grating arms, phase noise, polarization variations, bit misalignment, and shot and thermal noise. The influence of these effects on the interconnection's bit error rate (BER) is analyzed. The validity of the Gaussian assumption for the crosstalk noise statistics is discussed. Finally, the model is used to examine the mean crosstalk requirements for various numbers of network nodes.     

Enhancing Resilience to Rayleigh Crosstalk by Means of Line Coding and Electrical Filtering

We demonstrate a technique that ameliorates the performance of bidirectional systems impaired by in-band Rayleigh crosstalk, which is common in passive optical access networks based on centralized remote wavelength feeding. The technique is based on the combined use of a suitable line coding and ad hoc postdetection electrical filtering. Therefore, it can be seamless implemented in optical access systems and it is easily scalable with the data rate. We experimentally assess the technique by using a 8B10B coded 1.25-Gb/s signal. We report an increased tolerance to the signal-to-crosstalk ratio by about 5 dB.      

Scaling limitations in transparent optical networks due tolow-level crosstalk

As transparent optical networks are scaled up in size, stringent constraints must be placed on the in-band crosstalk generated by their components. Measurements show that transparent networks corrupted by interferometric signal-crosstalk beat noise from only 8 crosstalk fields require component crosstalk levels <-35 dB. Good agreement with theory is shown     

Effects of In-Band Crosstalk in Wavelength-Locked Fabry–PÉrot Laser-Diode-Based WDM PONs

We investigated the impact of in-band crosstalk on the system's performance in wavelength-locked Fabry-Perot laser-diode (FP-LD)-based wavelength-division-multiplexed passive optical networks (WDM PONs). As expected, wavelength-locked FP-LD, which was injected by using an incoherent broadband light source, was more tolerant to in-band crosstalk than distributed-feedback (DFB) laser diode. A 1-dB power penalty in the wavelength-locked FP-LD-based PON system was observed when the crosstalk-to-signal ratio was ~-9 dB. We also compared the measured power penalties with the calculated power penalties. It has been shown that the in-band crosstalk-induced power penalty in wavelength-locked FP-LD-based WDM PON could be estimated properly by taking into account both effects of power addition and signal-crosstalk beat noise.     

无源光网络的初步升级方案

利用 13 10nm/ 15 5 0nm粗波分复用器 (CWDM)与 15 5 0nm光纤型带内耦合器 (OFIBC) ,提出了无源光网络(PON)的初步升级方案 ,CWDM与OFIBC复用器大的通带间隔与温度不敏感性保证了可以采用现行的无制冷的F P腔激光器 ,实验表明根据OFIBC的通带 ,选择激光器中心波长 ,系统可以达到具有较小的功率损耗与串扰。     

Statistical study of in-band crosstalk noise using the multicanonical Monte Carlo method

In-band crosstalk can pose important limitations in an all-optical wavelength-division-multiplexed network. In this letter, the multicanonical Monte Carlo (MCMC) method is applied for the study of the statistical behavior of the in-band crosstalk noise. The proposed method is accurate, efficient, and easy to use. The obtained error probabilities are compared with a previously proposed semianalytical model and are found to be in excellent agreement. The MCMC method is also used to study the asymptotic behavior of in-band crosstalk noise.     

QoS-Friendly Wavelength Assignment in Dynamic Wavelength-Routed Optical Networks

In-band crosstalk has been widely considered as a major transmission impairment that significantly impacts the bit error rate (BER) performance of lightpaths in circuit-switched all-optical wavelength-routed networks. Such crosstalk usually occurs when multiple wavelengths pass through an optical crossconnect node, and the magnitude of the crosstalk is largely dependent on the wavelengths assigned to the lightpaths. Traditional wavelength assignment (WA) schemes pay little regard to the physical layer quality of service (QoS), and hence cannot provide optimized network performance in practical networks with imperfect physical transmission media. In this paper, we first present our categorization of in-band crosstalk based on the location of crosstalk generation, then we propose two QoS-friendly WA approaches, one of which selects the wavelength based on the estimated BERs, and the other based on the weighted crosstalk number counting. The two approaches have different computation complexities. Numerical results show that both approaches can significantly improve the BER blocking rate by suppressing the created in-band crosstalk, but the BER-based approach generally gives the better performance at the price of more extensive computation.This work was supported in part by DARPA Grants #N66001-00-1-8949 and #66001-01-1-8932 (co-funded by NSA).     

Accurate estimation of the error probability in the presence of in-band crosstalk noise in WDM networks

In-band crosstalk noise can pose important limitations in wavelength-division-multiplexing (WDM) optical networks. This paper describes a model that takes into account the statistical behavior of in-band crosstalk noise accurately and that can be used to estimate the error probability (EP) in a WDM receiver. It is based on the formulation of the moment-generating function of the decision variable in terms of a double integral, which allows the inclusion of the crosstalk-crosstalk noise, which was previously neglected in the literature. The optical amplifier noise and the electrical receiver noise are also incorporated, and the model is used to assess the implications of the crosstalk-crosstalk contribution. With the aid of some examples, it is shown that the crosstalk-crosstalk noise can influence the value of the EP, change the optimum receiver threshold, and introduce some power penalty.     

Coherent and incoherent crosstalk in WDM optical networks

The impact of coherent and incoherent crosstalk on an optical signal passing through optical cross-connect nodes (OXC's) in wavelength division multiplexing (WDM) optical networks is studied, and the analytical expressions are given. Such crosstalk will be generated when the optical propagation delay differences of optical paths in an OXC do not exceed the coherent time of the lasers. While causing fluctuation of signal power, coherent crosstalk may cause noise or not, depending on the relationship between the optical propagation delay differences and the time duration of one bit of the signal. Incoherent crosstalk may cause very high noise power, because it can be a coherent combination of crosstalk contributions. The statistical impact of all crosstalk contributions on signal is studied by simulation, and the concept of quantile is proposed to relax the crosstalk specification requirement for components. The crosstalk specification requirements are then obtained for components used in WDM optical networks with different scales     

Design Considerations for Transmission Systems in Optical Metropolitan Networks

Wavelength division multiplexing (WDM) has become a key technology in optical long-haul communications and wide area networks. Recently, interest in introducing WDM into metropolitan networks has increased. We look at some issues pertinent to the design of WDM transmission systems deploying optical add/drop multiplexers in these networks. In particular, we investigate the interaction of node-induced crosstalk with fiber nonlinearities in metropolitan ring networks. Two transmission systems are considered; namely a system of nonzero dispersion shifted fiber operating in the anomalous dispersion regime and another one of single mode fiber with post dispersion compensation. Data rate is assumed to be 10 Gb/s per wavelength. The dependence of the crosstalk/nonlinearity interaction and its system penalty on the frequency difference between signal and crosstalk carriers, input signal power, extinction ratio, number of nodes, and physical span of the network is examined in detail. It is shown that node-induced crosstalk can interact with fiber nonlinearities and introduce limitations on transmission performance. This interaction should therefore be taken into consideration in designing regional metropolitan networks.     

WDM光网络系统相干串扰与非相干串扰

同频串扰可以分为相干串扰与非相干串扰,本文提出了WDM光网络系统串扰相干性分析的数学模型,分析提出了相等的相干串扰代价和非干串扰代价下引起的WDM光网络系统功率代介的一致性,并与模拟相干串扰和非相干串扰结果进行了比较验证。实验结果表明,对应1dB功率代价下,WDM光网络系统对应相干串扰和非相干串扰代价容限步于－20dB和理论结果一致。串扰对于网络规模有一定的限制。     

Hybrid crosstalk aware Q-Factor analysis for selection of optical virtual private network connection

The presence of physical layer impairments (PLIs) in high-speed optical virtual private network (OVPN) over wavelength-division multiplexing/ dense-wavelength division multiplexing network degrades the connection quality (CQ). The quality can be numerically expressed as the quality factor (Q-Factor) of the connection. The CQ can be further affected by the increasing demand of connections and data speed. It is important to have an efficient OVPN control manager (OVPNCM) to maintain the CQ. OVPNCM can ensure better quality of transmission to the OVPN clients. Traditional routing and wavelength assignment (RWA) algorithms have less regards to the PLIs and cannot provide guaranteed OVPN connection (OVPNC) quality. In order to achieve a guaranteed CQ, we proposed a wavelength assignment (WA) scheme and a hybrid crosstalk model based on linear in-band and nonlinear four-wave mixing crosstalk. The performance of the proposed WA scheme with the hybrid crosstalk model is demonstrated. The results show that the proposed hybrid crosstalk model with WA scheme not only provides a guaranteed OVPNC, but also improves the OVPN performance in terms of blocking probability.     

Cross-phase modulation in multispan WDM optical fiber systems

The spectral characteristics of cross-phase modulation (XPM) in multispan intensity-modulation direct-detection (IM-DD) optical systems are investigated, both experimentally and theoretically. XPM crosstalk levels and its spectral features are found to be strongly dependent on fiber dispersion and optical signal channel spacing. Interference between XPM-induced crosstalk effects created in different amplified fiber spans is also found to be important to determine the overall frequency response of XPM crosstalk effects. XPM crosstalk between channels with different data rates is evaluated. The crosstalk level between higher and lower bit rate channels is found to be similar to that between two lower bit rate channels. The effect of dispersion compensation on XPM crosstalk in multispan optical systems is discussed and per span dispersion compensation was found to be the most effective way to minimize the effect of XPM crosstalk     

WDM光网络相干串扰实验研究

同频串扰可以分为同源串扰和非同源串扰 ,文中分析了 WDM光网络系统相干串扰的起源与特征 ,设计并模拟实验研究了不同相干串扰代价下 ,WDM光网络系统的功率代价。对应 1 d B功率代价下 ,WDM光网络系统对应相干串扰代价容限小于 - 1 9.7d B,对于 WDM系统实用化组网具有一定参考价值