Dirk Breuer

Comparison of NRZ- and RZ-modulation format for 40-Gb/s TDM standard-fiber systems

Nonreturn-to-zero (NRZ) and return-to-zero (RZ) signal transmission in dispersion-managed high-speed time-division multiplexed (TDM) systems operating at 1.55 /spl mu/m over the already installed standard-fiber network are compared by numerical simulations. It is shown that for upgrading the existing network to 40 Gb/s, the RZ-modulation format is superior compared to conventional NRZ-modulation. Standard fiber transmission distances of about 1200 km and 400 km are shown to be feasible within the RZ- and NRZ-format, respectively.

Performance analysis of wavelength converters based on cross-gain modulation in semiconductor-optical amplifiers

An analytical theory describing all-optical wavelength converters based on cross-gain modulation (XGM) in semiconductor-optical amplifiers is derived. Our theory consists of two parts: a large-signal analysis yielding the transmission function for the signal, and a small-signal analysis in order to describe the transformation of the signal and probe intensity noise. Both the large-signal as well as the small-signal theory reveal similar performance for the co- and the counterpropagating injection scheme for bit rates up to 2.5 Gb/s. This is confirmed by computer simulations. Consequently, the counterpropagating configuration is preferable because the implementation is simpler and conversion to the same wavelength is possible. In order to increase the conversion efficiency it is better to reduce the average signal power than to increase the probe power, which additionally reduces the output power range. However, there is a tradeoff between conversion efficiency and output extinction ratio. According to the small-signal analysis, the relative-intensity noise (RIN) due to the probe and due to the amplified spontaneous emission is negligible. Moreover, the converted signal has a lower RIN than the input signal.

Next-generation 100-gigabit metro ethernet (100 GbME) using multiwavelength optical rings

This paper investigates the challenges for developing the current local area network (LAN)-based Ethernet protocol into a technology for future network architectures that is capable of satisfying dynamic traffic demands with hard service guarantees using high-bit-rate channels (80...100 Gb/s). The objective is to combine high-speed optical transmission and physical interfaces (PHY) with a medium access control (MAC) protocol, designed to meet the service guarantees in future metropolitan-area networks (MANs). Ethernet is an ideal candidate for the extension into the MAN as it allows seamless compatibility with the majority of existing LANs. The proposed extension of the MAC protocol focuses on backward compatibility as well as on the exploitation of the wavelength domain for routing of variable traffic demands. The high bit rates envisaged will easily exhaust the capacity of a single optical fiber in the C band and will require network algorithms optimizing the reuse of wavelength resources. To investigate this, four different static and dynamic optical architectures were studied that potentially offer advantages over current link-based designs. Both analytical and numerical modeling techniques were applied to quantify and compare the network performance for all architectures in terms of achievable throughput, delay, and the number of required wavelengths and to investigate the impact of nonuniform traffic demands. The results show that significant resource savings can be achieved by using end-to-end dynamic lightpath allocation, but at the expense of high delay.

40 Gb/s and 4/spl times/40 Gb/s TDM/WDM standard fiber transmission

We investigate the possibilities of 40 and 4/spl times/40 Gb/s time division multiplexing wavelength division multiplexing (TDM/WDM) return-to-zero (RZ) transmission over embedded standard single-mode fibers (SMF) at a transmission wavelength of 1.55 /spl mu/m both experimentally and theoretically. Dispersion of the SMF is compensated by a dispersion compensating fiber (DCF). Transmission over a span of 150 km of SMF in the single-channel case and of 100 km SMF in the multichannel case are reported. Numerical calculations are employed to investigate the possibility of cascading the spans both for single-channel and multichannel transmission. For single-channel transmission, it is shown that optimum performance is achieved with postcompensation of the DCF. The input power at the SMF and DCF input have to be chosen carefully. For four channel transmission, the performance is mainly limited by residual dispersion in the outermost wavelength channels. It is shown numerically that improvement is achieved by employing the newest type DCF which also compensates the dispersion slope of the SMF. For a WDM channel separation of 2 nm no significant additional degradation due to cross-phase modulation (XPM) or four-wave mixing is observed.

Evolution of Terrestrial Optical System and Core Network Architecture

Optical systems and technologies have been radically changing the telecommunication networks for past 15 years; today wavelength division multiplexing (WDM) technology, optical amplifiers, and simple optical switching elements like optical add-drop multiplexers (OADMs) are used in the backbone networks of all operators worldwide. Optical systems nowadays provide the basis for cost-effective transmission of large amounts of bandwidth over the Internet, and will enable its future growth and the spreading of new applications and services. This paper summarizes the main trends in optical networking and investigates potential future application areas. Optical system technology has become so pervasive in network design that it needs to be considered in the context of provisioning new applications and services. Therefore, the analysis is not limited to the aspects of physical transmission, but also takes into account recent developments in integrated network design as well as network control and management. The following sections describe the key functionalities of future optical network architectures, and the key findings of the theoretical analysis are supported by the results of a field trial of advanced transmission technology

Unrepeated 40-Gb/s RZ single-channel transmission at 1.55 μm using various fiber types

We investigate experimentally and theoretically the effect of signal power and dispersion compensation scheme in unrepeated return-to-zero single-channel 40-Gb/s 150-km transmission using standard single-mode fiber (SMF), nonzero dispersion shifted fiber [true wave fiber (TWF)] and dispersion shifted fiber (DSF). It is shown, that standard SMF allows significantly higher fiber-input power than nonzero dispersion shifted fiber or dispersion shifted fiber and, therefore, offers larger transmission spans.

Measurements of PMD in the installed fiber plant of Deutsche Telekom

In this paper, PMD measurements that were carried out in the installed fiber plant of Deutsche Telekom, which consists solely of G.652 fiber, are presented. The measurements are performed all over Germany during the last three years on nearly 10,000 fiber sections whereby these fiber cables were installed from 1985 to 2001. It should be noted that pre-1994 cables PMD was not yet specified by cable manufacturers and PMD specification were only added around 1995. Fibers with lowest PMD were identified and reserved for high capacity transmission. The data indicate that no direct correlation of the first-order PMD coefficient value with the rollout of the PMD specification by the fiber and cable manufacturers is feasible. Even for cables which were installed during 1985 till 1991 a reasonable number of fibers is suitable for 40 Gbit/s transmission. For 10 Gbit/s selected fibers are used, thus PMD does not impose any limitations and therefore avoiding expensive exchange of fibers.

Noise characteristics of semiconductor-optical amplifiers used for wavelength conversion via cross-gain and cross-phase modulation

The amplified spontaneous emission of a semiconductor-optical amplifier saturated by two input waves is investigated theoretically and experimentally for both co- and counterpropagating injection. For the first time, an analytical expression for counterpropagating input waves is presented and compared with the copropagating case. It is shown, that copropagating injection can significantly reduce the noise level. The theoretical results are also compared with the experimental data and found to be in good agreement.

37.5 km urban field trial of OFDMA-PON using colorless ONUs with dynamic bandwidth allocation and TCM [invited]

The orthogonal frequency division multiple access (OFDMA)-based passive optical network (PON) is a potential candidate to meet the flexibility requirements for next-generation optical access networks. We propose an OFDMA-based PON with a transmission employing intensity modulation/direct detection in the downstream and a remodulation of a remotely seeded carrier provided by the optical line terminal with coherent detection in the upstream, which enables cost-effective colorless optical network units (ONUs). Furthermore, an OFDMA-PON field trial using the proposed scheme over 37.5 km feeder fiber is demonstrated. A power budget supporting 32 ONUs with dynamic bandwidth allocation and trellis coded modulation (TCM) is reported.

Next-generation optical access seamless evolution: concluding results of the European FP7 Project OASE

Increasing bandwidth demand drives the need for next-generation optical access (NGOA) networks that can meet future end-user service requirements. This paper gives an overview of NGOA solutions, the enabling optical access network technologies, architecture principles, and related economics and business models. NGOA requirements (including peak and sustainable data rate, reach, cost, node consolidation, and open access) are proposed, and the different solutions are compared against such requirements in different scenarios (in terms of population density and system migration). Unsurprisingly, it is found that different solutions are best suited for different scenarios. The conclusions drawn from such findings allow us to formulate recommendations in terms of technology, strategy, and policy. The paper is based on the main results of the European FP7 OASE Integrated Project that ran between January 1, 2010 and February 28, 2013.