Werner Weiershausen

Field trial results on statistics of fast polarization changes in long haul WDM transmission systems

Field trials were carried out to determine the statistics of fast polarization changes in optical networks. Important data enabling the definition of speed requirements for PMD compensators and adaptive equalizers could be obtained.

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

Dual output SOA based amplifier for PON extenders

A novel two-output PON amplifier is demonstrated to provide over 8-dB output power budget improvement over a conventional SOA, with negligible ASE noise. With an additional preamplifier it can accommodate up to 30 dB burst-to-burst power variation.

40 Gb/s field test on an installed fiber link with high PMD and investigation of differential group delay impact on the transmission performance

40-Gbit/s OTDM transmission over a field-installed dispersion-compensated 130-km single mode fibre (SMF) link was demonstrated successfully (BER < 10/sup -12/). The impact of high PMD (7.8 ps) in the order of the RZ pulse width (7 ps) was studied in detail.

Saturated collision amplifier reach extender for XGPON1 and TDM/DWDM PON

Saturated Collision Amplifier (SCA) is a novel amplification scheme that uses SOA saturation in order to maximize the output power and minimize the ASE noise and the polarization sensitivity. We demonstrate the SCA reach extension in a commercial single-wavelength XGPON1 prototype system where bidirectional optical budget of up to 50 dB is obtained. The traffic performances are compared between the SCA and the conventional SOA extender. The novel extension scheme is demonstrated also for two- and four-wavelength 10 Gbit/s unidirectional downstream configurations with 45 km and 100 km transmission distances with 58-dB maximum total optical budget for each wavelength.

Characterisation of the PMD Distribution along Optical Fibres and Improvement of the Backbone Fibre Infrastructure by a POTDR

Fibre links in optical networks generally comprise several relatively short fibre segments which have been spliced together in cables. These fibre segments or “sections” are assembled with optical connectors and have a typical length of some tens of km. The important characteristic parameters of the fibre sections are attenuation, chromatic dispersion (CD) and polarisation mode dispersion (PMD). However, the PMD of the optical fibres can hamper the upgrade of optical backbone networks towards higher data rates of 40 Gbit/s and beyond. The PMD distribution along a buried fibre link is not constant and can also significantly vary between the concatenated fibres of the same optical cable. In the absence of such spatial information, the whole cable with higher PMD-values may have to be replaced in order to transmit 40 Gbit/s transparently over long distances. But investigations have shown that frequently localized pieces within a section are the major contributors to the overall high PMD value of the whole fibre, rendering the link unsuitable for higher data rates. A new random-scrambling polarization optical time domain reflectometry (POTDR) measurement technique is used to investigate the spatial distribution of the cumulative PMD in deployed fibres. Results help to identify high-PMD fibre pieces or sections which need to be replaced to enable 40 Gbit/s transmission and beyond, rather than substitution of a whole fibre link. Techno-economical investigations show the high economic potential of this method leading to significant reduction of expenses for infrastructure improvements. These improvements will enable network operators to transmit high data rates without limitation given by PMD.

100GEthernet for aggregation and transport networks

Due to the doubling of the internet traffic every twelve month and upgrading existing optical metro-, regio- and long haul transport networks, the migration from existing networks toward high speed optical networks with channel data rates up to 100 Gbit/s/λ is one of the most important questions today and in the near future. Current WDM Systems in photonic networks are commonly operated at linerates of 2.5 and 10 Gbit/s/λ and major carriers already started the deployment of 40 Gbit/s/λ services. Due to the inherent increase of the bandwidth per channel, limitations due to linear and non-linear transmission impairments become stronger resulting in a highly increased complexity of link engineering, potentially increasing the operational expenditures (OPEX). Researchers, system vendors and -operators focus on investigations, targeting the relaxation of constraints for 100 Gbit/s transmission to find the most efficient upgrade strategies. The approaches towards increased robustness against signal distortions are the transmission of the 100 Gbit/s data signals via multiple fibers, wavelength, subcarriers or the introduction of more advanced modulation formats. Different modulation schemes and reduced baud rates show strongly different optical WDM transmission characteristics. The choice of the appropriate format does not only depend on the technical requirements, but also on economical considerations as an increased transmitter- and receiver-complexity will drive the transponder price. This article presents investigations on different approaches for the upgrade of existing metro-/ regio and long haul transport networks. The robustness against the main degrading physical effects and economy of scale are considered for different mitigation strategies.

Aggregation networks: Cost comparison of WDM ring vs. double star topology

Due to the increasing demand for higher transmission capacity, originated from upcoming Triple-Play services, network operators are forced to increase the transmission capacity in the backbone and aggregation networks and drive down the costs per bit/s. Many concepts have been presented, optimizing backbone network and increasing the network capacity by introducing higher data rates or channel count. In this paper we focus on aggregation network architectures investigating appropriate architectures for the aggregation of broadband services for an incumbent European network operator. These architectures have to be cost effective and ensure high service availability. These requirements can be met by either aggregating via star topology, using several stages of Ethernet aggregation nodes, by a ring topology using cost effective optical add/drop multiplexers (OADM), or furthermore a mixture of star and ring topologies. The right choice depends on the traffic load, the traffic forecast, distribution of the traffic matrix and underlying fiber graph.

Simulation and optimization of 100 Gbit/s single channel modulation formats

The performance of various modulation schemes for 100 Gbit/s single channel serial transmission is investigated by means of numerical simulations. Different ASK and PSK modulation formats are compared in terms of total system reach for a 10-9 BER requirement. RZ-DQPSK format with a 1,920 km reach, without FEC and the support of additional Raman amplification, outperforms all the other schemes including 10×10 Gbit/s NRZ DWDM inverse multiplexing.

Photonic balancing and its application in optical receivers and regenerators for fiber-optic systems

We present an optical receiver for RZ-DPSK signals that use photonic balancing. Photonic balancing is achieved through pulse counter-propagation and collision in a saturated SOA. We explain the principles of photonic balancing and show how it can lead to an improvement in RZ-DPSK detection by 3 dB, similar to electrical balancing. We also show how this scheme can be used as a Mamyshev-type regenerator.