For advanced FEC schemes with soft-decision decoding, the mutual information (MI) between sent and received symbols is the natural figure of merit at the decoder input. In this work, the transmission of signals modulated with rectangular quadrature amplitude modulation (QAM) of order 16, 64, and 256 is simulated over three different fiber links that are typical representatives of metro-area networks used by Deutsche Telekom. At the receiver, the MI between sent and received symbols is estimated using histograms for which the correct bin number is determined in a reliable way. As MI is the constrained capacity, the channel capacity of an optical communication system including all components at transmitter and receiver is found. From the capacity we can derive the maximum spectral efficiency and the maximum data rate over the entire available spectrum for a fixed transmitter, link, and receiver design. For an average metro-area network link, more than 26 Tbit/s at a 50 GHz spacing are possible over the entire C-band. By decreasing the spacing to be close to the Nyquist rate, a dual-polarization spectral efficiency of 10.8 bit/s/Hz is possible, which increases the maximum total data rate per fiber to an astonishing 43.2 Tbit/s.

ONT-reflection is used, additionally to GPON-EMS, to identify termination points in FTTH-PON-networks. OTN-reflectivity vs. wavelength is investigated. In-service OTDR-measurements from Central Office allow testing PON-branches and to distinguish optical length differences down to 2m.

Optical signals of long distance transmission systems accumulate amplifier noise along the transmission link. Conversely, advanced modulation formats for data rates of 100 Gbit/s and faster require higher signal-to-noise ratios than signals with lower data rates. By implementation of additional Raman amplifiers the performance of transmission systems can be improved. Raman amplification can be usefully applied to bridge distances significantly longer than 100 km of fibre between adjacent active points in order to reduce the number of active elements in a network or to bridge distances between endpoints of a transmission link with undersea cables where the installation of active elements is expensive. In case of local points of increased fibre attenuation or losses due to bending however, transmission fibres or active components can be destroyed by the high output power of pump lasers. The pump lasers' output wavelength in the range of 1383 nm may also be absorbed by the water peak of the fibres. To avoid all these hazards for fibre communication systems the fibre infrastructure used for high power pump lasers must be analysed and tested before active components are installed in order to avoid significant signal degradation or damage to active and passive components in the transmission link.

In this article we present a summary of the latest 100 Gbps field trials in the network of Deutsche Telekom AG with industry partners. We cover a brown field approach as alien wavelength on existing systems, a green field high speed overlay network approach and a high speed interface router-router coupling.

We present results from a transmission field trial for a cost-efficient 107 Gb/s channel using real-time data processing. The channel bit error ratio (BER) was sufficient for error-free performance after FEC for a 150 km mixed SSMF and DSF metro route in the Berlin area as part of the OCTET test bed. The DPSK-3ASK modulation format used in the trial was investigated as a lower-cost, metro-focused alternative to the DP-QPSK format, and was assembled using commercially available serializer and deserializer ICs and FPGA. Transmission results as well as latency measurements over a pair of 10GbE tributaries are described. Additionally, post-trial laboratory results for transmission distances up to 430 km with standard single-mode fiber are presented.

Successful 112 Gbit/s PDM-CSRZ-DQPSK transmission with coherent detection and digital electronic DSP post processing is reported over a 1730 km SSMF plus 300 km DCF field installed DWDM-system. A modular network approach with co-propagating 10 Gbit/s WDM-channels is achieved.

Local resolution of OTDR-measurements in concatenated PON and in-house networks depending on the reflectance of the demarcation point was investigated. Termination points of the PON from the Central Office with 1m length difference were distinguishable.

Optical fibre step by step substitutes existing copper cable infrastructure in the carriers' access networks, enabling new broadband services. One common approach, a passive optical network (PON) infrastructure, basically consists of optical fibres and splitters, which are lit up by G-PON (Gigabit/s-PON) or XG-PON (10 Gigabit/s-PON). These systems are attenuation limited, therefore the loss budget of a PON is of high importance. For the deployment process the total attenuation of the PON, between Central Office (CO, OLT) and customer site (ONT), must be accurately monitored and kept below the values specified in G.984.x and G.987.x standards. In FTTH scenarios the PON attenuation measurements must include the in-house networks up to the subscriber fibre cable termination unit. During operation, the Optical Line Supervision (OLS) parameters (e.g. G.984.2, Amd2) are continuously monitored, processed and correlated for appropriate alarm generation. In the case of a fibre failure, additionally non-intrusive in-service measurements from the CO site must be supported for fault localisation. This is enabled by an appropriate WDM-filter per PON in the CO, providing access to the PON for OTDR measurements at wavelengths of 1625/1650 nm. In this paper possible solutions for PON measurement and monitoring for the deployment and operation of FTTH networks will be described in detail from a carrier's perspective. All these activities must be carried out in a minimum of time and with low operational efforts in order to guarantee a cost efficient network operation.

In the access network area the optical fibre step by step substitutes the existing copper cable infrastructure in order to enable new services requiring a steadily increasing bandwidth. The optical fibre is capable to transmit significantly higher data rates over longer distances than the copper links. In the next years new architectures like Fibre-to-the-Building and Fibre-to-the-Home will be implemented in the access networks. These fibre links require a monitoring of the infrastructure by the network operator in order the guarantee a high quality of service. The monitoring is necessary during the fibre installation with final test, regular operation of the network and for fault location. The possibilities and particularities of fibre monitoring in transparent optical access networks in comparison to the core network are described. Considering the operational conditions the preferred and suitable solutions from a view point of a network operator are shown and described in detail.

The accumulated PMD along several fibers in an optical network was measured in order to identify those short fiber portions exhibiting high PMD. By replacing high-PMD-portion(s) in each fiber, the overall-PMD could be reduced significantly. Additionally the PMDaccumulation of different fibers in the same buried cable was investigated and compared to each other.

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.

In the access network area the optical fibre step by step substitutes the existing copper cable infrastructure in order to enable new services requiring a steadily increasing bandwidth. The optical fibre is capable to transmit significantly higher data rates over longer distances than the copper links. In the next years new architectures like Fibre-to-the-Building and Fibre-to-the-Home will be implemented in the access networks. These fibre links require a monitoring of the infrastructure by the network operator in order the guarantee a high quality of service. The monitoring is necessary during the fibre installation with final test, regular operation of the network and for fault location. The possibilities and particularities of fibre monitoring in transparent optical access networks in comparison to the core network are described. Considering the operational conditions the preferred and suitable solutions from a view point of a network operator are shown and described in detail.

PM-RZ-DQPSK with direct detection and fast optical polarisation tracking achieves 6dB noise margin over a long-haul field link. The crosstalk by 10&40G OOK channels at 50GHz spacing is analysed for high channel power.

8 times 107 Gbit/s DWDM transmission is achieved over a 500 km field installed fibre link in the Deutsche Telekom network, indicating high link utilization of 1 bit/s/Hz spectral efficiency, needed for Terabit/s network capacity, required in a mid-term timeframe.

The accumulated PMD along several fibres in an optical network was measured in order to identify those short fibre portions exhibiting high PMD. By replacing high-PMD-portion(s) in each fibre, the overall-PMD could be reduced significantly.

Electronic equalizers are more and more applied in optical transmission systems to compensate for static as well as time varying fiber distortions. In this paper we investigate the performance of 4-states and 16-states MLSE equalizers in 10 Gbit/s field trials over buried single mode fibers. Our results show that the MLSE equalizer enables the joint compensation of chromatic dispersion up to 4480 ps/nm and polarization mode dispersion up to 92 ps. This will increase the uncompensated transmission length and enables a more robust and flexible optical link design.

In this paper we analyze the effort of realizing advanced MLSE digital equalizer technology in optical 10 Gbit/s systems and evaluate its performance for ISI compensation in field applications by comparing 4-state vs. 16-state Viterbi decoders.

We investigate 16-states MLSE equalization over buried fibers having CD up to 4480 ps/nm, PMD up to 92 ps and launch powers up to 12 dBm. Results show a superior performance for joint compensation of all distortion effects.

The accumulated PMD along several fibers in an optical network were measured in order to identify those short fiber portions exhibiting high PMD. By replacing high-PMD-portion(s) in each fiber, the overall-PMD could be reduced significantly.