Armin Ehrhardt

Automatic PMD compensator in a 160-Gb/s OTDM transmission over deployed fiber using RZ-DPSK modulation format

We report on a magneto- and electrooptically tuned dynamic polarization-mode dispersion (PMD) compensator that enabled error-free single-channel 160-Gb/s RZ-DPSK transmission over a 75-km SMF link with a mean differential group delay (DGD) of more than 30% of the bit period. Polarization scrambling and DOP measurements were utilized to automatically adapt the compensator. We present bit error rate (BER) measurements and describe the operation of the compensator in detail.

Extension of all-optical network-transparent domains based on normalized transmission sections

This paper presents a technique that significantly simplifies the design and operation of transparent optical wavelength-division-multiplexing (WDM) networks. Since most of the signal degradations arise due to the interaction of linear and nonlinear physical effects along the fiber links, a link design concept based on erbium-doped fiber amplification is developed and optimized such that originally degrading effects mutually compensate each other, leading to approximately noise-limited transmission. In extensive numerical simulations as well as laboratory experiments, an optimized modular link design is identified. Regenerator-free transmission of a single-channel 10-Gb/s nonreturn-to-zero signal over 4000 km is achieved in a recirculating loop experiment with less than a 3-dB penalty. Reliable WDM transmission is demonstrated over 1600 km, showing the high robustness of this concept. Finally the link design concept is applied in a WDM field trial using deployed standard single-mode fibers (S-SMFs) of the optical network infrastructure of Deutsche Telekom. Between the German cities of Berlin and Darmstadt, 10-Gb/s synchronous digital hierarchy (SDH)-based data, 10-Gb/s duobinary-encoded data, and a native Gigabit Ethernet signal have been transmitted error-free over a maximum distance of 1720 km, thus demonstrating the feasibility of the design concept under realistic field conditions. The presented design approach substantially supports link setup and rerouting procedures by supplying simple rules to identify the maximum number of dispersion-compensated S-SMF amplified spans which can be cascaded for a given tolerable penalty.

Measuring the Link Distribution of PMD: Field Trial Using an RS-POTDR

A new POTDR measurement technique is used to investigate the spatial distribution of PMD in deployed fibers. Results help to identify high-PMD fiber sections that need to be replaced to enable 40Gbit/s transmission and beyond.

Analysis of Crosstalk in Mixed 43 Gb/s RZ-DQPSK and 10.7 Gb/s DWDM Systems at 50 GHz Channel Spacing

In DWDM field experiments over 1047 km of standard fiber and in simulations we analyze the impact of crosstalk on a 43 Gb/s RZ-DQPSK channel both by 10.7 Gb/s OOK and 43 Gb/s RZ-DQPSK neighbors at 50 GHz channel spacing.

Field demonstration of a transparent optical 10 Gbit/s-WDM-network based on normalized transmission sections

Error-free 10 Gbit/s transmission and flexible reconfiguration of transparent wavelength channels over a fully transparent optical network was demonstrated in a field experiment. The test network was realized by cascades of numerically optimized basic transmission sections consisting of a combination of standard single-mode fibers and dispersion compensating modules. A maximum optical path-length of 1720 km was successfully realized without opto-electrical signal conversion.

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.

Characterisation of the PMD distribution along optical fibres by a POTDR

Fibre links in an optical network generally comprise several relatively short fibre segments which have been spliced together in cables. These fibre segments or ldquosectionsrdquo are assembled with optical connectors and have lengths of some tens of kilometres. The characteristic parameters of the fibre sections are attenuation, chromatic dispersion (CD) and polarisation mode dispersion (PMD). However, PMD of the optical fibres can hamper the upgrade of the optical b0ackbone network towards higher data rates of 40 Gbit/s and beyond. The PMD distribution along a buried fibre link is not a constant and can also significantly vary between the different 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 of the 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.

Increasing the performance of MLSE equalization using a chirped transmitter: 10GBit/s field trial with high PMD and CD

A receiver using MLSE equalization is investigated in combination with a chirped transmitter in a 10Gbit/s field trial. Results show that the required OSNR at high CD and PMD can be decreased using appropriate chirp.

Field Trial to Upgrade an Existing 10 Gbit/s DWDM Link by 40 Gbit/s RZ-DQPSK Channels

Data rates generated in the access network by new services and customer demand on triple play influence on the transmission capacity and flexibility of the transport network. A field trial to upgrade an existing DWDM link with 10 Gbit/s RZ- and NRZ-channels by 40 Gbit/s RZ-DQPSK-channels was performed on a link consisting of legacy G.652 fibre with two ROADM and EDFA amplification only. The field link had a length of 1047 km. To obtain a high spectral efficiency of the 40 Gbit/s transport the channel spacing was reduced from 100 GHz to 50 GHz. We investigated channel crosstalk for 50 GHz and 100 GHz channel spacing, mixed types of neighbour channels, PMD and chromatic dispersion tolerance which influence on maximum transparent transmission length and signal quality of the 40 Gbit/s signal in a field experiment.

Field demonstration of a transparent optical WDM network with 10- Gbit/s maximum channel data rate applying an optimized optical link design

A concept to design robust and flexible, fully transparent, optical long-haul networks without additional Raman-Amplification is demonstrated theoretically and experimentally. Excellent performance and flexibility at data rates up to 10 Gbit/s and transparency lengths of more than 1700 km are predicted by computer-simulations and successfully demonstrated in a field-test. Error-free transmission of arbitrary data-rates up to 10 Gbit/s over variable link distances up to 1720 km could be demonstrated without intermediate 3R-regeneration and without additional Raman-Amplification and Forward Error Correction. This field-experiment demonstrates the technical feasibility of extensive and flexible, fully transparent optical WDM-Networks.