In the last few decades, interest in multimode optical fibers has been aroused for a wide range of applications in sensing, imaging and communication.
In this work, the spatial domain of multimode fibers is examined, increasing both, the data rate and data security. In a first step, modes of the MMF are shaped by a spatial light modulator and coupled into the fiber. Camera-based intensity measurement is used to examine the modes supported by the fiber towards space division multiplexing (SDM).
The obtained modes are restarted and the modal scrambling within the MMF is measured using digital holography. To investigate the optical setup’s coupling conditions, both the signal propagating through the MMF, including modal scrambling, and the internal portion reflected back from the output facet and propagating back to the transmitter side are measured through transmission matrix technology.
We investigate the interaction between linear and nonlinear compensation within back-propagation algorithm applied to
next-generation 400-Gbps systems. A significant performance improvement is reported by taking into account the
interaction of these two parts.
One of the major impairments in high-speed optical transmission links is Polarization-Mode Dispersion (PMD).
We propose the method of electronic predistortion (EPD) for the mitigation of PMD. This approach has already
been successfully applied for the compensation of Chromatic Dispersion (CD) and Fiber-Nonlinearities. The
advantage of this method is that impairments can efficiently be mitigated without the need for coherent reception.
The proposed scheme is based on the possibility to control the optical field at the transmitter by using two complex
modulators for the modulation of two orthogonally polarized optical signals.
If the physical origin of PMD is exactly known then the ideal predistorted field and the corresponding electrical
driving signals can be computed accurately. In practice, however, this information is not available. Therefore it
is shown how to determine appropriate driving signals for a set of measured PMD parameters.
Measurements will be communicated through a feedback channel in practice. We suggest a possible strategy
for application of this technique in scenarios, in which the adaptation speed is intrinsically limited due to the
round-trip delay.
Numerical simulations reveal that the use of EPD can significantly increase the tolerance towards PMD in
comparison to a system without compensation.
Deployment of 40-Gbit/s technology in metro and core networks is still attractive, to bring down costs and to increase transmission capacity. This paper summarises design issues of 40-Gbit/s WDM systems for their application in wavelength division multiplexed metro and core networks. Parameter tolerances and transmission distances for different modulation formats are numerically and experimentally investigated. Based on Deutsche Telekom's fibre infrastructure, upgrade studies show that polarisation mode dispersion will be the main obstacle when installing 40-Gbit/s technology in deployed fibre infrastructure.
The pressure on prices per bit and distance in operator networks requires an ongoing reduction of costs. In todays optical transport networks typical transparent transmission lengths are in the order of about 400 to 600 km. Then costly electrical 3R-regeneration is required. One way to deal with this cost-driver is to introduce ultra long haul (ULH) transparent WDM systems which are able to cover transmission length of e.g. up to 2000 km and thus decreasing the number of regenerative transponders. However, to maintain the flexibility of the network to add and drop traffic at required locations the use of optical add drop multiplexers (OADMs) or optical cross connects (OXCs) is mandatory in these systems, particularly for pan-European but even for European national networks. The design of such ULH-networks has to deal with a vast number of issues, in particular the physical layer design has to be very flexible and to allow for different optimization and adjustment schemes. In this paper based on computer simulations we will compare different approaches to reduce the design complexity of 10 Gbit/s ULH systems taking into account environmental constraints like availability of housing stations for different target distances.
The regenerator-free transmission distance of ultra-long-haul, dispersion-managed, optical WDM-transmission-links is ultimately determined by accumulating ASE-Noise of optical amplifiers and Polarisation-Mode-Dispersion (PMD) of the fiber-material. Therefore the applicability of the fiber-infrastructure of Deutsche Telekom to transport optical channels at 10 Gbit/s and 40 Gbit/s over sufficiently long distances is assessed both generally, applying PMD limit-values of ITU-T, and for a selected transmission link, evaluating numerical simulations using a worst-case simulation model.
The Global Seamless Network (GSN) Demonstrator is presented, a joint effort of system vendors and Deutsche Telekom Group R&D to demonstrate network functions and management integration and enable, for the first time, experiences with a carrier grade Automatically Switched Transport Network (ASTN) implementation and the envisaged main ASTN clients, IP and Ethernet. For end-to-end monitoring capability, integrating the view on the ASTN and Ethernet-MAN configuration, an UMS (Upper Monitoring System) is being developed. Furthermore broadband application were implemented to visualise the network functions. The ASTN backbone consists of four cross connects and an ULH-WDM system with 3x 10Gbit/s channels (OCh) between Berlin and Darmstadt, whereby each OCh is treated as a virtual fibre.
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.
Today's Metro networks are facing the challenge to transport different services like 2.5 Gbit/s and 10 Gbit/s SDH, Gigabit and 10G Ethernet, and different data formats at costs as low as possible. Particularly due to cost and associated performance reasons wavelength-division multiplex (WDM) transmission systems are an attractive candidate for the Metro area e.g. offering different services over different wavelengths. However, for cost-reduction it is mandatory to avoid expensive components like optical amplifiers (OAs) and dispersion compensating modules (DCMs) whenever possible. This leads to a limited extension of the transparent reach due to e.g. transmitter and receiver characteristics, fiber dispersion, and fiber nonlinearity. It is the object of this paper to investigate the potential of Metro WDM systems and to derive design guidelines without use of OAs and DCMs. Based on computer simulations different fiber infrastructures like Standard Single-Mode Fiber (SSMF, ITU-G.652), positive and negative dispersion Non-Zero Dispersion Shifted Fibers (NZDSF) are analyzed with respect to 2.5 Gbit/s and 10 Gbit/s data rate per channel with low-cost direct and chirp-free external modulation at both data rates. Non-Return-to-Zero- (NRZ-) intensity-modulation is assumed as standard modulation format. At 10 Gbit/s single channel transmission external modulation over pure SSMF results in transmission length of about 50km. Only for high-input powers fiber nonlinearity partly compensates the fiber dispersion and allows an increase in reach up to 90km. For WDM transmission the performance is limited by Self-Phase Modulation (SPM) and Cross-Phase Modulation (XPM) allowing 40x10 Gbit/s uncompensated low-cost transmission over 50km of existing SSMF.
Design, control and management of all-optical transparent islands based on fibers, optical amplifiers and transparent Optical Cross Connects (OXC) have to deal with a vast number of issues such as network topology, routing, protection, and restoration schemes. However, since in such a transparent network light-paths generally have to transit through several fiber sections, amplifiers, and OXCs, all of which add noise and degrade the signal performance, optical layer network protocols have to be aware of the end-to-end signal quality for each specific light-path. This information should be obtained without burdening these protocols with details of the physical layer. In this paper we propose a simplified network design approach based on normalized optical transmission sections where the physical links are built from a cascade of identical basic blocks. For an upper layer protocol only the number of traversed blocks has to be monitored for estimating signal quality. Using numerical simulations the maximum number of cascaded building blocks for 10 Gbit/s RZ modulation format for different basic building block-configurations is investigated and compared with the performance of NRZ based systems under similar conditions. It is shown that robust transparent islands of about 1600 km maximum link length without 3R regeneration are feasible for both modulation formats using the concept of normalized sections.
Optical fiber cable are worldwide installed, e.g. about 43 million kilometers in 1997, an annual growth rate of about 20% is expected. This infrastructure is an excellent basis to convert optical networks based on point-to point systems into managed photonic networks in which new additional photonic equipment is used. Deutsche Telekom started in 1997 some tests with new wavelength division multiplex (WDM) technology in their network in which standard single mode fiber is very dominant. We report on some of these tests and also on first WDM-links in the network carrying real traffic.
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