This Review summarizes the simultaneous transmission of several independent spatial channels of light along optical fibres to expand the data-carrying capacity of optical communications. Recent results achieved in both multicore and multimode optical fibres are documented.

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Space-division multiplexing in optical fibres

Orthogonal frequency division multiplexing (OFDM) is a modulation technique which is now used in most new and emerging broadband wired and wireless communication systems because it is an effective solution to intersymbol interference caused by a dispersive channel. Very recently a number of researchers have shown that OFDM is also a promising technology for optical communications. This paper gives a tutorial overview of OFDM highlighting the aspects that are likely to be important in optical applications. To achieve good performance in optical systems OFDM must be adapted in various ways. The constraints imposed by single mode optical fiber, multimode optical fiber and optical wireless are discussed and the new forms of optical OFDM which have been developed are outlined. The main drawbacks of OFDM are its high peak to average power ratio and its sensitivity to phase noise and frequency offset. The impairments that these cause are described and their implications for optical systems discussed.

OFDM for Optical Communications

Differential-phase-shift keying (DPSK) has recently been used to reach record distances in long-haul lightwave communication systems. This paper will review theoretical, as well as implementation, aspects of DPSK, and discuss experimental results.

Optical phase-shift-keyed transmission

We present theoretical and simulation results for the performance of asymmetrically-clipped optical OFDM (ACO-OFDM) and DC-biased optical OFDM (DCO-OFDM) in AWGN for intensity-modulated direct-detection systems. Constellations from 4 QAM to 1024 QAM are considered. For DCO-OFDM, the optimum bias depends on the constellation size which limits its performance in adaptive systems. ACO-OFDM requires less optical power for a given data rate than DCO-OFDM for all but the largest constellations and is better suited to adaptive systems as the same structure is optimum for all constellations.

Comparison of Asymmetrically Clipped Optical OFDM and DC-Biased Optical OFDM in AWGN

Space-division multiplexing (SDM) uses multiplicity of space channels to increase capacity for optical communication. It is applicable for optical communication in both free space and guided waves. This paper focuses on SDM for fiber-optic communication using few-mode fibers or multimode fibers, in particular on the critical challenge of mode crosstalk. Multiple-input–multiple-output (MIMO) equalization methods developed for wireless communication can be applied as an electronic method to equalize mode crosstalk. Optical approaches, including differential modal group delay management, strong mode coupling, and multicore fibers, are necessary to bring the computational complexity for MIMO mode crosstalk equalization to practical levels. Progress in passive devices, such as (de)multiplexers, and active devices, such as amplifiers and switches, which are considered straightforward challenges in comparison with mode crosstalk, are reviewed. Finally, we present the prospects for SDM in optical transmission and networking.

Space-division multiplexing: the next frontier in optical communication

A novel concept for transparent link design is presented, and evaluated numerically and experimentally 10 Gbit/s single channel transmission over more than 4000 km of Standard Single Mode Fibre is demonstrated At reduced transmission distances, the systems show a high robustness against variations of the system parameters

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Using Normalised Sections for the Design of All Optical Networks

A novel system-level simulation environment is presented for the evaluation of step-index polymer optical fibre transmission systems. Key element is a new fibre model, which incorporates the three major attributes describing light propagation in SI-POF: the mode-dependent attenuation, the modal dispersion and the mode coupling process. Inter-symbol interference (ISI) due to modal dispersion can be mitigated in the receiver by means of electronic dispersion compensation. In this work, we present the performance of an analog equaliser scheme based on a (sub-)optimal a-posteriori-probability (APP) technique, which increases the achievable fibre length for error-free transmission at 1 Gbit/s from 11 to 53m. Copyright © 2007 John Wiley & Sons, Ltd.

Analysis of electronic dispersion compensation for step‐index polymer optical fibre by use of an advanced simulation model

In this work, a significant reduction of the computational complexity of the back-propagation algorithm applied to dispersion managed links is proposed, without degrading the system performance.

Reduced complexity back-propagation for optical communication systems

For the first time penalties due to XPM crosstalk have been measured by switching neighbouring channels in a long distance 16/spl times/10 Gb/s ASK NRZ system based on standard single mode fibre (SMF) links with dispersion optimized transmission sections.

Penalties through XPM crosstalk in a switched long haul standard fiber WDM system based on normalized transmission sections

Optical duobinary transmission over 1720 km is successfully demonstrated in a field trial within a fully transparent German - wide WDM network. This proves the applicability of duobinary modulation for ultra long haul transmission.

http://ieeexplore.ieee.org/iel5/10668/33653/01601224.pdf

Norbert Hanik

Papers

Using Normalised Sections for the Design of All Optical Networks

Analysis of electronic dispersion compensation for step‐index polymer optical fibre by use of an advanced simulation model

Reduced complexity back-propagation for optical communication systems

Penalties through XPM crosstalk in a switched long haul standard fiber WDM system based on normalized transmission sections

Field Trial of Optical Duobinary Transmission Over 1720 km at 10 Gb/s