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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 19, Iss. 17 — Aug. 15, 2011
  • pp: 16574–16575
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Focus Issue: Space Multiplexed Optical Transmission

Guifang Li and Xiang Liu  »View Author Affiliations

Optics Express, Vol. 19, Issue 17, pp. 16574-16575 (2011)

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This Optics Express Focus Issue features the state-of-the-art research activities in MDM and SDM aimed at order-of-magnitude capacity growth in future optical communication systems.

This Focus Issue starts with two record-setting high-capacity transmission demonstrations using SDM in MCF. The first paper by B. Zhu et al. from OFS Labs and Bell Labs reports a transmission capacity of 112 Tb/s over a distance of 76.8-km using SDM in a 7-core fiber using SDM and DWDM in the C and L bands. Each of the 7 cores carried 160 polarization-division multiplexed quadrature phase-shift keying (PDM-QPSK) channels at 107-Gb/s on a 50-GHz grid, resulting in an aggregate spectral efficiency of 14 b/s/Hz. The impact of the inter-core crosstalk was experimentally investigated and the system implications of core-to-core crosstalk on long-haul transmission were discussed. The second paper by T. Hayashi et al. from Sumitomo Electric Industries reports an ultra-low-crosstalk MCF that is suitable for ultra-long-haul transmission. A remarkably low inter-core crosstalk level of below −60 dB was achieved in a 16.8-km 7-core fiber, by using a trench-assisted index profile. A transmission capacity of 109 Tb/s was demonstrated by using SDM and DWDM.

Following the two MCF transmission demonstrations are three papers on MDM-based transmission in FMF. C. Koebele et al. from Bell Labs, Kylia, Draka, and Irisa/Inria report the transmission of two 112-Gb/s PDM-QPSK signals over two orthogonal LP11 modes of a 40-km FMF, using liquid crystal on silicon (LCOS) based mode multiplexer and demultiplexer. 4 × 4 multiple-input multiple-output (MIMO) processing was used in an offline digital coherent receiver to achieve mode separation. A. Li et al. from The University of Melbourne reports successful transmission of two 17.65-Gb/s coherent optical orthogonal frequency-division multiplexing (CO-OFDM) signals over two orthogonal LP11 modes of a 26-km two-mode fibers using all-fiber mode converters and 4 × 4 MIMO-OFDM processing. S. Randel et al. from Bell Labs and OFS labs present the transmission of three 112-Gb/s PDM-QPSK signals over the fundamental mode (LP01) and two orthogonal LP11 modes of a 33-km FMF. 6 × 6 MIMO processing was used to achieve the separation of the 3 spatial modes and the 2 polarizations of the transmitted signals. These experiments show the feasibility of scaling capacity using MDM in FMF in combination with MIMO signal processing. Practical implementation tasks such as power-efficient optical amplification for FMF and hardware-efficient MIMO processing remain to be important for future research.

The emergence of MDM and SDM as potential breakthrough technologies for future optical networks also calls for fundamental study on the ultimate capacity limit and energy consumption. This Focus Issue concludes with three papers that theoretically address these important fundamental questions. P. Winzer and G. J. Foschini of Bell Labs study MIMO capacities and outage probabilities in spatially multiplexed optical transport systems. They found that in order to achieve the low-outage standards required for optical transport networks, SDM transponders should be capable of individually addressing, and preferably MIMO processing all modes supported by the optical SDM waveguide. The impact of mode-dependent loss (MDL) on system capacity and system outage was also investigated. K.-P. Ko and J. M. Kahn from Silicon Image and Stanford University investigate the fundamental performance limitations on MDM due to MDL. Information-theoretic channel capacities of mode-division-multiplexed systems in the presence of MDL were studied, including average and outage capacities, with and without channel state information. Finally, I. Djordjevic of University of Arizona discusses energy-efficient spatial-domain-based hybrid multi-dimensional coded-modulations for multi-Tb/s optical transport. Orbital angular momentum (OAM) was used as an additional dimension to further improve the overall optical channel capacity. Promising multi-dimensional signal constellations were suggested to maximize the information capacity, while taking the energy efficiency into consideration.

It is our hope that this Focus Issue on MDM and SDM has provided a comprehensive survey of the state-of-the-art research activities in MDM and SDM and it will stimulate future research on this subject to address the remaining fundamental and practical challenges, potentially enabling dramatic capacity growth in future optical communication systems.

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Original Manuscript: August 10, 2011
Published: August 15, 2011

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Space Multiplexed Optical Transmission (2011) Optics Express

Guifang Li and Xiang Liu, "Focus Issue: Space Multiplexed Optical Transmission," Opt. Express 19, 16574-16575 (2011)

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