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Mode Division Multiplexing

Acronym: MDM

Definition: a multiplexing technique for data transmission in fibers, where different fiber modes are used for different channels

More general term: optical multiplexing

Category: lightwave communications

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Mode division multiplexing (MDM) is a technique which is applied in some modern systems for optical fiber communications for increasing the data capacity. Essentially, the idea is using different guided modes of a multimode fiber for different transmission channels.

Components for MDM

The following types of components are typically used for mode division multiplexing:

  • Typically, the used multimode fibers have a relatively small number of guided modes and are thus called few-mode fibers. They may in principle be step-index fibers, but often one uses graded-index fibers optimized for minimum differential modal group delay (DMGD), because that allows the use of simpler receiver technology.
  • Certain kinds of spatial multiplexers (SMUX) are required for (a) injecting signals from multiple single-mode fibers into the core of a few-mode fiber and (b) for separating the signals after transmission, sending them to different photodetectors. Different kinds of spatial multiplexers have been developed. Some of them are based on certain phase plates, others on photonic laterns.
  • For maintaining sufficiently high signal powers over large distances, there are special fiber amplifiers (mostly erbium-doped fiber amplifiers = EDFAs) for few-mode fibers, which are optimized for minimum variations of modal gain.

Because there is always a substantial cross-talk between the different channels, receivers need to be equipped with special electronics based on MIMO techniques (multiple inputs / multiple outputs), similar to those which are already widely used for wireless data transmission, for example for WLAN.

The requirements on fusion splicers are more demanding than for splicing ordinary multimode fibers, since one needs to minimize mode -dependent losses.

Combination with Other Multiplexing Techniques

Mode division multiplexing can be combined with other techniques like wavelength division multiplexing. It is expected to become important for satisfying the first one rising demand of data transmission capacities.

For a more detailed discussion, including the comparison with other techniques, see the article on space division multiplexing.

Suppliers

The RP Photonics Buyer's Guide contains 2 suppliers for mode division multiplexing devices.

Questions and Comments from Users

2020-07-16

Can RP Fiber Power V7 be used to simulate a MDM transmission line/system?

How can I determine the effective index of a multicore multi-mode optical fiber?

Answer from the author:

Yes, RP Fiber Power can be used to perform beam propagation simulations, which you can apply to multi-core fibers. For example, you specify some optical input for one core only and simulate how that light may couple over to other cores – e.g. due to bending of the fiber.

For obtaining the effective refractive index, you may often just apply a mode solver to a single core. However, in cases with substantial coupling between the cores, you need a more refined method. Some mode solvers (unfortunately no our one) can be applied to multi-core configurations, and then deliver the effective indices of the supermodes. Another approach (also possible with RP Fiber Power) is to use numerical beam propagation and extract specific modes with a Fourier transform technique, exploiting the fact that the propagation constants are generally mode-dependent.

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Bibliography

[1]S. Berdagué and P. Facq, “Mode division multiplexing in optical fibers”, Appl. Opt. 21 (11), 1950 (1982), doi:10.1364/AO.21.001950
[2]F. Yaman et al., “Long distance transmission in few-mode fibers”, Opt. Express 18 (12), 13250 (2010), doi:10.1364/OE.18.013250
[3]B. Zhu et al., “70-Gb/s multicore multimode fiber transmissions for optical data links”, IEEE Photonics Technol. Lett. 22 (22), 1647 (2010), doi:10.1109/LPT.2010.2070490
[4]Y. Jung et al., “First demonstration and detailed characterization of a multimode amplifier for space division multiplexed transmission systems”, Opt. Express 19 (26), B952 (2011), doi:10.1364/OE.19.00B952
[5]T. Sakamoto et al., “Transmission over large-core few-mode photonic crystal fiber using distance-independent modal dispersion compensation technique”, Opt. Express 19 (26), B478 (2011), doi:10.1364/OE.19.00B478
[6]R. Ryf et al., “Mode-division multiplexing over 96 km of a few-mode fiber using coherent 6 × 6 MIMO processing”, J. Lightwave Technol. 30 (4), 521 (2012), doi:10.1109/JLT.2011.2174336
[7]J. D. Love and N. Riesen, “Mode-selective couplers for few-mode optical fiber networks”, Opt. Lett. 37 (19), 3990 (2012), doi:10.1364/OL.37.003990
[8]Q. Kang et al., “Accurate modal gain control in a multimode erbium doped fiber amplifier incorporating ring doping and a simple LP01 pump configuration”, Opt. Express 20 (19), 20835 (2012), doi:10.1364/OE.20.020835
[9]V. A. J. M. Sleiffer et al., “73.7 Tb/s (96 × 3 × 256-Gb/s) mode-division-multiplexed DP-16QAM transmission with inline MM-EDFA”, Opt. Express 20 (26), B428 (2012), doi:10.1364/OE.20.00B428
[10]D. J. Richardson, J. M. Fini and L. E. Nelson, “Space-division multiplexing in optical fibers”, Nat. Photonics 7 (5), 354 (2013), doi:10.1038/nphoton.2013.94
[11]T. Hayashi et al., “Physical interpretation of intercore crosstalk in multicore fiber: Effects of macrobend, structure fluctuation, and microbend”, Opt. Express 21 (5), 5401 (2013), doi:10.1364/OE.21.005401
[12]P. Sillard, M. Bigot-Astruc and D. Molin, “Few-mode fibers for mode-division-multiplexed systems”, J. Lightwave Technol. 32 (16), 2824 (2014), doi:10.1109/JLT.2014.2312845
[13]P. J. Winzer, “Making spatial multiplexing a reality”, Nat. Photonics 8 (5), 345 (2014), doi:10.1038/nphoton.2014.58
[14]R. G. H. van Uden et al., “Ultra-high-density spatial division multiplexing with a few-mode multicore fibre”, Nature Photonics 8, 865 (2014), doi:10.1038/nphoton.2014.243
[15]Y. Jung et al., “Cladding pumped few-mode EDFA for mode division multiplexed transmission”, Opt. Express 22 (23), 29008 (2014), doi:10.1364/OE.22.029008
[16]G. Lopez-Galmiche et al., “Few-mode erbium-doped fiber amplifier with photonic lantern for pump spatial mode control”, Opt. Lett. 41 (11), 2588 (2016), doi:10.1364/OL.41.002588

(Suggest additional literature!)

See also: space division multiplexing, few-mode fibers, graded-index fibers, fiber amplifiers
and other articles in the category lightwave communications

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