FEATURE FIBRE OPTIC NETWORKS
Modal-Chromatic Dispersion Higher-order modes have more delay
NE: Can you quantify the benefit of using dispersion compensated fibre?
Current Industry Ideal DMD
SM Modal-Chromatic Dispersion. Higher order modes have more delay. Panduit Confidential and Proprietary
the bandwidth, we started making a correlation between performance and actual differential mode delay data. We recognised that there had to be some kind of wavelength dependence associated with it. When we started looking at the VCSELs we realised that they did have a wavelength dependency that was neglected.
Signature Core™ DMD Profile Dispersion Compensated Multimode Fiber
an impact they have, and also looking at variations in fibres. Based on that, we came up with a new parameter that we can then specify. We actually have a new spec in place with both our manufacturers to introduce what we’re calling Signature Core Fibre, which is a dispersion compensated fibre designed specifically to optimise performance for VCSELs.
Resultant DMD Due to Chroma0c Dispersion Effects
Right shi2ed DMD fibres will fail maximum reach requirement
RP: The benefit varies because it is statistical. But the minimum benefit at a 1% failure probability is a gain of 60m, on both OM3 and OM4. And this gain can be much much greater for specific combinations of fibres and VCSELs or transmitters. The benefits are all completely statistical. If you happen to find a VCSEL that has a certain optical characteristic and you happen to pair that with a fibre that is optimised for that particular VCSEL characteristic, you can go 1000m.
NE: What applications can this technology be used in?
RP: It can be used for anything that uses VCSELs. It is good for 1G Ethernet, 10G Ethernet, and we’ve now demonstrated beyond that. We’re members of the Ethernet Alliance and they recently had what they call a Plug Fest, where all the equipment manufacturers go to check for intermateability and interoperability between all their equipment to make sure that 40/100G is working. We were able to demonstrate 700m transmission at 40/100G with a dispersion compensated fibre.
NE: Who do you think will be interested in this technology?
Signature Core™ SM Resultant Radial Delay NE: What did you do then?
Signature Core DMD Profile. Dispersion Compensated Multimode Fibre. Panduit Confidential and Proprietary
RP: We verified all the results, and then worked with our two fibre suppliers who also verified the performance. We now have a way of specifying fibre that is dispersion compensated for and matched to VCSELs. A statistical analysis was carried out, looking at a very large number of transceivers and characterising what these wavelength dependencies do and how much of
14 NETCOMMS europe Volume I, Issue 6 2011 Fibre is designed in a way that no
matter what path the light takes, all the different modes will get to the end of the fibre at the same time. But it’s such a difficult process to get this fibre to fit this profile well that this doesn’t really happen. So you get fibres that have different types of profiles, and the profiles vary statistically in different ways around that ideal profile. What we have discovered is that the fibre needs a very specific profile in order to perform well.
RP: Most customers have two concerns. Firstly, they are worried about future- proofing. A lot of companies will install higher bandwidth fibres today even though they don’t need them yet. This technology will appeal to customers who want the best fibre they can get, to be ready for future speeds. Other customers, who are now pushing reaches to get very long lengths, do have a very high failure probability of not being able to support their link with a transmitter and a fibre. These people may therefore want a dispersion compensated fibre to ensure zero probability of failure of that link. So any customer who is looking either for extra headroom, future-proofing or reliability would want the best fibre performance they can get.
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