Tuesday, February 26, 2008

Single mode fibre

Last week we did our first single-mode ('mono-mode') fibre job at Molinare. They are doing a job for the Beeb at Pinewood where they have to extend a dozen circuits provided by SohoNet for KVM and HD-SDi extension (the DS-Nitris editing station lives in Soho but the editor sits in Pinewood).
Anyhow - some things we discovered about single-mode over our usual multi-mode are;

  • For loose tube cable you really can't tell the difference between the skinny 9-micron and the relatively fat 62.5 micron fibres because the cladding on the glass is the same width - 125 microns (see the diagram). In fact, when you prepare the ends and get them into the fusion splicer you are hard-pushed to see the difference.
  • For testing you need to use a mono-mode light source and detector and the appropriate test leads. Thankfully Darren at DIS sorted me out with his tester. I'm going to look into buying one if we do more single-mode.
  • The Tritec Fase-2 splicers that we use have a mono-mode config that runs the laser cooler so that the little centre-core isn't blown away by a beam intended for the bigger cores.
For a quick explanation of mono-mode fibre see the Wikipedia article (link in the title).

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