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Lighting a dark fiber


Recently I was asked to start learning about "how to light a dark-fiber"

I'm a bit nw in the area but I have some basic knowledge.

Our dark fibers willl exced 100 km which is complicating a bit the whole thing (as far as I know it exceed the reach of any router or switch port)

So I'm looking for some documentation about how to deploy Optical networks, what type of problems can occur or any related documentation. Basicaly if somebody knows one "HOWTO Light a dark fiber" please let me know.

Thank you


Re: Lighting a dark fiber

Remember, "dark fiber" is just fiber with no optical signal on it. It's up to you to light it up. This can be as easy as direct point-to-point links with Gigabit Ethernet optical transceivers (GBICs or SFPs). Or it can be more complicated: SONET/SDH add-drop multiplexers like Cisco's ONS 15454, or (light-)wave division multiplexers like Cisco's CWDM or DWDM products.

The biggest issue you have to contend with in lighting long-distance dark fiber is optical signal loss. Optical amplifiers are generally used to get around that by boosting the signal power. At the power levels involved, optical attenuators also come into play, to diminish the signal at the receiving end (if it is too strong) so that it can be used.

Southeastern Universities Research Association (SURA) has a nice on-line reference for free:

SURA Optical Networking Cookbook

(Hint: download the PDF so you can read it off-line)

Cisco Press ( also has a few books which should help:

* DWDM Network Designs and Engineering Solutions

* Optical Network Design and Implementation

* Cisco Self-Study: Building Cisco Metro Optical Networks (METRO)

Also check out the Beginners' Guides at Light Reading's website (

Hope this helps.

Community Member

Re: Lighting a dark fiber

In telecom dark fiber does not mean "no light" it just means that its leased to another carrier for whatever their use maybe. Its considered "Dark" because we do not see the traffic riding the fiber we are leasing to a customer. Meaning we lease the fiber to the customer they put their own equipment on our fiber hence its not our "light" hitting the fiber. This is also called Indefeasible Right of Use (IRU) fiber.

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