Is there a minimum fiber distance between CWDM endpoints?

Answered Question
Mar 30th, 2010

I've made several connections via CWDM MUX8As between various buildings. However, I can't make a connection with the 1570 SFPs. The end-point fiber connections are approx 6 meters (2m on one end, 4m on the other). If I test it on the bench with a pair of spare muxes, I can get a connection only when I slightly disconnect any one of the fiber LC connections (either at the mux interface or the switch interface). Basically I'm creating a greater air gap between the end of the fiber and the SFP transceiver. This leads me to believe that the signal level might be too high, so the light needs to be attenuated.

Am I totally off track here, or is my fibre cabling distance too short? I can't find any info on the Internet with respect to this.

Note that all end-point connections are Cisco 6500s with VS-720-10GE and 3750s with advanced IP services IOS.

Dave

I have this problem too.
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Correct Answer by Tom Randstrom about 6 years 8 months ago

Yes.  The optical receiver has a maximum input power specification.  For the Cisco CWDM SFP/GBICs, the maximum receiver input power is -7 dBm.  For your test system, you need to install a 10dB optical attenuator on the fibers between the MUX8 filters.

Tom

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Correct Answer
Tom Randstrom Tue, 03/30/2010 - 09:43

Yes.  The optical receiver has a maximum input power specification.  For the Cisco CWDM SFP/GBICs, the maximum receiver input power is -7 dBm.  For your test system, you need to install a 10dB optical attenuator on the fibers between the MUX8 filters.

Tom

drhague Tue, 03/30/2010 - 10:28

Thanks Tom, exactly what I was looking for. Now to see if I can track down these elusive attenuators!

Dave

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