2012/1/26 David Storandt <dstorandt@teljet.com>
You can put a 3dB or 5dB optical pad on the link if the receiver can't handle zero-distance optical power.
We're using SFP LX for a couple of years even in back to back configuration for equipments within the same rack with a 1 meter patch cord without any problem. Max TX is -3dBm, Max RX sensivity is -3dBm so there is no problem. 1. I don't think I've ever had a LX SFP that TX at -3 dBm, they're usually around -5 to -7 dBm. and example in a live router : pymaunier@re1.tcr1.rb.par> show interfaces diagnostics optics ge-7/3/* | match "Laser output power " Laser output power : 0.3160 mW / -5.00 dBm Laser output power : 0.1800 mW / -7.45 dBm Laser output power : 0.2600 mW / -5.85 dBm Laser output power : 0.3210 mW / -4.93 dBm Laser output power : 0.3070 mW / -5.13 dBm Laser output power : 0.3200 mW / -4.95 dBm Laser output power : 0.3180 mW / -4.98 dBm Laser output power : 0.3140 mW / -5.03 dBm 2. You can assume a patch cord add between 0.2 to 0.5 dB of attenuation so even with a SFP TX at -3dBm, you won't receive at the Max RX sensitivity. -- Pierre-Yves Maunier