Hello. I'm plan to connect CRS326 and HEX-S with S-3553LC20D kit. Before put them "in production" I want to run them in lab with short LC patch cable, 1 meter or 2 meters to make all the configuration and tests. In this case is there any risks for SFP modules, can they be burned because the distance is very short? Also when I put them "in production", the distance will be about 250 meters. Is this a problem too? In spec. they wrote "to 20km" so maybe the lasers are very powerful and can damage SFP modules when used with short fiber lengths.

Thanks for help.

I have a very similar SM fiber link that has been in production for a few years. I actually used SFP’s from FS.com because they were the only ones that I could find 10km rated BiDi SFP transceivers they weren’t crazy expensive. The transmit power on the pair I use is -5db and they are currently running at at -5.7db receive with no issues ever. I max out the 1Gb link quite often and never get any errors. I’ll link the 2 transceivers I use below.

https://www.fs.com/products/75335.html
https://www.fs.com/products/75336.html

To actually answer your question, I don’t think it’ll be in issue. The actual specifications for the transceiver module are not published on the website. I deal with single mode links on a regular basis and I believe the 40km links I deal with have a transmit power of +2db and the transceivers get upset if the receive power is above -3db. The GPON links I deal with are a whole different animal. Anything hotter than -15db to the OLT SFP results in problems.

The SFP's will automatically increase/decrease power as needed. There's no minimum distance for a fiber cable. Maximum limitations are provided as there is loss / fade over long cable runs.

The SFP's will automatically increase/decrease power as needed. There's no minimum distance for a fiber cable. Maximum limitations are provided as there is loss / fade over long cable runs.

Maybe there are transceivers with auto-power adjustment, but definitely not all of them. Maybe you can mention some specific model which does that? Never seen that before..

Maybe someone from MikroTik support should give us answer, this is important question. At the moment opinions are 50:50 and there is not full technical data on product page.

For S-3553LC20D and such a short-range like 1-2 meters, you have yo use attenuators. Our SFP transceivers do not have auto-power adjustment.

Thank you @skylark. What should be the value of attenuators?

5dB will be enough.
Will work with 10dB aswell.

I understand. One last question - in the schemes attenuators should be on receiver. In my case sender and receiver is the same (only one fiber between SFP modules). So I should put attenuators only on one of SFP modules or on both? Also should I keep them "in production" - the real fiber link will be 250-300 meters?

According to the datasheet https://i.mt.lv/cdn/rb_files/SFP2-131002143606.pdf attenuators are not required as the maximum RX power accepted is at least 0dBm and the TX power will be between -3 and -9dBm.

If support say attenuators are required is the datasheet incorrect?

If support say attenuators are required is the datasheet incorrect?

You only have to use attenuators when you use transceivers for a distance of couple meters. S-3553LC20D range is 20 kilometers, for example, if you use them to interconnect two devices with range 10km, attenuators is not necessary.