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pmurdock
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CWDM (one side), SFP wavelength specific on other end

Fri Aug 30, 2019 5:17 pm

It seems like it would be possible to just use one CWDM mux (dual fiber) in the server room, and then if you daisy chain that fiber to multiple locations just pull off the specific wavelength using Mikrotik's wavelength specific SFP's..

Would that be a correct assessment? I see most diagrams needing to utilize 2 MUX/DMUX at either end, but if the SFP is already tuned to a specific wavelength why the need to DMUX it?
 
mkx
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Re: CWDM (one side), SFP wavelength specific on other end

Fri Aug 30, 2019 11:47 pm

My limited testing with a few types of SFP (and SFP+) modules (some branded Ericsson and some OEM) with wavelengths between 1290 and 1610nm, both CWDM and "usual" 1310nm ones, showed that receiving photo-diode is always wide-band. E.g. link successfully established between "usual" 1310nm SFP and 1570 nm CWDM SFP ... if connected with simple fibre cable without MUXes. Or link between CWDM SFPs for different wavelength.

Which essentally means one must use CWDM de-mux (on RX side).

Use of CWDM mux (on TX side) is highly recomended ... some measurements we did on CWDM SFPs in hars conditions (operating temperatures on the edge of declared temperature range) showed that some SFPs changed actual wavelength on TX enough that it was out of standard. If CWDM mux is used, then this means loss of single CWDM link, without using CWDM mux such malfunctioning SFP would interfere the adjacent CWDM channel as well.
In addition to that, quality CWDM muxes have almost neglectable loss[*] (around 0.2dB regardless the wavelength) while fussing with daisy-chains will most likely cause much higher loss.
[*] surely there will be double connector loss as compared to direct connection of fibre to SFP module
BR,
Metod
 
pmurdock
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Re: CWDM (one side), SFP wavelength specific on other end

Sat Aug 31, 2019 6:01 am

Excellent description. Understood, and it makes sense.
 
pmurdock
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Re: CWDM (one side), SFP wavelength specific on other end  [SOLVED]

Sun Sep 01, 2019 10:03 pm

For further light and knowledge concerning how to do the type of application where you are adding/dropping wavelengths at specific customers sites, you should use F-OADM and ROADM units.

"O"pitcal "A"dd "D"rop "M"ultiplexer..

So while the Mikrotik CWDM can multiplex, it's not the prescribed way to drop off / add wavelengths to a single fiber at customer drop locations.

cheers,
Paul

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