Can we connect multimode SFP with Single mode fiber?
Short answer is – No!
Extended answer is – You could try and, in some occasions, it may even work in very short distances, but we definitely not recommend it. Thing is – 1000Base-SX multimode transceiver uses LED as a light source. It’s possible because Multi-mode optical cables has very wide fiber core – 62.5µm (OM1) or 50 µm (OM2/OM3/OM4/OM5) – so this 1000Base-SX SFP’s transmitting interface is conditioned to connect LED source to this very wide fiber core. In contract – single mode optical cable core is narrow – 9 µm. When we connect multimode SFP with Single mode fiber only fraction of low-intensity LED emitted optical signal will get in much narrower fiber core, but sure – some part, what will escape intense attenuation of reflected signal, definitely will get there, but will fade after meter or less.
So technically speaking – it is possible to connect multimode SFP with Single mode fiber – but connection will be unreliable, unpredictable and very short. We don’t need such links in our networks, right?
Sure – some vendors are offering mode conditioning cables, thus allowing interconnect multi-mode transceivers with single mode cable infrastructure, but this solution should be treated as an instrument of last resort.
We don’t recommend to mix things – it’s always better to use single mode with single mode and multi-mode with multi-mode. And let’s remember a history – why there is multi-mode in first place? Because years ago, production cost of LED transceivers was much lower compared with Lasers used in 1000base-LX SFP. Also, production cost of multi-mode cables required much lower precision and cost. Nowadays cost of 1000Base-SX SFP multimode short-range transceivers are almost equal to 1000base-LX SFP – so decision what to use is mainly related to existing infrastructure.
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