What Drives Multimode to Single-mode Conversion Demand or vice versa?
So what's the cause of mix-using multimode and single-mode fiber? As we see, the optics applied in point-to-point interconnection are symmetrical. For instance, end A with a 10G SFP+ port houses a 10GBASE-SR SFP+ module. To realize the short-range direct connection to the end B switch with the same port, the same 10GBASE-SR SFP+ module should be plugged into the end B switch port. Then use a multimode fiber to connect the two ends. This is the most ideal and simple application scenario.
What if end B is located in another building, dozens of kilometers far away from end A? Or end B equipment is single-mode or must use a single-mode fiber connection? In the former case, you need to use single-mode fiber because the multimode fiber cannot reach that far. The problem is how to realize SMF connects to the end equipment multimode modules. For the latter, the problem is how to achieve the connection between one end multimode and the other end single mode.
In different cabling environments, optical fiber communication may require multimode to single-mode conversion or single-mode to multimode conversion. But the most typical application is the conversion from multimode to single-mode to boost the network transmission distance.
Top 3 Solutions to Converter Multimode to Single-Mode Fiber or vice versa
Next, I will introduce three fiber mode conversion methods, what they have in common is relying on single-to-multimode conversion products.
Solution 1: Using Fiber to Fiber Media Converters for Multimode to Single-Mode Conversion
Fiber to Fiber media converter provides multiple conversion functions, ie. multimode to single-mode conversion, duplex to simplex conversion, and standard to WDM wavelength conversion. To understand how fiber media converter transfer multimode to single-mode, take the multimode to single-mode fiber converter by QSFPTEK as an example. The product has two SFP/SFP+ slots, which can accommodate two SFP/SFP+ modules. To converter MMF to SMF, plug one of the slots with a 10GBASE-SR SFP+ transceiver for multimode fiber connection and the other slot with a 10GBASE-LR SFP+ transceiver for single-mode fiber link. Thus a local MMF link within 400m can boost up to at least 10km and up to 140km by matching difference optics.
In the application scenario below, two Ethernet switches located in two buildings are needed to be connected. Both the switches are equipped with multimode fiber modules, but the distance between the buildings is about 6km. We deploy a pair of 10G fiber-to-fiber media converters and two 10G-SR SFP+s to connect the Ethernet switches over OM3 MMFs. Then link the other media converter port at both ends with 10G-LR SFPs over an OS2 SMF.
Fig : Converter Multimode to single-mode with multimode to single-mode media converter
Solution 2: Using WDM Transponder for Multimode to Single-Mode Conversion
WDM transponder is also known as optical to electrical to optical (OEO). The WDM systems see wide adoption of WDM transponder (OEO) for converting legacy wavelength to CWDM or DWDM wavelength. Besides, OEO also functions for MMF-to-SMF conversion, which is achieved by converting the 850nm MMF to 1310nm SMF.
In the example below, the two ports of this WDM transponder have a single-mode SFP and a multi-mode SFP respectively. As in the previous solution, use an OM3 MMF to connect the multi-mode port of the OEO and the multi-mode port of the switch. Then link the WDM transponder SMF SFP ports via a single-mode OS2 fiber to extend reach between buildings.
Fig : Converter Multimode to single-mode with WDM transponder
Solution 3: Using Mode Conditioning Patch Cables For Single-Mode to Multimode Conversion
In structure, a mode conditioning patch (MCP) cable is a duplex fiber patch cable consisting of two strands of fibers. One end of one of the fibers terminates a single-mode connector and a short piece of SMF. The other three terminals are multimode connectors and MMFs. The only SMF leg in yellow of the MCP cable is for connecting the 1000BASE-LX and other capable modules in transmitting equipment. The requirement for MCP strictly limits the module types. For gigabit Ethernet, the requirement for MCP is specified only for 1000BASE-LX/LH 1G SFPs in the 1310 nm wavelength window. For 10 gigabit Ethernet, it is stipulated only for 10GBASE-LX4 and 10GBASE-LRM optics in the 1310 nm wavelength window. The MMF leg in orange is to link the receiving side. One thing to note is MCP fiber can only transfer single-mode to multimode, not vice versa.
Fig : Converter single-mode to Multimode with mode-conditioning patch cable