Since mode conversion in the optical network is universal, here are three methods that can realize multimode to single-mode fiber conversion.
Fiber to Fiber Media Converter for MMF-to-SMF Fiber Conversion
As we know, fiber optic media converter supports multimode to single-mode fiber conversion, dual fiber to single fiber conversion and wavelength conversion. Here we mainly talk about the conversion between multimode to single-mode fibers. A fiber-to-fiber media converter can extend a MM network across SM fiber with distances up to 140km in a cost-effective way. For example, a 550m/20km 850nm/1310nm SFP Gigabit Ethernet MMF-to-SMF fiber media converter can support mode conversion from multimode fiber (up to 550 m) to single-mode fiber (up to 20 km) for Gigabit Ethernet (1000 Mbps).
In the application of extending fiber network distances, two Ethernet switches equipped with multimode fiber ports are connected utilizing a pair of MMF-to-SMF converters which convert the multimode fiber to single-mode fiber and enable network connectivity across the distance between the switches, as shown in the picture below.
WDM Transponder for MMF-to-SMF Fiber Conversion
Similar to fiber-to-fiber media converter, WDM transponder also has the capability to convert multimode to single-mode fiber. As its name shows, transponder is often used in WDM systems, especially in DWDM systems. Because in long runs of DWDM transmission, MMF to SMF or SMF to MMF conversions are usually needed.
Mode Conditioning Fiber Cable for MMF-to-SMF Fiber Conversion
Compared with the two methods mentioned above, mode conditioning fiber cable is different in the conversion between multimode and single-mode fiber. Not able to convert signals into electrical ones as WDM transponder, mode conditioning patch cable launches the laser at a precise offset from the center of the multimode fiber. This causes the laser to spread across the diameter of the fiber core, reducing the effect known as differential mode delay (DMD) which occurs when the laser couples onto only a small number of available modes in multimode fiber. In addition, mode conditioning fiber cable is limited to be used in applications that using Gigabit 1000BASE-LX (or 10-Gigabit Ethernet 10GBASE-LRM and 10GBASE-LX4) equipment.