Multimode to Single-Mode Fiber Conversion

Fiber optics are mainly used for data transmission due to its efficiency and high transmission capacity. And fiber optic cables provide an effective transmission as they are less affected by internal and external interference. The transmission can be done by multimode fiber or single-mode fiber depending on the communication requirements.

Fiber mode conversion, especially multimode to single-mode fiber conversion (MMF-to-SMF conversion) is required when the distance is an important parameter to consider in optical applications. In this tutorial, three methods will be introduced to support mode conversion from multimode to single-mode fibers.

When Is Multimode to Single-Mode Conversion Required?

If you must know one thing about fiber optic cable, it’s the difference between single-mode and multimode fibers. Because of different fiber diameter of their cores, they have different applications. Single-mode fiber cable is preferred to use in long distance, high bandwidth runs, and multimode fiber cable is often used for short distance applications. However, a fiber optic network is not as simple as using only one type of fiber. Thus, we usually need mode conversion, especially MMF-to-SMF conversion during the transmission. Mode conversion between multimode and single-mode fibers is typically required when network distance exceeds the limit of multimode fiber. In addition, MMF-to-SMF conversion is also required depending on the equipment and connectivity type in the network. For instance, lower cost legacy equipment uses multimode port, and connectivity is required for single-mode equipment; or a building has multimode equipment, while the connection to the service provider is single-mode, etc.

How to Realize Multimode to Single-Mode Fiber Conversion?

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.

Source: community.fs

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