How to Convert Single Mode Fiber to Multimode Fiber (and vice versa)

In a perfect world, a building's fiber optic infrastructure will be installed with the same type of fiber, connectors and cable management accessories, ensuring everything is completely compatible. 

In the real world, this rarely happens -- often the demarcation point and possibly some major trunk runs are wired with fiber and additional drops are expanded over time as necessary. Demarcation wiring, telecom and ISP wiring, and longer cable drops are almost always single mode fiber; however, shorter cable runs and network patches are often multimode fiber. 

The issue is single mode (OS1 and OS2) fiber cannot be passively spliced or coupled to multimode (OM1, OM2, OM3 and OM4) fiber. This is why you rarely see yellow cables (single mode) in the same equipment rack or wall-box as aqua or orange cables (multimode). 

The issue is the fiber's diametral core size, or the size of the optical glass core. In single mode cables, this core size is typically 9 microns. In multimode cables, this core size is either 62.5 microns (OM1) or 50 microns (OM2, OM3 and OM4). Optical signals won't propagate properly when a smaller diameter core (9 microns) is butted up against a larger diameter core (50 or 62.5 microns); hence the issue when using a passive coupler or splice. 

Does that mean installations can't use both single mode and multimode fiber? No, though normally the two cable types must remain segregated. 

Coupling Different Fiber Types with a Media Converter

The TechLogix TL-MC-1S1S allows you to couple single mode and multimode fiber  optic cables in the same cabling run and/or installation using swappable SFP modules. 

The TL-MC-1S1S employs active circuitry to decode optical signals from one cable type and encode them for a different cable type. In practice, this means the TL-MC-1S1S will receive signals from single mode fiber and re-transmit them onto multimode fiber or vice versa. 

For proper operation, the TL-MC-1S1S requires SFP modules that are compatible with the formats of fiber being connected. Typically, this is a 1G multimode module (such as the TechLogix TL-1GSFP-MM550) for OM2, OM3 and OM4 fiber and a 1G single mode module (such as the TechLogix TL-1GSFP-SM20K) for OS1 and OS2 fiber. Single mode and multimode SFP modules are sold separately. 

The TL-MC-1S1S is IEEE 802.3z and 802.3ab compliant, is plug-and-play compliant, and includes a 5V power supply. 

Additional information is available online at www.tlnetworx.com.