Brief Introduction
Traditional fibre optic loopbacks can be regarded to be the two connectors on the same piece of simplex fibre optic patch cable put together, thus it forms a loop. Fibre optic loop backs are used in fibre optic test applications. The two most commonly used fibre optic loopbacks are SC type and LC type, while there are also ST, FC, and MTRJ, FDDI etc types. 
Just like fibre optic patch cable assemblies, fibre optic loopbacks are classified by single mode type and multimode type. Typically single mode SC type and LC type fibre optic loopbacks are blue color, typical multimode LC and SC type fibre loop backs are beige color, this also goes with the practice of fibre optic patch cables. Loopback fibre core can be 9/125 single mode or 50/125 multimode, or 62.5/125 multimode. 

Molded Fibre Optic Loopback
Besides the traditional fibre optic loopback, we also have the molded fibre optic loopbacks, which are with custom designed strain relief boot.By incorporating a rigid connector shell for fiber protection with an easy to use, ergonomic package, the molded fibre loopback is designed for durability and performance. The molded fibre optic loopbacks are available by SC and LC types, which are easy to use for fibre optic test purpose in the lab experiments or manufacturing environment.