LIEKKITM Er30-4/125 fibers are highly doped erbium fibers designed for C- and L-band amplifiers, and ASE sources. These fibers are available as low cut-off fibers (Er30-4/125) and high cut-off fibers (Er30-4/125HC). 
 

The high cut-off version has demonstrated the highest power conversion efficiency available in L-band: better than 50% for a typical fiber length of 20 m.