Hi guys,

I have a Holmium doped multimode fibre with a double cladding structure. But my available pump is only modest so without core pumping we won’t get amplification. What is the best way to check if the pump beam is efficiently coupled into the core?

The pump beam was conjugated from the 6 um core diameter SMF, expanded to about 35 um which is lightly smaller than the fibre core (40 um) using a pair of lens.

I am trying to look at the image at the other end, hoping to see the ASE glowing when the pump beam is strongly coupled to the core, as well as a minumum in total pump transmitted power. But do you know some more elegant way of doing this?

Thank you,

L