Dear Emrah,
I assume that the M12 fiber is an EDF. You can upload the emission and absorption spectra using the “Cross-sections” tab in the component properties popup window. You need to make sure that the structure/units of the file is correct. Please refer to the datasheet of the component that can be accessed using the “Help” button in the component window to check the structure and the unit of each parameter.
Regards,
Ahmad