Hi prakash
I havn’t worked with multimode amplifiers.I am attaching a few links below.
See if they can be of any help to you.
http://www.orc.soton.ac.uk/publications/57xx/5742.pdf
http://www.creol.ucf.edu/Research/Publications/4917.pdf
http://www-ee.stanford.edu/~jmk/pubs/MM-EDFA.PhotSoc.7-12.pdf
Good Luck
Regards