Thanks for your reply. I have figured out the effective index of the higher order mode, say 100 then I have tried to keep that index range to get this mode but I dont see any of the modes nearby 100 rather it stops at mode number 38 at index value 1.27. It clearly says that for mode 100 we should go along the index value near 1 but still I could not find the desiredd order mode. Please help in this regard.