Thanks Abdallah and Damian Marek
Actually i want to calculate confinement loss and dispersion, for this i need img{neff} and Re{neff} parameters.
From Abdullah’s answer i assume Modal index is neff
But from Damian merek i assume modal index is showing propagation constant which is as:
propagation constant=alpha+iBeta
please you people can remove this confussion?
Thanks.