So the physical understanding of the problem suggests that a solution which has an oscillatory behavior inside the core and decaying behavior inside the cladding is the appropriate choice. Any other solution is not acceptable because it is not consistent with the physical understanding of the modal propagation.
10.
Let us now look at the plot of the Bessel functions for various possibilities of (argument). There are three different types
of Bessel functions depending upon the nature of .
(a)
If is real then the solutions are
Bessel functions
Neumann functions
The quantity is called the order of the function and is called the argument of the function. Plots of the two functions as a function of their arguments are shown in the Figure 4-5.
(argument). There are three different types
. 
is real then the solutions are 
Bessel functions 
Neumann functions 
is called the order of the function and 
is called the argument of the function. Plots of the two functions as a function of their arguments are shown in the Figure 4-5. 
