
A more flexible design is to use the W-profile [65] as shown in Figure 15.16.
In this desi gn, a lower-index inner cladding or depressed cladding is added to the
step-index core. The design has four parameters to control: core refractive index
D
1
, core radius r
1
, depressed cladding refractive index D
2
, and the depressed
cladding radius r
2
. The addition of a depressed cladding offers more degrees of
freedom to the fiber design. With this design, different dispersion values can be
achieved. Especially, high positive dispersion is possible. Furthermore, the effec-
tive area can be kept small.
To show the effects of the depressed cladding on nonlinear