Summary form only given. The design rule for supercontinuum generation can be deduced in a rigorous way; however, the family of solutions is rather large owing to the high number of free parameters. We put constraints into our model, which ultimately leads to a design rule stating the peak wavelength of each active region as a function of its position in the cascade. In particular, we choose all intersubband active regions to be of the so-called "three-well vertical transition" type limit the number of active regions to 36, and set the total thickness of each active region and the preceding injector region to 50 nm.