A weakly guiding fibre with a particular graded core index has cut-off V-values for its 2nd, 3rd and 4th modes of 2.5, 3.9 and 5.2, respectively. The core radius is 4 microns, the core index is 1.47 and the cladding index is 1.46.
Determine the range of source wavelength values in nm for which the fibre is:
(a) single-mode
(b) two-mode,
(c) three-mode
(d) more than 3-mode.