Generalized expression for the growth of long period gratings

Experimental results have shown that the peak loss wavelength of long period gratings can shift in the direction of either shorter or longer wavelengths as the induced index change of the grating increases. An expression, which the authors believe to be novel, is derived and verified experimentally, to explain this phenomena. It is shown that the waveguide dispersion characteristics of the core and clad effective indices play a key role in the evolution of the transmission characteristics of the grating.