Third order material dispersion analysis in some types of glass optical fibres

An estimation of material dispersion is presented in some types of glass optical fibres. Using broadly applicable principles for group velocity, a simple expression is derived for material dispersion that includes the third derivative of the index of refraction with respect to the wavelength, d(3)n/d(3)lambda. It is shown that material dispersion persists around the so-called zero material dispersion wavelength when d(2)n/d(2)lambda = 0, meaning that a pulse of light centred on this zero material dispersion wavelength also suffers significant dispersion, necessitating that the third order term d(3)n/d(3)lambda be taken into account.