Material dispersion :

• Material dispersion arises from the variation of the refractive index of the core material as a function of wavelength. 
• Material dispersion is also referred to as chromatic dispersion. 
• This causes a wavelength dependence of group velocity of given mode. 
• So, it occurs because the index of refraction varies as a function of optical wavelength. 
• Material dispersion is an intra-modal dispersion effect and is for particular importance for single ode wave-guide.