Abstract:

 With the aid of  the definition of optical length in  gradient index (GRIN) medium, the eikonal equation was  deduced without the help of approximate theory, then the vector form of ray equation can be derived by eikonal equation, and finally the vector form of ray equation was simplified into its scalar form. The results of application example show  that the equation is especially applicable to determine the equation of ray track in terms of  known variation law of refractive index.

Key words: gradient index material, function of optical path, eikonal equation, equation of ray track, equation of ray