A standard microdisk and three kinds of variable microdisks resonant cavity with whispering gallery mode (WGM) are presented. By controlling the distance between waveguiding and micro-disk resonant cavity

as well as changing the geometry which can influence the coupling coefficient of the waveguiding and resonant cavity

  the coupling coefficients

resonant frequences

the distribution of modes

and Q-factors from mentioned four structures are calculated based on FDTD method. The degree of mode matching and the bending loss from input waveguide have influence on the Q-factors. There is opposite trend between the Q-factors of the four structures and the coupling coefficient. In order to obtain more efficient coupling efficiency

it is necessary to find a medium between the higher Q-factors and the larger coupling coefficient. Finally

an optimal microdick with curve input waveguide are obtained.