Parameters
lam : wavelength
e : thickness of the Fabry Perot
n : refraction index of the Fabry Perot
k : number of the dark or bright fringe ( counted from the center )
fi : effective focal length of the lens
Rb : radius of the bright fringe number k in the focal plane
mb : order of the bright fringe number k
Rd : radius of the dark fringe number k in the focal plane
md : order of the dark fringe number k
