Parameters
Ir : source intensity
x : position of the source along the X axis from the optical axis of the light guide
y : position of the source along the Y axis from the optical axis of the light guide
e : distance from the source to the light guide entrance facet along the light guide axis
Dl : light guide diameter
n : light guide refraction index
L : light guide length
Tl : transmission of the light guide per length unit
Pc : power capted by the light guide
Ptr : power transmitted by the light guide
