Exercise 1

We could say that the effective index of the core mode is approximately equal to the refraction index of the core, so that   and that the effective index of the jacket mode is almost equal to the index of the jacket, that is to say . With the first equation, we can calculate that:

In order to increase the sensitiveness of the sensor, we can insert a piece of multimode fiber where the micro curves are. The structure is then made up of a section of a multimode fiber, another section of monomode fiber and eventually another section of multimode fiber. The multimode fiber will make it possible to increase the coupling between the fundamental mode and the higher order modes. Nothing but the fundamental mode will be transmitted during the reinjection in the monomode fiber, consequently total leakages of the sensor will increased.