As already mentioned, the presence of a groove in the
core of an optical fiber disturbs the propagation of the optical
signal, resulting in an optical signal leakage to the exterior
of the fiber, thereby interacting with the surrounding
environment. Considering that the refractive index (RI) of
the surrounding medium is equal to the POF core RI, the
fiber and the surrounding environment can be considered
as continuous medium. Therefore the optical signal leakage
is minimum and the transmitted optical power is maximum.
If the surrounding medium have an RI that differ the
POF one, then the optical power leakage increase and the
transmitted signal power decreases. Considering that the
liquid refractive index does not change during the measurements
and have an intermediate value (1.33)
between the air RI (1.00) and the POF core RI (1.46),
then, each time a groove is fulfilled, the transmitted optical
power increase due to the reduction of the optical power
leakage. The amount of radiation lost to the outside
depends on the fiber’s external environment, the dimensions
of the grooves and its depth.