“…Besides the quality of the fibers, the low output signals of the analyzed fibers can be due to their low dye concentration, the short illuminated fiber-length ( z e = 5 cm), the absence of cladding in the fibers and the non-use of external devices. It is well-known that a thin cladding in a doped fiber causes a decrease in the transmission losses, and consequently, an increase in the overall efficiency [ 32 ]. Therefore, the output signal from the fibers could be easily improved by illuminating longer fiber-lengths, by employing higher dopant concentrations, by covering them with a thin cladding or by placing a mirror or a diffuser below them.…”