INJECTION EFFICIENCY FROM A SIDE-EXCITED THIN-FILM FLUORESCENT CLADDING OF A CIRCULAR WAVE-GUIDE

Experiments were conducted to verify a theoretical model on the injection efficiency of sources in the cladding of an optical fiber. The theoretical results predicted an increase in the injection efficiency for higher differences in refractive indices between the core and cladding. The experimental apparatus used consisted of a glass rod 50 cm long, coated at one end with a thin film of a fluorescent substance. The fluorescent substance was excited with side illumination, perpendicular to the rod axis, using a 476-nm argon-ion laser. Part of the excited fluorescence was injected into the core and guided to a detector. The signal was measured for several different cladding refractive indices. The cladding consisted of sugar dissolved in water, and the refractive index was changed by varying the sugar concentration in the solution. The results indicate that the power injected into the rod, due to evanescent wave injection, increases with the difference in refractive index, which is in qualitative agreement with theory.