Tip optical fiber refractive index sensor based on a thin copper film

We report a refractive index tip fiber optic sensor based on a modal interferometer coated with a thin copper film. This device can be used for solute concentration in aqueous mixture measurement. The copper film increases the device reflectivity and, as a result, increases the multimodal interference pattern visibility. To validate the sensor device, different water-glycerol weight concentrations were used in the range from 0 to 45 Glycerol %. The recorded spectral responses show a redshifting, and a sensitivity of 19 pm / (Glycerol % by weight) from 0 to 18 % and 4.7 pm / (Glycerol % by weight) from 18 to 45 % was achieved. Besides, using a phase analysis we calculated a sensitivity of -15 rad/RIU.