Hollow fiber taper with a silver micro-sphere used as refractive index sensor

We have experimentally studied the plasmon resonance phenomenon of a silver micro-sphere with a diameter of 2.3 μm in taper-shaped air cavity of a hollow fiber taper. To take insight into the plasmon resonance phenomenon, we move the micro-sphere along the fiber and observe the significant shift of the resonance peak. To explore this configuration as a sensor, we analyze the reflected optical spectrum changes as a function of the external refractive index by finite difference time domain method. The results show that this device can be used for a bio-chemical sensor to monitor the refractive index around it from 1.6 to 2.0. The further study supports that the variation was much more significantly for using the S polarized light as the incident source than P polarized light.