High sensitive fiber-optic liquid refractive index tip sensor based on a simple inline hollow glass micro-sphere

A high sensitive fiber-optic refractive index tip sensor based on a simple inline hollow glass micro-sphere is presented. The inline hollow glass micro-sphere can be automatically constructed at the splicing joint break time when splicing a hollow core photonic crystal fiber to an SMF. Simultaneously, the micro-sphere is tipped on the SMF end. It is temperature insensitive in the air due to its micro size and hollow cavity sphere structure. The ambient refractive index can be measured by detecting the extinction ratio variation of the sensor, with a high sensitivity.