Refractive Index Sensing Based on a Side-Polished Macrobend Plastic Optical Fiber Combining Surface Plasmon Resonance and Macrobending Loss

In this paper, we introduce a refractive index (RI) sensor based on the surface plasmon resonance (SPR) effect. A commercial plastic optical fiber (POF) is fabricated with a D-shaped macrobend structure by heat setting and side polishing techniques to expose the core and enhance the RI sensitivity. Gold is sputtered onto the polished surface of the POF, generating a film with a thickness of approximately 10 nm. When the RI of the environment changes, the propagation attenuation in the macrobend section and the SPR spectrum change simultaneously. Therefore, the RI can be determined by the dual mechanism of bending loss and spectral shift. The experimental results show that as the RI of the immersion liquid varies from 1.33 to 1.40, the sensing probe exhibits a bending loss change and a spectral shift. This result indicates that the sensitivities of the probe in regard to bending loss and SPR are 43 dB/RIU and 1570 nm/RIU, respectively.