Surface Plasmon Resonance Refractive Index Sensor Based on Tapered Coreless Optical Fiber Structure

In this paper, we announce the surface plasmon resonance (SPR) refractive index (RI) sensor based on tapered coreless fiber (TCF) structure. We take full advantage of the transmission characteristics of the coreless fiber, and the experimental results evidence that TCF is able to excite surface plasmon wave effectively. Compared with common SPR sensors, this sensor is easier to fabricate, has better mechanical stability, and offers a comparable sensitivity. The wavelength interrogation sensitivity of the proposed sensor is 2278.4 nm/RIU in the RI range of 1.33-1.391. As the structure of the proposed sensor can lead to multimode interference (MMI), and the gold film is only coated on one side of TCF, MMI spectra appear in the visible light band instead of in the near-infrared. When surrounding RI increases, the resonance wavelength shifts to shorter wavelengths. We get an ultrahigh wavelength interrogation sensitivity, 866.1 nm/RIU, compared with common MMI RI sensors, in the RI range of 1.3864-1.416. Because both SPR and MMI are sensitive to the change of surrounding RI, this sensor can achieve a wide detection range when we use these two phenomena together.