Fig. 1. Schematic diagram of SP-area. (a) Structural equivalence. (b) Optical transmission.

Fig. 2. The relationship between the energy of reflected and refracted light and the relative RI when the incident angle is θ.

Fig. 3. The variation of reflected light intensity with incident angle; the dotted line indicates n₀₁ = 0.9, and the solid line indicates n₀₁ = 1.1.

Fig. 4. Schematic diagram of the experimental setup.

Fig. 5. (a) Cross section of the POF. (b) Connection between POF and SMF using ceramic ferrule and ceramic mating sleeve.

Fig. 6. Schematic of experimental setup for polishing fibers.

Fig. 7. Transmission spectra of the RI sensor with different POF length.

Fig. 8. Transmission spectra of different SP-depths. (a) D=0 μm. (b) D=10 μm. (c) D=20 μm. (d) D=30 μm.

Fig. 9. Macro-bending diagram. (a) SDB. (b) ODB.

Fig. 10. Transmission spectra of different macro bending.

Fig. 11. Schematic diagram of stress change. (a) SDB. (b) ODB. The dotted line is evenly stressed and the solid line is not evenly stressed.

Fig. 12. Intensity response of RI sensor.

Fig. 13. Transmission response of the perfluorinated POF-based RI sensor at different temperature. (a) Output power response. (b) Wavelength response.