Fig. 1. Principle diagram of MCM fiber SPR sensors based on Ti₃C₂-MXene

Fig. 2. Spectral evolution with variation of refractive index for MCM fiber SPR sensors with different gold film thicknesses. (a) 20 nm; (b) 30 nm; (c) 40 nm; (d) 50 nm; (e) 60 nm; (f) 70 nm; (g) refractive index sensitivity of MCM fiber SPR sensors with gold film thicknesses of 20‒70 nm; (h) spectra of MCM fiber SPR sensors with coreless fiber lengths of 6‒14 mm when gold film thickness is 50 nm and external refractive index is 1.3519

Fig. 3. Spectral evolution with variation of refractive index for MCM fiber SPR sensors with different Ti₃C₂-MXene thicknesses. (a) 2 nm; (b) 3 nm; (c) 4 nm; (d) 5 nm; (e) 6 nm; (f) refractive index sensitivity of MCM fiber SPR sensors with Ti₃C₂-MXene thicknesses of 2‒6 nm

Fig. 4. Fabrication of MCM fiber SPR sensors based on Ti₃C₂-MXene. (a) Fuse; (b) hydroxylate; (c) coating Ti₃C₂-MXene; (d) sputtering; (e) coating Ti₃C₂-MXene

Fig. 5. SEM images of sensor coated with gold film surface: (a) 500×; (b) 50000×. SEM images of sensor coated with gold film cross-section: (c) 50000×; (d) 50000×. SEM images of sensor coated with Ti₃C₂-MXene surface: (e) 500×; (f) 25000×

Fig. 6. Energy spectra of optical fiber after surface modification with Au and Ti₃C₂-MXene

Fig. 7. Experimental setup

Fig. 8. Performance comparison of sensor before and after coating with Ti₃C₂-MXene. (a) Spectral evolution with variation of refractive index for MCM fiber SPR sensors before coating with Ti₃C₂-MXene; (b) spectral evolution for MCM fiber SPR sensors with one to four layers of Ti₃C₂-MXene at an external refractive index of 1.3330; (c) spectral evolution with variation of refractive index for MCM fiber SPR sensors after coating with Ti₃C₂-MXene; (d) comparison of RI sensitivity before and after coating with Ti₃C₂-MXene