Fig. 1. Basic properties of graphene materials. (a) Diagram of graphene structure^[20]; (b) three-dimensional energy band structure of graphene^[21]; (c) diagram of change in energy band structure induced by applying a perpendicular electric field in bilayer graphene. The dotted and solid curves indicate the band structure without and with strong perpendicular electric field, respectively^[

Fig. 2. Surface oxidation of graphite and structural model of GO. (a) Surface oxidation of graphite^[26]; (b) structural model of GO^[31]

Fig. 3. Basic components of optical fiber sensor^[37]

Fig. 4. Structure of graphene covered MNF^[39]

Fig. 5. Graphene-based current sensor with MNF coil resonator^[43]. (a) Diagram of graphene-based current sensor. The pale yellow thin sheets coated around both ends of the graphene sheet are Au electrodes. Inset shows micrograph of microfiber with diameter of ~4.5 μm; (b) photo of graphene-microfiber-integrated coil resonator

Fig. 6. Cross-sectional diagram of graphene/PCF hybrid waveguides. (a) Cross-sectional diagram of graphene/Ag-PCF SPR sensor^[50]; (b)cross-sectional diagram of Cu/graphene coated PCF sensor^[51]

Fig. 7. Diagram of MZI structure^[53]

Fig. 8. Two-dimensional cross section of graphene coated D-PCF hybrid waveguides. (a) Schematic diagram of PCF coated with silver and graphene^[56]; (b) two-dimensional cross section of D-type PCF-SPR sensing structure^[59]

Fig. 9. Electromagnetic field excitation process of SPR and LSPR. (a) Schematic of electromagnetic field of TM wave in metal-dielectric interface; (b) schematic of local surface plasmon excitation^[64]

Fig. 10. Schematic diagram of PCF sensor^[69]

Fig. 11. Structural schematic of graphene-coated microfiber Bragg grating^[73]

Fig. 12. Combination of graphene and fiber structure^[93-96]