Fig. 1. Electromagnetic field excitation processes of SPR and LSPR. (a) Schematic of electromagnetic field excitation of TM wave in metal-dielectric contact interface; (b) schematic of local surface plasmon excitation

Fig. 2. Structural diagrams of four types of D-type PCFs and preparation principle of D-type PCF. (a) Schematic of dual channel D-type PCF sensor[16]; (b) profile of double-parameter D-type PCF sensing structure [17]; (c) three-dimensional model of gold film coated D-type PCF SPR sensor [18]; (d) structural diagram of graphene layer coated D-type SPR-PCF sensor [19]; (e) SEM image of PCF before polishing; (f) cross-section of gold nanofilm coated D-type PCF; (g) side-polished surface of gold coat D-shap

Fig. 3. Slotted PCF-SPR sensor. (a) Cross-section of microstructured photonic bandgap SPR biosensor; (b) cross-section of microfluidic slotted PCF-SPR biosensor [25]

Fig. 4. Closed-type LC-PCF. (a) Cross-sectional diagram of LC-PCF sensor; (b) FEM meshing and boundary condition setting [29]

Fig. 5. PCF covered with liquid-filled metal layer. (a) Cross-sectional diagram of liquid-filled PCF sensor covered with gold layer; (b) cross-sectional diagram of liquid-filled PCF sensor covered with silver layer[31]

Fig. 6. Design of capillary-based SPR sensor. (a) Schematic of capillary-based multilayer-coated SPR sensor; (b) structure of capillary sensing region; (c) cross-section of sensing region[33]

Fig. 7. Structural diagram of DCHF-SPR sensor. (a) Structure A with left and right channel structures being same; (b) structure B with left and right channel structures not being same (left channel metal surface coated with high refractive index dielectric layer)[34]

Fig. 8. Advantages and disadvantages of main types of PCF-SPR sensors

Table 1. Structural parameters of different SPR-PCF refractive index sensors