Fig. 1. Single mode-hollow-single mode fiber^[15]. (a) Single mode-hollow-single mode fiber misalignment fusion structure; (b) physical production of sensing structure

Fig. 2. Coreless-D type-coreless optical fiber sensing structure, inset is cross section image of the DSF^[16]

Fig. 3. Simulated results of wide-angle beam propagation method^[19]. (a) Relationship between the energy of the evanescent wave and the diameter of the thin core; (b) relationship between the spectral wavelength and the refractive index of the cone diameter of 25 μm and 65 μm, the inset shows the response of the transmission spectra with the refractive index

Fig. 4. Relationship between transmission spectrum parameters and related parameters^[21]. (a) Relationship between transmission spectrum parameters and magnetic field strength; (b) relationship between transmission spectrum parameters and temperature

Fig. 5. Relationship between transmission spectrum parameters and related parameters^[23]. (a) Relationship between transmission spectrum parameters and magnetic field strength; (b) relationship between transmission spectrum parameters and temperature

Fig. 6. FBG cascaded macro-bend fiber. (a) FBG cascaded macro-bend fiber structure; (b) photo of FBG cascaded macro-bend fiber structure

Fig. 7. Thin cone and peanut-shaped thick cone cascaded FBG^[27]. (a) Thin cone and peanut-shaped thick cone cascade FBG structure; (b) sensing structure diagram under electron microscope

Fig. 8. Sensing structure and system of E-FLM^[28].(a) Mode interference structure with NCF and ECSF; (b) E-FLM

Fig. 9. Sensing structure and numerical simulation of MF filled PCF^[30].(a) Temperature and magnetic field sensing structure based on MF penetrating PCF; (b) when the optical frequency matches the resonance frequency, the electric field distribution of the microcavity

Fig. 10. PCF cross-sections in different literatures. (a) Schematic of the cross-section of the PCF^[33]; (b) schematic of the cross-section of the PCF^[34]

Fig. 11. System block diagram of composite interference structure^[36]