Fig. 1. Schematic diagram of Ex-TFG structure

Fig. 2. Mode coupling simulation results of Ex-TFG. (a) Coupling coefficients of different cladding modes with l=1,2,3 in Ex-TFG^[26]; (b) field distribution in Ex-TFG cladding mode

Fig. 3. Cladding mode effective indexes of TE and TM modes^[21]

Fig. 4. Resonance wavelengths versus axial periods of Ex-TFG with TE (solid line) and TM (dash line) modes for different orders^[23]. (a) m is in the range of 1‒9; (b) m is in the range of 10‒20; (c) m is in the range of 21‒30; (d) m is in the range of 29‒45

Fig. 5. Waveguide dispersion factors γ under different cladding mode orders and different cladding radius of Ex-TFG at 1550 nm^[22]

Fig. 6. Schematic diagrams of Ex-TFG inscription^[23]. (a) Front view; (b) top view of amplitude mask and fiber with 0 order diffraction inside fiber core

Fig. 7. Transmission spectra of Ex-TFG with 81° tilt angle^[23]. (a) A series of dual-peak resonances in 1300‒1700 nm; (b) one pair of dual-peaks measured by linear polarization light with different azimuth angles

Fig. 8. Spectra measurement of integrated TFG. (a) Experimental setup for Ex-TFG transmission spectra measurement with different linear polarizations^[23]; (b) transmission spectra of 81°-TFG measured by coupling a linear polarization light with different azimuth angles with respect to fast axis of grating^[23]; (c) microscopy images of hybrid 45°-TFG and 81°-TFG^[35]; (d) transmission spectra of hybrid 45°-TFG and 81°-TFG^[35]

Fig. 9. Refractive index sensing experiment of Ex-TFG. (a) Refractive index sensitivies for TE and TM modes with different cladding radii^[22]; (b) refractive index sensitivies for TM modes with different cladding mode orders^[24]

Fig. 10. Vector sensing experiment of Ex-TFG^[26]. (a) Near field light field distribution of Ex-TFG; (b) schematic diagram of Ex-TFG by sidely immersing; (c) transmission spectral responses for TM mode of Ex-TFG by sidely immersing and totally immersing; (d) wavelength shifts for TM cladding mode along different immersion angles

Fig. 11. Temperature sensitivities of Ex-TFG with different cladding mode orders^[24]

Table 1. Effective refractive indexes and refractive index sensitivities for TM modes of Ex-TFG with different tilt angles

Table 2. Effective refractive indexes and temperature sensitivities for TM modes of Ex-TFG with different tilt angles