Fig. 1. Experimental system diagram for fabricating MT-LPFG, and micrograph of MT-LPFG based on periodically tapered SMF. (a) Experimental system diagram for fabricating MT-LPFG; (b) micrograph of MT-LPFG based on periodically tapered SMF

Fig. 2. Transmission spectrum of MT-LPFG with grating period of 400 μm

Fig. 3. Transmission spectra of two cascaded MT-LPFGs with periods of 397 μm and 400 μm and MT-LPFG with period of 400 μm

Fig. 4. Transmission spectra of MT-LPFGs with different periods

Fig. 5. Transmission spectra of 3 cascaded MT-LPFGs and MT-LPFG with period of 400 μm

Fig. 6. Experimental setup for measuring bending characteristics of three cascaded MT-LPFGs

Fig. 7. Linear relationship between wavelength shift and curvature when curvature of MT-LPFG2 is larger than 1.16 m^-1, and influence of curvature on transmission spectra of 3 cascaded MT-LPFGs. (a) Linear relationship between wavelength shift and curvature when curvature of MT-LPFG2 is larger than 1.16 m^-1; (b) influence of curvature on transmission spectra of 3 cascaded MT-LPFGs