Fig. 1. Mechanically induced microbend LPG. (a) Mechanism of manufacture; (b)principle of adjusting grating period

Fig. 2. Effective refractive indices of four vector modes of the step-index fiber and phase matching curves

Fig. 3. Transmission spectra of vector modes. (a) Transmission spectra; (b) theoretical value of resonant wavelength

Fig. 4. Transmission spectra of high-order vector modes with different microbend amplitudes. (a) TM₀₁; (b) HE21p; (c)TE₀₁; (d) H

Fig. 5. Properties the inverse-parabolic index fiber. (a) Refractive index profile; (b) effective indices of four vector modes and phase matching curves

Fig. 6. Transmission spectra of vector modes in the mechanically induced microbend LPG based on the inverse-parabolic index fiber. (a) Transmission spectra; (b) theoretical value of resonant wavelength

Fig. 7. Transmission spectra of high-order modes and coupling coefficients as functions of microbend amplitude. (a) Transmission spectra of high-order modes; (b) coupling coefficients

Fig. 8. Transmission spectra of TE₀₁ mode and resonant wavelength versus angle θ. (a) Transmission spectra of TE₀₁ mode; (b) resonant wavelength