Fig. 1. Images of a position in the grating region captured by microscopy. (a) Cross-section; (b) side view

Fig. 2. Experimental transmission spectrum of the LPFG, where the inset is mode field distribution of LP₃₁ mode

Fig. 3. Ideal model diagrams of the strongly modulated LPFG regions. (a) Side view of the grating region; (b) cross-section structures of a grating region; (c) refractive index modulation in the core region

Fig. 4. Comparison of unmodulated and modulated mode fields. (a) LP₀₁ mode; (b) LP₃₁ mode

Fig. 5. Comparison of experimental and simulated transmission spectra

Fig. 6. Variation of transmission spectra for different grating periods

Fig. 7. Variation of grating period with resonance wavelength

Fig. 8. Transmission spectra for different numbers of grating periods

Fig. 9. Transmission spectra under different modulation depths