Fig. 1. Schematic diagram of the (N-1)-cavity structure formed by N-FBG

Fig. 2. Transmission spectra (solid lines) and corresponding stop bands (dashed lines) of a two-cavity structure composed of three FBGs. (a) Three FBGs with the same period; (b) three FBGs with different periods

Fig. 3. Transmission spectra (solid lines) and corresponding stop bands (dashed lines) of a two-cavity structure composed of three FBGs when the cavity lengths are elongated. (a) Three FBGs with the same period; (b) three FBGs with different periods

Fig. 4. Wavelength spacing versus Bragg wavelengths of the three FBGs (solid line), and stop bands of the three FBGs (dashed lines)

Fig. 5. Transmission spectra (solid lines) and corresponding stop bands (dashed lines) of a two-cavity structure composed of three FBGs when the refractive index modulation Δn is increased

Fig. 6. Triple-transmission with unequal spacings (solid lines) and corresponding stop bands (dashed lines) of a three-cavity structure composed of four asymmetric FBGs

Fig. 7. Influence of the accuracy of the cavity length on the transmission at wavelength of λ₁=1549.85 nm. (a) In the case when cavity is relatively short; (b) in the case when cavity is relatively long

Fig. 8. Influence of the three stop bands on the transmission at wavelength of λ₁=1549.85 nm. (a) In the case when cavity is relatively short; (b) in the case when cavity is relatively long