Fig. 1. Transmittivity curves under different numbers of cavities at 0° incident angle

Fig. 2. Flow chart of membrane system optimization algorithm

Fig. 3. Structural parameters and optical parameters of qualified membrane systems at C-band

Fig. 4. Transmittivity-wavelength curves of membrane system II at different incident angles. (a) 0° ; (b) 15°

Fig. 5. Transmittivity-wavelength curves of membrane system III at different incident angles. (a) 0°; (b) 15°

Fig. 6. Relationship between deviation of optical parameter and incident angle for membrane systems Ⅱ and Ⅲ

Fig. 7. Maximum tunable angle versus equivalent refractive index

Fig. 8. Relative value of each optical parameter versus maximum tunable angle