Fig. 1. Schematic of the ultra-narrwoband transmission filter consisting of the top and bottow gratings

Fig. 2. Transimittance as function of the incident wavelength and the grating thickness d₁

Fig. 3. Transimittance as function of the incident wavelength and the filling factor f₁ for d₁=8 nm

Fig. 4. Transmittance as function of the waveguide laryer thickness d₀ at λ₁=1589 nm ford₁=0 nm、8 nm

Fig. 5. Transmittance as function of the incident wavelength for d₁=8 nm

Fig. 6. Electric field intensity distribution of the guided mode for d₁=8 nm at λ₀=1589 nm

Fig. 7. Electric field intensity distribution of the guided mode for d₁=8 nm at λ₀=1580.4 nm

Fig. 8. Electric field intensity distribution of the guided mode for d₁=8 nm at λ₀=1550 nm

Fig. 9. Transmittance as function of the incident wavelength for Mode 3