Fig. 1. Schematic of the LNOI edge coupler with cladding grating. Top panel: 3D schematic structure and principle of the grating edge coupler. Bottom panel: cross-sections at different positions.

Fig. 2. Phase-matching condition and modal distributions. (a) Grating period Λ for momentum compensation at different wavelengths. (b) Modal distributions of the TM cladding mode and TM₀₀, TE₁₀, and TE₀₀ core modes at 1550 nm.

Fig. 3. Design for TM₀₀ coupling at 1550 nm. (a) The conversion efficiency along with the propagation at the period of 4.041 µm and the wavelength of 1550 nm. (b) Conversion spectrum at the position of 18Λ. (c) Efficiency spectra of conversions from TE cladding to TE₀₀ and TM cladding to TM00 at the position of 18Λ. (d) The conversion efficiency evolution of TM00 at different wavelengths. Electric field evolution of the TM cladding mode in (e) x–z and (f) y–z planes.

Fig. 4. Design for TE₁₀ coupling at 1550 nm. (a) The conversion efficiency along with the propagation at the period of 3.875 µm and the wavelength of 1550 nm. (b) Conversion spectrum at the position of 75Λ. (c) The conversion efficiency evolution of TE₁₀ at different wavelengths. Electric field evolution of the TM cladding mode in (d) x–z and (e) y–z planes.

Fig. 5. Conversion spectra at three typical grating periods Λ. (a) TM₀₀ mode. (b) TE₁₀ mode.

Fig. 6. Schematic of the LNOI edge coupler with asymmetric cladding grating. Top panel: 3D schematic structure. Bottom panel: cross-sections at different positions.

Fig. 7. Design for TE₀₀ coupling at 1550 nm. (a) Conversion efficiency along with the propagation at the period of 3.047 µm and the wavelength of 1550 nm. (b) Conversion spectrum at the position of 635Λ.

Fig. 8. Conversion spectra at different grating periods Λ for TE₀₀ mode.