Fig. 1. Schematic diagram of subwavelength line grating coupler simulation structure

Fig. 2. Effect of line grating period on coupling efficiency

Fig. 3. Dispersion of lower order guide mode in Si waveguide layer with respect to waveguide thickness

Fig. 4. Effect of line grating radius on coupling efficiency

Fig. 5. Effect of lower cladding thickness on coupling efficiency

Fig. 6. Coupling efficiency versus thickness of upper cladding

Fig. 7. Vertical coupling efficiency versus parameters of traditional rectangular grating. (a) Grating period; (b) etching depth; (c) thickness of BOX; (d) cladding thickness

Fig. 8. Light distribution in coupler. (a) Without grating; (b) with traditional rectangular grating; (c) with wire grating