Grating coupler and integrated grating coupler system

1. A grating coupler having first and second ends for coupling a light beam to a waveguide of a chip comprising:

a substrate configured to receive the light beam from the first end and transmit the light beam through the second end, the substrate having a first refractive index n1;

a grating structure having grating lines arranged on the substrate, the grating structure having a second refractive index n2, wherein the grating lines have line width w and height d and are arranged by a pitch Λ, wherein the second refractive index n2 is greater than first refractive index n1, wherein the grating structure is configured to maintain a diffraction angle of the light beam from the second end in a range between 33 degree and 90 degree; and

a cladding layer configured to cover the grating structure, wherein the cladding layer has a third refractive index n3, wherein the third refractive index n3 is less than the second refractive index n2, wherein the cladding layer is arranged so as to reflect the light beam diffracted from the grating structure toward below the cladding layer.

2. The grating coupler of claim 1 , wherein the grating structure further includes a waveguide layer to form a grating geometry connecting the grating lines on the waveguide layer, wherein the waveguide layer having a thickness d is arranged on the substrate.

3. The grating coupler of claim 2 , wherein the grating structure further includes sub-gratings having line width w 2 and the height d and a second pitch Λ 2 , wherein the pitch Λ is greater than the second pitch Λ 2 , wherein the sub-gratings are arranged on at least one side of each of the grating lines.

4. The grating coupler of claim 1 , wherein the pitch Λ is changed from the first end to the second end to focus the light beam on the waveguide of the chip according to a function of distances.

5. The grating coupler of claim 1 , wherein a ratio w/Λ between the line width w and the pitch Λ over is arranged to be approximately 0.5 for reducing a second order diffraction of the light beam from the grating structure.

6. The grating coupler of claim 1 , further comprising an end anti-reflection film arranged on the second end.

7. The grating coupler of claim 6 , wherein the end anti-reflection film consists of at least two layers with different materials.

8. The grating coupler of claim 1 , further comprising a dielectric film arranged on the cladding layer.

9. The grating coupler of claim 1 , wherein the third refractive index n3 of the cladding layer is approximately the same as the first refractive index n1 of the substrate.

10. The grating coupler of claim 1 , further comprising a second cladding layer arranged between the grating structure and the cladding layer, wherein the second cladding layer has a fourth refractive index n4, wherein the fourth refractive index n4 is less than the third refractive index n3.

11. The grating coupler of claim 1 , wherein the grating lines are elliptic grating lines arranged to focus the light beam to the waveguide of the chip.

12. The grating coupler of claim 1 , further comprising a second waveguide layer arranged on the substrate, wherein the grating lines of the grating structure are separately arranged above the second waveguide layer and burred in the cladding layer.

13. The grating coupler of claim 1 , wherein the grating lines of the grating structure are separately arranged between the substrate and the cladding layer.

14. The grating coupler of claim 1 , wherein the substrate is an InP substrate.