Grating coupler and optical waveguide device
The invention relates to a grating coupler and an optical waveguide device having a stripe width that can be easily realized where light is transferred by means of a beam of which the form is close to that of a Gaussian beam. A striped member that becomes a grating and that is formed of a material of which the refractive index is different from that of the core layer is divided into a plurality of sections, and at the same time, the distance between the core layer and the surface of the striped member on the side opposite the surface that faces the core layer is different for each section.
1. A grating coupler, comprising:
a substrate;
a first clad layer provided on the substrate;
a core layer provided on the first clad layer;
a second clad layer provided on the core layer; and
a grating provided between the core layer and either the first clad layer or the second clad layer, where a striped member is formed of a material of which the refractive index is different from that of the core layer is divided into a plurality of sections, wherein a distance between the core layer and a surface of the striped member on a side opposite a surface that faces the core layer is different from among the sections, and
the core layer does not have a striped pattern configured to form the grating.
2. The grating coupler according to claim 1 , wherein a low refractive index layer of which the refractive index is lower than that of the core layer is provided between the core layer and the striped member.
3. The grating coupler according to claim 2 , wherein the low refractive index layer is made of the same material as that of the clad layer.
4. The grating coupler according to claim 1 , wherein
a number of stripes provided in each section is the same,
the distance between the core layer and the surface of the striped member on the side opposite the surface that faces the core layer decreases section by section sequentially as the location gets closer to an end portion of the grating coupler, and
a size of the stripes in a direction in which light is guided in each section increases sequentially as the location gets closer to the end portion.
5. The grating coupler according to claim 4 , wherein the surface of the core layer that faces the striped member is a flat uniform surface.
6. The grating coupler according to claim 4 , wherein the surface of the core layer that faces the striped member is a stepped surface that provides different thicknesses of the core layer for each section.
7. The grating coupler according to claim 4 , wherein the number of stripes in each section is one, and a thickness and the size in the direction in which light is guided are the same for all the stripes.
8. The grating coupler according to claim 1 , wherein the grating is provided between the core layer and the second clad layer.
9. The grating coupler according to claim 1 , wherein
a number of stripes provided in each section is the same,
the distance between the core layer and the surface of the striped member on the side opposite the surface that faces the core layer increases section by section sequentially as the location gets closer to the an end portion of the grating coupler, and
a size of the stripes and a thickness of the stripes in the direction in which light is guided in each section increase sequentially as the location gets closer to the end portion.
10. The grating coupler according to claim 1 , wherein a number of sections of the striped member is two to four.
11. An optical waveguide device, comprising:
the grating coupler according to claim 1 ;
an optical fiber configured to couple with the grating in an end portion of the grating coupler optically; and
an optical waveguide configured to extend in the direction opposite the end portion of the grating coupler.