Silicon-based electro-optic device
In an electro-optic device, a stack structure including a first silicon layer of a first conductivity type and a second silicon layer of a second conductivity type has a rib waveguide shape so as to form an optical confinement area, and a slab portion of a rib waveguide includes an area to which a metal electrode is connected. The slab portion in the area to which the metal electrode is connected is thicker than a surrounding slab portion. The area to which the metal electrode is connected is set so that a range of a distance from the rib waveguide to the area to which the metal electrode is connected is such that when the distance is changed, an effective refractive index of the rib waveguide in a zeroth-order mode does not change.
1. A silicon-based electro-optic device comprising: a silicon body region doped to exhibit a first conductivity type; a silicon gate region doped to exhibit a second conductivity type, disposed at least in part over the silicon body region to define a contiguous area between the silicon body region and the silicon gate region; a dielectric layer disposed in the contiguous area between the silicon body region and the silicon gate region so that the combination of the silicon body region, the silicon gate region, and the interposed dielectric layer define an active region of the electro-optic device; a first electrical contact coupled to the silicon gate region; and a second electrical contact coupled to the silicon body region, wherein: upon application of an electrical signal to the first electrical contact and the second electrical contact, free carriers accumulate, deplete or invert within the silicon body region and the silicon gate region on both sides of the dielectric layer at the same time, such that an optical electric field of the optical signal substantially overlaps with a modulation area of free carrier concentration in the active region of the electro-optic device, a rib waveguide is formed by means of the silicon body region, the silicon gate region and the dielectric layer, the second electrical contact is coupled to a slab part of the rib waveguide via a rib electrode contact region, thickness of the rib electrode contact region being thicker than around a rib part of the rib waveguide, the rib part has a region coupled to an electrode contact region where thickness of the electrode contact region of the rib part is thicker than around the rib part, and a position of the rib electrode contact region of the rib part is located at a position apart from a center of the rib waveguide where an effective index value of the rib waveguide in a zeroth-order mode is constant when the distance between rib waveguide and the rib electrode contact region varies.
2. The silicon-based electro-optic device as defined in claim 1 , wherein a thickness of the rib electrode contact region of the rib part is the same as a thickness of the rib waveguide.
3. The silicon-based electro-optic device as defined in claim 1 , wherein a thickness of the rib electrode contact region of said rib part is the same as a thickness at least in part of a silicon-on-insulator (SOI) region of the rib waveguide.
4. The silicon-based electro-optic device as defined in claim 1 , wherein a width of the rib electrode contact region of the rib part is wider than a width of the rib waveguide.