A circuit board, a manufacturing method thereof, and an electro-optic apparatus having the circuit board are provided. The circuit board includes a substrate including a first dielectric layer and a first circuit layer disposed thereon, a waveguide layer disposed on a portion of the substrate, a second dielectric layer, a convex structure and a second circuit layer. The second dielectric layer is disposed on the substrate and the waveguide layer. The second dielectric layer has an opening exposing the sidewall of the waveguide layer and a portion of the first circuit layer. The convex structure is disposed on the sidewall of the waveguide layer. The convex structure and the waveguide layer respectively have refractive index n1 and n2, and |n1-n21|n1