An embodiment optical device includes a glass plate, a first trench disposed in the glass plate, and a second trench disposed in the glass plate. The second trench crosses the first trench, and the first trench has an open end in a first wall of the second trench. The optical device includes a waveguide disposed inside the first trench, where the waveguide is formed of a material having a refractive index different from that of the glass plate, and a mirror on a second wall of the second trench opposite the first wall and waveguide. The optical device includes an encapsulation layer filling the second trench and covering all of an upper surface of the waveguide and having a refractive index that is different from the waveguide and the glass plate.