Provided is an optical sensor and an optical sensor fabricating method. The optical sensor includes: a substrate; and an ommatidia located on or inside the substrate, the ommatidia comprising a microlens which receives light, an optical waveguide which transfers the light received through the microlens, and a cone structure comprising a first end connected to the microlens and a second end connected to the optical waveguide, the cone structure having a diameter or a width decreasing in a direction from the first end to the second end.