A photosensitive unit and a photo-insensitive unit are formed in a substrate. A lens is formed to cover the photosensitive unit and the photo-insensitive unit, and the lens has a single radius of curvature and an optical axis passing through a surface of the curvature at the center of the lens. The photosensitive unit is disposed at a first side of the optical axis and the photo-insensitive unit is disposed at a second side opposite to the first side of the optical axis, a light beam passing through the lens is simultaneously incident into the photosensitive unit and the photo-insensitive unit without being blocked, and the photosensitive unit detects the light beam while the photo-insensitive unit is ineffective in sensing the light beam. A conductive feature is formed over the substrate between the photosensitive unit and the photo-insensitive unit, wherein the optical axis of the lens passes the conductive feature.