An apparatus including a light detection and ranging (LiDAR) antenna of an optical phased array includes a silicon-on-insulator substrate including a silicon wire waveguide embedded within the substrate and a grating layer disposed over the substrate. The grating layer includes a silicon nitride layer coating the silicon-on-insulator substrate and including a plurality of etchings formed in a direction perpendicular to a longitudinal axis of the optical phased array and a silicon oxynitride layer coating the silicon nitride layer and filling the etchings. The etchings are relatively thin in the direction of the longitudinal axis of the optical phased array at a first end of the optical antenna and are relatively thick in the direction of the longitudinal axis at a second end. The etchings gradually increase in thickness between the first end of the optical phased array and the second end of the optical antenna.