A two-stage directional coupler structure is proposed to realize the two dimensional optical phased array, and a distinctive C-bend waveguide is designed for thermal regulation as optical phase shifter of array element. A method that compresses far field side lobes caused by high-order interference for sparse on-chip optical phased arrays is presented. Hill climbing algorithm is adopted to optimize the uniform antenna spacing and make it become non-uniform, which will greatly mitigate constructive interference conditions and then compress far field side lobes. Using finite-difference time-domain method to simulate the sparse optical grating coupler array designed at 1 310 nm wavelength showing that this optimization can realize a -6～-7 dB ratio of side lobe and main lobe.