Recently, there is an increasing interest to extend the concept of microwave antennas to optical frequencies leading to optical antennas. These antennas have the ability to control and steering the emission and scattering of optical beams with small-scale foot print. This thesis presents design concepts and performance evaluation of high directivity optical leaky-wave antennas (OLWAs) designed in CMOS-compatible silicon platform for 1550 and 1300 nm operation. The work consists of two main parts and supported by simulation results obtaining using Computer Simulation Technology (CST) software package version CST STUDIO SUITE 2013.The first part deals with the design and performance simulation of single-grating antenna (SGA). Parametric study is presented to address the effect of each antenna geometric parameters on radiation characteristics. Simulation results are presented for 1550 nm antenna designed with different number of silicon perturbations N embedded in silicon nitride waveguide. The simulation results reveal that the antenna radiation efficiency increases with N and reaches around 0.87 and 0.89 for N= 30 and 60, respectively. Investigation related to SGA operating at 1300 nm is also addressed and its performance is compared with that related to 1550 counterpart. The second part of this work addresses the possibility of design the OLWA using two silicon grating embedded in the waveguide. This yields a double grating antenna (DGA) suitable to produce two steering beams. The simulation results reveal that the radiation pattern can be splitted into two identical (symmetric) patterns when the antenna is designed with two identical gratings.