We have studied high-speed optical phased arrays (OPAs) using electro-optic (EO) polymers for various applications, including range imaging, three-dimensional shape measurement, spatial light communication, and image display. The suppression of the stray light caused by radiation loss in curved waveguides and coupling loss in optical splitters is very important in OPAs using EO polymer. Stray light causes degradation, for example, in the image quality on a display or the signal-to-noise ratio on an optical sensor. In this study, we investigate optical loss reduction by optimizing the design of a curved waveguide and an optical splitter to suppress stray light and improve the optical beam quality from OPAs. We perform numerical simulations and an experimental evaluation of the designed OPAs and confirm the effectiveness of the optimal design for stray light suppression.