The article considers individual factors of loss growth in polymer planar optical waveguides, which are included in the composition of optical-electronic buses, introduced in perspective new generation printing boards. The article proposes several approaches to reducing losses in optical radiation, which include losses at the end of the optical waveguide and the light transition to the input/output element of the optoelectronic bus of the printed circuit board. According to the results of modelling the modal structure of a polymer planar optical waveguide, made from a polymer material, polydimethylsiloxane (PDMS), in the software environment of Comsol Multiphysics, the dimensions of the core optical waveguide are determined, providing a single-mode structure of an optical waveguide. A measuring stand was developed and assembled for calculating the transmission losses in polymer planar optical waveguides of the optoelectronic bus of a printed circuit board, which meets the requirements of IEC 62596-2: 2017. The minimum measured loss in the manufactured polymer planar optical waveguides was 20 dB, which corresponds to foreign analogues of the optical-electronic bus of the printed circuit board.