Vertical Optical Waveguide Comprising Square Base Cuboid Cores with Size Modulation for Multilayer Chip-to-Chip Interconnection Topics: Photonic and Optoelectronic Materials and Devices In Proceedings of the 8th International Conference on Photonics, Optics and Laser Technology PHOTOPTICS - Volume 1, 174-179, 2020 , Valletta, Malta