Germanium is a very good candidate to host a versatile spintronics platform thanks to its unique spin and optical properties. Recently we focused on two approaches in order to tune the spin-orbit interaction (SOI) in this Ge-based platform. The first one relies on growing high quality epitaxial topological insulators (TIs) on a Ge (111) substrate, we developed an original method to probe the spin-to-charge conversion at the TI/Ge(111) interface by taking advantage of the Ge optical properties. The latter approach is to exploit the intrinsic SOI of Ge (111). By investigating the electrical properties of a thin Ge(111), we found a large unidirectional Rashba magnetoresistance, which we ascribe to the interplay between the externally applied magnetic field and the current-induced pseudo-magnetic field applied in the spin-splitted subsurface states of Ge (111). Both studies open a door towards spin manipulation with electric fields in an all-semiconductor technology platform.