In this work, we study the possibility of chip-to-chip interconnections via out-of-plane grating couplers or vertical grating couplers (VGCs) fabricated on silicon-on-insulator (SOI) technology. Mathematical and experimental results for the efficiency of coupling light between two such grating couplers have beenpresented. The VGCs are placed vertically against each other in order to study the effect of spatial misalignments on the light coupling efficiency.Waveguides and VGCs are designed according to standard SOI fabrication processes. A two-dimensional finite-difference time-domain method is used for the simulations. Measurements are performed on different combinations of 4 samples on the chip. Light coupling efficiency of ?8 dB is achieved and tolerances to misalignments in 3 spatial dimensions are provided. © 2012 Optical Society of America.