Fabrication tolerance evaluation of high efficient unidirectional optical coupler for though silicon photonic via in optoelectronic 3D-LSI

To realize very high performance computing system, we have proposed a novel opto-electronic 3-D LSI in which both electrical and optical devices are integrated. To realize such opto-electronic 3-D LSI, through Si photonic via (TSPV) is indispensable for vertical light transmission. In addition, vertically transmitted light has to be bended and coupled to a planar optical waveguide on the LSI chips. For this purpose, we have proposed unidirectional optical coupler and it shows very high coupling efficiency of the TSPV and the planar optical waveguide. In this work, we evaluated a fabrication tolerance of the high efficient unidirectional optical coupler by FDTD (Finite-Difference Time-Domain) method. From the simulation results, we found that a grating pitch of the coupler was most critical structural parameter to realize high efficient optical coupling. A standard variation of the grating pitch fluctuation should be less than 20nm to realize 80% coupling efficiency. We also showed that a misalignment tolerance of the unidirectional optical coupler. The misalignment of 1 μm induced 20% optical loss. If the misalignment could be less than 0.1 μm, the optical loss became almost negligible.