An attractive way of implementing efficient local interconnection networks is to use the Optical Transpose Interconnecting System (OTIS) architecture proposed in [8]. This system allows to optically interconnect some set of processors in a Free Space of Optical Interconnections (FSOI). Briefly, it consists of two lenslet arrays allowing a large number of optical interconnections from a set of transmitters to a set of receivers. Note that the OTIS architecture is indeed a three dimension (3D) one but it can always be modeled in a 2D-space. We first try to provide ways of determining if a given general network admits an OTIS layout or not. Then we study particular case of regular and symmetric networks. Finally we show that classical topologies like de Bruijn, Kautz and complete digraphs admit an OTIS2D -layout. At the end, the results obtained for the OTIS2D model are applied to the OTIS3D case.