摘要：A novel structure of spot size converter is designed to allow low loss and large alignment tolerance between single mode rib waveguide devices and fiber arrays *** spot size converter consists of a tapered rib core region and a double cladding *** optimizing parameters,an expanded mode field can be tightly confined in the inner cladding and thus radiation loss be reduced largely at the tapered *** influence of refractive index and thickness of the inner cladding on coupling loss is analyzed in particular.A novel,easy method of fabricating tapered rib spot size converter based on silicon on insulator material is proposed.