Patent ID: 7068888

Claim:
A planar optical interconnection device comprising: a periodic transition formed between a slab region and an array of radial waveguides arranged periodically with angular period α and focal point F located in the slab region, wherein said transition is a sequence of N sections, whose number N can be as small as one, and each section consists of two circular segments, one of which is a slab segment, and the other is an array segment consisting of radial waveguides arranged periodically with nonzero gap regions of lower refractive index between the waveguides, wherein the radial length L of each section is determined by a design parameter Δ given in degrees by the angle Δ = 180 ⁢ ° ⁢ ⁢ ρ ⁢ λ ⁢ ⁢ L ( α ⁢ ⁢ R ) 2 where R is the average radial distance of the section from the focal point, λ is the wavelength in the slab segment, ρ is a parameter whose value in the last section connected to the slab region is comprised between 1.0 and 1.25, and the value of Δ in the last section either exceeds 110° or is comprised between 50° and 90°.