Patent ID: 7343071

Claim:
An optical branching unit ( 1 ) formed on a substrate, the optical branching unit comprising waveguides for guiding light at a predetermined wavelength λ, the waveguides comprising a core region having a refractive index n core , the core region being embedded in a cladding ( 6 ) having a refractive index n clad , the waveguides comprising an input waveguide with an input core region ( 2 ) of width w in and at least two output waveguides having output core regions ( 301 , 302 ) of widths w out,i , a branching part ( 4 )—having a refractive index n core —for connecting the input and output waveguide cores, a splitting region ( 7 ) adjacent to the branching part, the width of the branching part being substantially equal to w in at its joint with the input waveguide core and to the sum of the widths w out,i at its joint with the output waveguide cores, the width of the branching part gradually expanding from its joint with the input waveguide core to allow the output waveguide cores to be branched off and diverge from each other in the splitting region wherein a multitude of M transversal waveguide core elements ( 5 ; 501 , 502 , 503 , 504 , 505 , 506 , 507 , 508 , 509 , 510 ) each having a width w i , a refractive index n trans,i and being embedded in said cladding are located in the splitting region forming paths with a mutual centre to centre distance of s i , said transversal waveguide core elements fully or partially connecting neighbouring output waveguide cores.