An optical system comprises: an optical circuit board (1) having an optical layer, comprising an optical waveguide (2) embedded between top and bottom faces, and a cut-out (27) having a bottom reference layer defining an X-Y plane, an optical coupling device having a positioning member (19) extending in the cut-out, a mechanical fixation system (31) attaching the optical circuit board to the optical coupling device, and comprising a fixation pin (32) extending through the optical circuit board at the positioning member (19).