Abstract: With the intention of simplifying an arrangement of a chip having at least one optical active surface and positioning the chip in a correct position in relation to an optical miniature capsule for optimum light transmission between an optical fiber and the optically active surface, the chip (1) is fastened on a foil substrate (9) which has at least one conductor (4) and which is provided with alignment marks and/or guide means (8) for correct positioning of the chip on the foil substrate and for correct positioning of the foil substrate/chip assembly on the capsule. After having fastened the chip on the foil substrate, the foil with the chip can be readily fastened to the capsule and by that means the chip will be fastened to the capsule.