Abstract: The invention is concerned with a method of and an arrangement for performing optical interference measurements by use of integrated optical means. The arrangement is comprised of a multi-mode waveguide mounted on a carrier means. A cover layer of dielectric material is disposed upon said multi-mode waveguide. The refractive index of the dielectric cover-layer is greater than that of the waveguide. Two modes are coupled to the waveguide the effective refractive indices of said modes differ from each other in such a manner that an interference period results which is detected through a sequence of photodetectors, being arranged in the cover layer and energetically coupled to the waveguide. The relative phase position of both modes varied through a measuring operation is measured. One of the photodetectors is employed to incrementally count the phase displacements and the other photodetectors are operative as an optical vernier so subdividing the scale in dependence on the number of photodetectors.