A method and arrangement of electrodes for increasing the resolution of a digital phase modulator for a fiber-optic signal transmission or measuring device. A predetermined total number m of electrodes of different lengths are arranged parallel and on both sides with respect to a light guiding path in or on an optical substrate. The electrodes are divided into two groups. A first group n of electrodes represents a coarse modulator with binary and more significant weighted electrodes of length ratio b.sub.n+0:b.sub.n=2, the longest electrode of which corresponds to the sum of lengths of all the remaining electrodes of the overall modulator. A second, smaller group of n.sub.0 non-binary and less significant weighted electrodes represents a fine modulator. The smallest output values are not formed by driving individual electrodes of the fine modulator, but rather by forming the difference, in each case, between two larger electrodes.