Abstract: For electrooptical measurement of distance with modulation of light external to the light source (1) a modulator system (5, 7, 8, 11) with low sensitivity to temperature and with a low modulating voltage is disclosed. The temperature dependence of the static birefringence of a modulating crystal (7) is compensated by passing the modulated light beam (6), after traversing the crystal (7), a quarterwave plate (11), the measured path (9) and the quarterwave plate (11) again--a second time through the crystal (7) with its polarization rotated by 90.degree.. The light beam returning from the measured path is separated from its source (1) by means of a polarizing beam splitter (5).