A distance measuring device comprises a light source (101) emitting light, and such an integrated electro-optic modulator (21, 22, 23) arranged such that the emitted light passes through an optical waveguide of the electro-optic modulator (21, 22, 23) in a first direction before being emitted from the distance measuring device, and after being reflected from a target passes through the electro-optic modulator (21, 22, 23) in a second direction which is opposite to the first direction, The forward electro-optic response of a modulating region (17) of the electro-optic modulator (21, 22, 23) is the same as the backward electro-optic response, and a centre of gravity of the modulation is independent of modulation frequency.