An electric-optic modulator includes a block of crystal having electro-optic properties, the block extending lengthways along a long axis and having a light guide which extends between a light guide input and a light guide output. An electric modulation signal acts on an interaction zone of the block via coplanar electrodes together with the light guide via a dielectric layer. The electrodes are disposed on a main long face of the block and the interaction zone is elongated more or less along the long axis. The light to be modulated arrives through an input optical fiber which is connected to the light guide at the light guide input on a first face of the block. The modulated light leaves the modulator through an output optical fiber connected to the light guide output on a second face of the block. The first face and the second face are one single face (D) which is parallel to the long axis.