A phase modulator for a light beam comprising a waveguide having a longitudinal axis, and a piezoelectric actuator to apply a mechanical stress within said waveguide in response to an electrical bias, said actuator comprising a first part covering a first side of the waveguide and having a first axis of symmetry essentially parallel to the longitudinal axis. The actuator comprises a second part covering a second side of the waveguide, said second part having a second axis of symmetry essentially parallel to the longitudinal axis.