Abstract: This polarization beam splitter for guided light is e.g. produced on Z-propagating, X-cut LiNbO.sub.3 :Ti and comprises in series a passive Y-junction (66), an active phase shifter (68) and an active directional coupler (70), independent of the polarization and able to constitute a 3 dB coupler. Thus, on supplying a light wave to the input of the Y-branch and with the coupler constituting a 3 dB coupler, the TM and TE modes of the input wave are respectively obtained at the outputs of the coupler by appropriately polarizing the phase shifter. Application to optical fiber sensors or transducers and to the coherent transmission of information by monomode optical fibers.