21 and 22 which extend in the longitudinal direction of the waveguide 4 and are arranged at both sides thereof by applying voltages to these electrodes the phase relationship of a wave traveling in the waveguide 4 can be influenced the means for reflection isolation in the arrangement shown in fig6 corresponds to the embodiment of the invention according to fig1 monolithically integratable according to fig6 the polarization filter 10 the directional coupler 13 the te tm converter 11 and the phase shifter 12 are combined the coupling location 25 of the 34 monitor 34 waveguide 26 should be provided with an anti reflection layer and or the coupling between the waveguides 4 and 26 should be low in order to avoid disturbing reflections from occurring fig7 and 8 show arrangements of a polarization filter 10 and of the local oscillator 2 as individual hybrid combinable components fig7 or respectively monolithically integrated on electro optical semiconductor material fig8 the incoupling location 15 and thus one reflection location can be avoided in the embodiment of fig8 on the other hand for example the interchangeability of the laser 2 is deteriorated since this must be obtained from the supplier together with the appertaining polarization filter 10 fig9 shows the jones vector diagram equivalent for the network 1 and the arrangement for reflection isolation wherein the arrows in the elements represent the jones matrices m n1 and m n2 or respectively the transposed jones matrices m n1 t and m n2 t the arrows between the elements represent jones vectors particularly the vectors j.