the coercive field lever of the crystal 12 maximum efficiency may be achieved by experimentally varying the field strength fig2 illustrates that before polarity reversal of the electric field applied across electrodes 14 and 16 from source 18 the properties of the crystal 12 spontaneous polarization is such that the light intensity from beams 20 and 22 is diverted almost entirely to beam 22 which emerges from the crystal with beam intensity i 2 39 u2248 i 1 i 2 fig2 b illustrates that after switching of the polarity from voltage source 18 the ferroelectric domains of the barium titanate crystal 12 are reoriented antiparallel to the original alignement and therefore the intensity of the beams 20 and 22 is 34 switched 34 to the beam 20 fig2 b thus illustrates that as beam 20 emerges from the crystal 12 its intensity is i 1 39 u2248 i 1 i 2 for the case where i 1 gt gt i 2 fig2 a illustrates that i 2 39 gt gt i 1 39 and fig2 b illustrates that i 1 39 gt gt i 2 39 on off ratios of 500 to 1 can be readily achieved with optical switching in 100 microseconds with this technique fig3 a and 3b illustrate an alternate embodiment of the present invention where the invention is used in a four wave mixing configuration in fig3 a and 3b an input.