be the same as that of beam 13 or to a polarization state suitable for subsequent recombination with beam 13 afterwards beam 13 and beam 23 are combined using the non polarizing beam splitter functioning as a beam combiner 30 to give a particularly polarized beam 34 the particularly polarized beam 34 is passed through a controllable spatial light modulator slm 70 which includes a reconfigurable liquid crystal device 35 a control device 85 and a storage device 81 the controllable slm 70 can be used to diffract beam 34 in any desired direction such as 41 42 or 43 the controllable slm 70 achieves this diffraction by using the control device 85 to control the reconfigurable liquid crystal device 35 using a predetermined drive signal stored in the storage device 81 the predetermined drive signals are determined using the metric and optimization method described in detail above when a certain switching function is desired the appropriate drive signal is retrieved from storage device 81 and applied to the reconfigurable liquid crystal device 35 by the control device 85 this allows the switching to be achieved using the full advantages of the speed and bandwidth of light transmission with a higher degree of accuracy and greater throughput than was possible in prior art with very high switching speeds because no recalculation is necessary and with virtually limitless reconfigurability in addition the actual characteristics of the reconfigurable liquid crystal device 35 are used and thus the method and apparatus do not depend on a possibly inaccurate model of its characteristics nor on unnecessary assumptions about its behavior although the embodiment illustrated in fig4 uses a transmissive slm the invention is equally applicable to a.