An LCOS (liquid crystal on silicon) telecommunications light beam routing device, the device comprising: an optical input; a plurality of optical outputs; a LCOS spatial light modulator in an optical path between said input and said output, for displaying a kinoform; a data processor, coupled to said SLM, configured to provide kinoform data for displaying said kinoform on said SLM; wherein said kinoform data defines a kinoform which routes a beam from said optical input to a selected said optical output; wherein said data processor is configured to input routing data defining said selected optical output and to calculate said kinoform data for routing said beam responsive to said routing data; and wherein said data processor is configured to calculate said kinoform data and comprises: means for determining an initial phase pattern for said kinoform; means for modifying said phase pattern of said kinoform responsive to data defining a model of a response of said liquid crystal on silicon (LCOS) SLM, wherein said modifying further comprises limiting a phase response of pixels of said SLM to account for limited deformation of said liquid crystal material which inhibits large changes in phase over a short distance across the SLM; means for calculating a replay field of said modified phase pattern; means for modifying an amplitude component of said replay field to represent a target replay field for said beam routing, retaining a phase component of said replay field to provide an updated replay field; means for performing a space-frequency transform on said updated replay field to determine an updated phase pattern for said kinoform; and means for repeating said modification of said phase pattern of said kinoform, said calculating and updating of said replay field and said performing of said space-frequency transform until said kinoform for display is determined; and means for outputting said kinoform data for display on said LCOS SLM. an optical input; a plurality of optical outputs; a LCOS spatial light modulator in an optical path between said input and said output, for displaying a kinoform; a data processor, coupled to said SLM, configured to provide kinoform data for displaying said kinoform on said SLM; wherein said kinoform data defines a kinoform which routes a beam from said optical input to a selected said optical output; wherein said data processor is configured to input routing data defining said selected optical output and to calculate said kinoform data for routing said beam responsive to said routing data; and wherein said data processor is configured to calculate said kinoform data and comprises: means for determining an initial phase pattern for said kinoform; means for modifying said phase pattern of said kinoform responsive to data defining a model of a response of said liquid crystal on silicon (LCOS) SLM, wherein said modifying further comprises limiting a phase response of pixels of said SLM to account for limited deformation of said liquid crystal material which inhibits large changes in phase over a short distance across the SLM; means for calculating a replay field of said modified phase pattern; means for modifying an amplitude component of said replay field to represent a target replay field for said beam routing, retaining a phase component of said replay field to provide an updated replay field; means for performing a space-frequency transform on said updated replay field to determine an updated phase pattern for said kinoform; and means for repeating said modification of said phase pattern of said kinoform, said calculating and updating of said replay field and said performing of said space-frequency transform until said kinoform for display is determined; and means for outputting said kinoform data for display on said LCOS SLM. means for determining an initial phase pattern for said kinoform; means for modifying said phase pattern of said kinoform responsive to data defining a model of a response of said liquid crystal on silicon (LCOS) SLM, wherein said modifying further comprises limiting a phase response of pixels of said SLM to account for limited deformation of said liquid crystal material which inhibits large changes in phase over a short distance across the SLM; means for calculating a replay field of said modified phase pattern; means for modifying an amplitude component of said replay field to represent a target replay field for said beam routing, retaining a phase component of said replay field to provide an updated replay field; means for performing a space-frequency transform on said updated replay field to determine an updated phase pattern for said kinoform; and means for repeating said modification of said phase pattern of said kinoform, said calculating and updating of said replay field and said performing of said space-frequency transform until said kinoform for display is determined; and means for outputting said kinoform data for display on said LCOS SLM.