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To operate an optical device comprising an SLM with a two-dimensional array of controllable phase-modulating elements groups of individual phase-modulating elements are delineated, and control data selected from a store for each delineated group of phase-modulating elements. The selected control dat

To operate an optical device comprising an SLM with a two-dimensional array of controllable phase-modulating elements groups of individual phase-modulating elements are delineated, and control data selected from a store for each delineated group of phase-modulating elements. The selected control data are used to generate holograms at each group and one or both of the delineation of the groups and the selection of control data is/are varied. In this way upon illumination of the groups by light beams, light beams emergent from the groups are controllable independently of each other.

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The invention claimed is: 1. A method of operating an optical device comprising an SLM having a two-dimensional array of controllable phase-modulating elements, the method comprising delineating groups of individual phase-modulating elements; selecting, from stored control data, control data for e

The invention claimed is: 1. A method of operating an optical device comprising an SLM having a two-dimensional array of controllable phase-modulating elements, the method comprising delineating groups of individual phase-modulating elements; selecting, from stored control data, control data for each group of phase-modulating elements; generating from the respective selected control data a respective hologram at each group of phase-modulating elements; and varying the delineation of the groups and/or the selection of control data whereby upon illumination of said groups by respective light beams, respective emergent light beams from the groups are controllable independently of each other. 2. A method of operating an optical device according to clam 1, wherein control of said light beams is selected from the group comprising: control of direction, control of power, focussing, aberration compensation, sampling and beam shaping. 3. A method of operating an optical device according to claim 1, wherein each phase modulating element is responsive to a respective applied voltage to provide a corresponding phase shift to emergent light, the method further comprising controlling said phase-modulating elements of the spatial light modulator to provide respective actual holograms derived from the respective generated holograms, wherein the controlling step comprises: resolving the respective generated holograms modulo 2pi. 4. A method of operating an optical device according to claim 1, comprising: providing a discrete number of voltages available for application to each phase modulating element; on the basis of the respective generated holograms, determining the desired level of phase modulation at a predetermined point on each phase modulating element and choosing for each phase modulating element the available voltage which corresponds most closely to the desired level. 5. A method of operating an optical device according to claim 1, comprising: providing a discrete number of voltages available for application to each phase modulating element; determining a subset of the available voltages which provides the best fit to the generated hologram. 6. A method of operating an optical device according to claim 1, further comprising the step of storing said control data wherein the step of storing said control data comprises calculating an initial hologram using a desired direction change of a beam of light, applying said initial hologram to a group of phase modulating elements, and correcting the initial hologram to obtain an improved result. 7. A method of operating an optical device according to claim 1, further comprising the step of providing sensors for detecting temperature change, and performing said varying step in response to the outputs of those sensors. 8. A method of operating an optical device according to claim 1, in which the SLM is integrated on a substrate and has an integrated quarter-wave plate whereby it is substantially polarisation insensitive. 9. A method of operating an optical device according to claim 1, wherein the phase-modulating elements are substantially reflective, whereby emergent beams are deflected from the specular reflection direction. 10. A method of operating an optical device according to claim 3 comprising, for at least one said group of phase-modulating elements, providing control data indicative of two holograms to be displayed by said group and generating a combined hologram before said resolving step. 11. An optical device comprising an SLM and a control circuit, the SLM having a two-dimensional array of controllable phase-modulating elements and the control circuit having a store constructed and arranged to hold plural items of control data, the control circuit being constructed and arranged to delineate groups of individual phase-modulating elements, to select, from stored control data, control data for each group of phase-modulating elements, and to generate from the respective selected control data a respective hologram at each group of phase-modulating elements, wherein the control circuit is further constructed and arranged to vary the delineation of the groups and/or the selection of control data, whereby upon illumination of said groups by respective light beams, respective emergent light beams from the groups are controllable independently of each other. 12. An optical device according to claim 11, having sensor devices arranged to detect light emergent from the SLM, the control circuit being responsive to signals from the sensor devices to vary said delineation and/or said selection. 13. An optical device according to claim 11, having temperature responsive devices constructed and arranged to feed signals indicative of device temperature to said control circuit, whereby said delineation and/or selection is varied. 14. An optical routing device having at least first and second SLMs and a control circuit, the first SLM being disposed to receive respective light beams from an input fibre array, and the second SLM being disposed to receive emergent light from the first SLM and to provide light to an output fibre array, the first and second SLMs each having a respective two-dimensional array of controllable phase-modulating elements and the control circuit having a store constructed and arranged to hold plural items of control data, the control circuit being constructed and arranged to delineate groups of individual phase-modulating elements, to select, from stored control data, control data for each group of phase-modulating elements, and to generate from the respective selected control data a respective hologram at each group of phase-modulating elements, wherein the control circuit is further constructed and arranged to vary the delineation of the groups and/or the selection of control data, whereby upon illumination of said groups by respective light beams, respective emergent light beams from the groups are controllable independently of each other.