A wavelength division multiplexed, WDM, reconfigurable optical switch, the switch comprising: a set of M arrays (S 1 - S 3) of optical beam connections, each array of the set of M arrays comprising an array (S i) of optical outputs and having an optical input to receive a WDM input optical signal; a first diffractive element to demultiplex said WDM input optical signal into a plurality of demultiplexed optical input beams, and to disperse said demultiplexed optical input beams spatially along a first axis (N x); first spherical relay optics (L 1) between said set of arrays (S 1 - S 3) of optical beam connections and said first diffractive element; a reconfigurable holographic array comprising a 2D array of reconfigurable sub-holograms defining sub-hologram rows and columns; further spherical relay optics (L 2) positioned between said first diffractive element and said reconfigurable holographic array; wherein said arrays (S i) of said set of arrays (S 1 - S 3) are at least one dimensional arrays extending spatially in a direction parallel to said first axis and arranged in a column defining a second axis (N y) orthogonal to said first axis; wherein said sub-hologram rows are aligned along said first axis (N x), and wherein said sub-hologram columns are aligned along said second axis(N x); wherein a number of said sub-hologram rows corresponds to at least a number of arrays in said set of arrays; and wherein each sub-hologram row is configured to receive a set of demultiplexed optical input beams at different carrier wavelengths demultiplexed from the optical input for the array of the set of arrays to which the row corresponds; wherein each of said sub-holograms in a sub-hologram row is reconfigurable to steer a respective wavelength channel of the WDM input signal for the array to which the sub-hologram row corresponds, towards a selected said optical output for the array; and wherein each said sub-hologram row is configured to steer the demultiplexed optical input beams for a respective array of the set of arrays of optical beam connections; the switch further comprising a set of M objective lenses on the same pitch as the set of M arrays for coupling to a fibre array. a set of M arrays (S 1 - S 3) of optical beam connections, each array of the set of M arrays comprising an array (S i) of optical outputs and having an optical input to receive a WDM input optical signal; a first diffractive element to demultiplex said WDM input optical signal into a plurality of demultiplexed optical input beams, and to disperse said demultiplexed optical input beams spatially along a first axis (N x); first spherical relay optics (L 1) between said set of arrays (S 1 - S 3) of optical beam connections and said first diffractive element; a reconfigurable holographic array comprising a 2D array of reconfigurable sub-holograms defining sub-hologram rows and columns; further spherical relay optics (L 2) positioned between said first diffractive element and said reconfigurable holographic array; wherein said arrays (S i) of said set of arrays (S 1 - S 3) are at least one dimensional arrays extending spatially in a direction parallel to said first axis and arranged in a column defining a second axis (N y) orthogonal to said first axis; wherein said sub-hologram rows are aligned along said first axis (N x), and wherein said sub-hologram columns are aligned along said second axis(N x); wherein a number of said sub-hologram rows corresponds to at least a number of arrays in said set of arrays; and wherein each sub-hologram row is configured to receive a set of demultiplexed optical input beams at different carrier wavelengths demultiplexed from the optical input for the array of the set of arrays to which the row corresponds; wherein each of said sub-holograms in a sub-hologram row is reconfigurable to steer a respective wavelength channel of the WDM input signal for the array to which the sub-hologram row corresponds, towards a selected said optical output for the array; and wherein each said sub-hologram row is configured to steer the demultiplexed optical input beams for a respective array of the set of arrays of optical beam connections;