An optical waveguide crosspoint comprising first and second single multimode interference sections , each single multimode interference section comprising an input face , an output face and sidewalls extending therebetween, the distance between the input face and output face for each single multimode interference section being the length of the multimode interference section , the lengths of the first and second multimode interference sections being L1 and L2 respectively; at least one primary input optical waveguide connected to the input face of the first single multimode interference section ; at least one primary output optical waveguide connected to the output face of the first single multimode interference section ; the first single multimode interference section comprising a symmetry axis extending from the center of the input face to the center of the output face ; at least one secondary input optical waveguide connected to the input face of the second single multimode interference section ; at least one secondary output optical waveguide connected to the output face of the second single multimode interference section ; the second single multimode interference section comprising a symmetry axis extending from the center of the input face to the center of the output face ; characterised in that the first and second single multimode interference sections intersect to form an L shaped compound multimode interference structure; and, for each single multimode interference section its width in a direction normal to its symmetry axis is less than 15% of the length of the other single multimode interference section . first and second single multimode interference sections , each single multimode interference section comprising an input face , an output face and sidewalls extending therebetween, the distance between the input face and output face for each single multimode interference section being the length of the multimode interference section , the lengths of the first and second multimode interference sections being L1 and L2 respectively; at least one primary input optical waveguide connected to the input face of the first single multimode interference section ; at least one primary output optical waveguide connected to the output face of the first single multimode interference section ; the first single multimode interference section comprising a symmetry axis extending from the center of the input face to the center of the output face ; at least one secondary input optical waveguide connected to the input face of the second single multimode interference section ; at least one secondary output optical waveguide connected to the output face of the second single multimode interference section ; the second single multimode interference section comprising a symmetry axis extending from the center of the input face to the center of the output face ; characterised in that the first and second single multimode interference sections intersect to form an L shaped compound multimode interference structure; and, for each single multimode interference section its width in a direction normal to its symmetry axis is less than 15% of the length of the other single multimode interference section . <EOS>