An optical waveguide crosspoint comprising first and second multimode interference sections , each comprising an input face , an output face and sidewalls extending therebetween, the distance between the input face and output face for each 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; the first multimode interference section being a single or ganged multimode interference section and the second multimode interference section being a single multimode interference section; at least one primary input optical waveguide connected to the input face of the first multimode interference section ; at least one primary output optical waveguide connected to the output face of the first multimode interference section ; the first 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 multimode interference section ; at least one secondary output optical waveguide connected to the output face of the second multimode interference section ; characterised in that the first and second multimode interference sections intersect to form a T shaped compound multimode interference structure with the first multimode interference section forming the arms of the T and the second multimode interference section forming the stem of the T; and, the width of the first multimode interference section in a direction normal to its symmetry axis being less than 15% of the length of the second multimode interference section . first and second multimode interference sections , each comprising an input face , an output face and sidewalls extending therebetween, the distance between the input face and output face for each 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; the first multimode interference section being a single or ganged multimode interference section and the second multimode interference section being a single multimode interference section; at least one primary input optical waveguide connected to the input face of the first multimode interference section ; at least one primary output optical waveguide connected to the output face of the first multimode interference section ; the first 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 multimode interference section ; at least one secondary output optical waveguide connected to the output face of the second multimode interference section ; characterised in that the first and second multimode interference sections intersect to form a T shaped compound multimode interference structure with the first multimode interference section forming the arms of the T and the second multimode interference section forming the stem of the T; and, the width of the first multimode interference section in a direction normal to its symmetry axis being less than 15% of the length of the second multimode interference section . <EOS>