An optical switching apparatus for a WDM optical network, the optical switching apparatus comprising: - a plurality of WDM optical input ports for receiving WDM optical signals from adjacent nodes (A to D), and - a plurality of WDM optical output ports for transmitting WDM optical signals to the adjacent nodes, and - a plurality of transit paths (6, 16, 116, 32, 34, 35) for transmitting optical signals from the WDM optical input ports to the WDM optical output ports of the optical switching apparatus, characterized in that the optical switching apparatus further comprises: - a plurality of primary input WSSs (3, 13, 103, 1003), each primary input WSS comprising an input port and a plurality of selective output ports (12, 18) and being arranged as a programmable wavelength demultiplexer, wherein the input port of each primary input WSS is connected to a respective one of the WDM optical input ports, and - a plurality of primary output WSSs (5, 15, 105, 1005), wherein each primary output WSS comprising an output port and a plurality of selective input ports (10, 11) and being arranged as a programmable wavelength multiplexer, wherein the output port of each primary output WSS is connected to a respective one of the WDM optical output ports, and - a plurality of secondary WSSs (4, 14, 104, 1004, 30, 36), each secondary WSS being selected in the group consisting of a secondary input WSS (30, 36) and a secondary output WSS (4, 14, 104, 1004), the secondary input WSS comprising an input port and a plurality of selective output ports and being arranged as a programmable wavelength demultiplexer, wherein the input port of the secondary input WSS is connected to an output port of a primary input WSS, and the secondary output WSS (4, 14, 104, 1004) comprising an output port and a plurality of selective input ports and being arranged as a programmable wavelength multiplexer, wherein the output port of the secondary output WSS is connected to an input port of a primary output WSS, and wherein each of the transit paths is selected in the group consisting of: - transit paths connecting an output port of a primary input WSS to an input port of a secondary output WSS, and - transit paths connecting an output port of a secondary input WSS to an input port of a primary output WSS. - a plurality of WDM optical input ports for receiving WDM optical signals from adjacent nodes (A to D), and - a plurality of WDM optical output ports for transmitting WDM optical signals to the adjacent nodes, and - a plurality of transit paths (6, 16, 116, 32, 34, 35) for transmitting optical signals from the WDM optical input ports to the WDM optical output ports of the optical switching apparatus, - a plurality of primary input WSSs (3, 13, 103, 1003), each primary input WSS comprising an input port and a plurality of selective output ports (12, 18) and being arranged as a programmable wavelength demultiplexer, wherein the input port of each primary input WSS is connected to a respective one of the WDM optical input ports, and - a plurality of primary output WSSs (5, 15, 105, 1005), wherein each primary output WSS comprising an output port and a plurality of selective input ports (10, 11) and being arranged as a programmable wavelength multiplexer, wherein the output port of each primary output WSS is connected to a respective one of the WDM optical output ports, and - a plurality of secondary WSSs (4, 14, 104, 1004, 30, 36), each secondary WSS being selected in the group consisting of a secondary input WSS (30, 36) and a secondary output WSS (4, 14, 104, 1004), the secondary input WSS comprising an input port and a plurality of selective output ports and being arranged as a programmable wavelength demultiplexer, wherein the input port of the secondary input WSS is connected to an output port of a primary input WSS, and the secondary output WSS (4, 14, 104, 1004) comprising an output port and a plurality of selective input ports and being arranged as a programmable wavelength multiplexer, wherein the output port of the secondary output WSS is connected to an input port of a primary output WSS, and wherein each of the transit paths is selected in the group consisting of: - transit paths connecting an output port of a primary input WSS to an input port of a secondary output WSS, and - transit paths connecting an output port of a secondary input WSS to an input port of a primary output WSS. wherein each of the transit paths is selected in the group consisting of: - transit paths connecting an output port of a primary input WSS to an input port of a secondary output WSS, and - transit paths connecting an output port of a secondary input WSS to an input port of a primary output WSS. - transit paths connecting an output port of a primary input WSS to an input port of a secondary output WSS, and - transit paths connecting an output port of a secondary input WSS to an input port of a primary output WSS.