A data centre network, comprising: a first group of optical ports for connection to respective servers of a first group of servers (110a-1); a second group of optical ports (110b-1) for connection to respective servers of a second group of servers; a first lower passive optical routing element (120a-1) arranged to route optical communication signals between the first group of optical ports (110a-1) and a first lower optical communication path (130a-1); a second lower passive optical routing element (120b-1) arranged to route optical communication signals between the second group of optical ports (110b-1) and a second lower optical communication path (130b-1); an upper passive optical routing element arranged to: (i) route optical communication signals between the first lower optical communication path (130a-1) and an upper optical communication path, and (ii) route optical communication signals between the second lower optical communication path (130b-1) and the upper optical communication path, wherein the first lower optical communication path comprises: a first routing server to receive optical signals from the servers of the first group of servers (110a-1) via the first lower passive optical routing element (120a-1) and retransmit the signals at respective wavelengths based on respective destinations of the signals, and a first intermediate passive optical routing element associated with the first routing server to route signals from the first routing server to the upper passive optical routing element or a second intermediate passive optical routing element associated with a routing server other than the first routing server. a first group of optical ports for connection to respective servers of a first group of servers (110a-1); a second group of optical ports (110b-1) for connection to respective servers of a second group of servers; a first lower passive optical routing element (120a-1) arranged to route optical communication signals between the first group of optical ports (110a-1) and a first lower optical communication path (130a-1); a second lower passive optical routing element (120b-1) arranged to route optical communication signals between the second group of optical ports (110b-1) and a second lower optical communication path (130b-1); an upper passive optical routing element arranged to: (i) route optical communication signals between the first lower optical communication path (130a-1) and an upper optical communication path, and (ii) route optical communication signals between the second lower optical communication path (130b-1) and the upper optical communication path, wherein the first lower optical communication path comprises: a first routing server to receive optical signals from the servers of the first group of servers (110a-1) via the first lower passive optical routing element (120a-1) and retransmit the signals at respective wavelengths based on respective destinations of the signals, and a first intermediate passive optical routing element associated with the first routing server to route signals from the first routing server to the upper passive optical routing element or a second intermediate passive optical routing element associated with a routing server other than the first routing server. (i) route optical communication signals between the first lower optical communication path (130a-1) and an upper optical communication path, and (ii) route optical communication signals between the second lower optical communication path (130b-1) and the upper optical communication path, a first routing server to receive optical signals from the servers of the first group of servers (110a-1) via the first lower passive optical routing element (120a-1) and retransmit the signals at respective wavelengths based on respective destinations of the signals, and a first intermediate passive optical routing element associated with the first routing server to route signals from the first routing server to the upper passive optical routing element or a second intermediate passive optical routing element associated with a routing server other than the first routing server.