Flexible WDM network architecture

A node for use in an optical communications network, comprising:

• means having a plurality of input ports and an output port, for optically coupling the plurality of input ports to the output port, the optical coupling means being arranged to combine the intensity of a multi-channel input optical signal present at each of the plurality of input ports into a multi-channel output optical signal present at the output port;
• and
• add circuitry connected to at least one of the input ports, for selectively filtering the respective multi-channel input optical signal;
• wherein the optical frequency ranges of the filtered and unfiltered signals is selected to be mutually non-interfering.

A bidirectional node for use in an optical communications network, comprising:

• means having a plurality of bidirectional west ports and a plurality of bidirectional east ports, for optically coupling the east ports to the west ports and the west ports to the east ports;
• and
• bidirectional optical filtering circuitry connected to at least one of the west ports;
• wherein at least another one of the west ports and at least one of the east ports are connectable to a main optical path and wherein wavelengths of optical signals coupled to the main optical path by the filtering circuitry and the optical coupling means are selected to be substantially non-interfering with respect to wavelengths occupied by optical signals arriving at the node along the main optical path.

A node for use in a fiber optic network, comprising:

• a broadband optical coupler having at least one input port and a plurality of output ports, the optical coupler being characterized by a through loss LTHROUGH;
• means for measuring the optical power PIN—CURRENT of a multi-channel optical signal present at said input port of said coupler;
• means for amplifying said multi-channel optical signal in accordance with a gain;
• and
• a processing unit connected to the amplifying means, said processing unit being operable to receive control information comprising at least the output power level POUT—PREV of a previous node in the network and to set said gain equal to a function of POUT—PREV, PIN—CURRENT, LTHROUGH and a local target power level TLOCAL.

A method of maintaining a target loss around a ring having a plurality of interconnected nodes comprising couplers, each node being characterized by a respective through loss, the method comprising the steps of, at each current node located between a respective previous node and a respective next node:

• receiving control information comprising at least the output power level POUT—PREV of the previous node;
• measuring the optical power level PIN—CURRENT of an optical information signal received from said previous node;
• determining a gain as a function of POUT—PREV, PIN—CURRENT, the through loss of the current node and a local target power level TLOCAL;
• and
• amplifying the optical information signal in accordance with said gain.

A fiber optic network comprising:

• a hub;
• and
• a plurality N of nodes, the hub and the N nodes being connected in a drop path for receiving optical signals transmitted by the hub, wherein each node in a first group of N−1 nodes comprises a broadband coupler for accessing optical signals travelling in the drop path, each coupler having an associated through loss and branch loss;
• wherein the through loss of the coupler of each node in the first group has a through loss which increases with the distance between the node and the hub.

A node for connection to a first adjacent node and to a second adjacent node in a main optical traffic-carrying path, the node comprising:

• a plurality of first ports and a plurality of second ports, at least one first port being connectable to the first adjacent node and at least one second port being connectable to the second adjacent node;
• means for optically coupling the first ports to the second ports and the second ports to the first ports;
• filtering circuitry connected to at least one of another one of the first input ports and another one of the second input ports, the filtering circuitry adapted to add specified wavelengths to or drop specified wavelengths from the main optical path;
• wherein the wavelengths to be added or dropped by the filtering circuitry may be changed without interrupting optical traffic along the main optical path.