Testing and measurement in optical networks

An optical node may include a plurality of optical input components operable to receive a plurality of signals communicated in an optical network and a plurality of optical output components operable to transmit a plurality of signals to be communicated in the optical network. The optical node may also include at least one of: (a) an optical drop component coupled to the plurality of optical input components, the optical drop component operable to select a signal and select a portion of the signal of a particular selectable wavelength to drop to an associated item of test equipment from any one of the plurality of optical input components; and (b) an optical add component coupled to the plurality of optical output components and operable to selectively transmit copies of a selected one or more of a plurality of optical add signals to the plurality of optical output components, wherein the plurality of optical add signals includes a signal of a particular selectable wavelength communicated to the optical add component from an associated item of test equipment, and wherein each optical output component is operable to select a signal to communicate in the optical network received from any one of the optical add component and the plurality of optical input components.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to optical networks and, more particularly, to testing and measurement in optical networks.

BACKGROUND

Telecommunications systems, cable television systems and data communication networks use optical networks to rapidly convey large amounts of information between remote points. In an optical network, information is conveyed in the form of optical signals through optical fibers. Optical fibers comprise thin strands of glass capable of communicating the signals over long distances with very low loss of signal strength.

In recent years, the use of telecommunication services has increased dramatically. As the demand for telecommunication services continue to grow, various topologies of optical networks are emerging. For example, ring network topologies are evolving into mesh network topologies. Ring network topologies have several inefficiencies, such as information having to travel through each intermediate node before reaching the destination node and the fallibility of the entire ring network if there are multiple failures. Mesh network topologies provide several benefits over a ring network. While the network topology can be improved, existing optical node architectures are not efficient and effective in the testing and measurement of mesh network topologies (e.g., testing and measurement of latency, optical power, chromatic dispersion, polarization mode dispersion, optical-signal-to-noise ratio, etc.). For example, conventional optical node architectures are not scalable to support testing and measurement of the increased connectivity of optical nodes in mesh network topologies.

SUMMARY

In accordance with the present invention, disadvantages and problems associated with conventional optical node architectures in mesh network topologies may be reduced or eliminated.

According to one embodiment of the present disclosure, an optical node may include a plurality of optical input components operable to receive a plurality of signals communicated in an optical network and a plurality of optical output components operable to transmit a plurality of signals to be communicated in the optical network. The optical node may also include at least one of: (a) an optical drop component coupled to the plurality of optical input components, the optical drop component operable to select a signal and select a portion of the signal of a particular selectable wavelength to drop to an associated item of test equipment from any one of the plurality of optical input components; and (b) an optical add component coupled to the plurality of optical output components and operable to selectively transmit copies of a selected one or more of a plurality of optical add signals to the plurality of optical output components, wherein the plurality of optical add signals includes a signal of a particular selectable wavelength communicated to the optical add component from an associated item of test equipment, and wherein each optical output component is operable to select a signal to communicate in the optical network received from any one of the optical add component and the plurality of optical input components.

It will be understood that the various embodiments of the present invention may include some, all, or none of the enumerated technical advantages. In addition, other technical advantages of the present invention may be readily apparent to one skilled in the art from the figures, description and claims included herein.

DETAILED DESCRIPTION

FIG. 1is a block diagram illustrating a mesh optical network10. Mesh optical network10may include one or more optical fibers12operable to transport one or more optical signals communicated by components of mesh network10. The components of mesh network10, coupled together by optical fibers12, may include a plurality of nodes20. In the illustrated network10, each node20is coupled to four other nodes to create a mesh. However, any suitable configuration of any suitable number of optical nodes20may create mesh network10. For example, one or more nodes20in mesh network10may have less or more interconnections with other nodes20. Mesh network10may represent all or a portion of a short-haul metropolitan network, a long-haul inter-city network, and/or any other suitable network or combination of networks. Optical fibers12represent any suitable type of fiber. For example, the optical fiber coupling two nodes20may comprise, as appropriate, a single uni-directional fiber, a single bi-directional fiber, or a plurality of uni- or bi-directional fibers. More particularly, optical fiber12may include a Single-Mode Fiber (SMF), Enhanced Large Effective Area Fiber (E-LEAF), TrueWave® Reduced Slope (TW-RS) fiber, or other suitable fiber.

As mentioned above, mesh network10may be operable to communicate optical signals carrying information from one node20to one or more other nodes20. In particular, mesh network10may allow client devices (not shown) coupled to a node20to communicate with one or more other client devices coupled to one or more of the other nodes20.

Mesh network10may communicate information or “traffic” over optical fibers12. As used herein, “traffic” means information transmitted, stored, or sorted in mesh network10. Such traffic may comprise optical signals having at least one characteristic modulated to encode audio, video, textual, and/or any other suitable data. The data may also be real-time or non-real-time. Modulation may be based on phase shift keying (PSK), intensity modulation (IM), or other suitable methodologies. Additionally, the traffic communicated in mesh network10may be structured in any appropriate manner including, but not limited to, being structured in frames, packets, or an unstructured bit stream.

Traffic may be carried in a single optical signal that comprises a number of optical channels or wavelengths. The process of communicating traffic at multiple channels of a single optical signal is referred to in optics as wavelength division multiplexing (WDM). Dense wavelength division multiplexing (DWDM) refers to multiplexing a larger (denser) number of wavelengths, usually greater than forty, into a fiber. The optical signal includes different channels combined as a single signal on optical fiber12. WDM, DWDM, or other suitable multi-channel multiplexing techniques may be employed in optical network10to increase the aggregate bandwidth per optical fiber12. Without WDM or DWDM, the bandwidth in network would be limited to the bit rate of only one wavelength. With more bandwidth, optical networks are capable of transmitting greater amounts of information. For example, node20in mesh network10is operable to transmit and receive disparate channels using WDM, DWDM, or other suitable multi-channel multiplexing technique.

Nodes20in mesh network10may comprise any suitable nodes operable to transmit and receive traffic in a plurality of channels. In the illustrated embodiment, each node20may be operable to transmit traffic directly to four other nodes20and receive traffic directly from the four other nodes20. For example, as illustrated inFIG. 1, node20fmay be capable of receiving input signals A-D from four nodes20and forwarding output signals A′-D′ to the four nodes20. Each output signal, A′-D′, may include traffic in one or more channels from one or more of the input signals and/or traffic added at node20f. In particular embodiments, nodes20include multi-degree architectures that are scalable with mesh optical network10. Nodes20will be discussed in more detail below with respect toFIG. 2.

Nodes20in mesh network10may use any suitable route to transmit traffic to a destination node20. As discussed above, fibers12may each be a single uni-directional fiber, a single bi-directional fiber, or a plurality of uni- or bi-directional fibers. For example, node20ftransmitting traffic to node20lmay transmit the traffic over fibers12a,12b, and12cor, alternatively, over fibers12a,12d, and12e. Many other paths are possible. Therefore, if fiber12bfails, node20fmay continue to transmit traffic to node20lover an alternate path. Fibers12may fail or break for any number of reasons, such as being cut, being tampered with, or other occurrences. Furthermore, one or more nodes or other equipment in a path may fail. Mesh network10addresses the possibility of failing fibers and/or equipment by allowing flexibility in transmitting traffic between nodes20.

One challenge faced by those attempting to implement a mesh network topology rather than a ring network topology is that existing optical node architectures for a mesh network topology do not allow for efficient testing and measurement within a network. Particular current node architectures include photonic cross-connect architectures and multi-degree reconfigurable optical add/drop multiplexer (ROADM) architectures based on Wavelength Selective Switches (WSS). A limitation of the traditional ROADM nodes is that these nodes have only local add/drop capability for each degree or wavelength. Accordingly, exhaustive testing and measurement at a node using current node architectures would require test equipment to be coupled to each add-drop port of the node. For these reasons, a conventional ROADM node and conventional testing and measurement approaches require the use of multiple items of test equipment or the sequential disconnection and reconnection of test equipment to add-drop ports.FIG. 2depicts a node architecture that interoperates with the increased flexibility of mesh network10and overcomes and/or reduces these disadvantages.

Modifications, additions, or omissions may be made to mesh network10without departing from the scope of the disclosure. The components and elements of mesh network10described may be integrated or separated according to particular needs. Moreover, the operations of mesh network10may be performed by more, fewer, or other components.

FIG. 2is a block diagram illustrating an example node20in mesh network10ofFIG. 1with an improved architecture for testing and measurement according to a particular embodiment of the present invention. Node20addresses the challenges discussed above with respect to testing and measurement in conventional node architectures in mesh network10.

In the illustrated embodiment, node20includes splitters22and26, WSSs24,28,36and38, multiplexers30, demultiplexers32, transponders34, and test equipment40coupled to form an architecture for testing and measurement. Splitters22and26represent optical couplers or any other suitable optical component operable to split an optical signal into multiple copies of the optical signal and transmit the copies to other components within node20. In the illustrated embodiment, each splitter22may receive an input signal from mesh network10and each splitter26may receive an optical signal added at node20. Splitters22and26may be configured to receive traffic over a particular fiber and split the received traffic into multiple copies. For example, splitters22may be configured to receive traffic over input fibers21and to split the traffic into P copies. Splitters26are configured to receive traffic from associated multiplexers30and split the traffic into n copies. Multiplexers30represent any suitable optical component operable to receive and combine add traffic in disparate optical channels, transmitted by associated transponders34from one or more client devices, into a WDM or other optical signal for communication to splitter26.

Splitters26may be included on the add side of node20to support full connectivity for traffic being added by node20. Having splitters26on the add side of node20supports the flexibility of transmission desired in mesh network10. Each splitter26may receive traffic from a multiplexer30and may be configured to pass a copy of the traffic to each WSS24over a fiber, port, or other connection. During operation, splitters26may pass traffic to WSSs24to be transmitted over another fiber21. Therefore, traffic may continue to be added from transponders34even if a fiber21fails. For example, if traffic is previously transmitted over fiber21abut fiber21afails, splitter26amay forward traffic to be transmitted over another operable fiber, such as fiber21c.

WSSs24,28,36and38may comprise any suitable optical components operable to receive multiple optical signals and output a portion or all of one or more of the received signals. In the illustrated embodiment, WSSs24may receive copies of one or more add signals from splitters26, WSSs28may receive copies of one or more input signals from splitters22, and WSS36may receive copies of one or more input signals from transponders34and test equipment40. WSS38may not copy an input signal, but may selectively transmit particular channels of the input signal to one or more of its outputs.

WSSs28may be included on the drop side of node20to support full connectivity for traffic being dropped at node20. Each WSS28may be configured to pass traffic received over a particular fiber21to an associated demultiplexer32, except for WSS28awhich may be configured to pass traffic received over fiber21ato WSS38. During operation, WSSs28other than WSS28amay be reconfigured to pass traffic from another fiber to the associated demultiplexers32(and then to associated transponders34), and/or WSS28amay be reconfigured to pass traffic from another fiber to its associated WSS38. Therefore, any transponder34may receive traffic from any input fiber. In addition, test equipment40may receive traffic from any input fiber, which supports the testing and measurement flexibility desired in mesh network10. Demultiplexers32represent any demultiplexers or other optical component operable to separate the disparate channels of WDM, DWDM, or other suitable multi-channel optical signals. Demultiplexers32may be operable to receive an optical signal carrying a plurality of multiplexed channels from WSS28, demultiplex the disparate channels in the optical signal, and pass the disparate channels to associated transponders34(for communication to one or more client devices). Transponders34represent any suitable optical components operable to transmit and/or receive traffic on a channel. Transponders34may communicate traffic to and from client devices. Test equipment40may represent any suitable optical components operable to transmit and/or receive traffic on a channel for testing or measurement purposes (e.g., to analyze a received signal and/or transmit a signal to be tested, measured or otherwise characterized).

In operation, each splitter22in node20may receive a WDM or other multi-channel input optical signal from mesh network10. Splitter22may split the received input signal into several copies. A copy of the input signal may be transmitted to each WSS24(where some or all of the channels may be passed through node20to mesh network10) and transmitted to each WSS28(where some or all of the channels may be dropped at node20). WSS24may perform signal (wavelength) blocking and/or filtering. For example, each WSS24may be configured to select one or more of the signals (wavelengths) received from splitters22(pass-through) and/or one or more of the signals (wavelengths) received from splitters26(add) for communication to network10. Each WSS28(other than WSS28a) may be configured to drop traffic received from a particular input fiber21to an associated demultiplexer32. WSS28amay be configured to drop traffic received from particular input fiber21ato associated WSS38. Each demultiplexer32may receive the traffic, separate the traffic into the constituent channels, and drop each channel to its associated transponder34. WSS38may receive traffic transmitted from WSS28a, and selectively transmit particular channels of the traffic to their associated transponders34and/or test equipment40. For example, splitter22amay receive traffic over input fiber21a. Splitter22amay copy the traffic and transmit a copy to each WSS24and each WSS28. In the illustrated embodiment, WSS28amay be configured to transmit traffic received over input fiber21ato WSS38and WSSs28other than WSS28amay be configured to transmit traffic received over input fiber21ato a demultiplexer32. Accordingly, each WSS28may receive copies of each input signal, but may select the signal received over fiber21afor transmission to a particular demultiplexer32. Such multiplexer may transmit the traffic to transponders34for communication to one or more client devices. In addition, WSS28amay receive copies of each input signal, but may selects the signal received over fiber21afor transmission to WSS38. WSS38may selectively transmit the traffic to transponders34for communication to one or more client devices and/or test equipment40for testing, measurement, or analysis.

As mentioned above, node20may also add traffic to mesh network10. Transponders34may transmit such traffic to an associated multiplexer30or WSS36and/or test equipment40may transmit test traffic to WSS36, and WSS36and each multiplexer30may combine traffic in multiple channels into a WDM signal and transmit the WDM signal to an associated splitter26over a fiber21. Each splitter26may create copies of a signal and transmit a copy to each WSS24. As mentioned above, each WSS24may be configured to transmit a particular received signal over a particular output fiber21. WSS24may forward the selected signal to mesh network10over the particular fiber21.

The architecture of node20may also improve testing and measurement flexibility by permitting the addition of test signals or test traffic to node20from test equipment40. For example, test equipment40may transmit a test signal or test traffic to WSS36. WSS36may transmit such signal or traffic (either along or combined with other signals from transponders34associated with WSS36) to splitter26avia fiber21a. Splitter26amay copy the test signal and provide a copy to each WSS24.

Modifications, additions, or omissions may be made to node20illustrated inFIG. 2. For example, multiplexers30and demultiplexers32may be replaced with WSSs for dynamic optical add/drop multiplexing capability. As another example, splitters22and26may be replaced with WSSs. Node20may include any suitable number of splitters22and26and WSSs24and28to handle any suitable number of degrees of node20. As yet another example, splitters22and26and WSSs24and28may be a hierarchical combination of devices to provide a higher number of splitter or WSS inputs or outputs to enable node scalability to higher degrees. For example, splitters22and26may be a combination of cascaded couplers or a combination of a coupler and two or more WSSs arranged hierarchically. As another example, WSSs24and28may be a combination of a coupler and two or more WSSs arranged hierarchically or a combination of cascaded WSSs. Moreover, the operations of node20described may be performed by more, fewer, or other components without departing from the scope of the present disclosure.

FIG. 3is a block diagram illustrating another example node20in the mesh network10ofFIG. 1with an improved architecture for testing and measurement according to a particular embodiment of the present invention. Node20ofFIG. 3is similar to node20ofFIG. 2, except that the add/drop components of node20ofFIG. 2are replaced with multiplexers42, demultiplexers44, and an optical cross-connect switch (OXC)66. Multiplexers42may be identical or similar to multiplexers30ofFIG. 2, and/or demultiplexers44may be identical or similar to demultiplexers32ofFIG. 2. OXC66can be implemented as a single large switch, multiple small switches or any other suitable implementation. OXC66may be configured to forward traffic from any demultiplexer44to transponders34and/or test equipment40, and from transponders34and/or test equipment40to any multiplexer42. OXC66may provide for dynamic reconfigurability such that signals from different channels and/or different degrees may be communicated to and/or from test equipment40. For example, OXC66may allow remote configuration of the pattern of connectivity between splitters22and transponders34/test equipment40, and the pattern of connectivity between transponders34/test equipment40and WSSs24.

The systems and methods described above may provide advantages over traditional approaches to testing in measurement in networks. For example, the approach described above allows for coupling test and measurement equipment to add and drop ports of a node which are “colorless” (e.g., any wavelength may be routed to or from the add or drop port coupled to the test equipment) and “steerable” (e.g., signals to or from any degree may be routed to or from the add or drop port coupled to the test equipment). This approach adds flexibility in testing and measurement as it allows sharing of the test equipment at a node among all wavelengths and degrees to be tested without the need to physically move or reconnect the test equipment, thus also improving the ability to conduct tests and measurements using remote management and control.

The approach described above also allows for in-service testing and measurement of all available channels and lightpaths for a given source-destination node pair. For example, the methods and systems described above may permit in-service testing and measurement of traffic among all available channels (e.g., all available wavelengths) and lightpaths (e.g., the path defined by fibers12a,12b, and12c, the path defined by fibers12a,12d, and12e, and all other suitable paths) between node20fand node20ldepicted inFIG. 1. In certain embodiments testing, measurement and/or characterization of lightpaths may be performed prior to activating traffic service for the lightpaths. Such tests and measurements may be applied to numerous applications. For example, test and measurement results may be stored in a database, and such data may be used to aid in the establishment of service in response to a request for service between two nodes (e.g., simplifying a path search or validating a path). Such results may also be used to assist in the operation of digital coherent receivers, troubleshooting of an optical network, or any other suitable use.

As a particular example, a network administrator or other person may desire to measure latency, chromatic dispersion, polarization mode dispersion, optical-signal-to-noise-ratio and/or one or more other characteristics of lightpaths between node20aand node20pdepicted inFIG. 1. In such a case, an item of test equipment (e.g., test equipment40) may be coupled to an add port of node20aand another item of test equipment may be coupled to a drop port of node20p, as shown inFIG. 2and/orFIG. 3. Various available lightpaths (e.g.,20a-20b-20c-20d-20h-20l-20p,20a-20e-20i-20m-20n-20o-20p,20a-20b-20f-20j-20k-20o-20p, or any other suitable lightpath between node20aand node20p) may be established one at a time for one or more available wavelengths via Generalized Multi-protocol Label Switching (GMPLS) control plane signaling or other suitable mechanism for setting up a light path. For each wavelength tested and/or measured, test equipment of node20amay transmit a signal at the wavelength to an add port of node20awhich may then be routed through the established lightpath and received at test equipment of node20pcoupled to a drop port of node20p. Such tests and/or measurements may be performed for each desired path and/or wavelength (e.g., to calculate the chromatic dispersion of each wavelength through each path). In certain embodiments, items of test equipment may also be placed at intermediate nodes within a lightpath to perform intermediate tests, measurements, or characterization.