An optical node and method

Abstract

The disclosure relates to an optical node, and a corresponding method for operating the optical node. The optical node comprises a photodiode, a placeholder signal generator, a NxM optical distribution device, and a wavelength selective switch (WSS). The photodiode is configured to determine if an optical signal is received by the NxM optical distribution device from a signal source. The NxM optical distribution device is configured to receive a placeholder optical signal from a placeholder signal generator and provide the placeholder optical signal to a first input of the WSS if the photodiode determines that the optical signal is not received by the NxM optical distribution device.

Description

[0001] AN OPTICAL NODE AND METHOD

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to an optical node. The disclosure proposes an optical node, and a corresponding method for operating the optical node. The optical node comprises a wavelength selective switch and additional components.

[0004] BACKGROUND

[0005] A link cut or failure between two nodes can result in partial optical power loss on all optical multiplex sections (OMSes) downstream of the node located downstream of the failure. Such power loss induces perturbation on the existing services, for example, due to the Kerr effect and the Stimulated Raman Scattering (SRS) effect. SRS is a physical effect in optical fibers, whereby optical power is transferred from the shorter to the longer wavelengths. The Kerr effect is a nonlinear optical effect in fibers where the refractive index increases with optical power, causing intensity-dependent phase shifts.

[0006] An optical placeholder signal generator is a broadband noise emitting device, i.e., it emits optical power on any channels that can be used in the system (e.g., on any link that starts at the considered node).

[0007] SUMMARY

[0008] In view of the above, an objective of this disclosure is to improve the efficiency, flexibility, and duration of recovering from signal disruptions, for example, link failures. Another objective is to keep the optical power on any egress link of an optical node constant. Another objective is to reduce the transient time (between failure and recovery) such that it does not exceed the ms timescale, for example, does not exceed 100 ms.

[0009] This and other objectives are achieved by the solutions of this disclosure as described in the independent claims. Advantageous implementations are further described in the dependent claims.

[0010] The solution of this disclosure is based on the following considerations.

[0011] If a wavelength selective switch (WSS) of an optical node receives only some channels from other optical nodes or add blocks, the complete spectrum should be powered up on the outgoing link. An optical placeholder signal source can emit power on all channels. The WSS may select the missing channels to be sent on the outgoing link from the optical placeholder signal and redirect those to the outgoing link.

[0012] Upon the failure of a link upstream of the considered optical node, the optical power on the link between another WSS and the WSS vanishes and one or more channels may no longer be powered up on the right link. To avoid this, when the failure is detected by the considered node, for example, with an optical channel monitor (OCM), a photodiode, or through control plane information, the WSS could be reconfigured to redirect the channels from the placeholder signal generator to the outgoing link. The WSS reconfiguration may be in a timescale of seconds, for example, in a range of 1 s to 10 s, and during the reconfiguration time, the power on the outgoing link varies, which may temporarily impact other services downstream of the considered node.

[0013] A first aspect of this disclosure provides an optical node comprising a photodiode, a placeholder signal generator, a NxM optical distribution device having N inputs and M outputs, and a WSS having a plurality of inputs, wherein N and M are positive integers and N is larger than M, wherein the NxM optical distribution device is optically connectable to a signal source, optically connected to the placeholder signal generator, and optically connected to a first input of the plurality of inputs of the WSS, wherein the photodiode is configured to determine if an optical signal is received by the NxM optical distribution device from the signal source, wherein the NxM optical distribution device is configured to: receive a placeholder optical signal from the placeholder signal generator and provide the placeholder optical signal to the first input of the WSS, for example, through the first output of the NxM optical distribution device, if the photodiode determines that the optical signal is not received by the NxM optical distribution device.

[0014] The optical node may be configured to provide the placeholder optical signal to the first input of the WSS by, for example, switching the input to output connections of the NxM optical distribution device. For example, the optical signal may be redirected from a particular input to a particular output of the NxM optical distribution device.

[0015] The photodiode may measure an optical power of the optical signal or determine that said optical power is zero or below some predefined threshold before said optical signal is received by the WSS. For example, the photodiode may be located in between the WSS and the NxM optical distribution device or at an input of the NxM optical distribution device.

[0016] The photodiode may be configured to directly or indirectly determine if an optical signal is received by the NxM optical distribution device from the signal source. For example, the photodiode may be configured to measure an optical power at a first output of the NxM optical distribution device or at a first input of the WSS. If the NxM switch is configured to provide the signals from the signal source to the first input of the WSS, then the photodiode can indirectly determine if the optical signal is received by the NxM optical distribution device from the signal source. Alternatively, the photodiode may be configured to measure an optical power at a second input of the NxM optical distribution device. Thus, the photodiode may directly determine if the optical signal is received by the NxM optical distribution device from the signal source.

[0017] The optical node may comprise a controller. The controller may be configured to determine if the optical signal is received by the NxM optical distribution device from the signal source by using the photodiode. The controller may be configured to modify the input to output connections of the NxM optical distribution device based on a measurement of the photodiode such that, for example, the optical placeholder signal is provided to the first input of the WSS if the controller and / or photodiode determine that the optical signal is not received by the NxM optical distribution device.

[0018] If the photodiode is located at the first input of the WSS and if there previously was a link failure such that the placeholder signal is provided through the NxM optical distribution device to the first input of the WSS, then the photodiode may only receive the placeholder signal and may not determine if the optical signal is received again by the NxM optical distribution device, for example, if the link is corrected again. The controller may determine or an operator may manually inform the optical node of the link recovery and instruct the NxM optical distribution device to switch back to the nominal state in which the NxM optical distribution device provides the optical signal to the first input of the WSS. In said nominal state the photodiode can determine if the optical signal is received by the NxM optical distribution device.

[0019] The optical distribution device may be a NxM optical switch.

[0020] The signal source may be another optical node, for example, a WSS of the other optical node.

[0021] The NxM optical distribution device may comprise one or more optical distribution devices. For example, the NxM optical distribution device may comprise one or more IxM” optical distribution devices, one or more N’xM’ optical distribution devices, and one or more other NxM optical distribution devices as described below. It will be apparent to those skilled in the art that said other NxM optical distribution devices would comprise N”’ inputs and M”’ outputs instead if said other NxM optical distribution devices are included in the NxM optical distribution device.

[0022] A series of fast switches can be included to the optical node to enable fast filling of the egress link with optical power on any sub-band of the optical spectrum, to cover any failure scenario.

[0023] The optical placeholder signal may, for example, be amplified spontaneous emission noise.

[0024] Existing broadband placeholder signal sources may be used rather than discrete light sources to avoid spectrum waste. The placeholder signal may be provided to the WSS at two or more inputs simultaneously. Thus, the optical node can recover from a link failure faster than it takes the WSS to reconfigure, as reconfiguring the WSS to shape the placeholder signal to the right spectrum using the second input of the WSS may be slower. Adding the NxM optical distribution device, for example, a fast switch, may enable the WSS to be keep its configuration during the link recovery.

[0025] The optical node can be protected against intra-node link failures.

[0026] In an implementation form of the first aspect, the NxM optical distribution device is further configured to: not provide the placeholder optical signal to the first input of the plurality of inputs of the WSS if the photodiode determines that the optical signal is received by the NxM optical distribution device. Thus, the first input of WSS does not receive the placeholder optical signal and can receive the optical signal if no link failure occurs.

[0027] In an implementation form of the first aspect, the NxM optical distribution device is further configured to: provide the optical signal to the first input of the plurality of inputs of the WSS if the photodiode determines that the optical signal is received by the NxM optical distribution device.

[0028] In a further implementation form of the first aspect, the NxM optical distribution device is optically connected to the placeholder signal generator through a first input of the N inputs, wherein the NxM optical distribution device is optically connected to the first input of the WSS through a first output of the M outputs, wherein the NxM optical distribution device is optically connectable to the signal source through a second input of the N inputs.

[0029] In a further implementation form of the first aspect, a second input of the plurality of inputs of the WSS is optically connected to the placeholder signal generator, and / or wherein the WSS is configured to receive the optical placeholder signal from the placeholder signal generator through the second input of the WSS. Thus, the WSS can receive the placeholder optical signal directly through the second input of the WSS from the placeholder signal generator, and indirectly through the NxM optical distribution device and the first input of the WSS. The NxM optical switch may enable faster and more efficient switching than the WSS.

[0030] In a further implementation form of the first aspect, N is larger than 2 and M is larger than 1, wherein the NxM optical distribution device is optically connectable to another signal source through a third input of the N inputs. For example, the optical node may comprise one NxM switch optically connected to the WSS, wherein the NxM switch is optically connected to a plurality of signal sources and is configured to route signals from the plurality of signal sources and / or the placeholder signal generator to at least some of the inputs of the plurality of inputs of the WSS.

[0031] In a further implementation form of the first aspect, the optical node further comprises a further photodiode and a N’xM’ optical distribution device having N’ inputs and M’ outputs, wherein N’ and M’ are positive integers and N’ is larger than M’, wherein the N’xM’ optical distribution device is optically connectable to another signal source, optically connected to the placeholder signal generator, and optically connected to a third input of the plurality of inputs of the WSS, wherein the further photodiode is configured to determine if an optical signal, for example, a further optical signal, is received by the N’xM’ optical distribution device from the other signal source, wherein the N’xM’ optical distribution device is configured to: receive a placeholder optical signal from the placeholder signal generator and provide the placeholder optical signal to the third input of the WSS if the further photodiode determines that the optical signal is not received by the N’xM’ optical distribution device. The other signal source may be an optical node. The controller may be configured to modify the input to output connections of the other N’xM’ optical distribution device based on a measurement of the further photodiode.

[0032] In a further implementation form of the first aspect, the optical node further comprises a IxM” optical distribution device having an input andM” outputs, wherein M” is an integer larger than 1, wherein an output of M” outputs of the IxM” optical distribution device is optically connected to the NxM optical distribution device, wherein the IxM’ ’ optical distribution device or the NxM optical distribution device is an optical switch, wherein the IxM” optical distribution device is configured to: receive the optical placeholder signal from the placeholder signal generator through the input of the IxM” optical distribution device, provide the optical placeholder signal through the output of the IxM” optical distribution device to the NxM optical distribution device, for example, the first input of the NxM optical distribution device.

[0033] The controller may be configured to modify the input to output connections of the IxM” optical distribution device based on a measurement of the photodiode such that, for example, the optical placeholder signal is provided to the NxM optical distribution device if the controller and / or photodiode determine that the optical signal is not received by the NxM optical distribution device. Thus, the optical placeholder signal may be efficiently provided to the first input or third input of the WSS if a link failure occurs.

[0034] In a further implementation form of the first aspect, at least one of: the IxM” optical distribution device is a IxM” optical coupler or a IxM” optical switch, the NxM optical distribution device is a NxM optical coupler or a NxM optical switch, and the N’xM’ optical distribution device is a N’xM’ optical coupler or a N’xM’ optical switch. The optical node may comprise passive and / or active optical distribution devices.

[0035] In a further implementation form of the first aspect, the other NxM optical distribution device is a NxM optical coupler or a NxM optical switch. The IxM” optical switch may be a IxM” WSS. The NxM optical switch may be a NxM WSS. The other NxM optical switch may be a NxM WSS. The N’xM’ optical switch may be a N’xM’ WSS.

[0036] In a further implementation form of the first aspect, the IxM” optical distribution device is a IxM” optical switch, wherein the IxM” optical distribution device is configured to provide the optical placeholder signal to the NxM optical distribution device if the photodiode determines that the optical signal is not received by the NxM optical distribution device, and / or wherein the IxM” optical distribution device is configured to not provide the optical placeholder signal to the NxM optical distribution device if the photodiode determines that the optical signal is received by the NxM optical distribution device.

[0037] The IxM” optical distribution device may further comprise an output for completely attenuating the placeholder optical signal. For example, if a controller determines that the placeholder optical signal is not required to be provided through the NxM optical distribution device to the first input of the WSS, then the IxM” optical distribution device may be configured to completely attenuate the placeholder optical signal.

[0038] In a further implementation form of the first aspect, another output of the M” outputs of the IxM” optical distribution device is optically connected to the N’xM’ switch, wherein the IxM” optical distribution device is further configured to: provide the optical placeholder signal through the other output of the IxM” optical distribution device to the N’xM’ optical distribution device, for example, if the further photodiode determines that the optical signal is not received by the N’xM’ optical distribution device.

[0039] In a further implementation form of the first aspect, wherein the lxM” optical distribution device is configured to provide the optical placeholder signal to the N’xM’ optical distribution device if the further photodiode determines that the optical signal is not received by the N’xM’ optical distribution device, and / or wherein the lxM” optical distribution device is configured to not provide the optical placeholder signal to the N’xM’ optical distribution device if the further photodiode determines that the optical signal is received by the N’xM’ optical distribution device.

[0040] In a further implementation form of the first aspect, the WSS comprises, for example, only, M”+l or M” inputs.

[0041] The WSS may only have the plurality of inputs. The WSS may have one more input than the lxM” optical distribution device has outputs. Alternately, the WSS may have the same number of inputs as the lxM” optical distribution device has outputs. Alternatively, the lxM” optical distribution device may be considered to have M”-l outputs instead, wherein the WSS may have M” or M”-l inputs.

[0042] In a further implementation form of the first aspect, N is 2 and M is 1 , and / or wherein N’ is 2 and M’ is 1. The optical node may comprise a plurality 2x1 optical distribution devices, for example, switches. Each optical distribution device of the plurality of 2x1 optical distribution devices may be optically connected with a respective output to a respective input of the plurality of inputs of the WSS.

[0043] In a further implementation form of the first aspect, the optical node further comprises another WSS having a plurality of inputs, another NxM optical distribution device having N inputs and M outputs, and another photodiode, wherein the other NxM optical distribution device is optically connectable to the signal source, optically connected to the placeholder signal generator, and optically connected to a first input of the plurality of inputs of the other WSS, wherein the other photodiode is configured to determine if another optical signal is received by the other NxM optical distribution device from the signal source, wherein the optical signal comprises a first frequency band and the other optical signal comprises a second frequency band, wherein the other NxM optical distribution device is configured to: receive the placeholder optical signal from the placeholder signal generator and provide the placeholder optical signal to the first input of the other WSS if the other photodiode determines that the other optical signal is not received by the other NxM optical distribution device. The controller may be configured to modify the input to output connections of the other NxM optical distribution device based on a measurement of the other photodiode.

[0044] In a further implementation form of the first aspect, another output of the M” outputs of the lxM” optical distribution device is optically connected to the other NxM optical distribution device, wherein the lxM” optical distribution device is further configured to: provide the optical placeholder signal through the other output of the lxM” optical distribution device to the other NxM optical distribution device.

[0045] In a further implementation form of the first aspect, the placeholder signal generator comprises a first placeholder signal generator configured to generate a first frequency band of the optical placeholder signal and a second placeholder signal generator configured to generate a second frequency band of the optical placeholder signal, wherein the placeholder signal generator is configured to combine the first frequency band of the optical placeholder signal and the second frequency band of the optical placeholder signal to form the optical placeholder signal.

[0046] In a further implementation form of the first aspect, the photodiode is configured to measure if the optical signal is received by the NxM optical distribution device from the signal source at an input of the NxM optical distribution device, or wherein wherein the photodiode is configured to measure if the optical signal is received by the NxM optical distribution device from the signal source at the first input of the WSS.

[0047] In a further implementation form of the first aspect, the further photodiode is configured to measure if the optical signal is received by the N’xM’ optical distribution device from the other signal source at an input of the N’xM’ optical distribution device, or wherein the further photodiode is configured to measure if the optical signal is received by the N’xM’ optical distribution device from the other signal source at the third input of the WSS.

[0048] In a further implementation form of the first aspect, the other photodiode is configured to measure if the optical signal is received by the other NxM optical distribution device from the signal source at an input of the other NxM optical distribution device, or wherein the other photodiode is configured to measure if the other optical signal is received by the NxM optical distribution device from the signal source at the third input of the WSS.

[0049] A second aspect of this disclosure provides a method of operating an optical node, the optical node comprising a photodiode, a placeholder signal generator, a NxM optical distribution device having N inputs and M outputs, and a WSS having a plurality of inputs, wherein N and M are positive integers and N is larger than M, wherein the NxM optical distribution device is optically connectable to a signal source, optically connected to the placeholder signal generator, and optically connected to a first input of the plurality of inputs of the WSS, wherein the method comprises: determining, with the photodiode, if an optical signal is received by the NxM optical distribution device from the signal source, receiving, with the NxM optical distribution device, a placeholder optical signal from the placeholder signal generator and providing the placeholder optical signal to the first input of the WSS if the photodiode determines that the optical signal is not received by the NxM optical distribution device.

[0050] The method of the second aspect may have implementation forms that correspond to the implementation forms of the optical node of the first aspect. The method of the second aspect and its implementation forms achieve the advantages and effects described above for the optical node of the first aspect and its respective implementation forms.

[0051] Further, in this disclosure, a first element and a second element are considered to be different elements, if not explicitly mentioned otherwise.

[0052] Further, in this disclosure, an element, another element, and a further element are considered to be different elements, if not explicitly mentioned otherwise.

[0053] Further, in this disclosure, terms such as "first" and "second" are merely intended for a purpose of description, and shall not be understood as an indication or implication of relative importance.

[0054] Further, in this disclosure, the term “link” and “OMS” may be used interchangeably.

[0055] Further, in this disclosure, the term “optical distribution device” may refer to an “active routing element”, for example, an optical switch or WSS, or a “passive routing element”, for example, an optical coupler. It has to be noted that all devices, elements, units and means described in the disclosure could be implemented in the software or hardware elements or any kind of combination thereof. All steps which are performed by the various entities described in the disclosure as well as the functionalities described to be performed by the various entities are intended to mean that the respective entity is adapted to or configured to perform the respective steps and functionalities.

[0056] Even if, in the following description of specific embodiments, a specific functionality or step to be performed by external entities is not reflected in the description of a specific detailed element of that entity which performs that specific step or functionality, it should be clear for a skilled person that these methods and functionalities can be implemented in respective software or hardware elements, or any kind of combination thereof.

[0057] BRIEF DESCRIPTION OF DRAWINGS

[0058] The above described aspects and implementation forms will be explained in the following description of specific embodiments in relation to the enclosed drawings, in which:

[0059] FIG. 1 shows an optical node according to this disclosure.

[0060] FIG. 2 shows an exemplary optical node according to this disclosure.

[0061] FIG. 3 shows an exemplary optical node according to this disclosure.

[0062] FIG. 4 shows exemplary components of an optical node according to this disclosure.

[0063] FIG. 5 shows an optical node according to this disclosure comprising a single-band placeholder signal generator and signal-band WSS or a multi-band placeholder signal generator and a multi-band band WSS.

[0064] FIG. 6 shows an optical node according to this disclosure comprising two parallel single-band placeholder signal generators and a multi-band WSS.

[0065] FIG. 7 shows an optical node according to this disclosure comprising a multi-band placeholder signal generator and two single-band WSSes.

[0066] FIG. 8 shows a method according to this disclosure.

[0067] DETAILED DESCRIPTION OF EMBODIMENTS

[0068] FIG. 1 shows an optical node 100 according to this disclosure. The optical node may be an integrated optical node.

[0069] The optical node 100 comprises a photodiode 101 , a placeholder signal generator 102, a NxM optical distribution device 103 having N inputs and M outputs, and a WSS 104 having a plurality of inputs 107, wherein N and M are positive integers and N is larger than M. The NxM optical distribution device 103 may be a NxM optical switch.

[0070] An optical placeholder signal generator 102 may, for example, be a power filling device or a noise loader. For example, the optical placeholder signal generator 102 may be a broadband noise emitting device that emits optical power on any channels that can be used by the optical node 100. The NxM optical distribution device 103 is optically connectable to a signal source 105, optically connected to the placeholder signal generator 102, and optically connected to a first input 107a of the plurality of inputs 107 of the WSS 104. The signal source may be another optical node. The NxM optical distribution device 103 may or may not be directly optically connected to the placeholder signal generator 102.

[0071] The photodiode 101 is configured to determine if an optical signal 108 is received by the NxM optical distribution device 103 from the signal source 105.

[0072] If the photodiode 101 determines that the optical signal 108 is not received by the NxM optical distribution device 103, then the NxM optical distribution device 103 is configured to receive a placeholder optical signal 108 from the placeholder signal generator 102 and provide the placeholder optical signal 108 to the first input 107a of the WSS 104, which is indicated by the dashed arrows in FIG. 1.

[0073] The NxM optical distribution device 103 may or may not be configured to receive the placeholder optical signal 108 from the placeholder signal generator 102 if the photodiode 101 determines that the optical signal 108 is received by the NxM optical distribution device 103. For example, if the NxM optical distribution device 103 receives the placeholder optical signal 109, the NxM optical distribution device 103 may route the placeholder optical signal 109 such that it is attenuated and route the optical signal 108 such that it is provided to the first input of the WSS 104. The NxM optical distribution device 103 may be configured to not provide the placeholder optical signal 109 to the first input of the WSS 104 if the photodiode 101 determines that the optical signal 108 is received by the NxM optical distribution device 103. Alternatively or additionally, The NxM optical distribution device 103 may be configured to not receive the placeholder optical signal 109 if the photodiode 101 determines that the optical signal 108 is received by the NxM optical distribution device 103.

[0074] An optical placeholder signal in optical communication is a controlled optical signal introduced into a transmission path to maintain channel integrity, enable continuity, or facilitate monitoring without carrying actual data. This signal may be used to ensure network elements like WSSs or other optical components continue functioning or to aid in diagnostics.

[0075] The optical placeholder signal may comprise a respective wavelength for each channel of the WSS.

[0076] The optical node 100 may use existing broadband sources for the placeholder optical signal 109.

[0077] The optical node 100 may comprise fast optical switching elements, for example, the NxM optical distribution device 103 may be a fast optical switch. In this disclosure “fast” switching elements may refer to a recovery time of one of: less than 100 ms less than 10 ms, and less than 1 ms.

[0078] The optical node 100 may use local decisions / determinations to improve recovery time. For example, using only intra-node mechanisms, from power loss detection to optical signal 108 or optical placeholder signal 109 redirection may improve recovery time.

[0079] In an optical node 100, for example, a Reconfigurable Optical Add-Drop Multiplexer (ROADM), WSSs 104 are used to direct specific wavelengths from a specific (ingress) degree, to a specific (egress) degree, which may be referred to as wavelength routing. Some of the degrees may be dedicated to add / drop services, e.g., the node is the first / last one of the route of the service.

[0080] The approach of the present disclosure may apply to any node where an optical signal source 105 is used for egress link power loading, and a WSS 104is used as a wavelength-routing element before an egress link. This may cover the so-called broadcast- and-select (where the optical signal 108 enters the optical node 100 through a power splitter) or route-and-select optical routing nodes (where the optical signal 108 enters the optical node 100 through a WSS).

[0081] Optical power on any egress link of the optical node may remain constant throughout a particular band of a particular channel associated with the egress link.

[0082] FIG. 2 shows an exemplary optical node 100 according to this disclosure.

[0083] The optical node 100 may comprise a lxM” optical distribution device 110, a NxM optical distribution device 103, aN’xM’ optical distribution device 111, a photodiode 101, a further photodiode 114, a WSS 104, and an optical placeholder signal generator 102. Further, the optical node may comprise an optical channel monitor (OCM) at an output of the WSS 104.

[0084] For example, the NxM optical distribution device 103 may be a 2x1 optical distribution device 103, and the N’xM’ optical distribution device 111 may be a 2x1 optical distribution device 111, as shown in FIG. 2.

[0085] The NxM optical distribution device 103 may be optically connected, for example, directly optically connected, to a first input 107a of a plurality of inputs 107 of the WSS 104. The N’xM’ optical distribution device 103 may be optically connected, for example, directly optically connected, to a third input 107c of the plurality of inputs 107 of the WSS 104. The optical placeholder signal generator 102 may be optically connected, for example, directly optically connected, to a second input 107b of the plurality of inputs 107 of the WSS 104.

[0086] The photodiode 101 may be located and / or configured to measure an optical power at the first input 107a of the WSS 104. The further photodiode 114 may be located and / or configured to measure an optical power at the third input 107c of the WSS 104.

[0087] The NxM optical distribution device 103 may be configured to receive an optical signal 108 from a signal source 105. The N’xM’ optical distribution device 111 may be configured to receive an optical signal 108, for example, a further optical signal, from another signal source 106.

[0088] In this example, the WSS 104 comprises M” inputs 107. The second input 107b may be dedicated / configured to receive an optical placeholder signal 109 from the placeholder signal generator 102, and the other inputs 107a, 107c of the plurality of inputs 107 may be dedicated / configured to receive to one or more signal sources 105, 106, for example, one or more other optical nodes.

[0089] The optical node 100 may comprise a power splitter, e.g., setting a 50% / 50% ratio or another ratio, directly optically connected to the optical placeholder signal generator 102. One of the outputs of the power splitter may be provided to the second input 107b of the WSS 104. A second output of the power splitter may be provided to the lxM” optical distribution device 110.

[0090] One of the outputs of the lxM” optical distribution device may be not connected to any other component for signal reception, for example, may be attenuated. Each of the remaining M”-l outputs may be optically connected to one of the M”-l inputs of WSS 104 that are not directly connected to placeholder signal generator 102 through the power splitter.

[0091] Between the lxM” optical distribution device 110 and the WSS 104 input ports the NxM optical distribution device 103, for example, a NxM optical switch, may be located. For example, the NxM optical distribution device 103 may be a 2x1 switch as shown in FIG. 2. Between the lxM” optical distribution device 110 and the WSS 104 input ports the N’xM’ optical distribution device 111, for example, a N’xM’ optical switch, may be located. For example, the N’xM’ optical distribution device 111 may be a 2x1 switch as shown in FIG. 2.

[0092] For example, one of the inputs of 2x1 switch 103 may be connected to the lxM” switch and the other input may be connected to one or more ingress WSSs 105 (or “add” blocks). The output of the 2x1 switch 103 may be connected to the first input of the WSS 104.

[0093] Under nominal operation (no failure cut), the lxM” optical switch may redirect the power from the placeholder signal generator 102 to the unused output port. The 2x1 switches 103, 111 shown in FIG. 2 may be configured to redirect optical signals 108 from the ingress WSSs 105, 106 to the inputs of the WSS 104. The optical node 100 may comprise a photodiode 101 for each of the input ports of the WSS 104.

[0094] FIG. 3 shows an exemplary optical node 100 according to this disclosure.

[0095] For example, FIG. 3 shows the exemplary optical node 100 shown in FIG. 2, wherein a link failure occurred. Upon the failure of a link between a signal source 105 and the WSS 104, the loss of power may be detected by a photodiode 101 at the input port of WSS 104. Alternatively, loss of power may be detected by a fast OCM at the output of WSS 104. An OCM is a device that measures the power of each channel (service) carried over a fiber.

[0096] The loss of power may be determined directly or indirectly by the photodiode 101. For example, the photodiode 101 may detect a loss of power at some point in the optical path at the WSS 104, which may directly indicate a loss of power at the input of the NxM switch that should have received the optical signal 108 form the signal source 105.

[0097] The lxM” optical distribution device 110 may be configured to redirect light from placeholder signal generator 102 to the input port of WSS 104 that is impacted by the failure. The corresponding NxM optical distribution device 103, for example, 2x1 switch, is configured to receive power from the lxM” optical distribution device 110 and redirect it to the WSS 104. By simultaneously configuring the lxM” and the NxM optical distribution device, the optical placeholder signal 109 can enter the input port of WSS 104 to replace the optical signal 108 components that are missing due to the failure. This light may be filtered by the WSS 104 as if there was no failure, such that the failure does not impact the optical signal 108 at the output of the WSS 104.

[0098] FIG. 4 shows exemplary components of an optical node 100 according to this disclosure. For example, the components of the optical nodes 100 shown in FIG. 2 and 3 may be replaced based on the following components.

[0099] The optical distribution device optically connected to the placeholder signal generator 102 may either be a lxM” optical distribution device 110 or a lx(M”-l) distribution device. The WSS 104 may comprise M” inputs orM”-l inputs.

[0100] For example, said optical distribution device may be one of:

[0101] • A lxM’ ’ optical switch as shown in FIG. 4a, configured to redirect light from the placeholder signal generator 102 to any output ports. One output of the M” output may attenuate the placeholder optical signal.

[0102] • A lx(M”-l) optical switch as shown in FIG. 4b, configured to redirect light from the placeholder signal generator 102 to any output ports. The optical placeholder signal 109 may or may not be blocked by a 1x2 switch connected to said output port ofthe lx(M”-l) optical switch. • A lxM” or lx(M”-l) power splitter as shown in FIG. 4c. An additional amplifier may be used to compensate for losses. Thus, costs may be reduced.

[0103] • A lx(M”-l) WSS as shown in FIG. 4d, preconfigured so that the output of each of its ports matches the desired input on the corresponding WSS 104 port 107a.

[0104] The photodiodes 101 may be located at the input of the NxM optical distribution device 103 as shown in FIG. 4e, for example, the 2x1 switch 103 that is directly optically connected to the signal source 105.

[0105] Small amplifiers may additionally be used to compensate for the loss of inserting additional components, for example, if the lxM” optical distribution device 110 is a power splitter or a WSS. The amplifiers may be located between the output of the 1 xM’ ’ or 1 x(M’ ’ - 1 ) optical distribution device and one of the inputs of the NxM optical distribution device 103 , or at the inputs of the WSS 104.

[0106] In multi-band systems, optical fibers carry signals over several transmission bands. Four exemplary implementations may be distinguished: The optical placeholder signals 108 may be wideband, for example, with one amplifier for several bands, or single-band, for example, with one amplifier per band. Additionally, the WSS 104 of the optical node 100 may be wideband or single-band.

[0107] FIG. 5 shows an optical node 100 according to this disclosure comprising a single-band placeholder signal generator 102 and signal-band WSS 104 or a multi-band placeholder signal generator 102 and a multi-band band WSS 104.

[0108] Multi-band systems may be implemented with parallel single-band optical placeholder signals 108 and parallel single-band WSSs 104. The method of the present disclosure may be applied for each band independently. For example, the optical node 100 may comprise at least one NxM switch, a lxM” switch, at least one photodiode 101, and a placeholder signal generator 102 for each band.

[0109] Alternatively, multi-band systems may be implemented with a multi-band optical placeholder signal 109 and a multi-band WSS 104.

[0110] FIG. 6 shows an optical node 100 according to this disclosure comprising two parallel single-band placeholder signal generators 102 and a multi-band WSS 104.

[0111] A plurality of single-band optical placeholder signals 108 may be first multiplexed with a multiplexer and the output of the multiplexer may enter a 1x2 splitter. For example, a C-band placeholder signal and a L-band placeholder signal may be merged before entering a splitter. One output of the 1x2 splitter may be directly optically connected to the lxM” optical distribution device 110 and another output of the 1x2 splitter may be directly optically connected to the WSS 104.

[0112] If the lxM” device is implemented with a plurality of single-band WSSs 104, then one single-band optical placeholder signal 109 may be kept per single-band WSS 104 that implements the lxM” device.

[0113] FIG. 7 shows an optical node 100 according to this disclosure comprising a multi-band placeholder signal generator 102 and two single-band WSSs 104, 112.

[0114] The optical node 100 may comprise a WSS 104, another WSS 114, a NxM optical distribution device 103, another NxM optical distribution device 115 , a photodiode 101, another photodiode 113. In the example shown in FIG. 7, N is 2 and M is 1. The optical placeholder signal 109 may be split (or band-demultiplexed) into separate bands, each entering a separate NxM optical distribution device 103, 115. The optical node 100 may comprise at least one NxM optical distribution device 103, 115 per band. For example, the NxM optical distribution device 103 may be for a first band, for example, a C-band, and the other NxM optical distribution device 103 may be for a second band, for example, a L-band.

[0115] Alternatively, the multi-band placeholder signal may propagate from the placeholder signal generator 102 to each WSS 104, 112. Each WSS 104 may filter out the signal components outside of their operating band. The optical node 100 may comprise one WSS 104 per band.

[0116] The optical node 100 may comprise or be connectable to a controller. The controller may be a processor.

[0117] Generally, the processor may be configured to perform, conduct or initiate the various operations of the optical node 100 described herein. The processor may comprise hardware and / or may be controlled by software. The hardware may comprise analog circuitry or digital circuitry, or both analog and digital circuitry. The digital circuitry may comprise components such as application-specific integrated circuits (ASICs), field-programmable arrays (FPGAs), digital signal processors (DSPs), or multi-purpose processors. The optical node 100 may further comprise memory circuitry, which stores one or more instruction(s) that can be executed by the processor, in particular under control of the software. For instance, the memory circuitry may comprise a non-transitory storage medium storing executable software code which, when executed by the processor, causes the various operations of the optical node 100 to be performed. In one embodiment, the optical node 100 may comprises one or more processors and a non-transitory memory connected to the one or more processors. The non-transitory memory may carry executable program code which, when executed by the one or more processors, causes the optical node 100 to perform, conduct or initiate the operations or methods described herein.

[0118] FIG. 8 shows a method 200 according to this disclosure. The method 200 is a method of operating an optical node 100.

[0119] The optical node 100 comprises a photodiode 101, a placeholder signal generator 102, a NxM optical distribution device 103 having N inputs and M outputs, and a WSS 104 having a plurality of inputs 107, wherein N and M are positive integers and N is larger than M.

[0120] The NxM optical distribution device 103 is optically connectable to a signal source 105, optically connected to the placeholder signal generator 102, and optically connected to a first input 107a of the plurality of inputs 107 of the WSS 104.

[0121] The method 200 comprises a step 201 of determining, with the photodiode 101, if an optical signal 108 is received by the NxM optical distribution device 103 from the signal source 105. Further, the method 200 comprises a step 202 of receiving, with the NxM optical distribution device 103, a placeholder optical signal 109 from the placeholder signal generator 102 and providing the placeholder optical signal 109 to the first input 107a of the WSS 104 if the photodiode 101 determines that the optical signal 108 is not received by the NxM optical distribution device 103.

[0122] The disclosure has been described in conjunction with various embodiments as examples as well as implementations. However, other variations can be understood and effected by those persons skilled in the art and practicing the claimed matter, from the studies of the drawings, this disclosure and the independent claims. In the claims as well as in the description the word “comprising” does not exclude other elements or steps and the indefinite article “a” or “an” does not exclude a plurality. A single element or other unit may fulfill the functions of several entities or items recited in the claims. The mere fact that certain measures are recited in the mutual different dependent claims does not indicate that a combination of these measures cannot be used in an advantageous implementation.

Claims

CLAIMS1. An optical node (100) comprising a photodiode ( 101 ), a placeholder signal generator ( 102), a NxM optical distribution device (103) having N inputs and M outputs, and a wavelength selective switch, WSS (104), having a plurality of inputs (107), wherein N and M are positive integers and N is larger than M, wherein the NxM optical distribution device (103) is optically connectable to a signal source (105), optically connected to the placeholder signal generator (102), and optically connected to a first input (107a) of the plurality of inputs (107) of the WSS, wherein the photodiode (101) is configured to determine if an optical signal (108) is received by the NxM optical distribution device (103) from the signal source (105), wherein the NxM optical distribution device (103) is configured to: receive a placeholder optical signal (108) from the placeholder signal generator (102) and provide the placeholder optical signal (108) to the first input (107a) of the WSS (104) if the photodiode (101) determines that the optical signal (108) is not received by the NxM optical distribution device (103).

2. The optical node (100) according to any one of the preceding claims, wherein the NxM optical distribution device (103) is further configured to: not provide the placeholder optical signal (108) to the first input (107a) of the plurality of inputs (107) of the WSS (104) if the photodiode (101) determines that the optical signal (108) is received by the NxM optical distribution device (103).

3. The optical node (100) according to any one of the preceding claims, wherein the NxM optical distribution device (103) is optically connected to the placeholder signal generator (102) through a first input of the N inputs, wherein the NxM optical distribution device (103) is optically connected to the first input (107a) of the WSS (104) through a first output of the M outputs, wherein the NxM optical distribution device (103) is optically connectable to the signal source (105) through a second input of the N inputs.

4. The optical node (100) according to any one of the preceding claims, wherein a second input (107b) of the plurality of inputs (107) of the WSS (104) is optically connected to the placeholder signal generator (102), and / or wherein the WSS (104) is configured to receive the optical placeholder signal (109) from the placeholder signal generator (102) through the second input (107b) of the WSS (104).

5. The optical node (100) according to any one of the preceding claims, wherein N is larger than 2 and M is larger than 1 , wherein the NxM optical distribution device (103) is optically connectable to another signal source (106) through a third input of the N inputs.

6. The optical node (100) according to any one of the preceding claims, wherein the optical node (100) further comprises a further photodiode (114) and a N’xM’ optical distribution device (111) having N’ inputs and M’ outputs, wherein N’ and M’ are positive integers and N’ is larger than M’, wherein the N’xM’ optical distribution device (111) is optically connectable to another signal source (106), optically connected to the placeholder signal generator (102), and optically connected to a third input (107c) of the plurality of inputs (107) of the WSS (104), wherein the further photodiode (114) is configured to determine if an optical signal (108) is received by the N’xM’ optical distribution device (111) from the other signal source (106), wherein the N’xM’ optical distribution device (111) is configured to: receive a placeholder optical signal (108) from the placeholder signal generator (102) and provide the placeholder optical signal (108) to the third input (107c) of the WSS (104) if the further photodiode (114) determines that the optical signal (108) is not received by the N’xM’ optical distribution device (111).

7. The optical node (100) according to any one of the preceding claims, wherein the optical node (100) further comprises a IxM” optical distribution device (110) having an input and M” outputs, wherein M” is an integer larger than 1, wherein an output of M” outputs of the IxM” optical distribution device (110) is optically connected to the NxM optical distribution device (103), wherein the IxM” optical distribution device (110) or the NxM optical distribution device (103) is an optical switch, wherein the IxM” optical distribution device (110) is configured to: receive the optical placeholder signal (109) from the placeholder signal generator (102) through the input of the IxM” optical distribution device, and provide the optical placeholder signal (109) through the output of the IxM” optical distribution device (110) to the NxM optical distribution device (103).

8. The optical node (100) according to any one of the preceding claims, wherein at least one of: the IxM” optical distribution device (110) is a IxM” optical coupler or a IxM” optical switch, the NxM optical distribution device (103) is a NxM optical coupler or a NxM optical switch, and the N’xM’ optical distribution device (111) is a N’xM’ optical coupler or a N’xM’ optical switch.

9. The optical node (100) according to any one of the preceding claims, wherein the lxM” optical distribution device (110) is a lxM” optical switch, wherein the lxM” optical distribution device (110) is configured to provide the optical placeholder signal (109) to the NxM optical distribution device (103) if the photodiode (101) determines that the optical signal (108) is not received by the NxM optical distribution device (103), and / or wherein the lxM” optical distribution device (110) is configured to not provide the optical placeholder signal (109) to the NxM optical distribution device (103) if the photodiode (101) determines that the optical signal (108) is received by the NxM optical distribution device (103).

10. The optical node (100) according to one of the claims 7 to 9, wherein the WSS (104) comprises M”+l or M” inputs.

11. The optical node (100) according to any one of the preceding claims, wherein N is 2 and M is 1 , and / or wherein N’ is 2 and M’ is 1.

12. The optical node (100) according to any one of the preceding claims, wherein the optical node (100) further comprises another WSS (112) having a plurality of inputs (107), another NxM optical distribution device (115) having N inputs and M outputs, and another photodiode (113), wherein the other NxM optical distribution device (115) is optically connectable to the signal source (105), optically connected to the placeholder signal generator (102), and optically connected to a first input (107a) of the plurality of inputs (107) of the other WSS (112), wherein the other photodiode (113) is configured to determine if another optical signal (108) is received by the other NxM optical distribution device (115) from the signal source (105), wherein the optical signal (108) comprises a first frequency band and the other optical signal (108) comprises a second frequency band, wherein the other NxM optical distribution device ( 115 ) is configured to : receive the placeholder optical signal (108) from the placeholder signal generator (102) and provide the placeholder optical signal (108) to the first input (107a) of the other WSS (112) if the other photodiode (113) determines that the other optical signal (108) is not received by the other NxM optical distribution device (115).

13. The optical node ( 100) according to claim 12, wherein another output of the M” outputs of the lxM” optical distribution device (110) is optically connected to the other NxM optical distribution device (115), wherein the lxM” optical distribution device (110) is further configured to:16provide the optical placeholder signal (109) through the other output of the IxM” optical distribution device (110) to the other NxM optical distribution device (115).

14. The optical node (100) according to any one of the preceding claims, the placeholder signal generator (102) comprises a first placeholder signal generator (102) configured to generate a first frequency band of the optical placeholder signal (109) and a second placeholder signal generator (102) configured to generate a second frequency band of the optical placeholder signal (109), wherein the placeholder signal generator (102) is configured to combine the first frequency band of the optical placeholder signal (109) and the second frequency band of the optical placeholder signal (109) to form the optical placeholder signal (109).

15. A method of operating an optical node (100), the optical node (100) comprising a photodiode (101), a placeholder signal generator (102), a NxM optical distribution device (103) having N inputs and M outputs, and a wavelength selective switch, WSS (104), having a plurality of inputs (107), wherein N and M are positive integers and N is larger than M, wherein the NxM optical distribution device (103) is optically connectable to a signal source (105), optically connected to the placeholder signal generator (102), and optically connected to a first input (107a) of the plurality of inputs (107) of the WSS (104), wherein the method comprises: determining, with the photodiode (101), if an optical signal (108) is received by the NxM optical distribution device (103) from the signal source (105), and receiving, with the NxM optical distribution device (103), a placeholder optical signal (108) from the placeholder signal generator (102) and providing the placeholder optical signal (108) to the first input (107a) of the WSS (104) if the photodiode (101) determines that the optical signal (108) is not received by the NxM optical distribution device (103).

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