EP4681358A1

EP4681358A1 - Programmable wavelength-selective splitter and a method for remotely configuring a programmable wavelength-selective splitter

Info

Publication number: EP4681358A1
Application number: EP23712831.9A
Authority: EP
Inventors: Luca Giorgi; Paola Iovanna; Alfredo Palagi
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 2023-03-15
Filing date: 2023-03-15
Publication date: 2026-01-21
Also published as: WO2024188463A1; CN120917686A

Abstract

A Programmable Wavelength-Selective Splitter, PWSS, and a method for remotely configuring a Programmable Wavelength-Selective Splitter is disclosed. The PWSS comprises an input port for receiving optical signals in a form of a comb of wavelengths. The method performed at the PWSS comprises determining (402) wavelengths of the comb not present in the received optical signals, selecting (404) at least one of the determined wavelengths for use in add and drop ports and recording (406) said at least one selected wavelength as a working wavelength for the add and drop ports in configuration information stored in a register of the PWSS.

Description

Programmable Wavelength-Selective Splitter And A Method For Remotely Configuring A Programmable Wavelength-Selective Splitter

Technical Field

The present invention relates to optical networks, in general, and, in particular, to a Programmable Wavelength-Selective Splitter and a method for remotely configuring a Programmable Wavelength-Selective Splitter.

The evolution of 5G to 5G-Beyond and 6G further enforces the need to use Dense Wavelength Division Multiplexing (DWDM) technology to meet high bandwidth and low latency requirements. Tunability is also required to save cost of inventory, reduce field operations both during the configuration phase and fault recovery and to support network planning, and on the fly reconfigurability. The evolution of Radio Access Networks (RAN) in Centralized and cloud RAN, benefits form usage of DWDM technology in the access segment to connect several antenna sites to the centralized site (typically the central office of the operator) with scalable bandwidth. In this case, different network topologies can be used to connect the antenna sites to the central hub (e.g. chain and tree). In some cases, the DWDM technology can be used to overlay RAN on already installed Passive Optical Network (PON) infrastructure and this enables the usage of a widely deployed fiber infrastructure.

Most of such scenarios are based on DWDM transceivers with fixed transmission wavelength. This impacts inventory because it is necessary to store several TRXs, one for each wavelength. Moreover, operations in the field (e.g., configuration or fault recovery) cannot be performed as simple plug and play because it is necessary to correctly connect the available fibres to the right TRX ports. Fixed filters and transceivers require a rigid wavelength planning from day one and do not allow changing it without non-trivial shuffling of the fibre connections in the field. To simplify inventory and operations, tunable TRX in transmission (i.e., using tunable lasers) have been realized. Such TRXs do not have tunable receivers, hence they are used in combination with demultiplexers (DeMUX) in the networks that allow to “color” each port (i.e., select a specific wavelength) and send correct wavelengths to the receivers. The assignment of the wavelengths is performed in advance (planning phase) for the network and the antenna sites. A tunable TRX makes use of algorithm for self-tuning that enables automatic procedure for configuration to simplify a bit the configuration. To realize a fully tunable TRX that can work as plug and play module, able to operate without planning of wavelengths in advance and simplify operation in the field it is necessary to make the receiver of the TRX fully tunable. In patent application WO2022/258432A1 solutions to dynamically control a fully tunable TRX have been identified. However, devices and operations as in the invention now to be described are neither disclosed nor suggested in this document.

Summary

According to a first aspect of the present invention there is provided a method for remotely configuring a Programmable Wavelength-Selective Splitter, PWSS. The PWSS comprises an input port for receiving optical signals in a form of a comb of wavelengths. The method performed at the PWSS comprises determining wavelengths of the comb that are not present in the received optical signals. The method also comprises selecting at least one of the determined wavelengths for use in add and drop ports and recording said at least one selected wavelength as a working wavelength for the add and drop ports in configuration information stored in a register of the PWSS

According to a second aspect of the present invention there is provided a Programmable Wavelength-Selective Splitter, PWSS. The PWSS comprises an input port for receiving optical signals in a form of a comb of wavelengths, a plurality of add ports and drop ports. An individual drop port comprises a photodetector or is configured to be connected to a photodetector. The PWSS is operative to determine wavelengths of the comb that are not present in the received optical signals and select at least one of the determined wavelengths for use in add and drop ports. Further, the PWSS is operative to record said at least one selected wavelength as a working wavelength for the add and drop ports in configuration information stored in a register of the PWSS.

According to a third aspect of the present invention there is provided a Programmable Wavelength-Selective Splitter, PWSS. The PWSS comprises an input port for receiving optical signals in a form of a comb of wavelengths and a plurality of add ports and drop ports. An individual drop port comprises a photodetector or is configured to be connected to a photodetector. The PWSS further comprises a processor and a memory, the memory contains instructions executable by the processor whereby the PWSS is operative to determine wavelengths of the comb that are not present in the received optical signals and to select at least one of the determined wavelengths for use in add and drop ports. The PWSS is also operative to record said at least one selected wavelength as a working wavelength for the add and drop ports in configuration information stored in a register of the PWSS.

Further features of the present invention are as claimed in the dependent claims.

The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which:

FIG. 1 A and IB illustrate two embodiments of a configurable device based on a Programmable Wavelength-Selective Splitter;

FIG. 2A and 2B illustrate two examples of spectrum allocation to downstream channels and upstream channels;

FIG. 3 A and 3B illustrate two embodiments of a Programmable Wavelength- Selective Splitter implemented in a section of a communications network;

FIG. 4 is a flowchart illustrating a method for remotely configuring a

Programmable Wavelength-Selective Splitter in one embodiment; FIG. 5 is a flowchart illustrating details of one possible practical embodiment of the method for remotely configuring a Programmable Wavelength- Selective Splitter as seen from a remote site where the PWSS is installed;

FIG. 6 illustrates operations of a Network Management System in a network in which a Programmable Wavelength- Selective Splitter is remotely configured in accordance with disclosed embodiments;

FIG. 7 is a block diagram illustrating one embodiment of a Programmable Wavelength-Selective Splitter;

FIG. 8 is a block diagram illustrating one embodiment of a Programmable Wavelength-Selective Splitter;

FIG. 9A and 9B illustrate two embodiments of an add/drop port for use in a PWSS.

Detailed description

In the following description, for purposes of explanation and not limitation, specific details are set forth such as particular architectures, interfaces, techniques, etc. in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known devices, circuits, and methods are omitted so as not to obscure the description of the invention with unnecessary details.

Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the present invention. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification are not necessarily all referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments. When in this document reference is made to Wavelength Division Multiplexing (WDM) it also includes Dense Wavelength Division Multiplexing (DWDM).

The inventors realized that to realise full tunability of the antenna site from a remote location, it is possible to consider a device/module based on tunable filter ports that allow dropping from the incoming downstream comb a subset of L wavelengths and to add to the outcoming upstream comb L new wavelengths locally generated. Such modules can be located both in the two end points (i.e. antenna site and central office, or in the remote site only). This is illustrated in Figure 1 A. One of the problems the solution to be disclosed addresses is that when used in practive on a remote site the reconfigurable device, 150-1, shown inFigure lAmay not have access to DCN and through it to Network Management system, or, in other words, the solution to be disclosed allows for configuration of a reconfigurable device, 150-1, in the absence of a control channel between the device and a Central Office and a Network Management System. Figure 1 A illustrates an embodiment based on a single bidirectional fibre 100. The above is true also for an embodiment of a configurable device, 150-2, based on two unidirectional fibres 102 and 104 as illustrated in Figure IB.

This document discloses a method for self-configuring a remote device with full compliance with existing tunable TRX in transmission to guarantee interworking with existing technology.

In one embodiment the invention defines a plug and play Programmable Wavelength-Selective Splitter (PWSS), which may operates in an optical communications network as illustrated in Figures la and lb. This document also discloses a method for configuration that allows tuning add and drop ports on available wavelengths. Embodiments of the solution disclosed in this document allow setting up wavelength selective paths as it is possible in the conventional DWDM networks with multiplexer/demultiplexer filters and OADMs (Optical Add-Drop Multiplexers).

After a field engineer installs a PWSS according to one embodiment of the present invention, he or she sends identification information (this may include serial number, part number, GPS coordinates, etc.) with the cabled ports to the network management system (NMS). In Central Office the NMS checks the received information validity and sends to the field engineer a permission to switch on the new device.

During the switching-on procedure a controller of the PWSS checks its configuration status register (CSR) in a EEPROM memory and in case the device has to be configured, the controller starts the inventive method disclosed herein. In a preferred embodiment, illustrated in Figure 7, the controller, 750, of the PWSS, 700, comprises a processor, 702, and a memory, 704. More details of the PWSS device will be discussed later.

The controller of the PWSS preferably uses one of the drop ports to find L adjacent drop wavelengths of the spectrum that are still not in use. A wavelength that is not in use is not present in optical signal detected at the drop port. In other words, no optical power is detected at a wavelength that is not in use. In case L adjacent wavelengths are not available the controller may iteratively reduce this number to find available group of adjacent wavelengths (adjacent channels). It may be that the network operator wants to configure the PWSS with 6 add and 6 drop channels (wavelengths), but there are only 4 consecutive channels (i.e. 4 add and 4 drop) available. In this case the method of this embodiment may find the remaining wavelengths in other part of the spectrum used in the network or it may be that there is no more available channels and the PWSS will be configured with only part of originally intended channels based on what is available in the network. Of course, in case the device is not able to find not even one available wavelength in the spectrum the procedure aborts and the device stays unconfigured. In practice, a technician in the field has information about how many ports for both the PWSS A and PWSS B he has to connect (these are PWSS devices at local (i.e. Central Office) and remote ends). When the fibre connections have been established the technician sends to the NMS in the central office ID information of the PWSS installed and the number of cabled ports. From the ID information the NMS detects the total number of the ports available on the PWSS, and from the number of actually cabled ports it detects the maximum number of connections it has to establish with the remote equipment. When the controller of the PWSS finds a group of adjacent wavelengths available, it tunes the drop ports and, consequently, the add ports following the selected policy for allocating channels, for example: downstream wavelength (drop) interleaved with an upstream wavelength (add); see Figure 2 A, downstream wavelengths belong to a first part of the spectrum and upstream wavelengths belong to a second part of the spectrum, see Figure 2B.

When the drop and add ports are tuned on the assigned wavelengths it results in establishing physical paths that will route optical wavelengths from the source transmitter to their respective assigned remote receivers.

To minimize timing asymmetry on a single transceiver between the signal transmitted on the downstream direction with respect to signal transmitted in the upstream direction the two corresponding wavelengths are preferably adjacent and the interleaved plan for downstream and upstream directions is preferred. This means that once identified the downstream wavelength the corresponding upstream is the adjacent one.

A second example of a predefined plan is one that splits the available spectrum in two contiguous sections, upper side sub-band and lower side sub-band. The downstream channels of the comb are allocated to the first sub-band and the upstream channels of the comb are allocated in the second one. In a preferred embodiment the distance, in term of wavelength, between downstream and upstream wavelength assigned to the same transceiver is a constant among the transceivers.

After the drop and add channels are allocated to their corresponding ports the controller records this in the CSR.

In the CO the NMS waits for the needed programming time and then starts a verification procedure for the scheduled links. If one or more link doesn’t go up the NMS raises an alarm and begins a procedure to evaluate and solve the issue (for example: remote device failure, transceivers failure, wrong connection, etc). Once the issue has been solved the Alarm is switched off and the NMS continue the operations. One skilled in the art can see that the operations in the physical layer are split into two parts. The first part covers the realization of physical circuits dedicated to the various assigned couple of wavelengths (add and drop) for end-to-end communication. The second part covers the control of the transceivers involved in setting-up and operation of the communication channels. The PWSS programming falls in the first part, whereas the switching-on of the communication channel in the second. In operation, the NMS surveys and acts on both these parts. In the first part the NMS leads the programming of the PWSS on the wanted add/drop channels using dummy signal(s), in the second part the NMS drives the switching on of the TRXs and establishing the communication channel. Only when the NMS tries to establish a new communication channel it can verify if the PWSS installation and programming has been correctly executed. A failure to establish a new communication channel indicates that either installation or programming or both failed. For completeness, in embodiments of the invention, the switching on the TRXs could be triggered by the same NMS or a different NMS/control (e.g. it could be the radio domain). For the sake of simplicity in the rest of the document it is assumed that it is the same NMS, but the invention would work the same in both embodiments.

Figure 3A illustrates a PWSS, 302a, in one embodiment of the present invention implemented in a section of a communications network, 300, realised as WDM optical network. In one embodiment it may be a fronthaul network between centralized radio controllers in the Central Office and radio heads (or antenna sites) of a Radio Access Network (RAN). The embodiment illustrated in Figure 3A operates with bidirectional fibres, 320 and 322, connected to Line, 304a, and Express, 306a, ports.

The PWSS, 302a, shows two bidirectional ports, Line, 304a, and Express, 306a, where the aggregated upstream and downstream signals of a WDM comb travel and 2L ports, 308, dedicated for the channels add/drop. The WDM comb includes N wavelenghts (channels), for example 48 wavelenghts dedicated to communication channels as shown in the example illustrated in Figure 2A and 2B. From the incoming downstream comb applied to the Line port, up to L wavelengths (with L<N) can be dropped and sent to the assigned receivers, 310, where L indicated the number of of drop ports. In a preferred embodiment the number of add ports will also be L, giving the total of 2L ports, 308, dedicated for the channels add/drop. A copy of this downstream comb, with or without the dropped wavelengths, is sent out from the PWSS, 302a, via the Exp port, 306a, to other PWSSs connected downstream in a chain. In the opposite direction, up to L wavelengths (with L<N) provided from transmitters, 312, connected to add ports can be multiplexed and added to the incoming upstream comb received at the Exp port, 306a. This upstream comb arrives from PWSSs connected in a chain on the left-hand side of Figure 3 A (not illustrated) and is sent out of the Line port, 304a, toward the central office of the network on the right-hand side of Figure 3 A (not illustrated).

With reference to Figure 3 A and Figure 4 embodiments of a method for remotely configuring a Programmable Wavelength- Selective Splitter, PWSS, 302a, will now be described. The PWSS, 302a, comprises an input port, 304a, for receiving downstream optical signals in a form of a comb of wavelengths. In one embodiment, as illustrated in Figure 3A the input port 304a is a bidirectional port (input/output) to which a single, bidirectional optical fibre is connected, linking the PWSS, 302a, to the Central Office. Similarly, in a preferred embodiment, the Express port, 306a, is a bidirectional port (input/output) to which a single, bidirectional optical fibre is connected, linking the PWSS, 302a, to another PWSS located downstream. Network architecture based on a single bidirectional fibre is a preferred option from the point of view of a network operator as it reduces the cost of leasing the optical fibre (single one for bidirectional option and two fibres for dual-fibre configuration). However, in alternative embodiments the method disclosed herein is also applicable to dual-fibre network architectures, as illustrated in Figure 3B in which one optical fibre is dedicated to downstream traffic (from the CO) and the other one to upstream traffic (to the CO). In the dual fibre configured embodiment the Line side of the device 302b has an input port 304b for receiving downstream signals from the CO and an output port 304c for transmitting upstream signals to the CO. On the Express side the device comprises an output port 306b for transmitting downstream signals to other antenna sites and an input port 306c for receiving upstream signals from the other antenna sites. In both embodiments (i.e. one bidirectional fibre configuration and in dual-fibre unidirectional configuration) only the tunable filters acting as drop ports detect the presence/absence of downstream wavelengths.

In a preferred embodiment, the method performed at the PWSS, 302a or 302b, comprises an operation of determining, 402, wavelengths of the comb not present in the received optical signals.

In order to identify wavelengths that are not used (i.e. not transmitted by the transceiver at the CO) the solution in one embodiment detects the channels that are used. A controller of the PWSS, 302a or 302b, knows the WDM comb, which means it knows the wavelengths assigned to individual channels of the WDM comb and after the photodetector or photodetectors detect which channels are used the controller determines which ones are not used and reports only the empty channels. In a preferred embodiment photodiodes may be used as the photodetectors. Alternatively, the controller may report the whole map of the comb showing which channels (wavelengths) are used and which ones are empty. The empty channels may be used to configure the PWSS.

In the following step, the method comprises selecting, 404, at least one of the determined wavelengths for use in add and drop ports. For the embodiment in which the architecture of network is based on dual fibre with one fibre used for upstream and one for downstream communication it is enough to select, 404, only one wavelength because the same wavelength may then be used for drop and add ports o the PWSS because the drop port will receive data on the downstream fibre and the add port will send data to the CO over the upstream fibre. Because upstream and downstream transmissions are separated there will be no interference even if the same wavelength is used in both directions.

However, in an alternative embodiment, in which the input port, 304a, operates as a bidirectional input/output port (Line port 304a) in the operation of selecting, 404, at least two, or a multiple of two, wavelengths are selected. In this embodiment a first half of the selected wavelengths are set as working drop wavelengths and a second half of the selected wavelengths are set as working add wavelengths. This solution avoids interference in the fibre because optical signals travelling in opposite directions do not have the same wavelength.

In the next step of the method the controller records, 406, said at least one selected wavelength as a working wavelength for the add and drop ports in configuration information stored in a register of the PWSS. For a PWSS operating with a bidirectional Line port at least two wavelengths are recorded in the register.

The operation of determining wavelengths of the comb that are not present in the received optical signals may be carried out in one of several embodiments. In one embodiment a photodetector at one drop port detects optical signals of the received comb by scanning the whole spectrum of the comb and from this operation the controller determines wavelengths of the comb for which absence of optical power has been observed.

In an alternative embodiment the operation of determining comprises detecting the optical signals of the received comb using photodetectors at a plurality of drop ports of the PWSS. The plurality of drop ports may include all drop ports of the PWSS (i.e. L drop ports) or, alternatively, only a portion of the L drop ports. In these embodiments an individual a photodetector at an individual drop port of the plurality of drop ports scans only a portion of the spectrum of the comb and the controller of the PWSS determines wavelengths of the comb for which absence of optical power has been observed. The sum of the portions of the comb scanned by the photodetectors at the drop ports cover the whole spectrum of the comb. By using a plurality of photodetectors operating in parallel to determine wavelengths of the comb that are not present in the received optical signals allows for speeding up the operation of determining.

In the embodiment using a bidirectional fibre for connecting the PWSS, 302a, to the CO the method comprises interleaving drop and add channels using the selected wavelengths.

Because there is no control channel in the network 300, in one embodiment the method comprises indicating to a centralised controller at the CO that the drop and add ports of the PWSS are configured with said selected wavelengths by establishing a working communication channel using said selected wavelengths. The centralised controller in one embodiment may comprise a Network Management System or an SDN Controller.

Preferably, if a plurality of sequences of adjacent wavelengths of the comb are determined as absent in the received optical signals, the method comprises identifying a largest sequence of said absent wavelengths and selecting from said largest sequence wavelengths for use in add and drop ports as required by configuration needs of the PWSS. Selecting adjacent wavelengths has the advantage of reducing timing discrepancy between different channels and this, in turn, helps with keeping the network synchronised.

In various embodiments the method disclosed in this document allows for remote configuration of add/drop ports of a PWSS and has the following characteristics:

• The method enables a self-configuration (tuning) of the PWSS by independently configuring wavelength- selective paths as in conventional DWDM network with commercial MUX/Demux/OADM filters, but without the need for MUX/Demux/OADM filters.

• The method takes over wavelengths assignment strategy from the Network Management System, but the NMS can still influence the PWSS’s configuration making the device to configure the add/drop ports with a specific set of wavelengths. This is achieved by the NMS controlling the CO to transmit optical power (dummy signals) on wavelengths that should not be used by the PWSS to be configured and keeping empty (not used) wavelengths that the NMS wants the PWSS to use as drop/add channels. This is possible because simultaneous configuration of more than one PWSS is not allowed to avoid multiple devices tuning their ports on the same wavelengths.

• No control messages are exchanged between the CO and remotely locate PWSS, which means this solution allows for configuring PWSSs in a network without a control channel. In consequence, the method provides numerous advantages, including simplified configuration and operation in the field with full compliance with existing tunable TRX. By allowing remote configuration the method helps reducing field visits for fault recovery and/or installation and/or reconfiguration. The method disclosed is compliant with any radio and transport architecture (e.g., configured by SDN controller and/or Network Management System) and is future-proof for O-RAN. It also simplifies planning operations as it does not require advance planning of assignment of wavelengths to remote sites. Further, the module configuration does not require installation of a specific communication and control channel between the Network Management System in central office CO and the module itself.

In one embodiment the NMS waits until all PWSSs connected to the network are connected and configured and because there is no control channel the NMS does not know the channel assignments and if all PWSSs have been successfully configured. Therefore, in one embodiment when the PWSS’ s configuration time is over the system (i.e. the NMS at the CO) can do a polling procedure to verify that the physical layer is configured and up. If communication between the antenna site connected to the add/drop ports of the PWSS is possible in both directions it indicates that the connections on the physical layer are correctly configured. Otherwise, an alarm is raised.

In an alternative embodiment the system (e.g., the radio controller, NMS, etc.) can receive a trigger, from the engineer in the field, that the transport network is configured.

In the above embodiments verification that the configuration was successful is carried out when all PWSSs in the network are connected and configured. However, it is also possible, in alternative embodiments, that such verification is carried after individual PWSS is configured or after a group of PWSSs has been configured.

Figure 5 illustrates more details of one possible practical embodiment of the method for remotely configuring a Programmable Wavelength-Selective Splitter, PWSS, as seen from the perspective of a remote site where the PWSS is installed.

After the installation, the PWSS has at least one pair of add/drop ports , which are cabled to transceivers, 502. Information identifying the PWSS (e.g. a serial number and/or part number), its location (e.g. GPS coordinates) and connections (cabled ports) are provided to the NMS, 504, using and additional communication channel (any way of notifying the NMS is possible, this could be a phone call from the field engineer to an operator in the Central Office, a text message, email, details filled-in on a web interface). Once the field engineer obtains an authorization from the CO to power on the PWSS, the PWSS is switched on, 506-510. The device's controller checks the configuration status register (CSR) on the EEPROM and in case the device is not yet configured, 512-514, the PWSS scans, 516, the whole downlink spectrum mapping the available downlink wavelengths (i.e. wavelengths of the WDM comb not used or, in other words, wavelengths of the WDM comb for which no optical power has been detected).

Three different scan methods can be applied, all based on the availability of a photodetector placed at the output of the drop port of the module detecting the presence of the optical power. The first scan method uses a preferred drop port of the PWSS that scans all the available downstream channels mapping the available channels (no optical power detected) and distinguishing them from the not available ones for which, in turn, optical power has been detected. The second method of scanning uses in parallel all the available drop ports (this number is indicated with 'L') to scan groups of wavelengths mapping the availability or unavailability for each of them. Finally, the third method is based on a parallel use of a number ‘K’ of drop ports, with K E [2; L-l], to scan groups of 'K' wavelengths mapping the availability or not availability for each of them. Comparing the three methods, methods two and three allow for faster determining of available channels because the photodetectors at the drop ports scan much smaller part of the spectrum of the comb compared to method one and do it in parallel.

After that, in a preferred embodiment, the controller of the PWSS identifies, 518, the first largest sequence of available and adjacent downlink wavelengths and writes in the CSR in the EEPROM memory the programming information. In case the programmed channels are lower than the PWSS’s add/drop ports number, the ports for which no available channels have been found remain unprogrammed. When a tunable device (e.g. a tunable laser of a TRX) is activated it requires voltage or current or both to bias the tunable device and switching on circuitry to control these physical quantities. Therefore, leaving unprogrammed ports that are not to be used allows for inactivating their corresponding tunable devices and allows for reducing power consumption. In case the device is not able to find not even one available downstream wavelength in the spectrum the procedure aborts and the device stays unconfigured.

When the controller of the PWSS finds the set of adjacent downstream wavelengths available it writes all the programming information in the EEPROM registers, then it sets the CSR at the appropriate value, 520. After that, it configures the add/drop ports (the tunable element's bias and its control is activated) and the method stops.

Figure 6 illustrates actions of a Network Management System in a network in which a Programmable Wavelength- Selective Splitter, PWSS, is remotely configured in accordance with embodiments of the present invention.

The Network Management System checks if all the provisioned links of the networks are configured and operational (i.e. if traffic is transmitter and received using these links), 602. If the answer is “yes” the method stops. If the answer is “no”, the NMS checks if there is information from the field concerning installation of new equipment, 604. In the answer is “no” the NMS waits for a trigger from the field and this may be repeatedly checked until such new information is received. If the answer in step, 604, is “yes” the NMS checks the received information, 608, and if information about a new installation is complete, 610-yes, the configuration of a remotely located PWSS may start. Depending on implementation, when a new PWSS module has been installed the NMS receives from a field engineer identification information that may help in identifying the PWSS installed and its location in the network. The information provided may include:

- serial number;

- part number;

- localization information;

- cabled ports. The NMS, assigns a subset of adjacent wavelengths to the new installed PWSS module, 612. In an optional step, 614, the NMS switches on, some unused transmitters in the central office to control the configuration of the PWSS in such a way that forces the PWSS to select specific wavelengths. Because in embodiments of the method the PWSS may select wavelengths not used by the central office for communication with other network elements, by switching-on a subset of unused wavelengths the NMS/CO creates dummy channels that appears to the PWSS as if they are being used for data communication by the CO/NMS. In consequence, the PWSS will not select wavelengths from this set of dummy channels, but from the remaining wavelengths not in use. In this way the NMS may direct configuration of the PWSS.

In the next step, 616, the NMS authorises switching on the PWSS module.

Once the configuration time elapsed, 618, the PWSS is configured using embodiments of the method described earlier and the NMS switches off the transmitters transmitting on the dummy channels, 620, if this option has been used, and starts a verification, 622, of the links configured by the PWSS using embodiments of the method described earlier. If one or more link doesn’t go up, 624-no, the NMS raises an alarm, 626, and begins a procedure to evaluate and solve the issue (for example: remote device failure, transceivers failure, wrong connection, etc), 628. Once the issue has been solved, 630, the alarm is switched off, 632, and the NMS continues the verification operation, 622, by checking if all the planned links are up and running. In the case of negative answer the operations 622, 624, 626, 628, 630 and 632 are performed in a loop. If it is confirmed that all newly allocated links are up, 624-yes, the method returns to step 602 where it is checked if all network links carry traffic. If the answer is “yes”, the method stops.

Figure 7 illustrates one embodiment of an PWSS, 700, which implements the method for remotely configuring the Programmable Wavelength- Selective Splitter, PWSS, 700, described earlier. The PWSS, 700, comprises a processing circuitry, 702, and a memory, 704. The processing circuitry, 702, and a memory, 704, form a controller, 750, which controls the operations of the PWSS, 700. In one embodiment the processing circuitry, 702, which may contain one or more processors, may be integrated with the memory 704 in a single chip. However, this is not required.

The memory, 704, contains instructions executable by the processing circuitry, 702, such that the PWSS, 700, is operative to determine wavelengths of the comb which are not present in the received optical signals, select at least one of the determined wavelengths for use in add and drop ports and then record said at least one selected wavelength as a working wavelength for the add and drop ports in configuration information stored in a register, 752, of the PWSS, 700.

The PWSS, 700, comprise a line port, 754, which connects the PWSS to the Central Office and an express port, 756, which connects the PWSS to another PWSS located downstream. If the network operates on a single bidirectional fibre, the line port and the express port are also bidirectional. In an alternative embodiment, in which the network is implemented based on dual fibre architecture the line port, 754, comprises two separate ports: input and output for receiving signals from the Central Office (input port) and for sending signals to the Central Office (output port). The express port, 756, in dual fibre architecture is arranged in the same way, with two separate ports one for sending signals downstream and one for receiving upstream signals. The PWSS, 700, also comprises a plurality (2L) of drop ports and add ports, 758. An individual drop port, 758- 2, may comprise a photodetector, 760, or is configured to be connected to a photodetector, 760.

The memory 704 may include a Read-Only-Memory (ROM), e.g., a flash ROM, a Random Access Memory (RAM), e.g., a Dynamic RAM (DRAM) or Static RAM (SRAM), a mass storage, e.g., a hard disk or solid state disk, or the like. The memory, 704, may include software in the form of suitably configured program code comprising instructions, 706, to be executed by the processor(s), 702, so as to implement the abovedescribed method as explained in connection with Figures 2 - 5.

It is to be understood that the structures as illustrated in Figure 7 are merely schematic and that the PWSS, 700, may actually include further components which, for the sake of clarity, have not been illustrated, e.g., further interfaces or processors. Also, it is to be understood that the memory, 704, may include further program code for implementing other and/or known functionalities.

According to some embodiments, also a computer program may be provided for implementing functionalities of the PWSS, 700, e.g., in the form of a physical medium storing the program code and/or other data to be stored in the memory 704, or by making the program code available for download or by streaming.

Figure 8 illustrates embodiment of a PWSS, 700, which implements the method for remotely configuring the Programmable Wavelength-Selective Splitter, PWSS, 700, described earlier. Figure 8 is focused on illustrating a structure, including optical connections between components of the PWSS, 700. On the left hand side of the PWSS the Line bidirectional port 304a is located. A bidirectional optical amplifier, 802, is connected between the Line port 304a and a 1 :N splitter (e.g. multiplexer/demultiplexer), 804. L number of ports of the splitter 804 (L<N) are connected to add/drop ports, 308, of the PWSS, 700. Wavelengths of the downstream WDM comb that are not to be dropped at the PWSS, 700, and wavelengths that are not to be added at the PWSS, 700, travel between the splitter and the Express port 306a. In an embodiment all wavelengths of the WDM comb may be connected to the add/drop ports 308 (in this embodiment L=N). The controller, 750, controls the amplifier, 8022, and the add/drop ports 308.

Alternative embodiments of add/drop ports, 308, are illustrated in Figures 9A and 9B. In a first embodiment, illustrated in Figure 9A, the add/drop, 308, port comprises a first tunable filter, 902, and a second tunable filter, 904, connected in series. The tunable first filter, 902, comprises three ports and is configured to pass through two wavelengths: a drop wavelength coming from the splitter, 804, and an add wavelength coming from a transmitter connected to an add port, A. The second tunable filter, 904, is configured to pass through only the drop wavelength coming from the splitter, 804, via the first tunable filter, 902, to a drop port, D. Figure 9B illustrates an alternative embodiment of an add/drop port, 308. In this embodiment a coupler/splitter, 910, connects the add/drop port to the 1:N splitter, 804, and via a third tunable filter, 906, connects to an add port, A, and via a fourth tunable filter, 908, connects to a drop port, D. The third filter, 906, lets through only an add wavelength and the fourth filter, 908, lets through only a drop wavelength.

The methods of the present disclosure may be implemented in hardware, or as software modules running on one or more processors. The methods may also be carried out according to the instructions of a computer program, and the present disclosure also provides a computer readable medium having stored thereon a program for carrying out any of the methods described herein. A computer program embodying the disclosure may be stored on a computer readable medium, or it could, for example, be in the form of a signal such as a downloadable data signal provided from an Internet website, or it could be in any other form.

It should be noted that the above-mentioned examples illustrate rather than limit the disclosure, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. The word “comprising” does not exclude the presence of elements or steps other than those listed in a claim, “a” or “an” does not exclude a plurality, and a single processor or other unit may fulfil the functions of several units recited in the claims. Any reference signs in the claims shall not be construed so as to limit their scope.

Claims

1. A method for remotely configuring a Programmable Wavelength- Selective Splitter, PWSS, the PWSS comprising an input port for receiving optical signals in a form of a comb of wavelengths, the method performed at the PWSS and comprising steps of:

- determining (402) wavelengths of the comb not present in the received optical signals;

- selecting (404) at least one of the determined wavelengths for use in add and drop ports;

- recording (406) said at least one selected wavelength as a working wavelength for the add and drop ports in configuration information stored in a register of the PWSS.

2. The method according to claim 1, wherein the input port operates as a bidirectional input/output port, and in the operation of selecting at least two, or a multiple of two, wavelengths are selected, and a first half of the selected wavelengths are set as working drop wavelengths and a second half of the selected wavelengths are set as working add wavelengths.

3. The method according to claim 1 or claim 2, wherein the operation of determining comprises detecting the optical signals of the received comb using a photodetector at one of drop ports of the PWSS and determining wavelengths of the comb for which absence of optical power has been observed.

4. The method according to claim 1 or claim 2 wherein the operation of determining comprises detecting the optical signals of the received comb using photodetectors at a plurality of drop ports of the PWSS, wherein a photodetector at an individual drop port of the plurality of drop ports determines wavelengths for which absence of optical power has been observed in a portion of the comb and the photodetectors at the plurality of drop ports cover the whole spectrum of the comb.

5. The method according to any one of claims 2 to 4, comprising interleaving drop and add channels using the selected wavelengths.

6. The method according to any one of preceding claims comprising indicating to a centralised controller that the drop and add ports of the PWSS are configured with said selected wavelengths by establishing a working communication channel using said selected wavelengths.

7. The method according to claim 6, wherein the centralised controller comprises a Network Management System or an SDN Controller.

8. The method according to any one of the preceding claims, wherein if a plurality of sequences of adjacent wavelengths of the comb are determined as absent in the received optical signals, the method comprises identifying largest sequence of said absent wavelengths and selecting from said largest sequence wavelengths for use in add and drop ports as required by configuration needs of the PWSS.

9. A Programmable Wavelength-Selective Splitter, PWSS, (302a, 302b, 700) the PWSS comprising an input port for receiving optical signals in a form of a comb of wavelengths, a plurality of add ports and drop ports, wherein an individual drop port comprises a photodetector or is configured to be connected to a photodetector, wherein the PWSS is operative to:

- determine wavelengths of the comb not present in the received optical signals;

- select at least one of the determined wavelengths for use in add and drop ports; - record said at least one selected wavelength as a working wavelength for the add and drop ports in configuration information stored in a register of the PWSS.

10. The PWSS according to claim 9, wherein the input port is configured to operate as a bidirectional input/output port, and the PWSS is operative to select at least two, or a multiple of two, wavelengths, wherein a first half of the selected wavelengths are set as working drop wavelengths and a second half of the selected wavelengths are set as working add wavelengths.

11. The PWSS according to claim 9 or claim 10, wherein to determine wavelengths of the comb not present in the received optical signals, the PWSS is operative to detect the optical signals of the received comb using a photodetector at one of the drop ports of the PWSS and to determine wavelengths of the comb for which absence of optical power has been observed.

12. The PWSS according to claim 9 or claim 10, wherein to determine wavelengths of the comb not present in the received optical signals, the PWSS is operative to detect the optical signals of the received comb using photodetectors at a plurality of the drop ports of the PWSS, wherein a photodetector at an individual drop port of the plurality of drop ports determines wavelengths for which absence of optical power has been observed in a portion of the comb and the photodetectors at the plurality of drop ports cover the whole spectrum of the comb.

13. The PWSS according to any one of claims 10 to 12, wherein drop and add channels using the selected wavelengths are interleaved.

14. The PWSS according to any one of claims 9 to 13, wherein the PWSS is operative to indicate to a centralised controller that the drop and add ports of the PWSS are configured with said selected wavelengths by establishing a working communication channel using said selected wavelengths.

15. The PWSS according to claim 14, wherein the centralised controller comprises a Network Management System or an SDN Controller.

16. The PWSS according to any one of claims 9 to 15, wherein if a plurality of sequences of adjacent wavelengths of the comb are determined as absent in the received optical signals, the PWSS is operative to identify largest sequence of said absent wavelengths and to select from said largest sequence wavelengths for use in add and drop ports as required by configuration needs of the PWSS.

17. A Programmable Wavelength- Selective Splitter (302a, 302b, 700), PWSS, comprising an input port (754) for receiving optical signals in a form of a comb of wavelengths, a plurality of add ports and drop ports (758), wherein an individual drop port (758-2) comprises a photodetector (760) or is configured to be connected to a photodetector (760), the PWSS (700) further comprises a processor (702) and a memory (704), the memory containing instructions (706) executable by the processor (702) whereby the PWSS (700) is operative to:

- select at least one of the determined wavelengths for use in add and drop ports;

- record said at least one selected wavelength as a working wavelength for the add and drop ports in configuration information stored in a register of the PWSS.

18. The PWSS according to claim 17 operative to carry out the method of any one of claims 2 - 8.