Programmable wavelength selection splitter and method for remotely configuring programmable wavelength selection splitter

Abstract

A programmable wavelength selective splitter (PWSS) and a method for remotely configuring a programmable wavelength selective splitter are disclosed. The PWSS includes an input port for receiving an optical signal in the form of a wavelength comb. The method performed at the PWSS comprises determining (402) wavelengths in the comb that are not present in the received optical signal, selecting (404) at least one of the determined wavelengths for use in an uplink port and a downlink port, and recording (406) the at least one selected wavelength as an operating wavelength for the uplink port and the downlink port in configuration information stored in a register of the PWSS.

Description

TECHNICAL FIELD

[0001] The present invention generally relates to optical networks, and in particular to a programmable wavelength selective splitter and to a method for remotely configuring a programmable wavelength selective splitter. BACKGROUND

[0002] The evolution of 5G towards 5G-Beyond and 6G further strengthens the need to use Dense Wavelength Division Multiplexing (DWDM) technology to meet high bandwidth and low latency requirements. Tunability is also required to save inventory costs, reduce field operations during the configuration phase and during fault recovery, and support network planning and instant reconfiguration capabilities. The evolution of the Radio Access Network (RAN) in centralized and cloud RAN benefits from the use of DWDM technology in the access segment to connect several antenna sites to a centralized site (usually the operator's central office) with scalable bandwidth. In this case, different network topologies (e.g. chain and tree) can be used to connect the antenna sites to the central hub. In some cases, DWDM technology can be used to overlay the RAN on already installed Passive Optical Network (PON) infrastructure, and this enables the use of the widely deployed fiber infrastructure.

[0003] Most of these scenarios are based on DWDM transceivers with fixed transmission wavelengths. This impacts inventory, as several TRXs are needed, one for each wavelength. Moreover, field operations (e.g. configuration or fault recovery) cannot be performed as a simple plug-and-play, as it is necessary to correctly connect the available fibers to the correct TRX ports. Fixed filters and transceivers require a strict wavelength plan from the first day, and do not allow changes to this plan without significant moves on the fiber connections in the field. To simplify inventory and operations, TRXs tunable on transmission have been implemented (i.e. using tunable lasers). Such TRXs do not have a tunable receiver, so they are used in combination with DeMultiplexers (DeMUXs) in the network, which allow to "color" (i.e. select a specific wavelength) each port and send the correct wavelength to the receiver. The assignment of the wavelengths is performed in advance (planning phase) for the network and the antenna sites. Tunable TRXs are self-tuned using algorithms, and self-tuning enables an automatic process for configuration to slightly simplify the configuration. To implement a fully tunable TRX that can work as a plug-and-play module, that can be operated without pre-planning the wavelengths, and that simplifies field operations, it is necessary to make the receiver of the TRX fully tunable. In patent application WO2022 / 258432A1 a solution has been identified to dynamically control a fully tunable TRX. However, neither the device nor the operations in the present invention as now to be described are disclosed or suggested in this document. SUMMARY

[0004] According to a first aspect of the application, there is provided a method for remotely configuring a programmable wavelength selective splitter, PWSS. The PWSS comprises an input port for receiving an optical signal in the form of a wavelength comb. The method performed by the PWSS comprises determining wavelengths in the comb that are not present in the received optical signal. The method further comprises selecting at least one of the determined wavelengths for use in an add port and a drop port, and recording the at least one selected wavelength as an operating wavelength for the add port and the drop port in configuration information stored in a register of the PWSS.

[0005] According to a second aspect of the application, there is provided a programmable wavelength selective splitter, PWSS. The PWSS comprises an input port for receiving an optical signal in the form of a wavelength comb, a plurality of add ports and drop ports. An individual drop port comprises an optical detector or is configured to be connected to an optical detector. The PWSS is operable to determine wavelengths in the comb that are not present in the received optical signal, and to select at least one of the determined wavelengths for use in an add port and a drop port. Furthermore, the PWSS is operable to record the at least one selected wavelength as an operating wavelength for the add port and the drop port in configuration information stored in a register of the PWSS.

[0006] According to a third aspect of the application, there is provided a programmable wavelength selective splitter, PWSS. The PWSS comprises an input port for receiving an optical signal in the form of a wavelength comb, and a plurality of add ports and drop ports. An individual drop port comprises an optical detector or is configured to be connected to an optical detector. The PWSS further comprises a processor and a memory, the memory containing instructions executable by the processor, whereby the PWSS is operable to determine wavelengths in the comb that are not present in the received optical signal, and to select at least one of the determined wavelengths for use in an add port and a drop port. The PWSS is further operable to record the at least one selected wavelength as an operating wavelength for the add port and the drop port in configuration information stored in a register of the PWSS.

[0007] Further features of the application are claimed in the dependent claims. BRIEF DESCRIPTION OF DRAWINGS

[0008] The application will be more fully understood and appreciated from the following detailed description, taken in conjunction with the accompanying drawings, of which: Figure 1A and 1B two embodiments of a configurable device based on a programmable wavelength selective splitter are shown; Figure 2A and 2B two examples of spectral allocation to downstream and upstream channels are shown; Figure 3A and 3BTwo embodiments of a programmable wavelength selective splitter implemented in a section of a communications network are shown; Figure 4 is a flowchart showing a method for remotely configuring a programmable wavelength selective splitter in one embodiment; Figure 5 is a flowchart showing details of one possible practice of a method for remotely configuring a programmable wavelength selective splitter as seen from a remote site where the PWSS is installed; Figure 6 Operation of a network management system in a network remotely configuring programmable wavelength selective splitters according to disclosed embodiments is shown; Figure 7 is a block diagram showing one embodiment of a programmable wavelength selective splitter; Figure 8 is a block diagram showing one embodiment of a programmable wavelength selective splitter; Figure 9A and 9B Two embodiments of add / drop ports for use in a PWSS are shown. DETAILED DESCRIPTION

[0009] 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 present invention. However, it will be apparent to those skilled in the art that the present invention can 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 present invention with unnecessary detail.

[0010] Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the 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 this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics can be combined in any suitable manner in one or more embodiments.

[0011] When reference is made in this document to wavelength division multiplexing (WDM), it also includes dense wavelength division multiplexing (DWDM).

[0012] The inventors have recognized that, in order to achieve full tunability of an antenna site from a remote location, it is possible to consider a device / module based on tunable filter ports that allow a subset of L wavelengths to be dropped from an incoming downlink comb and let L new wavelengths to be generated locally to be added to an outgoing uplink comb. Such a module can be housed at both endpoints (i.e. the antenna site and the central office) or only at the remote site. This is in Figure 1Aone of the problems solved by the solution to be disclosed is that when used in practice on remote sites, Figure 1A The reconfigurable device 150-1 shown in the figure can not have access to the DCN and access to the network management system through it, or in other words, the solution to be disclosed contemplates the configuration of the reconfigurable device 150-1 in the event that the device lacks a control channel between the device and the central office and the network management system. Figure 1A An embodiment based on a single bidirectional fiber 100 is shown. The above also applies to embodiments based on two unidirectional fibers 102 and 104 as Figure 1B An embodiment of the configurable device 150-2 based on two unidirectional fibers 102 and 104 is shown in the figure.

[0013] The present document discloses a method for self-configuration of remote devices, which is fully compatible with existing TRXs tunable on the transport to guarantee interworking with existing technology.

[0014] In one embodiment, the present invention defines a plug-and-play programmable wavelength selective splitter (PWSS) that can operate in an optical communication network as shown in Figures la and lb. The present document also discloses a method for configuration that allows the uplink and downlink ports to be tuned on the available wavelengths. Embodiments of the solution disclosed in the present document allow the establishment of wavelength selective paths as can be achieved in a conventional DWDM network employing multiplexer / demultiplexer filters and OADMs (optical add-drop multiplexers).

[0015] After the field engineer has installed the PWSS according to one embodiment of the present invention, he or she sends the identification information (this can include serial number, part number, GPS coordinates, etc.) to the network management system (NMS) with the ports to which the cables are connected. At the central office, the NMS checks the validity of the received information and sends the field engineer a license to turn on the new device.

[0016] During the turn-on process, the controller of the PWSS checks its configuration status register (CSR) in the EEPROM memory and, in the event that the device has to be configured, the controller starts the method of the invention disclosed herein. In the event that the device does not have to be configured, the controller sends a message to the NMS indicating that the device is ready to be used. Figure 7 In the preferred embodiment shown in the figure, 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.

[0017] The controller of the PWSS preferably uses one of the drop ports to find L adjacent unused wavelengths in the optical spectrum. There is no unused wavelength in the optical signal detected by the drop port. In other words, there is no optical power detected at the unused wavelength. In case the L adjacent wavelengths are not available, the controller can iteratively reduce this number to find a set of available adjacent wavelengths (adjacent channels). It can be that the network operator wants to configure 6 add and 6 drop channels (wavelengths) for the PWSS, but only 4 consecutive (i.e. 4 add and 4 drop) channels are available. In this case, the method of this embodiment can find the remaining wavelengths in other parts of the optical spectrum used in the network, or it can be that there are no more channels available, and the PWSS will be configured with only a part of the originally intended channels, based on the channels available in the network. Of course, in case the device cannot find even one available wavelength in the optical spectrum, the process aborts and the device remains unconfigured. In practice, the technician on site has information about how many ports he has to connect for both PWSS_A and PWSS_B (these are the PWSS devices at the local (i.e. central office) and remote end). When the fiber connections have been established, the technician sends the ID information of the installed PWSS and the number of ports of the cable connection to the NMS in the central office. From the ID information, the NMS detects the total number of available ports on the PWSS, and from the number of ports of the actual cable connection, it detects the maximum number of connections it has to establish with the remote device.

[0018] When the controller of the PWSS finds a set of available adjacent wavelengths, it tunes the drop ports and thus the add ports according to the selected strategy for allocating channels, for example: - the downstream wavelengths (drop) are interleaved with the upstream wavelengths (add); see Figure 2A , - the downstream wavelengths belong to a first part of the optical spectrum and the upstream wavelengths belong to a second part of the optical spectrum, see Figure 2B .

[0019] When the drop ports and the add ports are tuned to the assigned wavelengths, the result is that the physical paths that will route the optical wavelengths from the source transmitters to their respective assigned remote receivers are established.

[0020] In order to minimize the timing asymmetry between the signals transmitted in the downstream direction and the signals transmitted in the upstream direction on a single transceiver, the two corresponding wavelengths are preferably adjacent, and the interleaving plan for the downstream and upstream directions is preferably used. This means that, once a downstream wavelength is identified, the corresponding upstream wavelength is the one that is adjacent.

[0021] A second example of a predefined plan is one that splits the available spectrum into two contiguous segments, an upper and a lower edge sub-band. The down channels of a comb are allocated into the first sub-band and the up channels of the comb are allocated into the second sub-band. In a preferred embodiment, the distance (in wavelengths) between the down and up wavelengths assigned to the same transceiver is constant among these transceivers.

[0022] After the down and up channels are allocated to their corresponding ports, the controller records this in the CSR.

[0023] In the CO, the NMS waits for the required programming time and then starts the verification process for the scheduled links. If one or more links are not up, the NMS raises an alarm and starts the process of evaluating and resolving the problem (e.g. remote device failure, transceiver failure, wrong connection, etc.). Once the problem has been resolved, the alarm is closed and the NMS continues operation. As can be seen by those skilled in the art, the operation in the physical layer is split into two parts. The first part covers the implementation of the various physical circuits dedicated to the assigned pairs of wavelengths (up and down) for end-to-end communications. The second part covers the control of the transceivers involved in the establishment and operation of the communication channels. The PWSS programming belongs to the first part, while the opening of the communication channels belongs to the second part. In operation, the NMS oversees both parts and takes action on them. In the first part, the NMS uses the pseudo-signal(s) to direct the programming of the PWSS on the desired up / down channels, in the second part, the NMS drives the opening of the TRX and establishes the communication channels. Only when the NMS attempts to establish a new communication channel, it verifies whether the PWSS installation and programming have been performed correctly. The failure to establish a new communication channel indicates a failure in the installation or programming or both. For completeness, in embodiments of the present invention, the opening of the TRX can be triggered by the same NMS or a different NMS / control (e.g. it can be the radio domain). For simplicity, in the rest of this document, it is assumed that it is the same NMS, but the present invention works equally well in both embodiments.

[0024] Figure 3A A PWSS 302a in one embodiment of the present invention implemented in a certain section of a communication network 300 implemented as a WDM optical network is shown. In one embodiment, it can be a front-haul network between a centralized radio controller in a central office and the radio heads (or antenna sites) of a radio access network (RAN). Figure 3A The embodiment shown in Fig. 3 employs bidirectional fibers 320 and 322 connected to the Line ports 304a and the Express ports 306a to operate.

[0025] PWSS 302a shows two bi-directional ports, Line 304a and Express 306a, in which aggregated upstream and downstream signals of a WDM comb travel, as well as 2L ports 308 dedicated to channel add / drop. The WDM comb comprises N wavelengths (channels), for example 48 wavelengths dedicated to communication channels, as shown in the example illustrated in Figure 2A and Figure 2B The incoming downstream comb applied to the Line port, up to L wavelengths (where L < N) can be dropped and sent to the assigned receiver 310, where L designates the number of drop ports. In a preferred embodiment, given the total of 2L ports 308 dedicated to channel add / drop, the number of drop ports will also be L. A copy of this downstream comb (with or without dropped wavelengths) is launched from the PWSS 302a via the Exp port 306a, to other PWSSs connected in the chain downstream in the chain. In the opposite direction, up to L wavelengths (where L < N) provided from the transmitter 312 connected to the add port can be multiplexed and added to the incoming upstream comb received at the Exp port 306a. This upstream comb arrives from the PWSS (not shown) connected in the chain on the left-hand side of Figure 3A and is launched from the Line port 304a to the central office (not shown) of the network on the right-hand side of Figure 3A

[0026] With reference to Figure 3A 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 a downstream optical signal in the form of a wavelength comb. In one embodiment, as shown in Figure 3A the input port 304a is a bi-directional port (input / output) to which a single bi-directional fiber is connected, linking the PWSS 302a to a central office. Similarly, in a preferred embodiment, the Express port 306a is a bi-directional port (input / output) to which a single bi-directional fiber is connected, linking the PWSS 302a to another PWSS located downstream. From the network operator's point of view, a network architecture based on a single bi-directional fiber is the preferred option, as it reduces the cost of renting fibers (a single fiber is used for a bi-directional option, while two fibers are used for a dual fiber configuration). However, in an alternative embodiment, the methods disclosed herein are also applicable to a dual fiber network architecture, as shown in Figure 3B ​As shown in FIG. 3B, one of the optical fibers is dedicated to downstream traffic (from the CO) while the other optical fiber is dedicated to upstream traffic (to the CO). In embodiments of the dual fiber configuration, 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 includes an output port 306b for transmitting downstream signals to other antenna sites and an input port 306c for receiving upstream signals from other antenna sites.

[0027] In both embodiments (i.e., one bidirectional fiber configuration and in the dual fiber unidirectional configuration), only the tunable filter acting as a drop port detects the presence / absence of the downstream wavelengths.

[0028] In the preferred embodiment, the method performed at the PWSS 302a or 302b includes the operation of determining (402) the wavelengths in the comb that are not present in the received optical signal.

[0029] To identify the wavelengths that are not used (i.e., not transmitted by the transceiver at the CO), the solution in one embodiment detects which channels are used. The controller of the PWSS 302a or 302b knows the WDM comb, which means it knows the wavelengths assigned to each channel of the WDM comb, and after one or more photodetectors detect which channels are used, the controller determines which channels are not used and reports only the empty channels. In the preferred embodiment, photodiodes are used as photodetectors. Alternatively, the controller can report the entire map of the comb showing which channels (wavelengths) are used and which are empty. The empty channels can be used to configure the PWSS.

[0030] In the next step, the method includes selecting (404) at least one of the determined wavelengths for use in the add and drop ports. For embodiments of the network's architecture based on dual fibers, where one fiber is used for upstream communication and one fiber is used for downstream communication, since the drop port will receive data on the downstream fiber while the add port will send data to the CO through the upstream fiber, the same wavelength can be used for the drop port and the add port of the PWSS, so only one wavelength needs to be selected (404). Since the upstream and downstream transmissions are separate, there is no interference even if the same wavelength is used in both directions.

[0031] However, in alternative embodiments, in which the input ports 304a operate as bidirectional input / output ports (Line ports 304a), in the selecting (404) operation, at least two or an even number of 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 optical fiber, since optical signals traveling in opposite directions do not have the same wavelengths.

[0032] In the next step of the method, the controller records (406) the at least one selected wavelength as working wavelengths for the add and drop ports in the configuration information stored in the registers of the PWSS. For PWSSs operating with bidirectional Line ports, at least two wavelengths are recorded in the register.

[0033] The operation of determining the wavelengths in the comb that are not present in the received optical signal can be performed in one of several embodiments. In one embodiment, the optical detector of one drop port detects the optical signal of the received comb by scanning the entire spectrum of the comb, and from this operation, the controller determines the wavelengths in the comb for which optical power is missing.

[0034] In alternative embodiments, the determining operation includes using optical detectors at multiple drop ports of the PWSS to detect the optical signal of the received comb. The multiple drop ports can 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, the individual optical detectors at individual drop ports of the multiple drop ports scan only a portion of the spectrum of the comb, and the controller of the PWSS determines the wavelengths in the comb for which optical power is missing. The sum of the portions of the comb scanned by the optical detectors of these drop ports covers the entire spectrum of the comb. Using multiple optical detectors operating in parallel to determine the wavelengths in the comb that are not present in the received optical signal allows speeding up the determining operation.

[0035] In embodiments in which the PWSS 302a is connected to the CO using bidirectional optical fibers, the method includes interleaving the use of the drop and add channels of the selected wavelengths.

[0036] Since there are no control channels in the network 300, in one embodiment, the method includes indicating to a centralized controller at the CO to configure the drop and add ports of the PWSS with the selected wavelengths by establishing a working communication channel using the selected wavelengths. In one embodiment, the centralized controller can include a network management system or an SDN controller.

[0037] Preferably, if a plurality of sequences of contiguous wavelengths of the comb are determined to be missing in the received optical signal, the method comprises identifying the largest sequence of said missing wavelengths and selecting wavelengths from said largest sequence for use in the add and drop ports according to the requirements of the configuration of the PWSS. Selecting contiguous wavelengths has the advantage of reducing the timing differences between different channels, which in turn helps to maintain network synchronization.

[0038] In various embodiments, the method disclosed in this document allows for the remote configuration of the add / drop ports of a PWSS and has the following properties: • The method enables the self-configuration (tuning) of the PWSS by independently configuring the wavelength selection paths (as in a traditional DWDM network employing commercial MUX / Demux / OADM filters, but without the need for MUX / Demux / OADM filters); • The method takes over the wavelength assignment policy from the network management system, but the NMS can still influence the configuration of the PWSS, causing 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 the PWSS under configuration should not use and leaving the wavelengths that the NMS wants the PWSS to use as add / drop channels empty (unused). This is possible because no more than one PWSS is allowed to be configured at the same time, to avoid multiple devices tuning their ports to the same wavelengths; • No control messages are exchanged between the CO and the remotely located PWSS, which means that the present solution allows for the configuration of the PWSS in a network without control channels.

[0039] The method thus provides numerous advantages, including simplified configuration and field operations, and is fully compatible with existing tunable TRXs. By allowing remote configuration, the method helps to reduce the need for field visits for fault recovery and / or installation and / or reconfiguration. The disclosed method is compatible with any radio and transport architecture (e.g., configured by an SDN controller and / or a network management system) and is future-proof in terms of O-RAN. It also simplifies the planning operations, as it does not require pre-planning of the assignment of wavelengths to the remote sites. Furthermore, the module configuration does not require the installation of specific communication and control channels between the network management system in the central office CO and the module itself.

[0040] In one embodiment, the NMS waits until all the 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 whether all the PWSSs have been successfully configured. Therefore, in one embodiment, when the configuration time for the PWSSs is over, the system (i.e., the NMS at the CO) can perform a polling procedure to verify that the physical layer is configured and turned on. If communication between the antenna sites connected to the add / drop ports of the PWSSs is possible in both directions, this indicates that the connection on the physical layer is correctly configured. Otherwise, an alarm is raised.

[0041] In an alternative embodiment, the system (e.g., the radio controller, the NMS, etc.) can receive a trigger from a field engineer to configure the transport network.

[0042] In the above embodiment, the verification of the successful configuration is performed when all the PWSSs in the network are connected and configured. However, in an alternative embodiment, such verification can be performed after the configuration of an individual PWSS or after the configuration of a group of PWSSs.

[0043] Figure 5 More details of one possible implementation of an embodiment of a method for remotely configuring a programmable wavelength selective splitter PWSS are shown as seen from the perspective of a remote site where the PWSS is installed.

[0044] After installation, the PWSS has at least one pair of add / drop ports (502) connected with cables to transceivers. Information identifying the PWSS (e.g., serial number and / or part number), its location (e.g., GPS coordinates), and the connections (ports to which the cables are connected) is provided to the NMS (504), which uses an additional communication channel (any way of informing the NMS is possible, this can be a phone call from a field engineer to an operator in the central office, a text message, an email, details filled in on a web interface). Once the field engineer gets authorization from the CO to power up the PWSS, the PWSS is turned on (506-510). The controller of the device checks the configuration status register (CSR) on the EEPROM, and if the device has not been configured (512-514), the PWSS scans (516) the entire downlink spectrum, surveying for available downlink wavelengths (i.e., wavelengths in the WDM comb that are not used, or in other words, wavelengths in the WDM comb for which no optical power is detected).

[0045] Three different scanning methods can be applied, all of them based on the availability of the optical detectors placed at the output of the drop ports of the module detecting the presence of optical power. The first scanning method uses the preferred drop port of the PWSS, which scans all the available down channels, surveys (detects no optical power) the available channels and distinguishes them from the non-available channels for which the optical power has been detected accordingly. The second scanning method uses in parallel all the available drop ports (this number is indicated with 'L') to scan the set of wavelengths, surveying the availability or non-availability of each of them. Finally, the third method is based on the parallel use of a number of drop ports equal to 'K', with K e [2; L-1], to scan a set of 'K' wavelengths, surveying the availability or non-availability of each of them. Comparing the three methods, the second and the third one allow a faster determination of the available channels, since the optical detectors of the drop ports scan a much smaller portion of the spectrum of the comb and in parallel, compared to the first method.

[0046] Thereafter, in the preferred embodiment, the controller of the PWSS identifies (518) the first maximum sequence of available and adjacent downlink wavelengths and writes the programming information in the CSR in the EEPROM memory. In case the programmed channels are less than the number of add / drop ports of the PWSS, the ports for which no available channel has been found remain unprogrammed. When the tunable device (e.g. the tunable laser of the TRX) is activated, it requires a voltage or a current or both to bias the tunable device and turn on the circuit to control these physical quantities. Therefore, leaving unprogrammed the unused ports allows to deactivate their corresponding tunable device and to reduce the power consumption. In case the device is not able to find even one available downlink wavelength in the spectrum, the process is aborted and the device remains unconfigured.

[0047] When the controller of the PWSS finds a set of adjacent downlink wavelengths available, it writes all the programming information in the EEPROM registers and then it sets the CSR to the appropriate value (520). Thereafter, it configures the add / drop ports (the biasing of the tunable elements and their control are activated) and the method stops.

[0048] Figure 6 The actions of a network management system in a network remotely configuring a programmable wavelength selective splitter PWSS according to an embodiment of the application are shown.

[0049] The network management system checks whether all provisioning links of the network are configured and operational (i.e., whether traffic is transmitted and received using these links) (602). If the answer is "yes", the method stops. If the answer is "no", the NMS checks whether there is information from the field about a new device installation (604). If the answer is "no", the NMS waits for a trigger from the field, and this can be checked repeatedly until such new information is received. If the answer in step 604 is "yes", the NMS checks the received information (608), and if the information about the new installation is complete (610 - yes), the configuration of the remotely installed PWSS can begin. Depending on the implementation, when a new PWSS module has been installed, the NMS receives identification information from the field engineer, which can help to identify the installed PWSS and its location in the network. The information provided can include: - serial number; - part number; - positioning information; - ports of cable connections.

[0050] The NMS assigns a subset of adjacent wavelengths to the newly installed PWSS module (612). In an optional step 614, the NMS turns on some unused transmitters in the central office in such a way that forces the PWSS to select a particular wavelength, controlling the configuration of the PWSS. Because in embodiments of the method the PWSS can select a wavelength of the central office that is not used for communication with other network elements, the NMS / CO creates a pseudo channel that looks to the PWSS as if it is being used by the CO / NMS for data communication by turning on a subset of unused wavelengths. Thus, the PWSS does not select a wavelength from this pseudo channel set, but from the remaining unused wavelengths. In this way, the NMS can direct the configuration of the PWSS.

[0051] In the next step 616, the NMS authorizes the turning on of the PWSS module.

[0052] Once the configuration time has elapsed (618), the PWSS is configured using embodiments of the method described earlier, and if this option has been used, the NMS turns off the transmitter transmitting on the pseudo-channel (620) and starts the verification (622) of the links configured by the PWSS using embodiments of the method described earlier. If one or more links are not up (624 - No), the NMS raises an alarm (626) and starts the process of evaluating and solving the problem (e.g. remote device failure, transceiver failure, wrong connection, etc.) (628). Once the problem has been solved (630), the alarm is turned off (632) and the NMS continues the verification operation (622) by checking if all the planned links are up and running. In case of negative answer, the operations 622, 624, 626, 628, 630 and 632 are looped. If all the newly assigned links are confirmed to be up (624 - Yes), the method returns to step 602 where it is checked if all the network links are carrying traffic. If the answer is Yes, the method stops.

[0053] Figure 7 An embodiment of a PWSS 700 is shown, which implements the method described earlier for remotely configuring a programmable wavelength selective splitter PWSS 700. The PWSS 700 comprises a processing circuitry 702 and a memory 704. The processing circuitry 702 and the memory 704 form a controller 750 which controls the operation of the PWSS 700. In one embodiment, the processing circuitry 702, which can comprise one or more processors, can be integrated with the memory 704 in a single chip. However, this is not essential.

[0054] The memory 704 contains instructions executable by the processing circuitry 702, so that the PWSS 700 is operable to determine wavelengths that are not present in a received optical signal in a comb, select at least one of the determined wavelengths for use in an add port and a drop port, and then record the at least one selected wavelength in configuration information stored in a register 752 of the PWSS 700 as an operating wavelength for the add port and the drop port.

[0055] The PWSS 700 includes line ports 754 that connect the PWSS to a central office and pass-through ports 756 that connect the PWSS to another PWSS located downstream. If the network operates over a single bidirectional fiber, then the line and pass-through ports are also bidirectional. In an alternative embodiment in which the network is implemented based on a two-fiber architecture, the line ports 754 include two separate ports: an input and an output, for receiving signals from the central office (input port) and for transmitting signals to the central office (output port). The pass-through ports 756 in the two-fiber architecture are arranged in the same manner, with two separate ports, one for transmitting downstream signals and one for receiving upstream signals. The PWSS 700 also includes a plurality (2L) of add and drop ports 758. Individual drop ports 758-2 can include photodetectors 760, or be configured to connect to photodetectors 760.

[0056] The memory 704 can include read-only memory (ROM) (e.g., flash ROM), random access memory (RAM) (e.g., dynamic RAM (DRAM) or static RAM (SRAM)), mass storage (e.g., a hard disk or solid state disk), etc. The memory 704 can include software in the form of appropriate Figure 5

[0057] It is to be understood that the structure shown in Figure 7 is merely schematic, and that the PWSS 700 can in fact include additional components not shown for the sake of clarity, e.g., additional interfaces or processors. Further, it is to be understood that the memory 704 can include additional program code for implementing other and / or known functionality.

[0058] According to some embodiments, in order to implement the functionality of the PWSS 700, a computer program can also be provided, 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, for example.

[0059] Figure 8 An embodiment of a PWSS 700 is shown, which implements the method for remotely configuring a programmable wavelength selective splitter PWSS 700 described earlier. Figure 8 ​The structure including the optical connections between the components of the PWSS 700 is highlighted. The Line bidirectional port 304a is on the left hand side of the PWSS. A bidirectional optical amplifier 802 is connected between the Line port 304a and a 1 :N splitter (e.g., multiplexer / demultiplexer) 804. The L ports (L < N) of the splitter 804 are connected to the add / drop ports 308 of the PWSS 700. The wavelengths that are not dropped at the PWSS 700 and the wavelengths that are not added at the PWSS 700 travel between the splitter and the Express port 306a. In one embodiment, all the wavelengths of the WDM comb can 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.

[0060] In Figure 9A and Figure 9B alternative embodiments of the add / drop ports 308 are shown. In the first embodiment shown in Figure 9A the add / drop ports 308 include a first tunable filter 902 and a second tunable filter 904 connected in series. The tunable first filter 902 includes three ports and is configured to pass two wavelengths: the drop wavelengths from the splitter 804 and the add wavelengths from the transmitter connected to the add port A. The second tunable filter 904 is configured to pass only the drop wavelengths from the splitter 804 to the drop port D via the first tunable filter 902.

[0061] Figure 9B alternative embodiments of the add / drop ports 308 are shown. In this embodiment, a coupler / splitter 910 connects the add / drop ports to the 1 :N splitter 804 and to the add port A via a third tunable filter 906 and to the drop port D via a fourth tunable filter 908. The third filter 906 passes only the add wavelengths and the fourth filter 908 passes only the drop wavelengths.

[0062] The methods of the present disclosure can be implemented in hardware, or as software modules running on one or more processors. The methods can also be performed according to instructions in a computer program and the present disclosure also provides a computer readable medium having stored thereon a program for performing any of the methods described herein. A computer program implementing the present disclosure can be stored on a computer readable medium, or it can be in the form of a signal such as a downloadable data signal provided from an Internet website, or it can be in any other form.

[0063] 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 "one" or "an" does not exclude a plurality, and a single processor or other unit can fulfill the functions of several units recited in the claims. The application is not limited to the embodiments described above, but anyone skilled in the art will be able to devise alternative embodiments without departing from the scope of the appended claims.

Claims

1. A method for remotely configuring a programmable wavelength selective splitter, PWSS, the PWSS comprising an input port for receiving an optical signal in the form of a wavelength comb, the method being performed at the PWSS and comprising the steps of: - determining (402) wavelengths in the comb that are not present in the received optical signal; - selecting (404) at least one of the determined wavelengths for use in an add port and a drop port; - recording (406) the at least one selected wavelength as an operating wavelength for the add port and the drop port in configuration information stored in a register of the PWSS.

2. The method of claim 1, wherein, The input port operates as a bidirectional input / output port, and in the selecting operation at least two wavelengths or an even number of wavelengths are selected, and a first half of the selected wavelengths are set as operating drop wavelengths, while a second half of the selected wavelengths are set as operating add wavelengths.

3. The method of claim 1 or claim 2, wherein, The determining operation comprises using an optical detector at one of the drop ports of the PWSS to detect the optical signal of the received comb, and determining wavelengths in the comb for which an absence of optical power has been observed.

4. The method of claim 1 or claim 2, wherein, The determining operation comprises using optical detectors at a plurality of drop ports of the PWSS to detect the optical signal of the received comb, wherein the optical detector at an individual drop port of the plurality of drop ports determines wavelengths in a portion of the comb for which an absence of optical power has been observed, and the optical detectors at the plurality of drop ports cover the entire spectrum of the comb.

5. The method of any one of claims 2 to 4, comprising: Drop channels and add channels using the selected wavelengths are interleaved.

6. The method of any of the preceding claims, comprising: By establishing operating communication channels using the selected wavelengths, a centralized controller is instructed to configure the drop ports and the add ports of the PWSS with the selected wavelengths.

7. The method of claim 6, wherein, The centralized controller comprises a network management system or an SDN controller.

8. The method according to any of the preceding claims, wherein, If a plurality of sequences of adjacent wavelengths of the comb are determined to be absent in the received optical signal, the method comprises identifying a largest sequence of the absent wavelengths, and selecting wavelengths from the largest sequence for use in an add port and a drop port according to requirements of a configuration need of the PWSS.

9. A programmable wavelength selective splitter, PWSS (302a, 302b, 700), the PWSS comprising an input port for receiving an optical signal in the form of a wavelength comb, a plurality of add ports and a drop port, wherein, An individual drop port comprises an optical detector or is configured to be connected to an optical detector, wherein the PWSS is operable to: - determine wavelengths in the comb that are not present in the received optical signal; - select at least one of the determined wavelengths for use in an add port and a drop port; - record the at least one selected wavelength as an operating wavelength for the add port and the drop port in configuration information stored in a register of the PWSS.

10. The PWSS of claim 9, wherein, The input port is configured to operate as a bidirectional input / output port, and the PWSS is operable to select at least two wavelengths or an even number of wavelengths, wherein a first half of the selected wavelengths are set as operating drop wavelengths, while a second half of the selected wavelengths are set as operating add wavelengths.

11. The PWSS of claim 9 or claim 10, wherein, To determine the wavelengths in the comb that are not present in the received optical signal, the PWSS is operable to use an optical detector at one of the drop ports of the PWSS to detect the optical signal of the received comb and determine the wavelengths in the comb for which optical power absence has been observed.

12. The PWSS of claim 9 or claim 10, wherein, To determine the wavelengths in the comb that are not present in the received optical signal, the PWSS is operable to use optical detectors at a plurality of drop ports of the PWSS to detect the optical signal of the received comb, wherein the optical detector at an individual drop port of the plurality of drop ports determines the wavelengths in a portion of the comb for which optical power absence has been observed and the optical detectors at the plurality of drop ports cover the entire spectrum of the comb.

13. The PWSS of any of claims 10-12, wherein, Drop and add channels using the selected wavelengths are interleaved.

14. The PWSS of any one of claims 9 to 13, wherein, The PWSS is operable to indicate to a centralized controller to configure the drop and add ports of the PWSS with the selected wavelengths by establishing working communication channels using the selected wavelengths.

15. The PWSS of claim 14, wherein, The centralized controller comprises a network management system or an SDN controller.

16. The PWSS of any one of claims 9 to 15, wherein, If a plurality of sequences of adjacent wavelengths of the comb are determined to be absent in the received optical signal, the PWSS is operable to identify the largest sequence of the absent wavelengths and select wavelengths from the largest sequence for use in the add and drop ports according to requirements of the configuration needs of the PWSS.

17. A programmable wavelength selective splitter, PWSS (302a, 302b, 700), the PWSS comprising an input port (754) for receiving an optical signal in the form of a wavelength comb, a plurality of add ports and drop ports (758), wherein, An individual drop port (758-2) comprises or is configured to be connected to an optical detector (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 operable to: - determine the wavelengths in the comb that are not present in the received optical signal; - select at least one of the determined wavelengths for use in the add and drop ports; - record the at least one selected wavelength in the configuration information stored in a register of the PWSS as working wavelengths for the add and drop ports.

18. The PWSS of claim 17, the PWSS is operable to perform the method of any of claims 2 to 8.

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