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ROADM Technology

As the bandwidth requirements grow rapidly, optical network operators face continued challenges of modifying the current optical networks to meet this growing demand. In WDM networks, this modification mainly means adding new WLs, and sometimes changing the WL distribution within the network. The WDM solutions have scaled up in recent years from typically 8-16 Wavelengths to 44-88 Wavelengths solution, with different routes per each wavelengths and mesh connectivity between sites across the ring.

Network managers face the challenge to keep track of all the wavelengths, monitor their correct operation and deploy new wavelengths easily while reducing the operation cost of the network. In non ROADM networks, if not already pre-assigned, adding new services requires redesign or major network change which takes time, resources and poses risks of traffic disruptions.

Another major issue that usually requires manual handling in non-ROADM networks is the power balancing of the bypass wavelengths as opposed to locally added wavelengths on any particular node. It is necessary to balance the optical power of these WLs at the input point to an EDFA (Erbium-Doped  Fiber Amplifier).  Otherwise, in a link with many EDFAs and multiple channels, some channels might be lost due to a lack of optical power if not balanced along the path.

Ring network with East and West facing ROADM - diagram

Figure 1

The Reconfigurable Optical Add Drop Multiplexer (ROADM) adds the required flexibility so that adding WLs or changing the WL destination becomes easy and remotely managed process providing full control and monitoring over the entire high capacity infrastructure.

The basic element of the ROADM is the Wavelength Selective Switch (WSS). The WSS is an active component that performs the actual WL switching and monitoring. PacketLight’s ROADM offers the ultimate in flexibility and in a low cost WSS technology suitable for core and edge applications. The user can dynamically drop any wavelength to any port and then seamlessly change drop capacity on an as needed basis. The advanced ROADM core WSS component provides a flexible channel plan together with dynamic per-channel power equalization. With its industry leading footprint and switching speed WSS component in PacketLight’s ROADM product is the best wavelength routing solution for core metro and edge networks.  Together with OCM (Optical Channel Monitoring), it monitors and balances power across all channels using VOAs array.

Figure 1 above describes one particular node in the ring network with East and West facing ROADMs. The WSS can select any color to be routed towards the drop side of the local Node or bypass to the next Node.  The input port can receive the whole C band and the drop (or add) ports can drop, bypass or block any channel as chosen.

Combined with the Tunable Transceivers, the ROADM becomes the most flexible and easily scalable solution for optical networks. Figure illustrates WL provisioning for two Nodes. The management SW determines the WL for the two Transceivers and the relevant configuration for the ROADMs in the ring. Power balancing is performed automatically by the WSS.  The whole process is done from a remote site via a network management system.

The ROADM WSS and Tunable Transceivers - image illustration

Figure 2
: The ROADM WSS and Tunable Transceivers

A multi degree node is a node with more complex network architecture as in full mesh or ring with spur.  This requires a few WSS and PS (Power Splitters) as shown in Figure 3. This adds additional level of flexibility, letting WL route from any line to any line or be dropped anywhere.  In an event of failure of any of the services, the protecting WL routes its path through the network to overcome or bypass the failure. The number of node degrees depends on the number of the WSS components present on the node.  WSS normally is the building block that is chained together to form a multi degree node.

Multi degree node diagram
Figure 3: Multi degree Node

PackeLtlight ROADM solution follows the conceptual planning and design of the rest of PacketLight's product line which is based on 1U architecture. PacketLight’s PL1000RO not only saves space, power consumption and provides  easy scalability, but also provides high level of integrated optical elements such as EDFAs and Mux/ DeMuxes enclosed within a single 1U enclosure. This economical solution contains 1x2 WSS on the add ports and a PS (Power Splitter) on the drop ports. Together with the internal OCM and VOA per each WL, PL-1000RO handles the switching of the WL, as well as the power balancing and is future proof for 40 Gb/s, 100 Gb/s and 400Gb/s with 50Ghz and 100GHz channel spacing support. This compact solution also contains the Booster and the Pre Amplifier and two PSU for redundancy. The passive Mux/Demux are FRUs (Field Replaceable Units) giving the user the ability to economically design the network according to network manager's needs.

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