Widely tunable lasers: Unleashing the power of intelligent optical networks
By SAEID ARAMIDEH, iolon Lightwave--Due to ever-increasing data requirements, network carriers must find a way to upgrade networks while driving down costs--and they must do it fast before the demand for data services overtakes their capabilities to deliver. As such, tunable lasers have become the "Holy Grail" for next-generation DWDM and the catalyst for flexible intelligent optical networks.
Applications such as dynamically configurable networks and bandwidth on demand will provide new revenue opportunities for carriers.
By SAEID ARAMIDEH, iolon Lightwave--Due to ever-increasing data requirements, network carriers must find a way to upgrade networks while driving down costs--and they must do it fast before the demand for data services overtakes their capabilities to deliver. As such, tunable lasers have become the "Holy Grail" for next-generation DWDM and the catalyst for flexible intelligent optical networks. These devices address the dynamic requirements to not only reduce the cost of responding to bandwidth demand and network failures, but also to enable an entirely new range of revenue generating opportunities.
Tunable lasers only recently met the basic optical performance requirements necessary for telecommunications applications, although this technology has been under development for more than a decade. New advancements, maturation, and integration with other technologies such as modulation are finally allowing tunable lasers to compete with the performance levels of fixed-wavelength devices.
Today, tunable lasers meet requirements to support "five-nines" network reliability, wavelength locking, and hitless tuning--avoiding other wavelengths during tuning. Small form factors and low power consumption make it easy to integrate these devices into existing systems, all at a comparable cost to fixed interfaces.
Until now, the use of tunable technology has primarily involved narrowly tunable devices with tuning ranges of about 4 nm in limited network applications. However, narrowly tunable lasers do not fully address issues such as inventory management, or wavelength contention when two sets of traffic ride the same wavelength.
Widely tunable lasers, which can offer tuning ranges spanning 40 nm, can support many applications in intelligent optical networks reducing the cost of network operation and increasing revenue opportunities through advanced service offerings. Unlike narrowly tunable lasers, widely tunable devices enable fast provisioning, wavelength conversion, re-configurable optical add/drop multiplexing (OADM) and optical switching, protection and restoration, and new services such as bandwidth on demand.
In fixed-wavelength systems, each laser that is carrying traffic requires its own spare, which results in immense cost and space requirements. Widely tunable interfaces are deployed at nodes in the network, replacing an entire array of fixed lasers. This reduces inventory costs and complexities. For example, using widely tunable interfaces for sparing a 200-channel DWDM system could result in a sparing cost reduction because one laser could spare all 200 channels. Inventory expenses from a system manufacturing perspective can be similarly reduced.
Dynamic traffic applications
Tunable lasers can also offer significant benefits during dynamic or high traffic churn scenarios over a short period of time--a major sporting event or convention, for example. These devices enable a reconfigurable DWDM layer for just-in-time bandwidth provisioning. This fast provisioning increases carrier time-to-revenue because it reduces the provisioning time of a channel from months or weeks to minutes. It also eliminates the pre-provisioning cost of additional interfaces.
Moreover, tunable interfaces in intelligent optical networks enable full network transparency with respect to dynamic traffic patterns. Wavelength blocking frequently occurs at the intersection of multiple rings. Dynamic wavelength conversion or regeneration via tunable interfaces can alleviate the need to have pre-computed or dedicated fixed banks of transmit (Tx) and receive (Rx) modules reducing overall costs.
The savings from implementing wavelength conversion stems from the eliminated cost of additional Tx/Rx wavelength banks. A nationwide network of six large rings with an average capacity of 60 channels per ring could potentially encounter 5% wavelength blocking at each junction, therefore network operators must provision wavelength banks for relief on one-third of the blocking scenarios.
Both point-to-point and intelligent optical networking topologies require tunable interfaces to obtain a fully re-configurable OADM and optical switching capability. Tunable lasers enable wavelengths to be dynamically dropped or added, depending on traffic demand, at different points throughout a network. This capability opens new revenue opportunities in dynamic networks.
The use of fixed lasers results in systems where add/drop wavelengths are not dynamic, creating a very rigid network. Tunability will enable the access of any wavelength at any site, creating a flexible and agile architecture.
In today's long haul networks, protection bandwidth is pre-provisioned, waiting idly for potential use. When a fault does occur with the working path, an automatic switch moves traffic to the protection path.
Tunable interfaces can provide bandwidth-efficient optical protection and restoration. When there is a disruption in working traffic, the system will determine the optimal protection path and then tune to an alternative path dynamically. This path is either a different wavelength, or various wavelengths if the geographical distance is great and the traffic must transverse multiple junctions. Using tunable lasers at the ingress and egress of the network allows the output to revert back to the original wavelength. The protection path is automatically decommissioned once the primary path has been restored.
The ability to provision bandwidth in and out quickly based on demand is a major challenge for carriers today. In the present mode of operation, a great deal of manual intervention is required to ensure that the correct line cards are provisioned throughout all the nodes in the network. With tunability, each card has access to the entire tuning range. Therefore, line cards placed once in the network are tuned using software, negating the need for human intervention and truck rolls.
For the first time, tunable technology provides a more compelling business case than traditional fixed laser solutions. Tunable lasers enable many applications in addition to sparing and inventory management. These devices can support dynamic traffic patterns, allowing network operators to provision, and re-provision, existing interfaces for new revenue generating opportunities. By provisioning dynamic circuits, tunable interfaces help eliminate fixed interfaces and enable a high level of network flexibility, finally making the truly intelligent optical network a reality.