Optical fiber and dense wavelength division multiplex (DWDM) technology are moving towards the edges of networks. In the case of new 5G networks, operators will need more fiber capacity to interconnect the increased density of cell sites, often requiring replacing legacy time-division multiplexing transmission with higher-capacity DWDM links. In the case of cable and other fixed access networks, new distributed access architectures like Remote PHY free up ports in cable operator headends to serve more bandwidth to more customers.
A report by Deloitte summarizes the reasons to expand the reach and capacity of optical access networks: “Extending fiber deeper into communities is a critical economic driver, promoting competition, increasing connectivity for the rural and underserved, and supporting densification for wireless.”
To achieve such a deep fiber deployment, operators look to DWDM solutions to expand their fiber capacity without the expensive laying of new fiber. DWDM technology has become more affordable than ever due to the availability of low-cost filters and SFP transceiver modules with greater photonic integration and manufacturing volumes. Furthermore, self-tuning technology has made the installation and maintenance of transceivers easier and more affordable.
Despite the advantages of DWDM solutions, their price still causes operators to second-guess whether the upgrade is worth it. For example, mobile fronthaul applications don’t require all 40, 80, or 100 channels of many existing tunable modules. Fortunately, operators can now choose between narrow- or full-band tunable solutions that offer a greater variety of wavelength channels to fit different budgets and network requirements.
Example: Fullband Tunables in Cable Networks
Let’s look at what happens when a fixed access network needs to migrate to a distributed access architecture like Remote PHY.
A provider has a legacy access network with eight optical nodes, and each node services 500 customers. To give higher bandwidth capacity to these 500 customers, the provider wants to split each node into ten new nodes for fifty customers. Thus, the provider goes from having eight to eighty nodes. Each node requires the provider to assign a new DWDM channel, occupying more and more of the optical C-band. This network upgrade is an example that requires a fullband tunable module with coverage across the entire C-band to provide many DWDM channels with narrow (50 GHz) grid spacing.
Furthermore, using a fullband tunable module means that a single part number can handle all the necessary wavelengths for the network. In the past, network operators used fixed wavelength DWDM modules that must go into specific ports. For example, an SFP+ module with a C16 wavelength could only work with the C16 wavelength port of a DWDM multiplexer. However, tunable SFP+ modules can connect to any port of a DWDM multiplexer. This advantage means technicians no longer have to navigate a confusing sea of fixed modules with specific wavelengths; a single tunable module and part number will do the job.
Overall, fullband tunable modules will fit applications that need a large number of wavelength channels to maximize the capacity of fiber infrastructure. Metro transport or data center interconnects (DCIs) are good examples of applications with such requirements.
Example: Narrowband Tunables in Mobile Fronthaul
The transition to 5G and beyond will require a significant restructuring of mobile network architecture. 5G networks will use higher frequency bands, which require more cell sites and antennas to cover the same geographical areas as 4G. Existing antennas must upgrade to denser antenna arrays. These requirements will put more pressure on the existing fiber infrastructure, and mobile network operators are expected to deliver their 5G promises with relatively little expansion in their fiber infrastructure.
DWDM solutions will be vital for mobile network operators to scale capacity without laying new fiber. However, operators often regard traditional fullband tunable modules as expensive for this application. Mobile fronthaul links don’t need anything close to the 40 or 80 DWDM channels of a fullband transceiver. It’s like having a cable subscription where you only watch 10 out of the 80 TV channels.
This issue led EFFECT Photonics to develop narrowband tunable modules with just nine channels. They offer a more affordable and moderate capacity expansion that better fits the needs of mobile fronthaul networks. These networks often feature nodes that aggregate two or three different cell sites, each with three antenna arrays (each antenna provides 120° coverage at the tower) with their unique wavelength channel. Therefore, these aggregation points often need six or nine different wavelength channels, but not the entire 80-100 channels of a typical fullband module.
With the narrowband tunable option, operators can reduce their part number inventory compared to grey transceivers while avoiding the cost of a fullband transceiver.
Synergizing with Self-Tuning Algorithms
The number of channels in a tunable module (up to 100 in the case of EFFECT Photonics fullband modules) can quickly become overwhelming for technicians in the field. There will be more records to examine, more programming for tuning equipment, more trucks to load with tuning equipment, and more verifications to do in the field. These tasks can take a couple of hours just for a single node. If there are hundreds of nodes to install or repair, the required hours of labor will quickly rack up into the thousands and the associated costs into hundreds of thousands.
Self-tuning allows technicians to treat DWDM tunable modules the same way they treat grey transceivers. There is no need for additional training for technicians to install the tunable module. There is no need to program tuning equipment or obsessively check the wavelength records and tables to avoid deployment errors on the field. Technicians only need to follow the typical cleaning and handling procedures, plug the transceiver, and the device will automatically scan and find the correct wavelength once plugged. This feature can save providers thousands of person-hours in their network installation and maintenance and reduce the probability of human errors, effectively reducing capital and operational expenditures.
Self-tuning algorithms make installing and maintaining narrowband and fullband tunable modules more straightforward and affordable for network deployment.
Fullband self-tuning modules will allow providers to deploy extensive fiber capacity upgrades more quickly than ever. However, in use cases such as mobile access networks where operators don’t need a wide array of DWDM channels, they can opt for narrowband solutions that are more affordable than their fullband alternatives. By combining fullband and narrowband solutions with self-tuning algorithms, operators can expand their networks in the most affordable and accessible ways for their budget and network requirements.