Fiber optic and DWDM technology move at the edges of networks. Meeting the ambitious performance goals of 5G architectures will require more fiber links than ever before between small cellular sites and when replacing legacy TDM transmissions with higher-capacity DWDM links (Figure 1). In the case of fixed access, new architectures such as Remote PHY free up ports in cable operators’ headends that can be used to provide more bandwidth to more customers.
A Deloitte report summarizes the rationale for the need to extend the reach and capacity of optical access networks: “The extension of fiber deeper into communities is a critical economic driver that drives competition, increases connectivity for the rural and underserved people, and the Aggregation supported for wireless networks.”
To meet the current goals, operators in fixed and mobile networks in densely populated areas need to make optimal use of their fiber capacity, which is why they want to deploy DWDM. The technology has become cheaper than ever due to the availability of low-cost filters and SFP transceivers with greater photonic integration. In addition, self-tuning modules have made transceiver installation and maintenance easier and less expensive.
Despite the advantages of DWDM, the price often leads operators to doubt whether the upgrade is worth it. Fortunately, you can now choose between tunable narrowband and fullband modules that offer different numbers of wavelength channels. These choices provide the best fit for budget and network requirements.
Applications tunable for a full band
Let’s look at what happens when fixed access networks need to be migrated to a distributed access architecture like Remote PHY. A single optical node serving 500 customers is split into 10 nodes serving 50 customers. By splitting an optical node into 10, a provider can expand from 8 to 80 nodes. For each of these nodes, the cable provider must allocate a new DWDM channel, requiring the provider to use more and more of the C-band optical spectrum to accommodate all of these DWDM channels. Network upgrades like this typify a situation where tunable modules that cover the entire C-band and have a narrow grid spacing are useful (Figure 2).
In addition, a single full-band DWDM transceiver part number can handle all required wavelengths for the network. In the past, network operators used fixed-wavelength DWDM modules that could only be used in certain 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 be connected 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 does the job.
Overall, full-band tunable transceivers are suitable for applications that require a large number of wavelength channels to maximize fiber infrastructure capacity. Subway transportation or Data Center Interconnects (DCIs) are good examples of applications with such requirements.
Applications for a narrowband tunable
The transition to 5G requires a significant restructuring of the mobile network architecture. 5G networks will use higher frequency bands, which will require the deployment of more cell sites and antennas to cover the same geographic areas as 4G. In addition, existing antennas must be upgraded to denser antenna arrays. These demands will put more pressure on the existing fiber infrastructure, and mobile network operators are expected to deliver on their 5G promises with relatively little expansion of their fiber footprint.
DWDM will be crucial for mobile network operators as the required capacity in cell towers increases sharply with the new 5G architectures. Tunable DWDM SFP+ transceivers can handle this increased optical traffic, but operators often consider traditional full-band tunable modules expensive for this application. Mobile fronthaul links do not require all 40-80 channels of a full-band transceiver. It’s like having a cable subscription where you only watch 10 of the 80 TV channels.
Therefore, an alternative approach is to develop narrow-band DWDM transceivers with only eight channels. They offer an alternative that allows for cheaper and more moderate capacity expansion. Photonic integration and packaging advances are now enabling modules that can help cost-effectively scale mobile access networks. These modules allow operators to reduce inventory compared to gray transceivers while avoiding the cost of a full-band transceiver.
Overall, tunable narrowband transceivers are suitable for applications in areas of the network that require relatively low-density aggregation.
Synergy with self-optimizing algorithms
The sheer number of channels in a tunable module (up to 100 in the case of high-end full-band modules) can quickly become overwhelming for technicians in the field. There’s more records to examine, more tuning equipment programming, more tuning equipment trucks to load, and more on-site checks to do. These tasks can take a few hours for just a single node. When hundreds of nodes need to be installed or repaired, the man-hours required quickly add up to thousands and the associated costs add up to hundreds of thousands. Self-tuning modules play an important role in overcoming these problems, making network deployment and maintenance easier and less expensive.
Auto-tuning allows engineers to treat tunable DWDM modules the same way they treat gray transceivers. No additional training is required for technicians to install the tunable module. There is no need to program tuners or compulsively review wavelength records and tables to avoid on-site errors. Technicians only need to follow typical cleaning and handling procedures, connect the transceiver and the device will automatically scan and find the correct wavelength once connected. This feature can save providers thousands of man-hours installing and maintaining their network and reducing the likelihood of human error, effectively reducing capital and operational expenses.
Full-band self-tuning modules will enable providers to deploy comprehensive network upgrades faster than ever. However, in use cases such as mobile access networks, where operators do not need a wide range of DWDM channels, they can opt for narrowband transceivers, which are cheaper than their fullband alternatives. By combining full-band and narrow-band modules with self-optimizing algorithms, operators can expand their networks in an affordable and accessible way.
JOOST VERBERK is Head of Product Management at EFFECT Photonics. He made his career in product management, working for ENGIE before joining EFFECT Photonics where he leads the cross-functional product management team.