With the continued growth of cloud computing, big data, artificial intelligence, and 5G services, data centers and carrier networks are facing increasing traffic pressure. Upgrading networks to 100G and 400G has become the mainstream direction for industry development. While bandwidth continues to increase, balancing transmission distance, power consumption, and deployment costs has become a crucial issue that network construction must consider.
Against this backdrop, QSFP28 PAM4 optical modules have gradually gained market attention. They combine PAM4 modulation technology with DWDM (Dense Wavelength Division Multiplexing), achieving higher data transmission efficiency and longer transmission distances while maintaining the compact QSFP28 package. Compared to traditional solutions, it can achieve 100G high-speed transmission with lower power consumption and support long-distance fiber optic links of approximately 80-100 kilometers, while effectively improving fiber resource utilization.
Since entering the market around 2016, the QSFP28 PAM4 DWDM solution has been successively applied in various scenarios such as large data center interconnection, metropolitan area network transmission, and 5G bearer networks, becoming one of the important technical routes for 100G long-distance optical communication.
This article will focus on the QSFP28 PAM4 optical module, analyze the PAM4 signal transmission principle, discuss its main technical advantages, and combine typical application scenarios to help readers understand why it has become an important interconnection solution in the current construction of 100G and even 400G networks.
What is QSFP28 PAM4 signal technology?
Traditional QSFP28 optical modules typically use four 25Gbps NRZ (Non-Return-to-Zero) signals to achieve 100G transmission, with the total bandwidth completed by four independent channels.
PAM4 (Four-Level Pulse Amplitude Modulation) adopts a different transmission approach. It utilizes four different voltage levels to represent data, with each symbol carrying two bits of information (corresponding to combinations of 00, 01, 10, and 11). Compared to NRZ, where each symbol can only represent one bit, this doubles the data carrying capacity. This means that at the same baud rate, PAM4 can achieve higher data rates.
For example, a single 50Gb/s PAM4 channel can complete 100Gb/s data transmission, equivalent to the total bandwidth of two 25Gb/s NRZ channels. Because a single channel can handle more data, the overall number of optical channels required is reduced, making the module design simpler and helping to reduce power consumption and system complexity. In QSFP28 products, this technology typically uses two 50G PAM4 channels to achieve 100G or 200G transmission, or a single 100G PAM4 channel can be used to build a more compact 100G interconnect solution.
While PAM4 offers higher data efficiency at the same bandwidth compared to NRZ, it is also more sensitive to noise, crosstalk, and signal attenuation due to its multi-level signal. Therefore, modern QSFP28 PAM4 optical modules typically integrate DSP (Digital Signal Processing) and FEC (Forward Error Correction) technologies to perform real-time signal compensation and error correction, thereby ensuring stability and reliability during long-distance transmission.
It is precisely through the combination of these technologies that PAM4 not only breaks through the bandwidth bottleneck of traditional NRZ but also further improves spectral efficiency. Currently, it has become one of the most mainstream modulation technologies for 100G, 400G, and even higher-speed Ethernet optical interconnects, and is also an important foundation for the development of next-generation high-speed networks.
Key Advantages of QSFP28 PAM4 DWDM: Higher Transmission Capacity, Improved Fiber Utilization
One of the biggest advantages of PAM4 is its ability to transmit more data on a single wavelength. Because the data carrying capacity of each channel is doubled, the same number of wavelengths can provide a higher overall bandwidth.
Taking a dual-laser QSFP28 PAM4 DWDM optical module as an example, under standard 100GHz DWDM channel spacing, it can support 40 100G wavelengths multiplexed, with a maximum total transmission capacity of 4Tb/s per fiber and a transmission distance of approximately 80 kilometers. For data center interconnects (DCI) and metropolitan area networks, this means significantly increasing network capacity without requiring a large amount of additional fiber resources, a particularly significant advantage in environments with limited fiber resources.
Reduced Unit Bandwidth Cost
Compared to the traditional 4×25G architecture, the 100G single-wavelength solution greatly simplifies the internal design of the optical module and reduces the number of required optical components.
Previously, achieving 100G typically required four independent optical signals, while the PAM4 solution only needs one or two lasers to complete the same transmission task, reducing not only component costs but also the number of fibers and overall cabling complexity. Industry experts generally believe that this solution offers a cost advantage of several times over compared to the previous generation of technology. For the continuous expansion of 100G and 400G networks, it can effectively reduce the cost per bit of transmission and improve the overall return on investment.
Lower Power Consumption and Higher Energy Efficiency
In addition to cost advantages, PAM4 optical modules also excel in power consumption control.
Currently, mainstream QSFP28 PAM4 modules generally adopt silicon photonics integration and DSP digital signal processing technology, with the power consumption of a single 100G link typically controlled at around 5W. Simultaneously, due to the significant reduction in the number of lasers—for example, some bidirectional transmission schemes can reduce from multiple lasers to two—the overall heat generation is also reduced, which is more conducive to equipment heat dissipation and high-density deployment.
To ensure the stability of PAM4 signals during long-distance transmission, the module typically incorporates FEC forward error correction, equalization algorithms, and digital compensation technology to optimize the signal in real time, reducing the bit error rate while ensuring link reliability. Therefore, in terms of overall energy consumption, the PAM4 solution has lower energy consumption per bit compared to the traditional NRZ multi-laser architecture.
Seamless Compatibility with DWDM Networks
QSFP28 PAM4 DWDM optical modules not only offer high-speed transmission capabilities but also integrate directly into existing DWDM networks.
Most products comply with the standard 100GHz ITU DWDM channel specification. Modulation, multiplexing, and demultiplexing functions are integrated within the module, allowing switches and routers to deploy them directly like ordinary QSFP28 modules, without requiring additional complex optical layer equipment.
Furthermore, most modules support multiple C-band channels and have built-in FEC functionality. Therefore, in many scenarios, wavelength division multiplexing (WDM) transmission can be achieved without deploying separate Mux/Demux devices. This design retains the advantages of pluggable optical modules—simple deployment and easy maintenance—while also providing the long-distance transmission capabilities of carrier-grade DWDM systems. For hybrid networks requiring simultaneous compatibility with multiple speeds such as 10G and 100G, upgrades and expansions can be completed more flexibly.
Typical Application Scenarios of QSFP28 PAM4 DWDM: 5G Fronthaul and Backhaul Networks
5G network construction places higher demands on transmission bandwidth and latency, especially between DU (Distributed Unit), CU (Centralized Unit), and the core network, requiring numerous high-speed links for data exchange. QSFP28 PAM4 DWDM perfectly meets the dual requirements of capacity and transmission distance in these scenarios.
A single wavelength can provide 100G bandwidth, efficiently aggregating data traffic from multiple base stations to meet the ever-increasing demand for 5G service support. Simultaneously, its transmission range of approximately 40 to 80 kilometers matches the deployment distances of DU and CU in most metropolitan 5G networks. Because DWDM can transmit multiple wavelengths on a single fiber, it not only reduces fiber resource consumption but also decreases the number of intermediate devices, simplifying the network structure and further reducing latency and subsequent maintenance costs.
Data Center Interconnect (DCI)
As enterprises increasingly adopt multi-data center deployments, cross-campus data synchronization, disaster recovery backup, and service scheduling place higher demands on interconnect networks. For data center interconnects within a 40-80 km range, QSFP28 PAM4 DWDM has become a mature solution.
Each DWDM wavelength can support 100G or even higher bandwidth, providing stable transmission capabilities for virtual machine migration, massive data backup, and service load balancing. Combined with EDFA optical amplifiers and dispersion compensation schemes, 100G Ethernet links can cover the vast majority of metropolitan area DCI applications.
Furthermore, DWDM can transmit multiple service wavelengths on the same fiber pair, significantly improving fiber utilization. For companies leasing fiber resources, this also helps reduce long-term line costs.
Metropolitan Area Networks and Campus Backbone Networks
Whether it’s a carrier’s metropolitan area network or a large campus network, the backbone layer undertakes a large number of service aggregation and data forwarding tasks. With the continued growth of enterprise leased lines, home broadband, and mobile internet services, traditional 100G networks are gradually upgrading to 400G.
QSFP28 PAM4 DWDM can fully utilize existing fiber resources to complete bandwidth expansion, achieving network upgrades without laying new lines. This protects existing infrastructure investments while reducing overall construction costs. Therefore, for users planning to gradually evolve to higher-speed networks, this is a relatively manageable upgrade option.
Enterprise Core Networks
Large enterprises, financial institutions, and government sectors typically have higher requirements for network stability, security, and business continuity. Their core networks not only need high-speed transmission but also reliable data isolation capabilities.
DWDM, by carrying independent services using different wavelengths, achieves natural physical isolation, making it ideal for financial transactions, enterprise private networks, and other applications with high data security requirements. Simultaneously, QSFP28 PAM4 optical modules, which support tunable wavelengths, can flexibly configure links according to network resources, quickly deploying high-bandwidth leased lines and improving network deployment efficiency.
Overall, QSFP28 PAM4 DWDM combines the advantages of high speed, long distance, and high-density deployment. It not only fully utilizes existing fiber resources but also reduces network upgrade costs, providing a more flexible, efficient, and energy-saving optical interconnect solution for the evolution from 100G to 400G networks. Therefore, it has become an important choice for data centers, carrier networks, and enterprise backbone networks.
Summary
With the increasing prevalence of 100G and 400G networks, traditional optical interconnect solutions are struggling to balance bandwidth, cost, and energy consumption. QSFP28 PAM4 DWDM optical modules, with their higher single-wavelength transmission capability, lower cost per bit, and higher fiber utilization, are becoming an important solution for data center interconnects, metropolitan area networks (MANs), and 5G transport networks.
6COMGIGA’s QSFP28 100G PAM4 DWDM optical module complies with the IEEE 802.3bm standard, supports Digital Diagnostic Monitoring (DDM) functionality, and can be combined with EDFA optical amplifiers and TDCM dispersion compensation modules to achieve stable transmission over distances up to approximately 80 kilometers. It provides reliable and efficient 100G optical connectivity for data center interconnects, campus backbone networks, and carrier metropolitan area networks.
For users planning to upgrade to 100G networks or gradually evolve to 400G, the QSFP28 PAM4 DWDM can not only make full use of existing fiber resources, but also effectively control deployment costs and energy consumption, providing a more flexible and sustainable interconnection foundation for the construction of future higher-speed data centers and communication networks.