DFT 400G Ethernet Optical Module Solution for Transmission over Different Distances

As a result of the increasing demands from AI workloads, cloud services, and large-scale data centers, 400G Ethernet has emerged as a dominant interconnect speed for modern networks. However, the deployment requirements for network technologies, such as 400G, vary significantly across different scenarios including intra-data center, inter-building, and data center interconnect (DCI) environments. Each scenario presents unique constraints related to transmission distance, power consumption, and cost. As no single 400G optical module fits all use cases, selecting the right 400G solution based on transmission distance is critical to building an efficient and scalable network.

Key Technologies Enabling Multi-Distance 400G Transmission

The ability of 400G optical modules to deliver high data rates over varying reaches is enabled by a suite of advanced technologies:

PAM4 Modulation: By encoding 2 bits per symbol, PAM4 doubles the data capacity per lane compared with NRZ. This helps reduce bandwidth demands on optical components while taking into account both high performance and cost efficiency.

Forward Error Correction (FEC) is a critical technology for enhancing data integrity in high-speed 400G networks. By encoding data at the transmitter with redundancy and error correction codes, FEC enables receivers to detect and correct errors autonomously, without the need for retransmission. This process is essential for maintaining reliable communication over long distances, as it ensures that data arrives at its destination accurately, even in the presence of noise or signal degradation.

Wavelength Division Multiplexing (WDM) leverages either Coarse Wavelength Division Multiplexing (CWDM) or Dense Wavelength Division Multiplexing (DWDM) to simultaneously transmit multiple 400G data signals over a single fiber, thereby significantly enhancing transmission capacity and efficiency. WDM technology enhances fiber utilization, thereby supporting high-capacity applications in metro networks and data center interconnectivity (DCI). transport.

Coherent Technology, utilizing PM-16QAM modulation, encodes data across the amplitude, phase, and polarization of light. Leveraging advanced DSP to mitigate long-haul impairments such as chromatic dispersion (CD) and polarization mode dispersion (PMD), 400G signals can now travel thousands of kilometers without the need for physical repeaters. This capability is pivotal for the deployment of 400G technology in regional and long-haul backbone networks, as evidenced by the successful transmission of 400G signals over 3000 kilometers using Nyquist filtering technology, as demonstrated by ZTE.

Leveraging advanced technologies, 400G optical transceivers are designed to accommodate a wide range of transmission distances, ensuring they meet the stringent performance criteria. Ethernet standards and complying with industry MSA agreements.

DFT 400G Solutions for Different Transmission Distance

While 400G Ethernet standards define the technical boundaries of transmission, practical network design requires selecting the most suitable solution based on specific distance requirements and deployment scenarios. DFT provides a comprehensive portfolio of 400G optical modules and connectivity options that address short-, mid-, and long-reach applications across modern data center and DCI architectures.

400G SR for Short-Reach Connectivity

DFT's 400G SR solutions are designed to meet the growing demand for high-speed, short-reach connectivity in data centers, catering to the needs of advanced applications such as AI/HPC clusters and hyperscale data centers. These environments are designed to accommodate high port density and prioritize the management of significant east-west traffic at the rack level, reflecting the shift in network traffic patterns within data centers. As the industry transitions to 400Gbps networking, ensuring low latency and signal integrity across dense multimode fiber is paramount, given the challenges of maintaining high performance in high-speed data transmission.

To address these needs, DFT provides a comprehensive Our portfolio encompasses a comprehensive range of 400G SR optical solutions, such as 400G VSR4, 400G SR4, 400G SR4.2, and 400G SR8, all engineered on the foundation of parallel-optics multimode fiber (MMF) architectures. These solutions are designed to meet the growing demand for high-speed, high-capacity, and low-latency communication technologies, as evidenced by the robust market growth and the increasing adoption of 400G modules in key applications like data centers and cloud computing. DFT 400G SR portfolio enables scalable short-reach connectivity across access and aggregation layers, supporting smooth upgrades from 50G, 100G, and 200G to 400G, while also supporting higher-bandwidth port configurations and breakout use cases to accommodate future network scaling, including transitions toward 800G environments. By DFT 400G SR modules, rigorously tested and verified for optical performance, empower network operators to build high-bandwidth, low-latency, and dependable high-performance networks.

400G DR/FR/LR for Mid-Reach Single-Mode Connectivity

DFT 400G mid-reach solutions target distances from 0.5km to 10km, supporting inter-hall and inter-building links in hyperscale data centers, campus networks, and short-reach DCI scenarios where signal integrity performance is required. At these distances, PAM4-based 400G links encounter challenges from optical path loss and noise tolerance, which can lead to elevated Bit Error Rates (BER) and link instability. For instance, the use of multiple DACs to control LD Driver in laser transmission, as mentioned in the application of a dual MCU-based 400G PAM4 optical module, highlights the complexity and the need for advanced solutions to maintain link stability.

To ensure reliable operation under these conditions, DFT offers a comprehensive mid-reach portfolio including DR4, FR4, LR4, LR8, as well as extended variants such as XDR4 and PLR4. These 400G modules are validated to deliver low-BER performance with sufficient link margin, enabling high signal integrity across mid-reach links. This design helps 400G Ethernet transceivers are engineered to ensure stable network uptime and prevent packet loss in high-bandwidth deployments, such as those required by modern data centers and cloud computing environments. In addition, some DFT 400G modules adopt silicon photonics (SiPh) technology to reduce power consumption while maintaining high-density deployment, such as QDD-DR4-400G-Si.

400G ER/ZR/ZR+ for Long-Reach and DCI Connectivity

For long-reach and DCI (Data Center Interconnect) scenarios, 400G connectivity must support significantly extended transmission distances while maintaining high performance and reliability. Such applications are commonly found in metro networks, regional interconnects, and data center interconnect architectures spanning tens or even hundreds of kilometers. At these distances, optical signal attenuation, chromatic dispersion accumulation, and stringent OSNR requirements place higher demands on signal integrity and transmission stability.

DFT 400G ER4L and 400G ER8 transceivers provide reliable point-to-point SMF links for 30–40km reaches. For extended DCI, DFT 400G ZR modules use coherent DP16QAM or DP-QPSK modulation and are commonly deployed up to ~40km unamplified and ~120km amplified, while ZR+ modules support extended reach beyond 120km depending on the line system. By enabling IPoverDWDM architectures, DFT coherent solutions can reduce or eliminate external transponders in some DCI/metro deployments, helping save rack space and power consumption while maintaining reliable longreach connectivity.

DFT Comprehensive Connectivity Solutions for Data Center Networking

To build a high-performance and scalable 400G network, a combination of diverse interconnect technologies is required to meet the specific needs of different network layers. DFT provides a full-stack product portfolio that supports the complete construction of data center networks. By integrating high-speed cables and optical transceivers, DFT delivers tailored solutions for every connection point, ensuring that distance, power efficiency, and cost-effectiveness are optimized according to customer requirements.

In a typical multi-tier data center architecture, DFT solutions tackle various interconnect challenges across different tiers. At the access layer, where high-density server-to-switch (ToR) connections are crucial, DFT 100G DAC and AOC cables offer the most cost-effective, low-latency links for distances under 30 meters. For the leaf-to-spine and spine-to-core layers, DFT high-bandwidth 400G optical modules (SR/DR/FR/LR) are utilized to manage massive east-west traffic and long-reach requirements, providing the necessary scalability and signal integrity for a robust network backbone.