400G QSFP-DD FR4 vs FR8: Key Differences, Advantages, and Applications

The 400G QSFP-DD transceiver is a leading form factor in next-generation networks, known for its low power consumption, compact size, and high-speed performance. Among the options available for 2km WDM solutions, the 400G QSFP-DD FR4 and 400G QSFP-DD FR8 modules stand out. But what sets these two modules apart, and how do you choose the right one for your needs? This article explores their key differences and helps you determine which module best suits your requirements.

What Is 400G QSFP-DD FR4?

The 400G QSFP-DD FR4 optical module is a 400Gbps hot-pluggable transceiver in a QSFP-DD form factor and supports SMF links up to 2km reach over duplex LC connectors. It incorporates 4 independent lanes on CWDM4 center wavelengths of 1271/1291/1311/1331nm running at 100Gbps per lane and compliant with 100G Single Lambda MSA specification.

What Is 400G QSFP-DD FR8?

The 400G QSFP-DD FR8 module adopts the same 50G PAM4 modulation technology as the 400G QSFP-DD SR8. It uses eight channels to transmit data and every channel can reach a transmission rate of 53.125Gbps, achieving a total transmission rate of 400Gbps. Unlike the SR8, which is suited only for short-distance transmission, the FR8 supports longer distances with a maximum reach of 2km.

400G QSFP-DD FR4 VS FR8 Optical Modules: 4 Key Differences

Reliability

The baud rates for the 400G QSFP-DD FR4 and FR8 are 53.125GBd and 26.5625GBd, respectively. As the baud rate increases, the MPI cost and CD cost of PAM4 gradually rise. That is to say, the excessive cost will make it hard to maintain long-term reliable and stable operation, thus requiring a more robust FEC. Both optical modules use KP4 FEC; however, 400G QSFP-DD FR4 has more than 80% channel margin and 400G QSFP-DD FR8 has more than 90% channel margin, making the latter QSFP-DD FR8 module more reliable than the former.

Modulation

On the electrical side, there is no difference between the 400G QSFP-DD FR4 and 400G QSFP-DD FR8, which are both 8-channel 53Gbps PAM4 modulation. However, on the optical side, the FR8 module uses 8-channel 53Gbps PAM4 modulation, and the 400G FR4 module uses four channels of 106Gbps PAM4 modulation.

For an in-depth look, please read PAM4 for 400G Ethernet applications.

Latency

The 400G QSFP-DD FR4 uses an 8:4 Gearbox internally, resulting in a poor latency performance of about 102ns, while the 400G QSFP-DD FR8 has only about 84ns. As a result, 400G QSFP-DD FR8 performs with lower latency. Therefore, the 400G QSFP-DD FR8 is more suitable for scenarios requiring high-performance computing.

Power Consumption

On the one hand, the 400G QSFP-DD FR8 offers improved link budgets. On the other hand, the total laser cost per module is higher due to the adoption of more lasers, resulting in lower output and higher production costs. In contrast, the 400G QSFP-DD FR4 has lower power consumption and simpler heat treatment capabilities.

How to Choose 400G QSFP-DD FR4 and 400G QSFP-DD FR8?

When selecting between the 400G QSFP-DD FR4 and FR8 optical modules, consider the following key factors:

- Performance: Both modules offer high performance, excellent bandwidth, speed, and reliability.

- Power Consumption: The primary difference lies in power consumption and cost. The 400G QSFP-DD FR4 is more energy-efficient and cost-effective, making it a better fit for business data centers.

- Application: The 400G QSFP-DD FR8, while more expensive, is ideal for high-performance computing environments due to its higher power and performance capabilities.

For more information and to explore our full range of 400G optical modules, visit FS.com. Let us help you find the perfect solution to meet your network requirements.