For the data center, high-performance computing networks, enterprise core, and distribution layers, and service provider applications, the Cisco 400GBASE Quad Small Form-Factor Pluggable Double Density (QSFP-DD) portfolio offers customers a wide variety of super high-density transceiver modules and the flexibility of 400 Gigabit Ethernet connectivity options. Our latest generation of 400G transceiver modules is based on the QSFP-DD form factor, and they are known as QSFP-DD modules. This QSFP-DD connector gives data centers the ability to effectively increase and enhance cloud capacity as needed because it is the best solution for the 400G optical transceiver form factor.

Difference between 400G QSFP-DD FR4 and 400G QSFP-DD FR8?

  • Reliability

The baud rates for the 400G QSFP-DD FR4 and FR8 are respectively 53.125GBd and 26.5625GBd. The challenge of long-term dependable operation, which necessitates a more robust FEC and addressing interoperability difficulties, is presented by the progressive increase in MPI cost and CD cost of PAM4 as baud increases. Both optical modules use KP4 FEC; however, 400G QSFP-DD FR8 has >90% margin per channel compared to 400G QSFP-DD FR4’s >80% margin per channel, making the latter module more reliable overall.

  • DSP Latency

The internal 8:4 Gearbox of the 400G QSFP-DD FR4 results in a subpar latency performance of around 102ns, while the 400G QSFP-DD FR8 has only approximately 84ns latency. Therefore, 400G QSFP-DD FR8 provides greater performance in terms of latency. High-performance computing scenarios are better suited for the 400G QSFP-DD FR8.

  • Modulation

On the electrical side, there is no difference between the 400G QSFP-DD FR4 and 400G QSFP-DD FR8, which both use 8-channel 53Gbps PAM4 modulation. Eight channels of 53 Gbps PAM4 modulation are used on the FR8 optical port side; four channels of 106 Gbps PAM4 modulation are used on the FR4 optical interface side. The two electrical interface inputs are multiplexed into one signal internally by the Gearbox chip, which then modulates the signal for the optical interface. With four channels of 106Gbps PAM4 signals, the optical interface side’s rate is therefore twice as fast as the electrical interface side. The dispersion tolerance is decreased and the modulation is increased from 50G PAM4 to 100G PAM4.

  • Power Consumption

The 400G QSFP-DD FR8 delivers better link costs, on the one hand. However, employing more lasers makes the modules consume more power, increases the cost of the total lasers used per module, and makes the optical package more complex, all of which lead to poorer output and higher production costs. The 400G QSFP-DD FR4, in contrast, uses less power and has easier heat treatment capabilities.

What are the benefits of 400G QSFP-DD DR4 Silicon Photonics Optical Transceiver?

There are two different kinds of 400G QSFP-DD DR4 optical modules: the conventional electric-optical chip-separated optical modules and the more contemporary electric-optical chip-integrated silicon photonics optical modules. The typical 7nm DSP chip used in the 400G DR4 silicon photonics optical module’s power consumption of less than 10W satisfies the data center’s green application requirements. The number of lasers can be significantly decreased by using 400G DR4 silicon photonics optical modules instead of conventional optical modules with a 4-channel 100G EML solution.

The 400G QSFP-DD DR4 silicon photonics optical module, on the other hand, adopts the COB packaging method, enabling passive coupling between the optical fiber and silicon optical chip. Additionally, the optimized design eliminates TEC temperature control components, making it simpler to achieve mass production and more obviously demonstrating cost advantages. The 400G QSFP-DD DR4 silicon photonics optical module can save 10%–30% of the cost compared to the conventional optical transceiver, according to the pertinent statistics. The market for digital communication high-speed optical modules is anticipated to reach $6.5 billion in 2024, according to LightCounting, a renowned research organization in the optical communication market. Silicon photonics optical modules will be widely commercialized, and they will hold a 60% market share.


For 400G optical network connections in the data center, Quad Small Form-factor Pluggable-Double Density (QSFP-DD) 400G transceivers based on PAM4 modulation have gained popularity. PAM4 technology is used in applications for 400G Ethernet in the 400G ZR, DR4, FR4, LR4, and SR8 QSFP-DD optics. DAC & AOC cables, fiber optic cables, WDM &PLC splitters, and other networking series are all currently available from Fiber Mall, a professional optical communication integrated supplier.

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