especially OSFP, QSFP-DD, and CFP8. 3Coptics 400G QSFP-DD LR4 and 400G QSFP-DD LR8 are designed uniquely, supporting not only high-speed optical transmission but also Long Range (LR) transmission, as shown in the following table.

These two modules are designed for Data Center 400G Ethernet links reaching up to 10km over SMF with duplex LC connectors. In addition to their superior functions, the products are designed to meet the harshest external operating conditions including temperature, humidity, and EMI interference. However, 400G LR4 transceivers and 400G LR8 transceivers are different in transmission modes, leading diversity in power consumption, signal integrity, etc.

Baud is a unit representing the symbol rate and is becoming significantly important for 400G transmission. It's important to make a difference between baud rate and bit rate. Because PAM4 carries 2 bits per symbol. 50Gbps PAM4 (50 gigabit per second with PAM4 modulation) will have a line transmission at 25GBdps (Gigabaud per second). It means the symbol rate for 50Gbps PAM4 remains at 25 Gigabaud, while the symbol rate for 100Gbps PAM4 is 50 Gbaud.

The 400G transceivers (QSFP-DD and OSFP) always have 8 lanes of 50Gbps PAM4 on the electrical side. On the optical side, 400G QSFP-DD LR8 has 8 lasers of 50Gbps PAM4, and 400G QSFP-DD LR4 has 4 lasers of 100Gbps PAM4, requiring an electrical conversion (Gearbox) from 8×50Gbps PAM4 to 4×100Gbps PAM4. Relatively more lasers in 400G LR8 modules lead to higher production costs.

Pros and Cons

The explosive traffic growth in cloud data centers has led to an increased demand for 400G optical modules. Featured with low-power, high-density, and high-speed, QSFP-DD LR4 and QSFP-DD LR8 are optimal for long-distance transmission in next-generation data centers.

<p class="blog_p padding_top_none community_blog_detail_p community_blog_detail_p1" background-color:#ffffff;"="" style="margin-top: 20px; margin-bottom: 0px; padding: 0px; text-size-adjust: none; font-family: "microsoft yahei", Arial, Helvetica, sans-serif; font-size: 14px; text-wrap: wrap; color: rgb(25, 25, 26); text-align: justify;">Due to the differences mentioned above, the application of these two modules will change following the needs of data centers in the future. Compared with 8×50G modules, The 4×100G modules lower the power consumption, reduce the hardware complexity and relax the requirement on xWDM gird, even though they present a challenge in term of reach. Therefore, 400GBASE-LR4 may be mainstream for lower costs in the future. At the same time, the electrical port of 400GBSAE-LR4 may also be gradually upgraded to the form of 4×100G PAM4 to save power consumption and costs by eliminating the Gearbox.