400G Optical Transceiver

Date: Jan 15, 2025

The advanced PAM4 modulation technology used in 400G optical module can achieve high-speed, low-latency data transmission while reducing costs. There are 3 main Encapsulation forms, namely OSFP, QSFP-DD and QSFP112.

OSFP Optical Transceiver (Octal Small Formfactor Pluggable)
OSFP Octal refers to 8, which means octal, which means that 56G electrical signals are used directly, 8*56G, but the 56G signal is formed by 25G DML laser under PAM4 modulation. This standard is a new interface standard and is incompatible with existing optoelectronic interfaces. OSFP comes with a heat sink and has relatively low power consumption, with a maximum of only 15W, but it is slightly larger than QSFP-DD, so it requires a larger PCB area, and the mechanical structure of the PCB, Hosting cage, and 1RU front panel needs to be customized. The pins of its electrical interface are different from those of QSFP-DD, with one row on the top and one row on the bottom.

QSFP-DD Optical Transceiver (Quad Small Form Factor Pluggable-Double Density)
Q in QSFP-DD refers to "Quad", which means 4 channels. Each QSFP56 is 4*56G, forming a 200G signal; DD refers to "Double Density", which means two QSFP56s in parallel, and 2*200G generates a 400G signal. This solution is an extension of QSFP, adding one row to the original 4-channel interface to become 8 channels. It is smaller than OSFP and is compatible with existing 40G QSFP and 100G QSFP28 interfaces. The original QSFP28 module can still be used, and only one more module needs to be inserted to achieve a smooth upgrade.

QSFP112 Optical Transceiver
QSFP112 is a fiber channel module, also known as a 400G QSFP-DD MSA module. It uses parallel optical technology and is based on CML (Current Mode Logic) drivers and four independent channels, supporting 112G PAM4 signal modulation with a total rate of up to 400G. The module uses MTP/MPO connectors to connect to Fiber Channel and supports multimode fiber and single-mode fiber.
Compared with traditional QSFP+ modules, QSFP112 modules provide higher density within the same physical size and can support a total data transmission rate of up to 400Gbps in one module. In general, the QSFP112 standard is a high-performance, high-density Fiber Channel module standard that is backward compatible with QSFP series QSFP 40G (4x10G), 100G (4x25G), 200G (4x 56G), etc. It has signal integrity, high density and excellent heat dissipation, providing a simple upgrade path for existing solutions, and is suitable for application scenarios that require high-speed data transmission, such as data centers, cloud computing, storage and other fields.

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