Development and Status Quo of 400G Optical Modules

In the current 400G optical module, the optical port side mainly uses 8-way 53Gbps PAM4 (400G-SR8, FR8, LR8) and 4-way 106Gbps PAM4 (400G-DR4, FR4, LR4) to achieve 400G signal transmission; Use 8-way 53Gbps PAM4 electrical signal at the electrical port side.

The package types of 400G optical modules are OSFP and QSFP-DD respectively. The package size of QSFP-DD is smaller, which is more suitable for data center applications; OSFP package size is slightly larger, and it is more suitable for telecom applications because it can provide more power consumption. The following is a brief introduction to the packaging types of 400G optical modules.

1. The full name of OSFP is Octal Small Formfactor Pluggable. This standard is a new interface standard, which is incompatible with the existing photoelectric interface.

2. The full name of QSFP-DD is Quad Small Form Factor Pluggable Double Density. This solution is an extension of the QSFP interface. The original 4-channel interface is added to 8-channel interface, which is called dual density.

3. CFP8 is an extension of CFP4. The number of channels is increased to 8. The cost of this solution is high, and 16 25G lasers are required.

4. CWDM8 is an extension of CWDM4 standard. The rate of each wavelength is 50G, which can also reach 400G. Four new central wavelengths, namely 1351/1371/1391/1411nm, have been added.

5. The full name of COBO is consortium for on board optics, which means that all optical elements are placed on the PCB. The main advantages of this solution are good heat dissipation and small size.

The 400G product system is increasingly improved and standardized. The 400G Ethernet (IEEE 802.3bs) was officially approved as early as December 2017. In this standard, forward error correction (FEC) and other new technologies are standardized to improve the error code performance and increase the credibility of data communication. At present, some suppliers in the industry have developed 400G switches according to relevant standards and put them into the market, such as Cisco 400G Nexus, Arista 400G 7060X4 series, Mellanox Spectrum-2, etc.