According to the predictions of many professional organizations, 400G will undoubtedly be the dominant rate in the future market with the explosive growth of network traffic. At present, the standard of 400G optical transceiver has not been unified. Let's see the different packages of it.
①QSFP-DD (Quad Small Form Factor Pluggable-Double Density)
This solution is an extension of QSFP, adding another row on the original 4-channel interface to become 8-channel, which is the called double density. It is compatible with the QSFP solution, but QSFP28 transceiver can also be used, just insert another one.
②OSFP (Octal Small Formfactor Pluggable)
OSFP optical transceiver uses 8 of 56G channels to achieve 400G. The 56G signal is formed by a 25G DML laser under PAM4 modulation. It is a new interface standard and not compatible with the current photoelectric interface. OSFP comes with a heat sink, the size is much smaller than CFP8 but slightly larger than QSFP-DD, and the power consumption is low, with a maximum of only 15W.
CFP8 is an extension of CFP4. The number of channels has increased to 8 channels, size is increased accordingly. Si the cost of this solution is higher. It needs to use 16 of 25G lasers, or use PLC splitter to reduce the number of lasers, but the LOSS of the splitter is too high, which directly leads to the large emission power of the laser and high power consumption, therefore increased the cost.
There isn't a particularly perfect solution for current 400G optical transceiver, it is constantly optimized. QSFP-DD is the better one for now. But It will take some time to prove which is the most suitable one..