The 400G QSFP-DD (Quad Small Form Factor Pluggable Double Density) module is a hot-pluggable form factor designed for high speed optical networking applications. QSFP-DD outlook and connector is similar to current QSFP form factor, but it has an additional row of contacts provided for an eight lane electrical interface that operate at 50 Gbps using PAM4 modulation supporting speeds up to 400G. Nowadays 400G is one of the highest data rates in the Ethernet world, offering improved capabilities for key aggregation and high‑bandwidth interconnection applications. These applications cover a wide range such as: Hyperscale Data Centers, Internet Exchanges, Colocation Services, Wireless Infrastructure Core, Service Provider and Operator Core Networks and Video Distribution Infrastructure. 400G QSFP-DD has been defined by the QSFP-DD MSA Group as a next generation, high-density, high-speed pluggable modules that are backwards compatible with 100G QSFP28 and even 40G QSFP+. Our compatible QSFP-DD portfolio consists of transceivers which can operate over Single-Mode or Multi-Mode optical Fiber, can be used for connection distances from a couple of meters up to 40 kilometers and can support up to 425 Gbps data rate and 400G Ethernet application. Our QSFP-DD portfolio consist of 400GBASE-SR8, 400GBASE-DR4, 400GBASE-FR4, 400GBASE-LR4, 400GBASE-ER4 Lite which are defined by QSFP-DD MSA, 100G Lambda MSA, CMIS 4.0 and IEEE 802.3bs 400 Gbps specification.