A 400G optical transceiver is a high-speed pluggable device used to connect networking equipment such as switches, routers, and servers. PAM4 (4-Level Pulse Amplitude Modulation): This is the predominant modulation technique used in 400G modules. Multi-Mode Fiber (MMF):. The Cisco 400G QSFP-DD Ultra Long-Haul Coherent Optics Module enables 400G traffic anywhere over dense wavelength division multiplexing amplified networks, and is available in both C-band and L-band. Cisco has expanded the range of 400G digital coherent QSFP-DD transceivers with the 400G QSFP-DD. 400 Gigabit Ethernet (400G) transceivers are optical modules capable of handling data rates of 400 Gbps. Juniper's 400G transceivers use the QSFP-DD form factor. The wide variety of modules gives you flexible and cost-effective options for all types of interfaces.