400G transceivers are high speed optical modules designed for 400Gbps data transmission. They are commonly used in data centres, cloud computing, high performance computing (HPC) and AI environments. PAM4 (4-Level Pulse Amplitude Modulation): This is the predominant modulation technique used in 400G modules. 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. This shift is driven by multiple forces: hyperscale data centers require greater east-west bandwidth to support massive internal data. With the 400G speed-up, the optical interconnect infrastructure has seen significant developments, giving rise to several interface designs and form factors, such as QSFP-DD and OSFP. This article introduces the fundamentals, standards, and market trends surrounding 400G optical modules, a core technology for modern AI and cloud networks.
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