Advances in DSP and optical device manufacturing have enabled coherent optical modules to deliver higher speeds and longer distances, offering superior performance and broad application potential. Optical modules are key components in fiber-optic systems, converting electrical signals to optical. Coherent optics is expanding beyond traditional long-haul networks into metro, data center interconnect, fiber access and even space-based satellite communications, driven by AI workloads and bandwidth demand. This paper explores the basics of. VIAVI has developed versatile, industry-leading solutions to support the unique design validation, compliance testing, and manufacturing requirements of coherent optical modules. With the release of the IEEE 802. 3ct standard, coherent optics can now be used to carry 400G over extremely long.