PAM4 and NRZ

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Key words:PAM4，NRZ，200G optical module，400G optical module，800G optical module

PAM4 (Pulse Amplitude Modulation with 4 levels) is a type of PAM (Pulse Amplitude Modulation) technique. Unlike NRZ (Non-Return-to-Zero) signaling, PAM4 employs four distinct signal levels for signal transmission, allowing each symbol period to represent 2 bits of logical information (0, 1, 2, 3), i.e., four levels within one time unit. Therefore, at the same baud rate, PAM4 doubles the throughput compared to NRZ, meaning that PAM4 can increase network bandwidth without the need for additional optical fibers, effectively enhancing bandwidth utilization.

NRZ (Non-Return-to-Zero) utilizes two signal levels for signal transmission, with each symbol period capable of transmitting 1 bit of logical information (1, 0).

PAM4 employs a high-order modulation scheme, which can reduce the number of optical components and lower the performance requirements for them, achieving a balance in cost, power consumption, and density.

Currently, PAM4 with baud rates of 25G and 50G is widely used in data centers, such as in 200G/400G/800G Ethernet. As an efficient modulation technique, PAM4 has become an inevitable trend in the development of 200G/400G/800G high-speed connectivity interfaces. Leveraging its own advantages (such as high performance), PAM4 will become the mainstream modulation method for 200G/400G/800G Ethernet optical modules.

FiberWDM is a high-tech enterprise integrating research and development, production, and sales. As a leading provider of optical components and optical network equipment, the company focuses on supplying high-performance optical interconnect products and DCI (Data Center Interconnect) optical connectivity solutions to domestic and international operators, cloud service providers, system integrators, internet companies, computing power centers, artificial intelligence, cloud computing, edge computing, and more.