In this blog, ETU-LINK will talk about the 50G SFP56 SR optical module using PAM4 modulation technology. Since the PAM4 signal has four level values, the PAM4 signal can be used in the same physical bandwidth of the channel. Downlink transmission is twice the amount of information compared to NRZ signals, enabling single-channel 50G applications. Therefore, PAM4 signal modulation has become the preferred technical direction of the next-generation high-speed communication standards 50G BASE, 200G BASE, and 400G BASE.

The electrical signal and optical signal of the 50G SFP56 SR optical module are both PAM4 modulated, the working wavelength is 850nm, and the SFP56 package is adopted. The transmission distance through multimode fiber can reach up to 70m (OM3) or 100m (OM4).

As our society's thirst for data continues to grow, not only with more data, but with faster data transfer rates, older modulation schemes based on NRZ-type encodings are becoming increasingly inadequate. Generally, there are three ways to increase the transmission rate of optical communication: increase the modulation rate, increase the number of WDM channels, and increase the number of levels.

Since the PAM4 signal can transmit 2 bits of information per symbol period, to achieve the same signal transmission capability, the symbol rate of the PAM4 signal only needs to reach half of the NRZ signal, so the loss caused by the transmission channel is greatly reduced. With the development of future technology, the possibility of using more levels of PAM8 and even PAM16 signals for information transmission is not ruled out.

PAM4 technology can effectively improve the efficiency of bandwidth utilization. At the same time, PAM4 adopts a high-order modulation format, which is an effective way to reduce the number of optical devices used, reduce the performance requirements of optical devices, and reduce the performance, cost, power consumption and performance in different applications. There is a balance between density.