Innovative Optical Interconnects for Future Data Center Networking

As application scenarios evolve, user demands for data center networks, optical transceivers in paticular, are continually changing. For long-distance wavelength division applications, users prioritize performance, striving for extended transmission distances and enhanced spectral efficiency. In contrast, for short-distance applications within data centers, users focus more on cost, considering factors such as distance, size, and power consumption.

Gordon Moore, the co-founder of Intel, introduced Moore's Law, which forecasts that the number of transistors on an integrated circuit doubles every 18 months, a principle that has guided the semiconductor industry for over fifty years. Similarly, in optoelectronics, there is the "Optical Moore's Law," which states that short-distance optical transceivers undergo significant advancements approximately every four years, leading to a reduction in cost per bit and power consumption by half.

To attain higher data rates, optical transceivers typically utilize three strategies: enhancing the speed of optical devices (higher baud rates), increasing the number of channels (multi-lane), and employing advanced modulation techniques. These approaches help reduce the transmission cost per bit, thereby adhering to the requirements of "Optical Moore's Law."

Adoption of PAM4 Advanced Modulation Technique

PAM4 (Pulse Amplitude Modulation 4) technology is a highly efficient modulation technique that significantly improves optical transceiver bandwidth utilization. PAM4 signals are becoming popular for signal transmission, succeeding the NRZ (Non-Return-to-Zero) encoding method.

NRZ signals utilize two signal levels, high and low, to represent digital logic signals 1 and 0, respectively, transmitting 1 bit of logical information per clock cycle. In contrast, PAM4 signals use four distinct signal levels, allowing the transmission of 2 bits of logical information per clock cycle, represented by 00, 01, 10, and 11. As a result, PAM4 signals achieve twice the bit rate of NRZ signals at the same baud rate, effectively doubling transmission efficiency and reducing costs.

The adoption of PAM4 technology in 400G transceivers will enhance transmission efficiency and help lower transceiver costs.

Increasing the Number of Channels (Multi-lane)

Historical data has indicated that solutions with more than 8 lanes (such as x10, x16) can encounter challenges in channel yield and reliability, making it difficult for them to become mainstream solutions. A cost- and power-efficient multi-lane architecture typically relies on x4 or x8 configurations.

For instance, the 100G CWDM4 and 100G SR4 transceivers, based on a 4x25G architecture, have become the mainstream solutions for the previous generation of data center optical interconnects.

Higher Baud Rate Optoelectronic Chips

Data center 100G optical transceivers, based on the 25Gbaud optoelectronic chip industry chain (DML, VCSEL), use NRZ signaling and have achieved commercial success with a 4-channel architecture. Various 25Gbaud optoelectronic chips (DML, EML, VCSEL) are now evolving toward higher baud rates of 56Gbaud. The 56Gbaud EML industry chain is already available, while the 56Gbaud DML and VCSEL are still under research and development.

Chip Requirements in the Data Center Network

Conclusion

Looking ahead, with sustained technological innovation and advancement, we anticipate the emergence of more groundbreaking optical interconnect solutions, delivering superior performance and reduced total ownership costs to data center networks. Choosing the right data center networking solution is critical. FS delivers dependable data center networking solutions and top-notch data center transceivers.