Data Centre Connectivity: The Surge of Coherent Optical Transceiver Technology

According to the optical transceiver report from the Yole Group, the revenue generated by optical transceivers in 2022 was approximately $11 billion. Forecasts indicate substantial growth in this field, with projections reaching $22.2 billion by 2028.

As data centres witness increased investments and rapid growth in traffic, the optical module market undergoes a transformative phase. The mainstream adoption of silicon photonics technology in optical transceivers is a key trend fueling this evolution, as data centre operators aim to maximise their infrastructure capabilities.

Click to learn more about the trends in the data centre optical module market: New Trends of Optical Transceiver Market in Data Centers | FS Community

Advancements in Coherent Optical Module Technology and Standardization Trends

Coherent technology has emerged as the leading solution for Data Center Interconnect (DCI) applications, spanning distances of 80 to 120 km in data communication. The evolution of applications has brought forth new demands for coherent optical transceiver systems. This shift has led to the development of coherent transceiver units, transitioning from initial integration with line cards and Multi-Source Agreements (MSA) transceivers to independent, standardized pluggable optical transceivers.

The latest advancements in Complementary Metal-Oxide-Semiconductor (CMOS) technology digital signal processor (DSP) chips and integrated photonics technology have paved the way for developing smaller, lower power-consuming pluggable coherent optical transceivers. The trajectory of coherent optical modules applied in metropolitan and backbone networks is characterized by high speed, miniaturization, low power consumption, and standardization of interoperability.

Presently, commercial coherent technology has progressed to support single-wavelength 800G transmission. Nonetheless, the industry lacks standardized specifications for 800G. In contrast, 400G coherent technology has reached maturity, adhering to standards like 400ZROpenROADM, and OpenZR+. The Optical Internetworking Forum (OIF) is currently deliberating on the next-generation coherent technology standard, tentatively named 800ZR.

Coherent Modulation vs. PAM4 in 800G Optical Transmission

Coherent modulation used in coherent optical communication involves altering the frequency, phase, and amplitude of the optical carrier to transmit signals. Unlike intensity detection, coherent modulation requires coherent light with clear frequency and phase, primarily used for high-speed and long-distance transmission. PAM4 is suitable for high-speed, medium-short distance transmission, making it ideal for internal connections in next-generation data centres.

For example, FS OSFP 800G SR8 optical transceivers employ PAM4 modulation, suitable for use in InfiniBand NDR end-to-end systems, designed for Quantum-2 air-cooled switches. They are the ideal solution for the supercomputing and artificial intelligence industries, seamlessly integrating into compute and storage infrastructures, ensuring efficient high-performance connectivity.

In the context of long-distance Data Center Interconnect (DCI) scenarios, PAM4 faces competition from coherent modulation based on the 400ZR protocol. As data centre speeds enter the era of 800G, the differences between PAM4 and coherent technology are gradually diminishing. The competitiveness of each technology depends on factors such as cost and power consumption.

Choosing Between InP and Silicon Photonics

In the context of coherent technology, the choice between InP (Indium Phosphide) and silicon photonics for I/Q modulators and receivers becomes crucial. Despite being cost-effective, silicon photonics exhibits lower performance, known for its high peak voltage and limited bandwidth. In contrast, InP offers lower peak voltage and superior bandwidth but at a higher cost. In PAM4 and coherent technologies, InP transceivers are often more expensive, while silicon photonics provides a more economical alternative.

Coherent vs. PAM4 in High-Speed Transmission

Regarding power consumption, with the evolution of chip technology from 7nm to 5nm and even 3nm, enhancement is not limited to an increase in DSP processing rates. It also extends to superior power reduction performance.


Several companies have validated these methods through experiments. FS believes that with increased production and reduced costs, coherent methods can achieve cost competitiveness with PAM4 by requiring only a laser, modulator, and receiver. This remains true even as optical equipment becomes more complex. Consistency in solutions enables higher flexibility and performance, distinguishing them. In conclusion, the competition between coherent transmission technology and PAM4 transmission technology continues, with future developments determining the mainstream approach.

As a leading solutions provider in the industry, FS has an abundant stock of 800G modules, ensuring your needs are met from quality to rapid delivery. Visit the FS website now for more product and solution information.

Read more about the detailed content on coherent modules: Advancements in Coherent Optical Module Technology and Standardization Trends | FS Community

Coherent Modulation vs. PAM4 in 800G Optical Transmission | FS Community