800G DCO Coherent Optical Module | Host Interface, Line Protocol & 400G vs 800G

1. What Is an 800G DCO Optical Module?

With the rapid development of AI computing, cloud data centers, and hyperscale networks, optical transmission is gradually evolving from the 400G era to the 800G era. The 800G DCO (Digital Coherent Optics) is a new generation of pluggable coherent optical module based on 400G DCO technology. It highly integrates a coherent DSP, coherent optical components, and high-speed electrical interfaces, enabling switches and routers to connect directly to DWDM optical networks without requiring traditional standalone coherent transmission equipment.

Compared with 400G DCO, the most significant change is not only the doubling of bandwidth, but also the adoption of the OSFP form factor to support higher power consumption, improved thermal performance, and next-generation 112G high-speed electrical interfaces.

2. Host Interface (Host Protocol) of 800G DCO

The Host Interface is the high-speed electrical interface between the switch ASIC and the coherent optical module.

The current Host Interface specifications are as follows:

DCO 800G/400G/200G/100G DWDM Coherent Transceiver丨C-LIGHT

The 800G DCO platform has fully entered the 112G SerDes era, providing several advantages over the 400G platform:

• Higher bandwidth per lane

• Simpler PCB routing

• Better signal integrity

• Higher port density

• Lower power consumption per transmitted bit

As 800G switch ASICs become increasingly mainstream, 800GAUI-8 has become the standard Host Interface for future high-speed coherent optical networking. Consequently, 800G DCO offers greater market value than 400G DCO.

3. Line Protocol of 800G DCO

The Line Protocol determines how the module transmits optical signals over fiber.

800G DCO typically adopts the latest generation coherent DSP and supports the following modulation formats in ZR+ mode:

• DP-QPSK (56G/112G SerDes)

• DP-16QAM (118GB)

• PCS-16QAM (124GB)

• Probabilistic Constellation Shaping (PCS)

• Adaptive Modulation

According to different transmission distances, the module can flexibly operate at:

• 800G (1×800G / 2×400G / 4×200G / 8×100G)

• 600G (3×200G / 6×100G)

• 400G (1×400G / 2×200G / 4×100G)

• Flex Rate

The DSP automatically adjusts the modulation format based on OSNR, transmission distance, and fiber quality, improving spectral efficiency while maintaining stable transmission performance.

4. 800G DCO vs. 400G DCO

As shown above, 800G DCO not only doubles the transmission capacity, but also achieves comprehensive improvements in interface speed, thermal performance, DSP capability, and future scalability. The introduction of the OSFP form factor is an important milestone in the evolution toward higher-performance coherent optical modules, making 800G DCO more suitable for modern AI and HPC interconnect applications.

5. Advantages of OSFP over QSFP-DD for 800G DCO

C-LIGHT provides both OSFP and QSFP-DD versions of 800G DCO optical modules to meet different deployment requirements.

Compared with QSFP-DD, the OSFP form factor offers the following advantages:

• Larger heat dissipation area

• Higher power handling capability

• Better airflow design

• More robust mechanical structure

• Scalability for future 1.6T coherent optical modules

Therefore, OSFP has become one of the primary development directions for 800G DCO and next-generation high-speed coherent optical modules.

6. Typical Applications of 800G DCO

800G DCO is mainly designed for high-bandwidth and high-reliability optical transmission applications, including:

• AI Data Center Interconnect (DCI)

• Metro Optical Networks

• Backbone Network Upgrades

• Cloud Service Provider Networks

• IP over DWDM

• Coherent Router-to-Router Interconnection

As 800G Ethernet becomes increasingly widespread, 800G DCO will further promote the evolution of optical networks toward higher integration, lower latency, and lower deployment costs.

7. Future Development Trends

Over the next several years, the large-scale deployment of AI and HPC infrastructure will continue driving rapid growth in 800G and 1.6T coherent optical communications for DCI applications. Major industry trends include:

• Widespread adoption of 112G SerDes

• AI workloads accelerating 800G network deployment

• Pluggable coherent optics replacing portions of traditional telecom OTN transport equipment

• Continuous improvements in DSP power efficiency

• OSFP becoming the mainstream form factor

• Ongoing evolution toward 1.6T coherent optical modules

800G DCO is not merely a bandwidth upgrade over 400G DCO; it represents an important step toward higher-performance, more intelligent, and more scalable coherent optical networking. C-LIGHT has already been actively exploring and investing in this emerging market trend.