Exploring 800G Optical Transceiver Technologies and Applications

The Application Trends of 800G Optical Transceivers

In an age dominated by digital transformation, the utilization of 800G optical transceivers has become indispensable across a spectrum of application scenarios. Ranging from the short distances covered by SR (100m) to the extensive spans of ER/ZR (40km/80km), these optical transceivers play a pivotal role in enabling high-speed data transmission across diverse networking environments.

AI Computing Cluster and Conventional Cluster

The TOR-to-Leaf switch connection spans a short distance, while major internet firms opt for 100G links, gradually advancing to 200G/400G from 2021 onwards, with some adopting 800G by 2023. Leaf-to-Spine switch connections extend up to 2km or even 10km. Data centers are often interconnected for load balancing or disaster recovery, covering distances of several kilometers. This is achieved through dense wavelength division multiplexing and coherent communication, maximizing fiber optic resource utilization.

800G Optical Transceiver Interface Architectures

Currently, 800G optical modules are mainly divided into three interface architectures:

• First generation: 8x100G optical interface and 8x100G electrical interface

• Second generation: 4x200G optical interface and 8x100G electrical interface

• Third generation: 4x200G optical interface and 4x200G electrical interface

Electrical Interfaces Architectures

Regarding the electrical interfaces, when the individual channel rate matches that of the optical interface, the optical transceiver's architecture achieves optimal performance, boasting advantages like low power consumption and cost-effectiveness. Specifically, the single-channel 100G electrical interface proves optimal for the 8x100G optical transceiver, while the single-channel 200G electrical interface suits the 4x200G optical transceiver ideally. As for packaging, the 800G optical transceiver may be available in various formats such as QSFP-DD and OSFP. More details about QSFP-DD and OSFP，you can check: 800G Transceiver Overview: QSFP-DD and OSFP Packages.

Optical Interface Architectures

There are three main types of optical interface architectures for 800G optical modules:

• 8x100G PAM4: The PAM4 transceiver operates at 53 Gbd and uses 8 pairs of digital-to-analog converters (DAC) and analog-to-digital converters (ADC), 8 lasers, 8 pairs of optical transceivers, and 1 pair of 8-channel coarse wavelength division multiplexers (CWDM).

• 4x200G PAM4: The PAM4 transceiver operates at 106Gbd and uses 4 pairs of DACs and ADCs, 4 pairs of optical transceivers (including 4 lasers), and 1 pair of 4-channel CWDM.

• 800G Coherent: It uses 4 pairs of DACs and ADCs, 1 laser and 1 pair of optical transceivers and fixed wavelength lasers can be used in data center coherent optical modules to reduce cost and power consumption.

Application Scenarios of 800G Optical Transceivers

800G SR8

In the 800G SR scenario, two technical solutions are prominent: those based on DML/EML and those based on SiPh technology. The 800G SR8 DML/EML solution utilizes 8x100G DSP and employs DML/EML optical chips with identical wavelengths. It utilizes 8 optical fibers for transmission and reception (PSM8) and utilizes 24-core or 16-core MPO connectors.

The 800G SR8 SiPh solution leverages 8xSiPh MZ modulator/continuous fiber laser technology. It employs silicon light for transmission, while the modulator and light source are separated, enabling a parallel multi-channel shared light source setup. Properly managing insertion loss allows for using 1-2 light sources to support 8 parallel channels, providing a significant cost advantage to the system. For more details, please refer to: 8×100G Solution for SR Scenario.

800G DR

In the 800G DR/FR scenario, the 4x200G solution presents a cost advantage. The 800G DR4 (EML/SiPh) solution integrates 4x200G DSP, utilizing optical chips featuring 4xEML/SiPh with matching wavelengths. Given the current limitations in bandwidth development, this solution opts out of DML usage. Both transmitting and receiving ends employ 4 optical fibers (PSM4) of identical wavelengths, facilitated by 12-core MPO connectors.

800G FR

In the 800G 2km (FR) scenario, a single-channel 200G PAM4 technology is employed. With the rate doubling from 100G to 200G, the baud rate also doubles, resulting in a sensitivity degradation of approximately 3dB. Consequently, a more robust FEC is necessary to uphold a high receiver sensitivity of -5dBm.

Summary

The development trends in 800G technology reflect a concerted effort to enhance network performance, scalability, and efficiency. By embracing single-mode transmission, single-wavelength 200G solutions, and coherent transmission techniques, the industry is paving the way for next-generation optical networks capable of meeting the evolving demands of modern data-intensive applications.