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Unleashing Next-Generation Connectivity: The Rise of 800G Optical Transceivers

Posted on Dec 18, 2023 by
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In today's fast-paced world, the demand for high-speed data transmission has reached unprecedented levels. The emergence of AI applications and large-scale models, such as ChatGPT, has made computing power a critical infrastructure for the AI industry. With the increasing need for faster communication in supercomputing, high-speed optical modules have become an essential component for AI servers. This article delves into the exciting advancements in 800G optical transceivers and their immense potential in the AI era.

Evolution of 800G Optical Transceiver

Increasing Bandwidth Demand

The growth of bandwidth demand has had a significant impact on high-speed optical modules. With the proliferation of emerging technologies and the need for large-scale data transmission, traditional 100G, 200G, and 400G optical modules are no longer able to fully meet market demands. To address the ever-increasing bandwidth requirements, 800G optical modules are emerging as a prominent trend.

Unlocking the Potential of LPO Technology

In the era of 800G optical transceivers, Linear-drive Pluggable Optics (LPO) technology stands out as a promising solution. LPO utilizes linear analog components in the data link, eliminating the need for complex CDR or DSP designs. Compared to DSP solutions, LPOs offer substantial reductions in power consumption and latency, making them ideal for short-range, high-bandwidth, low-power, and low-latency data connectivity requirements in AI computing centers. As cloud service providers expand their computing resources, LPO solutions, including 800G LPO, are poised to capture a significant market share.

Electrical and Optical Interface Architectures of 800G Ethernet

Research indicates that matching the single-channel speed of electrical and optical interfaces optimizes the architecture of optical modules, resulting in lower power consumption and reduced costs. For instance, an 8×100 Gbit/s optical transceiver benefits from a single-channel 100 Gbit/s electrical interface, while a 4×200 Gbit/s optical transceiver pairs well with a single-channel 200 Gbit/s electrical interface. The packaging of 800G optical transceivers may take different forms, such as the double-density four-channel small form-factor pluggable (800G QSFP-DD) and eight-channel small form-factor pluggable (800G OSFP).

There are three main optical interface architectures for 800 Gbit/s optical transceivers:

8×100 Gbit/s PAM4 Optical Transceiver

This transceiver operates at 53 Gbd and utilizes eight pairs of digital-to-analog converters (DACs) and analog-to-digital converters (ADCs), along with eight lasers, optical transceivers, and a pair of 8-channel coarse wavelength division multiplexing (CWDM) or LAN-WDM multiplexer and demultiplexer.

4×200 Gbit/s PAM4 Optical Transceiver

Operating at 106 Gbd, this transceiver employs four pairs of DACs and ADCs, four pairs of optical transceivers (including four lasers), and a pair of 4-channel CWDM or LAN-WDM multiplexer and demultiplexer .

800 Gbit/s Coherent Optical Transceiver

Operating at 128 Gbd with 16QAM modulation, this transceiver utilizes four pairs of DACs and ADCs, one laser, and one pair of optical transceivers. Additionally, data center coherent optical modules can integrate fixed-wavelength lasers to reduce costs and power consumption.

Development Trends of 800G Optical Transceiver

The evolution of 800G optical transceivers is still in its early stages and will continue to progress over the next five years. Key trends include:

Single-Mode Migration:

Multimode fibers have bandwidth limitations, restricting the transmission distance of 100 Gbit/s PAM4 VCSEL+multimode fibers to 50 meters. To overcome this, the industry is shifting towards single-mode optical interface solutions, which benefit from SiPh (Silicon Photonics) technology.

Arrival of Single-Wavelength 200 Gbit/s:

While there have been rapid advancements in 112 Gbd EML (Electroabsorption Modulated Laser) technology, the availability of 55 GHz bandwidth resources is slightly limited. The future holds promise for SiPh modulators and silicon-based thin-film lithium niobate in enabling 200 Gbit/s single-wavelength solutions.

Coherent Migration

Coherent technology solutions are advancing to cover shorter distances (40, 20, and 10 km) in addition to the existing 80 km range. Non-coherent solutions are also expanding their reach to longer distances. Coherent solutions are cost competitive with PAM4 due to their use of one laser, modulator, and receiver compared to PAM4's requirement for four of each. Despite the complexity at 800 Gbit/s, these devices effectively reduce system costs, ensuring PAM4's competitiveness. The ongoing competition between coherent and PAM4 transmission requires continuous observation to determine the outcome.

The Impact of the Al on 800G Optical Transceiver Deployment

Why is 800G More Significant than 400G for Al Servers?

Firstly, Al servers necessitate high data transmission rates and low latency, requiring top-of-rack switches that match the underlying bandwidth. These switches may also require latency redundancy, which calls for high-speed optical modules. For instance, the NVIDIA DGX H100 server is equipped with 8* H100 GPU modules, where each GPU requires 2* 200G optical modules. Thus, each server needs a minimum of 16* 200G modules, and the corresponding top-of-rack switch ports require at least 4* 800G.

Secondly, 800G optical chips offer greater cost efficiency and economic benefits. They utilize 100G EML chips, whereas 200G/400G uses 50G optical chips. Calculations reveal that, for the same rate, the cost of a 100G optical chip is 30% lower than that of two 50G optical chips.

However, it is important to note that 400G optical transceivers still hold significance in the industry. While they may not match the speed of 800G optical transceivers, they provide a significant boost in bandwidth compared to older technologies, making them a cost-effective solution for many organizations. Additionally, certain applications may not require the full capabilities of an 800G Ethernet, making a 400G Ethernet a more practical choice.

400G/800G Transceivers

FS offers high-speed optical network products and complete HPC networking solutions to customers across various industries, including Financial, Healthcare, Education, Government, and Telecom. To provide the latest optical connectivity solutions, FS has introduced 400G and 800G optical transceiver products on its official website.

 Data Rate  PN  Product Specification
400G Transceivers
 OSFP-SR4-400G-FL  NVIDIA InfiniBand Compatible OSFP 400G SR4 PAM4 850nm 50m DOM Dual MPO-12/APC NDR MMF Optical Transceiver, Flat Top
 OSFP-DR4-400G-FL  NVIDIA InfiniBand Compatible OSFP 400G DR4 PAM4 1310nm 500m DOM MPO-12/APC NDR SMF Optical Transceiver, Flat Top
800G Transceivers
 OSFP-SR8-800G  NVIDIA InfiniBand MMA4Z00-NS Compatible OSFP 800G SR8 PAM4 2x SR4 850nm 50m DOM Dual MPO-12/APC NDR MMF Optical Transceiver, Finned Top
 OSFP-DR8-800G  NVIDIA InfiniBand MMS4X00-NM Compatible OSFP 800G DR8 PAM4 2x DR4 1310nm 500m DOM Dual MPO-12/APC NDR SMF Optical Transceiver, Finned Top
 OSFP-2FR4-800G
NVIDIA InfiniBand MMS4X50-NM Compatible OSFP 800G 2FR4 PAM4 1310nm 2km DOM Dual LC Duplex NDR SMF Optical Transceiver, Finned Top

As the demand for faster and more efficient data transmission continues to surge, the era of 800G optical transceivers has arrived. With their remarkable bandwidth capabilities and advancements in LPO technology, these transceivers are set to revolutionize the AI industry and transform data centers. The deployment of 800G optical transceivers brings us closer to unlocking the full potential of AI.

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