800G Transceiver Market Overview - NADDOD Blog

800G Transceiver Market Overview

NADDOD Adam Connectivity Solutions Consultant Jan 24, 2024

The application scenarios for 800G optical modules are primarily divided into SR (100m), DF/FR/LR (500m/2km/10km), and ER/ZR (40km/80km). The connection distance between Top of Rack (TOR) switches and Leaf switches is relatively short. Large internet companies commonly employ 100G connection technology and have begun to gradually transition to 200G/400G since 2021. Some companies are adopting 800G technology in 2023.

 

CLOS Network Structure

The connection between the Leaf and Spine switches can reach distances of up to 2km or even 10km. Data center interconnection typically involves load balancing or disaster recovery backup connections between adjacent data centers. In such cases, the connection distance can extend for several tens of kilometers, and dense wavelength division multiplexing (DWDM) combined with coherent communication is primarily used to maximize the utilization of optical fiber resources.

 

Typical Optical module evolution

The evolution of the 800G technology solution includes three generations. The first generation is 8 optical lanes and 8 electrical lanes, with an optical interface of 8x100G and an electrical interface of 8x100G. It was commercially available in 2021. The second generation is 4 optical lanes and 8 electrical lanes, with an optical interface of 4x200G and an electrical interface of 8x100G. It is expected to be commercially available in 2024. The third generation is 4 optical lanes and 4 electrical lanes, with an optical interface of 4x200G. It is projected to be commercially available in 2026. Currently, single-channel 200G optoelectronic chip devices and equalization techniques are not yet mature.

 

In terms of electrical interfaces, when the single-channel rate matches the single-channel rate of the optical interface, the architecture of the optical module will reach an optimal state and will have advantages such as low power consumption and low cost. A single-channel 100G electrical interface will be the ideal electrical interface for 8x100G optical modules, and a single-channel 200G electrical interface will be the ideal electrical interface for 4x200G optical modules. In terms of packaging, 800G optical modules may come in different forms such as dual-density quad small form-factor pluggable (QSFP-DD800) and octal small form-factor pluggable (OSFP).

 

There are three main optical interface architectures for 800G optical modules: 8x100G 4-level pulse amplitude modulation (PAM4), 4x200G PAM4, and 800G coherent optical modules. The 8x100G PAM4 optical module operates at 53 Gbd and uses 8 pairs of digital-to-analog converters (DAC) and analog-to-digital converters (ADC), 8 laser diodes, 8 optical transceivers, and 1 pair of 8-channel coarse wavelength division multiplexers (CWDM). The 4x200G PAM4 optical module operates at 106 Gbd and uses 4 pairs of DAC and ADC, 4 optical transceivers (including 4 laser diodes), and 1 pair of 4-channel CWDM. The 800G coherent optical module uses 4 pairs of DAC and ADC, 1 laser diode, and 1 pair of optical transceivers. It can utilize fixed-wavelength lasers in data center coherent optical modules to reduce cost and power consumption.

 

The 8x100G direct detection solution can leverage existing technology architectures, and related technologies and standards are relatively mature, with a relatively complete supply chain. In the SR scenario, VCSEL 100G technology faces challenges. Improving the performance of multimode solutions and reducing the cost of multimode fibers will be key factors for the continuous evolution of this technology. Single-mode technologies represented by silicon photonics (SiPh) and directly modulated lasers (DML) are developing rapidly. Among them, SiPh technology is developing more rapidly and is expected to compete with multimode solutions in applications with transmission distances of 100m or less. In the DR/FR scenario, there are three options: electro-absorption modulated laser (EML), DML, and SiPh. In the LR scenario, there are 800G LR8 solutions based on CWDM, LWDM, and nLWDM.

 

In the 4x200G direct detection solution, the single-channel 200G continues to use PAM4 modulation, which can utilize the relatively mature industrial foundation of PAM4. For the 4x200G DR and FR applications, there are currently two technical solutions: 4-channel single-mode parallel (PSM4) and CWDM4, both of which still face many challenges. For the LR application scenario, there are 800G LR4 solutions based on CWDM, LWDM, and nLWDM. However, this solution requires high-bandwidth optoelectronic chip devices, stronger equalization technology, and forward error correction (FEC) to ensure a low bit error rate (BER), posing high technical challenges.

 

In the 800G SR scenario, the technical solutions include those based on DML/EML and SiPh. The 800G SR8 DML/EML solution uses an 8x100G DSP, the same-wavelength DML/EML optical chip, with 8 fibers (PSM8 parallel single-mode 8 channels) used on both the transmitter and receiver sides, and employs 24-core or 16-core MPO connectors. The 800G SR8 SiPh solution uses 8xSiPh MZ modulators/continuous-wave fiber lasers (silicon photonics as the transmitter, with the modulator and light source separated), enabling parallel and shared light sources for multiple channels. With proper control of insertion loss, using 1-2 light sources to achieve 8-channel parallelism can provide cost advantages for the system.

 

 

In the 800G DR/FR scenario, the 4x200G solution has a lower cost advantage. The 800G DR4 (EML/SiPh) solution uses a 4x200G DSP. The optical chip adopts 4xEML/SiPh of the same wavelength. Due to limited bandwidth development, the solution does not use DML. Both the transmitter and receiver sides use 4 fibers (PSM4 parallel single-mode 4 channels), all of which are of the same wavelength, and employ a 12-core MPO connector. The 800G 2km (FR) solution utilizes PAM4 technology for single-channel 200G. When the rate increases from 100G to 200G, the baud rate doubles, and the sensitivity worsens by approximately 3dB. Therefore, a more powerful FEC is required to maintain a higher sensitivity (-5dBm) at the receiver.

 

 

The development trends of 800G include single-mode migration, the advent of single-wavelength 200G, and coherent migration. Single-mode migration. Due to the limited bandwidth of multimode fibers, the transmission distance of 100G PAM4 VCSEL+multimode fiber is limited to 50m. The migration to single-mode interface is a development trend that facilitates the coverage of 800G SiPh solutions in massive 100m SR scenarios. The advent of single-wavelength 200G. Although 112 Gbd EML technology is developing rapidly, the availability of 55 GHz bandwidth resources is slightly insufficient. The application prospects of SiPh modulators and silicon-based thin-film lithium niobate are very promising for 200G PAM4 rate levels. Coherent migration. With the increase in transmission rates, coherent technology solutions will further expand their applications to shorter distances such as 40km, 20km, and 10km, building upon the foundation of 80km transmission distance. Coherent solutions require only one laser, modulator, and receiver, and they have cost competitiveness compared to PAM4.