800G Transceiver - Technical Analysis in 4x200G FR4 Scenario
The relentless progression of internet traffic and the continuous push for higher data rates has paved the way for the advent of the 800G transceiver. As network infrastructure evolves, the implementation of such advanced optical modules becomes critical to meet the surging demands of data centers and telecommunication networks. This article delves into the technical intricacies of the 800G transceiver within the specific context of a 4x200G FR4 scenario. By exploring the nuances of this high-capacity transceiver, we will analyze its technical requirements and evolution route, and introduce the DFT 800G FR4 solution.
Analysis of Technical Requirements in 800G FR4 Scenarios
Single-channel 200G PAM4 (Pulse Amplitude Modulation) technology represents a critical advancement in the arena of intensity-modulated, direct-detection interconnects, poised to lay the groundwork for quad-channel 800G links and serve as a pivotal component for upcoming 1.6Tb/s interconnect solutions. As depicted in the picture below, the Multi-Source Agreement (MSA) is set to define a comprehensive Physical Medium Dependent (PMD) layer and a segment of the Physical Medium Attachment (PMA) layer. This includes the introduction of novel low-power, low-latency Forward Error Correction (FEC) schemes that build upon the existing KP4 FEC for 112G electrical input signals, enhancing the modulators' net coding gain (NCG).
One of the prime objectives of this industry consortium is to spearhead the development of new broadband electrical and optical analog components designed for both transmitters and receivers. The innovation funnel includes ambitious plans for Digital-to-Analog (DAC) and Analog-to-Digital (AD/DA) converters. To meet the demanding power constraints of pluggable modules, Digital Signal Processor (DSP) chips are to be designed using advanced, lower-nanometer CMOS processes, incorporating power-efficient signal processing algorithms to achieve optimal channel equalization.
800G 2xFR4 OSFP Evolution Route
The current 800G 2xFR4 OSFP configuration utilizes two sets of 4-wavelength CWDM 100G EML lasers, each comprising 4 lasers. However, future advancements will transition towards an FR4 setup employing 4 CWDM wavelength 200G EML lasers.
This shift to 800G FR4 necessitates using 4-wavelength CWDM lasers in silicon photonics solutions, eliminating any cost advantage. Currently, the mainstream preference lies with the EML scheme, with no ongoing exploration of silicon photonics schemes by manufacturers. The DFT 800G 2xFR4 OSFP transceiver has cutting-edge features such as a self-developed 53G EML laser chip and a built-in Broadcom 7nm DSP chip, ensuring unparalleled performance and reliability.
4x200G Packaging Solution Analysis
For the 4x200G optical modules, a reassessment of the packaging for both transmitters and receivers is required to ensure the signal integrity of high-speed signals within the Nyquist frequency range, which is around 56GHz. The following figure demonstrates two possible solutions for the transmitter configuration.
Solution A adopts a traditional method where the modulator driver (DRV) is close to the modulator. This conventional setup has been the norm in previous designs. On the other hand, Solution B employs an advanced approach by utilizing a flip-chip design for the DRV, which is co-packaged with the Digital Signal Processor (DSP) unit. This is aimed at optimizing signal integrity along the RF transmission lines.
Both solutions are feasible with cutting-edge technology. Preliminary simulations have suggested that Solution B can achieve favorable results, ensuring a bandwidth greater than 56GHz. The ripple observed in Solution A's S21 curve is attributed to reflections at the input of the DRV, which could be mitigated through a matching design of the DRV.
Ultimately, it is anticipated that by refining the matching network, Solution A’s overall performance might be further enhanced, representing a significant stride forward in securing the fidelity of communication signals in high-speed data modules.
DFT 800G FR4 Solution Introduction
To meet the needs of rapid business development, many large Internet companies need to build 800G data centers or upgrade their data centers from 400G speed to 800G speed. The DFT data center 800G FR4 optical module solution can meet various networking requirements of customers, helping customers achieve more efficient and stable data transmission.
The Architecture of DFT 800G FR4 Solution
The Core switch is upgraded to 800G and adopts 800G 2xFR4/2xLR4 modules. The Spine switch maintains a 400G rate and adopts the 400G FR4/LR4 module, which is connected to the Core switch by Breakout mode. The Leaf switch maintains a 400G rate, uses 400G DR4, and connects to TOR. In this breakout solution, 800G FR4 is typically used for the Spine or Core layer, supporting transmission distances of up to 2km. It has four optical ports that can be used to connect two 400G modules over a Dual CS cable. Additionally, 800G FR4 supports CMIS5.0, offering extensive module status monitoring and information diagnostic capabilities, which are very helpful for network operation and maintenance. Below is the solution topology that upgrades the network from 400G to 800G using 2xFR4.
Key Benefits of DFT 800G FR4 Solution
DFT provides professional solutions for large data center users who need to fully upgrade to 800G rates to quickly increase data center network bandwidth and meet the rapid growth of their business. The comprehensive networking solutions and product requirements for customers not only help customers save costs but also reduce power consumption, thus bringing higher value to customers.
High Density: Deploying QSFP-DD/OSFP modules in high density increases transmission capacity and can provide a higher bandwidth rate.
Low Power Consumption: The use of a smaller 7nm DSP chip ensures high integration of the product, thereby achieving lower power consumption than the industry average and reducing customer investment costs.
Flexible Deployment: Provide different ways of breakout or direct connection schemes, which are more abundant, flexible, and convenient for a smooth upgrade transition afterward.
800G FR4 Solution Product List
Product Type Part Number Parameter
Optical Module OSFP-2FR4-800G PAM4 1310nm 2km DOM Duplex LC/UPC SMF
QDD-FR4-400G PAM4 1310nm 2km DOM Duplex LC/UPC SMF
QSFP-DR-100G Single Lambda 1310nm 500m DOM Duplex LC/UPC SMF
DAC Cable QSFP-100G-PC01 1-meter, Passive, QSFP28 to QSFP28, 30AWG
Fiber Optic Cable HD-SMFULCDX 1m (3ft) LC UPC to LC UPC Duplex OS2
Server TS4620 6U Tower Server, 4 x 3.5''/2.5'' Hot-swap SAS/SATA/SSD Drive Bays, 2 x RJ45 1GbE Ports, 550W Redundant
Switch MSN4410-WS2FC 24 x 100Gb QSFP28-DD, with 8 x 400Gb QSFP-DD
Forward Error Correction Coding (FEC) in Single Channel 200G
To meet the sensitivity requirements for a 200G PAM receiver, which entails a pre-FEC bit error rate threshold performance of 2E-3, a more powerful FEC is needed. The following figure illustrates the comparison between terminated schemes and concatenated (serial) schemes.
In the first option, KP4 will be terminated and replaced with a new FEC that has a higher overhead. This scheme has advantages in terms of Net Coding Gain (NCG) and overhead. In the second option, the concatenated scheme retains KP4 as the outer code and combines it with a new inner code. This cascaded concatenation approach provides advantages in latency and power consumption, making it more suitable for the 800G-FR4 application scenario.
Summary
As the industry moves forward, continued innovation in photonics and electronics will undoubtedly drive enhancements in 800G technology. The 4x200G FR4 scenario is just the beginning, with evolving standards and expanding use cases set to unlock new frontiers in the world of telecommunications. The successful integration of these high-speed modules will pave the way for unprecedented data transmission capabilities, anchoring the backbone of next-generation networks that will fuel the data-hungry applications of tomorrow.