With the rapid development of technologies such as cloud computing, artificial intelligence, and the Internet of Things (IoT), the demand for data centers is increasing. In response to this demand, the 400G SR8 module has emerged.
This optical transceiver incorporates several key technologies, including VCSEL lasers, multi-mode lens PD design, and COB packaging design, to achieve high-speed and high-density data transmission.
In this article, we will delve into these key technologies and their principles, providing you with a comprehensive introduction to the features and advantages of the 400G SR8 optical transceiver.
Principle of 400G SR8 Optical Transceiver
The NADDOD 400G SR8 optical transceiver conforms to the IEEE 802.3cm (Draft) standard and meets the transmission link requirements of 70m OM3 and 100m OM4/OM5.
The block diagram of the 400G SR8 optical transceiver is shown in the figure below. The transceiver uses a standard 16-core multi-mode MPO connector and consists of six main components: the receiver, transmitter, VCSEL driver, transimpedance amplifier (TIA), PAM4 business chip (oDSP), controller, and others. The eight-channel optical and electrical components of the transmitter and receiver are compactly placed within the QSFP-DD package through engineering design.
400G SR8 Schematic Diagram
The 400G SR8 optical transceiver consists of 8 channels, with each channel carrying a 53.125Gbps signal. It adopts PAM4 high-order modulation, and the internal oDSP of the module performs functions such as clock recovery, signal shaping, and conditioning.
Key Technologies of NADDOD 400G SR8
To meet the requirements of high performance, low cost, and deliverable 400G SR8 multi-mode short-reach optical transceivers for data center applications, NADDOD has employed several key technologies, including:
High-performance VCSEL Lasers
With the advent of the 400GE era, the modulation technology of optical transceivers has transitioned from 25.78125Gbaud NRZ signals to 26.5625Gbaud PAM4 signals.
To ensure the transmission performance of PAM4 services, NADDOD utilizes industry-leading high-bandwidth VCSEL lasers with a typical bandwidth of 19GHz.
The simplified diagram of the VCSEL structure is shown below. This laser achieves higher bandwidth (typical bandwidth of approximately 13-15GHz) compared to 25Gbaud NRZ devices by:
a. Reducing the oxide aperture to increase photon density.
b. Optimizing the design of the metal electrode to reduce parasitic parameters.
These improvements provide performance assurance for 400G service transmission.
VCSEL Structural Diagram
(Left) VCSEL Design for NRZ Application (Right) VCSEL Design for PAM4 Application
Multi-mode Lens PD Design
The 400G SR8 optical transceiver utilizes high-performance multi-mode PD detector with a typical bandwidth of 20GHz. The chip incorporates a lens design. The schematic diagram below illustrates the structure.
Compared to traditional surface-illuminated PDs, the lens PD exhibits focusing characteristics, resulting in stronger light reception and a 30% to 40% increase in coupling tolerance. This not only enhances the performance of the transceiver's receiving end but also reduces the precision requirements of the production process.
Schematic Diagram of Multimode Lens PD Structure
(Left) Traditional Surface-Illuminated PD (Right) Lens-Integrated PD
Chip-On-Board (COB) Packaging Design
The NADDOD 400G SR8 transceiver employs COB packaging for both the receiver and transmitter optical chips (VCSEL, PD) as well as the electrical chips (Driver, TIA). This design utilizes chip mounting and bonding processes to attach the chips onto the PCBA board.
COB packaging enables a more compact transceiver optical component design compared to other packaging forms. It also allows for automated production processes, offering advantages such as high performance and low cost.
Schematic Diagram of COB Design
Furthermore, NADDOD has conducted joint optimization of the optical and electrical systems from multiple dimensions, including structure and processes. This optimization has resulted in a 40% reduction in the size of the multi-channel lens, enabling a single-sided layout for the lens components at the receiver and transmitter ends. The transceiver length has been shortened by 9mm compared to the standard QSFP-DD Type 2, providing more space for fiber layout inside the cabinet and avoiding fiber top doors.
Other
In addition, the 400G SR8 optical transceiver also incorporates low-noise, high-performance TIA, high-bandwidth driver, and 7nm advanced process technology PAM4 oDSP chip. It possesses characteristics of low cost and high performance.
Conclusion
In summary, the application of the 400G SR8 optical transceiver will provide strong support for high-speed and high-density data transmission in data centers. As a leading provider of comprehensive optical network solutions, NADDOD is committed to building a connected and intelligent world with innovative computing and networking solutions.
Key technologies adopted by NADDOD, such as VCSEL lasers, multi-mode lens PD design, and COB packaging, enable the 400G SR8 optical transceiver to offer advantages such as high reliability, low power consumption, and high-speed transmission. We believe that in the near future, the 400G SR8 optical transceiver will be widely applied and promoted.
