Configuration Scheme for Co-packaged Photonics QSFP28

A co-packaged photonics QSFP28 configuration integrates optical transceivers directly with switch ASICs, using PAM4 modulation, low-cost photodiodes, and optimized hardware/firmware for high-speed, low-latency data transmission.

Overview of Co-Packaged Photonics QSFP28

Co-packaged photonics (CoP) QSFP28 modules aim to reduce electrical interconnect losses by placing optical transceivers in close proximity to the switch ASIC. This approach improves signal integrity, power efficiency, and bandwidth density in data center environments . QSFP28 modules typically support 100Gbps per port, with variants for short-reach (SR), long-reach (LR), and extended-reach (ER/ZR) applications .

Key Components and Modulation

A typical configuration scheme includes:

• Electro-absorption modulated lasers (EMLs) or directly modulated lasers for high-speed optical signal generation .
• Transmitter Optical Sub-Assembly (TOSA) and Receiver Optical Sub-Assembly (ROSA) for coupling light into fibers and detecting incoming signals .
• Positive-Intrinsic-Negative (PIN) photodiodes for cost-effective detection, or Avalanche Photodiodes (APDs) for longer reach .
• PAM4 modulation to double the data rate per lane while maintaining signal integrity over distances up to 40 km for standard QSFP28 modules .
• Coherent optics (e.g., QPSK or DP-QPSK) for extended reach up to 300 km over DWDM networks .

Hardware and Firmware Design

The configuration scheme involves:

• ASIC interface integration: The optical module is co-packaged with the switch ASIC to minimize electrical trace length and reduce power consumption .
• Firmware control: Implements CMIS 5.2 management interface for monitoring module status, temperature, and optical power levels .
• Power management: QSFP28 modules operate typically at 5–6 W, with industrial temperature variants requiring careful thermal design .
• Error correction: ITU-T standard-compliant staircase FEC ensures reliable transmission over long distances .

Implementation Considerations

• Form factor: QSFP28 modules maintain a compact footprint compatible with SFF-8636 and IEEE 802.3 standards .
• Optical interface: LC or MPO connectors are used depending on single-mode or multi-mode fiber deployment .
• Testing and verification: Bit error rate (BER) testing ensures PAM4 signals meet long-reach requirements, typically up to 40 km with PIN-PD receivers .
• Scalability: Co-packaged photonics allows multiple QSFP28 modules to be integrated closely with high-density switch fabrics, supporting future 400G and beyond deployments .

Summary

A co-packaged photonics QSFP28 configuration combines high-speed optical components, PAM4 modulation, and integrated hardware/firmware design to achieve low-latency, high-bandwidth, and energy-efficient data transmission. By co-locating optical transceivers with switch ASICs, this scheme reduces electrical losses, simplifies thermal management, and supports scalable data center interconnects and metro networks .