A 100G optical module uses four light receivers because it splits the 100 Gbps data rate into four parallel 25 Gbps channels, each detected independently to achieve the total 100 Gbps throughput.

Parallel Channel Design

100G optical modules, such as QSFP28, often implement a 4x25 Gbps architecture, meaning the total 100 Gbps data stream is divided into four separate channels. Each channel has its own transmitter and receiver, allowing the module to handle high-speed data efficiently without requiring a single extremely fast laser or photodetector . This design reduces complexity, power consumption, and cost compared to a single-lambda 100 Gbps solution.

Types of 100G Modules Using Four Receivers

• 100GBASE-SR4: Uses four independent transmit and receive channels over multimode fiber, each at 25 Gbps, typically for short-reach data center links .
• 100GBASE-PSM4: Uses four single-mode fibers for transmit and four for receive, each at 25 Gbps, supporting distances up to 500 meters in data centers .
• 100GBASE-CWDM4 / LR4: Uses wavelength division multiplexing to combine four 25 Gbps channels onto a single fiber pair, with each channel at a distinct wavelength, reducing fiber count while maintaining 100 Gbps throughput .

Advantages of Four Receivers

1. Signal Integrity: Lower per-channel speed (25 Gbps) reduces signal degradation and allows simpler photodetector design.
2. Scalability: Modules can be upgraded to higher speeds (e.g., 400G uses 4x100G channels) using the same multi-lane principle .
3. Cost Efficiency: Multi-lane modules are cheaper to manufacture and easier to integrate into existing fiber infrastructure.
4. Flexibility: Supports both short-reach multimode and longer-reach single-mode applications depending on the module type . In summary, four light receivers in a 100G optical module enable parallel detection of four 25 Gbps channels, balancing high-speed performance, cost, and reliability across different network distances and fiber types. This multi-lane approach is a standard design choice in modern data center and metro optical networks.