Which optical modules require CDR

High-speed and long-distance optical modules, such as 10G SFP+ ER/ZR, 25G, 100G, 200G, 400G QSFP-DD, and 800G modules, typically require CDR to maintain signal integrity and reduce bit error rates.

Why CDR Is Needed

Clock and Data Recovery (CDR) is essential in optical modules to extract clock information from received signals and retime data, eliminating jitter and waveform distortion caused by fiber loss, dispersion, and noise interference.

CD

R performs re-amplification, reshaping, and retiming (3R regeneration), which is critical for long-haul and high-speed transmissions.

Without CD

R, high-speed signals may degrade, leading to increased bit error rates (BER) and unreliable communication. Optical Modules That Typically Include CDR10G SFP+ ER/ZR: Used for long-distance 10G Ethernet and optical transport networks, often supporting distances up to 80 km. 25G, 100G, 200G, 400G QSFP-DD and OSFP modules: High-speed data center interconnects and backbone networks rely on CDR to maintain signal quality over multi-lane PAM-4 or NRZ transmissions.

CFP2-DCO modules: Coherent optical modules for metro and long-haul applications include CDR and DSP-based retiming to handle complex signal processing and maintain low BER. 800G modules: Emerging high-bandwidth modules for hyperscale data centers and long-haul links also integrate CDR to ensure reliable performance.

Special Considerations

Some applications, such as ultra-low latency environments (e.g., high-frequency trading or AI clusters), may use CDR bypass to reduce latency to less than 5 ns. However, bypassed modules require high-quality optical signals and optimized laser performance since the signal is not retimed.

Summary

In general, any optical module operating at high data rates (≥10G) or over long distances will require CDR to ensure signal integrity. This includes SFP+, QSFP, QSFP-DD, OSFP, CFP2-DCO, and next-generation 400G–800G modules. Modules designed for short-reach, low-speed, or ultra-low latency applications may bypass CDR if the optical signal quality is sufficient.