How much light does a 40km optical module receive

For a 40km single-mode optical module, the typical receiver sensitivity is around -18 dBm, with a maximum safe receive power of approximately -3 to -2. 3 dBm.

Receiver Sensitivity and Thresholds

A 40km optical module, such as a 40GBASE-ER4 QSFP+, is designed for long-reach single-mode fiber transmission. The receiver sensitivity (minimum optical power required for error-free operation) is typically around -18 dBm, while the maximum safe receive power is usually -3 dBm to -2. 3 dBm to prevent damage to the photodiode or avalanche photodiode (APD) in the module.

This defines the dynamic range of the module, which is the difference between the maximum and minimum acceptable optical power, often around 20 dB for 40km modules.

Practical Considerations

Overload Protection: If the received optical power exceeds the maximum threshold, it can permanently damage the receiver, reduce sensitivity, or increase bit error rates.

Short-

Distance Connections: When connecting a 40km module over a short fiber (e.g., 10km), the received power may exceed the safe limit. In such cases, an optical attenuator is recommended, typically ≥10 dB, to reduce the power to a safe level. Monitoring: Use an optical power meter to measure the received power before connecting the module.

Ensure the R

X power is below the maximum threshold (e.g., less than -4 dBm for long-term stability) to avoid damage. Summary of Typical Values for 40km ModulesParameterTypical ValueReceiver Sensitivity-18 dBmMaximum Receive Power-3 to -2. 3 dBmDynamic Range~20 dBRecommended Attenuator for Short Links≥10 dBBy maintaining the received optical power within this range, a 40km optical module can operate reliably, ensuring stable high-speed data transmission over long distances without risking damage to the receiver components.