Average output optical power of optical transmitter

The output optical power of an optical transmitter should be within the range that ensures the receiver receives sufficient signal without exceeding its maximum input, typically measured in dBm and adjusted according to link loss and transceiver specifications.

Definition and Importance

The output optical power refers to the average optical power emitted by the transmitter at the sending end of the optical transceiver, usually expressed in dBm, mW, or W. It is a critical parameter because it directly affects the transmission distance, signal quality, and lifetime of the optical module. If the output power is too low, the receiver may not detect the signal, leading to link failure.

If it is too high, it can overload the receiver, degrade signal quality, and reduce transceiver lifespan.

Typical Ranges

The normal output power range depends on the type of optical transceiver and fiber used. For example, small form-factor pluggable (SFP) modules often have output powers ranging from -13 dBm to +1 dBm, while higher-speed modules like QSFP28 may have slightly different ranges. The output should always be within the receiver's input sensitivity range to maintain a reliable link.

Measurement and Monitoring

Output power can be measured using: Digital Diagnostics Monitoring (DDM/DOM) on the transceiver, which provides real-time optical power readings. Optical power meters, calibrated to the transmitter wavelength, connected via reference cables or patch cords. Eye diagram analysis, which evaluates emitted optical power along with signal quality metrics like extinction ratio and rise/fall times.

Practical Considerations

Power Budget: Ensure the difference between transmitter power and receiver sensitivity exceeds total link loss (fiber + connectors). Attenuation: If the fiber has lower loss than expected, use attenuators to prevent receiver overload. Bias Current Adjustment: For high-speed transceivers, adjusting the bias current can help maintain output power within the optimal range.

Maintaining the output optical power within the recommended range ensures reliable data transmission, minimal bit errors, and optimal transceiver performance.