Emitting power of the optical module

The emitting optical power of an optical module is the average optical power output by its transmitter, typically measured in watts (W), milliwatts (mW), or decibels-milliwatts (dBm).

Definition and Measurement

The emitting optical power refers to the optical power generated by the transmitter of an optical module, such as a laser diode or LED, under normal operating conditions. It represents the intensity of light emitted to transmit data over fiber-optic networks. The measured power depends on the proportion of "1"s in the transmitted data signal; when sending a pseudo-random sequence with roughly equal "1"s and "0"s, the measured value is considered the average transmit power ( ). Units commonly used include:

• Watts (W) or milliwatts (mW) for linear measurement
• dBm for logarithmic measurement, which is standard in optical communications ( ).

Key Parameters

1. Average Transmit Power: The typical optical power output under normal conditions, reflecting the luminous intensity of the transmitter ( ).
2. Extinction Ratio: The ratio of optical power when transmitting a "1" versus a "0", indicating the laser's ability to distinguish signal levels ( ).
3. Overload Optical Power: The maximum optical power the receiver can handle without errors or damage, measured in dBm ( ).
4. Receiver Sensitivity: The minimum optical power required for the receiver to detect signals reliably, also in dBm ( ).

Factors Affecting Emitting Power

• Laser Type: VCSELs (vertical-cavity surface-emitting lasers) are used for short-distance, high-speed applications, while DFB (distributed-feedback) lasers are preferred for medium- and long-distance transmissions due to higher output power and stability ( ).
• Modulation Current: In directly modulated lasers, the current controls the output intensity, affecting the emitted optical power ( ).
• Automatic Power Control (APC): Many optical modules include APC circuits to maintain consistent output power despite temperature or voltage variations ( ).

Practical Considerations

• The average transmit power is critical for ensuring sufficient signal strength over the fiber link without exceeding the receiver's overload limit.
• Proper optical power management prevents bit errors and ensures reliable communication in high-speed networks ( ). In summary, the emitting optical power of an optical module is a fundamental parameter that determines the module's ability to transmit data effectively over fiber-optic networks, influenced by laser type, modulation, and control circuits.