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How much light does the optical module normally emit

Optical network knowledge brief Published 30 Dec 2022

Prepared for preliminary research by the COETZER OPTICAL knowledge desk. Confirm compatibility, loss budgets and installation requirements against current standards and product documentation.

The normal light emitted by an optical module is defined by its average optical power, typically measured in dBm, mW, or W, and depends on the data signal and module specifications.Average Optical Power

The average optical power represents the intensity of light emitted by the optical module's transmitter under normal working conditions. It is measured when the module sends a pseudo-random sequence of data, where the number of "1"s and "0"s is roughly equal, providing a representative average output. This power is usually expressed in dBm, mW, or W, with dBm being the most common logarithmic unit in communications systems . The actual value depends on the module type, transmission rate, and wavelength, with typical values ranging from -8 dBm to +3 dBm for standard short-range modules, though high-power modules may exceed this range.

Extinction Ratio

The extinction ratio is the ratio of the optical power when transmitting all "1"s to the power when transmitting all "0"s. It indicates the module's ability to distinguish between logical "1" and "0" signals. A typical minimum extinction ratio is 8.2 dB to 10 dB, ensuring reliable signal detection .

Overload Optical Power

The overload or saturated optical power is the maximum optical power the receiver can safely handle without causing errors or damage. Exceeding this power can saturate the photodetector, reduce receiver sensitivity, and lead to bit errors. Users should avoid exposing the module to light above this threshold .

Receiver Sensitivity

The receiver sensitivity defines the minimum optical power the module can detect while maintaining a low bit error rate (BER, typically 10^-12). Normal operation requires the transmitted optical power to be above this sensitivity level to ensure reliable communication .

Practical Considerations
  • The emitted light varies with the proportion of "1"s in the data signal; more "1"s result in higher optical power .
  • Environmental factors, such as temperature, can affect the module's output power and stability .
  • For DLP or projection-based optical modules, brightness is also measured in lumens, reflecting the visible light output, which depends on the white point and optical efficiency . In summary, an optical module should emit light at its specified average optical power, sufficient to exceed receiver sensitivity but below the overload limit, with a proper extinction ratio to ensure signal integrity.

How much light does the optical module normally emit - COETZER OPTICAL SYSTEMS (Pty) Ltd [PDF]

How much light does the optical module normally emit

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This reference is intended for preliminary optical-network research. Compatibility, link budgets, installation methods, test limits and applicable standards must be verified for the specific project.

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