Emitting values ​​of optical modules

The emitting values of optical modules are primarily characterized by the average transmitted optical power and the extinction ratio, which define the intensity and quality of the emitted optical signal.Transmitting Optical Sub-Assembly (TOSA)

The TOSA is the component responsible for light emission in an optical module. It converts electrical signals into optical signals using a laser diode (LD) or a light-emitting diode (LED). Laser diodes are preferred in most modern modules due to their higher output power, lower energy consumption, and better coupling efficiency, while LEDs are used for low-rate, short-distance applications because of their lower cost and longer lifespan. The TOSA also includes an automatic optical power control (APC) circuit to maintain stable output power during operation .

Key Emission Parameters

1. Average Transmitted Optical Power This represents the optical power output by the module under normal working conditions and is measured in mW, W, or dBm. The transmitted power depends on the proportion of “1”s in the data signal; more “1”s result in higher optical power. It is a critical factor affecting the transmission distance and overall link performance .
2. Extinction Ratio The extinction ratio measures the ability of the laser to distinguish between logical “1” and “0” signals. It is defined as the ratio of the average optical power when transmitting all “1”s to the average power when transmitting all “0”s, expressed in dB. A higher extinction ratio indicates better signal clarity and operational efficiency, but it must meet standard requirements (e.g., IEEE 802.3) rather than being maximized indiscriminately .
3. Central Wavelength The wavelength of the emitted light is another important parameter, as it affects fiber attenuation and compatibility with other network components. Typical modules operate at standard wavelengths such as 850 nm, 1310 nm, or 1550 nm depending on the application.

Measurement Methods

The emitted optical power can be measured using several techniques:

• Digital Diagnostic Monitoring (DDM) via network switches
• Optical power meters or spectrometers
• Eye diagram tests to evaluate signal quality and modulation performance These measurements ensure that the optical module operates within safe and effective ranges, avoiding excessive bit error rates or signal degradation .

Practical Considerations

• Maintaining stable optical power is crucial for reliable communication.
• Excessive power can saturate receivers, while insufficient power may cause signal loss.
• The APC circuit in TOSA helps maintain consistent emission despite temperature or voltage variations.
• Extinction ratio and average power together determine the signal integrity over the fiber link. In summary, the emitting values of optical modules are defined by the average transmitted optical power, extinction ratio, and wavelength, all of which are carefully controlled and monitored to ensure efficient and reliable optical communication .