About Optical Module Optical Power Parameters

In the purchase of SFP+ optical modules believe that many customers have noticed the TX/RX optical power parameters, these two parameters are one of the important parameters to ensure the normal communication of optical modules. Among them, TX refers to the transmitting optical power, RX refers to the receiving optical power. So how much do you know about transmitting optical power and receiving optical power? What are the normal range values of both? And how to test the optical power of the optical module in the normal range? You will find the answer after reading this article.

What is the transmit/receive optical power? What is its normal range value?

Transmit optical power refers to the output optical power of the light source at the transmitting end of the optical module, and receive optical power refers to the input optical power of the light source at the receiving end of the optical module, both are in dBm, and both are one of the important parameters that affect the signal transmission distance. Usually, only when the transmit optical power and receive optical power of the optical module is within the upper and lower threshold values, to ensure its good transmission performance. However, different wavelengths, distances and rates of optical modules have different transmit optical power and receive optical power. For example, 500 meters SFP1G-SX-85 optical module (center wavelength of 850nm) transmit optical power in -9.5dBm ~ -2.5dBm, the received optical power of -17dBm ~ 0dBm; 10 km SFP1G-SX-31 optical module (center wavelength of 1310nm) transmit optical power in -9.5dBm ~ -3dBm, the received optical power is -20dBm~-3.0dBm.

How to test the transmit/receive optical power?

Optical module to have good transmission performance, its transmit optical power and receive optical power must be within the normal range of values, so how to test the optical module's transmit optical power and receive optical power is within the normal range of values?

Generally speaking, customers can directly monitor whether the transmit optical power and receive optical power of the optical module are normal through the DDM function (digital diagnostic monitoring function) of the optical module. However, if the DDM information of the optical module is abnormal or the function is not supported, we suggest you troubleshoot the optical module first and then solve its fault problem to get the values of the transmit optical power and receive optical power of the optical module.

In addition, you can also use an optical power meter to obtain the transmit optical power value of the optical module. Take the 10GBASE-LR SFP+ optical module as an example, the test steps are as follows.

First, insert the 10GBASE-LR SFP+ optical module into the SFP+ port of the 10G switch.

Then, connect the optical module to the optical power meter using an LC-FC fibre patch cable.

Finally, press the key to turn on the optical power, press "λ" to modulate the band of the 10GBASE-LR SFP+ optical module (that is, modulate the band to 1310nm), the value may change during the test, and the test is completed when the value is stationary, at this time, the optical power displayed on the screen is the optical power of the optical module. The optical power displayed on the screen is the emitted optical power of the module. Note: The transmitted optical power from the short distance test is equivalent to the received optical power at the opposite end.