When we browse the web at home when the broadband network speed is not stable, watching video suddenly lag, the game is playing when the excitement suddenly disconnected and other phenomena occur, it is likely that the home optical cat ONU weak light!

What is called optical cat ONU weak light?ONU is what we commonly known as optical cat equipment, used to convert optical signals on the optical fiber into electrical signals, when the optical cat's received optical power strength is less than the minimum sensitivity of optical cat reception, the optical cat is weak light.ONU reception sensitivity refers to the minimum optical power that can be received when the ONU works normally, usually, the home wide ONU reception sensitivity indicator is -27.0dBm Although from 2018, the relevant standards in the ONU reception sensitivity indicator has been raised to -28.0dBm, but because most of the ONU in the current network are products before 2018, so, generally the ONU received optical power below -27.0dBm is defined as ONU weak light. When the optical cat ONU weak light when our home broadband Internet user experience will be affected, such as reduced network speed, network delays and even occasional disconnections.

The current ONU weak light phenomenon is very common, and the weak light rate of ONU (the percentage of ONU with received optical power lower than -27.0dBm) in some provinces is even more than 4.5%. Such a high rate of weak light will certainly have a negative impact on the user's Internet experience.

There are many factors that affect the user's Internet experience, and ONU low light mainly affects the network speed. In order to understand the impact of ONU low light on user's Internet speed, we can test it by the following model.

In the figure, between the incoming skin cable and the ONU, a patch fiber is connected in series with an adjustable attenuator and a PON optical power meter, so that the received optical power of the ONU can be measured online with a PON optical power meter (the difference between the tested downlink optical power and the received optical power of the ONU is the attenuation of one patch fiber, which is about 0.3 dB).

The actual test site looks like this.

By adjusting the attenuation of the adjustable attenuator, the attenuation of the ODN link can be increased, causing a change in the received optical power of the ONU. The change in network speed is then tested by connecting the ONU with a network cable through a laptop. The results of the test with this method for 300M broadband are shown in the table below.

The "ONU receive light (dBm)" in the table above is actually the test results of the PON optical power meter. From the test results can be seen, ONU optical power is higher than -27.98dBm can still work normally. When the optical power is lower than -27.98dBm, the downlink network speed with the reduction of the optical power to reduce the rapid decline, and in a certain range of optical power to maintain a very low network speed until the network is completely disrupted.

You may have noticed that the difference between the uplink and downlink Internet speeds is due to the carrier's uplink speed limit for home broadband.

However, the uplink network speed is basically unaffected by the weak light of the ONU, which only passively emits light when it receives the downlink optical signal, and the network uplink is interrupted when the ONU fails to receive the downlink optical signal.

With the gradual coverage of 10G PON network, there will be two downlink signal wavelengths 1490nm (for 100M/200M/300M broadband rate home users) and 1577nm (for 500M/1000M broadband rate home users) on the fiber of fiber to the home network, the value measured by traditional power meter is the sum of these two signal powers, so to accurately measure 1490nm signal power and 1577nm signal power, you need to use 10G PON's split-wave power meter to measure in order to avoid the missed judgment of weak light users.