If the light receiving power is too low, it needs to be dealt with, and if it is too high, it needs to be dealt with as well. The optical module receiver has an overload point. If it is operated at the upper limit for a long time, it will cause bit errors and packet loss. In severe cases, the port will be disconnected repeatedly. At this time, what should be added to the link is a fixed optical attenuator instead of replacing a more expensive module.

First distinguish two boundaries: sensitivity and overload point

In the manual, the receiving sensitivity determines how much the weakest signal can be received, and the overload point determines how much the strongest signal cannot be exceeded. Taking the common Gigabit single-mode 10KM range as an example, the sensitivity is about -20dBm and the overload point is about -3dBm. The light collection should fall between these two points, leaving about 3dB margin at both ends. If the DDM reading is higher than -5dBm for a long time, you should be wary of strong light reception. It is recommended to copy these two limits into the link ledger and compare them directly for subsequent maintenance without having to read the manual every time.

Typical overload scenario: short distance with long distance module

The link in the computer room renovation is actually only 1 to 2 kilometers long, but the 40KM module is still used: the luminous power is high, the line attenuation is small, and the receiving end is directly above the overload point. Forcibly adding loss by bending the optical fiber will damage the optical fiber and make it unstable. The standard method is to insert a fixed attenuator in series to push the light collection back to the middle of the range. When the test instrument is directly connected to the interface with a high-power light source, attenuation should also be added first and then measured. If the DDM of a newly cut-over link displays the top bar of light but does not report an alarm for a long time, it is often a signal that the light intensity is too strong.

Three steps after confirming overload: actual measurement, value selection, and retesting

First use an optical power meter to measure at the receiving end, and compare the overload point in the module manual to calculate the number of dB that needs to be suppressed; then use the nearest higher level to get the standard value, which can be comparedSFP+ 10G single-mode dual-fiber 10km optical moduleCheck the receiving interval of this type of model; re-measure the received optical power after serialization, and observe the 24-hour bit error and DDM curves. The processing is completed only when the reading falls back to the middle of the interval, and the results are recorded in the link ledger. If you are unsure about the parameter range, you can report the module model to EB-LINK technical support for assistance in querying the overload point, call 0755-83179002.