Symptom
In network Q with many spans, only one wavelength is added in the system and the OSNR at the receive end is too low. Thus, services at the receive end cannot be provisioned.
As shown in Figure 1, the 40-channel system adds a wavelength and the service is transmitted from A to B.
Cause analysis
The possible causes of the fault are as follows:
- Insertion losses of line spans are high.
- Line commissioning fails.
In a system with few wavelengths, effects of noise should be considered. The best way is to make the single-wavelength optical power consistent with the nominal single-wavelength optical power by using an optical spectrum ***yzer.
Procedure
- The actual attenuation of multiple spans is higher than the design value. Decrease the span attenuation through the VOA adjustment before optical amplification.
- Query the optical power on the link. It is found that the total output optical power is consistent with the typical nominal single-wavelength optical power. Effects of the accumulative noise power of multiple levels of OAs are not taken into consideration. In the current system with one wavelength added, the accumulative noise is obvious and the testing result of the optical power meter is inaccurate. It is suggested that field engineers commission the optical power according to the testing result of the optical spectrum ***yzer.
