Symptom
In a certain 40G WDM project, the NE of the OptiX BWS 1600G equipment is of version 5.8.7.12. An end-to-end chain network is formed as A-B-C-D-E. In the network, A and E are OTM stations using TMX40S boards, B and D are OLA stations, C is an OEQ station using DEG boards. Two wavelengths of services are configured in the system, that is, 196.0 THz and 195.9 THz.
After the configuration of system optical power, monitor the performance of the OTU boards at station A and station E for a long time by using the NMS. The monitoring result shows that the received optical power on the two OTU boards at station A vary with time by 3 dB to 4 dB. Sometimes, the received optical power on one OTU board becomes higher while that of the other OTU board becomes lower. According to a further check, the total optical power of the multiplexed wavelength detected by each amplifier board along the service route from station E to station A (included) varies by not more than 0.5 dB, when the received optical power of the OTU board changes abnormally. This variation range is normal.
Cause analysis
The possible causes of the preceding problem are as follows:
- A change of system optical power is usually caused by improper connection, contamination, or press of line fibers. An improper fiber connection results in only abnormal line attenuation, which does not vary sharply with time.
- As aforementioned, the variations of the received power on the two OTU boards are equal and the optical power varies reversely (optical power on one OTU increases and that on the other decreases). This shows that a fiber connector on the line may be contaminated and the contamination results in excessive PDL. Due to the PDL, the received optical power varies with the polarization states of wavelengths in the system.
- It is less likely to occur that a contaminated fiber connector results in degrade of PDL. Thus, it is probable that the contamination article features excessive PDL.
Procedure
- Replace the DGE board at station C with a flange and remain the configuration unchanged. In this case, the detected optical power of the wavelengths varies by less than 0.2 dB, but the received optical power of the OTU board at station A varies by more than 3 dB. Thus, the problem is not caused by the DGE board.
- Check the OLA stations from station C to station A by using a spectrum ***yzer according to the binary search algorithm. According to the check result, other stations are not faulty and the cause of the problem is focused lies in station A.
- It is suspected that certain boards (such as VA4 boards, OAU boards, D40 boards) are faulty. Replace the boards. This possibility is excluded after checks based on board replacement and scanning on the spectrum ***yzer. In addition, the spectrum ***yzer shows that the optical power of the two wavelengths at the IN interface on the FIU board varies by more than 4 dB.
- Clean the line fibers and connectors of fiber jumpers on the ODF. After that, the insertion loss is reduced by 4.2 dB and the variation of the received optical power on the OTU boards is reduced to 0.5 dB. This power variation range is normal. In this case, the problem is resolved.
