Cause analysis
The possible causes of the fault are as follows:
- The networkwide dispersion topology is not optimal.
- The input optical power of the DCM is high. In this case, the non-linear effect is strong.
- The input/output optical power of the OA does not reach the rated input/output optical power.
Procedure
- Measure the input/output optical power of OAs at all sites and calculate the OSNR (value A). The value A complies with the OSNR obtained in a test of the network.
- Based on allocation of OAs on the network, calculate the networkwide OSNR by means of emulation. This OSNR value is considered as value B. The value B is 1.5 dB higher than the value A, and therefore the network still needs optimization.
- Check the input/output optical power of OAs on the entire network and ensure that the optical power is adjusted based on the rated value. Then, the optical-layer performance becomes optimal.
- Change the positions of the DCM and VOA, and ensure that the VOA is located before the DCM. Make sure that the input optical power of the DCM is sufficiently low.
- Keep the total dispersion unchanged and change the dispersion topology. In addition, monitor the system performance to ensure that the system performance is optimal.
- Change the attenuation of the VOA so as to make the input/output optical power of the OA as close as the rated input/output optical power.
- After networkwide reconstruction, services are available.
Reference Information
Conclusions and suggestions for this case are as follows:
- If a link is long, the dispersion topology and residual dispersion of each wavelength vary drastically. Therefore, accurately calculate residual dispersion of each wavelength to find out the optimal dispersion topology.
- It is recommended to insert the DCM into the TDC or RDC port of the OAU. If the insertion loss of the DCM is large and the DCM needs to be placed in the middle of a line, place the DCM before the VOA to ensure that the input optical power of the DCM is sufficiently low and satisfies the requirement for the input optical power of the DCM. The input optical power of a single wavelength needs to be lower than or equal to -3 dBm.
- Although the gain of the OA is adjustable, it is recommended to adopt the rated gain and rated input/output optical power of the OA as possible.
