Symptom
In a OptiX OSN 6800 40-channel project, the TN11OAU101 (gain ranges from 20 dB to 31 dB and the per-channel standard output optical power is +4 dBm) is used. In the initial stage, no DCM is configured between optical interface TDC and RDC of the OAU1. The nominal gain of the OAU1 is set to 20 dB on the T2000 and the per-channel input/output optical power is -16 dBm/+4 dBm. In later stages, a DCM(B) (it compensates for 40 km dispersion and the insertion loss is 5 dB) is added between TDC and RDC of the OAU1 because of dispersion issues. In this case, engineers are wondering if the nominal gain of the OAU1 should be re-set on the T2000, so that the per-channel output optical power of the board remains +4 dBm? Or the OAU1 adjusts the gain automatically to ensure that the per-channel output optical power remains +4 dBm?
Cause analysis
None.
Procedure
1. Check if the DCM insertion loss meets the requirement before replacing the DCM.
2. Allowable DCM insertion loss = Gain of the OAU1 - Nominal gain (the setting on the T2000) If the insertion loss between TDC and RDC is very large and exceeds the adjustment range of the OAU1, the OAU1 reports the VOA_ADJUST_FAIL, which is a minor alarm. In this case, check if the fiber insertion loss is very large. If it is very large, remove the fiber faults.
3. If the DCM insertion loss meets the requirements and the fiber faults are removed, engineers do not need to re-set the nominal gain on the T2000. The OAU1 adopts the automatic gain control (AGC) mode. The OAU1 monitors the output and input optical power in real time, so that the gain (the difference between the input and output optical power) of the OAU1 keeps the same as the value set on the T2000. Whether TDC and RDC interfaces are connected directly through a fiber jumper or a DCM is added between them, the per-channel input/output optical power is always -16 dBm/+4 dBm and the gain remains 20 dB.
