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Whether the nominal gain should be reset after the change of the DCM type in the OAU1 in the OptiX OSN 6800

Publication Date:  2012-07-25 Views:  44 Downloads:  0
Issue Description
In the OptiX OSN 6800 40 wavelength project, the TN11OAU101 (the gain ranges from 20 dB to 31 dB and the single wavelength standard output optical power is +4 dBm) is used.
In the earlier stage, the DCM is not configured between the TDC and RDC in the OAU1. In the T2000, the nominal gain is set to 20 dB. The single wavelength input optical power is -16 dBm and the output optical power is +4 dBm.
To solve the dispersion problem in the later stage, the DCM (B) is added between the TDC and RDC in the QAU1 to compensate the 40-km dispersion with 5 dB insertion loss. At this time, the customer does now know whether to set the nominal gain of the OAU1 in the T2000 to keep the output optical power +4 dBm unchanged, or whether the OAU1 automatically adjusts the gain to keep the output power of the single wavelength as +4 dBm. 
Alarm Information
Handling Process
Before the replacement, engineers should check whether the DCM insertion loss meets the requirements.
The allowed DCM insertion loss = OAU1 gain � nominal gain (the value configured in the T2000)
The insertion loss between the TDC optical interface and the RDC optical interface is too large, which exceeds the adjustment range of the OAU1. The OAU1 reports the minor alarm VOA_ADJUST_FAIL. At this time, engineers should check whether the insertion loss of the optical fiber is too large. As a result, the fiber is normal.
If the problem is solved, engineers need not set the nominal gain in the T2000 again. The OAU1 adopts the automatic gain control (AGC) mode. The OAU1 monitors the input and output optical power in real time to keep the gain (the difference between the output and input optical power) to be the same as the nominal gain configured in the T2000. The single wavelength input and output optical power of the OAU1 board is -16 dBm/+4 dBm and the nominal gain remains unchanged (20 dB), regardless of whether the TDC and RDC optical interfaces are short-circuited through a fiber or the access of the DCM (B). 
Root Cause