Symptom
In the OptiX OSN 6800 project with 40 wavelengths, the TN11OAU101 (the gain ranges from 20 dB to 31 dB and the standard single-wavelength output optical power is +4 dBm) is used.
In initial phase of the project, the DCM module is not configured between the TDC optical interface and the RDC optical interface on the TN11OAU101. On the T2000, the nominal gain of the TN11OAU101 is set to 20 dB, and the input and output optical power of a single wavelength are set to -16 dBm and +4 dBm respectively.
In the later phase, the DCM module (type B) is configured between the TDC optical interface and the RDC optical interface on the TN11OAU101 to compensate for the 40-km dispersion. The insertion loss of the DCM module is 5 dB. After the DCM module is configured, it is required to determine whether the nominal gain of the TN11OAU101 need to be reset on the T2000 to ensure that the output optical power of a single wavelength remains at +4 dBm, or whether the TN11OAU101 is able to automatically adjust the gain to keep the output optical power of a single wavelength unchanged.
Cause analysis
The TN11OAU1 series support automatic gain control. The TN11OAU101 monitors the input and output optical power in real time to ensure that the gain (the difference between the output and input optical power) is consistent with the nominal gain as set on the T2000.
The single-wavelength input or output optical power of the TN11OAU101 is always -16 dBm or +4 dBm and the nominal gain remains unchanged (20 dB), regardless of whether the TDC optical interface and RDC optical interface are short-circuited by using a fiber or the DCM module (type B) is configured between the two optical interfaces.
Procedure
1. Check whether the insertion loss between the TDC and RDC optical interfaces is normal before the DCM is replaced with another DCM. The permitted maximum insertion loss between the TDC and RDC optical interfaces = Maximum gain of TN11OAU101 (31 dB) - Nominal gain (set on the T2000).
A. In the NE Explorer, select the OAU board and then choose Configuration > WDM Interface from the Function Tree.
B. On the right of the user interface, select By Board/Port (Channel).
C. On the Basic Attributes tab page, click Query to query the nominal gain of the OAU board in the Nominal Gain(dB) field.
2. If the insertion loss between the TDC and the RDC optical interfaces is very high, that is, if the insertion loss exceeds the adjustment range of the TN11OAU101, the TN11OAU101 reports the VOA_ADJUST_FAIL. In this case, check whether the fiber insertion loss is very high and whether the TDC and RDC optical interfaces on the TN11OAU101 are clean.
Result
In the case of the TN11OAU1, after the DCM is replaced with the DCM of a different type, you do not need to reset the nominal gain.
