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Abnormal FIU insertion loss due to wrong test methods

Publication Date:  2012-07-25 Views:  41 Downloads:  0
Issue Description
The OptiX OSN 6800 is used to build the Metro WDM system. In the commissioning phase, the insertion loss from the IN interface to the TC interface of the FIU board in the entire network is 4 dB. According to the FIU board description, the theoretic insertion loss is less than 1.5 dB. Hence, the practical value is inconsistent with the theoretic value. The board may be faulty. 
Alarm Information
None. 
Handling Process
Engineers should remove the tail fiber at the RM interface of the FIU at the transmit end so that only the signal light is emitted from the FIU. The difference of the optical power tested between the IN interface of the FIU at the receive end and the TC interface is 1 dB. The value meets the requirement. 
Root Cause
1. The same fault occurs in all FIU boards. All boards are seldom faulty at the same time. Usually, the fault does not result from the board.
2. Possible causes are as follows:
The test method used by the engineering supervisor is incorrect.
The insertion loss description in the document is incorrect.
3. According to relevant documents, the insertion loss is smaller than 1.5 dB. The OptiX OSN 6800 is available in another city and the same problem is not fed back. According to the engineering supervisor, the insertion loss in the test is about 1 dB. Hence, the description in the document is correct.
4. On-site test method: After the test of the receive optical power in the IN interface of the FIU, the difference of the transmit optical power tested at the TC interface is 4 dB. The optical power of the IN interface of the FIU board is from the FIU at the opposite station.
5. Engineers query the FIU configuration at the transmit end site. The RM interface of the FIU board is accessed with the supervisory channel light, that is, the optical power signal tested at the IN interface of the FIU board at the receive end is the combination of the signal light and supervisory channel light. At the TC interface of the FIU board, only the strength of the signal light can be tested, without the supervisory channel light. The error of the optical power tested at the TC interface is quite different from the optical power tested at the IN interface. 
 
Suggestions
Engineers should familiar with the signal flow in handling the fault of the OptiX DWDM product equipment. 

END