Here I have attached an .osd file of an implementation of a bidirectional system which makes use of coherent QAM both in downstream and upstream. When the downstream signal passes through the channel, it is splitted to two branches, with one going to the downstream receiver and the other to upstream transmitter, to be used as an optical source instead of the laser (which is the whole point of using remodulation technique, BTW). The problem is, though, that there is no upstream signal after the bidirectional fiber, as it can be seen by ‘Optical Spectrum Analyzer_2’. What is the problem?
The system error is not important for me here. I just want to have the signal. Thank you in advance!