I am working to produce mm-wave signal with data rate of 7Gb/s and fiber lenght 40km by using two uncorrelated lasers(hetrodying),it is working fine with the few main parameters specifications: lasers power =8dBm and linewidth less than 1MHz-5MHz and MZM extinction ratio=30.At receiver,detection of mm-wave signal is also ok.When i calculate the receiver sensitivity(input power to photo-detector(PD)) against BER.I have observed unusual results (without fiber(B2B) and 40Km fiber length),for example,logically BER of 1*e-9 should achieve over B2B connection on less input power compare with 40km lenght,but my case is totally reverse(note:-around 1dBm difference between B2B and 40km length).In simple words,system performance over 40km is showed better than B2B!!!
looking forward for constructive discussion and specially Mohamed A. A. Abouseif comments.
Regards,
Muhammad Saqlain
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