Very late reply so you might not see it. Modern systems use coherent (phase&amplitude and polarisation, typically QAM formats), together with relatively high ov

Very late reply so you might not see it. Modern systems use coherent (phase&amplitude and polarisation, typically QAM formats), together with relatively high overhead (~20%) FEC. The consequence is that for demonstration experiments you do offline processing, which significantly constrains how many bits you can measure (good experiments measure a few million per measurement point). So what people do is measure to the FEC threshold (10e-2) and assume the FEC works (usually a valid assumption). Sometimes people implement the FEC and show error free operation to 10e-6 or so. Also we use Generalized Mutual Information as a more accurate measure of the information content (it essentially measures how much information can be transmitted given a bitwise coding FEC). In other experiments people show FEC implementations running on banks of FPGAs to show that we actually get down to BER 10e-12, but these take weeks on large number of high end FPGAs.