Circuit for measurement of the signal quality in digital optical fiber transmission networks by interpreting the signal histogram

A circuit for identifying a bit error probability of an optical signal in an optical fiber communication system comprising:

• an analyzer for determining an optical signal-to-noise ratio of an optical message signal, said optical message signal having a signal power;
• a receiver supplied with said optical message signal for demodulating said optical message signal, said receiver including an optical filter having a bandwidth, a photodetector including a photodiode having a dark current and a sensitivity, and an amplifier having an equivalent spectral input noise current density, said receiver having an overall bandwidth and producing a demodulated signal with a plurality of amplitude values;
• a histogram calculator supplied with said demodulated signal for calculating a histogram representing respective frequencies of occurrence of said amplitude values of said demodulated signal, each of said amplitude values being allocated to a different random process and each random process having an average value, and said histogram calculator calculating a standard deviation for each random process from said optical signal-to-noise ratio, said signal power, said overall bandwidth of said receiver, said bandwidth of said optical filter, said dark current of said photodiode and said sensitivity of said photodiode;
• and
• a bit error probability calculator which calculates a probability, based on said average value and said standard deviation for each random process, of each random process crossing a predetermined threshold, and which calculates a bit error probability for said optical message signal as a sum of the respective probabilities for the random processes.