The effect of nonideal optical hybrids on the performance of {2×2} and {3×3} CPFSK phase diversity homodyne receivers

The optical hybrid provides a means of recovering the modulated optical signal without phase locking. This analysis is performed for shot noise limited reception. Asymptotic methods are employed to give estimates of the bit-error-rate dependence for each type of receiver. The results show that, for zero laser linewidths, the effect on the {3×3} CPFSK phase diversity receiver sensitivity is much less than on the {2×2} one and that, for the latter, CPFSK modulation is a little more sensitive than differential phase-shift keying