Abstract:Time-resolved optical filtering (TROF) measures the spectrogram or sonogram by a fast photodiode followed a tunable narrowband optical filter. For periodic signal and to match the sonogram, numerical TROF algorithm is used to find the original complex electric field or equivalently both the amplitude and phase. For phase-modulated optical signals, the TROF algorithm is initiated using the craters and ridges of the sonogram.

The variance of nonlinear phase noise is analyzed by including the effect of intrachannel cross-phase modulation (IXPM)-induced nonlinear phase noise. Consistent with Ho and Wang 1 but in contrary to the conclusion of both Kumar 2 and Green et al. 3 , the variance of nonlinear phase noise does not decrease much with the increase of chromatic dispersion. The results are consistent with a careful reexamination of both Kumar 2 and Green et al. 3 .c 2017 Optical Society of America OCIS codes: 060.2330OCIS codes: 060. , 190.4370, 190.4380, 260.2030 Keywords: nonlinear phase noise, intrachannel cross-phase modulation.Recently, phase-modulated optical communication systems are found to have wide applications in long-haul lightwave transmission systems 4,5 . Added directly to the signal phase, nonlinear phase noise is the major degradation for phase-modulation signals 1 . However, the recent paper by Kumar 2 and early paper by Green et al. 3 shown that, in contrary to Ho and Wang 1 , nonlinear phase noise becomes much smaller for highly dispersive transmission system than that for a system with no dispersion. The main purpose of this paper is to reconcile the discrepancy among those three letters (9) When white Gaussian noise with infinite bandwidth is assumed, the noise power approaches infinity. A finite signal-to-noise ratio requires some types of optical filter and an optical matched filter has the smallest bandwidth and does not distort the signal. Optical matched filter is used in some experimental measurements to improve the receiver sensitivity 8,9 .To make a direct comparison with Refs. 2,6, we consider a transmission system consisting of two segments of equal length within an amplified fiber span. The dispersion of the first segment is anomalous whereas that of the second segment is equal in magnitude but opposite in sign. Within each fiber span, the accumulated dispersion as a function of distance is given by S(z) = β 2 min(z, L − z) where β 2 is the group-velocity

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