Intensity distortion induced by cross-phase modulation and chromatic dispersion in optical-fiber transmissions with dispersion compensation

Abstract

Abstract-In dispersion compensated systems, the intensity distortion induced by the interplay between cross-phase modulation and fiber chromatic dispersion can be a primary cause of transmission degradation. This interplay is mostly studied by time-consuming computer simulations. This letter introduces a new model of this interplay in fiber transmissions with dispersion compensation, leading to a linear filter that, applied to the input intensity of a modulated interfering channel, gives the intensity distortion of a continuous-wave probe signal at the receiver. The model can be of significant value in the search for optimized dispersion maps.

Degree of polarization degradation due to cross-phase modulation and its impact on polarization-mode dispersion compensators

“…The small discrepancies around the values of minimum DOP can be attributed mostly to the assumption of a -independent pivot of the carousel model (there was a walk-off of 6.4 b over the entire link) and in minor part to the fact that also the probe is modulated. In the periodic pump case, (14) gives a less accurate approximation of the simulated curves. We verified that this is due to the GVD distorting effect on the pump bits, which were neglected in our calculations.…”

“…Since in (17) is real, it coincides with , and thus . Hence again the DOP formula is given by (14). A useful and tight lower bound is found by setting in the integrand in (17) (18) from which it is clear that very similar considerations about the effect of system parameters as in (13) apply.…”

“…Now using (13) in (9) gives (14) where the dependence of the DOP on the relative pump-probe polarization angle is implicit in and . From (14) and (13) we can conclude that, if polarization control of the signals ( or cannot be achieved, e.g., due to PMD, the basic countermeasure against DOP degradation is to increase the bit walk-off by further spacing the channels or by using a more dispersive fiber, so as to reduce the argument of the Bessel function. Clearly, also increasing the bit rate implies a reduction of XPM-induced DOP degradation.…”

“…3, we compared the analytical DOP curves obtained by (14) (solid line) to those evaluated with the Manakov equation through the BPM (dashed line with crosses) when both channels are modulated with NRZ supporting pulses at 10 Gb/s, with no power on zeros . The system consisted of three perfectly compensated links of TeraLight fiber ( 0.2 dB/km, 1.68W/km, and 8 ps/nm/km) of 100 km each, with spacing 0.8 nm.…”

“…The model assumes a continuous-wave probe and leads to an explicit formula for the DOP, which is based on the walk-off-induced linear filtering of the pump channel, similarly to related well-known results in the analysis of both XPM in scalar nonlinear propagation [13], [14] and of pump-induced relative intensity noise in Raman amplifiers [15], [16]. The DOP formula turns out to be quite simple when the pump is ON-OFF keying (OOK) modulated by a square wave emulating an infinite alternation of marks and spaces, while it is slightly more complex with random pump bit sequences (RBS).…”