The outage probability (OP) in short-haul directdetection (DD) optical links supported by weakly-coupled multicore fiber (MCF) impaired by intercore crosstalk (ICXT) and using on-off keying signaling is assessed theoretically and through simulation. A closed-form expression for the OP is proposed for a single interfering core. This expression is useful to provide fast and reliable performance estimates in preliminary studies of weakly-coupled MCF-based systems where the ICXT is highly correlated along the signal bandwidth, i. e., when the skew-bit rate product is small. Particularly, results for a 20 kmlong link at 10 Gbit/s and walk-off below 1 ps/km are detailed. For high skew-bit rate products, i. e., when the ICXT is decorrelated along the signal bandwidth, simulation results show that, for a typical OP of 10 −4 , the tolerance to ICXT increases above 4 dB, when compared with low skew-bit rate products. It is also shown that DD links with finite extinction ratio are more robust to outage induced by the ICXT than those with ideal extinction ratio.

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In this work, the optimization of level spacing in terms of the extinction ratio variation in quaternary optical communication systems is investigated, for signal-dependent noise dominance. It is shown that the performance of optically preamplified quaternary communication systems can be optimized in terms of levels spacing using very simple formulas, also derived in this work. For the null extinction ratio, sensitivity improvements of about 6 dB can be achieved by proper location of signal levels in comparison with the sensitivity of equally spaced levels. At high extinction ratio, this improvement is not so significant.

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