Traffic in datacenters has been significantly increasing over the last few years. As a result, it is necessary to
scale the connections of the datacenters to accommodate such an increase of traffic. The solution considered
in this work is to use four-level pulse amplitude modulation (PAM4) and weakly-coupled multicore fibers
(MCFs) to support intra-datacenter connections. However, transmission in weakly-coupled MCFs may be significantly
degraded by inter-core crosstalk (ICXT). In this work, the impact of ICXT on the performance of
PAM4 transmission in short-haul direct-detection links is evaluated considering two-level PAM (PAM2) signals
in the interfering cores. The ICXT impact on the performance of the tested core with PAM4 transmission
is evaluated using the bit error rate (BER), outage probability (OP) and eye-pattern analysis. Comparing to
PAM2 transmission in the tested core, a 7.6 dB lower ICXT level is required to achieve an acceptable OP for
a reference BER of 3.810􀀀3 in the PAM4 link.