The explosive growth of optical communication (i.e., 6G or beyond 5G) will transform the way of communication. Advanced modulation schemes, guided media, high data rate, minimum dispersion, low transmission noise, and sign. The explosive growth of optical communication (i.e., 6G or beyond 5G) will transform the way of communication. Advanced modulation schemes, guided media, high data rate, minimum dispersion, low transmission noise, and signal processing techniques are available to enrich optical networks. The multicore fiber (MCF) will play a significant role in spatial division multiplexing. The major bottleneck of the MCF is the crosstalk in different cores. This article analyzed the crosstalk in multicore fiber (i.e., 2, 3, 4, and five core) as a transmission length function and compared the Q factor, bit error rate, and output power by considering all nonlinearities of the fiber. Maximum BER obtained for 5, 4, 3, and 2 core MCF is 10-14, whereas minimum BER for 5, 4,3, and 2 core MCF are 10–248, 10–248, 10–281, a. Multicore fiberCrosstalkNumber of coresQ factorAccording to the world-leading wireless carriers, the preparation for 6G development is getting started in several regions worldwide, but 5G network deployment is still in its beginning in several areas worldwide. (Moritz, 2020) 6G communication is probable to use super high-frequency terahertz signal (THz) and deliver a very high data rate (Gpbs) (https://, 2020). The fusion of technologies will contribute to implementing the 6G technology by using spatial division multiplexing, distributed MIMO, artificial intelligence, machine learning (AI/ML), etc. (Chowdhury et al., 2020). The explosive growth of future data services requires the space-division multiplexing (SDM) using multicore fiber (MCF) is one solution to meet the expected capacity demand for long haul amplified t. WDM is a technology for boosting the mixing of closely spaced optical systems(Ionescu et al., 2022). A WDM system uses optical carrier waves of marginally varied wavelengths that flow through the same fiber in different cores to transmit complex and dynamic signals. The intensity increases the refractive index. The several channels that are supposed to be independent can begin to interact at high intensity. The bit error rate (BER) shows the crosstalk between channels. The origin of nonlinear crosstalk in optical fiber is due to the intensity-dependent refractive index known as the Kerr effect. It depends on ultra-fast third-order susceptibility. The self-phase modulation (SPM), cross-phase modulation (XPM) & four-wave mixing (FWM) occurs due real part of the nonlinear refractive index. The FWM is a phase-se. This investigation considers all nonlinearities distortions such as group velocity dispersion, third-order dispersion, self-phase modulation, and differential group delay. The experiment setup in Fig. 2 has a continuous laser source of 1550 nm wavelength with 0dBm input power, and the PN Sequence generator generates the 10 Gbps signals with a sample rate of 1.28e + 12 Hz and a length of the sample of 128 bits. The number of samples has taken 16384, and the symbol rate of 10Gbps. This bit sequence is converted into a pulse from the NRZ (no-return zero) pulse generator. Fiber characteristics are given the Table 1.Table 1. Fiber Characteristics.The optically modulated signals are transmitted through the optical fiber and r.