QPSK (Quadrature Phase Shift Keying) modulation is a widely used modulation technique in advanced optical transmission systems. It offers several key benefits for long-haul and high-capacity networks. QPSK reduces the required Optical Signal-to-Noise Ratio (OSNR), which improves system performance under noisy conditions. It also mitigates fiber nonlinear effects because the signal changes are more gradual compared to higher-level modulations. Moreover, QPSK improves tolerance to chromatic dispersion and Polarization Mode Dispersion (PMD), two major impairments in fiber optics. These improvements lead to better signal integrity over longer distances and support higher data rates with fewer errors, making QPSK favorable in HCIP-Transmission environments where robust, high-capacity transmission is essential.