Complete Coherent QPSK Modulation and Demodulation System Built with VPI

In this optical experiment, we constructed a complete coherent QPSK modulation and demodulation system using VPI photonics simulation software. The implementation employs quadrature phase-shift keying (QPSK) modulation techniques where the system encodes data by modulating both the phase and amplitude of optical signals. The demodulation process utilizes coherent detection methods with digital signal processing algorithms for phase recovery and symbol decision. This system demonstrates remarkable success in high-speed data transmission applications by achieving low bit error rates while significantly enhancing data transmission bandwidth. The core implementation leverages the advantages of coherent QPSK modulation through precise phase and amplitude adjustments of optical signals, enabling more efficient data transmission. The system architecture includes carrier recovery algorithms, adaptive equalization modules, and forward error correction coding implementation. We further optimized the program with robust error-handling mechanisms and environmental adaptation features to ensure stable operation across varying conditions. Key functional components include constellation diagram generation, phase noise compensation algorithms, and signal-to-noise ratio monitoring modules. The system's modular design allows for parameter tuning through configuration files, with main processing loops handling real-time signal processing tasks. This program serves as a crucial and practical tool in optical communication experiments, providing a comprehensive framework for testing and validating coherent optical transmission systems.