Abstract In this paper, a zero cross-correlation code (ZCC)–based optical code division multiple access passive optical network (OCDMA-PON) is presented. The proposed ZCC assigns a unique and non-overlapping set of wavelengths to each optical network unit (ONU), ensuring zero cross-correlation among users. Unlike conventional codes such as multi-diagonal (MD) or modified quadratic congruence (MQC), the proposed ZCC offers a simpler recursive construction, flexible scalability, and complete elimination of multiple access interference. An eight-user ZCC-based PON system is designed and its performance is evaluated in terms of bit error rate (BER) and Q-factor. Simulation results show that the proposed system achieves a BER below 10 −15 and a Q-factor of approximately 9 dB at a transmission distance of 10 km, demonstrating improved interference suppression and reliable performance compared to previously reported OCDMA schemes. These results confirm the suitability of ZCC for secure and efficient next-generation optical access networks.

Abstract Information and communication technology (ICT) has advanced significantly in the modern era, and the majority of smart technology utilized in smart cities are Internet of things (IoT) based. Hybrid passive optical networks (PON) consist of wavelength division multiplexing (WDM) and time division multiplexing (TDM) are of the most encouraging and widely utilized technologies in optical distribution networks (ODN) required for security, encryption data and bandwidth. The security of the mystery/private cryptographic key is crucial to the encryption process’s ability to secure data. Any strong encryption algorithm would be compromised by poor key management. In order to enhance the physical security, so as to protect the secret data during transmission across the channel and to ensure a secure exchange of the encryption key between the transmitter and the recipient, a hybrid system that incorporates cryptography, steganography, and key hiding techniques has been employed. To the best of our knowledge, Opti-System software with python devices combine to create a secure WDM/TDM-PON system depending on the Hill Group cipher and ITU-T G.989.2 standards. Simulation studies indicate that, a bidirectional fiber distance with a splitting ratio 1:64 and a symmetrical 40 Gbps can be accomplished successfully out at 60 km. The least amount of acceptable receiver sensitivity is −28.1 dBm for uplink (U/S) and −23.7 dBm for downlink (D/S).

Abstract The performance of free-space optical (FSO) communication systems is significantly affected by weather conditions and alignment losses between the transmitter and receiver, which can degrade signal quality. These challenges can be mitigated by optimizing key system parameters, particularly the divergence angle, which controls the optical beam’s spread during transmission. In this paper, we present a multi-verse optimizer (MVO) model to identify the optimal divergence angle, enhancing FSO system reliability under adverse conditions. Our approach evaluates the impact of divergence angles on system metrics such as link margin, deviation angle, and signal-to-noise ratio (SNR). We compare the performance of MVO with particle swarm optimization (PSO), demonstrating that MVO achieves an average improvement of 20 %–30 % in link margin across different conditions. Simulation results validate the efficiency of MVO in optimizing FSO systems, identifying configurations that minimize link margin degradation and maximize system robustness. These findings offer actionable insights for designing resilient and efficient FSO communication links, ensuring dependable performance in diverse environmental scenarios.

Abstract Optical orthogonal frequency division multiplexing (Optical OFDM) is a key modulation technique for high-speed optical communication systems; however, its performance is significantly degraded by chromatic dispersion and phase noise, which impair subcarrier orthogonality and introduce inter-symbol and inter-carrier interference. To overcome these limitations, this work proposes an enhanced signal detection scheme for optical OFDM based on a hybrid equalization framework integrated with quasi-reduced maximum likelihood detection (QRM-MLD). The proposed approach is evaluated against conventional detection methods, including zero-forcing equalization, minimum mean square error, maximum likelihood, and successive interference cancellation. MATLAB-based simulation results demonstrate that the hybrid QRM-MLD scheme achieves substantial performance gains under various channel impairment conditions. At a target bit error rate of 10 −3 , the proposed method requires up to 10 dB lower signal-to-noise ratio compared to uncompensated optical OFDM and offers approximately 2–7 dB improvement over conventional detection schemes. Capacity analysis further confirms its superiority, achieving a value of 290 at an SNR of 50 dB. Overall, the proposed hybrid detection strategy significantly improves detection accuracy, spectral efficiency, and robustness, making it a strong candidate for next-generation high-capacity optical OFDM communication systems.

Abstract This paper presents a comparative investigation of two quantum communication architectures – standard quantum key distribution (QKD) and semi-quantum key distribution (SQKD) – operating over noisy RF channels and enhanced with quantum phase estimation (QPE) feedback for phase noise mitigation. In QKD, both communicating parties are fully quantum-capable, while in SQKD, one party is restricted to limited classical-level quantum operations. The study evaluates performance under realistic noise models incorporating depolarizing noise, thermal relaxation, and Gaussian-distributed phase noise, examining the impact of QPE pilot configurations on phase tracking, residual error, and error rates. Simulation results reveal that while QPE feedback significantly improves robustness in both architectures, the SQKD configuration exhibits slower convergence, higher residual errors, and more variable key error rates due to the classical party’s limited corrective capabilities. These findings highlight the trade-offs between hardware complexity and performance in quantum-secured RF communication systems.

Abstract Multicore fibers (MCF) can overcome the capacity limitations of the network by enabling space-division multiplexing (SDM). Based on inter-core interaction, classification puts the MCFs into two groups. The first group is weakly-coupled (WC) MCFs. The second group is strongly-coupled (SC) MCFs. WC-MCFs are the weakly-coupled MCFs that minimize crosstalk through optimized core spacing and refractive-index engineering. Many researchers consider the independent transmission channels suitable for long-haul networks, high-capacity optical links, and emerging 5G/6G fronthaul deployment due to their stability and compatibility with existing infrastructure. Recent research highlights the complementary nature of WC and SC designs: WC-MCF is better for low-crosstalk independent-channel long-haul and practical deployment, while SC-MCF is better for maximizing spatial-spectral capacity and petabit-class core transport. In terms of capacity, strongly coupled MCF (SC-MCF) is better because its supermode-based spatial multiplexing supports far higher spatial channel counts and ultra-high petabit-class throughput compared to weakly coupled MCF.

Abstract Underwater optical wireless communication (UOWC) presents a promising solution for achieving high-speed underwater data transmission. This study investigates the performance of non-return-to-zero (NRZ), duobinary, and alternate mark inversion (AMI) modulation formats at 10 Gbps under diverse aquatic environments including pure sea (PS), clear ocean (CO), coastal ocean (CS), harbor I (HI), and harbor II (HII). Quantitative performance is evaluated in terms of Q factor, bit error rate (BER), and eye diagram analysis with increasing transmission range. For example, in PS water at 50 m, NRZ achieves a Q factor of 6.21 dB and BER of 10 −9.6 , outperforming duobinary ( Q = 4.79 dB, BER = 10 −6.8 ) and AMI ( Q = 3.69 dB, BER = 10 −3.96 ). Across all ranges and water types, NRZ consistently provides the best performance, while duobinary offers intermediate results and AMI shows the highest degradation in turbid waters such as harbor I and harbor II. The findings highlight NRZ’s robustness for high-speed UOWC links, particularly in clear waters, and its relative advantage over duobinary and AMI in maintaining reliability over extended distances.

Abstract This paper introduces a novel underwater visible light optical communications (UVLC) system architecture employing optical Minimum Shift Keying modulation with independent pulse shaping (IPS-MSK). The system under consideration is configured with a non-line- of-sight (NLOS) channel, and its performance is evaluated numerically under various aquatic conditions, such as different water types (pure seawater, clear ocean, and coastal ocean), depths, link ranges and turbulence strengths, considering different data rates. The effect of transmitter optical power and receiver aperture diameter has also been investigated. The key parameters used are bit error rate (BER), quality factor (Q), eye diagram and signal to noise ratio (SNR). Results shown that, when combined with IPS-MSK modulator, UVLC system demonstrates enhanced capacity, extended transmission range, and improved performance, particularly, in clear water. At data rate up to 40 Gbps, an underwater distance of 102 m and 100 m is achieved in the pure seawater and clear ocean, respectively, with a target Q-factor of 6. Coastal water demonstrated shorter transmission distance of 1 m while maintaining similar Q-factor. The findings confirm that the proposed system could be advantageous choice for higher data rate UVLC system over long-range in clear water, and for short-range applications in turbid water.

Abstract Visible light communication (VLC) has gained significant attention as a next-generation wireless technology due to its unlicensed bandwidth, high security, and seamless integration with LED illumination. To support high data rates and user scalability, power-domain non-orthogonal multiple access (NOMA) with 1024-QAM modulation enhances spectral efficiency; however, this combination introduces high peak-to-average power ratio (PAPR), resulting in nonlinear signal distortion and degraded bit error rate (BER) performance in intensity-modulated optical systems. To overcome these limitations, this paper proposes a deep learning-based nonlinear companding framework for waveform optimization in Optical NOMA. The proposed technique significantly reduces PAPR, achieving 3.2 dB, 4.4 dB, and 5.3 dB at a CCDF of 10 −3 for 256, 512, and 1024 subcarriers, respectively, outperforming A-Law, μ-Law, and PTS by up to 7.5 dB improvement. BER analysis further confirms its superiority, achieving a BER of 10 −3 at only 8.9 dB SNR, compared to 15.2 dB (A-Law), 13.1 dB (μ-Law), 11.4 dB (PTS), and 17.8 dB for the unprocessed Optical NOMA waveform. These results demonstrate improved power efficiency, reduced nonlinear distortion, and enhanced detection reliability, making the proposed method a strong candidate for high-speed VLC-based NOMA systems.

Abstract Affine Frequency Division Multiplexing (AFDM) has emerged as a robust modulation scheme capable of handling the challenges posed by doubly dispersive wireless channels. By utilizing chirp-based waveforms, AFDM offers inherent resilience against time and frequency dispersion, positioning it as a potential alternative to Orthogonal Frequency Division Multiplexing (OFDM), especially in high-mobility environments. However, like OFDM, AFDM is still susceptible to Intercarrier Interference (ICI), particularly in the presence of Carrier Frequency Offset (CFO). In this work, I derive analytical expressions for the ICI coefficients and the resulting Carrier-to-Interference Ratio (CIR) in AFDM. To understand the impact of ICI, I evaluate the Bit Error Rate (BER) performance of AFDM under both Additive White Gaussian Noise (AWGN) and Rayleigh fading channels. Simulations results compare the BER performance of AFDM with and without ICI, clearly highlighting the performance degradation due to ICI.