Abstract This paper investigates the enhancement of communication performance in mixed radio frequency–free space optical (RF–FSO) wireless networks by employing unmanned aerial vehicles (UAVs) as mobile relays. A dual-hop transmission model is considered, where the UAV acts as an intermediary between a fixed ground source and multiple mobile users distributed along the boundary of a predefined geographical region. To improve the reliability and efficiency of the system, we propose a joint optimization framework that determines the UAV’s optimal altitude and horizontal location. Additionally, an opportunistic user scheduling mechanism is implemented, selecting the mobile user with the highest instantaneous signal-to-noise ratio (SNR) for communication. The RF link is modeled using Rayleigh fading statistics, and the FSO link is modeled using the Gamma–Gamma fading distribution, capturing the effects of atmospheric turbulence, pointing errors, and angle-of-arrival fluctuations. Closed-form expressions for outage probability and its asymptotic approximation at high SNR levels are derived to evaluate system performance analytically. The analytical results are further validated through Monte Carlo simulations. The outcomes demonstrate that the proposed UAV positioning strategy and user scheduling scheme effectively minimize outage probability and significantly enhance the robustness of the RF–FSO communication system. These results provide valuable insights for the deployment of UAV-assisted hybrid optical wireless networks in dynamic or infrastructure-constrained environments.

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 This work presents an integrated framework combining optical signal processing and VLSI system design for the performance evaluation and optimization of 5G waveform candidates under different modulation schemes. The analysis focuses on four major waveforms – OFDM, FBMC, NOMA, and OTFS – and examines their performance based on bit error rate (BER), peak-to-average power ratio (PAPR), and power spectral density (PSD) metrics. Simulation results demonstrate that OTFS outperforms the other waveforms, achieving a BER of 10 −3 at an SNR range of 7–10 dB, corresponding to an SNR gain of up to 8 dB over OFDM. Furthermore, OTFS exhibits a PAPR reduction of approximately 3.5 dB and the lowest out-of-band emissions with a PSD of around −310 dBW/MHz, indicating superior spectral efficiency and reduced interference. These characteristics make OTFS a promising waveform for high-mobility, high-capacity 5G and future 6G communication environments. The integration of optical signal processing techniques enhances system bandwidth and energy efficiency, while VLSI-based architectures support low-latency, high-throughput implementation. Future advancements will explore optical-VLSI codesign and machine learning–assisted frameworks for real-time adaptive processing, improving scalability, power optimization, and intelligent signal handling in next-generation wireless and optical communication systems.

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 This work offers an extra free-space optical (FSO) and protected fiber connection channel with self-repair capabilities to protect against fiber failures in gigabit passive optical networks (GPON). The new optical network unit (ONU) and optical line terminal (OLT) in the suggested PON architecture provide self-protective capability against fiber breakpoints. An integrated single mode fiber (SMF)/FSO link not only keeps data transfer uninterrupted even when fiber link installation is limited by environmental boundaries, like a wide river or the space between two mountains. In clear Iraq’s atmospheric conditions, the network system gets an optimum range transmission of favorable weather (fog) in both directions simultaneously to wired and wireless users over a bidirectional feeder fiber link 75 km and 430 m FSO or distribution fiber (DF) for downstream (D/S) and fiber feeder link 75 km and 230 m FSO or DF for upstream (U/S) with improved fault protection capability for both directions, while the range of FSO is reduced to 400 m, 260 m, and 250 m for D/S and 220 m, 160 m, and 150 m for U/S for snow, rain, and dust respectively. Asymmetric 2.5/1.25 Gbps for D/S and U/S has been used to achieve an acceptable minimum receiver sensitivity of −33.4 dB m for uplink and −34.4 dB m for downlink with a splitting ratio of 1:16.

Abstract This paper has clarified the simulation study of optical time division multiplexing/wavelength division multiplexing system based static/dynamic optical transparent networks demonstration through all-optical fiber amplifiers. Received signal power per channel is measured against network reach for both static and dynamic networks in the presence of all-optical Raman/erbium doped fiber amplifier/semiconductor optical amplifier amplifiers. Data rate transmission per channel is demonstrated against repeater spacing for all proposed optical fiber amplifiers based on various near infrared operating wavelengths for both static and dynamic optical transparent networks. In addition, the overall signal per noise ratio is clarified in relation to network throughput and various near infrared operating wavelengths for the static and dynamic transparent optical network based on all proposed amplification techniques. Moreover, the overall system bit error rate is studied and tested against network throughput and various near infrared operating wavelengths for both static and dynamic transparent optical networks based on all proposed amplification techniques.

Abstract This paper has highlighted the simulative performance evaluation of high speed long distance soliton propagation data transmission system based on dispersion control in optical fiber system. The dispersion management for the soliton fiber system is demonstrated based on both symmetrical fiber Bragg grating (FBG) and symmetrical dispersion compensated fiber (DCF) fiber compensation system. The soliton pulse dispersion is measured versus the single mode fiber cable and symmetrical FBG compensation lengths based on the different data rates transmission. Overall system dispersion, overall system data rate transmission, overall optical/electrical system signal per noise ratio, overall system transmission distance and overall system bit error rate are demonstrated clearly against various symmetrical DCF compensation lengths with/without the soliton fiber transmission system. Improvement ratio in both dispersion management and data rate transmission are clarified against symmetrical FBG and DCF compensation techniques and single mode fiber cable length variations. As well as the overall system dispersion and data rate transmission are studied and highlighted in relation to hybrid FBG/DCF compensation techniques and without any dispersion compensation in the presence and absence of soliton fiber transmission system.

Abstract Supercontinuum generation with improved coherence is very important issue in the optical communication system especially in the application of optical coherence tomography (OCT) that maintains the phase stability of the propagating pulse. In this work all fiber setups that consist of two interferometers were used to make compactness and alignment free compared with free space bulk optics setup, one with five nested Mach–Zehnder inferometer (MZI) and the second with Sagnac MZI interferometers. The sensing heads of the two interferometers high nonlinear fiber double clad fiber DCF13 that etched using 40%HF acid in four levels leads to decrease its diameter. Obtaining these levels is achieved by varying the time interval of the etching process as (10, 20, 30, and 40) minutes. Supercontinuum generation with Sagnac interferometer in this work has good performance when compared with nested MZI setup. This performance due to feedback the pulses and make counterclockwise propagating pulse that interfere with the clock wise pulse and leads to enhance the optical signal to noise ratio. The maximum OSNR was obtained that is 9.577 dB for Sagnac interferometer and 30 us rising time and 18 dBm amplification value of EDFA and 99.3 nW output power with 3 nm band (1,529.5–1,532.5) nm while for the first interferometer the output power in uW but with minimum OSNR that is 8.94 dB and −32.5 dBm noise power and 50 us rising time.

Abstract In optical communication technology, the coupling efficiency (CE) remains a big challenge. The slight misalignment between the fiber and the lens causes light to bounce back from the fiber end, which creates reflected intensity noise (RIN). This research presents a theoretical framework for estimating RIN in the case of laser diode (LD) excitation of triangular index fiber (TIF) through a single-mode upside down tapered cylindrical microlens (UDTCML) on the circular core fiber tip. The analysis takes care of different RIN values based on possible lateral misalignments in case of two wavelengths, 1.3 µm and 1.5 µm, and TIFs with three different V numbers in the coupling system. Using the ABCD matrix formalism, we analytically evaluate the CE when there is a lateral mismatch and thereof RIN as well. It deserves mentioning in this connection that increase of lateral mismatch causes both increase of loss due to RIN and decrease of coupling efficiency as well. The results given are useful for reducing RIN and improving CE. This information will benefit the designers and packagers concerned with optical couplers.

Abstract A tunable fiber laser comb is experimentally demonstrated in linear Brillouin erbium fiber laser (BEFL) cavity with an assistant of four wave mixing (FWM) process. Two nonlinear processes are contributed, stimulated Brillouin scattering (SBS) and FWM in this study, to improve the efficiency of the laser cavity. The number of the generated Stokes and anti-Stokes signals is improved to be 120 Single space channels. The recorded Stokes lines cover 9 nm in L-band region of 1,580 nm. Furthermore, the tuning range of the proposed cavity is also improved to 50 nm that covers C- and L-band regions from 1,550 to 1,600 nm. Three parameters are associated to achieve such wide tuning range in the proposed setup: high Brillouin pump (Bp) of 8 dBm, pre-amplification technique for inserting Bp signal, and using wide erbium emission peak in FWM section.