arXiv subjects

Trevor J. Hall

Publications and source records attributed to Trevor J. Hall.

5 recordsLinked to original sources

arXiv2026

Vernier-assisted mode-selective PT symmetry in optoelectronic oscillators

Mode-selective PT-symmetry is the manifestation of Vernier-assisted cross-injection between oscillators with unequal delays. PT-symmetry has been proposed as a mechanism for achieving low-noise single-mode operation in optoelectronic oscillators, but existing formulations are typically based on matched delay loops and frequency-independent coupling, leading to symmetry transitions that are global in frequency and therefore not intrinsically mode selective. A more general formulation of PT-symmetric time-delay oscillators is developed in which the coupling operator is allowed to be dispersive. This permits frequency-selective PT-symmetry transitions and removes the requirement for matched delay loops. Two mathematically equivalent but physically distinct realisations are derived. The first corresponds to coupled gain-loss loops connected by a dispersive coupler, while the second corresponds to a pair of equal-gain oscillators coupled through symmetric cross-injection with unequal delays. Numerical simulations confirm the predicted behaviour and demonstrate strong sidemode suppression while preserving the low phase-noise characteristics of large-delay oscillators. The results establish a direct connection between PT-symmetry, cross-injection architectures, and Vernier oscillator design.

physics.optics↗

arXiv2026

PT-symmetric time delay oscillator modelling beyond the weak coupling limit via a scattering matrix formulation

Parity-time (PT) symmetry in time-delay oscillators such as lasers and optoelectronic oscillators provides a potential route to enhanced spectral purity, including reduced phase noise and improved sidemode suppression. Existing theoretical descriptions are typically based on coupled-mode formulations derived under slowly varying envelope and near-degeneracy assumptions, which restrict their validity to weak coupling, small gain/loss contrast, and small detuning. In this work, a non-perturbative formulation of PT symmetric time-delay oscillators is developed based on a delay-difference equation and a scattering matrix representation of the coupling network. The approach treats propagation delay explicitly and does not rely on modal truncation, remaining valid for arbitrary coupling strength, gain/loss imbalance, and resonance detuning. The exact eigenvalue structure of the system is obtained in closed form, yielding a complete characterization of the unbroken and broken PT symmetric regimes as well as the associated exceptional points. A dimensionless order parameter is introduced that governs the symmetry transition over the full parameter space. It is further shown that conventional coupled-mode theory is recovered as an asymptotic limit of the exact formulation for small parameters. The results provide a unified and physically transparent framework for analysing PT symmetric delay systems beyond the weak-coupling limit, with direct implications for the design and optimisation of low-noise oscillators and photonic systems.

physics.optics↗

arXiv2026

Multiscale phase dynamics and $2π$ phase kinks in injection-locked optoelectronic oscillators with large delay

Injection locking of optoelectronic oscillators (OEOs) with large delay gives rise to phase dynamics that lie beyond the scope of classical single mode locking theory, including the spontaneous formation of persistent $2π$ phase kinks. In this work, a multiscale theoretical framework is developed that explains the origin, structure, and stability of these phase slip phenomena in injection locked (IL) OEOs operating in large-delay regime. Starting from a complex envelope delay differential equation that explicitly incorporates hard-limiting gain saturation and RF BPF dynamics, a reduced phase-only description valid for nearly constant oscillation amplitude is derived. Exploiting the separation between fast round-trip dynamics and slow inter-round-trip evolution, a two-timescale reduction yields a continuum of Adler equations governing phase difference between injected signal and oscillator as a function of round-trip time. Analytical solutions obtained for weak injection and small detuning show how initially smooth phase profiles sharpen into localized $2π$ phase kinks, with p kinks appearing per round trip when the injection is tuned near the pth adjacent mode. Time-domain simulations of full complex-envelope model validate the predicted phase kink formation mechanism and reveal essential role of RF resonator dynamics in determining their persistence. While the reduced phase-only model correctly predicts kink sharpening, resonator-induced amplitude excursions associated with steep phase gradients can erase the kinks when the complex-envelope trajectory fails to encircle the origin, restoring conventional phase locking. These results provide a unified physical interpretation of $2π$phase kinks in IL-OEOs and delineate the limits of phase-only models in the presence of large, fast phase transients, identifying a regime of frequency locking without phase locking in large delay oscillators.

physics.optics↗

arXiv2021

The Convergence of Blockchain, IoT and 6G: Potential, Opportunities, Challenges and Research Roadmap

The world is undergoing a profound transformation with the advent of intelligent information era. 6G networks envisioned being the game changer in next generation wireless communication systems that will address the challenges of limited information speed escalated with the augmentation of billions of data applications encountered by the current fifth generation (5G) networks. Some key radical technologies in 6G together with existing 5G candidate schemes will guarantee the expected quality of experience (QoE) to attain ubiquitous wireless connectivity for the Internet of Everything (IoE) ranging from the telecom industry to digital smart industries. Blockchain technology (BCT) has gained significant attention due to undertake the decentralization, transparency, spectrum resource scarcity, inherent privacy and security, poor interoperability, confidentiality, and emerging smart applications domains including Industrial IoT and Industry 4.0. The mismatch between the requirements of many data intensive disruptive IoT applications and 5G network capabilities steered the demand of decentralized BCT based 6G architecture. Inspired by these facts, this paper studies an extensive survey to draw a new direction of blockchain integration into 6G mobile networks, IoT technologies, and smart industries focusing the potential merits and challenges in terms of infrastructure sharing, computational loads, latency, bandwidth overhead, business model, sustainability goals, and edge intelligence. We highlighted the convergence of IoT in blockchain to enable intelligent distribution in future industrial IoT and the technical model of 6G networks to realize the successful deployment of BCT schemes. This paper pointed out the current intriguing challenges, canvassed the mitigation techniques, and plausible future research opportunities that may benefit the pursuit of this vision.

eess.SP↗

arXiv2020

A Contemporary Survey on Free Space Optical Communication: Potential, Technical Challenges, Recent Advances and Research Direction

Optical wireless communication (OWC) covering an ultra-wide range of unlicensed spectrum has emerged as an extent efficient solution to mitigate conventional RF spectrum scarcity ranging from communication distances from nm to several kilometers. Free space optical (FSO) systems operating near IR (NIR) band in OWC links has received substantial attention for enormous data transmission between fixed transceivers covering few kilometers path distance due to high optical bandwidth and higher bit rate as well. Despite the potential benefits of FSO technology, its widespread link reliability suffers especially in the long-range deployment due to atmospheric turbulence, cloud induced fading, some other environmental factors such as fog, aerosol, temperature variations, storms, heavy rain, cloud, pointing error, and scintillation. FSO has the potential to offloading massive traffic demands from RF networks, consequently the combined application of FSO/RF and radio over FSO (RoFSO) systems is regarded as an excellent solution to support 5G and beyond for improving the limitations of an individual system. This survey presents the overview of several key technologies and implications of state-of-the-art criteria in terms of spectrum reuse, classification, architecture and applications are described for understanding FSO. This paper provides principle, significance, demonstration, and recent technological development of FSO technology among different appealing optical wireless technologies. The opportunities in the near future, the potential challenges that need to be addressed to realize the successful deployment of FSO schemes are outlined.

cs.IT↗