ABSTRACT
In this study, we employ the Rytov approximation to investigate the detection probability of orbital angular momentum (OAM) in multi-Gaussian correlated anomalous vortex (MGCAV) beams under non-Kolmogorov maritime atmospheric turbulence. Our results demonstrate that the OAM detection probability of a MGCAV beam is influenced by various factors, including beam parameters and the characteristics of maritime atmospheric turbulence. Specifically, an increase in propagation distance, beam order, and beam index, or a decrease in inner scale, spatial coherence width, and non-Kolmogorov parameter, leads to a decrease in the OAM detection probability. The phase characteristics of partially coherent vortex modes are affected by both atmospheric turbulence phase and initial random phase, resulting in reduced robustness compared to fully coherent vortex modes. Furthermore, a comparative analysis between Gaussian-Schell correlated anomalous vortex (GSCAV) beams and MGCAV beams reveals the superior resilience of GSCAV beams in mitigating the impact of maritime atmospheric turbulence. Moreover, specific combinations of beam order, topological charge, and beam waist, or the optimal beam width, yield maximum OAM detection probability or minimum scintillation. These findings provide valuable insights applicable to optical communication, particularly in scenarios above sea and ocean levels.
ABSTRACT
White light cavities with broadband resonance are usually filled with negative dispersion medium, which inevitably leads to gain. In this article, pure passive white light cavities are designed, in which negative dispersion medium is no longer necessary. Theoretically, if the reflection phase of the cavity wall can exhibit a negative dispersion slope, then it can also satisfy white light cavities conditions without medium. In practice, the negative dispersion property of the cavity wall can be realized by two metal coatings with different reflection coefficients. Therefore, our white light cavities are composite cavities, in which the main cavity provides resonance while the auxiliary cavity forms the cavity wall, providing negative dispersion reflection phase. Further, atomic gas can be employed to improve the performance of the white light cavities. Atomic gas exploits effects such as Electromagnetic Induced Transparency (EIT), enabling the white light cavities to be controlled by coherent driving field. With the passive characters, our design can be realized and implemented much more easily.
ABSTRACT
The correlation function and the detection probability of orbital angular momentum (OAM) of a perfect optical vortex beam (POVB) were obtained under atmospheric turbulence conditions and then used to estimate the POVB propagation model through atmospheric turbulence. The POVB propagation in a turbulence-free channel can be divided into anti-diffraction and self-focusing stages. The beam profile size can be well preserved in the anti-diffraction stage as the transmission distance increases. After shrinking and focusing the POVB in the self-focusing region, the beam profile size expands in the self-focusing stage. The influence of topological charge on the beam intensity and profile size differs depending on the propagation stage. The POVB degenerates into a Bessel-Gaussian beam (BGB)-like when the ratio of the ring radius to the Gaussian beam waist approaches 1. The unique self-focusing effect of the POVB enables higher received probability compared to the BGB when propagating over long distances in atmospheric turbulence. However, the property of the POVB that its initial beam profile size is not affected by topological charge does not contribute to the POVB achieving a higher received probability than the BGB in short-range transmission application scenarios. The BGB anti-diffraction is stronger than that of the POVB, assuming a similar initial beam profile size at short-range transmission.
ABSTRACT
Vortex X-waves with coupling effects of orbital angular momentum (OAM) and spatiotemporal invariance are introduced into the research of underwater wireless optical communication systems (UWOCSs). We establish the OAM probability density of vortex X-waves and channel capacity of UWOCS using Rytov approximation and correlation function. Furthermore, an in-depth analysis of OAM detection probability and channel capacity is performed on vortex X-waves carrying OAM in von Kármán oceanic turbulence with anisotropy. The results show that an increase in OAM quantum number results in a "hollow X" shape in the received plane, where the energy of vortex X-waves is injected into the lobes, reducing the received probability of the vortex X-waves transmitted to the receiving end. As the Bessel cone angle increases, the energy gradually concentrates toward the energy distribution center, and the vortex X-waves become more localized. Our research may trigger the development of UWOCS for bulk data transfer based on OAM encoding.
ABSTRACT
Theoretical and experimental explorations have demonstrated that both anisotropy and unstable stratification exist in general ocean turbulence. Recent analyses of temporal broadening of ultrashort optical pulses in oceanic turbulence have adopted the assumptions that the propagation path in the z direction was isotropic, or turbulent cells are simply premised on circular symmetry in the xy plane. In this paper, circular symmetry of turbulent cells in the xy plane is no longer maintained, and two anisotropic factors describing the anisotropic scales in the xy plane are introduced to study the temporal broadening of ultrashort optical pulses. Moreover, unstable stratification of oceanic turbulence indicates the eddy diffusivities of temperature and salt are no longer equal. By Rytov approximation and the temporal-moments method, a new model is proposed for the temporal broadening of ultrashort optical pulse propagation in general ocean turbulence. We focus on the effects of asymmetric turbulent cells, unstable stratification, and other characteristics in general ocean turbulence on the temporal broadening. This work provides a theoretical basis for improving the transmission quality of ultrashort optical pulses and the performance of underwater optical communication systems.
ABSTRACT
The anaerobic ammonium oxidation (anammox) basedtechnology has been considered as an economic and efficient way to remove nitrogen. However, the anammox bacteria could be strongly inhibited by antibiotics. In present research, inhibiting properties of oxytetracycline, penicillin and polymyxin sulfate upon the anammox activity were investigated through batch experiment. The results implied that anammox activity was significantly inhibited by oxytetracycline and polymyxin sulfate. The non-competitive inhibiting model showed that the inhibiting constants (Ki) of oxytetracycline and polymyxin sulfate were 188.5 and 17.7 mg/L, respectively. Meanwhile, the anammox process was not suppressed while the concentration of penicillin reached 3000 mg/L. In long-run experiment, the influent oxytetracycline concentration of the anammox coupled denitrifying reactor was operated at 20 mg/L. It was observed that the anammox performance completely deteriorated, while the NO2--N removing efficiency reached 15.8%. The obtained findings could provide important instruction for the treatment of antibiotic contaminated wastewater.
Subject(s)
Ammonium Compounds , Oxytetracycline , Anaerobic Ammonia Oxidation , Anaerobiosis , Anti-Bacterial Agents , Bioreactors/microbiology , Denitrification , Nitrogen , Oxidation-Reduction , Sewage/microbiologyABSTRACT
In this study, we introduce the phase correlation arc of an orbital angular momentum (OAM) beam to investigate the evolution of OAM entanglement. We reveal that the entanglement decay of all OAM states of Laguerre-Gaussian modes in atmospheric turbulence is universal via both numerical predictions and experimental data. A similar evolution law is also theoretically confirmed to exist in Bessel-Gaussian modes. Finally, by using the phase correlation arc, the precise formula of the decay distance dependence on the OAM number is derived, and it exhibits excellent agreement with previous experimental conclusions.
