查看更多>>摘要：We investigate and establish the fact that, a topological edge-state and transverse localized state can coexist due to the interplay of band topology and deliberate refractive index disorder in 1-D photonic lattice. We found that two exclusive states of light are supported by a 10 mm long specialty topological lattice in presence of optimum disorder. The signature of the edge-state is identified by its robust loss-less nature whereas transverse localized state is identified by the exponentially decaying tail of the transverse intensity distributions. The specialty topological lattice used as test-bed is made by combining two periodic lattices of different topologies. The topological nature of the lattices are identified by the associated Zak phases of the corresponding bands. The studies in this direction are necessary to explore novel optical communication schemes in 1-D lattices which are robust to the fabrication imperfections.
查看更多>>摘要：Flexible broadband terahertz absorbers (FBTAs) have attracted great attention in recent years due to their promising potential for nonplanar objects, however, these applications are limited by rigorous requirements for being insensitive to arbitrary incident angles. Herein, we have proposed an ameliorated angular insensitivity method by integrating the appropriate amount and type of building absorbers into a hybrid flexible array according to spatial distributions and surface curvatures. Based on the integrable strategy, we have successfully designed three types of FBTAs with diverse robustness and insensitivity for wide incident angles. The radar cross section (RCS) reductions for these FBTAs are theoretically investigated to further validate their absorption performance. Additionally, the equivalent circuit theory is employed to reveal the underlying physical mechanism of the bandwidth expansion. It can be deduced that our proposed strategy would be beneficial to broaden the bandwidth and enhance the angular independence of flexible absorbers and provide several promising prospects in the development of emerging functional THz technologies.
查看更多>>摘要：A controllable energy method, which considers the undersampling issue of the transfer function and valid spectral energy of a source signal, is proposed to implement angular spectrum diffraction calculation in near and far fields. The proposed method provides an optimized frequency boundary within which it always keeps controllable energy to be diffracted. The controllable energy angular spectrum method significantly reduces the number of samples while having the same accuracy as previous angular spectrum methods, implying a higher calculation efficiency. The new perspective of analyzing spectral energy is shown to improve the performance of relevant diffraction calculations.
查看更多>>摘要：Free space optical (FSO) communication in a maritime environment involves unique challenges due to the existing environmental conditions. An important degradation factor is atmospheric turbulence that causes irradiance fluctuations (scintillation) at the detector. A significant amount of theoretical and experimental research has been conducted to quantify those effects. This paper presents the results of an experimental campaign that took place during September and October of 2020 over the Monterey Bay in California. The main goal of this campaign was to measure atmospheric turbulence over the water and compare the results with a theoretical model called the Navy Surface Layer Model (NAVSLaM), developed by the Meteorology Department at the Naval Postgraduate School (NPS), as well as conduct a regression analysis for turbulence predictive modeling based on environmental parameters. The results showed very good agreement between theory and experiment.
Jadoon, Zeeshan Ali SafdarHassan, Aisar-ulNoh, Heung-RyoulKim, Jin-Tae...
5页
查看更多>>摘要：The effects of neighboring transitions through Doppler broadening on the electromagnetically induced absorption (EIA) and electromagnetically induced transparency (EIT) of the degenerate two-level system (DTLS) in Rb-85 atoms with respect to the linear parallel polarization configuration of coupling and probe lasers have been investigated. The calculated coherent absorption profiles with and without neighboring effects have been compared to elucidate the neighboring effects between the DTLS and nearby states for the conversion between EIA and EIT. Even in the case of the closed system, i.e., F-g=3 -> F-e=4 of Rb-85, for the first time, EIT instead of EIA has been observed owing to the neighboring effect of dominant F-g=3 -> F-e=3 on the linear parallel polarization configuration case of Rb-85 in the low power regime. All the transitions (F-g=3 -> F-e = 2 and 3 and F-g=2 -> F-e = 1, 2, and 3) of linear parallel polarization cases exhibit EIT owing to dominant neighboring EIT in the DTLS. In each polarization scheme, the observed spectral trends of the transitions are similar owing to the neighboring effect. The EIT spectral trends with the neighboring effect of F-g=2 -> F-e = 1, 2, and 3 are governed by the openness of pure DTLS calculation.
查看更多>>摘要：In this paper we propose a chiral resolution technique based on laser-induced continuum structure (LICS). We show that the two enantiomers can have a different ionization profile based on implemented LICS excitation. We treat a cyclic excitation between two bound states and a continuum state and show how asymmetric ionization can be achieved based on different trapping of the enantiomers due to the additional coupling between the bound states. Alternatively, when multiple states are involved in the interaction we investigate a multilevel LICS strategy of asymmetric ionization based on dark-bright state trapping. In this latter case one of the enantiomers is trapped in a dark state, which is immune to ionization, while the other is driven in a bright state, from which the population leaks into the continuum.
查看更多>>摘要：Underwater wireless optical communication (UWOC) becomes a hot topic in current researches. It suffers from severe absorption, scattering and turbulence, which result in a low reception power even in a short communication distance. To address this challenge, a single-photon avalanche diode (SPAD) based UWOC with signal accumulation method is proposed in this paper. Bit error rate (BER) performance of above method considering nonzero SPAD dead time over generalized gamma turbulence channels is investigated. For this goal, we first derive the expression for the instantaneous BER of above UWOC system. Then we obtain the optimal decision threshold corresponding to the minimum average BER. Based on those obtain expressions, we construct a useful closed form expression for the average BER corresponding to the minimum BER. With those expressions, the effects of the system parameters on the BER performance under turbulence channels are studied. The simulations show that a poor BER performance of 0.0094 for the system without using the signal accumulation under turbulence alpha(2) = 0.31 can be improved to 7.5 x 10(-7) by using 10 accumulation times, which indicates that the signal accumulation can overcome the adverse turbulence effect. Besides, we also find that even with quiet low receive power of 1 photon/bit, the UWOC system can still obtain a good BER performance of smaller than 10(-6).
查看更多>>摘要：A broadband multi-frequency microwave photonic up-conversion scheme with a tunable phase shift is proposed and demonstrated based on a cavity-less ultrashort optical pulse source and a dual-polarization dual-parallel Mach-Zehnder modulator (DP-DPMZM). In this scheme, the intermediate-frequency (IF) signal is loaded onto the optical frequency comb from a cavity-less ultrashort pulse source via carrier-suppressed double-sideband (CS-DSB) modulation by using a DP-DPMZM and a 90 electric hybrid coupler (HC). Through mutual beating between multi-groups of optical modulation sidebands and multi-tone optical carrier at the photodetector (PD), multi-frequency up-converted microwave signals are obtained after coherent superposition. Meanwhile, the phase of the generated signals can be continuously tuned through varying the bias voltages of the DP-DPMZM. Simulation results show that the multi-frequency up-conversion is with a 3-dB operation bandwidth of 36 GHz and a phase shift tuning range over 360. Hence, this scheme is a potential candidate to simultaneously realize broadband multi-frequency operation and generate the large-scale tunable phase shift in modern radar systems.
查看更多>>摘要：The three-dimensional optical diagnostic method has received extensive attention from researchers because of its ability to provide three-dimensional physical information for reactive flow studies such as combustion. Computed tomography of chemiluminescence (CTC) has become a commonly used technique for three-dimensional, transient flame reconstruction purposes. However, due to view number limitations and considerable computational costs, the spatial resolution achieved and accuracy of the reconstruction are less satisfactory compared with applications such as in the medical fields. This investigation focuses on a few methods for improving the experimental and numerical performance of the CTC methods. Firstly, a cylindrical ChArUco calibration target was introduced and a multi-camera calibration method considering the position constraints of cameras was proposed to eliminate the registration error due to the rotation of the calibration target. Furthermore, a sub-voxel method was adopted to improve the spatial resolution of flame reconstructions. Finally, a non-negative algebraic reconstruction technique (NNART) was developed. The algorithm was verified with a simulated jet flame and then was tested against a diffusion jet flame and a swirl flame experimentally.
查看更多>>摘要：To enhance the flatness of received optical power distribution, a hybrid immune clonal bat algorithm (ICBA) combining the bat algorithm (BA) with an immune clonal algorithm (ICA) has been proposed to optimize the light source layout of indoor visible-light communication (VLC) systems. Taking 16 light-emitting diode (LED) lamps under a rectangular layout as an example, the variance of the received light power on the receiving plane is set as the fitness function. Specifically, the fitness value is optimized by the variables of 18 elements consisting of the LED position parameters and their half-power angles. The results show that compared with the non-optimized case, BA, and ICA, the fitness value of ICBA decrease by 97.70%, 96.77% and 98.81%, respectively. The signal-to-noise ratio (SNR) variance optimized by the ICBA is the lowest, approximately 0.1037 dB, and the variance of illuminance optimized by ICBA is 62.99% lower than that optimized by ICA. Besides, compared with the non-optimized case, the BER performance of this VLC system has also been improved significantly after ICBA optimization. This study will benefit the research and development of indoor VLC systems.
NSTL
Elsevier