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In laser science and industry, considerable effort is directed toward designing fibers for fiber laser and fiber amplifier applications, each of which offers a particular advantage over the others. Evanescently coupled multicore fibers, however, have been studied less extensively due to the relatively small mode area in the single-mode regime. Here, by proposing a new structure with stress-applying parts in a 37-core fiber and optimizing this structure through a comprehensive framework, we present 21 solutions characterized by large-mode-area and high beam quality in the single-mode, single-polarization regime. Different fiber designs are optimal for different output parameters. In one design, the mode area can significantly increase to above 880 μ m 2 , which is comparable with that of photonic-crystal fibers. Moreover, besides the single-mode operation, the beam quality factor ( M 2 factor) of the fundamental mode is considered an output parameter in the bent state and is improved up to 1.05 in another design. A comprehensive tolerance analysis is then performed to assess the performance of the designs under deviations from normal conditions. Moreover, in spite of the shifts in the loss of modes, the proposed high beam quality LMA fibers maintain single-polarization, single-mode operation across a wide range of core pitches, bending orientation angles, and bending radius deviations. Our results highlight the potential of multicore fibers for the efficient operation of fiber lasers and amplifiers. [ABSTRACT FROM AUTHOR]

In this paper, we present a set of optimal graphene-based multilayer surface plasmon resonance (SPR) biosensors for highly sensitive detection of biomolecules. To optimize the biosensor structure, we employed a multi-objective gray wolf optimizer (MOGWO) to maximize the sensitivity and minimize the structure full width at half maximum (FWHM). The main advantages of the optimized structures are high sensitivity, low FWHM, as well as easy implementation. We developed an algorithm that enables us to achieve nine different optimized structures. The best sensitivity, FWHM and FOM are obtained equal to 264.6°/RIU (for the structure #5), 1.905° and 56.6/RIU (for the structure #8), respectively. The results of this paper pave the way for the development of highly-sensitive SPR biosensors. [ABSTRACT FROM AUTHOR]

Despite the wide range of applications and versatility, actively Q‐switched fiber lasers (AQS‐FLs) suffer from the multi‐peak phenomenon or stepwise pulse generation under certain conditions. As such, the advantage of the stepwise tendency in AQS‐FL to modify the pulse shape and create a temporal profile that minimizes the power of stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS) Stokes components is taken. Accordingly a multi‐objective genetic algorithm (GA) and a Monte‐Carlo method is developed to solve the improved model for SBS. Additionally, the suppression of SRS is predicted and examined successfully. The proposed method is deployed for the simulation of the 5 and 10 kW peak and 10 ns wide pulses on a 4 m long, single‐mode, ytterbium‐doped double clad fiber under the narrow linewidth of 0.05 nm with promising suppression of SBS and SRS effects. To the best of the authors' knowledge this is the first time that such a pulse‐shaping strategy is demonstrated for the SBS or SRS suppression. Furthermore reaching a 10 kW peak on single mode fibers was previously only possible via custom made fibers. Our novel method offers the possibility of optimizing and improving the utilization of different fiber types in AQS‐FL systems. [ABSTRACT FROM AUTHOR]

We are reporting the design procedure for a narrow-band ultra-low-power reflective optical modulator that operates at the critical coupling of an appropriately designed two-dimensional grating with the center frequency of a quarter wavelength distributed Bragg reflector (DBR). By sandwiching a three-layer stack of gated ITO/HfO2/ITO between the DBR and the grating, we can make the optical modulator operational, taking advantage of the tunable property of the ultrathin layer at the ITO/HfO2 interface accumulated by electrons under an ultra-low applied voltage (−0.1 V). The corresponding energy consumption is ∼5.5 fJ/bit. Moreover, our simulations show that the capacitance limited modulation speed is more than 80 Mbps. Our numerical results also predict the influence of possible fabrication errors on the guided-mode resonance wavelength. This investigation shows that a ±3 nm deviation in the grating pitch affects the modulator performance profoundly. Furthermore, the numerical results demonstrate the modulation depth of ∼24 dB is achievable for an appropriately designed modulator with an acceptable insertion loss of ∼0.05 dB. This paper paves the way for developing next-generation optical modulators with high modulation depth, low insertion loss, and ultra-low energy consumption. [ABSTRACT FROM AUTHOR]

A new multiobjective optimization framework is presented for designing large mode area photonic crystal fibers (LMA-PCFs) with effective single-mode operation in the bent state. For optimizing the structure, we utilize the multiobjective gray wolf optimizer (MOGWO) to maximize the effective mode area (EMA) and the bending loss of higher order modes (HOMs), while minimizing the fundamental mode (FM) loss. The simulation results demonstrate that this framework enables us to improve the EMA by a factor of 1.26 and increase (decrease) the bending loss of the HOMs (the FM) by a factor of 7 (17), compared to the nonoptimal design. In addition, we investigate the dependence of the optical characteristics of the optimized LMA-PCFs on the wavelength and the bending radius. We found that some optimal structures are highly wavelength dependent and are not suitable for wideband applications. Furthermore, we found that the HOM loss is very sensitive to the bending radius. The proposed framework is comprehensive and can be employed to find a broad range of optimal designs for a wide range of applications. [ABSTRACT FROM AUTHOR]

In this paper, the gain, phase, and refractive index dynamics of photonic crystal quantum-dot semiconductor optical amplifiers (PC-QDSOAs) are investigated for the first time. For this purpose, we establish a comprehensive nonlinear state space model with 1088 state variables to simulate the carrier dynamics of the inhomogeneously broadened InAs/GaAs QD active region embedded in a flat-band slow-light photonic crystal waveguide. The gain and phase recovery responses are monitored during the amplification of an ultrashort pump pulse. Simulation results show that changes in refractive index in the PC-QDSOA active region are much stronger than the index changes in the conventional QDSOAs. In addition, the gain and phase recovery time in PC-QDSOAs are similar to those in the conventional QDSOAs based on ridge waveguide structures. Also, we found that the injected current and the consumed power in PC-QDSOAs can be two orders of magnitude less than those values in the conventional QDSOAs. [ABSTRACT FROM AUTHOR]

A novel design of electrically pumped photonic crystal quantum-dot semiconductor optical amplifiers (PC-QDSOAs) is presented in this paper. Therefore, we design a single-mode flat-band slow light photonic crystal waveguide (SL-PCW) for an InAs/GaAs QDSOA in which the pumping is done by passing a current through a laterally doped p+–p–n+ structure. In addition, for the first time to our knowledge, we propose a nonlinear state space model (NSSM) for PC-QDSOAs, in which the effects of the SL-PCW dispersion relation as well as the effects of the homogeneous and inhomogeneous broadenings of QDs are considered. To do so, the SL effects on the gain enhancement factor and increase of the optical losses are evaluated by considering the wavelength dependence of the modal confinement factor, the group index dispersion, and the SL-enhanced absorption and scattering losses in the SL-PCWs with QD active region. The gain saturation characteristics and modal gain spectra of the PC-QDSOA are investigated under different conditions including pump current and the amplifier length. Simulation results show that the SL-PCWs can be used to reduce the transparency current of the amplifier by a factor of 20 and even more compared with the conventional QDSOAs based on ridge waveguide structures, and enhance the net modal gain of the QD active region by a factor of two to six over a broad wavelength range of about 62 nm. We found that the power consumption of PC-QDSOAs can be decreased by a factor of about 100, and also the amplifier length can be reduced by a factor of five and beyond, compared with the conventional QDSOAs. The results of this paper are useful for many applications where low power consumption and small size of the optical amplifiers are important. [ABSTRACT FROM AUTHOR]

SUMMARY In this article, quantum-dot semiconductor optical amplifiers (QD-SOAs) have been modelled using state space method. To derive this model, we have manipulated the rate equation model of the QD-SOA, where the average values of the occupation probabilities along the QD-SOA cavity are considered as the state variables of the system. Using these variables, the distance dependence of the rate equations is eliminated. The derived state space model gives the optical gain and output signal of the amplifier with a high accuracy. Simulation results show that the derived model is not only much simpler and faster than conventional rate equation models, but also the optical gain and output signal of the investigated QD-SOA are calculated with a higher precision compared to the rate equation model. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A simple and accurate dynamic model for QD-SOAs is proposed. The proposed model is based on the state space theory, where by eliminating the distance dependence of the rate equation model of the QD-SOA; we derive a state space model for the device. A comparison is made between the rate equation model and the state space model under both steady state and transient regimes. Simulation results demonstrate that the derived state space model not only is much simpler and faster than the rate equation model, but also it is as accurate as the rate equation model. [ABSTRACT FROM AUTHOR]

In this paper, the effects of homogeneous and inhomogeneous broadenings on the response of quantumdot semiconductor optical amplifier (QD-SOAs) are investigated. For the first time, the state space model is used to simulate static and dynamic characteristics of the QD-SOA. It is found that with decreasing the homogeneous and inhomogeneous broadenings, the saturation power of the QD-SOA decreases and the optical gain and the ultrafast gain compression increase. Simulation results show that with decreasing the homogeneous broadening from 20 to 1 meV, the gain compression increases from 40% to 90%, the unsaturated optical gain becomes approximately tripled, and the saturation power becomes two times less. Also, simulations demonstrate that with decreasing the inhomogeneous broadening from 50 to 25 meV, the gain compression increases from less than 50% to more than 90%, the unsaturated optical gain becomes approximately 10-fold, and the saturation power becomes three times less. In addition, it is found that the homogeneous and inhomogeneous linewidths should be small for nonlinear applications. The homogeneous and inhomogeneous broadenings need to be large enough for linear applications. [ABSTRACT FROM AUTHOR]

Candida auris is an emerging fungal pathogen considered as a global health threat. Recently there has been growing concern regarding drug resistance, difficulty in identification, as well as problems with eradication. Although outbreaks have been reported throughout the globe including from several Arab countries, there were no previous reports from Lebanon. We herein report the first cases of C. auris infection from the American University of Beirut Medical Center, a tertiary care center in Lebanon describing the clinical features of the affected patients in addition to the infection control investigation and applied interventions to control the outbreak. Fourteen patients with C. auris infection/colonization identified using MALDI-TOF and VITEK 2- Compact system were reported over a period of 13 weeks. Patients were admitted to four separate critical care units. All of them came through the emergency room and had comorbid conditions. Half of the patients were infected with COVID-19 prior to isolation of the C. auris. C. auris was isolated from blood (two isolates), urine (three isolates), respiratory tract (10 isolates) and skin (one isolate). All the patients had received broad spectrum antibiotics prior to isolation of C. auris. Six patients received antifungal treatment, while the remaining eight patients were considered colonized. Environmental cultures were taken from all four units and failed to isolate the organism from any cultured surfaces. A series of interventions were initiated by the Infection Prevention and Control team to contain the outbreak. Rapid detection and reporting of cases are essential to prevent further hospital transmission. A national standardized infection control registry needs to be established to identify widespread colonization. [ABSTRACT FROM AUTHOR]