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A two‐mode optical packet switching architecture using an optical multiport mode‐division multiplexing label generator and processor is proposed. By combining optical labels on two modes, the number of labels is increased exponentially. Beat noise significantly affects the label error rate, when multimode crosstalk is maximum. This impairment can be mitigated by time shifting the optical labels of the two modes by half of the label duration. [ABSTRACT FROM AUTHOR]

Gram staining differentiates bacteria as gram‐positive and gram‐negative, depending on their cell wall constituents, and coloring cells in violet and pink, respectively. Sometimes, a subpopulation of the same bacterial species assumes different colors, ranging from pink to violet, for reasons that are not completely understood yet. We analyze conventional brightfield images and use an automated pipeline to count pink and violet cells. The ImageJ‐based processing algorithm quantifies the gram variability in Acinetobacter baumannii ACICU in the stationary phase of growth with a percentage of 66% pink cells. Different bacterial strains and cell growth stages have been considered. Research Highlights: Gram staining differentiates bacteria into gram‐positive (violet) and gram‐negative (pink). Gram variability represents an inhomogeneous distribution of pink and violet cells within the same species. We developed an ImageJ‐based pipeline for the quantification of Gram variability in Acinetobacter baumannii. [ABSTRACT FROM AUTHOR]

The spread of Acinetobacter baumannii in clinical settings is a great concern at the time being, given the epidemic potential and the capacity to elude the effects of drugs of this bacterial species. How A. baumannii achieves its resistance determinants is not yet exactly understood, hence the need for new studies aimed at resolving its structure and functions. In this work, we employ Re-scan Confocal Microscopy (RCM), an emerging super-resolution technique, for investigating the morphology of this pathogen. Interestingly, about 1.5% of the imaged cells were found to be filamentous without internal division septa, in both logarithmic and stationary phases, which, to our knowledge, has not been previously reported. Since filamenting represents one of the first mechanisms adopted by bacteria to resist antibiotic effects, we also focus on evaluating the sensitivity of A. baumannii to colistin. For this, the LIVE/DEAD ratio is assessed by means of a fluorometric approach based on SYTO9 and KK114 dyes, two stains that we also used for RCM imaging. Their dual role demonstrated here can potentially be exploited in-tandem in multimodal systems for imaging and fluorometry. [ABSTRACT FROM AUTHOR]

A polarization multiplexed all-optical orthogonal frequency division multiplexing (AO-OFDM) system is investigated analytically and numerically, with 12.5 Gbaud symbol rate, that is compatible with the International Telecommunication Union flexible grid. We demonstrate that fast adaptive filtering is not require at the receiver and chromatic dispersion with polarization mode dispersion can be compensated without the cyclic prefix insertion, with the maximum spectral efficiency by using proper optical filter. System performance are numerically and analytically evaluated considering nonlinear effects and power consumption, evidencing a good agreement between the theoretical model and numerical results. We compare AO-OFDM performance with coherent OFDM scheme using the derived theoretical formula and numerical results. 21 subcarriers are investigated with quadrature phase shift keying modulation and 7 subcarriers in case of 16-quadrature amplitude modulation, with a total capacity of 976.5 Gb/s and 651 Gb/s, respectively, considering 7% forward error correction overhead. [ABSTRACT FROM AUTHOR]

Background In recent years, a variety of imaging techniques operating at nanoscale resolution have been reported. These techniques have the potential to enrich our understanding of bacterial species relevant to human health, such as antibiotic-resistant pathogens. However, owing to the novelty of these techniques, their use is still confined to addressing very particular applications, and their availability is limited owing to associated costs and required expertise. Among these, scattering-type scanning near field optical microscopy (s-SNOM) has been demonstrated as a powerful tool for exploring important optical properties at nanoscale resolution, depending only on the size of a sharp tip. Despite its huge potential to resolve aspects that cannot be tackled otherwise, the penetration of s-SNOM into the life sciences is still proceeding at a slow pace for the aforementioned reasons. Results In this work we introduce SSNOMBACTER, a set of s-SNOM images collected on 15 bacterial species. These come accompanied by registered Atomic Force Microscopy images, which are useful for placing nanoscale optical information in a relevant topographic context. Conclusions The proposed dataset aims to augment the popularity of s-SNOM and for accelerating its penetration in life sciences. Furthermore, we consider this dataset to be useful for the development and benchmarking of image analysis tools dedicated to s-SNOM imaging, which are scarce, despite the high need. In this latter context we discuss a series of image processing and analysis applications where SSNOMBACTER could be of help. [ABSTRACT FROM AUTHOR]

Super‐resolution microscopy techniques can provide answers to still pending questions on prokaryotic organisms but are yet to be used at their full potential for this purpose. To address this, we evaluate the ability of the rhodamine‐like KK114 dye to label various types of bacteria, to enable imaging of fine structural details with stimulated emission depletion microscopy (STED). We assessed fluorescent labeling with KK114 for eleven Gram‐positive and Gram‐negative bacterial species and observed that this contrast agent binds to their cell membranes. Significant differences in the labeling outputs were noticed across the tested bacterial species, but importantly, KK114‐staining allowed the observation of subtle nanometric cell details in some cases. For example, a helix pattern resembling a cytoskeleton arrangement was detected in Bacillus subtilis. Furthermore, we found that KK114 easily penetrates the membrane of bacterial microorganism that lost their viability, which can be useful to discriminate between living and dead cells. [ABSTRACT FROM AUTHOR]

Two new arrayed waveguide grating (AWG) architectures are presented, for flat-top multiplexing and for the generation of Nyquist sinc-shaped optical pulses. We demonstrate that an AWG, with a number of grating arms double with respect to a conventional configuration, and an input y-branch, is equivalent to a synchronized router, composed of a Mach–Zehnder interferometer and an AWG in tandem. The proposed device is more compact, with reduced losses and dispersion sensitivity, and a more flat-top frequency behavior. To generate and process a sinc-shaped optical pulse train, a new AWG is used, that implements the fractional Fourier transform (FrFT), followed by a dispersion compensating fiber. We use the time-lens effect and the chirped modulation introduced by a fully passive FrFT-AWG to optically transform a sinc -shaped transfer function into a sinc-shaped impulse response, and vice versa. Detailed AWG design guidelines for wavelength division multiplexing and orthogonal frequency division multiplexing multiplexing are also provided, evidencing the different roles played by the two slab couplers, in a signal processing framework. [ABSTRACT FROM PUBLISHER]

We present the design guidelines for novel passive arrayed waveguide grating (AWG) devices to all-optically implement time-frequency packing techniques in orthogonal frequency division multiplexing (OFDM) systems. The proposed approach can increase the spectral efficiency in long-haul fiber links. We analyze the system performances, evaluating the maximum achievable information rate and spectral efficiency, and we found the optimal AWG layout to maximize the overall system capacity. We demonstrate, through simulations, that an overall 1.4 Tb/s transmission over 200 GHz bandwidth can be reached, using two polarizations, quadrature phase shift keying modulation, and digital feedback equalization. [ABSTRACT FROM PUBLISHER]

We propose and experiment a novel asynchronous 10G-passive optical network (PON) system based on optical code division multiplexing (OCDM), where a set of cascaded multiport encoder/decoders (E/Ds) are used in the remote node to suppress multiple access interference (MAI) noise. We demonstrate that the proposed configuration drastically suppresses both MAI and coherent beat noises in a fully asynchronous 160 Gb/s (10 Gb/s × 16 optical network units) PON. We also demonstrate the transmission of an OCDM signal with spectral efficiency 12.5 GHz/code, over a 50-km link without dispersion compensation. [ABSTRACT FROM PUBLISHER]

We propose an energy efficient optical code (OC) receiver, based on a RAKE configuration, using a single passive multiport encoder/decoder (E/D). We numerically demonstrate the crosstalk signals are used to enhance the energy efficiency and the label recognition performance, using only a combiner and optical delay lines (ODL), without any additional photo detector (PD). We numerically analyze the system performance and experimentally investigate the influence of the beat noise, that can be eliminated. [ABSTRACT FROM PUBLISHER]

We present a recursive approach to implement the Discrete Hartley Transform in the optical domain by using a passive fiber network of asymmetric couplers, without phase shifters. The optical implementation of Discrete Cosine Transform is also derived, resulting in effective and flexible tools for optical data compression and signal processing. [ABSTRACT FROM AUTHOR]

We demonstrate that fast tunable optical switches and tunable slow-light devices can be designed as optical cavities entangled with quantum dots. We derive the analytical conditions for switching and tuning the filter transmittance, considering both dipole-induced transparency and electromagnetic-induced transparency effects. [ABSTRACT FROM AUTHOR]

Polarization gratings are nondepolarizing polarization elements that alter the polarization state of the transmitted light in a periodic way, yielding a polarization-dependent diffraction. Using both the Jones and Stokes formalisms, we demonstrate that the polarization states of the higher order waves do not depend on the polarization state of the incoming light and that they are fully characterized by the polarization grating vector. We furnish a general model for polarization gratings that can be advantageously used for their design and show that a chain of three polarization gratings is a achromatic in-line polarimeter. In addition, we show that polarization gratings can be used as a tool to measure polarization mode dispersion. [ABSTRACT FROM AUTHOR]

Propagation-invariant electromagnetic beams, propagating along the optical axis of a uniaxially anisotropic crystal, are investigated. The beams are a superposition of propagation-invariant ordinary and extraordinary fields, with different polarizations states and Bessel profiles. The analytical expression of the Poynting vector reveals an azimuthal transverse energy flow that becomes pure longitudinal, if the complex amplitudes of the ordinary and extraordinary fields are either in phase or in phase opposition. [ABSTRACT FROM AUTHOR]

Evaluates the discrete Fourier transform (DFT) of linear array using asymmetric optical couplers. Measurement of power coupling ratio; Usefulness of DFT in optical communications systems; Importance in subband filtering.

Addresses the window design problem of linear arrays to be used in wide-band beamforming systems. Beam pattern formulations; Optimization procedure; Results with the first beam pattern formulation.

Investigates the diffraction properties of Hermite-Gaussian beams in uniaxially anisotropic crystal. Propagation of Gaussian beams along the optical axis; Effects of the anisotropy on the diffraction properties of beams; Identification of the superposition of Hermite-Gauss modes.

Presents information on a study which proposed a tissue spectral imaging technique based on the wavelet packets decomposition for a frequency decomposition (FD) of ultrasound images. Properties of Wavelet Transform; Evaluation of the performances of the proposed FD method; Lesion contrast enhancement with frequency compounding; Conclusions.

Proposes an optimization method for linear arrays to be used in ultrasound systems under wide-band operation. Description of the optimization algorithm; Optimization of a dense linear array; Weight distribution of the optimized arrays.

Presents a study which examined the effect of the human body attenuation on the performances of transducer arrays. Computational approach used; Numerical results; Conclusion.