In line with Our World in Data analysts’ Internet user growth statistics, the exponential growth of user data and customer demands for high-quality data transmission speeds drive demand for next-generation (NG) access networks — fiber optic access networks with improved parameters. This paper evaluates the performance of (DB) and non-return to zero (NRZ) modulation formats widely spread in wavelength division multiplexed passive optical networks (WDM-PONs). Within wavelength division multiplexing (WDM) transmission systems, forward error correction methods have emerged as most indispensable techniques for enhancing data transmission reliability and bolstering service quality (QoS). The paper’s authors also compare different FEC codes, due to its abilities to attain the lowest bit error ratio (BER) as possible. Alongside FEC code utilization and digital equalization, methods enhance the performance of WDM-PON systems by smoothening the system’s imperfection. This paper studies the efficiency of WDM-PON systems with 8 and 16 channels by implementing FEC techniques such as Reed-Solomon (RS) with 6.69% and 8.5% overheads (OH). These codes are employed for long haul data transmission systems as described in ITU-T G.975 standardization. This paper evaluates the performance of 8 and 16-channel DB, and NRZ modulated WDM-PON transmission systems with 100 GHz spacing, each operating at data rates of 10, 20 and 40 Gbit/s (for each channel), utilizing ITU-T G.652 standardization-corresponding optical link section.

With the increasing demand for high-speed and bandwidth-intensive applications, the deployment of wavelength-division multiplexing passive optical network (WDM-PON) systems has gained significant traction. This work addresses the critical aspects of designing and maintaining rare-earth-doped fiber amplifiers (REDFAs) for WDM-PON transmission systems, focusing on optimizing performance, reliability, and ease of maintenance. The design phase involves meticulously exploring rare-earth-doped fibers, emphasising selecting dopants that enhance amplification efficiency and maintain signal integrity across multiple wavelengths. Experimental results and performance evaluations highlight the designed REDFA’s effectiveness in enhancing WDM-PON systems’ transmission capabilities. The findings advance the understanding of rare-earth-doped fiber amplifiers and provide practical guidelines for deploying and maintaining high-performance WDM-PON transmission systems in telecommunications networks. This research lays the foundation for more robust and efficient next-generation (NG) optical access networks capable of meeting the escalating demands of modern communication infrastructures. An experimental model of REDFA is tested in different conditions using a 16-channel non-return-to-zero (NRZ) modulated WDM-PON transmission system operated in C-band, where BER quality below 1×10 −9 is used as a threshold. Designed REDFA is realized with both co-propagation (980 nm) and counter-propagation (1480 nm) pump laser configuration to find optimal pumping laser parameters for the maximum performance of the optical communication system.

In this work lasers with pulse durations from mu s to fs were used to clean zinc heritage objects from atmospheric corrosion deposits. Wavelengths at 355, 532, 800, 1064 nm were tested. The surface was studied by Raman spectroscopy, Scanning electron microscopy, X-ray diffraction and optical microscopy. It was shown that for all lasers used there is no self-limiting cleaning effect, and the metal melting threshold is lower than the corrosion complete removal threshold. A femtosecond laser produces the least surface melting with 100 fs pulse duration, the shortest in this study. Yellowing of corrosion layers due to temperature modification of zincite was observed with irradiation by all lasers used.(c) 2023 Consiglio Nazionale delle Ricerche (CNR). Published by Elsevier Masson SAS. All rights reserved.

We study the Mie-like scattering from an open subwavelength resonator made of a high-index dielectric material, when its parameters are tuned to the regime of interfering resonances. We uncover a novel mechanism of superscattering, closely linked to strong coupling of the resonant modes and described by the physics of bound states in the continuum (BICs). We demonstrate that the enhanced scattering occurs due to constructive interference described by the Friedrich-Wintgen mechanism of interfering resonances, allowing to push the scattering cross section of a multipole resonance beyond the currently established limit. We develop a general non-Hermitian model to describe interfering resonances of the quasi-normal modes, and study subwavelength dielectric nonspherical resonators exhibiting avoided crossing resonances associated with quasi-BIC states. We confirm our theoretical findings by a scattering experiment conducted in the microwave frequency range. Our results reveal a new strategy to boost scattering from non-Hermitian systems, suggesting important implications for metadevices.

The first experimental results on the functioning of liquid crystal cells doped with CoFe2O4 nanoparticles are presented. Transmission spectra in the visible and near-infrared range, dynamic parameters of the Fredericks effect, refractive characteristics, as well as wetting angles of the mesophase sensitized surfaces have been obtained. The measured surfaces were the K8 Crown glass, the conductive ITO and the ITO treated with a surface electromagnetic wave. The experiment was performed in order to establish the prospect of using such reliefs as a novel liquid crystal composite orientator sensitized with CoFe2O4 nanoparticles. A color change of the liquid crystal matrix, its refractive coefficients alterations, and the variation of inclination angle of the sensitized liquid crystal droplets on the considered reliefs were established. The time reaction parameters and the medium relaxation parameters were measured. It was proposed that the liquid crystal composition is a kind of an immersion medium that preserves properties of the introduced nanoparticles, which expands their application scope in optoelectronics and biomedicine.

We consider the scattering of electromagnetic waves by non-spherical dielectric resonators and reveal that it can be linked to the exceptional points underpinned by the physics of non-Hermitian systems. We demonstrate how symmetry breaking in the shape of an isolated dielectric nanoparticle can be associated with the existence of an exceptional point in the eigenvalue spectrum and formulate the general conditions for the strong coupling of resonances, illustrating them for the example of the electric dipole and magnetic dipole modes supported by a silicon nanoparticle. We argue that any two modes of a dielectric nanoparticle can lead to an exceptional point provided their resonant frequencies cross as a function of a tuning parameter, such as, e.g. its aspect ratio, and their field distributions should have opposite signs after a reflection in the transverse plane of the structure. The coupled modes radiate as a mixture of electric and magnetic dipoles, which result in a strong magnetoelectric response, being easily controlled by the symmetry breaking perturbation. We also investigate the influence of a dielectric substrate, demonstrating how the latter provides an additional mechanism to tune the position of exceptional points in the parameter space. Finally, we discuss applications of magnetoelectric exceptional points for refractive index sensing.

Public road infrastructure is developed all around the world. To save resources, ensure public safety, and provide longer-lasting road infrastructure, structural health monitoring (SHM) applications for roads have to be researched and developed. Asphalt is one of the largest used surface materials for the road building industry. This material also provides relatively easy fiber optical sensor technology installment, which can be effectively used for SHM applications—road infrastructure monitoring as well as for resource optimization when road building or their repairs are planned. This article focuses on the research of the fiber Bragg grating (FBG) optical temperature and strain sensor applications in road SHM, which is part of the greater interdisciplinary research project started at the Riga Technical University in the year 2017. Experimental work described in this article was realized in one of the largest Latvian road sites where the FBG strain and temperature sensors were installed into asphalt pavement, and experiments were carried out in two main scenarios. Firstly, in a controlled environment with a calibrated falling weight deflectometer (FWD) to test the installed FBG sensors. Secondly, by evaluating the real-time traffic impact on the measured strain and temperature, where different types of vehicles passed the asphalt span in which the sensors were embedded. The findings in this research illustrate that by gathering and combining data from calibrated FWD measurements, measurements from embedded FBG optical sensors which were providing the essential information of how the pavement structure could sustain the load and information about the traffic intensity on the specific road section, and the structural life of the pavement can be evaluated and predicted. Thus, it enables the optimal pavement future design for necessary requirements and constraints as well as efficient use, maintenance, and timely repairs of the public roads, directly contributing to the overall safety of our transportation system.

Focused laser beams allow controlling mechanical motion of objects and can serve as a tool for assembling complex micro and nano structures in space. While in a vast majority of cases small particles experience attractive gradient forces and repulsive radiation pressure, introduction of additional degrees of freedom into optomechanical manipulation suggests approaching new capabilities. Here we analyze optical forces acting on a high refractive index silicon sphere in a focused Gaussian beam and reveal new regimes of particles anti-trapping. Multipolar analysis allows separating an optical force into interception and recoil components, which have a completely different physical nature resulting in different mechanical actions. In particular, interplaying interception radial forces and multipolar resonances within a particle can lead to either trapping or anti-trapping scenarios, depending of the overall system parameters. At the same time, the recoil force generates a significant azimuthal component along with an angular-dependent radial force. Those contribution enable enhancing either trapping or anti-trapping regimes and also introduce bending reactions. These effects are linked to the far-field multipole interference resulting and, specifically, to its asymmetric scattering diagrams. The later approach is extremely useful, as it allows assessing the nature of optomechanical motion by observing far-field patterns. Multipolar engineering of optical forces, being quite general approach, is not necessarily linked to simple spherical shapes and paves a way to new possibilities in microfluidic applications, including sorting and micro assembly of nontrivial volumetric geometries.

We uncover a novel mechanism for superscattering of subwavelength resonators closely associated with the physics of bound states in the continuum. We demonstrate that superscattering occurs as a consequence of constructive interference driven by the Friedrich-Wintgen mechanism, and it may exceed the currently established limits for the cross-section of a single open scattering channel, within the channel itself. We develop a non-Hermitian model to describe interfering resonances of quasi-normal modes to show that this effect can only occur for scatterers violating the spherical symmetry, and therefore it cannot be predicted with the classical Mie solutions. Our results reveal unusual physics of non-Hermitian systems having important implications for functional metadevices.

Modern nanophotonics has witnessed the rise of “electric anapoles” (EDAs), destructive interferences of electric and toroidal electric dipoles, actively exploited to resonantly decrease radiation from nanoresonators. However, the inherent duality in Maxwell equations suggests the intriguing possibility of “magnetic anapoles,” involving a nonradiating composition of a magnetic dipole and a magnetic toroidal dipole. Here, a hybrid anapole (HA) of mixed electric and magnetic character is predicted and observed experimentally via dark field spectroscopy, with all the dominant multipoles being suppressed by the toroidal terms in a nanocylinder. Breaking the spherical symmetry allows to overlap up to four anapoles stemming from different multipoles with just two tuning parameters. This effect is due to a symmetry‐allowed connection between the resonator multipolar response and its eigenstates. The authors delve into the physics of such current configurations in the stationary and transient regimes and explore new ultrafast phenomena arising at sub‐picosecond timescales, associated with the HA dynamics. The theoretical results allow the design of non‐Huygens metasurfaces featuring a dual functionality: perfect transparency in the stationary regime and controllable ultrashort pulse beatings in the transient. Besides offering significant advantages with respect to EDAs, HAs can play an essential role in developing the emerging field of ultrafast resonant phenomena.

In this paper we present results from the study of optical signal amplification using Raman assisted fiber optical parametric amplifier with considerable benefits for S-band telecommunication systems where the use of widely used erbium-doped fiber amplifier is limited. We have created detailed models and performed computer simulations of combined Raman and fiber optical parametric amplification in a 16-channel 40 Gbps/channel wavelength division multiplexed transmission system. Achieved gain bandwidth, as well as transmission system parameters-signal-to-noise ratio and bit-error-ratio-were analyzed by comparing the Raman assisted fiber optical parametric amplifier to the single pump fiber optical parametric amplifier. Results show that the 3 dB gain bandwidth in the case of combined amplification is up to 0.2 THz wider with 1.9 dB difference between the lowest and highest gain.

Unique and flexible properties of non-Hermitian photonic systems attract ever-increasing attention via delivering a whole bunch of novel optical effects and allowing for efficient tuning light-matter interactions on nano- and microscales. Together with an increasing demand for the fast and spatially compact methods of light governing, this peculiar approach paves a broad avenue to novel optical applications. Here, unifying the approaches of disordered metamaterials and non-Hermitian photonics, we propose a conceptually new and simple architecture driven by disordered loss-gain multilayers and, therefore, providing a powerful tool to control both the passage time and the wave-front shape of incident light with different switching times. For the first time we show the possibility to switch on and off kink formation by changing the level of disorder in the case of adiabatically raising wave fronts. At the same time, we deliver flexible tuning of the output intensity by using the nonlinear effect of loss and gain saturation. Since the disorder strength in our system can be conveniently controlled with the power of the external pump, our approach can be considered as a basis for different active photonic devices.

All-dielectric nanophotonics has become one of the most active fields of research in modern optics, largely due to the opportunities offered by the simultaneous resonant control of electric and magnetic components of light at the nanoscale. In this rapidly evolving scenario, the possibility to design artificial Huygens sources by overlapping electric and magnetic resonances has established a new paradigm in flat optics, bringing devices closer to efficient wavefront shaping with direct phase engineering at the level of the individual meta-atoms. However, their efficiency is fundamentally limited by the near-field coupling between the constituents of the metalattice. In this work, we challenge this well-conceived notion and propose an alternative concept to achieve phase control and full transmission in metasurfaces, based on the unusual properties of the nonradiating sources known as hybrid anapoles (HAs). We analyze theoretically an array of such sources and demonstrate that HAs are characterized by negligible coupling with their neighbors. Therefore, in contrast to Huygens particles, the proposed sources can operate as individual meta-atoms even in highly compact designs, becoming robust against strong disorder and preserving its characteristics when deposited on dielectric substrates. Remarkably, the phase of the transmitted wave can be modulated with negligible reflection. To illustrate the capabilities of our platform, we also utilize a disordered HA array to implement a controlled phase modulation to an ultrafast Gaussian pulse. The results of our study represent a departure from the currently established designs and open an avenue toward the realization of new devices for flat optics with unprecedented efficiency.

Bound states in the continuum (BICs) enable unique features in tailoring light-matter interaction on nanoscale. These radiationless localized states drive theoretically infinite quality factors and lifetimes for modern nanophotonics, making room for a variety of emerging applications. Here we use the peculiar properties possessed by the so-called $\mathcal{PT}$ symmetric optical structures to propose the novel mechanism for the quasi-BIC manifestation governed by the $\mathcal{PT}$ symmetry breaking. In particular, we study regularities of the spontaneous $\mathcal{PT}$ symmetry breaking in trilayer structures with the outer loss and gain layers consisting of materials with permittivity close to zero. We reveal singular points on the curves separating $\mathcal{PT}$ symmetric and broken-$\mathcal{PT}$ symmetry states in the parametric space of the light frequency and the angle of incidence. These singularities remarkably coincide with the BIC positions at the frequency of volume plasmon excitation, where the dielectric permittivity vanishes. The loss and gain value acts as an asymmetry parameter that disturbs conditions of the ideal BIC inducing the quasi-BIC. Fascinating properties of these quasi-BICs having ultrahigh quality factors and almost perfect transmission can be utilized in sensing, nonlinear optics, and other applications.

Structured environment controls dynamics of light-matter interaction processes via modified local density of electromagnetic states. In typical scenarios, where nanosecond-scale fluorescent processes are involved, mechanical conformational changes of the environment during the interaction processes can be safely neglected. However, slow decaying phosphorescent complexes (e.g., lanthanides) can efficiently probe micro- and millisecond scale motion via near-field interactions with nearby structures. As the result, lifetime statistics can inherit information about nanoscale mechanical motion. Here we study light-matter interaction dynamics of phosphorescent dyes, diffusing in a proximity of a plasmonic nanoantenna. The interplay between time-varying Purcell enhancement and stochastic motion of molecules is considered via a modified diffusion equation, and collective decay phenomena is analysed. Fluid properties, such as local temperature and diffusivity, are mapped on phosphorescent lifetime distribution and then extracted with the help of inverse Laplace transformation. The presented photonic platform enables performing contactless all-optical thermometry and diffusion measurements, paving a way for a range of possible applications. In particular, detailed studies of nanofluidic processes in lab-on-a-chip devices, challenging for analysis with other optical methods, can be performed with time-dependent phosphorescence.

The ever-growing field of microfluidics is currently in the need of a variety of controllable components to perform operations inside microchambers. Brand-new nanophotonic approaches can significantly enhance existing capabilities via light-matter interactions. We propose a novel concept featuring dual on-chip functionality: boosted optically-driven diffusion and sorting. Recently, well-designed high-index nanoantennae have been shown to mediate strong spin-orbit coupling from a laser beam, producing subwavelength optical nanovortices that drive spiral motion of absorbing nanoparticles (NPs) by means of scattering forces. In this work, we exploit further this idea and take the first step towards the realization of directional fluid navigation, investigating near field interactions of two optical nanovortices generated by a dielectric dimer structure.

Carefully designed nanostructures can inspire new type of optomechanical interactions and allow surpassing limitations set by classical diffractive optical elements. Apart from strong near-field localization, nanostructured environment allows controlling scattering channels and might tailor many-body interactions. Here we investigate an effect of optical binding, where several particles demonstrate a collective mechanical behaviour of bunching together in a light field. In contrary to classical binding, where separation distances between particles are diffraction limited, an auxiliary hyperbolic metasurface is shown here to break this barrier by introducing several controllable near-field interaction channels. Strong material dispersion of the hyperbolic metamaterial along with high spatial confinement of optical modes, which it supports, allow achieving superior tuning capabilities and efficient control over binding distances on the nanoscale. In addition, a careful choice of the metamaterial slabs thickness enables decreasing optical binding distances by orders of magnitude compared to free space scenarios due to the multiple reflections of volumetric modes from the substrate. Auxiliary tunable metamaterials, which allow controlling collective optomechanical interactions on the nanoscale, open a venue for new investigations including collective nanofluidic interactions, triggered bio-chemical reactions and many others.

The ever-growing field of microfluidics requires precise and flexible control over fluid flow at the micro- and nanoscales. Current constraints demand a variety of controllable components for performing different operations inside closed microchambers and microreactors. In this context, novel nanophotonic approaches can significantly enhance existing capabilities and provide new functionalities via finely tuned light-matter interaction mechanisms. Here we propose a novel design, featuring a dual functionality on-chip: boosted optically-driven particle diffusion and nanoparticle sorting. Our methodology is based on a specially designed high-index dielectric nanoantenna, which strongly enhances spin-orbit angular momentum transfer from an incident laser beam to the scattered field. As a result, exceptionally compact, subwavelength optical nanovortices are formed and drive spiral motion of peculiar plasmonic nanoparticles via the efficient interplay between curled spin optical forces and radiation pressure. The nanovortex size is an order of magnitude smaller than that provided by conventional beam-based approaches. The nanoparticles mediate nano-confined fluid motion enabling nanomixing without a need of moving bulk elements inside a microchamber. Moreover, precise sorting of gold nanoparticles, demanded for on-chip separation and filtering, can be achieved by exploiting the non-trivial dependence of the curled optical forces on the nanoobject size. Altogether, this study introduces a versatile platform for further miniaturization of moving-part-free, optically driven microfluidic chips for fast chemical synthesis and analysis, preparation of emulsions, or generation of chemical gradients with light-controlled navigation of nanoparticles, viruses or biomolecules.

The development of new approaches to tuning the resonant magnetic response of simple all-dielectric nanostructures is very important in modern nanophotonics. Here, it is shown that a resonant magnetic octupole (MOCT) response can be obtained by dividing a solid rectangular silicon block to a quadrumer structure with the introduction of narrow gaps between four nanocubes. The spectral position of the MOCT resonance is controlled and tuned by varying the distance between the nanocubes. It is demonstrated that several magnetic hot-spots related to the MOCT resonance can be located in the gaps creating a strong magnetic field gradient in free space. It is observed that the resonant excitation of the MOCT moment leads to a significant enhancement of light absorption in the system at the spectral region, where light absorption in bulk silicon is weak. The results of this work can be applied to design new composite antennas and metamaterials based on complex building blocks, energy harvesting devices, and molecular trapping with magnetic hot-spots.

Modern nanophotonics has witnessed the rise of "electric anapoles", destructive interferences of electric dipoles and toroidal electric dipoles, actively exploited to cancel electric dipole radiation from nanoresonators. However, the inherent duality of Maxwell's equations suggests the intriguing possibility of "magnetic anapoles", involving a nonradiating composition of a magnetic dipole and a magnetic toroidal dipole. Here, we predict, fabricate and observe experimentally via a series of dark field spectroscopy measurements a hybrid anapole of mixed electric and magnetic character, with all the dominant multipoles being suppressed by the toroidal terms in a nanocylinder. We delve into the physics of such exotic current configurations in the stationary and transient regimes and predict a number of ultrafast phenomena taking place within sub-ps times after the breakdown of the hybrid anapole. Based on the preceding theory, we design a non-Huygens metasurface featuring a dual functionality: perfect transparency in the stationary regime and controllable ultrashort pulse beatings in the transient.