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Set-Membership Filter (SMF) has been extensively studied for state estimation in the presence of bounded noises with unknown statistics. Since it was first introduced in the 1960s, the studies on SMF have used the set-based description as its mathematical framework. One important issue that has been overlooked is the optimality of SMF. In this work, we put forward a new mathematical framework for SMF using concepts of uncertain variables. We first establish two basic properties of uncertain variables, namely, the law of total range (a non-stochastic version of the law of total probability) and the equivalent Bayes' rule. This enables us to put forward a general SMFing framework with established optimality. Furthermore, we obtain the optimal SMF under a non-stochastic Markov condition, which is shown to be fundamentally equivalent to the Bayes filter. Note that the classical SMF in the literature is only equivalent to the optimal SMF we obtained under the non-stochastic Markov condition. When this condition is violated, we show that the classical SMF is not optimal and it only gives an outer bound on the optimal estimation., 8 pages, 3 figures

Plasmon resonance is the resonant oscillation of conduction electrons at the interface between negative and positive permittivity material stimulated by incident light, which forms the fundamental basis of many cutting-edge industrial applications. We are concerned with the quantitative theoretical understanding of this peculiar resonance phenomenon. It is known that the occurrence of plasmon resonance as well as its quantitative behaviours critically depend on the geometry of the material structure, the corresponding material parameters and the operating wave frequency, which are delicately coupled together. In this paper, we study the plasmon resonance for a 2D nanorod structure, which presents an anisotropic geometry and arises in the transverse electromagnetic scattering. We present delicate spectral and asymptotic analysis to establish the accurate resonant conditions as well as sharply characterize the quantitative behaviours of the resonant field., 26 pages

This work focuses on the design improvement of the long-short blades (LSB) impeller by using pitched short blades (SBs) to regulate the flow field in the stirred vessel. After mesh size evaluation and velocity field validation by the particle image velocimetry, large eddy simulation method coupled with sliding mesh approach was used to study the effect of the pitched SBs on the flow characteristics. We changed the inclined angles of the SBs from 30° to 60° and compared the flow characteristics when the impeller was operated in the down-pumping and up-pumping modes. In the case of down-pumping mode, the power number is relatively smaller and vortexes below the SBs are suppressed, leading to turbulence intensification in the bottom of the vessel. Whereas in the case of up-pumping mode, the axial flow rate in the center increased significantly with bigger power number, resulting in more efficient mass exchange between the axial and radial flows in the whole vessel. The LSB with 45° inclined angle of the SBs in the up-pumping mode has the most uniform distributions of flow field and turbulent kinetic energy compared with other impeller configurations.

The optical Bloch oscillation (OBO) is an optical-quantum analogy effect that is significant for light field manipulations, such as light beam localization, oscillation and tunneling. As an intra-band oscillation, OBO was important for optical investigations in photonic lattices and atomic vapors over an extended period of time. However, OBO in reconfigurable platforms is still an open topic, even though tunability is highly desired in developing modern photonic techniques. Here we theoretically establish and experimentally demonstrate OBO in an electromagnetically induced photonic lattice with a ramping refractive index, established in a coherently-prepared three-level 85Rb atomic vapor under the electromagnetically induced transparency condition. This is achieved by interfering two coupling beams with Gaussian profiles and launching a probe beam that exhibits OBO within the resulting lattice. The induced reconfigurable photonic lattice possesses a transverse gradient, due to the innate edges of Gaussian beams, and sets a new stage for guiding the flow of light in periodic photonic environments. Our results should motivate better understanding of peculiar physical properties of an intriguing quantum-optical analogy in an atomic setting.

The traditional ways of tuning a silicon photonic network are mainly based on the thermo-optic effect or the free carrier dispersion. The drawbacks of these methods are the volatile nature and the extremely small change in the complex refractive index (Δn

The performance of silicon photonic components and integrated circuits has improved dramatically in recent years. As a key enabler, heterogeneous integration not only provides the optical gain which is absent from native Si substrates and enables complete photonic functionalities on chip, but also lays the foundation of versatile integrated photonic device performance engineering. This paper reviews recent progress of high-performance silicon photonics using heterogeneous integration, with emphasis on ultra-low-loss waveguides, single-wavelength lasers, comb lasers, and photonic integrated circuits including optical phased arrays for LiDAR and optical transceivers for datacenter interconnects.

A typical Fabry–Pérot diode laser is used to study the relationship between the laser spectrum and the interference signal obtained from a Michelson interferometer. The interference signal is measured over a range of path length differences of a few centimeters, and the laser spectrum is obtained with a spectrometer of a high resolution of 0.005 nm. Contrary to the laser datasheet, the laser is found to have several longitudinal modes even at high injection currents well above the threshold current. A simple model based on treating the laser's longitudinal modes as pure sinusoidal waves is derived and successfully used in modeling the complex and repetitive interference signal. The spectral spacing and the laser cavity length can be found from the interference signal without the need to use a spectrometer, provided that the interference signal is measured over a long enough range of path length differences.

Experimental data for the generation of optical frequency combs in magnesium fluoride microcavities with whispering gallery modes at 780 nm are presented. This wavelength corresponds to the normal group velocity dispersion for pumping by a laser diode operating in self-injection locking regime. It is shown that the excitation of frequency combs is caused both by the processes in the microresonator and by the processes in the laser diode. It is found that, in the self-injection locking regime, initially suppressed, longitudinal modes of the laser diode can be amplified, which leads to the generation of hybrid, laser-enhanced side components. As a result, combs with a highly effective conversion of pumping energy and a low level of phase noise are excited.

Graphene with tunable thermo-mechanical property is of great importance for next-generation thermal management devices. Distinct from previously reported porous graphene materials that tune the thermal conductivity at the cost of degrading their mechanical properties, non-porous hydrogenated graphene origami metamaterial exhibits a unique combination of tunable thermal conductivity, high strength, and enhanced stretchability. Through molecular dynamics simulation, an extremely broad range of thermal conductivity can be obtained by tuning the geometrical parameters of the Miura-ori nanoarchitecture of graphene origami, altering the adatom types and density, designing new origami patterns, and applying mechanical strains. By analyzing and comparing the results from atomistic and continuum-based simulations, the effect of length scale on the thermal property of graphene origami metamaterials is explored. The temperature distribution and the phonon density of states of the proposed graphene origami are examined to illustrate the heat conduction mechanism. Finally, 3D graphene origami metamaterials are constructed based on the coupling and assembling of graphene origami strips, and their thermo-mechanical performance is elucidated. Negative coefficients of thermal expansion are obtained in graphene origami nanotubes. The introduced strategy for controlling the thermo-mechanical properties of graphene metamaterials can open up new avenues for developing thermoelectric devices, heat management systems, and flexible nanoelectronics.

Photons (Solar) are the main source of energy available on Earth and provide hope of clean energy in the future, photon energy has particle characteristics, and there is an inevitable connection between the wave behavior and the particle behavior of light, in-depth understanding and exploration are required. Based on the hypothesis of the strong interaction between electrons and protons to generate photons, the energy and behaviors of photons are discussed herein. By analyzing and calculating the photon speed, the negative photon speed was found to be in excellent agreement with the existing light speed constant. The Compton effect wavelength shift was analyzed and deduced considering the interaction of positive photons and atoms, and new conclusions are drawn, proposing the reason why X-rays are positive photons. Based on existing data, the observed estimation value of the negative photon velocity shift is 0.0295 ppm. From the interaction of the spin-charged particles, the relationship between the photon wavelength and its magnetic moment was calculated. In addition, we analyzed and calculated the characteristics of photon orbits, inferred the mechanism of atomic luminescence, and qualitatively explained the phenomenon of blackbody radiation. Based on the effect of charged spin photons and the electromagnetic potential field, we explain the reason for the simultaneous existence of reflection and refraction. The relationship between the incident angle and the reflectivity was analyzed, and refractive index formulas were derived to reasonably explain the characteristics of the X-ray refractive index. As a result, edge diffraction is considered a special case of refraction. By analyzing the fluctuation of the potential field inside the atom, the diffraction phenomenon of charged particles is described, and a particle explanation of the phenomenon of light waves and beat frequencies interference is provided. It is believed that the physical model of photon charging conforms to the existing physical laws. Photon energy is kinetic energy and is derived from the potential energy of electrons or protons.

This work aims to present and discuss a complete model for the analysis of compound solar sail performance for the simple solar photon thruster configuration. A nonideal formulation of the problem ...

A numerical simulation model has been established to obtain the deformation, strain and stress concentration of slab narrow side. The simulated temperature profiles of slab show a agreement with the results of measured temperatures by using infrared thermal camera. Moreover, the deformation, stress and strain of the slab have been investigated systematically, especially at the slab narrow side along the thickness direction. The relationship between the reduction amount and deformation, stress and strain concentration of slab narrow face has been investigated.

The bulge deformation of slab narrow face can cause surface defects of hot rolled steel plate. A three-dimensional bulging model, was proposed to simulate the evolution of deformation behavior of the continuous casting slab during heavy reduction (HR). The model was taken to investigate the non-uniform deformation of slab during HR process. The bulging deformation behavior of the slab was then calculated in one segment included seven pairs of rollers. To improve the edge defect on hot-rolled steel plates, the relationship between the reduction amount and bulge deformation of slab narrow face has been investigated.

The dye laser analysis depends on the gain equation that contains cross sections of the relevant emission and absorption molecular transitions involved in the lasing process. The absorption cross-section σs (v) is directly related to the absorbance curves of the dye. The emission cross-section σem (v) has been derived in terms of directly measurable spectroscopic quantities. The low frequency tail of the absorption curves is minutely diminishing for very dilute solutions(~=10-5 mole/lit) usually used in laser system. This low frequency tail overlaps the operating frequency band of the laser. The linear dependence of the dye absorption on the dye concentration (Beer- Lambert law), is used to solve the low frequency tail problem. The intrinsic gain characteristics are calculated for the dye Rhodamine "B" and the results are in good agreement with the rep orted experimental results.

We present an experimental investigation of vibrational strong coupling of C=O bonds in poly(methyl methacrylate) to surface lattice resonances (SLRs) on arrays of gold particles in infrared and Raman spectra. SLRs are generated from the enhanced radiative coupling of localized resonances in single particles by diffraction in the array. Compared to previous studies in Fabry-Perot cavities, particle arrays provide a fully open system that easily couples with external radiation while having large field confinement close to the array. We control the coupling by tuning the period of the array, as evidenced by the splitting of the C=O vibration resonance in the lower and upper vibro-polaritons of the IR extinction spectra. Despite clear evidence of vibrational strong coupling in IR transmission spectra, both Raman spectroscopy and micro-Raman mapping do not show any polariton signatures. Our results suggest that the search for vibrational strong coupling in Raman spectra may need alternative cavity designs or a different experimental approach.

Retroreflectors that can accurately redirect the incident waves in free space back along their original channels provide unprecedented opportunities for light manipulation. However, to the best of our knowledge, they suffer from either the bulky size, narrow angular bandwidths, or time-consuming postprocessing, which essentially limits their further applications. Here, a scheme for designing ultrathin all-angle real-time retroreflectors based on hyperbolic plasmonic metasurfaces is proposed and experimentally demonstrated. The physical mechanism underlying the scheme is the orthogonality between the traveling waves in free space and the canalized spoof surface plasmon on the hyperbolic plasmonic metasurfaces, which guarantee their high-efficiency and all-angle mutual conversion. In this case, the strong confinement characteristic that benefited from the enhanced light-matter interaction enables us to route and retroreflect the canalized spoof surface plasmon with extremely thin structures. As proof of the scheme, a retroreflector prototype with a thickness approximately equal to the central wavelength is designed and fabricated. Further experimental investigation obtains a half-power field of view up to 53° and a maximum efficiency of 83.2%. This scheme can find promising applications in target detection, remote sensing, and diverse on-chip light control devices.

An electromagnetic short laser pulse is considered as amplitude modulated in time. To study the advancement of amplitude-modulated short laser pulses in a plasma, we preformed numerical modelling using time-dependent generalized nonlinear Schrödinger wave equation. This analysis is limited to one-dimensional geometry, as the transverse profile is considered as uniform. Paraxial like approach is used to derive dimensionless nonlinear pulse-compression parameter equation. The effect of amplitude modulation on nonlinear compression is studied. A significant enhancement in laser intensity is observed due to the amplitude modulation of the electromagnetic pulse. We observe about 50% increase in laser intensity as compared to the unmodulated laser pulse. Our results may be useful in the clean and affordable energy goal of sustainable development goals.

Surfactant-free nontoxic Au-Ag alloy nanoparticles were synthesized via re-irradiation of laser generated mono metallic colloidal mixtures with 532 nm radiations from Nd: YAG nanosecond laser. The impact of re-irradiating laser energy in alloy formation kinetics was investigated. The alloy formation process was analyzed with UV-Visible absorption spectra at different time intervals of laser irradiation. The generated nanoparticles were characterized with dynamic light scattering size analysis, zeta potential studies, and HRTEM imaging. Photothermal properties of the samples were investigated employing thermal lens method. Alloy formation became faster with a slight blue shift in the plasmonic band wavelength with increase in irradiation energy. Reduction in nanoparticle size and stability were also observed at high irradiation energies.

We have designed one dimensional photonic crystals of Silica /Metal oxides (Alumina and ZnO), Silica/Graphite oxide on DNA template and investigated their optical responses in the 200 -2000 nm region of electromagnetic wave spectra theoretically using transfer matrix method (TMM). It is observed that in the presence of DNA template, the number, width and position of the photonic band gap are changed significantly. These results point that DNA templated proposed photonic crystals can be used for tuning the bandgap for desired spectra. This feature of DNA templated photonic crystals can be used for enhancing the transmission properties of photonic crystals. By tuning the bandgap effect for the desired frequency, the DNA templated photonic crystals can be applied for sensing the biomarkers. The theoretical results show that the DNA templated Silica based photonic crystals will be a promise for cost effective and fast responding label free biosensing applications.

Optical fiber is a glass or plastic like wired structure used to transmit information in the form of optical signal from transmitter to receiver end. Whenever we talk about any communication system, we always look over losses. This paper is focused on dispersion loss and how to reduce it. When the pulses travel through optical fiber, after travelling some distance, each pulses start spreading and overlaps with each other and leads to dispersion loss. A phenomenon in which the optical signal gets spread into different colors, each color has its own wavelength and respectively each wavelength travels in different velocity, which cause time delay, and this leads to chromatic dispersion. This paper analyzed the optical fiber performance and reduced dispersion loss in fiber by taking various of FBG function and grating length into consideration. The performance of FBG examined in terms of bit error rate, quality factor value in eye height.

Robustly manipulating waves on subwavelength scales can be achieved by, first, designing a structure with a subwavelength band gap and, second, introducing a defect so that eigenfrequencies fall within the band gap. Such frequencies are well known to correspond to localized modes. We study a one-dimensional array of subwavelength resonators, prove that there is a subwavelength band gap, and show that by introducing a dislocation we can place localized modes at any point within the band gap. We complement this analysis by studying the stability properties of the corresponding finite array of resonators, demonstrating the value of being able to customize the position of eigenvalues within the band gap., Journal of the London Mathematical Society, 106 (3), ISSN:0024-6107, ISSN:1469-7750

Polaritons in polar biaxial crystals with extreme anisotropy offer a promising route to manipulate nanoscale light-matter interactions. The dynamical modulation of their dispersion is great significance for future integrated nano-optics but remains challenging. Here, we report a momentum-directed strategy, a coupling between the modes with extra momentum supported by the interface and in-plane hyperbolic polaritons, to tailor topological transitions of anisotropic polaritons in biaxial crystals. We experimentally demonstrate such tailored polaritons at the interface of heterostructures between graphene and {\alpha}-phase molybdenum trioxide ({\alpha}-MoO3). The interlayer coupling can be electrically modulated by changing the Fermi level in graphene, enabling a dynamic topological transition. More interestingly, we found that the topological transition occurs at a constant Fermi level when tuning the thickness of {\alpha}-MoO3. The momentum-directed strategy implemented by interface engineering offers new insights for optical topological transitions, which may shed new light for programmable polaritonics, energy transfer and neuromorphic photonics.

Optical microresonators with low quality factor ( Q $Q$ ) can be efficiently excited by and scatter freely propagating optical waves, but those with high Q $Q$ typically cannot. Here, we present a universal model for resonators interacting with freely propagating waves and show that the stored energy of a resonator excited by a plane wave is proportional to the product of its Q $Q$ and directivity. Guided by this result, we devise a microdisk with periodic protrusions in its circumference that couples efficiently to normally incident plane waves. We experimentally demonstrate several microdisk designs, including one with a radius of 0.75 λ 0 ${\lambda }_{0}$ and Q $Q$ of 15,000. Our observation of thermally-induced bistability in this resonator at input powers as low as 0.7 mW confirms strong excitation. Their small footprints and mode volumes and the simplicity of their excitation and fabrication make wavelength-scale, free-space-coupled microdisks attractive for sensing, enhancing emission and nonlinearity, and as micro-laser cavities.

Generation of PP and PS angle gathers for elastic reverse time migration (ERTM) has important applications in velocity model updating and subsurface parameter inversion. The Poynting-vector-based method provides a cost-effective way to extract angle gathers from ERTM. However, the estimated propagation directions or angles based on Poynting vectors at or near zero points are unstable, and the reflection energy at these points is likely to be placed in an incorrect angle bin. This instability problem severely limits its use in the generation of high-quality angle gathers. To overcome this problem, we add the conventional Poynting vector with an ancillary one of the Hilbert transformed wavefield, a 90° phase-shifted version of the original wavefield. The Poynting vector of the Hilbert transformed wavefield points in the same propagation direction as the conventional Poynting vector, but they have different zero-point distributions. Adding them together allows us to obtain a stabilized Poynting vector which thoroughly eliminates the zero points within the wave propagation range, and thus we obtain a stable algorithm to extract high-quality angle gathers from ERTM. The Hilbert transformed wavefield already exists in the P/S and up/down wavefield decomposition procedure, which has become a necessary step for ERTM to separate overlapping wavefields at reflectors before the computation of Poynting vectors. Results from two synthetic numerical examples indicate the effectiveness of our method in generating high-quality angle gathers for ERTM.

Discovery of low-dimensional materials has been of great interest in physics and material science. Optical permittivity is an optical fingerprint of material electronic structures, and thus it is an important parameter in the study of the properties of materials. Spectroscopic ellipsometry provides a fast, robust, and noninvasive method for obtaining the optical permittivity spectra of newly discovered materials. Atomically thin low-dimensional materials have an extremely short vertical optical path length inside them, making the spectroscopic ellipsometry of low-dimensional materials unique, compared to traditional ellipsometry. Here, we introduce the fundamentals of spectroscopic ellipsometry for two-dimensional (2D) materials and review recent progress. We also discuss technical challenges and future directions in spectroscopic ellipsometry for low-dimensional materials.

In this paper, we demonstrate that multiple tapers in optical fibers allow for quasi-distributed refractive index sensing via a high spatial resolution Brillouin Optical Frequency-Domain Analysis (BOFDA) configuration. We first characterize, theoretically and experimentally, the variation of the Brillouin frequency shift (BFS) with the diameter of the tapered fiber. Then, we characterize the dependence of the BFS from the outer refractive index in an optical fiber taper with a waist diameter of 10 micron. Finally, we show that more tapers can be realized along the same fiber, in order to provide multi-point refractive index sensing.

Silicene, a zero-gap semi-metallic advanced material, has received much attention due to its extraordinary electronic and optical characteristics, which could be used in plasmonics nano-devices. This material presenting as a tunable material without degrading its high carrier mobility. By applying the rigorous numerical techniques, the optical and electrical properties of silicene at high terahertz frequencies are calculated here. Beneath the influence of environmental effects such as the Fermi level, temperature, and external electric field, on the optical conductivity and refractive index of silicene are investigated using the tight-binding model. The effect of Fermi level from zero to 1 eV, external electric field from zero to 2.5 eV, and temperature from 5 to 400 K are investigated on the optical properties of silicene. One of the interesting features of Silicene is its adjustable bandgap, which we are present here.

Geometric arrays of vortices found in various systems owe their regular structure to mutual interactions within a confined system. In optics, such vortex crystals may form spontaneously within a resonator. Their crystallization is relevant in many areas of physics, although their usefulness is limited by the lack of control over their topology. On the other hand, programmable devices like spatial light modulators allow the design of nearly arbitrary vortex distributions but without any intrinsic evolution. By combining non-Hermitian optics with on-demand topological transformations enabled by metasurfaces, we report a solid-state laser that generates 10 × 10 vortex laser arrays with actively tunable topologies and non-local coupling dictated by the array’s topology. The vortex arrays exhibit sharp Bragg diffraction peaks, witnessing their coherence and topological charge purity, which we spatially resolve over the whole lattice by introducing a parallelized analysis technique. By structuring light at the source, we enable complex transformations that allow to arbitrarily partition orbital angular momentum within the cavity and to heal topological charge defects, thus realizing robust and versatile resonators for applications in topological optics.

Hong–Ou–Mandel (HOM) interference—the bunching of indistinguishable photons at a beamsplitter—is a staple of quantum optics and lies at the heart of many quantum sensing approaches and recent optical quantum computers. Here we report a full-field, scan-free quantum imaging technique that exploits HOM interference to reconstruct the surface depth profile of transparent samples. We demonstrate the ability to retrieve images with micrometre-scale depth features with photon flux as small as seven photon pairs per frame. Using a single-photon avalanche diode camera, we measure both bunched and anti-bunched photon-pair distributions at the output of an HOM interferometer, which are combined to provide a lower-noise image of the sample. This approach demonstrates the possibility of HOM microscopy as a tool for the label-free imaging of transparent samples in the very low photon regime.

A waveguide power divider based on ridge waveguide to microstrip line transition is presented in this paper. To improve the isolation performance, a probe insulator is inserted into the contact face from the center of the waveguide side wall, also two chip resistors are mounted on a planar substrate and connected with the probe to absorb the coupled energy. The impedance transformation is accomplished by ridge waveguide to microstrip line transition, which is hidden in the waveguide. This proposed power divider shows merits of waveguide power dividers and substrate-integrated waveguide power dividers simultaneously, i.e. planar output ports, compact size, and high isolation. For verification, a power divider operating at the Ka-band is simulated, fabricated, and measured. The obtained results show the return loss and isolation are better than 10 and 20 dB, respectively. The measured insertion loss is

The fiber-optic communication lines and fiber-optic transmission systems using fiber-optic cable, receiving and transmitting optical modules based on WDM and DWDM (Wavelength Division Multiplexing & Dense WDM) technologies are studied. A method for calculating the transmission characteristics fiber-optic communication lines is proposed and relationships are obtained that establish an analytical relationship between the length regeneration section and the transmission rate. This paper discusses the study and analysis indicators fiber-optic communication lines using spectral WDM and DWDM technologies.

In the article there have been considered the issues of mathematical and computer modeling of fiber Bragg granting’s, using the method of transfer matrix. Method of transfer matrix allows specify the spectral characteristics of optical components, based on theory of bound modes and matrix description of electromagnetic wave, passing through optic fiber. There have been analyzed fiber Bragg granting’s with different lengths in accordance with spectral characteristics, such as, transmittance and reflection spectra. As well, there was carried out the experiment with influence of various parameters at fiber Bragg granting’s spectral characteristics. Fiber Bragg granting’s spectral characteristics were studied and optimal grating parameters were selected for developing the fiber-optic sensors, based on fiber Bragg granting’s. Developed and studied a computer model of flow-diagram of communication modes theory and Transfer Matrix Method. From the studied model it might be noticed, that in MATLAB software, selected for modeling, were formed for implementation into the MATLAB code. As well, in MATLAB software there were used fiber Bragg granting’s principal features and selected for studying influence of external factors, such as deformation, strain and temperature at FBG sensor’s reflection spectrum.

The design and modeling of a metasurface is carried out, which makes it possible to transform an incident linearly polarized electromagnetic wave into a transmitted wave with elliptical polarization close to circular. At the same time, the reflection coefficient of the wave is close to zero at the resonant frequency, since the metasurface is similar to the free space in its wave resistance. The resonant elements of the meta-surface (meta-atoms) are two-turn planar spirals with balanced dielectric and magnetic properties. Such spirals exhibit radically different properties with respect to waves with right and left circular polarization. The metasurface as a polarization converter has strong chiral properties, since it contains planar spirals of only one direction of twisting, and can be manufactured within the framework of printed circuit board technologies.

Optical polarization has attracted considerable research attention by extra detection dimension in angular space, flourishing modern optoelectronic applications. Nonetheless, purposive polarization controlling at nanoscales and even at the single-particle level constitutes a challenge. Plasmonic nanoantenna opens up new perspectives in polarization state modification. Herein, we report angular-dependent upconversion luminescence (UCL) of rare-earth ions doped upconversion nanoparticles (UCNPs) in both emission and excitation polarization via constructing angularly anisotropic plasmonic local-field distributions in gold nanorods (Au NRs) antennae with different configurations at a single-particle level. The UCL of UCNP tailored by plasmonic Au NRs nanoantennae is enhanced and exhibits linear polarization. The highest enhancement factor of 138 is obtained in the collinear Au NR-UCNP-Au NR configuration under parallel excitation. Simultaneously, the maximum degree of linear polarization (DOLP) of UCL with factors of 85% and 81% are achieved in the same structure in emission and excitation polarization measurements, respectively. The observed linear polarizations and UCL enhancements are due to varied resonant responses at 660 nm and the anisotropic near-field enhancement in different nanoantennae-load UCNP. The theoretical simulations reveal the periodic changing of near-field enhancement factors of nanoantennae in angular space with the incident light polarization angles and are well-matched with the experimental results.

The recent discovery of natural biaxial hyperbolicity in van der Waals crystals, such as α-MoO3, has opened up new avenues for mid-IR nanophotonics due to their deep subwavelength phonon polaritons. However, a significant challenge is the lack of active tunability of these hyperbolic phonon polaritons. In this work, we investigate heterostructures of graphene and α-MoO3 for actively tunable hybrid plasmon phonon polariton modes via electrostatic gating in the mid-infrared spectral region. We observe a unique propagation direction dependent hybridization of graphene plasmon polaritons with hyperbolic phonon polaritons for experimentally feasible values of graphene chemical potential. We further report an application to tunable valley quantum interference in this system with a broad operational bandwidth due to the formation of these hybrid modes. This work presents a lithography-free alternative for actively tunable, anisotropic spontaneous emission enhancement using a sub-wavelength thick naturally biaxial hyperbolic material.

Metal-dielectric thin film structure metamaterials can be designed to absorb solar light radiation over a wide spectral band. By using Kirchhoff's law, metal-dielectric thin film metamaterials are investigated for obtaining high equilibrium temperatures under direct solar light radiation at normal incidence. It is found that among all metal-dielectric thin film structures, the dielectric layer on metal (DLM) surface structure is the optimal structure for producing the highest thermal equilibrium temperature under direct solar optical radiation.

Significant potential for acoustic metamaterials to provide a breakthrough in sound attenuation has been unlocked in recent times due to advancements in additive manufacturing techniques. These materials allow the targeting of specific frequencies for sound attenuation. To date, acoustic metamaterials have not been demonstrated in a commercial automotive silencer for performance enhancement. A significant obstacle to the practical use of acoustic metamaterials is the need for low cost and efficient modelling strategies in the design phase. This study investigates the effect of acoustic metamaterials within a representative automotive silencer. The acoustic metamaterial design is achieved using a combination of analytical and finite element models, validated by experiment. The acoustic metamaterial is then compared with commonly used techniques in the silencer industry to gauge the effectiveness of the acoustic metamaterials. COMSOL simulations were used to validate the developed test rig and were compared to experimental results which were obtained using the two-load transmission loss test method. Through this testing method, the implementation of a labyrinthine metamaterial cylinder proved to be a significant improvement in transmission loss within the silencer, with an increase in transmission loss of 40 dB at 1500 Hz. The research has successfully shown that acoustic metamaterials can be used in practical settings, such as an automotive silencer, to improve the overall sound attenuating performance. The described analytical model demonstrates the potential for industrially relevant low cost design tools.

With the rapid development of microwave photonics technology, high-speed processing and ultra-weak signal detection capability have become the main bottlenecks in many applications. Thanks to the ultra-weak signal detection capability and the extremely low timing jitter properties of single-photon detectors, the combination of single-photon detection and classical microwave photonics technology may provide a solution to break the above bottlenecks. In this paper, we first report a novel concept of single-photon microwave photonics (SP-MWP), a SP-MWP signal processing system with phase shifting and frequency filtering functionalities is demonstrated based on a superconducting nanowire single photon detector (SNSPD) and a successive time-correlated single photon counting (TCSPC) module. Experimental results show that an ultrahigh optical sensitivity down to −100 dBm has been achieved, and the signal processing bandwidth is only limited by the timing jitter of single-photon detectors. In the meantime, the proposed system demonstrates an ultrahigh anti-interference capability, only the signal which is phase locked by the trigger signal in TCSPC can be extracted from the detected signals combining with noise and strong interference. The proposed SP-MWP concept paves a way to a novel interdisciplinary field of microwave photonics and quantum mechanism, named by quantum microwave photonics.

Visible radiation spectra of polycrystalline graphite under electrical and laser excitation is studied. It is shown that two different mechanisms of photon emission with a broadband spectrum are implemented in this material. The radiation arising as a result of resistive heating is thermal radiation, whose parameters are close to those of blackbody radiation. The laser-induced secondary radiation in the visible range is anti-Stokes luminescence. A red shift of the laser-induced radiation from fine-grained graphite with respect to the similar spectrum of a bulk sample is observed.

A wideband omnidirectional circularly polarized (CP) antenna using a conformal artificial anisotropic polarizer is proposed for millimeter-wave applications. The antenna consists of three parts: an omnidirectional linearly polarized (LP) radiator, an annular hyperbolic lens, and a conformal anisotropic polarizer. The annular hyperbolic lens regulates the spherical wavefront from the LP radiator into a cylindrical shape prior to propagating into the conformal artificial anisotropic polarizer. Each curved slab of the polarizer is conformally tilted 45 degrees to the incident electric field. Therefore, the conformal polarizer is the three-dimensionalization of the two-dimensional planar artificial anisotropic polarizer. The polarizer designing methodology is the first of its kind to generate wideband CP wave omnidirectionally. The hyperbolic lens and the conformal polarizer are fabricated together using stereolithography (SLA) 3D printing technology. Measurement results show that the antenna has a wide operating bandwidth of 45% (from 24 to 38 GHz), which completely covers potential 5G 28-GHz spectra. The proposed design has a low fabrication complexity and brings possibilities for high-speed wireless communications utilizing circular polarization.

Dynamic inversion of the planar-chiral responses of a metasurface is experimentally demonstrated in the terahertz regime. To realize this inversion, the critical transition of the checkerboard-like metallic structures is used. Resonant structures with planar chirality and their complementary enantiomeric patterns are embedded in the checkerboard. Using vanadium dioxide as a variable resistance, the metasurface is implemented in the terahertz regime. The responses of the metasurface to circularly polarized waves are then characterized by terahertz time-domain spectroscopy. Further, the sign of the circular conversion dichroism, which is closely related to the handedness of the planar chirality of the metasurface, is observed to be inverted at 0.64 THz by varying the temperature. Such invertible planar-chiral responses can be applied practically to the handedness-invertible chiral mirrors.

Plastic tuning of multicell superconducting accelerating cavities is crucial in the development cycle of cavities for particle accelerators. Cavities must meet stringent requirements regarding the operating mode frequency, field flatness, and eccentricity before lining them up in a cryomodule string. After dressing bare cavities with helium vessels, the welded vessel prevents access to individual cavity cells disallowing any further localized tuning. Currently, there is no straightforward way to tune dressed cavities other than cutting the vessel and then tuning the bare cavity and dressing it back, which would significantly impact cost and schedule. In this paper, we present a novel tuning technique for already jacketed cavities that is non-invasive and cost-effective. The proposed scheme employs pressurized balloons to be temporarily deployed inside the cavity as a means to localize mechanical deformation in specific cells. The proposed tuning technique was successfully utilized to recover a 9-cell 1.3 GHz tesla-style cavity.

We present a detailed simulation study on plasmonic-organic hybrid electro-optic modulators based on coupled symmetric or asymmetric plasmonic slots. An electro-optic polymer is exploited as an active material, and the device is compatible with a silicon photonics platform. The proposed device operates at 1550 nm wavelength, typical of data center or long-haul telecommunication systems. The device performance in terms of area, plasmonic losses, optical bandwidth, intrinsic modulation bandwidth and energy dissipation are comparable to already proposed Mach-Zehnder solutions, but with potentially better extinction ratio, coupling losses due to photonic-plasmonic transitions, and flexibility in exploiting, without any performance penalty, asymmetric slots to shift the ON and OFF states bias. Finally, the bias dependence of the modulation chirp is investigated, comparing through and cross-coupling configurations.

In this paper, we realize tunable Fano and electromagnetically induced transparency (EIT)-like resonances in the outputs of a nested feedback ring resonator. Compared with the traditional add-drop ring resonator, the feedback arm introduces interference between different resonance modes. Using coupled mode theory, we reveal the output Fano resonances are the interference of discrete modes and continuum modes, whereas the EIT-like resonance only appears in the over-coupled state. We experimentally confirm the two effects using optical fiber ring resonators, finding that the Fano effect can be easily controlled with phase shifts in the feedback arm. Moreover, we achieve the double Fano resonance, which displays an X type lineshape utilizing one ring resonator, predicting it to be a good candidate in wavelength monitor. The proposed simple configuration provides a platform to study Fano and EIT-like effect, which is useful in the optical filter, fast and slow light, optical switching, and optical sensing

The square lattice phononic crystal (PnC) has been used extensively to demonstrate metamaterial effects. Here, positive and negative refraction and reflection are observed simultaneously due to the presence of Umklapp scattering of sound at the surface of PnC and square-like equifrequency contours (EFCs). It is found that a shift in the EFC of the third transmission band away from the center of the Brillouin zone results in an effectively inverted EFC. The overlap of the EFC of the second and third band produce quasimomentum-matching conditions that lead to multi-refringence phenomena from a single incident beam without the introduction of defects into the lattice. Additionally, the coupling of a near-normal incident wave to a propagating almost perpendicular Bloch mode is shown to lead to strong right-angle redirection and collimation of the incident acoustic beam. Each effect is demonstrated both numerically and experimentally for scattering of ultrasound at a 10-period PnC slab in water environment.

Incorporating active components in photonic structures with a topological configuration has been shown to achieve lasing at topological edge states. Here, we report an electrically tunable topological edge-state laser in a one-dimensional complex Su–Schrieffer–Heeger chain. The proposed design is realized in an electrically injected Fabry–Perot (FP) laser chain. The lasing in topologically induced edge states is experimentally observed and a selective enhancement is realized by introducing a topological defect in the center. This work presents a versatile platform to investigate novel concepts such as the topological mode for mainstream photonic applications.

Experiments of our earlier work on the study of stimulated thermal scattering of the second harmonic of neodymium laser radiation in toluene are reproduced in order to confirm the put forward hypothesis about the nature of the laser beam structure decay in the focal plane of a short-focus lens. Experiments were carried out under similar conditions, but with a liquid (CCl4), in which there is no two-photon absorption of the second harmonic radiation from a neodymium laser. A conclusion is made that the spatial structure decay of the laser beam of the second harmonic of the Nd : YAG laser radiation focused by short-focus lenses with a numerical aperture NA ∼ 0.1 in toluene is associated with two-photon absorption.

Nonlinear effects in a high-power laser amplification system based on thin-rod active elements are experimentally investigated. It is shown that the most important nonlinear effect is the Kerr effect leading to self-focusing and self-phase modulation of laser radiation. The observed luminescence in Yb : YAG crystals in the visible region of the spectrum is caused by the charge transfer luminescence effect, which, in turn, is due to multiphoton absorption of laser radiation. Second-order nonlinearity in the crystal is used to effectively convert femtosecond pulses to second harmonic and sum-frequency waves which exhibit radiations of green and UV spectra.

We report an ultracompact on-fiber multiparameter sensor that employs multiple guided-wave surface plasmon resonances (GWSPRs) and machine learning based signal processing. The sensor structure entails a gold plasmonic crystal cavity covered with a planar dielectric waveguide on the end-face of a single-mode fiber. Incident light on the gold gratings of the plasmonic crystal cavity excites surface plasmon resonances, which are coupled into the waveguide and induce multiple, high-Q GWSPRs. Due to the difference in the field distributions of these resonance modes, the resonance dips in the sensor reflection spectrum have distinctive responses to external stimuli, which enables simultaneous measurement of multiple parameters. To enhance the sensing accuracy, a neural network model is used to demodulate the sensor responses. A proof-of-concept sensor using a UV-curable polymer as a waveguide material is demonstrated for simultaneous measurement of temperature and salinity of salt solutions. Although we only demonstrate the measurement of two parameters, the proposed sensor has the capability to measure more parameters if a multilayer waveguide structure made of different functional materials is used. The proposed sensor can benefit multifunctional analysis in a broad range of biological, chemical, and environmental monitoring applications.

Among typical metamaterials, we focus on the light "function" and chiral "element" in this chiral light metamaterial minireview. The authors are interested in inorganic materials, especially transition metal complexes. Metal complexes are compounds that have been studied for a long time for their optical properties (light absorption) and chirality (chiroptical spectroscopy, structural crystal chemistry, and asymmetric catalytic reactions). However, since the unit is a "molecule", few examples as (optical) metamaterials have been reported to date. Is it possible to add a function as a composite material using one method? No, the functions resulting from the nano pattern are very difficult to retrofit. Is there a way to fuse the rich compounds at the boundary between inorganic and organic with state-of-the-art optical metamaterials?