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Compact and highly performing photonic devices are characterized by non-intuitive geometries, a large number of parameters, and multiple figures of merit. Optimization and machine learning techniques have been explored to handle these complex designs, but the existing approaches often overlook stochastic quantities. As an example, random fabrication uncertainties critically determines experimental device performance. Here, we present a novel approach for the stochastic multi-objective design of photonic devices combining unsupervised dimensionality reduction and Gaussian process regression. The proposed approach allows to efficiently identify promising alternative designs and model the statistic of their response. Incorporating both deterministic and stochastic quantities into the design process enables a comprehensive analysis of the device and of the possible trade-offs between different performance metrics. As a proof-of-concept, we investigate surface gratings for fiber coupling in a silicon-on-insulator platform, considering variability in structure sizes, silicon thickness, and multi-step etch alignment. We analyze 86 alternative designs presenting comparable performance when neglecting variability, discovering on the contrary marked differences in yield and worst-case figures for both fiber coupling efficiency and back-reflections. Pareto frontiers demonstrating optimized device robustness are identified as well, offering a powerful tool for the design and optimization of photonic devices with stochastic figures of merit. [ABSTRACT FROM AUTHOR]

In several European rural communities, woody biomass is counted among the most important energy sources for heating and cooking. However, the use of old-fashioned fireplaces may affect indoor and outdoor air quality. To depict this situation and to plan the necessary improvement interventions, a pilot action was implemented in a typical mountainous Mediterranean area (Anogeia, Crete). The action involved: (1) identification of the quantities, use and source of the woody biomass used in the community based on the analysis of data collected through a systematic survey; (2) on-site indoor and outdoor measurements of air quality (CO2, CO, NOX, PM), during winter and summer. Based on this survey, around 70% of the study area households in Anogeia using woody biomass for heating purposes in low energy efficiency systems resulted in high firewood consumption. Fifty-three per cent of occupants did not consider indoor air quality as a result of wood burning. The air quality analysis showed very high concentrations of indoor air pollutants in most old buildings with seniors using traditional heating systems. The type of main/supplementary heating system used in a dwelling depends on factors such as the size of the dwelling, year of construction, education level and age of occupants. The results also demonstrate a strong correlation between the heating season (summer/winter) and the concentrations of air pollutants in the sampling sites. [ABSTRACT FROM AUTHOR]

The Chauvet-Pont d'Arc Cave (Ardèche, France), famous for its remarkable rock art, also contains unique thermal-alterations such as rock spalling and color changes on the walls. These alterations resulted from intense fires that have not been observed in the other decorated caves thus far discovered. The functions of these unusual fires challenge archaeologists. To characterize these combustions, we used a numerical tool, previously validated with experimental data, to study the thermo-alterations in the Megaceros Gallery. This unprecedented approach in cave art research enabled us to assess the wood quantities and locations of the hearths responsible for the thermo-alterations. We report here that at least ten fires took place in the Megaceros Gallery while burning more than 170 kg of wood. Both simulation and in situ observations suggest that the branches were arranged in a tepee shape and purposefully positioned, some distance from the walls. This method therefore enables further analysis of the functions of these fires. [ABSTRACT FROM AUTHOR]

We introduce a new two-step method to fabricate silver-silicon gratings that can excite surface plasmons efficiently. The grating structure was firstly created on a flat silicon substrate by single-pulse nanosecond laser interference lithography. Next, a silver layer of 50 nm was evaporated on the silicon substrate. With proper laser energy, a silver-silicon grating with a period of 1120 nm and depth of 18 nm was successfully fabricated. This grating can produce high-quality surface plasmon resonance (SPR) peaks at various incident angles. Moreover, a SPR sensor was experimentally demonstrated based on the silver-silicon grating, which had high sensitivity of 961.5 nm/RIU and figure of merit of 60. Our method is an efficient way to fabricate periodically nanostructured metals at high speed and low cost. [ABSTRACT FROM AUTHOR]

In this paper, a dual grating structure for unidirectional transmission is presented. The forward and backward transmission performances have been investigated by finite element method. To enhance the forward transmission and to suppress the backward transmission simultaneously, we suggested to cut grooves on the surfaces of one of the gratings, and the effects of the grooves on the optical transmission have been studied. The numerical simulation results reveal that the transmission contrast ratio and the optical unidirectional transmission of the structure can be improved markedly by properly arranging the size and the position of the grooves. The forward transmission can be more than 90%, while the backward transmission transmittance is less than 5%. [ABSTRACT FROM AUTHOR]

Highly sensitive and selective long-period grating (LPG) fiber-optic sensors modified with molecularly imprinted TiO2 nanothin films were fabricated. The films were deposited onto the surface of the optical fiber via liquid-phase deposition (LPD), using tetrakis(N-methylpyridinium-4-yl)porphyrin (TMPyP) as a template. Three LPG resonance bands were monitored during film deposition, which was of duration 4.5 h. Prior to template removal, heat treatment at 60 °C under high-humidity conditions led to an increase in refractive index of the TiO2 film, evidenced by changes in the central wavelengths of the attenuation bands. After template removal using HCl solution (0.01 M), the TMPyP-imprinted film-modified LPG sensor showed higher sensitivity to the template molecule than to structurally related guest molecules. This was measured at the 1st and 2nd resonance bands, with wavelengths ranging from 690 to 738 nm and 815 to 905 nm, respectively. No selective binding of the template was observed with a non-imprinted TiO2 film prepared in the same manner. Furthermore, the heat-treated imprinted films exhibited a substantial enhancement of photocatalytic activity for template irradiation. In particular, the self-cleaning property of the imprinted film-modified LPG sensor under ultraviolet irradiation led to highly efficient and selective binding to the template. The mechanism of the interaction between the template and the TiO2 matrix was investigated by UV–vis and Fourier-transform infrared (FTIR) spectroscopies. Additionally, morphological studies using scanning electron microscopy (SEM) were conducted. [ABSTRACT FROM AUTHOR]

The possibility of inducing population gratings in a three-level resonant medium using a pair of unipolar attosecond pulses that do not overlap in the medium has been studied theoretically. It has been shown that the results of the approximate solution of the Schrödinger equation agree with the results of the numerical solution of the system of equations for the density matrix of a three-level medium whose parameters are close to the parameters of atomic vapors of rubidium. [ABSTRACT FROM AUTHOR]

In this study, we present and establish a gold surface plasmon polariton (SPP) GaAs photodetector that achieves high internal quantum efficiency (IQE). At a wavelength of 600 nm, the IQE with the SPP was 85%, while the IQE without the SPP was 42%, an enhancement of 43%. Also, at a wavelength of 675 nm, the IQE with SPP was 82%, whereas the IQE without SPP was 45%, which constitutes an increase of 37%. Such excellent performance is ascribed to the subwavelength scope of the optical power in the photoconductive-based gold SPP GaAs that provides high IQE. Moreover, the recombination of the SPP in the photodetector provides greater photocurrent and responsivity. [ABSTRACT FROM AUTHOR]

The need for an easy to fabricate perfect and narrowband light absorber in the visible range of electromagnetic (EM) spectrum has always been in demand for many scientific and device applications. Here, we propose a metal-dielectric-metal (MDM) 1-D grating plasmonic structure as a perfect narrow band light absorber in the visible and its application in glucose detection. The proposed structure consists of a 1- D grating of gold on the top of a dielectric layer on a gold film. Optimization for dielectric grating index (n), grating thickness (t), grating width (W), and grating period (P) has been done to improve the performance of plasmonic structure by calculating its quality factor and figure-of-merit (FOM). The optimized plasmonic structure behaves as a perfect narrowband light absorber. The flexibility to work at a specific wavelength is also offered by the proposed structure through an appropriate selection of the geometrical parameters and refractive index of the dielectric grating. The equivalent RC model is used to understand different components of the proposed structure on the optical response. The absorption response of the structure is invariant to the incident angle. Moreover, the calculated absorbance of the proposed plasmonic structure is ~ 100% with a narrow full-width half maxima (FWHM) of ~ 2.8 nm. We have numerically demonstrated a potential application of the proposed MDM absorber as a plasmonic glucose sensor in the visible range with detection sensitivity in the range of 140 to 195 nm/RIU. [ABSTRACT FROM AUTHOR]

To realize a surface plasmon resonance-enhanced zinc oxide (ZnO) ultraviolet photodetector based on a sub-wavelength metal grating, we take advantage of the sensitivity of the resonance condition of a sub-wavelength metal grating to the refractive index of the surrounding medium. We theoretically design a sub-wavelength Ag grating covered with a high-refractive-index medium layer and apply it to a ZnO ultraviolet photodetector. By optimizing the parameters (angle of incidence, grating period, grating spacing, grating thickness, high-refractive-index medium layer thickness, refractive index of the covering), the optical field is localized at the interface of the sub-wavelength Ag grating and the ZnO thin film; that is, surface plasmon resonance is realized within the device. Compared with the device without a high-refractive-index medium layer, the maximum absorption enhancement factor of the designed device can reach up to 108. This work will provide theoretical guidance to realize a surface plasmon resonance-enhanced ZnO ultraviolet photodetector with a sub-wavelength metal grating. [ABSTRACT FROM AUTHOR]

Van der Waals materials and heterostructures that manifest strongly bound exciton states at room temperature also exhibit emergent physical phenomena and are of great promise for optoelectronic applications. Here, we demonstrate that nanostructured, multilayer transition metal dichalcogenides (TMDCs) by themselves provide an ideal platform for excitation and control of excitonic modes, paving the way to exciton-photonics. Hence, we show that by patterning the TMDCs into nanoresonators, strong dispersion and avoided crossing of exciton, cavity photons and plasmon polaritons with effective separation energy exceeding 410 meV can be controlled with great precision. We further observe that inherently strong TMDC exciton absorption resonances may be completely suppressed due to excitation of hybrid light-matter states and their interference. Our work paves the way to the next generation of integrated exciton optoelectronic nano-devices and applications in light generation, computing, and sensing. The authors investigate the optical properties of a heterostructure formed by a metallic substrate and a nanostructured transition metal dichalcogenide multilayer by measuring the reflectance spectrum at different multilayer thicknesses, filling factors and grating periods. The spectra show strong dispersion and avoided crossing of excitons, plasmons and cavity photons along with excitonic mode suppression at the anti-crossing point. [ABSTRACT FROM AUTHOR]

To achieve a high-sensitivity surface plasmon resonance sensor, a sensor based on Ag-MgF2 grating was designed and fabricated. A suitable-thickness MgF2 was suggested to prevent the oxidation of silver while avoiding reducing its plasmonic properties. The combination of an interference lithography approach, the material used for the fabrication of grating, and angular interrogation method led to a less costly sensor. The sensitivity and figure of merit of the proposed sensor approached 85.61 deg/RIU and 51 RIU−1, respectively, which is higher than the experimental values reported so far for grating-based sensors. It was shown that by optimization of the silver-based structure, it has great potential for use in sensor applications. It was observed that based on the made grating pattern, the numerical results were closer to experimental results by considering the grating pattern in a sine form. The effect of temperature on sensor performance was experimentally investigated. It was demonstrated that the change in the resonance angle with the temperature in this structure was equal to 0.02 deg/°C and it was also experimentally shown that temperature changes in the analyte refractive index had the most effect on the variations of the SPR response with temperature. [ABSTRACT FROM AUTHOR]

Beam shape is a key parameter in process optimisation for all laser applications. Among these shapes, a square–flat-top beam is fundamental and is in high demand. To obtain a beam with an aimed structure, various beam-shaping methods have been developed. Among them, an adaptive beam-shaping technique that uses phase grating encoded on a spatial light modulator with spatial frequency filtering in the Fourier plane in a 4f system has been developed. In this paper, using precise and simple beam shaping to produce a square and flat-top beam, we examine in detail the phase grating structure via simulations. The directions of the grating vectors inside and outside of the aimed area, i.e. kg-inside and kg-outside, and the normal vectors of the square and flat-top area, i.e. k1 and k2, critically affect the separation of the extracted and residual components on the Fourier plane. To extract the high spatial frequency component for precise shaping, a non-parallel configuration of the grating vectors to the normal vectors of the square beam is found to be effective. This method ensures precision beam shaping as well as keeping of pulse width and wavefront over the shaped area. [ABSTRACT FROM AUTHOR]

We study theoretically and experimentally superradiant dynamics in multiple-section GaAs/AlGaAs laser structures. We develop a model based on the one-dimensional Maxwell curl equations without making use of the slowly-varying envelope approximation and demonstrate that strong transient periodic modulation of both e – h density and refractive index drastically affect the dynamics of emission generation in semiconductor media. We show that the coherent λ/2 transient population and the relative permittivity gratings facilitate e – h self-ordering and the onset of the superradiant phase transition in the e – h system. [ABSTRACT FROM AUTHOR]

A structure of gratings consisting of conducting dipoles located in a dielectric layer is considered. The dispersion of the effective permittivity of this structure is calculated on the basis of the solution of the diffraction problem. It is found that the dispersion has a relaxation character. It is shown that it is possible to change the dispersion characteristic within wide limits by varying the structure parameters. The characteristic structure dimension providing for the adequate homogenization procedure is estimated. [ABSTRACT FROM AUTHOR]

Sampled fiber grating is a special superstructure fiber Bragg grating with a wide range of applications in many fields. In this work, based on drawing tower in-line fabrication system, a new preparation method of the sampled fiber grating is proposed and experimentally demonstrated. Experimental result shows that the obtained sampled fiber gratings possess dense reflection spectra, with a minimum reflection peak interval of only 0.09nm. This method exhibits promising application prospect in the fabrication of the high-quality sampled fiber grating. On the other hand, the spectral characteristics of the sampled fiber grating are analyzed when the sub-grating is affected by the external physical quantities such as, in this paper, strain. Wavelength shift and intensity change in the reflection peak of the spectra indicate that the grating is affected differently by micro strains, due to the different spatial positions along the axis of the sampled fiber grating. This work is aimed at exploring the potential applications of the sampled fiber grating in quasi-distributed micro-area sensing with the millimeter level. [ABSTRACT FROM AUTHOR]

The proposed technique demonstrates a fiber ring resonator interrogated by an optical time domain reflectometer (OTDR), for intensity sensing. By using this methodology, a cavity round trip time of 2.85 μs was obtained. For a proof of concept, a long-period grating was inserted in the resonant cavity operating as a curvature sensing device. A novel signal processing approach was outlined, regarding to the logarithmic behavior of the OTDR. Through analyzing the experimental results, an increase in the measured sensitivities was obtained by increasing applied bending. With curvatures performed from 1.8 m−1 to 4.5 m−1, the sensitivity values ranged from 2.94 dB·km−1 to 5.15 dB·km−1. In its turn, the sensitivities obtained presented a linear behavior when studied as a function of the applied curvature, following a slope of 0.86×10−3 dB. The advantages of applying this technique were also discussed, demonstrating two similar fiber rings multiplexed in a series of configurations. [ABSTRACT FROM AUTHOR]

The rigorous coupled-wave analysis (RCWA), also known as Fourier modal method, is one of the most popular methods for the modeling of diffraction gratings. It has been proven to be particularly effective for lamellar gratings. However, for non-lamellar metallic gratings, in TM polarization, the differential method (DM) or the RCWA need to be associated with the fast Fourier factorization (FFF) to provide more accurate solutions. In this study, we present the effectiveness of the FFF when it is associated with the DM and the RCWA for different grating's profiles, and we show how to circumvent on the case where the FFF can diverge when the metal permittivity is close to a pure negative real value. [ABSTRACT FROM AUTHOR]

In photonic integrated circuits grating couplers are commonly used to establish an efficient and stable fiber-to-chip link. However, the actual coupling efficiency of a fiber-to-chip interface depends strongly on the used wavelength and exhibits a maximum at a distinct target wavelength, determined by grating design parameters. In this paper, an enhancement of the optical bandwidth of silicon grating couplers by adding integrated dispersive structures is discussed. These are realized by single layers, prism-like geometries and additional silicon nitride gratings. Theoretical considerations for a bandwidth-enhancement by dispersive layers are performed and applied to an existing grating coupler design. A simulated 1dB-bandwidth of up to 90 nm at a maximum efficiency of − 0.65 dB in the C-band could be achieved, which is an enhancement to a factor of about 2 compared with the original coupler design. [ABSTRACT FROM AUTHOR]

An investigation of the plasmonic micro-antenna characteristics using an optical modified add–drop multiplexer embedded gold grating is proposed. A device consisting of a main microring and two nano-ring phase modulators is known as a Panda-ring resonator. A gold grating is embedded at the main ring center to induce plasmonic polariton, which is the plasmonic wave that oscillates with plasma frequency. At the resonance, the whispering gallery mode (WGM) of propagation light fields can be obtained by controlling the two suitable side ring parameters, from which the plasma resonant frequency is obtained by the graphical method called the Optiwave program. In manipulation, the light source with the wavelength of 1.55 μm is fed into the system. The input power was varied from 1 to 10 mW, from which the Bragg wavelength at the resonant peak is employed for all calculations. The directivity and gain of the plasmonic micro-antenna of 2.8 mW (4.47 dBm) and 0.78 mW (− 1.08 dBm) are obtained. The motivation for this study is that the plasmonic micro-antenna enhances the performance of optical/communication devices due to its extraordinary properties. The key finding is the operation of the plasmonic micro-antenna at optical frequencies using the Panda-ring circuit, which has dual modes for wireless and cable connections. In applications, the large-area antenna (multi-antennas) has the potential for atom, cell, and brain communication network investigations; regarding the linear relationship trend of the output gain, the use of the circuit for application in sensors is also possible. [ABSTRACT FROM AUTHOR]

A polarization beam splitter (PBS) based on the plasmonic subwavelength grating (PSWG) is proposed and investigated. The PBS is composed by a directional coupler with a PSWG as the coupling region, which offers additional freedom for index tailoring. The mode properties are strongly modified by the unique structure of the PSWG resulting in selective coupling with the two polarization states in the neighbor waveguides. The calculations show that the insertion loss of PBS is less than 1 dB, and the extinction ratios of transverse electric and transverse magnetic polarizations are as high as 27 dB and 30 dB respectively with nearly 4-μm coupling region length. In addition, the fabrication tolerance of the device is investigated in detail. [ABSTRACT FROM AUTHOR]

One limitation in characterizing exoplanet candidates is the availability of infrared, high-resolution spectrographs. An important factor in the scarcity of high precision IR spectrographs is the high cost of these instruments. We present a new optical design, which leads to a cost-effective solution. Our instrument is a high-resolution (R = 60,000) infrared spectrograph with a R6 Echelle grating and an image slicer. We compare the best possible performance of quasi-Littrow and White Pupil setups, and prefer the latter because it achieves higher image quality. The instrument is proposed for the University of Tokyo Atacama Observatory (TAO) 6.5 m telescope in Chile. The Tao Aiuc high Resolution (d) Y band Spectrograph (TARdYS) covers 0.843-1.117 μ m. To reduce the cost, we squeeze 42 spectral orders onto a 1K detector with a semi-cryogenic solution. We obtain excellent resolution even when taking realistic manufacturing and alignment tolerances as well as thermal variations into account. In this paper, we present early results from the prototype of this spectrograph at ambient temperature. [ABSTRACT FROM AUTHOR]

The discrete spectrum of ultracold neutrons (UCNs) diffracting from a moving grating has been measured using a time-of-flight Fourier spectrometer. It is shown that, choosing an appropriate depth of grating profile, one can change significantly the ratio of wave intensities for different diffraction orders. The experimental results are found to be in good agreement with the theoretical predictions based on the multiwave dynamical theory of neutron diffraction from a volume periodic grating. [ABSTRACT FROM AUTHOR]

Due to the emergent need of identifying biomolecules at very low densities to diagnose illnesses, as well as detect dangerous gases for health, early on, designing a high-quality sensor with simple structure is one of the most important targets for the researchers. Because of this issue, a graphene-gold grating surface plasmon resonance (SPR) sensor with excellent performance has been proposed. The sensitivity of the proposed sensor is calculated by the wavelength peak shift of the extinction curve, which is due to changes in the refractive index of the sensing medium which are, in turn, due to changes in the density of the identified molecule. Two modes of plasmon have been created in the near-infrared region, and both of them had very good characteristics, including sensitivity and high quality. By optimizing the structure and characteristics of the incident light beam, the highest sensitivity 1100 nm/RIU and the quality factor 3929 for the first mode (mode 1) and the notable sensitivity 1180 nm/RIU and the quality factor 9833 were obtained for the second mode (mode 2). The label-free SPR proposed sensor can, by measuring the refractive index, detect changes in the concentration of a wide range of materials including gases such as most alloys, and biomolecules such as hemoglobin, breast cancer, and leukemia, and generally materials with a refractive index from 1.000 to 1.600, up to a precision of 0.0001. [ABSTRACT FROM AUTHOR]

A dual-wavelength filter was experimentally demonstrated using subwavelength grating (SWG)/waveguide structure. We designed the structural parameters of the SWG and the waveguide to find the reflection peaks in the visible wavelength region. To investigate the optical response of the designed SWG/waveguide structure, finite-difference time-domain (FDTD) numerical calculations were performed for electromagnetic field distribution. The dual reflection peaks from our proposed structure were predicted in visible wavelength regions by the FDTD calculation. The calculated electromagnetic field distribution also revealed that the reflection peaks were associated with resonances in the SWG and waveguides. We fabricated the SWG/waveguide with typical electron-beam lithography techniques, and two reflection peaks were observed at wavelengths of 486 nm and 590 nm with bandwidths of 45 nm and 58 nm, respectively. These experimental results indicate that dual-wavelength filters can be successfully realized without complex fabrication processes. [ABSTRACT FROM AUTHOR]

Two-dimensional Ag/SiO2 nanocomposite gratings of 400 and 600 nm in grating constant are fabricated by etching the SiO2 slabs implanted with Ag ions, and their plasmonic extinction, absorption, and reflection behaviors are investigated. Our results indicate that no scattering light fields can exist near the localized surface plasmon (LSP) resonance wavelength (about 405 nm) of Ag nanoparticles (NPs) due to the intense LSP resonance absorption. Especially, when the gaps between nanocomposite veins have a width close in value to the LSP resonance wavelength of Ag NPs, the local light fields in the grating plane can be slightly enhanced due to an in-phase addition of the incident light fields and the diffractive light fields induced by the gap diffraction, leading to a slight red shift of LSP resonance mode of Ag NPs. Moreover, in the LSP resonance absorption region, although the grating diffraction can still occur, the diffractive light fields are extremely weak, and thus, the local light fields in the grating plane cannot be modified by coherently adding these extremely weak diffractive light fields to the incident light fields. As a result, the LSP resonance mode of Ag NPs will keep its position unchanged even though the grating constant is set to make the first grating order rightly change from evanescent to radiative character. [ABSTRACT FROM AUTHOR]

The radiation intensity redistribution of the probe field upon its scattering by spatially periodic atomic population gratings in a medium with a four-level tripod configuration of atomic states is investigated theoretically. Conditions are found under which a significant redistribution of the probe-wave field intensity occurs, and a "diffraction" pattern is formed with an efficient probe-field intensity transfer to the first-order maxima. [ABSTRACT FROM AUTHOR]

In this paper, we study the dark decay dynamic behavior of field-induced photorefractive (PR) grating in a Mn:Fe:KTN crystal under different conditions. The spatial distribution and temporal evolutions of field-induced PR grating dark decay are visualized in situ and monitored quantitatively by means of digital holographic microscopy. Subsequently, the dark decay time of phase grating can be achieved according to the dynamic behavior, which can be improved drastically by a writing field and is insensitive to the grating period. The mechanism of enhanced lifetime of grating is interpreted by the potential well model. The external field enhances the growth of polar nanoregions, forming a potential well that binds the carriers, ultimately prolonging the dark decay time. This work provides an effect way for enhancing lifetime of PR grating, which can be very useful for a variety of applications, including PR storage and holographic optical elements. [ABSTRACT FROM AUTHOR]

We present results of experimental studies, theoretical analysis, and numerical modeling of specific features of photorefractive gratings that are formed by a high-contrast interference pattern of writing laser beams in an X-cut plate of a LiNbO3:Cu crystal created from a metal film by diffusion doping. [ABSTRACT FROM AUTHOR]

The present work investigates the effect of geometrical parameters of 1D nanograting on surface plasmon resonance (SPR) and plasmonic bandgap (PBG). The use of plasmonic grating device in various electronic devices is based on correct value of bandgap energy. For this purpose, various nanograting structures having regular periodic ridges in 1D has been modeled in the form of a gold film on glass substrate using finite element analysis in RFRF Module of COMSOL (Multiphysics) 5.3a licensed version. In the designed structures, firstly, the periodicity of the grating varied while keeping the slit width and film thickness constant. Furthermore, the thickness of the grating also varied while the periodicity and slit width is kept constant and transmitted mode for each structure is studied to find the suitable value of film thickness for optimizing the device. At the end, the slit width varied while keeping the periodicity and film thickness constant. Due to increase in slit width, the bandgap energy increases until slit width equals to nearly half of periodicity after this bandgap energy decreases and associated with the sinusoidal behavior of the device which support fundamental plasmonic mode. The increase in film thickness results a linear increase in bandgap energy as long as the film thickness is comparable to the skin depth of gold and plasmonic bandgap energy is high for smaller values of periodicity and decreases with increasing periodicity. Due to the ability to control the optical properties, the PBG is expected to have a major impact on technology. [ABSTRACT FROM AUTHOR]

Transmission through subwavelength apertures enables separation of the incidence half-space and the exit half-space, which leads to that the spatial distribution of the field in the latter is not affected by the distribution in the former. The distribution in the exit half-space is mainly determined by the properties of surface plasmons (SPs) at the exit-side interface. In this paper, for the microwave structures with one-side concentric corrugations around a single annular hole, we demonstrate the possible connections between asymmetric transmission in the beaming regime and collimation of the waves incident at different angles, which can be considered as two sides of the same phenomenon occurring due to the common effect of such a separation and the radiation shaping effect being possible due to the spoof SPs at the corrugated exit interface. Collimation manifests itself in that the waves incident at different angles from a wide range contribute to the single outgoing beam so that a far-zone observer cannot distinguish between the contributions of different angles of arrival. Asymmetry in transmission manifests itself in that the spatial shaping of radiation (beaming) in the exit half-space appears only for one of the two opposite incidence directions. Moreover, even in the structures with the same corrugations on both sides, i.e., without asymmetric transmission, spatial separation of two wave processes, e.g., two symmetric or asymmetric collimation processes, can be obtained for a wide range of nonzero angles of incidence. [ABSTRACT FROM AUTHOR]

We have theoretically studied the possibility of using the phenomenon of phase switching of coherent population trapping for creating a switch of light propagation direction in electromagnetically induced gratings in a medium with Λ-atoms. The permissible region of this effect application is determined and the parameters are found which ensure the obtaining of a high-efficiency scheme of the spatial redistribution of probing field intensity on atomic density gratings. [ABSTRACT FROM AUTHOR]

A simulation study for the opening of plasmonic bandgap (PBG) with control over it by varying the slit width (SW) for exposed and buried 1D metallic gratings has been reported by using COMSOL Multiphysics, RF module. We observe excitation of surface plasmon polaritons (SPPs) and splitting up of surface plasmon resonance (SPR) dip to induce PBG by keeping the periodicity constant and varying the slit width for each grating. The resonance wavelengths are taken through far-field transmission and reflection spectra of exposed and buried gratings of different slit widths respectively. The new trends of bandgap energy for varying slit width of exposed and buried metallic gratings have been reported and discussed. In each trend, range of optimum value of slit widths are obtained around half of the periodicity which is a significant observation. The comparison of PBG energy for different metallic devices and the opening of PBG in the dispersion curves is also presented by the variation of incident angles. The potential applications of these devices are to control the surface-enhanced Raman scattering (SERs), light-emitting diodes (LEDs), and solar cell applications. [ABSTRACT FROM AUTHOR]

Theory of plasmon-exciton coupling is developed for a metal nanocylinder grating located in the vicinity of a semiconductor quantum well. In dipole approximation, the effective polarizability of cylinders is derived, taking into account generation of quantum-well excitons in the near field of surface plasmons. Given the polarizability, the spectra of reflection and absorption are calculated for metal-semiconductor systems to study the effect of plasmon-exciton interaction. The excitonic response is shown to be enhanced by high-quality plasmons of Ag cylinders, although strong coupling is not attained for realistic nanostructure parameters. [ABSTRACT FROM AUTHOR]

A radioabsorbing structure shielding a metal plane in the form of a ferrite layer with a dielectric layer containing a grating of resistive squares has been considered. The diffraction problem of a plane electromagnetic wave incident perpendicular to the surface of the structure has been solved. Based on the solution of the optimization problem, it is shown that, in contrast to the ferrite layer, which has a low reflection coefficient in the decimeter and meter wavelength ranges, a combined structure with a total thickness of less than 5 cm provides low reflection in the centimeter range. [ABSTRACT FROM AUTHOR]

Waste incineration is a treatment system that reduces waste volume while capturing or destroying potentially harmful substances and recovers energy and chemical contents from wastes. Grate incinerator is one of the thermal treatment methods in waste incinerations. The incineration grates are exposed to high heat flux due to the occurrence of combustion on their surface. Therefore, cooling the incineration grate is one of the main issues in these treatments. In this study, the conjugate heat transfer between the cooling water and incineration grate is investigated numerically. We consider different geometries of the internal guide vane in the cooling channel and analyze the effects of the shapes of the guide vane on the heat transfer performance in the incineration grate. We also calculate the fluid residence time in the cooling channel and investigate the relation between the heat transfer performance and residence time of the cooling fluid. Results confirm that the maximum residence time of the cooling fluid can be reduced, from which the heat transfer performance can be improved. [ABSTRACT FROM AUTHOR]

A novel approach to the intensity of archaeological fires is proposed, based on a combination of archaeological observations and analyses of sedimentary hearths with relevant proxies obtained from using experimental combustion structures. In this work, two different structures were built and monitored. They aimed at reproducing two types of archaeological hearth morphology encountered at the Bronze Age site of the cave of Les Fraux (Saint Martin de Fressengeas, Dordogne, France). A series of fires was constructed and a large amount of data was collected: temperature curves, wood consumption and observations on substratum evolution. A numerical code for heat transfer was developed to model heat propagation from the surface to the underlying sedimentary layers, the input parameters of which were adapted to fit the thermal evolution observed with the experimental fires. We found that two archaeological parameters are fundamental to characterise the intensity of the fire: the paleotemperature reached at the surface of the burnt sediment (which in our case was determined by thermoluminescence analyses) and the depth of the rubefaction front as an indicator of a 250 °C isothermal surface. We then estimated the duration of an equivalent single fire that would correspond to one of the archaeological hearths investigated. Finally, with the wood consumption recorded during the fire experiments, and the estimated firing duration, the energy involved was evaluated. When generalised to the study of archaeological hearths, this approach could be of great interest in firing intensity evaluation (temperature/time/energy). [ABSTRACT FROM AUTHOR]

Automated monitoring systems of debris flow hearths, their purpose, and the role in decreasing debris flow risks are considered. A brief review of the tools for measuring parameters of debris flows used in systems for monitoring and warning of debris flow hazards is given. The description of foreign and Russian hardware-software systems for monitoring debris flow hearths is presented. [ABSTRACT FROM AUTHOR]

Recently, numerous fires have started in Finland around roof penetrations of metal chimneys. One reason for the fires is the high flue gas temperatures of fireplaces. EN standards do not determine the flue gas temperatures of fireplaces meant for the specification of temperature classes of chimneys. At present, the design of chimneys is based on the temperature indicated in the CE marking of fireplaces. The temperature indicated in the CE marking is the mean temperature of the nominal test. In order to investigate how representative and safe this mean temperature is, tests on different fireplaces were conducted. Flue gas temperatures of the fireplaces were measured during a nominal test, a safety test and extra heating. Even in the nominal test, the highest flue gas temperature was 37°C to 212°C higher than the mean temperature. The highest flue gas temperature in the safety tests was about 120°C to 380°C higher than the mean temperature indicated in the CE marking. During the extra heating test, the highest flue gas temperature was 160°C to 350°C higher than that indicated in the CE marking. Due to the present method of determining flue gas temperatures, chimneys may be tested at a too low temperature. [ABSTRACT FROM AUTHOR]

Reheating furnace walking hearth type (RFWHT) has been used for the iron and wire rods of the reheating process in Ratchasima Steel Products Co., Ltd. Factory (Nakhon Ratchasima, Thailand). Ratchasima Steel Products Co., Ltd. is among the companies with the highest energy consumption in Thailand. The company is confronted by problems related to performance improvement in terms of temperature control and reduction of fuel consumption. Since the reheating furnace was installed in 1964 and with the adjustment of some of its devices, the system has required an optimal controller for controlling the temperature inside each zone of the reheating furnace. This study aimed at investigating the mathematical model from the experimental data in the manufacturing process of rolling wire rod production and subsystem by using system identification with genetic algorithm. Results can be used to design a proportional-integral controller for temperature control in each zone and to reduce fuel. [ABSTRACT FROM AUTHOR]

The objective of this study is to evaluate experimentally and numerically the transport behaviour of a moving bed on a forward acting grate. Therefore, the grate was operated with expanded clay and wood chips without combustion. Frequency and amplitude of the grate bars and feed rate were subject to change. Experimental findings showed that large particles have shorter residence times than small particles which is due to segregation on the grate. Additionally, the experiments indicated that increased frequencies of the grate bars lead to reduced residence times whereas the amplitude had no significant effect. The motion of a packed bed e.g., its particles was described numerically by the discrete element method (DEM). Thus, detailed data on all the particle’s paths and velocities are available. These data were used within the mean velocity method (MVM) and the tracking method (TM) to estimate the residence time of a packed bed. Both methods confirmed the dependency of the residence time on particle size, however, better predictions were obtained by the Tracking Method. The mean residence times varies from 40 to 120 min depending on the particle size. [ABSTRACT FROM AUTHOR]

An increase in the stability of the main roof of an open-hearth furnace is resolved successfully by filling the joints of roof lining with plates made of plastic refractory material with programmed properties ((Plasogneupor-PS) produced by NPK ZAO Rosmetallkomplekt. The technology makes it possible to increase considerably the life of a open-hearth furnace roof lining and to reduce fuel consumption. [ABSTRACT FROM AUTHOR]

A precisely tunable true time delay line (TTDL) based on lithium niobate on insulator waveguide grating is proposed. Utilizing the electro-optic effect of lithium niobate, active tuning of reflected wavelength and time delay can be realized. The numerical simulation results show that, with the optimized grating structure and flexible electrode distribution, wide tuning range and high tuning accuracy of time delay can be achieved by simply controlling the charging position of the electrodes. This TTDL is applied to a tunable bandpass microwave photonic filter (TBMPF), which using PM-IM conversion to suppressed dc signal to achieve bandpass. In the TBMPF, the TTDL plays the role of introducing the dispersion for PM-IM conversion, time delay between the taps and tuning of central frequency. This TTDL can reduce the system complexity and cost of microwave photonic filter. [ABSTRACT FROM AUTHOR]

We study the peculiar response of photo-sensitive polymer films irradiated with a certain type of interference pattern where one interfering beam is S-polarized, while the second one is P-polarized. The polymer film, although in a glassy state, deforms following the local polarization distribution of the incident light, and a surface relief grating (SRG) appears whose period is half the optical one. All other types of interference patterns result in the matching of both periods. The topographical response is triggered by the alignment of photo-responsive azobenzene containing polymer side chains orthogonal to the local electrical field, resulting in a bulk birefringence grating (BBG). We investigate the process of dual grating formation (SRG and BBG) in a polymer film utilizing a dedicated set-up that combines probe beam diffraction and atomic force microscopy (AFM) measurements, and permits acquiring in situ and in real-time information about changes in local topography and birefringence. We find that the SRG maxima appear at the positions of linearly polarized light (tilted by 45° relative to the grating vector), causing the formation of the half-period topography. This permits to inscribe symmetric and asymmetric topography gratings with sub-wavelength period, while changing only slightly the polarization of one of the interfering beams. We demonstrate an easy generation of sawtooth profiles (blazed gratings) with adjustable shape. With these results, we have taken a significant step in understanding the photo-induced deformation of azo-polymer films. [ABSTRACT FROM AUTHOR]

We design and numerically investigate the spectral properties of two kinds of 2D Ag structured surfaces. The first structure is composed of Ag achieving a maximum absorption of 90% with the optimal structured parameters. The insertion of a metal layer between the grating layer and the substrate improved not only the absorption (greater than 95%) but also the sensor performance. Numerical computation is conducted to obtain the spectral distribution of powers with different structural parameters using the rigorous coupled-wave analysis method. Thus, we have demonstrated that any considered silver structure behaves either as a thermal source or a plasmonic sensor in the infrared range. The degree of directivity of each thermal source studied depends on several geometric and optical parameters. The best directivity is characterized by a narrow band of the full width at half maximum equal to 10.46 mrad with a nearly perfect absorption. Then, the performance of this source is identified by a quality factor (Q) equal to 176.52. The proposed structure as a perfect absorber sensor gives a maximum sensitivity of 4000 nm/RIU , a maximum absorption of 100 % (demonstrated by strong fields distribution), and a maximum value of figure of merit equal to 52.71 RIU - 1 for analyte refractive index ranging from 1.33 to 1.4. The proposed structures have great potential as biosensors. [ABSTRACT FROM AUTHOR]

To the article "Polarization Transformation of Electromagnetic Radiation Upon Excitation of Surface Plasmon-Polaritons on a Metallic Grating," by I. Z. Indutnyi, V. I. Mynko, M. V. Sopinskyy, and K. V. Svezhentsova, Vol. 86, No. 6, pp. 1058–1063, January, 2020. [ABSTRACT FROM AUTHOR]

We report on the experimental and theoretical interpretation of the diffraction of a probe beam during inscription of a surface relief grating with an interference pattern into a photo-responsive polymer film. For this, we developed a set-up allowing for the simultaneous recording of the diffraction efficiency (DE), the fine structure of the diffraction spot and the topographical changes, in situ and in real time while the film is irradiated. The time dependence of the DE, as the surface relief deepens, follows a Bessel function exhibiting maxima and minima. The size of the probe beam relative to the inscribed grating (i.e., to the size of the writing beams) matters and has to be considered for the interpretation of the DE signal. It is also at the origin of a fine structure within the diffraction spot where ring-shaped features appear once an irradiation time corresponding to the first maximum of the DE has been exceeded. [ABSTRACT FROM AUTHOR]

To realize double-band perfect absorption, in this paper, we present a theoretical study of plasmonic absorption based on a metal–dielectric grating nanostructure. The structure consists of subwavelength periodic Al 2 O 3 grating covered with metal grating with a metal substrate. Results show that the one of the two absorption bands is caused by the Fabry–Perot resonance in the gold grating slits, and the other absorption band is caused by the gap plasmonic resonance of the Al 2 O 3 dielectric grating. The effect of structural parameters on absorption is also studied, the field distribution of the proposed nanostructure is presented to illustrate the absorption mechanism. Moreover, the two absorption peaks can be adjusted individually with different geometrical parameters. The results will pave the way towards the design of double-band plasmonic perfect absorber, which may have potential application in plasmonic absorption switch, plasmonic sensors and photodetectors. [ABSTRACT FROM AUTHOR]

We propose a novel embedded long-period waveguide grating (LPWG) for the implementation of a broadband mode conversion. The proposed LPWG is formed in the inner of waveguide where the two coupled modes have the largest field overlap and, hence, features an ultra-short length and a wide bandwidth. Besides, the bandwidth of the proposed LPWG is further increased by manipulating its phase-matching curve. Our proof-of-principle device, fabricated with polymer for the conversion between the E11 and E21 modes, contains only two periods and achieves a mode conversion efficiency larger than 98.2% (99.2%) for the x (y) polarization over the C + L band. The proposed LPWG could find applications as an ultra-compact and broadband mode converter in mode-division-multiplexing system. [ABSTRACT FROM AUTHOR]

In this paper, a surface plasmon resonance based D-shaped single mode fiber sensor with a gold grating over the polished fiber surface, is analyzed by finite element method for refractive index sensing. Benefitted from the localized surface plasmon resonance effect of gold grating, the proposed sensor achieves a reasonably good wavelength sensitivity of 7590 nm/RIU for the refractive index range varying from 1.34 to 1.38 and the corresponding resolution is 1.31 × 10−5 RIU. Furthermore, the maximum amplitude sensitivity of the sensor is calculated to be 676.08 RIU−1. The good sensing performance, low cost and simple structure makes this sensor a potential candidate for application in the areas of food processing, environmental monitoring and biochemical analysis. [ABSTRACT FROM AUTHOR]