Maximum Reflectivity Research Articles

ELECTRODEPOSITION AND PROPERTIES OF IRON DEPOSITS OBTAINED IN A MAGNETIC FIELD OF WEAK INDUCTION

The paper presented the electrodeposition, morphology and properties of iron deposits were obtained using a low-induction magnetic field of 0.001 T in the electrocrystallization process. The vector of magnetic field induction was directed perpendicular to the electrode surface. Iron deposits were obtained in an electrolyte FeSO4·7H2O – 1.5 mol/l and Al2(SO4)3·18H2O – 0.15 mol/l. The current density was 7 A/dm2. Deposits were obtained on a copper base. The influence of the magnetic field on the process of electrodeposition of deposits was studied using the method of stationary potentiometry and cyclic voltammetry. Determination of the influence of the magnetic field on the morphology of deposits was carried out using scanning electron microscopy. Determination of the properties of the obtained iron deposits was carried out by measuring microhardness, reflectivity and corrosion resistance. Studies have shown that a magnetic field with an inductance of 0.001 T affects the processes of electrodeposition of an iron deposit, increasing its overvoltage by more than 1 volt. The morphology of the deposits does not change significantly, but the crystallites obtained in the magnetic field have a more rounded shape and the surface of the deposit is more uniform. The microhardness of deposits obtained by electrodeposition without the use of a magnetic field was 2610 MPa, and with a magnetic field – 2720 MPa. The reflectivity of deposits obtained in a magnetic field is 17% higher. The corrosion resistance of deposits obtained in a magnetic field is approximately two times higher. After conducting corrosion studies, the microhardness of the deposits obtained using a magnetic field did not change (2630 MPa), however, the microhardness of the deposits obtained under normal conditions decreased by approximately two times. Electrolysis parameters for maximum corrosion resistance, microhardness and reflectivity are proposed in the work.

Spectral Engineering of Hybrid Biotemplated Photonic/Photocatalytic Nanoarchitectures.

Solar radiation is a cheap and abundant energy for water remediation, hydrogen generation by water splitting, and CO2 reduction. Supported photocatalysts have to be tuned to the pollutants to be eliminated. Spectral engineering may be a handy tool to increase the efficiency or the selectivity of these. Photonic nanoarchitectures of biological origin with hierarchical organization from nanometers to centimeters are candidates for such applications. We used the blue wing surface of laboratory-reared male Polyommatus icarus butterflies in combination with atomic layer deposition (ALD) of conformal ZnO coating and octahedral Cu2O nanoparticles (NP) to explore the possibilities of engineering the optical and catalytic properties of hybrid photonic nanoarchitectures. The samples were characterized by UV-Vis spectroscopy and optical and scanning electron microscopy. Their photocatalytic performance was benchmarked by comparing the initial decomposition rates of rhodamine B. Cu2O NPs alone or on the butterfly wings, covered by a 5 nm thick layer of ZnO, showed poor performance. Butterfly wings, or ZnO coated butterfly wings with 15 nm ALD layer showed a 3 to 3.5 times enhancement as compared to bare glass. The best performance of almost 4.3 times increase was obtained for the wings conformally coated with 15 nm ZnO, deposited with Cu2O NPs, followed by conformal coating with an additional 5 nm of ZnO by ALD. This enhanced efficiency is associated with slow light effects on the red edge of the reflectance maximum of the photonic nanoarchitectures and with enhanced carrier separation through the n-type ZnO and the p-type Cu2O heterojunction. Properly chosen biologic photonic nanoarchitectures in combination with carefully selected photocatalyst(s) can significantly increase the photodegradation of pollutants in water under visible light illumination.

Responses of trace elements and optical textures of ultra-deep pyrobitumen to hydrothermal alteration

The hydrothermal activity in the Ediacaran Dengying (DY) Formation in central Sichuan has modified the reservoirs and paleo-oil reservoirs; however, these modifications are not specific due to the challenges in recovering the hydrothermal scale. This paper classified pyrobitumen in the DY Formation into five categories by optical textures and analyzed the physical structure and trace element composition of the different pyrobitumen using scanning electron microscope, reflectance, and trace elements. Finally, the responses of the trace element concentrations and optical textures of the pyrobitumen to hydrothermal alteration were discussed and used to restore the hydrothermal scale in the central Sichuan Basin. The results show that isotropic, fine-grained, medium-grained, coarse-grained mosaic, and fibrous pyrobitumen develop in the DY Formation. As the optical texture of the pyrobitumen changes from isotropic to mosaic to fibrous, the order degree of aromatic lamella in pyrobitumen gradually increases, the maturity, the maximum reflectance, and the bireflectance of pyrobitumen gradually increase. Except for isotropic pyrobitumen, anisotropic pyrobitumen is subject to varying degrees of hydrothermal alteration. The hydrothermal alteration on pyrobitumen is primarily in the form of material exchange, precipitating illite, salt, and barium-enriched minerals in pyrobitumen pores and enriching some elements (Ba, Cr, Nb, and Sr) in the pyrobitumen. As the optical texture changes from isotropic to mosaic to fibrous, the element enrichment degree gradually increases. Medium-grained mosaic, coarse-grained mosaic, and fibrous pyrobitumen are widely observed in central Sichuan. Therefore, hydrothermal modification on the DY reservoirs and paleo-oil reservoirs is not limited to the deep faults but widely develop in central Sichuan, and should be an essential part of the further study of hydrocarbon accumulation.

Structural, magnetic and microwave absorption properties of novel hollow core–shell (SrMnCoFe10 O19/MnCoFe2O4)/SiO2 composite microfibers synthesized via electrospinning

Ferrites were among the earliest types of microwave absorbers due to their high magnetic dissipation and low cost. Ferrites, on the other hand, have some disadvantages, such as a low natural resonance frequency (fr), a lack of dielectric loss, and a high density. We effectively generated (SrMnCoFe10O19/MnCoFe2O4)/SiO2 samples with hollow microfiber morphologies and most of the effective parameters suggested to overcome these disadvantages and increase the microwave dissipation properties of ferrites. Hard and soft SrMnCoFe10O19/MnCoFe2O4 hollow microfibers were obtained using sol-gel and electrospinning technology. After heat treatment at 1050 °C for 3 h, the binary ferrites are formed. (Hard ferrite/soft ferrite)/SiO2 core-shell structures were fabricated by the Stober process, so their microwave absorption performance is greatly influenced by the hard/soft mass ratio and SiO2 thickness of the sample. The fabricated fibers were characterized by x-ray diffraction (XRD), vibrating sample magnetometer (VSM), field emission scanning electron microscopy (FESEM), FTIR spectroscopy, and vector network analyzer (VNA). The single-phase structure of all microfibers was determined by X-ray diffraction (XRD) analysis. The phase formation of the coated microfibers is also elaborated using Fourier transform infrared spectroscopy (FTIR) based on identified chemical bonds. According to the (FESEM) analysis results, the microfibers manufactured have a homogeneous core–shell structure. A vector network analyzer was used to investigate the samples' dielectric constants and microwave absorption properties between 12 and 18 GHz at room temperature. The results showed that when the mass ratio is hard/soft (8: 2) and the mass ratio of ferrite/SiO2 (1:1), the maximum reflectance loss is −27 dB and the absorption bandwidth is 2 GHz. The magnetic saturation (Ms) was calculated at 43.44 emu/g and the calculated coercivity values (1163.07 Oe) confirm the hard ferrite/soft ferrite/SiO2 core-shell structures.

Correlation analysis between lightning flashes and rainfall rate during a flash flood thunderstorm

This paper presents the correlation analysis between lightning flashes and the rainfall rate of a thunderstorm when a flash flood event happened in Melaka on 11 August 2020. Four types of data have been collected from the electric field mill (EFM), fast antenna (FA) system, constant altitude plan position indicator (CAPPI) radar and world wide lightning location network (WWLLN). Two storms have been detected by the EFM occurred between 04:00:00 and 14:00:00. The FA system recorded a total of 33 lightning flashes had detected with the highest number occurrence of flashes which positive narrow bipolar event (+NBE) around 21 flashes, the maximum rainfall rate and reflectivity have been detected by radar during the first storm were 8 mm h-1 and 37 dBZ, respectively (light rain). During the second storm, there was a total of 980 lightning flashes detected by the FA system with the highest number occurrence of flashes around 429 flashes (IC), the highest value of rainfall rate and reflectivity is 50 mm h-1 and 50 dBZ, respectively (heavy rain). Analyses of the lightning and rainfall rate data also show a close link between the occurrence of major thunderstorms systems and flash flooding on a regional scale.

Extraction Method of Stand Density Based on High-Resolution Remote Sensing Imagery

In this paper, a stand density extraction method is proposed based on QuickBird high-resolution satellite image data of Baisha artificial forest farm in Minhou, Fujian. Firstly, through the analysis band canopy image of QuickBird panchromatic, it is known that there is a maximum reflectivity point in the canopy. Then, the vegetation-covered area was extracted by the normalized difference vegetation index ( NDVI ). The canopy image of the forest was extracted through the decision tree classification algorithm. The texture information and spectral information were comprehensively utilized to classify the images. Then, the number of stand trees was extracted by the maximum filtering method, and the stand density was calculated to produce the stand density map. The experiment verified that this method can meet the needs of a stand density survey.

A novel method for fabricating guided-mode resonance filters by dip-coating colloidal nanospheres

A guided-mode resonance filter (GMRF) with nanosphere grating layer fabricated by a modified dip-coating method is designed and demonstrated through experiment. The influence of waveguide thickness, radius of nanosphere, incident angle and polarization characteristics on the spectral reflectance are investigated, and optimized structure parameters are obtained. Field distributions of the designed GMRF at resonance and non-resonance wavelength are simulated, and proved that GMR effect will generate when strong coupling occurs between the waveguide layer and the grating layer. In the end, GMRF with 260 nm diameter nanospheres grating layer is experimentally fabricated, neat hexagonal close row structure and a maximum reflectance of 82 % at around 402.3 nm wavelength are obtained.

Nanoporous Alumina Support Covered by Imidazole Moiety-Based Ionic Liquids: Optical Characterization and Application.

This work analyzes chemical surface and optical characteristics of a commercial nanoporous alumina structure (NPAS) as a result of surface coverage by different imidazolium-based ionic liquids (1-butyl-3-metylimidazolium hexafluorophosphate, 3-methyl-1-octylimidazolium hexafluorophosphate, or 1-ethyl-3-methylimidazolium tetrafluoroborate). Optical characteristics of the IL/NPAS samples were determined by photoluminescence (at different excitation wavelengths (from 300 nm to 400 nm), ellipsometry spectroscopy, and light transmittance/reflectance measurements for a range of wavelengths that provide information on modifications related to both visible and near-infrared regions. Chemical surface characterization of the three IL/NPAS samples was performed by X-ray photoelectron spectroscopy (XPS), which indicates almost total support coverage by the ILs. The IL/NPAS analyzed samples exhibit different photoluminescence behavior, high transparency (<85%), and a reflection maximum at wavelength ~380 nm, with slight differences depending on the IL, while the refractive index values are rather similar to those shown by the ILs. Moreover, the illuminated I−V curves (under standard conditions) of the IL/NPAS samples were also measured for determining the efficiency energy conversion to estimate their possible application as solar cells. On the other hand, a computational quantum mechanical modeling method (DFT) was used to establish the most stable bond between the ILs and the NPAS support.

Optical Properties of Coal after Ex-Situ Experimental Simulation of Underground Gasification at Pressures of 10 and 40 bar

Coal gasification experiments were carried out in a reactor used to simulate underground coal gasification (UCG) processes under ex situ conditions at pressures of 10 and 40 bar. Changes in the optical properties of the organic matter were analyzed and the influence of temperature on coal during the UGC process was subsequently determined. The values of the true maximum reflectance determined for the gasification residue at pressures of 10 and 40 bar, and at distances of 0.75 and 1.75 m, reached a level corresponding to semi-graphite. Furthermore, it was found that the values of the true maximum reflectance and bireflectance decrease with increasing distance from the reactor chamber inlet. In addition, the results show that, regardless of the pressure used during the experiment, the temperature influence on the coal decreased with increasing distance from the reactor chamber inlet. The true temperatures operating during the experiment were higher than those recorded by the thermocouples, regardless of the pressure used. However, it was found that the distance at which the influence of temperature on the coal is still marked during the gasification process depends on the pressure used in the experiment. For example, in the case of the experiment at a pressure of 10 bar, the estimated distance is approximately 60 m, while for a pressure of 40 bar, it is approximately 35 m. These results can, and should, be taken into account for the planning of an UGC process.

Mesogen-jacketed liquid crystal like block copolymers: synthesis and self-assembly to prepare 1D PC thin films

One dimensional photonic crystals (1D PCs) show great potential application in light control, sensors and functional displays. Self-assembly of block copolymer is a facile method to prepare 1D PCs in large area and easy processing. However, due to the low refractive index of polymer and the chain entanglement at very high molecular weight, it is difficult to prepare 1D PCs by self-assembly of linear block copolymers. In this work, mesogen-jacketed liquid crystals like block copolymers with two different lumbar connected benzene terephthalate derivatives and polynorbornene backbone are designed and synthesized. The big steric hindrance of the mesogenic benzene terephthalate derivatives extends the polymer backbone to be rigid, and the resultant block copolymers are rapidly self-assembled into lamellar structures with big domain spacing. The refractive indexes of the two blocks is differentiated by selecting the phenyl and decyl substitute group of benzene terephthalate derivatives. Hence, 1D PCs are prepared by self-assembly of mesogen-jacketed liquid crystals like block copolymers. The maximum reflectance is ranged from ultraviolet to near infrared by increasing the polymerization degree of the block copolymers from 400 to 1400 gradually. The lamellar structures are characterized by cross section scanning electron microscope and small angle X ray scattering. Mesogen-jacketed liquid crystal like block copolymer is favored in 1D PC preparation for its facile synthesis and flexible structure design.

TiO2:ZnO/CuO thin film solar cells prepared via reactive direct-current (DC) magnetron sputtering

TiO2:ZnO/CuO thin-film solar cells are manufactured using reactive direct-current magnetron sputtering. For the first time, the TiO2:ZnO layers have been used as an emitter in TiO2:ZnO/CuO solar cells by self-produced Ti-ZnO targets. The structural and morphological characterization of the TiO2:ZnO/CuO solar cells was studied using physical methods of investigation: X-ray diffraction (XRD), scanning electron microscopy (SEM), and current-voltage (I-V) characteristics. From the XRD study, thin films were observed in CuO, ZnO, TiO2 and Ti3O5 phases. Basic morphological characterizations like thickness, mechanism of growth, and average grain sizes were analyzed via scanning electron microscopy. The thicknesses of the TiO2:ZnO and CuO layers were in the range of 170 to 354 nm and from 508 to 1634 nm, respectively. Furthermore, average grain sizes of CuO layers were in the range of 40–150 nm. The I-V study confirms the photovoltaic behavior of TiO2:ZnO/CuO thin-film solar cells. The open-circuit voltage (Voc) and short-circuit current density (Jsc) values of the photovoltaic devices ranged from 1.5 to 49.0 mV and from 0.45 to 7.26 µA/cm3, respectively. Additionally, the authors calculated and analyzed the values of Pmax, Isc, FF, Rs and Rsh. Finally, the optical properties of the thin film were studied. The total light transmission through the structure does not exceed 25% and the absorption coefficient below 600 nm is in the range 2 × 104–2 × 105 cm−1. The maximum reflectance value is observed in the UV-visible region and does not exceed 42%. The extinction coefficient varies between 0.1 and 0.9 depending on the wavelength and sample. The refractive index at 400 nm depends on the sample and is in the range of 1.7 to 4.5. The obtained values of the optical band gap for the investigated samples are 1.02 eV, 1.25 eV, 1.26 eV and 1.28 eV.

Petroleum source rock evaluation of organic black shales in the Paleogene N'kapa Formation, Douala Basin, Cameroon

Black shales outcropping in the Douala Basin were studied using organic petrography and Rock-Eval pyrolysis. The goal of this study was to use organic petrography and bulk geochemical analysis to evaluate N'kapa Formation shales in terms of organic matter (macerals) composition and its relationship to oil and gas productivity potentials. The quantity of organic matter, kerogen type and thermal maturity were determined, and their relationship to oil and gas generation was evaluated. The results of this investigation indicate that the nine samples analyzed had average random vitrinite reflectance values (VRo random) between 0.48 and 0.57% and are indicative of immature source rocks. Calculated maximum reflectance values (VRo maximum) ranged from 0.50 to 0.59%, showing a maximum volatile C bituminous rank and Liptinite macerals were found to fluoresce in the yellow-green to the yellow range, which is consistent with the indicated rank. The total organic carbon (TOC) of the samples ranges from 0.55 to 2.23 wt% (average of 1.18 wt%), implying fair to good concentration of organic matter, while the S1 values range from 0.04 to 0.10 mg HC/g rock (average of 0.07 mg HC/g rock) and S2 values range from 0.10 to 0.91 mg HC/g rock (average of 0.38 mg HC/g rock) and are described as showing poor source potential. Based on Genetic Potential (GP = S1+S2) values (0.18-1.01 mg HC/g rock), the studied N'kapa Formation shales are dominated by type III gas-prone kerogen with a minor association of type IV kerogen. The hydrogen index (HI<50mg HC/g TOC) and oxygen index (OI<75mg CO2/g TOC) values are too low for the shales to have generated hydrocarbons. The low values HI and OI and the absence of type II and mixed type II/III may be due to some degree of weathering of the samples.

High-quality n-type conductive Si-doped AlInN/GaN DBRs with hydrogen cleaning

We proposed and investigated hydrogen cleaning for decreasing pits and threading dislocations generated at interfaces of GaN on AlInN in Si-doped graded AlInN/GaN DBRs. We found that hydrogen cleaning was very useful to suppress the threading dislocation generations, resulting in two orders of magnitude less than the case without hydrogen cleaning. A high-quality conductive Si-doped AlInN/GaN DBR was obtained with hydrogen cleaning, showing a maximum reflectivity of 99.8%, a low pit density of less than 106 cm−2, and a reasonably low vertical resistance of 15 Ω.

Growth Optimization of Nonpolar Al0.7Sc0.3N(112¯0)/Al2O3(11¯02) Thin Films Using Reactive Magnetron Sputter Epitaxy

A‐plane Al0.7Sc0.3N) thin films are grown on r‐plane Al2O3() substrates using reactive pulsed‐DC magnetron sputter epitaxy. This is the first report of successful synthesis of nonpolar epitaxial AlScN films with a high scandium concentration (30%). The influence of different sputtering conditions, such as magnetron power, temperature, and process gas flow rates, is investigated. The film characteristics are also compared on different substrate offcuts. Controlling the diffusion of adatoms on surface of the substrate is found to have the highest influence on film quality. The X‐ray diffraction measurements confirm in‐plane oriented AlScN) layers and the final optimized films show significant improvement in rocking curve full width at half maximum (ω‐FWHM) of reflection. Corresponding atomic force microscopy (AFM) measurements show mean root square surface roughness (R q &lt; 0.4 nm) nearing atomically smooth levels. The optimized films also exhibit anisotropic growth characteristics. A growth model for a‐plane AlScN has been proposed based on the growth parameters of the film.

V. Relationships Between Bio-Optical Parameters of the Black Sea Waters and Spectral Reflectance Coefficient in Spring 2019

The paper presents an analysis of field measurements of the spectral reflectance of the Black Sea and the bio-optical and colorimetric characteristics calculated from it, as well as chlorophyll concentrations and the Secchi disk depth. For the regions of the Black Sea with different characteristics, the averaged values of the calculated characteristics are presented: the effective and dominant wavelength in the reflectance spectrum, the purity of the water color. Using the previously developed bio-optical algorithm, the concentration of chlorophyll, absorption by dissolved organic matter, backscattering by suspended matter, and the vertical light attenuation coefficient were calculated.Inverse relationships are established between the Secchi disk depth and the maximum reflectance, as well as between the Secchi disk depth and the dominant wavelength. Linear relationships with high correlation coefficients are obtained between the surface chlorophyll concentration and the effective and dominant wavelength. A significant relationship was also established between the surface chlorophyll concentration and the maximum reflectance. Among the relationships between bio-optical and colorimetric parameters, a high correlation is observed between the vertical light attenuation coefficient and color purity.Chlorophyll concentrations calculated from the data of the spectral reflectance coefficient using a semi-analytical algorithm are in good agreement with the data of field measurements. Comparison of calculated and measured chlorophyll concentrations with satellite products of optical ocean color scanners shows an overestimation of chlorophyll concentrations by satellite data processing algorithms. The obtained correlations can be used in the future to assess bio-optical parameters in the northern part of the Black Sea.

From halfmetallicity to dielectric tensor: Atomistic study of phase stability and optical spectrum of Sr2FeMoO6 double perovskite and its potential applications

Structures and the physical properties of the current physical materials and other hypothetical models can be visualized and estimated with considerable success using density functional theory. As promising materials Double Perovskites satisfy the need of fulfillment of energy requirements in current scenario. Probing and investigating such structures theoretically, saves time and curtails the expenditure. This Perspective highlights the optical response functions viz Dielectric Tensor, Polarizability, Reflectivity, Optical conductivity, Absorption Coefficient and Extinction Coefficient of the material in the presence of electromagnetic field of varying energy (0–5eV) and offers an outlook of the potential use of such properties in spintronics and sensors. In our study the effective PBE (Perdew, Burke, Ernzerhof) functional was used to investigate the electronic and optical properties of Sr2FeMoO6 and the thermodynamic stability of the material was estimated using the convex hull approach. The formation energy calculated from total energies of the bulk material (SFMO) and the individual total energies of the constituent elements in their corresponding pure bulk phase indicate the simulated structure to be thermodynamically stable with an energy value of −2.533eV. The study confirms SFMO as an anisotropic dispersive medium, with non-linear optical properties wherein apart from differential rates of absorption along different axis of polarization, nonlinearity and dispersion with respect to optical conductivity, dielectric constant can also be observed. The absorptive bandwidth of the material estimated by density functional approach lies between 2 and 4.5 eV and the absorption function resembles the Gaussian curve. The optical conductivity curve indicates that Sr2FeMoO6 is a direct band gap material with a bandgap of 2.1 eV. The absorption coefficient “μ” peaks at an energy values of 3.2 eV and the material is absorptive for most part of the ultra violet region. The pourbiax analysis of the material has been presented and the stability in presence of varying chemical potentials and pH scales suggest non toxicity and stability associated with the material. The extinction coefficient “K” for the two directions of polarizing field behave analogous to their respective imaginary dielectric functions and the peak value of the extinction coefficient shoots to 0.8. The reflectivity plots indicate the maximum reflectance reaches to about 0.2 (20% reflectance) and then decreases with the increase in the energy of the perturbing field. Spin Polarization and the observed TDOS (total density of sates) APDOS (atom projected density of states) graphics suggest that Sr2FeMoO6 exhibits near-half metallic behaviour and can dramatically enhance device performance by controlling speed and various other properties wherein spin can be manipulated. Consequently, SFMO can be tailored for spintronic applications especially in case of multilayered spin-operated junctions/devices and nonvolatile memory elements, quantum computing and faster data processing speeds.

Microphysical Differences in the Concentric Eyewalls of Typhoon Lekima (2019)

AbstractUsing polarimetric radar observations, different microphysical characteristics were found in the asymmetric concentric eyewalls of Typhoon Lekima (2019). In addition to the differential reflectivity (ZDR) column, a typical size‐sorting radar signature was evident in the upright inner eyewall: a cyclonically upwind offset of the ZDR maximum relative to the horizontal reflectivity (ZH) and specific differential phase (KDP) maxima. In contrast, the large values of ZDR were located above the melting layer along the upper edge of the more tilted outer eyewall and did not extend downward to form a ZDR column. In the cyclonic direction, moreover, the large values of the three polarimetric variables in the outer eyewall almost overlapped, without the cyclonic offset of typical size‐sorting radar signature. Thus, more active warm‐cloud (cold‐cloud) processes dominate in the outer (inner) eyewall, particularly for the production of large drops, closely associated with the intrinsic dynamical structure of the concentric eyewalls.

Tunable Semiconductor Laser Based on Surface High-Order Bragg Gratings With 62 × 50 GHz Wavelength Tuning

A tunable semiconductor laser based on surface high-order Bragg gratings with 50 GHz channel spacing is demonstrated for the first time. The tunable semiconductor laser can cover 62 channels at 25 °C, and the side mode suppression ratio (SMSR) of each channel is larger than 34 dB. To achieve such properties, the number, depth and periods of the slots of the tunable semiconductor laser are optimized by the 2-D scattering matrix method (SMM) to obtain denser reflection peaks with smaller full width at half maximum (FWHM) and higher reflectivity. The tunable semiconductor laser can be widely used in dense wavelength division multiplexing (DWDM) systems and can provide a promising light source for photonic integrated circuits.

Gate‐Tunable Graphene Optical Modulator on Fiber Tip: Design and Demonstration

AbstractA fiber‐end‐face‐integrated electrically tunable optical modulator based on graphene field‐effect transistor and the fabrication technique are proposed and demonstrated. The all‐fiber device features a scheme of compactness and high integration when applied to fiber optical system, as well as a low insertion loss since spatial coupling of light is avoided. A reflecting structure is used and the electro‐optic modulator shows vivid modulation when gate voltage gets tuned, with maximum optical reflectance modulation depth over 1% in demonstration. To the best of the authors’ knowledge, it is the first time to build an all‐solid gate‐control modulator directly on fiber facet. The fabrication methods introduce workflows of silicon‐on‐insulator processing into the optical fiber end‐face micromachining domain which can be applied to more comprehensive configurations, broadening the path of fiber‐end‐face integrated device.

Broadening the absorption bandwidth based on heavily doped semiconductor nanostructures.

Broadband light absorption is a basis for the proper functionality of various materials, microstructures, and devices. Despite numerous studies, however, many aspects of broadband absorption remain uncovered. In this paper, we demonstrate an inverse-problem approach to designing nanostructures with a very low optical reflection and high absorption through a frequency band. Particular emphasis is made on a subwavelength transparent film as a top layer and anisotropic substrate. The polarization-dependent metamaterial absorber based on a subwavelenth semiconductor multicomponent multilayer structure is proposed and numerically investigated. For an illustration, we consider a four-component heavily doped silicon lattice with a thin undoped silicon top layer. The dielectric response of the structure is engineered by controlling the free carrier density and filling factor of each layer. A simulation study reveals a power law dependence of the bandwidth on the maximum reflectivity within the band.