Optical Transmission Enhancement Research Articles

Enhancement of growth perfection and optical transmission in rhodamine B-doped KDP single crystal for photonic applications

In recent years, because of the rapid development persisting in the modern electronic industries, materials with the ability to produce highly efficient harmonic generation have acquired great demand as they are suitable for high-speed devices and the progressing field of optical communication systems. The present work reports the growth, diffraction and spectroscopic features of the pure and Rhodamine B (RB)-doped potassium dihydrogen phosphate (KDP) crystals. The crystals were grown by employing the conventional slow evaporation technique. The XRD and UV–visible spectral studies have been carried out to examine the structural and optical behavior of the grown crystals. An optical microscopic technique has been utilized to explore the surface features of the crystals. Based on the growth features and the observed analytical results, it is authenticated that the RB-doped KDP crystal possesses a better crystalline nature and optical transmittance than the pure KDP crystal thereby it is strongly suggested for the applications of photonic devices.

Window layer based on ZnO and Ag thin films incorporated in solar cells as a part of hybrid energy-saving system

We have started a new research project on a hybrid power generation system consisting of piezoelectric, thermoelectric and solar cell modules. In the first step, we have focused on the antireflection coating based on zinc oxide (ZnO) and metal nanolayers incorporated in solar cells. In layered structure containing ZnO and metal nanoscale layers, we have presented the possibility of increasing wave transmission in the visible region by adding the top and bottom cap layers. The enhancement of optical transmission is very important in improving the performance of sensor protections, solar cells, UV protective films and transparent conductive display panels electrode. It is found that, the structure containing both the top and bottom cap layers (S3) yields larger transmittance than the structures S1 without any cap or S2 just with one cap layer. The maximum transmittance in the visible range can be increased from 33% to 67%. In addition, for the TE mode (TM mode), the maximum value of transmission in the S1 and S2 structures occurs at angles close to normal incidence while in the S3 multilayer it happens around 1 radian, that is, the behavior of the TE mode is the opposite of the TM mode. Also, when the incident angle varies, the band edges experience a blue shift. The amount of TE shift is more pronounced than TM one. Moreover, the metal with higher plasma frequency will move the band gap edges to the higher frequencies.

Fabrication of porous and visible light active ZnO nanorods and ZnO@TiO2 core-shell photocatalysts for self-cleaning applications.

Highly transparent and self-cleaning ZnO nanorods (NRs) and ZnO@TiO2 core-shell (CS) nanoarrays were fabricated using the sol-gel dip-coating technique. TiO2 nanoparticles (NPs) were coated as a shell layer over the hydrothermally grown ZnO NRs. The number of shell layers on the ZnO NRs was varied by modulating the number of dipping cycles from 1 to 3 to optimize their transmittance. The optimized CS nanoarrays with two dipping cycles display a 2% enhancement of optical transmission compared to the ZnO NRs. In addition, superhydrophilicity (contact angle ∼of 12°) stimulates the self-cleaning nature of the thin films. A water contact angle of 12° was noted for the ZnO@TiO2: 2 cycle sample, indicating their superhydrophilic nature. Moreover, the photocatalytic activity of the pristine ZnO NRs and ZnO@TiO2 CS nanoarrays was tested under UV and direct sunlight through the dye degradation of methylene blue (MB). Based upon the TiO2 morphology and accessibility of the ZnO@TiO2 heterojunction interface, CS nanoarrays with two shell layers exhibit the highest degree of dye photodegradation efficiency of 68.72% and 91% under sunlight and UV light irradiation, respectively. The CS nanoarrays demonstrate medium sunlight and excellent UV-light-driven photocatalytic activity. Our findings suggest that the ZnO@TiO2 CS nanoarrays are potential photocatalysts for dye degradation and self-cleaning applications in solar cell coverings.

Security Enhancement in Coherent OFDM Optical Transmission With Chaotic Three-Dimensional Constellation Scrambling

In this paper, we propose and experimentally demonstrate a novel hybrid chaos-based three-dimensional (3-D) constellation scrambling scheme to simultaneously improve the physical layer security and transmission performance of the coherent optical orthogonal frequency division multiplexing (CO-OFDM) system. A 3-D regular hexahedron signal constellation is constructed by the constellation figure of merit principle, which not only expands the encryption dimension but improves the error performance. The dynamic parameters for constellation scrambling are generated by the 5-D hybrid chaotic scheme based on the combination of a 3-D hyperchaotic Hénon mapping and two independent 1-D Logistic mappings, as such a key space of ∼10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">133</sup> is introduced to enhance the security level of OFDM data encryption during transmission. Furthermore, a transmission experiment for encryption of 144 Gbps 16-quadrature-amplitude-modulation OFDM data over a 100 km standard single-mode fiber in a CO-OFDM system is demonstrated. Compared with the case of using the 3-D rectangular constellation, a 2 dB bit error rate performance improvement is achieved. The results show that the proposed scheme could effectively enhance the system security and transmission performance, which suggests a scalable strategy for future physically secured CO-OFDM systems.

Dielectric dynamics and optical behaviour of surfactant free LC/silicone oil based non-aqueous emulsions

ABSTRACT We are presenting the non-aqueous emulsions comprising of liquid crystal 8CB (4′-Octyl-4-biphenylcarbonitrile) and silicone oil in varying ratios (5:95, 10:90, 25:75 and 50:50 wt./wt.%). Emulsions are self-stabilised via dipolar interactions, alignment and anchoring without the use of any surfactant. The formation of distinct defects geometries over the studied concentration range of silicone oil in the liquid crystal matrix has been discussed. The dielectric dynamics of the non-aqueous emulsions have been studied in the smectic (30°C) and nematic (38°C) phases over the continuous broadband of frequency 50Hz–1MHz. In both cases (smectic and nematic regions), dielectric permittivity decreases with a rise in the content of the silicone oil in the emulsion systems. The proposed mechanism for such dielectric behaviour has been discussed considering charge/defects boundary interactions and decrement of resultant dipole moment. A relaxation mode in the lower frequency range has been observed for all the emulsion systems. In addition, the emulsion systems have shown significant optical transmission behaviour. A significant enhancement in optical transmission about 82% has been noticed for 25 wt% comparing to 5 wt% emulsion system. Such self-stabilised systems could pave a way to develop dual-frequency LCs systems for progressive technological applications, tunable polarisation filters, and adaptive optics.

Electrically switchable and optically tunable liquid crystal/ silicone oil based non-aqueous emulsions for electro-optical device applications

Liquid crystal/silicone oil based emulsions have been prepared and characterized for interfacial interactions, optical and electro-optical behaviour. Emulsions are stabilized without any surface-active agent via non-covalent interactions, surface alignment and anchoring conditions. Emulsions are characterized by polarizing optical microscopy. Distinct mesomorphic phases, droplet geometries (radial, hedgehog, bipolar) and transitions viz. radial to bipolar and bipolar to broken bipolar are observed as a function of varying silicone oil concentration in liquid crystal. These emulsions are quite stable and show reversible characteristics as a function of time and temperature. The stability of these emulsions has been explained considering hydrophobic interactions, decrease in internal surface tension and anchoring energy etc. Further, the liquid crystal/silicone oil devices have been fabricated and tested for switching and electro-optical behaviour. The emulsion contains 25% silicone oil in liquid crystal matrix shows the best switching characteristics at low deriving voltage 5 V, about 87% enhancement in optical transmission, 8.3 dB contrast and lower Frederiks threshold ~65%. Such switchable and optically tuneable surfactant-free emulsions with controlled morphological dynamics can provide a new door to design novel functional soft material platform for better optical, electro-optical, photonics, sensing and liquid crystals elastomer applications. • Surfactant-free, electrically switchable and optical tuneable liquid crystals/silicone oil emulsions. • 87% enhancement in transmission, 8.3 dB contrast and lower Fredrick's threshold ~65% has been achieved in emulsion systems. • Tuning of optical and electro-optical parameters depends on the boundary conditions, topological deformations.

Enhanced infrared Faraday rotations and transmission in nonreciprocal magneto-optical structure

At present, most of all the micro/nano scale structure is reciprocal material, that is, behave as reciprocity. Corresponding to the reciprocal material, the nonreciprocal materials can break the time reversal and detailed balance due to the special nonreciprocal effect, which can lead to nonreciprocal optical devices when magnetism is applied. In this paper, the Faraday rotation effect of an open square hole magnetic plasma structure with periodic corner openings has been studied. The size of the magneto-optical plasmon film is only 600 nm, which is extremely small compared to a hundred-micron magneto-optical garnet film. It is found that the Faraday deflection angle can be adjusted by changing the size of the applied magnetic field without affecting the transmittance. Moreover, the influence of the width of the metal structure and the thickness of the magneto-optical material on the Faraday effect is studied. The maximum Faraday deflection angle can be achieved as 22° and the transmittance is up to 0.63, as the side length of corner openings is set to 100 nm. At the same time, the mechanism of the giant Faraday effect is further explained through the output electric field distribution. It is found that the optical isolation had a high non-reciprocal Faraday rotation and optical transmission enhancement, which will has application in infrared optical isolation.

Enhancement in structural, optical and morphological properties of sprayed In2O3 thin films induced by low energy electron beam irradiation

In2O3 thin films have been synthesized on glass substrates by spray pyrolysis then irradiated by electron beam (EB) at low energy of 0.8 MeV for three fluencies 4.1016, 35.1016 and 42.1016 electron/cm2. EB irradiation was performed by an industrial electron accelerator owned to COFICAB Company. Structural, optical, photoluminescence and morphological properties of In2O3 thin films have been investigated before and after EB irradiation by X-ray diffraction, spectrophotometer, SEM and fluorescence spectrometer. After EB irradiation at 4.1016 electron/cm2, the preferred orientation of In2O3 thin film was moved from (222) to (400) with a simultaneous improvement in grain size. For EB fluency of 35.1016 electron/cm2, In2O3 thin film has been strangely transformed from polycrystalline phase to a single crystal structure. After irradiation at 42.1016 electron/cm2 fluency, In2O3 thin film became amorphous. A clear enhancement in optical transmission has been observed after irradiation with a slight variation in band gap energy. Surface morphology of the irradiated In2O3 thin films has been transformed from rough to continuous, uniform and smooth surface. This study have shown that EB irradiation can be considered as a useful mean for enhancement of In2O3 thin films physical properties and suggest its use for the space optoelectronic applications.

In Situ Dynamics during Heating of Copper-Intercalated Bismuth Telluride

Summary The presence of a van der Waals gap within layered materials enables the intercalation of guest species, which can be used for tuning properties. The introduction of intercalant species may also lead to structural transformations across a range of temperatures and use conditions, but we have a limited understanding of the high-temperature evolution of intercalated layered materials. Here, we use in situ transmission electron microscopy to investigate temperature-dependent structural evolution of Bi2Te3, a layered material with well-known application as a thermoelectric, which contains intercalated Cu. As temperature is increased, the initially disordered Cu undergoes local ordering within the van der Waals gap, along with anisotropic sublimation behavior of the crystals. As the temperature is raised further, layered Cu2Te crystals nucleate and grow with a crystallographic relationship to the Bi2Te3 lattice. Notably, the presence of Cu decreases the thermal stability of the Bi2Te3 and substantially alters the transformation pathways during heating.

Plasmonics Induced Multifunction Optical Device via Hoof-Shaped Subwavelength Structure

The electromagnetic spectrum includes the frequency range (spectrum) of electromagnetic radiation and its corresponding wavelength and energy. Due to the unique properties of different frequency ranges of the electromagnetic spectrum, a series of functional devices working in each frequency rang have been proposed. Here, we propose a periodic subwavelength hoof-shaped structure array, which contains a variety of geometric configurations, including U-shaped and rectangle structures. The results show that the enhanced optical transmission (EOT) effect of the surface plasmon excited by the hoof-shaped structure is highly sensitive to the polarization of the incident light, which leads to the peak’s location shift and the amplitude intensity variety of transmission peaks of U-shaped structure in the case of coupling based on the surface plasmon of rectangle structure. In addition, take advantage of the EOT effect realized in the periodic hoof-shaped structure array, we propose a multifunctional plasmon optical device in the infrared range. By adjusting the polarization angle of the incident light, the functions of the optical splitter in the near-infrared range and the optical switch in the mid-infrared range are realized. Moreover, with the changes of the polarization angle, different proportions of optical intensities split are realized. The device has theoretically confirmed the feasibility of designing multifunctional integrated devices through a hoof-shaped-based metamaterial nanostructure, which provides a broad prospect for the extensive use of multiple physical mechanisms in the future to achieve numerous functions in simple nanostructures.

Fabrication of arrangement-controlled and vertically grown ZnO nanorods by metal nanotransfer printing

Vertically aligned ZnO nanorods have been widely investigated for use in piezoelectric generators, photovoltaic devices, nanotemplates, photoelectrochemical applications, etc. In addition to vertical alignment, intentional arrangement of ZnO nanorods according to a careful design can enhance the device performance. In this work, we used metal nanotransfer printing to fabricate arrangement-controlled and vertically grown ZnO nanorods on both hard and flexible substrates. Highly vertical growth and periodical arrangement of the ZnO nanorods were confirmed by microscope images. Their crystallinity and photoluminescence characteristics were also investigated. Transmission spectra of the substrates show the enhancement of optical transmission after the nanorod growth. We believe that this fabrication technique lends itself to simple fabrication of arrangement-controlled and vertically grown one-dimensional nanostructures on both hard and flexible substrates for application in solar cells, water splitting, metamaterials, etc.

Enhancing optical transmission of multilayer composites using interfacial nanostructures

We demonstrate the suppression of light reflections at solid-solid interfaces in multilayer thin and thick films using interfacial nanostructures. The embedded nanostructures have subwavelength features and function as a gradient-index medium to eliminate Fresnel losses induced by refractive index mismatch between dissimilar materials. Suppressing the interfacial reflection can reduce interference effects in thin films, and the transmittance measurement of a polymer on a silica substrate demonstrates a two-fold decrease in interference fringe contrast. A thick multilayer composite consisting of three fused silica and two polymer layers has also been fabricated and demonstrates the enhancement of optical transmission up to 30% at high incident angles. The effects of the interfacial structure geometry are examined by theoretical models based on rigorous coupled-wave analysis methods. The experimental results agree well with simulation models, which predicts that further improvements can be achieved using the optimized tapered profile. This work indicates that interfacial nanostructures can improve the broadband and wide-angle response of multilayers and can find applications in thin-film optics, optoelectronic devices, and composite windows.

Massive Enhancement of Optical Transmission across a Thin Metal Film via Wave Vector Matching in Grating-Coupled Surface Plasmon Resonance.

We demonstrate how distinct surface plasmon resonance modes on opposite sides of a metal-coated grating can be coupled across the metal film. This coupling occurs by matching the resonance conditions on each side of the grating by tuning the refractive index directly adjacent to the metal film. In the first example, we deposited a high refractive index layer of tin oxide on top of the grating to red-shift the front side surface plasmon until it coupled with the backside surface plasmon across a semitransparent ∼45 nm thin silver grating. By shifting the resonance condition of the nearby surface plasmon, this high refractive index coating creates an effective matching of wave vectors across the metal film, allowing them to couple and enhance the optical response. A massive increase in the magnitude of enhanced transmission is observed, increasing from a 6-fold transmission enhancement through a bare silver grating to a near 100-fold enhancement after deposition of a tin oxide layer of appropriate thickness (∼310 nm). This optical transmission enhancement is then probed through computational modeling and by experiments with liquids of various refractive index values. The matched system shows an increased amplitude sensitivity with respect to refractive index changes and a waveguide like behavior within the tin oxide film. As an alternative configuration, we also demonstrate coupling the front and back-side plasmon modes by using a lower refractive index substrate in order to blue-shift the back-side surface plasmon. Coupling between the two plasmon modes is then demonstrated by introducing aqueous solutions of various refractive index values. Under the proper conditions, this matched system also shows a substantial enhancement in transmission. This technique of wave vector matching provides a route to substantially increasing the plasmon enhanced optical transmission through metal gratings, which has potential application in improved plasmonic sensing, spectroscopy, and plasmon-based optical devices.

Enhanced Optical Transmission Assisted Near-Infrared Plasmonic Optical Filter via Hybrid Subwavelength Structures

Enhanced optical transmission (EOT), which results from the incident light interacting with the subwavelength nanostructures patterned in a metallic film, showcases the excitation of surface plasmon modes on both surfaces of the metallic film and their intercoupling effects. Here, we numerically study the EOT phenomenon from the incident light acting on the periodic subwavelength hybrid arrays in a metallic film, which contains annular concentric core and aperture unit structure undergoing multiple geometrical configurations. It is shown that several configurations, which consist of a core with a different number of apertures, of the unit structure, are possible to facilitate the intercoupling between the surface plasmon polariton resonance mode of the core and the localized surface plasmon resonance mode of the aperture. Moreover, taking advantage of the EOT effect realized in the periodic structure arrays including a concentric core with triple-aperture unit structure, we propose a plasmonic optical filter (POF) in the near-infrared region. By adjusting both the periods and the width difference between the nearest-neighbor two apertures of the unit structure, the realization of near-infrared POF accompanies with tunable positions and amplitudes of the EOT peaks. Additionally, these behaviors could also be extended to the case of a concentric core with a multiple-aperture unit structure for actualizing near- or mid-infrared POF effect. Our results promise new avenues for plasmonic devices and enrich the application range of metallic structures in the field of optical communications and information processing.

Enhancement of extraordinary optical transmission and sensing performance through coupling between metal nanohole and nanoparticle arrays

The extraordinary optical transmission (EOT) of sub-wavelength nanohole array is significantly enhanced through introducing nanoparticles, including nanospheres and nanocylinders, into the centers of the nanoholes. Maxima of 56% and 48% for nanocylinder and nanosphere matrices are achieved, compared with that of 37% for a none-in-hole nanohole array gold film. The mechanism behind the phenomena is discussed, indicating that surface plasmon mode coupling between nanoholes and nanoparticles rather than Fabry–Pérot resonance is the cause for the EOT enhancement. High near-field intensity enhancement also leads to the interaction between analytes and optical field increasing, therefore an improved sensitivity and figure of merit for biosensing. The modified structures are highly promising in practical sensing applications due to the incident angle independence. Similar results are obtained for a hexagonal array of nanohole gold film and nanoparticle modifications thereof.

Enhanced Faraday rotation and magneto-optical figure of merit in gold grating/graphene/silicon hybrid magneto-plasmonic devices

Graphene is a promising THz magneto-optical material. However, high Faraday rotation is only achievable at a low THz frequency range in single layer graphene. In this paper, we report simultaneous Faraday rotation and optical transmission enhancement in Au grating/graphene/silicon hybrid plasmonic structures across a wide frequency range from 0.43 to 24 THz using extraordinary transmission of THz spoof surface plasmons. In a broad frequency range up to 13.1 THz, the Faraday rotation and magneto-optical figure of merit in this hybrid structure can exceed the maximum value of single layer graphene at the low THz frequency range. Numerical analysis on the device dispersion relation indicates that the mechanism of simultaneous Faraday rotation and transmission enhancement is due to coupling of the TE waveguide mode with the TM hybrid waveguide-plasmon mode. Our work demonstrates the hybrid plasmonic structure as a promising candidate for THz nonreciprocal photonic device applications.

Fast vertical mode expansion method for the simulation of extraordinary terahertz field enhancement in an annular nanogap

This paper is concerned with electromagnetic wave scattering of an annular nanogap in the terahertz regime. We present an efficient vertical mode expansion method (VMEM) to solve the scattering problem, and study the extraordinary optical transmission and field enhancement for the nanostructure with various configurations. The VMEM expands the electromagnetic field in and outside the nanogap along the invariant direction by the one-dimensional modes, where the expansion coefficients satisfy scalar two-dimensional Helmholtz equations on the cross-sectional plane. The continuity conditions of electromagnetic fields on the vertical boundaries of neighboring regions are then employed to establish the linear system for the unknown coefficients. Based on the numerical simulations, we investigate the field enhancement in the nanogap. In particular, we investigate the nanostructure with a series of gap sizes and push the gap width limit to 1 nm in the numerical simulation. The normal and oblique incidence cases and the transverse electric (TE) and transverse magnetic (TM) polarization cases are considered.

A Compact Optical Switch via Plasmonics of Subwavelength Circular‐Sharp Hole Arrays in Metal Films

AbstractWe studied numerically the enhanced optical transmission (EOT) through periodic subwavelength circular‐sharp hole arrays in metallic films with different edge sharp distribution features of unit structures. Detailed studies indicate that the unit structure edge sharp distribution features strongly influence the surface plasmons (SPs). These results demonstrate that the number of edge sharp activated the localized surface plamons (LSP) resonance on the unit structure is changed by rotating the polarization of the incident light, leading to change the infrared transmittance of the array. Moreover, a compact plasmonic switch via periodic circular‐sharp hole arrays based on the dependence of SPs on unit structural edge sharp distributions is proposed. The finding provides a new idea for designing plasmonics devices, and expands the application range of metal micro‐nano structure in the field of optical communications and information processing.

Investigation on the bulk growth of $${\upalpha }$$ α - $$\hbox {LiIO}_{3}$$ LiIO 3 single crystals and the influence of pH on its structural, morphological and optical characteristics

\(\upalpha \)-\(\hbox {LiIO}_{3}\) is an excellent optical material exhibiting strong nonlinear optical, piezoelectric and elasto-optic properties. However, its practical applications are limited by the insufficient reproducibility of the mentioned properties caused by the strong influence of the growth conditions, and, in particular, pH of the solution from which \(\upalpha \)-\(\hbox {LiIO}_{3}\) crystal is grown. Herein, we investigate to grow bulk size good quality crystals of \(\upalpha \)-\(\hbox {LiIO}_{3}\) based on the observed problems during its crystallization process. A systematic investigation was carried out to find the effect of pH on solubility, crystal growth, structural, surface and laser damage properties of \(\upalpha \)-\(\hbox {LiIO}_{3}\) single crystals. The structure and phase of \(\hbox {LiIO}_{3}\) were confirmed by powder X-ray diffractometer analysis. The functional groups of the compound were identified using Fourier transform infrared spectroscopy. Surface defects of the grown crystals were studied by etch patterns. The crystal grown at pH 10 showed 10% optical transmission enhancement in comparison to the crystals grown at pH 2. The indirect optical bandgap of the crystal was reinvestigated using ultraviolet–Visible–near-infrared transmittance spectrum. The laser damage threshold studies of the crystals grown at pH 10 reveal the higher optical radiation stability against 532 nm laser. The second-order nonlinear optical behaviour of \(\upalpha \)-\(\hbox {LiIO}_{3}\) crystals grown at different pH conditions have been investigated by using Kurtz and Perry powder technique with Nd:YAG laser pulses at the wavelength of 1064 nm.

Zn doping induced conductivity transformation in NiO films for realization of p-n homo junction diode

Mixed transition metal oxide, zinc doped NiO, ZnxNi1−xO (x = 0, 0.01, 0.02, 0.05, and 0.10), thin films have been fabricated by the RF magnetron sputtering technique in an oxygen deficit ambience at a growth temperature of 400 °C. The present report highlights the effect of Zn doping in NiO thin films on its structural, optical, and electrical properties. Optical transmission enhancement and band gap engineering in a-axis oriented NiO films have been demonstrated via Zn substitution. Hall effect measurements of the prepared samples revealed a transition from p-type to n-type conductivity in NiO at 2% Zn doping. A NiO based transparent p-n homojunction diode has been fabricated successfully, and the conduction mechanism dominating the diode properties is reported in detail. Current-voltage (I-V) characteristics of the homojunction diode are found to obey the Space Charge Limited Conduction mechanism with non-ideal square law behaviour.