A multilayer photonic band gap structure is proposed for sensing applications in visible wavelength range. The structure is designed by introducing alternate layers of dielectric material on a glass substrate. To ease the analyte infiltration and to improve the sensitivity, porosity is introduced deliberately within each layer. Extensive analysis is carried out to optimize the number of dielectric layers, their thickness, and percentage of porosity. The transmission/reflection spectral characteristic and sensitivity of the proposed structure are analyzed by a three-dimensional finite difference time domain method. The porosity value and structural parameters are optimized to obtain highest possible sensitivity. The proposed structure exhibits a 0.05-nm shift in reflection/transmission wavelength with corresponding refractive index change of ^{10  −  3}. Analyte can also be distinguished by seeing the sample color change with naked eyes. Thus, multiparametric characterization of the proposed structure demonstrates its potential for sensing applications.

This guest editorial summarizes the JNP Special Section on Semiconductor UV Photonics.

We have successfully fabricated 7-μm 155-nm-thick undercut microdisk cavities with AlN  /  Al_0.60Ga_0.40N (5.5  nm  /  2.5  nm) multiple quantum wells epitaxially grown on Si substrate by metal–organic chemical vapor deposition. Upon optical pumping, whispering-gallery modes (WGMs) with wavelengths around ∼250  nm can be observed throughout the photoluminescence spectrum at room temperature, with quality factors around 500 to 1000. These cavity modes have been analyzed by theoretical calculations. Our results suggest great potentials to demonstrate WGM lasing in the UVC range from these AlGaN/AlN-on-Si microdisk cavities monolithically grown on a Si platform.

This work reports AlGaN-based deep ultraviolet light-emitting diode (DUV LED) possessing a specifically Al_xGa_{1  −  x}N  /  Al_yGa_{1  −  y}N  /  Al_xGa_{1  −  x}N (x  >  y) structured p-electron blocking layer (p-EBL) to achieve the high external quantum efficiency (EQE). The impact of the p-EBL with Al_yGa_{1  −  y}N insertion layer at different positions and with different AlN compositions on the hole and electron injection is systematically investigated. Our results show that, for the DUV LED structure in this work, both electrons and holes can be most efficiently injected into the active region by keeping the Al_yGa_{1  −  y}N insertion layer near to the p-region. The AlN composition for the Al_yGa_{1  −  y}N insertion layer has also to be optimized for maximizing the carrier injection.

In recent decades, literatures about visible vertical cavity surface emitting lasers (VCSELs) have been reported. However, due to high optical loss in the cavity, lasing from deep ultraviolet (DUV) VCSEL was still rarely achieved. The optical loss in nitride DUV microcavity was analyzed in detail. DUV nitride vertical Fabry–Pérot microcavity with active layer of AlGaN-based quantum dots and double-side HfO₂  /  SiO₂ distributed bragger reflectors was fabricated. Optical losses with of the order of 10³  cm^−  1 were deduced from the Q value of the cavity modes. The main origination of optical loss in DUV cavity was calculated and ascribed to the interface scattering. The interface roughness appearing after laser lift-off process and overlap between rough interface and standing optical wave were two key parameters that contributed to interface scattering loss. We believe that our results will provide useful information for improving DUV VCSEL devices.

The paper demonstrates the design, simulation, fabrication, and analysis of InGaN/GaN superlattice (SL) solar cell with photonic crystal (PhC) structure at the top surface. Ten pairs of In0.18Ga0.82N  /  GaN structure were grown by metal organic chemical vapor deposition technique and had been used as an absorbing layer for solar cell device. PhC light-trapping structure (LTS) was prepared with the top indium tin oxide and p-GaN layers. Both simulation and experimental results demonstrate that PhC LTS structure considerably enhances the efficiency of solar cells. The simulation parameters were optimized and calculated using rigorous-coupled wave analysis method. The experimental studies under 1-sun illumination at standard test conditions exhibit efficiency enhancement of 59% compared to SL structure without PhC LTS.

The effect of the magnetic field on the exciton radiation of ZnO films formed by randomly packed nanorods and covered with Ag nanoparticles has been discovered and studied at room temperature. Photoexcitation was performed by third and fourth harmonics of Nd:YAG laser. The radiation of the investigated samples consisted of exciton luminescence and random lasing in the near UV range. Several percent enhancement of the exciton radiation intensity was observed at some areas of the films subjected to the magnetic field H  ∼  1  T. The enhancement depends slightly on the excitation level. At the same time, in some other areas of the same films, the effect was negligible or absent. It is supposed that the observed effect is related to magnetoexcitons, which are possibly formed due to increasing of the exciton momentum nearby the Ag nanoparticles. The probability of magnetoexciton recombination increases significantly even in a weak magnetic field due to strong stretching of its wave function.

AlGaN-based near-ultraviolet light-emitting diodes (NUV-LEDs) emitting at 370 nm were grown on Si(111) substrates by metal-organic chemical vapor deposition. The effect of growth parameters of Si-doped n-type AlGaN thick layer on the material quality and optical performance was studied. Photoluminescence measurements showed that the near-band-edge emission of n-AlGaN was greatly increased and the yellow luminescence (YL) was substantially reduced, when the n-AlGaN layer was grown at a high temperature, a high chamber pressure, and a low growth rate. It was found that the reduced unintentional carbon incorporation in the n-AlGaN layer under those growth conditions was responsible for the improved optical property. The NUV-LED employing the optimized growth parameters of n-AlGaN showed an enhanced light output power and a suppressed YL emission, as well as a better color purity, as compared with the reference one. The results indicate that performance of NUV-LED can be significantly improved by suppressing unintentional carbon incorporation and the defects-related absorption/re-emission in the n-AlGaN.

Group III-nitride semiconductor materials especially AlGaN are key-emerging candidates for the advancement of ultraviolet (UV) photonic devices. Numerous nanophotonics approaches using nanostructures (e.g., nanowires, nanorods, and quantum dots/disks) and nanofabrication (e.g., substrate patterning, photonic crystals, nanogratings, and surface-plasmons) have been demonstrated to address the material growth challenges and to enhance the device efficiencies of photonic devices operating at UV wavelengths. Here, we review the progress of nanophotonics implementations using nanostructured interfaces and nanofabrication approaches for the group III-nitride semiconductors to realize efficient UV-based photonic devices. The existing challenges of nanophotonics applications are presented. This review aims to provide analysis of state-of-the-art nanophotonic approaches in advancing the UV-photonic devices based on group III-nitride semiconductors.

We report the regrown Al-rich of n-AlGaN material with improved crystalline quality and reduced stress on nanoporous AlGaN template, which was prepared by the electrochemical etching (EC). First, the EC of Al-rich Al_xGa_1-xN (x  >  50  %  ) material was investigated to get suitable nanoporous template. Various anodizing voltage and anodizing time were applied to fabricate the nanoporous AlGaN template. The nanopore size and density were found to increase as the anodizing voltage and the anodizing time increase. Moreover, branching pores and vertical pores were apt to be formed at low and high voltages, respectively. Photoluminescence (PL) measurement and Raman spectra indicate that the nanoporous AlGaN materials exhibit higher PL intensity and dramatical release of stress compared to the as-grown AlGaN films due to the presence of nanopores. Furthermore, the nearly stress-free regrown n-AlGaN with high quality using optimized nanoporous AlGaN material as the template was also obtained, which demonstrates that the nanoporous AlGaN template could potentially be applied to heteroepitaxy of efficient AlGaN-based ultraviolet optoelectronic.

AlGaN-based ultraviolet light-emitting diodes (UV LEDs) are promising next-generation UV sources for a wide variety of applications. The state-of-the-art AlGaN-based UV LEDs exhibit much lower output power and external quantum efficiency than highly commercialized GaN visible LEDs. One key issue for UV LEDs is the poor light-extraction efficiency. We have reviewed the recent progress in the light extraction approaches for AlGaN-based UV LEDs, including the highly reflective techniques, and the surface/interface modification for total internal reflection mitigating. Moreover, AlGaN-based UV LEDs in the nanoscale structures, such as nanopillar, nanorod, and nanowire structures, are also discussed.

There have been recent research advances in AlGaN-based self-assembled nanowires (NWs) as building blocks for ultraviolet (UV) optoelectronics grown by plasma-assisted molecular beam epitaxy. We review the basic growth kinetics on various foundry-compatible-metal/silicon-based substrates and the epistructure design for UV devices. We highlight the use of diffusion-barrier-metal thin film on silicon substrate as a solution to enhance device performance. NWs offer the opportunity to mitigate the detrimental quantum-confined Stark effect (QCSE), which lowers the recombination rate thereby reducing the device efficiency. On the other hand, the polarization-induced doping from the graded composition along NWs can be advantageous for eluding the inefficient doping in AlGaN-based UV devices. Sidewall surface states and the associate passivation treatment, as well as the use of ultrafast electron-microscopy characterization, are crucial investigations in shedding light on device performance under the influence of surface dangling bonds. For investigating the electrical performance of individual NWs and NWs light-emitting diode as a single entity, recent reports based on conductive atomic force microscopy measurements provide fast-prototyping in-process pass-fail evaluation and a means of improving growth for high-performance devices. Stress tests of NWs devices, crucial for reliable operation, are also discussed. Beyond applications in LEDs, an AlGaN-based NWs solar-blind photodetector demonstrated leveraging on the dislocation-free active region, reduced QCSE, enhanced light absorption, and tunable-composition features. The review opens pathways and offers insights for practical realization of AlGaN-based axial NWs devices on scalable and low-cost silicon substrates.

On the base of density functional theory (DFT) calculations, it was ascertained that the GaN/AlN heterointerfaces without Al and Ga contacting layers intermixing and with the total substitution of the contacting layers are energetically more probable than the heterointerfaces with another amount of intermixing. The displacement of nitrogen atom from its site to second coordinate sphere between Ga and Al contacting layers is more probable than the displacement to the Al part of the cluster. The presence of nitrogen atom vacancy in the heterointerface does not influence the Al and Ga contacting layers intermixing, but complex defect nitrogen vacancy + interstitial N atom in the second coordinate sphere can be stable in contrast to the case of Al vacancy + interstitial Al atom in the second coordinate sphere. On the base of comparison of calculated and experimental data, it was ascertained that the most probable location of nitrogen vacancy in the vicinity of GaN/AlN interface is the location in the first Ga layer in respect to the GaN/AlN interface.

Ultraviolet (UV) components are widely used in industry, and the scientific and medical research fields. However, they are known to be inefficient (due to high absorption loss of UV light), expensive, and bulky. Special ultrawide bandgap dielectric metasurface should have a high efficiency due to low absorption and can be used to control the amplitude, polarization, and phase of UV light. We demonstrate UV metalens design specifically at representative UVC (244 nm), UVB (308 nm), and UVA (375 nm) wavelength, respectively. Both one-dimensional and two-dimensional metalenses are demonstrated for light convergence. The designed metalens is composed of high-aspect-ratio aluminum nitride nanorod array, with the corresponding conversion efficiency estimated to be as high as 91.15%, 89.92%, and 79.46%. Our designed UV metalens and the method demonstrated would promote the miniaturization and high-density integration of the UV nanophotonics.

A graphene-based tunable absorber consisting of a graphene monolayer on a dielectric grating and dielectric gap layer backed with a substrate is proposed and investigated. The absorber exhibits higher than 80% absorption at resonance, which is attributed to the guided mode resonances (GMRs) of a simple one-dimensional dielectric grating. Furthermore, the ultranarrow spectrum and antenna-like response make it able to be used as a thermal emitter with high directionality. The physical mechanism of such perfect absorption performance is disclosed by the illustrated electric field distributions. Lastly, the influence of Fermi level and relaxation time on the absorption spectra is investigated, which will benefit the design of graphene-based devices. The results indicate that it will promote the development of graphene-based tunable devices when combining graphene with general GMRs effect.

Graphene plasmonic-based nanophotonic devices are of most interest because of their potential applications in the field of optical communications. Graphene plasmonic waveguides are studied and the effect of graphene chemical potential modulation is investigated. The chemical potential modulation is applied and controlled via electrical biasing of patterned substrate with different thickness. Energy band diagram analysis of the periodically modulated waveguide shows the creation of a periodic bandgap around 30 THz and the results are confirmed by transmission spectrum calculations, which show a rejected band around the forbidden bandgap of the structure. A further study is performed around structure dependence of filtering mechanism in the proposed structure.

The synthesis and characterization of yttria-based organic–inorganic hybrid nanophosphors (HNP) are reported. These materials were synthesized by microwave-assisted solvothermal method in a short time of around 2 h and 30 min without any further thermal annealing. According to x-ray diffraction and transmission electron microscopy measurements, HNP have a lamellar structure formed by interleaved layers of organic species and inorganic yttria species. The luminescent properties of HNP are generated by the presence of Sm^3  + ions, which produced light emission at 570, 610, 650, and 716 nm due to the G_{5  /  2}4 to H_{5  /  2}6, H_{7  /  2}6, H_{9  /  2}6, and H_{11  /  2}6 transitions, respectively; and a wide broadband centered at 446 nm as a result of the presence of organic species, particularly benzene rings. Hybrid phosphors have tunable luminescent properties as a function of the used excitation wavelength producing blue, white, and red light emission. Those properties are due to the hybrid’s absorption properties and the subsequent simultaneous organic and inorganic light emissions.

Influence of the magnetic field on the energy levels and the excitation energy (EE) between the two states of the magnetopolaron strongly coupled in asymmetric Gaussian quantum wells is examined by the variational method of Pekar type. Then, we discover the temperature and magnetic field effects on the energy levels and EE with quantum statistics theory. According to the results of the article, the energy levels and the EE are a function relationship with the temperature rising and magnetic field increasing.

We propose an optical nanoantenna, which is an individual nanosphere consisting of two identical metal strips separated by a dielectric spacer (Ag–Ge–Ag) with a notch. Such design integrates the advantages of array dielectric antenna and plasmonic antenna such as high directivity, emission direction control, and highly localized field enhancement based on excitation of electric and magnetic multipoles of high-orders and localized surface plasmons in the symmetry breaking of this nanomatryoshka. Major properties of this nanoantenna have been revealed theoretically and numerically. We compare our hybrid nanoantenna with plasmonic and dielectric nanoantenna of similar geometry, and the proposed nanoantenna exhibits better directivity and efficiency. By suitably positioning the feed inside the notch, this compact nanoantenna can spectrally sort the electromagnetic emission, together with a high value in directivity up to 13.5. In addition, we have also revealed that displacement of the emitter along the y-axis leads to beam rotation. In contrast to other conventional nanoantenna in subwavelength, the proposed nanoantenna may exhibit higher directivity and Purcell factor due to effective excitation of electric and magnetic multipoles of high-orders inside the nanoparticle and localized surface plasmons in the outmost metal shell. The ultradirectional nanoantenna may shed light to the design of compact nanoantennas, which may find various applications in biosensing and quantum communications.

A method based on harmony search (HS) algorithm for designing an optical comb generator with excellent flatness is proposed. The comb generator with simple structure consists of four phase modulators with a single laser as the input, single radio frequency (RF) bias with different amplitudes, and DC bias for each modulator. No RF phase shifter, filter, or fiber loop is needed. Instead of following a classic mathematical model for finding the values of RF amplitudes and DC voltages for generating an optical comb, HS algorithm is implemented, which is an intelligent algorithm inspired from the improvisation of music players and seeks for the most harmonized answers corresponding to flat optical combs. The simulation results of generating two sets of optical combs by HS algorithm with 43 and 53 lines with flatness of 0.51 and 0.59 dB and then after inclusion of power conversion efficiency in the objective function of HS algorithm, two other sets of combs with 47 and 55 lines, flatness of 1.64 and 1.77 dB, and power conversion efficiency of 28% and 32% are presented. Such a device can be used in wavelength-division multiplexing systems and many other applications.

Laser ablation of a silver target confined in distilled water allowed us to obtain silver nanoparticles. However, to have knowledge of their production by this method, common instruments for measurement of the silver concentration in a colloidal solution are employed, this is due to laser ablation and is usually considered a top-down physical approach in the synthesis of nanoparticles. In consequence, this research has suggested an alternative to know the silver nanoparticles production through theoretical considerations, which depends on laser parameters and intrinsic properties of a silver target. Theoretically, this result has given us a silver concentration around 0.029  mg ml^−  1 and from of transmission electron micrographs were obtained a size distribution, where it was fitted with one Gaussian peak, being the smaller sizes the most frequent. The mean peak was centered at 12 nm, having a nanoparticle mass of 7  ×  10^−  18  g, and regarding a relation with the silver concentration, the nanoparticles production was around 4  ×  10¹² nanoparticles ml^−  1.

Bright-soliton frequency comb generation in a thin-film silicon nitride microresonator at optical telecommunication wavelengths is numerically demonstrated using our recently developed approach for dispersion engineering by virtue of coupling dispersion between two coupled microresonators. By coupling two identical resonators through an asymmetric Mach–Zehnder structure, sinusoidal splitting of the resonance frequencies can be achieved. This enables the engineering of the dispersion of the resulting modes of the coupled structure. Using this approach, anomalous dispersion of the resonant modes can be achieved at the pumping wavelength (which is selected to be the optical telecommunication wavelength, i.e., 1.55  μm) to enable Kerr-comb generation. In addition, by utilizing soliton-induced Cherenkov radiation in the coupled-resonator structure, we can increase the bandwidth of the resulting Kerr-comb signal.

Cross-shaped resonator topologies for realization of metal–insulator–metal (MIM) plasmonic filters are introduced and comprehensively studied. The structures are numerically simulated using finite difference time domain method. It is shown that single-mode MIM filters can be obtained using the proposed topologies for the wavelength range of 400 nm to 2  μm. Analytical formulas for designing the filters have also been proposed. As an important application, the cross-shaped resonators can be used for design of low-cross-talk waveguide intersections. The simplicity of the design, the ability to use analytical formulas, and obtaining a single-mode resonance are the benefits of the proposed cross-shaped topologies.

Predictions for the photon absorption coefficient (α) and photoluminescence (PL) of quasitype II CdS/ZnS core/shell nanocrystals [quantum dots (QDs)] have been obtained using a straightforward developed procedure. The developed procedure begins by solving the three-dimensional (3-D) Schrodinger equation written in spherical coordinates. Then, α is obtained by solving an equation based on the strict k-selection approach, and PL is derived by solving the Kubo–Martin–Schwinger relationship. This formulation allows the prediction of fundamental QD energy properties as a function of the QD radius. The predicted properties include quantized energy levels, effective bandgap, effective photon absorption wavelength, and effective photon emission wavelength. In addition, CdS/ZnS QDs were synthetized and stabilized based on previously reported procedures. Experimental measurements of α and PL were found to be very well matched to the calculated results. Hence, the developed procedures can be of great interest for designers who correlate theoretical results with experimental measurements to predict next generation QD performance for nanophotonics applications.

A method is presented that senses a refractive index by way of an active device that varies the coupling coefficient between a plasmonic ring resonator and a movable bus waveguide. It requires only one wavelength and senses the refractive index of the medium that surrounds the resonator and the waveguide. The gap between the resonator and the waveguide is adjusted by moving the waveguide, which affects the coupling coefficient. The gap value is used to determine the refractive index. Numerical evaluation of the sensitivity revealed a refractive index change of 5  ×  10^−  3 at a 633-nm wavelength for a controlled gap between 33.5 and 29.4 nm. This simple configuration was shown to be applicable for use in integrated photonic devices.

Exciton binding energies as a function of core/shell radius ratio are studied for the InP/ZnS core/shell quantum dot and ZnS/InP inverted core/shell quantum dot theoretically. The self-interaction potential due to the interaction between the exciton and its image charge and the built-in internal fields between inner and outer core materials are included in the Hamiltonian. The optical nonlinear susceptibilities for the second-harmonic generation and the third-harmonic generation with the photon energy for a constant radius are obtained for the core/shell and inverted core/shell quantum dots. The third-order Kerr effect as a function of photon energy is found for core/shell and inverted core/shell quantum dots of InP/ZnS and ZnS/InP semiconductors, respectively. The Kerr effect is studied using the real part of the third-order optical susceptibility.

A wholly passivated silicon core–shell nanowire solar cell incorporating a nickel silicide (NiSi) contact shows reduced series resistance. The configuration’s highly ordered vertical nanowire array is produced by the top-down method on a silicon solar-cell surface. The prepared samples demonstrate reflectance of ∼65  %   to 7%. The sample without the NiSi contact has a high short-circuit current density of 31.0  mA  /  cm². The cells with ∼5  nm NiSi show an improved fill factor of 70%, contributing to a high power-conversion efficiency of 10.8%.

We have studied the visible and infrared radiation emitted by multiwalled carbon nanotubes (MWCNTs) of different diameters when exposed to 2.45-GHz microwaves. A comparison of the spectra suggests that MWCNTs with larger diameters emit radiation of greater intensity than those with smaller diameters. Furthermore, the MWCNTs continue to emit visible and infrared radiation over the course of several microwave-irradiation cycles, with no degradation in the intensity of the emitted radiation. A comparison of Raman D- to G-band peak-intensity ratios reveals that microwave-irradiation did not significantly impact the MWCNTs’ defect densities. The results of our experiments suggest that MWCNTs may have the potential for use in lighting technologies and that ohmic heating caused by the polarization of the MWCNTs in the microwave field is likely responsible for the observed emissions of visible and infrared radiation.

A photonic crystal fiber (PCF) based on local surface plasmon resonance (LSPR) sensor with silver nanowires deposited in two microfluidic detection channels is designed. The coupling characteristics and sensing properties of the proposed sensor are analyzed numerically by finite-element method (FEM). The optical loss spectra of the proposed PCF-LSPR sensor can be effectively tuned by the parameters of the PCF structure and silver nanowires configuration. When the cylindrical silver nanowires number is 12 (single-detection channel), arranged in an even way, and the angle between adjacent cylindrical silver nanowires is 10 deg, an average wavelength sensitivity of 5507.1  nm  /  RIU is obtained in the refractive index (RI) range from 1.330 to 1.360, and a maximum wavelength sensitivity of 9000  nm  /  RIU is achieved in the RI sensing range from 1.355 to 1.360, corresponding to a maximum RI resolution of 1.11  ×  10^−  5  RIU, which can be used to detect slight changes in the RI of an unknown analyte.

Quantum dots (QDs), highly luminescent semiconductor nanocrystals, have found extensive applications spanning from optoelectronics to chemo- and biosensors to bioimaging. In addition to these QDs, semiconductor alloy nanostructures with tunable composition provide excellent material platform for biological applications. This paper reports the effect of composition of alloyed QDs on resonance energy transfer between hydrophilic ternary alloyed CdSeS/ZnS QDs (donor) and Rhodamine 640 dye (acceptor) employing steady state and time-resolved fluorescence spectroscopic techniques. Time-resolved decay curves of QDs obtained in the presence and absence of Rhodamine 640 dye have been recorded and the values of spectral overlap, Förster distance, and transfer efficiency are determined. The fluorescence resonance energy transfer of these systems was investigated as a function of spectral overlap between the QD donor emission and acceptor absorption as well as composition of the QDs. It is found that the efficiency significantly increases with varying compositions of the QD. In addition, the fluorescence quenching studies have been carried out using both absorption and emission data. The present study opens up the possibility of such QD-dye pairs performing as sensitive chemical and biosensors.

Three absorption improvement techniques are numerically applied to a multiband metamaterial absorber design for solar energy harvesting. These techniques are the following: the reshaping of the back metallic plate, the integrating of graphene sheets, and the utilizing of indium tin oxide (ITO), in the design. Based on numerical simulation results, each of these methods has the capacity to enhance total absorption rates. In addition to the enhancement in the total absorption rates, new absorption peaks are also obtained within the various frequency regions (infrared and ultraviolet). Furthermore, the absorption enhancement abilities of the mentioned methods are also compared. Among all the techniques, ITO provides the highest absorption rates, as it enhanced the total absorption rate by 48.5%.

We report on a humidity sensor based on passband spectrum resulting due to self-imaging effect in single-mode–multimode–single-mode fiber structure experimentally. The sensor performance with varying NCF diameter was investigated to find appropriate size of maximized evanescent fields. Different tuned diameters of NCF of 100, 80, 60, and 40  μm were obtained by chemical etching process based on hydrofluoric (HF) acid immersion. The experimental results reveal that almost a threefold increase in sensitivity was obtained at the proposed optimum NCF diameter of 60  μm coated with copper oxide nanoparticles embedded in poly polyvinyl alcohol. The highest wavelength and intensity sensitivity of −0.581  nm  /  RH  %   and −0.456  dB  /  RH  %   were obtained, respectively, in the RH range of 30% to 100% with 8.11-s response time. To the best of our knowledge, this is the first demonstration of RH sensor based on NCF coated with CuO NPs thin film.

Development work was conducted on ferroelectric materials that are widely used for optical modulation, light generation, optical filtering, and nanophotonic devices. Ferroelectric crystals with periodic variations in the second-order nonlinearity have been applied in laser frequency conversion, generation of entangled photons, and optical solitary wave devices. Here, we show electrical and optical characteristics of a ferroelectric crystal 0.25Pb(In_1/2Nb_1/2)O₃–0.42Pb(Mg_1/3Nb_2/3)O₃–0.33PbTiO₃ (short as PIMNT). The coercive field of PIMNT crystal with different orientation ranges from 4.9 to 5.8  kV  /  mm. Optical transmission and refractive indices of the crystal are investigated after being poled along different directions. The dispersion curves were fitted with Cauchy dispersion equations. The optical transmission of [011]-poled PIMNT single crystal is more than 65% above 0.5  μm, which is much higher than that of [001] and [111] directions. Orientation dependence of transition energies is presented in detail. Direct band gap, indirect band gap, and phonon energy can be adjusted with different orientations. The coercive field of PIMNT crystal is much lower than that of LiNbO₃ crystal (21  kV  /  mm). These results show that PIMNT single crystal is a promising candidate material in nanophotonics.

Ultrafast passive all-optical full-function logic gates (FLOGs), such as AND, NOT, XOR, XNOR, and OR gates, are studied and designed. FLOGs can be realized only by changing the state of input ports in a designed micro-Sagnac waveguide ring unit. The whole chip is internally passive with unified off-chip source fabricated on a silicon-on-insulator substrate. The transmission performance of FLOGs waveguide ring and integrated chip unit are investigated by both the finite-difference time-domain method and beam propagation method. The research shows that FLOGs have the advantages of low power (μW) consuming, multifunctional, and high transmission rate. The simulated device cascades are indicated that the FLOG structure can be well cascaded, which may be used to form the neural network element. There will be potential applications in all-optical communication networks and large-scale integration circuits in the future.

A moth-eye antireflective coating (M-ARC) on the surface of a glass substrate is reported for enhanced efficiency of an organic light-emitting diode (OLED). The M-ARC reflects the light trapped in the substrate modes of the device. Fresnel’s theory was applied to study the reflection and absorption of light on the M-ARC. The effect of the M-ARC on the OLED for light out-coupling efficiency was analyzed using the finite-difference time-domain method. The improvement in light extraction efficiency of the OLED was optimized by investigating the parameters of pitch, thickness, refractive indices, and height of the M-ARC. The enhancement in peak extraction efficiency of the moth-eye-based OLED as a function of wavelength is ∼3.0 compared to conventional OLEDs.

We propose an asymmetric to quasisymmetric behavioral tunability of a structured filter operating in the mid-infrared (IR) spectral region, where the atmospheric transparency is high. The structure is designed through electromagnetic wave analysis using finite-difference time-domain computations. The behavioral tunability provides dynamic control of the optical behavior of the IR filter without geometric and structural changes and opens up a field of research area in the tunable IR devices. It is shown that optical characteristic can be switched from an optical diode (unidirectional isolator or asymmetric light transmission) to the bidirectional isolator (quasisymmetric behavior) based on the phase transition of vanadium dioxide in the entire mid-IR spectrum. The proposed structure can be fabricated with the current nano and microfabrication techniques and can be utilized in smart front IR windows for protecting delicate sensors in the IR imaging systems and IR missile seekers under strong IR laser radiation.