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Light-emitting diodes (LEDs) have been known as the most widely used light source in lighting and displays for more than 60 years. There is still room for progress in the performance of LEDs, especially since the current devices with various types of different light-emitting layer materials have converged to unity in terms of internal quantum efficiency, and there is an urgent need to improve the light extraction efficiency. Metasurfaces (MSs) have received attention from researchers as structures that can be integrated with LEDs to efficiently modulate the phase and amplitude of light through resonance and scattering, which can reduce light loss. This paper reviews the development of metasurfaces in LEDs so far. The different working mechanisms of metasurfaces composed of different materials are first analyzed in depth. Subsequently, three aspects of light extraction, angle change, and polarization modulation are described in detail according to different applications of metasurfaces in LEDs. Finally, the current status of metasurface applications in LEDs is summarized, and the future development prospects are envisioned. [ABSTRACT FROM AUTHOR]

Optical edge detection can significantly compress the data volume and is highly pursued in imaging processing. The commonly used methods extract the optical edge information but lose the capability to distinguish colors, which is another key information for imaging. Here, a design for color-selective optical edge detection is proposed and demonstrated with a cholesteric liquid crystal q-plate. The corresponding optical edge detection exhibits a narrow reflection band characteristic due to the one-dimensional photonic crystal configuration of the cholesteric liquid crystal. The monochromatic band is thermally and reversibly tuned ∼300 nm within 5.3 °C. Color-selective optical edge detection is verified by a series of chromatic images. This work introduces a thermally responsive liquid crystal device to release the color dimension of optical edge detection, which may upgrade existing imaging processing techniques. [ABSTRACT FROM AUTHOR]

Bessel vortex beams (BVBs) are endowed with non-diffracting properties and carry specific orbital angular momentum, which adds a new degree of freedom in the manipulation of light. A patterned liquid crystal polymer (LCP)-based optical anisotropic film is proposed and demonstrated for generation of non-diffracting BVBs. The optical axis distribution is induced by the functionalized film, which can simultaneously modulate the amplitude and phase of the wavefront. Different BVB modes can be obtained in this manner. The topological charges and non-diffracting properties of the BVBs are experimentally verified. The multifunctional LCP film exhibits the merits of low power consumption, low cost, and easy fabrication. It may provide a new strategy for beam shaping and planar optics. [ABSTRACT FROM AUTHOR]

The manipulation of spatial parameters of light is at the cutting edge of optics. It is an interesting and important task to explore wavefront modulation approaches with a continuously tunable working band and dynamically switchable functions. Here, we program the alignment of a polymerizable cholesteric liquid crystal by a dynamic photo-patterning technique. After UV curing and a wash-out-refill process, the designed chiral superstructure is well reconstructed. By this means, a Dammann grating encoded q-plate is fabricated and its function as an optical vortex processor is demonstrated. The working band is electrically tuned and covers a broad range of 137 nm. The switching of mode conversion is achieved on a second scale for given wavelengths based on the electric-driven band shift. This strategy offers a platform for multi-dimensional dynamic control of light and may bring more possibilities to optical imaging, informatics, and micromanipulations. [ABSTRACT FROM AUTHOR]

Featuring a nontrivial coupling between the orbital angular momentum of light and spatially inhomogeneous polarization, hybrid-order Poincaré sphere (HyOPS) beams have recently triggered numerous curiosities, especially in classical and quantum informatics. Despite much effort devoted to creating single HyOPS beam, it is still a formidable challenge to simultaneously harness multichannel and diverse HyOPS beams in a simple and efficient manner. Here, we propose a digitalized geometric phase optical element via photo-induced liquid crystal microstructures and demonstrate flexible and spin-controlled massive channels of HyOPS beams. By tuning the incident polarization, any state on up to 24 diverse HyOPSs is simultaneously mapped from common Poincaré sphere in high efficiency and good energy uniformity. All experimental results match well with the theoretical predictions of such a planar multifunctional device. This adds an extra spatial degree of freedom to advanced light tailoring and may facilitate parallel optical trapping, high-capacity communication, and high-dimensional quantum entanglement. [ABSTRACT FROM AUTHOR]

The polaritons in a two-dimensional artificial ionic-type crystal have been proposed and experimentally demonstrated from the two-dimensional periodically poled LiTaO3. In this artificially micro-structured materials, the anisotropic piezoelectric coefficients and the two-dimensional symmetric result in strong and complex couplings of the incident electromagnetic waves and the two-dimensional superlattice vibrations. We studied the dielectric anomalies, the coupling and transforming between two ordinary polariton modes etc., which reveal that, by engineering the ferroelectric domain's distribution, the artificial ionic-type crystal may establish a new member of meta-materials, and will facilitate access to the device applications such as multi-directional and frequency transducers. [ABSTRACT FROM AUTHOR]

We proposed a design of a tunable optical isolator. The electro-optic (EO) effects in periodically poled lithium niobate (PPLN) with a defect were studied. EO effects and second harmonic generation (SHG) allow three-wave coupling in this nonlinear optics process. A defect is inserted in an asymmetrical position in PPLN to break the reciprocity of the fundamental-wave transmission in two reversed propagating directions. We numerically demonstrated that the contrast of this optical isolator can be tuned from -1 to 1 by simply changing the external dc electric field. With EO effects, the position of the defect can be designed more flexibly maintaining a high contrast of the optical isolation. [ABSTRACT FROM AUTHOR]

Photonic crystal fiber (PCF) modal interferometer is studied for sensing applications. There is a trade-off between high sensitivity and wide sensing range due to the intrinsic two-beam interference. We propose and experimentally demonstrate a three-beam path reflective interferometer by exciting mode conversion at the end surface of a dual-mode PCF. Approximately 5% mode conversion is taken place at the PCF end surface according to our model. In comparison with the normal dual-mode interference in a PCF, the mode conversion induced three-beam interference generates sharper spectrum and expanded sensing range. Gas sensing experiment is implemented with a sensitivity of 3019 nm/RIU. The advantage of expanded sensing range is also experimentally demonstrated. [ABSTRACT FROM AUTHOR]

The acousto-optic (AO) effects of photonic crystals (PCs) were studied. Both the PCs’ periodicity and their index distribution could be modulated instantly by the propagating acoustic wave. As a consequence, the PCs’ band structure becomes tunable. In addition to band gap shift in an ideal PC, AO frequency modulation was observed in a PC with single defect, which is quite different from normal AO tunable filters and gives rise to some interesting applications. Furthermore, in dual-defect situation, synchronized and desynchronized modulations were realized at different acoustic wavelengths. Interesting phenomena such as dual frequency sweeping and dual frequency Q-switching were demonstrated. [ABSTRACT FROM AUTHOR]

Theoretical study of the optical diffraction properties of holographic polymer-dispersed liquid crystal (HPDLC)-based thick volume grating was presented. It is found that the HPDLC grating can selectively diffract the s-polarized light only, p-polarized light only, or both s and p beams by selecting suitable grating parameters. When an electric field is applied, the s- and p-polarized lights exhibit different diffraction behaviors and, thus, the tunable dual-state or three-state polarization switching could be realized. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Terahertz (THz) metadevices featured by high-Q Fano resonance are applicable for ultrasensitive biodetection. The active tuning of Fano resonance further extends their applications to switching and filtering. Here, we propose a dynamic Fano cloaking in a liquid crystal (LC) integrated THz metasurface. The metasurface is composed of two-gap asymmetric split rings. Its Fano resonance is intensively dependent on the incident polarization. The Fano resonance occurs when illuminated by THz waves with polarization perpendicular to the gaps, while for parallel polarization, the Fano resonance vanishes, namely, the cloaking of Fano resonators. A 250-μm-thick LC layer functions as an integrated tunable polarization converter. Thus, the device can be electrically switched between the sharp Fano state and the high-transmission state. The modulation depth reaches over 50% in a broad frequency range of 660 GHz. This work may inspire various advanced active THz apparatuses for biosensing, switching, and filtering. [ABSTRACT FROM AUTHOR]

As a continuous transition between the Hermite-Gaussian and Laguerre-Gaussian beams, the Ince-Gaussian beams form a family of exact orthogonal solutions of the free-space paraxial wave equation in elliptic coordinates. Ince-Gaussian beams have multiple transverse mode patterns, which make them unique in terms of application in the fields of bioengineering, particle manipulation, and quantum entanglement. Here, based on binary nonlinear computer-generated holograms with a domain structure (realized via electric field poling at room temperature), we generate a second-harmonic Ince-Gaussian beam pumped with a fundamental Gaussian beam. In this process, the transverse part of the phase-matching condition is satisfied, which is called the Raman–Nath-type nonlinear diffraction. Both frequency conversion and beam shaping can be realized simultaneously, thereby offering the advantage of integration of both functions into a single device. [ABSTRACT FROM AUTHOR]

Twisted light, or orbital angular momentum (OAM) carrying light, has been gradually becoming an important subfield of nonlinear optics. Compared with ordinary light, its chiral phase front provides an additional interface for shaping the phase-matching condition of nonlinear interactions and in consequence reveals a feasible way to tailor light's transverse structure. Here, we explore the nonlinear propagation of twisted light during focused stimulated Brillouin scattering (SBS). Unlike ordinary light that will experience a time-reversal nonlinear reflection, OAM carrying light will break up into corresponding petal-like degenerate OAM modes that carry no net OAM, whereas the superposed OAM modes that carry no net OAM, as the input field, are still time–reversed in focused-SBS. This unexpected phenomenon, resulting from a unique OAM selection rule of noise-initiated SBS, gives more insight into the underlying principle of OAM conservation in electromagnetic interactions and provides an approach to shaping light via nonlinear propagation. [ABSTRACT FROM AUTHOR]

The band structure of surface plasmon polaritons (SPPs) on the Ag surface in the presence of gratings and SPP-based surface-enhanced Raman scattering (SERS) are investigated theoretically and experimentally. The SPP bandgap position can be tuned by geometric parameters. The SPP band edge dominates the SERS behavior. The template stripping process is introduced to reduce SPP propagation losses, improving SERS sensitivity by ~40. Apart from flexibility and a moderate SERS enhancement factor of the order of 105-106, the SPP band structure is highly reproducible with a relative standard deviation of 10.9%. Our results open opportunities for SPP band structures to serve as SERS substrates. [ABSTRACT FROM AUTHOR]

Spiral holographic imaging in the Hong-Ou-Mandel interference scheme is introduced. Using spontaneous parametric down-conversion as a source of photon pairs, we analyze the joint orbital angular momentum spectrum of a reference photon and the photon encoding information of the object. The first-order interference of light beams in standard holographic imaging is replaced by the quantum interference of two-photon probability amplitudes. The difficulty in retrieving the amplitude and phase structure of an unknown photon is thereby avoided as classical interferometric techniques such as optical holography do not apply. Our results show that the full information of the object's transmission function can be recorded in the spiral hologram, which originates directly from the joint orbital angular momentum spectrum. This presents a lateral demonstration of compressive imaging and can potentially be used for remote sensing. [ABSTRACT FROM AUTHOR]

An inverted organic solar cell (OSC) device structure by incorporating pixelated speckle image holography carrier fringes (SIHFs) for efficient superimposed light harvesting is demonstrated. The proposed SIHF based OSCs yield an 18.2% increase in power conversion efficiency (PCE) compared to that of the flat control devices. Moreover, compared to the common two-dimensional (2D) periodic grating patterned OSCs, SIHF based devices achieve 7.8% higher short-circuit current (JSC) and 10.0% higher PCE. This observable improvement in PCE of SIHF based OSCs is mainly ascribed to the geometric effect due to the unique chaotic carrier fringes of SIHFs. [ABSTRACT FROM AUTHOR]

Light with transverse polarization structures, such as radial and azimuthal polarization, enables and revives lots of applications based on a light-matter interaction due to its unique focal properties. To date, studies referring to this topic mainly concentrate on a weak-light domain, yet it should have gained more attention in a high-energy domain. Here, we demonstrate the generation of strong single-longitudinal-mode (SLM) cylindrical vector (CV) short pulses via stimulated Brillouin amplification. As a proof-of-principle work, the energy is transferred from a pair of 700 ps pumps to a 300 ps Stokes pulse via parametrically exciting coherent phonons in fluorocarbon liquid. After amplification, a 100 mJ-level SLM CV pulse light with 300 ps duration is obtained. Meanwhile, the phase and polarization structures are high fidelity maintained. This result provides a practicable way to generate strong CV light, and by further extending this mechanism into the beam combination system, even an ultra-high intensity CV light can be expected. [ABSTRACT FROM AUTHOR]

A tunable dual-wavelength filter is experimentally demonstrated in domainengineered lithium niobate. Application of an electric field on the y-surfaces of the sample results in the optical axes rotating clockwise and anticlockwise, which makes selective polarization rotation. The quasi phase-matching wavelengths could be adjusted through suitable domain design. Aunique dual valley spectrum is obtained in a periodically poled lithium niobate structure with a central defect if the sample is placed between two parallel polarizers. The expected bandwidth could be varied from ~1 nm to ~40 nm. Moreover, both the spectral response and group delay dispersion could be engineered. [ABSTRACT FROM AUTHOR]

Self-healing and transverse accelerating optical vortices are generated via modulating Gaussian beams through subsequent liquid crystal q-plate and polarization Airy mask. We analyze the propagation dynamics of these vortex Airy beams, and find that they possess the features of both optical vortices and Airy beams. Topological charges and characteristics of nondiffraction, self-healing, and transverse acceleration are experimentally verified. In addition, vortex Airy beams with both topological charge and radial index are demonstrated and mode switch among Gaussian, vortex, vector, Airy beams and their combinations can be acquired easily. Our design provides a flexible and highly efficient way to generate unique optical vortices with self-healing and transverse acceleration properties, and facilitates prospective applications in optics and photonics. Published by AIP Publishing. [ABSTRACT FROM AUTHOR]

The doping mechanism in organic-semiconductor films has been quantitatively studied via ultrahigh-sensitivity ultraviolet photoelectron spectroscopy of N,N-bis(1-naphthyl)-N,N-diphenyl-1,1-biphenyl-4,4-diamine (α-NPD) films doped with hexaazatriphenylene-hexacarbonitrile [HAT(CN)6]. We observed that HOMO of α-NPD shifts to the Fermi level (EF) in two different rates with the doping concentration of HAT(CN)6, but HOMO distributions of both pristine and doped amorphous α-NPD films are excellently approximated with a same Gaussian distribution without exponential tail states over ∼5 × 1018 cm-3 eV-1. From the theoretical simulation of the HAT(CN)6-concentration dependence of the HOMO in doped films, we show that the passivation of Gaussian-distributed hole traps, which peak at 1.1 eV above the HOMO onset, occurs at ultralow doping [HAT(CN)6 molecular ratio (MR) < 0.01], leading to a strong HOMO shift of ∼0.40 eV towards EF, and MR dependence of HOMO changes abruptly at MR∼0.01 to a weaker dependence for MR>0.01 due to future of the dopant acceptor level. [ABSTRACT FROM AUTHOR]

Ferroelectric domain inversion and its effect on the stability of lithium niobate thin films on insulator (LNOI) are experimentally characterized. Two sets of specimens with different thicknesses varying from submicron to microns are selected. For micron thick samples (∼28 μm), domain structures are achieved by pulsed electric field poling with electrodes patterned via photolithography. No domain structure deterioration has been observed for a month as inspected using polarizing optical microscopy and etching. As for submicron (540 nm) films, large-area domain inversion is realized by scanning a biased conductive tip in a piezoelectric force microscope. A graphic processing method is taken to evaluate the domain retention. A domain life time of 25.0 h is obtained and possible mechanisms are discussed. Our study gives a direct reference for domain structure-related applications of LNOI, including guiding wave nonlinear frequency conversion, nonlinear wavefront tailoring, electro-optic modulation, and piezoelectric devices. [ABSTRACT FROM AUTHOR]

Arbitrary vector beams (VBs) are realized by the designed polarization converters and corresponding vector-photoaligned q-plates. The polarization converter is a specific twisted nematic cell with one substrate homogeneously aligned and the other space-variantly aligned. By combining a polarization-sensitive alignment agent with a dynamic micro-lithography system, various categories of liquid crystal polarization converters are demonstrated. Besides, traditional radially/ azimuthally polarized light, high-order and multi-ringed VBs, and a VB array with different orders are generated. The obtained converters are further utilized as polarization masks to implement vector-photoaligning. The technique facilitates both the volume duplication of these converters and the generation of another promising optical element, the q-plate, which is suitable for the generation of VBs for coherent lasers. The combination of proposed polarization converters and correspondingly fabricated q-plates would drastically enhance the capability of polarization control and may bring more possibilities for the design of photonic devices. [ABSTRACT FROM AUTHOR]

A graphene-based electrical current sensor is proposed utilizing a microfiber coil resonator. Monolayer graphene sheet with a large sheet resistance is transferred onto the surface of a glass capillary rod. A microfiber is spirally wrapped around the graphene sheet to form a coil resonator. Heat generated from electrical current shifts the resonant wavelength because of the thermal effect in the microfiber resonator. The sensor exhibits a very good performance with a high sensitivity of 67.297 μm/A², which is two orders of magnitude higher than that reported earlier. Our results show that microfiber-graphene-integrated devices have great potential for miniature and highly sensitive fiber sensors for monitoring electrical current. [ABSTRACT FROM AUTHOR]

Polytype stability is very important for high quality SiC single crystal growth. However, the growth conditions for the 4H, 6H and 15R polytypes are similar, and the mechanism of polytype stability is not clear. The kinetics aspects, such as surfacestep nucleation, are important. The kinetic Monte Carlo method is a common tool to study surface kinetics in crystal growth. However, the present lattice models for kinetic Monte Carlo simulations cannot solve the problem of the competitive growth of two or more lattice structures. In this study, a competitive lattice model was developed for kinetic Monte Carlo simulation of the competition growth of the 4H and 6H polytypes of SiC. The site positions are fixed at the perfect crystal lattice positions without any adjustment of the site positions. Surface steps on seeds and large ratios of diffusion/deposition have positive effects on the 4H polytype stability. The 3D polytype distribution in a physical vapor transport method grown SiC ingot showed that the facet preserved the 4H polytype even if the 6H polytype dominated the growth surface. The theoretical and experimental results of polytype growth in SiC suggest that retaining the step growth mode is an important factor to maintain a stable single 4H polytype during SiC growth. [ABSTRACT FROM AUTHOR]

We constructed a concept of the full-organic carrier collection layer (CCL) used for polymer solar cells. The CCL is composed of dipyrazino[2,3-f:2',3'-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile as hole collection layer (HCL) and chlorine-free solvents (formic acid (FA)) processed 4,7-Diphenyl-1,10-phenanthroline (Bphen) as electron collection layer, exhibiting good solubility, and environmental protection. The FA based device shows ideal power conversion efficiency (3.75%), which is higher than that of control device (3.6%). Besides, the HCL shows a different mechanism in hole extraction by functioning as a charge recombination zone for electrons injected from anode and holes extracted from the donor materials. [ABSTRACT FROM AUTHOR]

The impact of illumination on the connection part of the tandem organic light-emitting diodes was studied by using a special organic multilayer sample consisted of two organic active layers coupled with different transition metal oxide (TMO)-based intermediate connectors (ICs). Through measuring the current density-voltage characteristic, interfacial electronic structures, and capacitance-voltage characteristic, we observe an unsymmetrical phenomenon in current densityvoltage and capacitance-voltage curves of Mg:Alq3/MoO3 and MoO3 composed devices, which was induced by the charge spouting zone near the ICs region and the recombination state in the MoO3 layer. Moreover, Mg:Alq3/MoO3 composed device displays a photovoltaic effect and the Voc shifts to forward bias under illumination. Our results demonstrate that the TMO-based IC structure coupled with photovoltaic effect can be a good approach for the study of photodetector, light sensor, and so on. [ABSTRACT FROM AUTHOR]

The nonmaximally entangled state is a special kind of entangled state, which has important applications in quantum information processing. It has been generated in quantum circuits based on bulk optical elements. However, corresponding schemes in integrated quantum circuits have been rarely considered. In this Letter, we propose an effective solution for this problem. An electro-optically tunable nonmaximally mode-entangled photon state is generated in an on-chip domain-engineered lithium niobate (LN) waveguide. Spontaneous parametric down-conversion and electro-optic interaction are effectively combined through suitable domain design to transform the entangled state into our desired formation. Moreover, this is a flexible approach to entanglement architectures. Other kinds of reconfigurable entanglements are also achievable through this method. LN provides a very promising platform for future quantum circuit integration. [ABSTRACT FROM AUTHOR]

Hybrid graphene-metal gratings with tunable Fano resonance are proposed and theoretically investigated in THz band. The grating contains alternately aligned metal and graphene stripes, which could be viewed as the superposition of two kinds of gratings with the same period. Due to different material properties, the resonance coupling between the metal and graphene parts forms typical Fano-type transmitting spectra. The related physical mechanism is studied by inspecting the induced dipole moment and local surface charge distributions at different wavelengths. Both of the resonance amplitude and frequency of the structure thus are adjustable by tuning graphene's Fermi energy and the grating's geometrical parameters. Furthermore, the Fano-type spectra are also quite sensitive to environmental indices, which supply another kind of tunability. All these features should have promising applications in tunable THz filters, switches, and modulators. [ABSTRACT FROM AUTHOR]

We propose and investigate a type of hybrid plasmonic waveguide in a metal Vgroove. A high-permittivity nanowire was placed in the metal channel covered with a dielectric film of lower permittivity. Deeper sub-wavelength confinement and much longer propagation distance were achieved in comparison with conventional channel plasmonic waveguides. The overall performance was improved as compared with the conventional hybrid plasmonic structure based on a flat metal surface. Finite element analysis showed that both the mode propagation and field profile can be adjusted by changing the nanowire radius and film thickness. Some benefits, such as a reduced scattering loss caused by the surface roughness, are also expected owing to the unique mode profile. The proposed approach has potential for application in high-level photonic integration. [ABSTRACT FROM AUTHOR]

A simple and efficient method has been developed to modify the anode interface of polymer light-emitting diode by incorporating solution-processable graphene oxide as hole transport layer. Interface engineering of ultraviolet-ozone treatment on graphene oxide is demonstrated to dramatically enhance the electrical properties, leading to 15% increase in efficiency compared to that with a traditionally used poly(styrenesulfonate)-doped poly(3,4-ethylenedioxythiophene) layer. As determined by photoelectron spectroscopy and impedance spectroscopy, an optimized ultraviolet-ozone treatment results in a more favorable energy level alignment and a decrease in series resistance, which can subsequently facilitate charge injection at the anodic interface. [ABSTRACT FROM AUTHOR]

The effect of cesium carbonate (Cs2CO3) doping on the electron transport properties of 4,7-diphenyl-1, 10-phenanthroline (BPhen) layer has been investigated in organic light-emitting diodes (OLEDs). Temperature-dependent admittance spectroscopy studies show that the incorporation of Cs2CO3 from 0 to 42 wt. % can decrease the activation energy of the BPhen layer from 1.3 to 0.18 eV, resulting in the enhanced electron injection and transport with respect to reduced injection barrier and increased conductivity of the BPhen layer. This is consistent with the performance improvement in OLEDs, which yields better electrical characteristics and enhanced luminance efficiency. [ABSTRACT FROM AUTHOR]

The polarization independence of liquid crystal gratings with alternate orthogonal aligned regions is theoritically studied and demonstrated by means of photoalignment technique. The different alignments in adjecent regions are achieved by two-step photo exposure to guide orientations of sulfonic azo dye layers and further align the liquid crystal molecules. Both one-dimensional and two-dimensional switchable phase gratings have been demonstrated. Such polarizer-free gratings show very high transmittance (∼92%), diffraction efficiency (over 31%), and optical contrast (over 150) including low power consumption. [ABSTRACT FROM AUTHOR]

To study theoretically the relationship between the integral interference angle and the scattering angle in collisional quantum interference, the integral interference angle of atom-2∏[case(a)] diatomic molecules system is described. To simulate the experiment theoretically, the theoretical model on collision-induced rotational energy transfer in an atom-2∏[case(a)] diatom system is presented based on the first order Born approximation taking into account of the long-range interaction potential. For the 2∏ electronic state in the Hund's case(a) diatom, the degree of the interference is discussed. The interference angles of collision-induced rotational energy transfer of CN(A2∏) in Hund's case(a) with He, Ne, and Ar are calculated quantitatively. The key parameters in the determination of integral interference angles are obtained. [ABSTRACT FROM AUTHOR]

As a further theoretical study of the collision-induced quantum interference on rotational energy transfer in an atom-diatom system, based on the first-Born approximation of time-dependent perturbation theory, taking into account the anisotropic Lennard–Jones interaction potential and the long-range interaction potential, the differential interference angles in singlet-triplet mixed states of CO A1 ∏(v = 0)-e3σ− (v = l) system in collision with He, Ne, Ar, and other partners were calculated theoretically. The relationships of differential interference angle versus impact parameters, including collision parameter b and velocity, are obtained. [ABSTRACT FROM AUTHOR]

Ni reaction with amorphous SiGe (a-SiGe) thin film on SiO2 substrate through rapid thermal annealing (RTA) was investigated. The amorphous SiGe thin film was deposited by ion beam sputtering. X-ray diffraction (XRD), Auger electron spectroscopy (AES) depth profiling, and four point probe (FPP) were used to check the phase formation, atom distribution, and sheet resistance during the reaction. It was found that the Ni reaction with a-SiGe was different from the Ni reaction with poly-SiGe. Besides an orthorhombic NiSi phase, a tetragonal η-NiSi phase was formed during Ni reaction with an a-SiGe layer and remained stable after 800 °C annealing. A NiSi2 phase was formed at temperature as low as 550 °C along with the crystallization of SiGe.When annealed at a higher temperature, Ge outdiffused to the surface and Ni diffused to the interface of SiGe/SiO2 where it formed a thin layer of Ni silicide. The cause of the reduced temperature for formation of NiSi2 from Ni reaction with amorphous SiGe is discussed. [ABSTRACT FROM AUTHOR]

A particle velocity-strain, finite-difference (FD) method with a perfectly matched layer (PML) absorbing boundary condition is developed for the simulation of elastic wave propagation in multidimensional heterogeneous poroelastic media. Instead of the widely used second-order differential equations, a first-order hyperbolic leap-frog system is obtained from Biot's equations. To achieve a high accuracy, the first-order hyperbolic system is discretized on a staggered grid both in time and space. The perfectly matched layer is used at the computational edge to absorb the outgoing waves. The performance of the PML is investigated by calculating the reflection from the boundary. The numerical method is validated by analytical solutions. This FD algorithm is used to study the interaction of elastic waves with a buried land mine. Three cases are simulated for a mine-like object buried in 'sand,' in purely dry 'sand' and in 'mud.' The results show that the wave responses are significantly different in these cases. The target can be detected by using acoustic measurements after processing. © 2001 Acoustical Society of America. [ABSTRACT FROM AUTHOR]

Inverted polymer solar cell is developed using small molecular tris(8-hydroxyquinolinato) aluminum (Alq3) as an electron collection layer between the active layer and indium-tin-oxide bottom cathode. Upon post-processing light irradiation by simulated solar illumination, the open-circuit voltage of the inverted device increases from 0.52 V to 0.60 V, resulting in the enhancement of the power conversion efficiency from 2.54% to 3.33% with negligible change in the short-circuit current. The performance improvement is attributed to the removal of surface potential due to irradiation-induced molecular dipole reorientation in the Alq3 layer, which reduces the charge transport barrier and improves the charge collection efficiency. [ABSTRACT FROM AUTHOR]

We study a versatile structurally favorable periodic sp2-bonded carbon atomic planar sheet with C4v symmetry by means of the first-principles calculations. This carbon allotrope is composed of carbon octagons and squares with two bond lengths and is thus dubbed as octagraphene. It is a semimetal with the Fermi surface consisting of one hole and one electron pocket, whose low-energy physics can be well described by a tight-binding model of π-electrons. Its Young's modulus, breaking strength, and Poisson's ratio are obtained to be 306 N/m, 34.4 N/m, and 0.13, respectively, which are close to those of graphene. The novel sawtooth and armchair carbon nanotubes as well as unconventional fullerenes can also be constructed from octagraphene. It is found that the Ti-absorbed octagraphene can be allowed for hydrogen storage with capacity around 7.76 wt. %. [ABSTRACT FROM AUTHOR]

Polymer optical fiber (POF) with a core of azopolymer has been fabricated. Based on the photoinduced birefringence of azopolymer materials, a mechanism for writing POF gratings is presented. After writing in azopolymer optical fiber (APOF) by two beams of mutually orthogonal polarizations, a birefringence grating was formed, and then the gratings could be erased almost totally for a short time by the circularly polarized beam at the same wavelength. By manipulating the APOF gratings, the transmittance through APOF at 632.8 nm can be adjustable as revealed by the transmittance change during write-erase-write procedure. [ABSTRACT FROM AUTHOR]

Efficient UV-blue polymer light-emitting diodes based on a fluorene-based nonconjugated polymer, poly[2,7-(9,9-dihexylfluorene)-alt-4,4′-phenylether] (PFPE), are fabricated. The device with PFPE as emitting layer shows a very narrow ultraviolet-blue electroluminescence emission with a peak at 397 nm and a maximal external quantum efficiency of 1.07%. By blending PFPE into poly(N-vinylcarbazole) (PVK), the device performance can be further improved. A maximum external quantum efficiency of 1.81%, with a maximum irradiance power density of 1223 μW/cm2, was reached by using a blend of PVK and PFPE in the weight ratio of 95:5 as emitting layer. [ABSTRACT FROM AUTHOR]

Dual-frequency addressed hybrid-aligned nematic (HAN) liquid crystal cell is demonstrated as a variable optical attenuator at 1.55 μm wavelength. By controlling the low- and high-frequency electric field, the dual-frequency liquid crystal (DFLC) molecules can be reoriented parallel or perpendicular to the substrates so that the maximum obtainable phase modulation is doubled. In comparison to a homogeneous cell, the DFLC HAN cell shows a lower operating voltage and faster response time. Furthermore, the DFLC HAN cell exhibits three stable states that have some applications such as ternary photonic devices. [ABSTRACT FROM AUTHOR]

Phonon-polaritons are studied both theoretically and experimentally in a one-dimensional two-component generalized quasiperiodic piezoelectric superlattice. The experimental observation of phonon-polaritons through dielectric abnormality is carried out at the microwave region. Some potential applications are discussed. [ABSTRACT FROM AUTHOR]

Tunable light switch using a photonic crystal fiber filled with nematic liquid crystal is demonstrated. The original hand-gap-guiding fiber structure was transformed to a total internal reflection-guiding photonic crystal fiber by tilling liquid crystal into the air core and cladding air holes. By applying external voltage to the liquid-crystal-filled fiber, we have demonstrated an electrically tunable fiber-optical switch with over 30 dB attenuation at 60 Vrms for a Hc-Nc laser beam. This liquid-crystal-filled photonic crystal fiber will find useful applications in fiber-optic communication systems. [ABSTRACT FROM AUTHOR]

We propose a high-frequency traveling-wave integrated electro-optic modulator based on a periodically poled LiNbO[sub 3]. The traveling velocity of the optical wave and the electrical wave velocity in the waveguide can be quasimatched due to the periodic structure. Using this design, a modulation frequency of several hundred GHz can be realized. Wide-bandwidth modulation is also achievable by employing an aperiodic domain grating. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Studies the frequency tunneling of optical parametric generator in superlattice LiNbO[sub3] by electro-optic effect. Wavelength change achieved; Tuning rates; Phenomenon of dispersion in electro-optic tuning.

We report the 390 and 385 nm violet light generation by frequency doubling of a tunable 90 fs, 82 MHz Ti:sapphire laser in two optical superlattice LiNbO3 samples through third-order quasiphase matching (QPM). With the average incident infrared light power of 770 mW, 9.7 and 2.9 mW output second-harmonic lights were obtained without photorefractive damage. The QPM wavelength acceptance bandwidth measurement indicates that violet light generation with higher efficiency is possible. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Assesses the growth of optical superlattice LiNbO[sub 3] with different modulating periods using the Czochralski method. Application of an asymmetric temperature field system; Frequency doubling efficiency for generating light; Measurement of angle tuning tolerance of the superlattice.

Reports the growth of Nd[sub 2]O[sub 3] and MgO codoped LiNbO[sub 3] crystals with periodic ferroelectric domain structures. Use of platinum crucible Czochralski method for growth of single crystals; Measurement of fluorescence spectra using titanium:sapphire laser excitation; Generation of green fluorescence from self-frequency doubling in a cavity.

Liquid crystal q-Airy-plates with director distributions integrated by q-plates and polarization Airy masks are proposed and demonstrated via the photoalignment technique. Single/dual vortex Airy beams of opposite topological charges and orthogonal circular polarizations are directly generated with polarization-controllable characteristic. The singular phase of the vortex part is verified by both astigmatic transformation and digital holography. The trajectory of vortex Airy beams is investigated, manifesting separate propagation dynamics of optical vortices and Airy beams. Meanwhile, Airy beams still keep their intrinsic transverse acceleration, self-healing, and nondiffraction features. This work provides a versatile candidate for generating high-quality vortex Airy beams. [ABSTRACT FROM AUTHOR]

The electro-optic effect of periodically poled optical superlattice LiNbO[sub 3] (PPLN) was studied. Because of the periodic electro-optic (EO) coefficient, the reciprocal vector of the periodic structure can be used to compensate for the phase mismatch between the ordinary and extraordinary waves, which is similar to the nonlinear optical frequency conversion process. If the quasi-phase-matching condition is satisfied, polarization of a light propagated in PPLN can rotate linearly with the applied electric field, which shows that PPLN may be used as a precise spectral filter or an EO switch. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]