Polarization Of Incident Beam Research Articles

Selected Organometallic Compounds for Third Order Nonlinear Optical Application.

In this paper, we present the third harmonic generation response of Znq2 (Bis-(8-hydroxyquinolinato)zinc), Cuq2 (8-Hydroxyquinoline copper(II)), and Alq3 (Tris-(8-hydroxyquinoline)aluminum) organometallic compounds. An experiment was conducted for s and p polarizations of incident beam, using the Maker fringes technique. The third order nonlinear susceptibility χ(3) was estimated using the Kubodera and Kobayashi comparative model, on the grounds that presented compounds exhibit high linear absorption of the generated third harmonic wavelength (355 nm). These complexes were deposited as thin films using the physical vapor deposition (PVD) method. Investigated complexes vary in terms of the coordination center and number of quinoline ligands, which visibly influence their nonlinear response. The global hybrid B3LYP functional with the basis set 6-31G(d) was used in computing the linear and non-linear optical properties. The computed γtot value (8765.36 × 10−36 esu for Cuq2) is superior to that of methylene blue (γ = 32.00 × 10−36 esu). The calculated theoretical values were found to be in good agreement with the experimental results.

Diffraction-distortion-induced deflection of guided waves in two-dimensional Ag/SiO2 nanocomposite grating coupler

Two-dimensional Ag/SiO2 nanocomposite grating coupler with a periodicity of 600 nm was fabricated by etching an Ag-ion-implanted SiO2 waveguide slab, which was evidenced to be able to convert a vertically incident beam in the wavelength range of 620–880 nm into four beams of guided waves without regard for the polarization of incident beam. Employing this coupler, the deflection of guided waves due to the diffraction distortion in the case of oblique incidence was clearly demonstrated. Moreover, to accurately predict the propagating direction of guided wave in the SiO2 waveguide layer, a simple relation of the deflected angle of guided wave to the polar and azimuth angles of incident beam was deduced according to the oblique coupling of a one-dimensional Ag/SiO2 nanocomposite grating coupler. The calculated results by using the deduced relation revealed that increasing the polar angle and/or azimuth angle of incident beam could lead to an increase in deflected angle of guided wave. Especially, for an azimuth angle of 90°, the calculated results agreed well with the experimental data, justifying the deduced relation. The above findings might be useful for the packaging and applications of grating couplers.

Deflecting transmissive light beams with metasurfaces based on crystalline silicon high-contrast grating

Dielectric metasurfaces have emerged and expanded rapidly for their success in realizing high-efficiency wavefront control in the optical and infrared ranges. However, devices have either been demonstrated at near-infrared regime using high-index semiconductors such as silicon, or they use lower index dielectric materials such as TiO2 or Si3N4 and operate in the visible wavelength regime to avoid the optical loss of dielectric materials. It seems that dielectric metasurfaces could not achieve either high index or high device efficiency, simultaneously. Here, we provide a crystalline silicon metasurface scheme to efficiently modulate transmitted light beams at the wavelengths as short as to 532 nm. The unit cell of the metasurfaces consists of high-contrast grating (HCG), which provides full 2π phase control for circular polarized incident beams in thin film. The demonstration of HCG deflector shows that the device enables high deflecting efficiency as high as those made by transparent materials. Our results provide a paradigm to functionalize transmitted light beams based on crystalline silicon in the visible wavelength regime.

Unveiling the spin Hall effect of light in Imbert-Fedorov shift at the Brewster angle with weak measurements

The Imbert-Fedorov (IF) shift is defined as the transverse shift of barycenter of the entire beam when a circular or elliptically polarized incident beam is reflected. In this work, we examine the IF shift of Gaussian beam at the Brewster angle. Interestingly, the spin Hall effect of light takes place in the IF shift at the same time. Furthermore, this interesting phenomenon is experimentally observed using weak measurements. These findings may have useful applications in spin optics.

Polarization Split Lensing via Polarization and Phase Control with Metasurfaces at Visible Frequencies

Under the trend of miniaturization and reduction of system complexity, conventional bulky photonic elements are expected to be replaced by new compact and multi-functional photonic elements. In this letter, we propose a birefringent dielectric metasurface (DM) that could provide both phase and polarization control at visible wavelength. Within this platform, we successfully realize a multi-functional polarization split metalens. Such a single metalens can perform the multiple functions of a polarizing resolve imaging system without additional optical elements. Polarization properties of light are resolved, an arbitrarily polarized incident beam is split into two orthogonally polarized beams, in which the transverse magnetic (TM) component and the transverse electric (TE) component are focused on the right and left side of the central axis, respectively. The metalens maintains diffraction-limited focal spots with high focusing efficiencies (above 80%). This multi-functional metalens may found potential applications in polarization-resolved imaging, spectroscopy, and on-chip optoelectronic devices.

Measurement of Giant Spin Splitting of Reflected Gaussian Beams

We investigate theoretically and experimentally the beam shifts of a Gaussian beam reflected by an air-glass interface at Brewster incidence. For a linearly polarized incident beam, the reflected beam will undergo a spatial spin splitting within the plane of incidence. This spin splitting is up to 83 μm when the incident beam waist is 90 μm. Additionally, the reflected beam will be deflected along the direction perpendicular to the incident plane, i.e., undergo an angular shift. The maximum angular shift has been theoretically predicted and experimentally confirmed. Both the spatial spin splitting and angular shift can be controlled by the incident polarization state. These controllable giant beam shifts have potential applications in the design of spin-photonic devices and the optical sensing.

QUOKKA, the pinhole small-angle neutron scattering instrument at the OPAL Research Reactor, Australia: design, performance, operation and scientific highlights

QUOKKA is a 40 m pinhole small-angle neutron scattering instrument in routine user operation at the OPAL research reactor at the Australian Nuclear Science and Technology Organisation. Operating with a neutron velocity selector enabling variable wavelength, QUOKKA has an adjustable collimation system providing source–sample distances of up to 20 m. Following the large-area sample position, a two-dimensional 1 m2 position-sensitive detector measures neutrons scattered from the sample over a secondary flight path of up to 20 m. Also offering incident beam polarization and analysis capability as well as lens focusing optics, QUOKKA has been designed as a general purpose SANS instrument to conduct research across a broad range of scientific disciplines, from structural biology to magnetism. As it has recently generated its first 100 publications through serving the needs of the domestic and international user communities, it is timely to detail a description of its as-built design, performance and operation as well as its scientific highlights. Scientific examples presented here reflect the Australian context, as do the industrial applications, many combined with innovative and unique sample environments.

LP01 to LP11 mode convertor based on side-polished small-core single-mode fiber

An all-fiber LP01-LP11 mode convertor based on side-polished small-core single-mode fibers (SMFs) is numerically demonstrated. The linearly polarized incident beam in one arm experiences π shift through a fiber half waveplate, and the side-polished parts merge into an equivalent twin-core fiber (TCF) which spatially shapes the incident LP01 modes to the LP11 mode supported by the step-index few-mode fiber (FMF). Optimum conditions for the highest conversion efficiency are investigated using the beam propagation method (BPM) with an approximate efficiency as high as 96.7%. The proposed scheme can operate within a wide wavelength range from 1.3 μm to1.7 μm with overall conversion efficiency greater than 95%. The effective mode area and coupling loss are also characterized in detail by finite element method (FEM).

Micro-patterned liquid crystal Pancharatnam–Berry axilens

A liquid crystal Pancharatnam–Berry (PB) axilens is proposed and fabricated via a digital micro-mirror-device-based photo-patterning system. The polarization-dependent device behaves as an axilens for a left-handed circularly polarized incident beam, for which an optical ring is focused with a long focal depth in the transverse direction at the output, and an anti-axilens for a right-handed circularly polarized incident beam, for which an optical ring gradually expands at the output. The modification of the size and the sharpness of the diffracted ring beam is demonstrated by encoding a positive (negative) PB lens term into the director expression of a PB (anti-)axicon.

Effects of fabrication errors on the focusing performance of a sector metalens

Using e-beam lithography, a 16-sector spiral metalens was fabricated in an amorphous silicon, capable of converting linearly polarized incident light into an azimuthally polarized optical vortex. When illuminated by a 633-nm linearly polarized laser beam, the metalens generated a near-surface subwavelength focal spot equal to 0.75 of the incident wavelength at full-width of half-maximum intensity. The focusing performance of the spiral metalens was numerically shown to be sensitive to the deviation of the factual microrelief from the calculated height. For the designed microrelief height, a circularly polarized incident beam was focused into a bright ring with a reverse energy flow occurring at its center. For the microrelief height other than the designed one, the energy backflow effect did not occur.

Design of beam deflector, splitters, wave plates and metalens using photonic elements with dielectric metasurface

Under the trend of miniaturization and reduction of system complexity, conventional bulky photonic elements are expected to be replaced by new compact and ultrathin dielectric metasurface elements. In this letter, we propose an αTiO2 dielectric metasurface (DM) platform that could be exploited to design high efficiency wave-front control devices at visible wavelength. Combining with fundamental principles and full wave simulations (Lumerical FDTD 3D solver ®), we successfully realize four DM devices, such as anomalous beam deflectors, polarization insensitive metalens, wave plates and polarization beam splitters. All these devices can achieve high transmission efficiencies (larger than 80%). Among them, the anomalous refraction beam deflectors can bend light propagation to any desired directions; the polarization insensitive metalens maintains diffraction limited focus (focal spot as small as 0.67λ); the quarter-wave and half-wave plates have broadband working wavelengths from 550 to 1000 nm; and the polarization beam splitter can split an arbitrarily polarized incident beam into two orthogonally polarized beams, the TM components is deflected to the right side, and the TE components is deflected to the left side. These devices may find applications in the areas of imaging, polarization control, spectroscopy, and on-chip optoelectronic systems etc., and our studies may richen the design of all-dielectric optical elements at visible wavelength.

Spectrally Tunable Optical Transmission of Titanium Nitride Split Ring Resonators

In this paper, the optical properties of titanium nitride split ring resonators as an intermetallic metamaterial nanostructure were studied. Our simulation shows the presence of plasmon and LC resonances in the transmission spectrum of a cell consists of four u-shape split ring resonators. The effect of different parameters of resonator such as size, periodic constant, and the material between arms in addition to the polarization of incident beam was examined on the resonance behavior of the system. Also, the optical properties of a cell consist of four complementary split ring resonators within titanium nitride thin film were investigated. An excited mode was observed at λ = 840 nm that was attributed to the plasmon resonance. Changing the arrangement and configuration of the system from C 1v to C 2v symmetry led to the presence of the LC mode beside the plasmon mode in the transmission spectrum. Also, we explored a connection between the complementary split ring resonators and orderly perforated surface plasmon systems. It was determined that a transition occurred from resonator-type to surface plasmon behavior by increasing the size of resonator above 170 nm.

Localized terahertz electromagnetically-induced transparency-like phenomenon in a conductively coupled trimer metamolecule.

We experimentally investigate the terahertz (THz) electromagnetically-induced transparency (EIT)-like phenomenon in a metamolecule (MM) of three-body system. This system involves a couple of geometrically identical split-ring resonators (SRRs) in orthogonal layout conductively coupled by a cut-wire resonator. Such a three-body system exhibits two frequency response properties upon to the polarization of incident THz beam: One is the dark-bright-bright layout to the horizontally polarized THz beam, where there is no EIT-like effect; the other is bright-dark-dark layout to the vertically polarized THz beam, where an EIT-like effect is observable. The transparency window can be tuned from 0.71 THz to 0.74 THz by the displacement of cut-wire inside the trimer MM. A maximum of 7.5 ps group delay of THz wave is found at the transparent window of 0.74 THz. When the cut-wire moved to the mid-point of lateral-side of SRR, the EIT-like phenomenon disappears, this leads to a localized THz slow-light effect. The distribution of surface currents and electric energy reveals that the excited inductive-capacitive (LC) oscillation of bright-SRR dominates the high frequency side-mode, which is isolated to the displacement of cut-wire resonator. However, the low frequency side-mode originates from the constructive hybridization of LC resonance in dark-SRR coupled with a localized S-shaped dipole oscillator, which is tunable by the displacement of cut-wire. As a consequence, the group delay as well as the spectral configuration of transparency window can be manipulated by tuning one side-mode while fixing the other. Such an experimental finding reveal the EIT-like effect in a conductively coupled three-body system and manifests a novel approach to achieve tunable THz slow-light device.

Spiraling Light with Magnetic Metamaterial Quarter-Wave Turbines

Miniaturized quarter-wave plate devices empower spin to orbital angular momentum conversion and vector polarization formation, which serve as bridges connecting conventional optical beam and structured light. Enabling the manipulability of additional dimensions as the complex polarization and phase of light, quarter-wave plate devices are essential for exploring a plethora of applications based on orbital angular momentum or vector polarization, such as optical sensing, holography, and communication. Here we propose and demonstrate the magnetic metamaterial quarter-wave turbines at visible wavelength to produce radially and azimuthally polarized vector vortices from circularly polarized incident beam. The magnetic metamaterials function excellently as quarter-wave plates at single wavelength and maintain the quarter-wave phase retardation in broadband, while the turbine blades consist of multiple polar sections, each of which contains homogeneously oriented magnetic metamaterial gratings near azimuthal or radial directions to effectively convert circular polarization to linear polarization and induce phase shift under Pancharatnum-Berry’s phase principle. The perspective concept of multiple polar sections of magnetic metamaterials can extend to other analogous designs in the strongly coupled nanostructures to accomplish many types of light phase-polarization manipulation and structured light conversion in the desired manner.

Tailoring the plasmon-induced transparency resonances in terahertz metamaterials.

We experimentally demonstrate that a coupled metamaterial composed of sub-wavelength split-ring-resonators (SRRs) and closed-ring-resonators (CRRs) can tailor the plasmon-induced-transparency (PIT) resonances when the external electric field is parallel to the gaps of SRRs. Rotating or moving SRRs in vertical direction plays a critical role in the EIT functionality, while an excellent robust performance can be acquired via moving SRRs in the horizontal direction. Based on the results, a polarization-independent and polarization-dependent planar metamaterial are designed, fabricated and measured. In contrast to the spectral property of the polarization-independent medium, the polarization-dependent one is featured by isolated PIT phenomena in the frequency-domain, with respect to the horizontal and vertical polarized incident beam. Transmission responses of the PIT metamaterial are characterized with terahertz time-domain spectroscopy, showing a good agreement with the rigorous numerical simulation results. The presented work delivers a unique way to excite and modulate the PIT response, toward developing polarization-independent and polarization-dependent slow-light building blocks, ultrasensitive sensors and narrow-band filters functioning in the THz regime.

Spin–orbit interaction of light and diffraction of polarized beams

The edge diffraction of a homogeneously polarized light beam is studied theoretically based on the paraxial optics and Fresnel–Kirchhoff approximation, and the dependence of the diffracted beam pattern of the incident beam polarization is predicted. If the incident beam is circularly polarized, the trajectory of the diffracted beam center of gravity exhibits a small angular deviation from the geometrically expected direction. The deviation is parallel to the screen edge and reverses the sign with the polarization handedness; it is explicitly calculated for the case of a Gaussian incident beam with a plane wavefront. This effect is a manifestation of the spin–orbit interaction of light and can be interpreted as a revelation of the internal spin energy flow immanent in circularly polarized beams. It also exposes the vortex character of the weak longitudinal field component associated with the circularly polarized incident beam.

Free space excitation of coupled Anderson-localized modes in photonic crystal waveguides with polarization tailored beam

We experimentally demonstrate free space excitation of coupled Anderson-localized modes in photonic crystal (PhC) line-defect waveguides (W1) with polarization tailored beams. The corresponding light beam is tightly focused on a pristine W1, and out-of-plane scattering is imaged. By integrating the scattering spectra along the guide, at the W1 modal cut-off, Anderson-localized cavities are observed due to residual W1 fabrication-disorder. Their spectral lines exhibit high quality Q factors up to 2 × 105. The incident beam polarization and scattering intensities of the localized modes characterize the efficiency of free-space coupling. The coupling is studied for linearly and radially polarized input beams and for different input coupling locations along the W1 guide. The proposed coupling scheme is particularly attractive for excitation of PhC waveguide modes and Anderson-localized cavities by beam steering and scanning microscopy for sensing applications.

All‐Dielectric C‐Shaped Nanoantennas for Light Manipulation: Tailoring Both Magnetic and Electric Resonances to the Desire

A systematic study is carried out on the interaction of electromagnetic waves with a nonsymmetric all‐dielectric C‐shaped nanoantenna to achieve an ultimate control over the independent and relative spectral positions of the excited magnetic and electric dipolar modes. By properly determining the structural parameters (inner and outer radii and the opening angle) and tailoring the interference of geometrical resonances, an ultrathin C‐element metasurface is designed, which can highly transmit the linearly polarized incident beam (>80%) with full phase‐agility (2π) in the red light of visible regime. The investigation on the physical mechanism behind this nanoantenna reveals the confinement of magnetic and electric fields corresponding to the magnetic and electric dipolar modes mainly inside the hollow and opening angle, i.e., outside the constituent high‐index material of C‐element. This feature allows making building blocks less dependent on the material loss and dispersion. Three different approaches based on only varying the inner/outer radius or the opening angle are proposed which can facilitate the design complexity, the encoding of the desired phase distribution for specific functionality, and easing the fabrication procedure. The proposed approaches are leveraged to design several highly transparent graded‐pattern metasurfaces with the capability of beam steering, focusing, flat‐top generation, and holography.

Terahertz transmission control using polarization-independent metamaterials.

We present terahertz (THz) transmission control by several uniquely designed patterns of nano-slot antenna array. Collinearly aligned slot antenna arrays have been usually applied to THz filters with frequency band tunability by their geometry. Normally the amplitude in transmission (reflection) in the collinear alignment case can be varied via rotating the azimuthal angle with a sinusoidal trend, which can limit their utilization and performance only at fixed angle between the alignment of the resonant antennas and incident beam polarization. To pursue a variety of metamaterial uses, here, we present polarization-independent THz filters using variously aligned antenna array (asterisk, chlorophyll, and honeycomb patterns) in such counter-intuitive aspects. Besides, unprecedented multi resonance behaviors were observed in chlorophyll and honeycomb patterns, which can be explained with interferences by adjacent structures. The measured spectra were analyzed by harmonic oscillator model with simplified coupling between slots and their adjacent.

Creation of a longitudinally polarized photonic nanojet via an engineered microsphere.

Dielectric microspheres exhibit the ability to focus an incident beam to a subwavelength spot with strong localized field intensity. In this Letter, a high beam quality of a longitudinally polarized electromagnetic component is created by decorating the surface of the microsphere with engineered structures. By changing the design of the engineered microspheres, the relative contribution of the longitudinal and radial components of a radially polarized incident beam to the photonic nanojet can be modified efficiently, leading to a sharp spot size which exceeds the optical diffraction limit. More importantly, a high conversion efficiency of 0.89 is achieved. At a wavelength of 633 nm, a focal spot of 266 nm (0.42λ) is achieved numerically by illuminating the engineered microsphere with a focusing beam at a numerical aperture of 0.7.