Beam Steering Applications Research Articles

Generation of vector beams with liquid crystal disclination lines.

We report that light beams, guided along liquid crystal defect lines, can be transformed into vector beams with various polarization profiles. Using finite-difference time-domain numerical solving of Maxwell equations, we confirm that the defect in the orientational order of the liquid crystal induces a defect in the light field with twice the winding number of the liquid crystal defect, coupling the topological invariants of both fields. For example, it is possible to transform uniformly polarized light into light with a radial polarization profile. Our approach also correctly yields a zero-intensity region near the defect core, which is always present in areas of discontinuous light polarization or phase. Using circularly polarized incident light, we show that defects with noninteger winding numbers can be obtained, where topological constants are preserved by phase vortices, demonstrating coupling between the light's spin, orbital angular momentum, and polarization profile. Further, we find that an ultrafast femtosecond laser pulse traveling along a defect line splits into multiple intensity regions, again depending on the defect's winding number, allowing applications in beam steering and filtering. Finally, our approach describing the generation of complex optical fields via coupling with topological defect lines in optically birefringent nematic fluids can be easily extended to high-intensity beams that affect nematic ordering.

A pseudo-planar metasurface for a polarization rotator.

New demonstrations of effective interaction between light and artificially electromagnetic interface, or the metasurface, have stimulated intensive research interests on control of light to realize applications in beam steering, optical imaging and light focusing, etc. Here we reported a new type of planar metasurface of which every individual metamolecule is single metallic layer with stereo structure and the metasurface is name as Pseudo-Planar Metasurface (PPM). The metamolecule of the PPM is a chiral structure and therefore derives significant optical activity.

Subwavelength plasmonics for graded-index optics on a chip

Planar plasmonic devices are becoming attractive for myriad applications, owing to their potential compatibility with standard microelectronics technology and the capability for densely integrating a large variety of plasmonic devices on a chip. Mitigating the challenges of using plasmonics in on-chip configurations requires precise control over the properties of plasmonic modes, in particular their shape and size. Here we achieve this goal by demonstrating a planar plasmonic graded-index lens focusing surface plasmons propagating along the device. The plasmonic mode is manipulated by carving subwavelength features into a dielectric layer positioned on top of a uniform metal film, allowing the local effective index of the plasmonic mode to be controlled using a single binary lithographic step. Focusing and divergence of surface plasmons is demonstrated experimentally. The demonstrated approach can be used for manipulating the propagation of surface plasmons, e.g., for beam steering, splitting, cloaking, mode matching, and beam shaping applications.

Technique for reduction of noise resistance in a balanced low-noise amplifier for beam-steering applications

This paper, following up on the previous work, investigates the effect of the input coupler's load termination of a balanced amplifier in a beam-steering system. The noise generated in this load termination deteriorates the amplifier noise resistance, which increases the noise temperature due to a varying active reflection coefficient at the antenna ports as a function of scan angle. In reducing this effect, the balanced configuration is made more favorable for radio astronomy applications. By lowering the value of the impedance termination on the fourth port of the quadrature coupler an improvement in noise temperature sensitivity is achieved at the cost of reduced power matching.

A New Low Cost Leaky Wave Coplanar Waveguide Continuous Transverse Stub Antenna Array Using Metamaterial-Based Phase Shifters for Beam Steering

In this paper, we have proposed a new leaky-wave coplanar waveguide (CPW) continuous transverse stub (CTS) antenna array with metamaterial-based phase shifters for beam steering applications. The array integrates three CTS elements and two 6-stage negative reflective index (NRI) phase shifters, and is fed by CPW transmission line. Beam steering capabilities are achieved by tuning the values of the NRI phase shifters. The proposed CPW-CTS array is fabricated for 2.4-GHz wireless local area network (WLAN). The measured data, including parameters, radiation patterns and gain, agree well with the simulation results. A scan-angle range from 58 to 124 of unidirectional radiation pattern is measured in the -plane with good impedance matching (-1 dB ). Designs incorporating continuous beam steering using tunable NRI metamaterial phase shifters are also discussed.

Two-dimensional reconfigurable gradient index memory metasurface

Creation and control of spatial gradients in electromagnetic properties is a central theme underlying optical device design. In this work, we demonstrate that through modification of the spatial and temporal distribution of current, we can obtain increased control over the shape of these gradients. We are able to write spatially sharp gradients with ∼50% change in the index of refraction over length scales of only a few wavelengths as observed through diffraction limited terahertz spectroscopy. Furthermore, we assess the potentials for such gradients for beam-steering applications.

Reflection characteristics of a composite planar AMC surface

This study investigates the reflection characteristics of a composite Artificial Magnetic Conductor (AMC) surface consisting of multiple orthogonal gradient AMC surfaces arranged in a two-dimensional periodic pattern. The gradient AMC surface in this study consists of square metal patches of variable size printed on a grounded dielectric substrate. Due to the orthogonal placement of the gradient AMC surface, the incident energy of a plane wave normally incident on the composite AMC surface will be reflected into four major lobes away from the impinging direction. To achieve a systematical design, a simple formula based on array antenna theory was developed to determine the reflection pattern of the gradient AMC surface illuminated by a normal incident plane wave. A time-domain full-wave simulation was also carried out to calculate the electromagnetic fields in the structure and the far-field patterns. The scattering patterns of the structure were measured in an electromagnetic anechoic chamber. Results confirm the design principle and procedures in this research. Since such a composite AMC surface can be easily fabricated using the standard printed circuit board technique without via-hole process, it may have potential applications in beam-steering and radar cross section reduction.

One-Dimensional Off-Chip Beam Steering and Shaping Using Optical Phased Arrays on Silicon-on-Insulator

Optical beam steering can find applications in several domains such as laser scanning, LiDAR (Light Detection And Ranging), wireless data transfer and optical switches and interconnects. As present beam steering approaches use mechanical motion such as moving mirrors or MEMS (MicroElectroMechanical Systems) or molecular movement using liquid crystals, they are usually limited in speed and/or performance. Therefore we have studied the possibilities of the integrated silicon photonics platform in beam steering applications. In this paper, we have investigated a 16 element one-dimensional optical phased array on silicon-on-insulator with a field-of-view of 23. Using thermo-optic phase tuners, we have shown beam steering over the complete field-of-view. By programming the phase tuners as a lens, we have also shown the focusing capabilities of this one-dimensional optical phased array. The field-of-view can easily be increased by decreasing the width of the waveguides. This clearly shows the potential of silicon photonics in beam steering and scanning applications.

Design and characterization of a tunable DNG metamaterial superstrate for small beam steering antennas

The design and the characterization of a tunable double negative metamaterial is proposed in order to create a superstrate for beam steering applications in small antennas. The tunable metamaterial is based on an omega shaped unit cell and is investigated and validated by waveguide measurements. An appropriate loading of the metamaterial unit cell, through the use of a varactor diode, enables to vary the medium index of the superstrate within an interesting range. This metamaterial superstrate is then associated to a patch antenna in its near field zone permitting to steer the beam in several directions within elevation plane.

Thickness Reduction and Performance Enhancement of Steerable Square Loop Antenna Using Hybrid High Impedance Surface

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In order to reduce the thickness of a steerable beam square loop antenna, the effects of combining it with various periodic high impedance surfaces (HISs) are investigated. When a via-less HIS is used, the radiation pattern has high side lobes, which are shown to be due to surface waves propagating in the HIS lattice. Using a HIS with vias between the plates and ground removes the surface waves, but the beam is distorted due to strong coupling between the HIS's vias and the antenna element. Consequently a hybrid HIS is designed. This uses a via-less lattice beneath the loop, with vias at the edge of the HIS to suppress surface wave propagation. Consequently, a square loop antenna with four feeds on a hybrid HIS substrate is proposed for beam steering applications. This antenna has a low-profile with a total thickness of 4.69 mm for a test frequency band of 4.3 GHz to 5.0 GHz. It exhibits a gain of 8.65 dB at the test frequency (4.7 GHz). Compared to the earlier reported steerable square loop antenna, the new antenna achieves a 61% reduction in substrate thickness, a bandwidth enhancement by 150 MHz and an increase in gain by 1.95 dB. </para>

Longitudinal and Angular Dispersions in Photonic Crystals: A Synergistic Perspective on Slow Light and Superprism Effects

The slow-light effect and the superprism effect are two important effects in photonic crystal structures. In this paper, we will review some of our recent works on the fundamental physics and device applications of these two effects. We will present a synergistic perspective that examines these two effects as a whole. Apparently, the slow light effect is due to the dispersion of a photonic crystal along the direction of light propagation, namely the longitudinal direction, and the superprism effect is related to angular dispersion. However, a deep analysis will show that the superprism effect has an elusive dependence on the longitudinal dispersion as well. Some subtle connections and distinctions between the slow-light effect and the superprism effect will be revealed through our physical analysis. This allows us to treat these two effects under a common theoretical framework. As an example, we will apply this framework to make a direct comparison of the slow-light optical phase array approach and the superprism approach to beam steering applications. Dispersive effects are frequently accompanied by high optical loss and/or narrow bandwidths. We will discuss these issues for both longitudinal and angular dispersions. For the slow light effect, we will give a simple proof of the scaling of fabrication-imperfection related random scattering losses in a slow-light photonic crystal waveguide. Similar to the bandwidth-delay product for the longitudinal dispersion, we will introduce a simple, yet fundamental, limit that governs the bandwidth and angular sensitivities of the superprism effect. We will also discuss the application of the slow-light effect to making compact silicon optical modulators and switches.

Modular Broadband Phased-Arrays Based on a Nonuniform Distribution of Elements Along the Peano-Gosper Space-Filling Curve

The Peano-Gosper space-filling curve provides an excellent framework for designing broadband planar antenna arrays with highly modular architectures. Uniformly distributing elements along the curve leads to an element distribution with a triangular lattice that has an irregular fractal boundary contour. This boundary contour allows for a modular subarray configuration and better sidelobe suppression than conventional triangular lattice arrays with a regular boundary contour. While they have a greater bandwidth than square-lattice distributions, arrays based on a triangular lattice still possess a rather limited bandwidth for beam steering applications due to the formation of grating lobes. In this communication it will be shown that the beam steering capabilities of the Peano-Gosper array can be enhanced by introducing perturbations into the basic recursive array generation scheme. With the proper implementation, the perturbed arrays retain the attractive features of modularity and recursive beamforming that are associated with the standard Peano-Gosper array. Examples will be presented for several stages of Peano-Gosper arrays that were designed for 2:1 broadband performance while scanning within a 30° conical volume. Full-wave simulations will be used to examine the effects of mutual coupling on these aperiodic array layouts.

Radiation testing of liquid crystal optical devices for space laser communication

Liquid crystal optical phased arrays are an enabling technology for a variety of photonic and electronic beam manipulation functions, including steering, control of polarization, and amplitude and phase modulation. For applications in the emerging field of space laser communications, such devices would need to survive in the space environment for 10 to 15 years. To assess suitability and identify potential issues, a series of experiments were conducted in which nematic liquid crystal devices were subjected to three radiation environments: total dose (gamma), prompt dose (x rays), and fast neutrons. Tests were conducted using simple phase retarder devices, which served as surrogates for beamsteering devices. Impacts to optical and electrical characteristics of the devices at 1.55 µm were measured after incremental exposure trials. Modest effects were observed, but none were deemed significant enough to impact performance of the devices for space communication beamsteering applications.

Dipole antenna and distributed MEMS phase shifter fully integrated in a single wafer process for beam steering applications

This paper reports on the design and fabrication of a fully integrated antenna beam steering concept for airborne applications at 17 GHz. The system is based on a single wafer process including a dipole antenna, a balun and a 2-bit distributed MEMS phase shifter (in a 7 × 3 mm high-resistivity-silicon dice). To our knowledge, it is the first time that such integration has been done. First results of individual devices are reported and simulations of the whole concept are originally presented.

Mode Control in Photonic Crystal Vertical-Cavity Surface-Emitting Lasers and Coherent Arrays

We demonstrate transverse mode control in vertical-cavity surface-emitting lasers (VCSELs) and 2-D VCSEL arrays. By etching a periodic arrangement of circular holes into the top distributed Bragg reflector mirror, we are able to control the lasing modes through index and loss confinement. Theoretical modeling of these confinement effects are shown to be consistent with experimental measurements. Photonic crystal etched patterns and ion-implanted photonic lattices have been employed to fabricate coherently-coupled 2-D arrays. Control of the array supermodes from the out-of-phase and in-phase conditions is discussed. Designs of photonic crystal coherent VCSEL arrays for high-power emission and beam steering applications are described.

Fabrication of three-dimensional (3D) woodpile structure photonic crystal with layer by layer e-beam lithography

Photonic crystal based superprism offers a way to design new optical components for beam steering and DWDM (Dense Wavelength Division Multiplexing) application. Three-dimensional (3D) photonic crystals are especially attractive as they could offer more control of the light beam. A FCT (Face-Centered-Tetragonal) woodpile structure has been fabricated using layer by layer stacking techniques with E-Beam lithography. Special planarizations and processes have been introduced to ensure the survivability and good alignment of the fabricated nanostructures. Scanning electron microscopy results proved the structure uniformity. With the proper design, the structure exhibits superprism effects around 1550 nm, and such effects have been observed in the experiments.

Tunable frequency-selective surfaces for beam-steering applications

First results from a study on tunable frequency-selective surfaces (FSSs) used for beam-steering applications are reported. In particular, the scattering response of a multilayer passband FSS based on varactor-loaded rectangular slots has been investigated. Simulated and measured results show that tunable FSSs can be employed to locally control the phase of the transmitted field with limited amplitude losses.

Polyaniline as an automatic beam steering material

AbstractThis study deals with a preliminary study of automatic beam steering property in conducting polyaniline. Polyaniline in its undoped and doped state was prepared from aniline by the chemical oxidative polymerization method. Dielectric properties of the samples were studied at S‐band microwave frequencies using cavity perturbation technique. It is found that undoped polyaniline is having greater dielectric loss and conductivity compared with the doped samples. The beam steering property is studied using a perspex rod antenna and HP 8510C vector network analyzer. The shift in the radiated beam is studied for different d.c voltages. The results show that polyaniline is a good material for beam steering applications. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 422–425, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23115

Direct current balancing algorithm for FLCOS binary phase holograms

The need for DC balancing phase pixels in ferroelectric liquid-crystal-on-silicon spatial light modulators leads to control schemes that limit their use in beam steering applications where a continuous display of a routing hologram is required. By analyzing the phase redundancy in binary phase holograms, a new DC balancing algorithm has been developed that allows more general beam splitting and multiple beam steering functions. The theoretical derivation of the algorithm and experimentally measured properties of the optical beams are presented and discussed.

Practical realization of dual S arm antenna for beam steering applications

A dual S shaped micro strip antenna with a realistic feed is proposed for generation of tilted beam radiation pattern pertaining for beam steering applications. To achieve this, four feeding points are located at a distance of 5.6 mm from the antenna centre. These feeding points when excited one by one generate four tilted beams in four different space quadrants, thus yielding a beam steerable antenna. Importantly, since the proposed antenna is symmetrical in the structure, all the four tilted beams have the same radiation pattern characteristics. A further enhancement of the antenna bandwidth is also achieved using 100-μm capacitive coupling between the feed and the antenna strip.