A nanoscale robotic cleaner.

A simple single-layer reconfigurable leaky-wave antenna (LWA) is presented that has polarization agility and beam-scanning functionality. This LWA system realizes a scanned beam that can be switched between all of its linear polarization (LP) and circular polarization (CP) states using only one dc biasing source. A slot-loaded substrate-integrated waveguide (SIW)-based LWA is first explored to attain CP performance with continuous beam scanning through broadside. This CP LWA realizes a measured CP performance with a 3 dB gain variance within 2.75–3.35 GHz for scan angles ranging from −28.6° to +31.5°. A row of shorted stubs is then incorporated into the CP LWA to obtain similar LP performance. Finally, by introducing p-i-n diodes into this LP LWA configuration to facilitate reconfigurable connections between the main patch and the shorted stubs, the radiated fields can be switched between all of its CP and LP states. The measured results of all three antennas confirm their simulated performance. It is demonstrated that the main beam of the polarization-reconfigurable LWA can be scanned from −31.5° to +17.1° with gain variations between 9.5 and 12.8 dBic in its CP state and from −34.3° to +20° with them between 7.8 and 11.7 dBi in its LP state.

A polarization agile patch antenna resonating at 2.4 GHz ISM band is presented. The antenna is based on a rectangular radiating element along with reconfigurable parasitic patches located at its periphery of the radiating element. Two switching diodes are used to reconfigure the geometry of the radiating element. Upon proper biasing of the switching diodes the antenna attains linear or circular (LHCP/RHCP) polarization states. The entire antenna is modelled using a high-frequency structure simulator and is validated using an Agilent network analyser (N9925A) and antenna test systems for measuring impedance and radiation characteristics. Over the entire operating band, the antenna shows better impedance matching and achieves −10 dB impedance bandwidth of 100 MHz (2.40-2.5 GHz) in linear state and 85 MHz (2.41-2.495 GHz) in the circularly polarization states along with peak gain of 5.61 dBi for LP state and 4.98 dBi for CP state in the operatingrange.

An electronically reconfigurable microstrip antenna with circular and linear polarization switching is presented. The prototype fabricated on a substrate of dielectric constant (ε <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> ) 4.4 and height (h) 1.6 mm is fed by a proximity feed fabricated using the same substrate. By controlling the bias voltage of two PIN diodes, the polarization of the antenna can be switched between three states; two states for linear polarization (horizontal and vertical) and one state for circular polarization (RHCP). Simulation and experimental results show that the proposed antenna has a cross polar level better than 10 dB in the linear polarization state and 18 MHz axial ratio bandwidth in the circular polarization state. The frequency and polarization diversities of this design could potentially improve the reliability of wireless communication systems.

Fogs, low lying clouds, and other highly scattering environments pose a challenge for many commercial and national security sensing systems. Current autonomous systems rely on optical sensors for navigation whose performance is degraded by highly scattering environments. In our previous simulation work, we have shown that polarized light can penetrate through a scattering environment such as fog. We have demonstrated that circularly polarized light maintains its initial polarization state better than linearly polarized light, even through large numbers of scattering events and thus ranges. This has recently been experimentally verified by other researchers. In this work, we present the design, construction, and testing of active polarization imagers at short-wave infrared and visible wavelengths. We explore multiple polarimetric configurations for the imagers, focusing on linear and circular polarization states. The polarized imagers were tested at the Sandia National Laboratories Fog Chamber under realistic fog conditions. We show that active circular polarization imagers can increase range and contrast in fog better than linear polarization imagers. We show that when imaging typical road sign and safety retro-reflective films, circularly polarized imaging has enhanced contrast throughout most fog densities/ranges compared to linearly polarized imaging and can penetrate over 15 to 25m into the fog beyond the range limit of linearly polarized imaging, with a strong dependence on the interaction of the polarization state with the target materials.

This work is dedicated to the diagnosis and grading of colon cancer by a combined use of Poincaré sphere and 2D Stokes vector polarimetry mapping approaches. The major challenge consists in exploring the applicability of polarized light for noninvasive screening of the histological abnormalities within the samples of biological tissues. Experimental studies were conducted in ex vivo colon sample, excised after surgical procedure for colon tumor removal of G2-adenocarcinoma lesion. Polarimetric measurements in linear and circular regime were carried via personally developed polarimetric, optical set-up, using supercontinuous fiber laser with irradiation fixed at 635 nm. We apply the Poincaré sphere and two-dimensional Stokes vector scanning approach for screening the corresponding tissue samples. A comparison between linear and circular polarization states is made both for quantitative and qualitative evaluations. It is shown that circular polarization has better diagnostic capabilities than linear polarization, with higher dynamic ranges of the polarimetric parameters and better values of the diagnostic quantities. In addition to the standard polarimetry parameters, utilized as essential diagnostic markers, we apply statistical analysis to obtain more detailed information in frame of the applied diagnostic approach.

Heavy fogs and other highly scattering environments pose a challenge for many commercial and national security sensing systems. Current autonomous systems rely on a range of optical sensors for guidance and remote sensing that can be degraded by highly scattering environments. In our previous and on-going simulation work, we have shown polarized light can increase signal or range through a scattering environment such as fog. Specifically, we have shown circularly polarized light maintains its polarized signal through a larger number of scattering events and thus range, better than linearly polarized light. In this work we present an active polarization imager in the short-wave infrared. We explore multiple polarimetric configurations for the imager, focusing on linear and circular polarization states. We also describe initial testing of the imager in the Sandia Fog Facility. The Sandia Fog Facility is a 180 ft. by 10 ft. chamber that can create fog-like conditions for optical testing. This facility offers a repeatable fog scattering environment ideally suited to test the imager's performance in fog conditions.

A compact, single-layer reconfigurable leaky-wave antenna capable of both linear polarization (LP) and circular polarization (CP) with beam scanning is presented in this study. The antenna utilizes copper strips inserted between shorted stubs and a patch to achieve LP and CP states. An H-shaped arrangement of horizontal and vertical slots enables wideband CRLH characteristics, supporting dual-polarization operation from 10 GHz to 20 GHz for LP state and from 12.8 GHz to 20 GHz for CP state. The dimensions of the proposed antenna are relatively small, with a size of (3.25 × 0.4 × 0.07) λ3 and provided continuous beam scanning across a range of −70° to 37° for CP states with the maximum gain of 10.37 dB. However, LP state is offered from −69° to 61° with the peak gain of 10.42 dB. The antenna exhibits an axial ratio below 3 dB within the CP bandwidth and efficiency exceeding 90% for both LP and CP states.

Metasurfaces are artificially intelligent planar optical devices that can realize excellent functions by optimizing the design of nanostructures and arrays. Metasurfaces have become the preferred approach for fabricating integrated and compact optical systems with micro‐ and nano‐scale solutions for realizing multi‐dimensional modulated optical devices. Herein, the realization of multi‐fold phase holography is demonstrated by combining switchable optical frequencies with hybrid circular and linear polarization states. The original holographic phase distribution can be inversely optimized using an adaptive momentum gradient descent algorithm. Furthermore, completely different images can be reconstructed when the phase values are several times the original values. The multi‐fold phase modulation can be achieved by optimizing the structural distribution of the dielectric metasurface with the incident changeable light frequency and decoupled circular and linear polarization. Different polarization combinations enhance the flexibility of multiple holographic modulations. This technology provides new solutions for dynamic multi‐fold beam directional refraction and excitation, orbital angular momentum communication, multi‐fold holographic displays, optical encryption and camouflage, light switching, and shaping.

To understand how light propagates through a medium we need to know the basics of electromagnetic theory, polarization, reflection, and diffraction. In this chapter we shall address the principles of polarization. We shall consider the nature of polarization and how linear, circular and elliptical polarization states are just different aspects of the same rotation of the electric field as is best demonstrated by the Poincare sphere. Unpolarized light can be polarized by subjecting it to various physical effects which we shall consider. We then move on to describe how polarized light can be created. Polarization can be caused by a transmissive polarizing device, by reflection, by refraction or by scattering. The production of polarized light can result in linear, circular or elliptical polarization and also depends upon the nature of the light approaching the cause of polarization, e.g. randomly (or unpolarized) light, partially polarized and linear, circular or elliptical states of polarization. We also have the Faraday Effect where an electromagnetic field impinging upon an electromagnetic wave can cause polarization of the wave. Using, manipulating, and understanding polarization leads to many practical uses in the fields of biology, medicine, geology, astronomy and many other physical sciences including communications.

High cross-polarization isolation (CPI) is crucial to the accurate polarization measurement for the fully polarimetric phased array radar (PPAR). In this paper, we propose a polarization state configuration (PSC) method to improve the cross-polarization isolation based on the triple feed microstrip patch element. Compared with the conventional fixed polarization state of radiated wave whether it has linear, circular or elliptical polarization state, our PSC approach configures the polarization state on the basis of beam steering. The CPI improvement is formulated as an optimization problem, thereby achieving the optimum configuration of magnitude and phase for the fully polarimetric antenna. To facilitate the uniform representation for the polarization measurement application of PPAR, the universal expressions of intrinsic and measured backscatter matrices are derived for arbitrary polarization states. The dual-polarization dipole array is used to evaluate the priority of the proposed method. Simulation results reveal that our approach could obtain higher cross-polarization isolation while being available in a larger scanning range. The configured CPI could improve the polarization measurement accuracy for the fully PPAR.

In order to obtain focal spot with high power and spot size comparable to wavelength scale, a novel approach to achieving the coherent combination of beam array by tightly focusing is proposed. The physical model of coherent beam combination of beam array via tightly focusing is built up by the use of the vector diffraction integral. Therefore the influences of beam configuration, polarization state, beam width, beam interval and numerical aperture of the tight focusing system on the characteristics of the combined beam are discussed in detail. The results indicate that the coherent combination effect of beam array with linear and circular polarization via tight focusing is the first best, and that with the radial polarization is the second best but that with the azimuthal polarization is the worst. The beam array of linear and circular polarization with rectangle configuration can be tightly focused onto center point, and the beam array with hexagon is also focused onto center point but with lower efficiency. In addition, by enlarging the beam width and the beam interval to a certain extent, the combination efficiency can be increased. By optimizing the beam configuration, beam width and interval, and selecting rational numerical aperture of the tightly focusing geometry, the focal spot with high energy concentration can be obtained with high beam quality and combination efficiency.

Graphene is a good candidate material in designing tunable terahertz devices due to its tunability of sheet conductivity. In this paper, we propose a scheme to design switchable quarter-wave plate for terahertz wave that is composed of graphene based grating and metallic grating structures. The proposed active device can dynamically switch the transmission wave among left-handed, right-handed circular polarization and linear polarization states by electrically controlling the Fermi energy of the graphene grating. The device is analyzed with grating circular polarizer theory and its performance is investigated through full wave simulations on practically realizable geometry. The proposed quarter-wave plate having a subwavelength thickness demonstrates a wide angle of incidence tolerance, and a broad bandwidth operation. This device concept offers a further step in developing tunable polarizers and polarization switchers, which may be applied in practical terahertz image and communication systems.

A wideband antenna with quad-polarization reconfigurable operation is proposed. It consists of a crossed tri-port feed linearly polarized (LP) radiation structure and a switchable feed network. A dual-port LP element with wideband characteristic and good port isolation is first introduced. The inherent 180° phase difference (PD) between two feed ports vastly simplifies the complexity of the design and improves the efficiency of the feed network. By assembling two grooved LP elements, the crossed tri-port feed radiation structure is formed. Meanwhile, a wideband 90° phase shifter and an unequal Wilkinson power divider are applied in designing the switchable feed network. Through controlling the PIN diodes implanted in the feed line, four working modes with equal amplitude and reconfigurable PD (0° or 90°) are achieved. Based on this, the desired quad-polarization reconfiguration, including two orthogonal linear polarization (LP) states and two orthogonal circular polarization (CP) states, is realized. Measured results show that the proposed antenna has a wide overlapped operation impedance bandwidth of 84.5%, ranging from 1.36 ~ 3.35 GHz, for all polarization states within a compact volume. The measured 3-dB AR bandwidth is 100%, covering the operation impedance frequency range. Radiation patterns exhibit unidirectional and stable quality from the point view of beam slant and split. Besides, a peak efficiency of 75% and a peak gain of 7.8 dBi are achieved.

Directionally duplexed metalenses manipulated by the geometric phase of a silicon nano-bar are theoretically designed to generate multifunctional structured light. It is numerically demonstrated that incident light with different linear and circular polarization states, along forward and backward propagation directions, can be differentially converted into multiple focusing structured beams of arbitrary topological charges, either of vector light with azimuthally variant polarizations or of vortex light with helical phases. Due to the all-silicon and nonresonant metastructural design, the resultant high working efficiencies of our proposed metalens are promising for applications such as optical communication, nanoparticle manipulation, and other direction-duplexed multifunctional optical meta-devices.

To make full use of the polarization information of electromagnetic waves for the polarimetric sensor array, we derive the orthogonality expression of the polarization state based on the Poincaré sphere (PS) representation. The ellipticity angle and the orientation angle of the ellipse are used to describe the polarization ellipse and the point on the surface of the Poincaré sphere. The derivation shows that two points that characterize a pair of orthogonal polarization states are distributed in the opposite positions. Compared with the conventional linear and circular polarization state, the flexible elliptical polarization state would result in the maximum separation of co-polarization and cross-polarization components, thereby enhancing the accuracy of polarization information measurement. The simulation result displays the correctness of the theoretical derivation, which could provide a basis for the further polarization state configuration.