Orthogonal Linear Polarizations Research Articles

A highly sensitive imaging polarimeter in the x-ray regime

We report on the development of a highly sensitive imaging polarimeter that allows for the investigation of polarization changing properties of materials in the x-ray regime. By combining a microfocus rotating anode, collimating multilayer mirrors, and two germanium polarizer crystals, we achieved a polarization purity of the two orthogonal linear polarization states of 8 × 10−8. This enables the detection of an ellipticity on the same order or a rotation of the polarization plane of 6 arcsec. The high sensitivity combined with the imaging techniques allows us to study the microcrystalline structure of materials. As an example, we investigated beryllium sheets of different grades, which are commonly used for fabricating x-ray lenses, with a spatial resolution of 200 μm, and observed a strong degradation of the polarization purity due to the polycrystalline nature of beryllium. This makes x-ray lenses made of beryllium unsuitable for imaging polarimeter with higher spatial resolution. The results are important for the development of x-ray optical instruments that combine high spatial resolution and high sensitivity to polarization.

A Method for Determining the Bearing and Roll Angles of an Aircraft by an Orthogonally Linearly Polarized Beacon Signal

Orthogonally linearly polarized radio-beacon signals are emitted simultaneously from two spatially separated points in the horizontal plane to determine the bearing and roll angles. The resulting vector signals from the radio beacon are received by a receiving antenna on board an aircraft. The antenna irradiator is equipped with a polarizing modulator in the form of a ferrite rotator of the polarization plane. The bearing and roll angles are estimated at the receiver output at a frequency that is a multiple of the polarization-modulation frequency of the received beacon signals. The layout of the apparatus that performs this method is described. The results of measuring the navigation elements are presented. The mean square errors of the bearing and roll angle measurements were 0.48° and 0.35°, respectively.

Light‐Field Imaging: Virtual‐Moving Metalens Array Enabling Light‐Field Imaging with Enhanced Resolution (Advanced Optical Materials 21/2020)

A virtual-moving metalens array (VMMA) enabling light-field imaging with enhanced resolution has been proposed and developed by Sang-Shin Lee and co-workers (see article number 2000820). The VMMA is based on a multifunctional dielectric metasurface, playing the role of imposing polarization-sensitive phase profiles for orthogonal linear polarizations. The periodic sampling position of the VMMA can be switched depending on the incident polarization.

Two-frequency sub-Doppler spectroscopy of the caesium D1 line in various configurations of counterpropagating laser beams

Sub-Doppler resonances in caesium vapours are studied in a laser field produced by counterpropagating two-frequency light beams with mutually orthogonal linear polarisations. The beams are in resonance with optical transitions in the D1 line, the frequency difference of the field spectral components being equal to the hyperfine ground-state splitting in the Cs atom (∼9.2 GHz). It has already been shown that in this configuration, the hypercontrast effect can be observed for sub-Doppler resonances, which makes this configuration promising for the employment in new-generation miniature optical frequency standards. In the present work, two different two-frequency configurations are compared with each other and with the single-frequency configuration widely used in practice for observing saturated absorption resonances. The parameters of nonlinear resonances are measured at various temperatures of caesium vapours and at different optical field intensities. The results of the investigations performed make it possible to find an optimal two-frequency scheme for exciting nonlinear resonances and to estimate a potential of the scheme for its applications in quantum metrology.

Split-cube-resonator-based metamaterials for polarization-selective asymmetric perfect absorption

A split-cube-resonator-based metamaterial structure that can act as a polarization- and direction-selective perfect absorber for the infrared region is theoretically and experimentally demonstrated. The structure, fabricated by direct laser writing and electroless silver plating, is comprised of four layers of conductively-coupled split-cube magnetic resonators, appropriately rotated to each other to bestow the desired electromagnetic properties. We show narrowband polarization-selective perfect absorption when the structure is illuminated from one side; the situation is reversed when illuminating from the other side, with the orthogonal linear polarization being absorbed. The absorption peak can be tuned in a wide frequency range by a sparser or denser arrangement of the split cube resonators, allowing to cover the entire atmospheric transparency window. The proposed metamaterial structure can find applications in polarization-selective thermal emission at the IR atmospheric transparency window for radiative cooling, in cost-effective infrared sensing devices, and in narrowband filters and linear polarizers in reflection mode.

Polarization-gradient cooling of 1D and 2D ion Coulomb crystals

We present experiments on polarization gradient cooling of Ca+ multi-ion Coulomb crystals in a linear Paul trap. Polarization gradient cooling of the collective modes of motion whose eigenvectors have overlap with the symmetry axis of the trap is achieved by two counter-propagating laser beams with mutually orthogonal linear polarizations that are blue-detuned from the S1/2 ↔ P1/2 transition. We demonstrate cooling of linear chains of up to 51 ions and 2D-crystals in zig-zag configuration with 22 ions. The cooling results are compared with numerical simulations and the predictions of a simple model of cooling in a moving polarization gradient.

Polarization-Reconfigurable Yagi-Configured Electrically Small Antenna

An electrically small, high-directivity, Yagi-configured, near-field resonant parasitic (NFRP) antenna with four reconfigurable polarization states is presented. The antenna is composed of two NFRP elements and a customized, electrically controlled, reconfigurable driven element. The elements are stacked vertically in a Yagi configuration. The upper NFRP element acts as the director, and the lower one acts as the reflector. Both elements have a cross-shaped Egyptian axe dipole form. By integrating four p-i-n (PIN) diodes into its coax-fed asymmetric driven element, four polarization states, i.e., two orthogonal linear polarization (LP) and two circular polarization (LHCP and RHCP), are enabled which are controlled with the ON/OFF-states of the PIN diodes. The measured and simulated results of this electrically small (ka = 0.7) sized polarization-reconfigurable system are in good agreement. This simple, Yagi-configured antenna exhibits stable radiation performance in all four of its polarization states. The measured results demonstrate that, in its x (y)-LP state, the peak realized gain, front-to-back ratio, and radiation efficiency values are, respectively, ~3.08 (3.2) dBi, ~11.0 (11.05) dB, and ~77% (73%), and that, in its LHCP (RHCP) state, they are, respectively, ~3.0 (3.1) dBi, ~12.1 (11.18) dB, and ~72% (70%).

Dual-Polarized Wideband Plate Array Antenna With High Polarization Isolation and Low Cross Polarization for D-Band High-Capacity Wireless Application

This letter presents a dual-polarized wideband plate array antenna in D-band for future fixed high-capacity wireless communication. To achieve the high polarization isolation and wideband operation at the same time, a two-stage multimode cavity is introduced, consisting of a polarization isolation cavity and a cascaded dividing cavity. They are combined to optimize and improve the bandwidth of the dual-polarized antenna array. The TE210 and TE120 degenerate modes are selected to resonate in the cavity. They can be used to generate two orthogonal linear polarization modes with the extremely low cross polarization after cascading four integrated horns with a proper placement. To validate the design, an 8 × 8 element array is fabricated by the diffusion bonding of laminated thin copper plates technology. The gain is more than 24.5 dBi from 130 to 149 GHz. The isolation between two channels is higher than 50 dB and the cross polarization level is below −45 dB over the whole band.

Plasmonic crystal with independently tunable double resonances

This paper reports the design and fabrication of large-area periodic arrays of metal nanostructures that can support dual-wavelength resonance with spatially overlapping hot spots. Gold films with protruding posts arranged in a rectangular lattice are stripped from silicon templates containing shallow hole arrays, defined by laser interference lithography. The plasmonic resonances at the band edges for the two orthogonal linear polarizations can be tuned independently by changing the corresponding lattice spacing. WSe2 monolayers and IR-140 dye molecules demonstrate directional and linearly polarized photoluminescence when coupled with such plasmonic crystals. The anisotropic lattice can enable enhancements at both the excitation and emission wavelengths. The emission is preferentially coupled to the first diffraction orders of the plasmonic crystals, resulting in a directional beam.

Deterministic aperiodic photonic crystal with a 2D array of metallic nanoparticles as polarization-sensitive dichroic filter

We demonstrate the possibility of using a two-dimensional array of spheroidal metallic nanoparticles embedded in a one-dimensional photonic crystal to obtain a narrow-bandpass, polarization-sensitive dichroic filter operating in the near-UV and visible domains. The optical anisotropy of the array of identically oriented nanoparticles results in two spectrally distinct plasmon resonances independently excited for two mutually orthogonal linear polarization states of light, which ensures polarization and spectral selectivity of the composite structure. The narrow transmission bands of the filter are defect modes due to a layer located at the center of the structure and hosting the nanoparticle array. In order to suppress these transmission windows, it is essential that the defect modes closely coincide with the plasmon resonances excited in the array. We show that the use of deterministic aperiodic distributed reflectors surrounding the defect layer makes it possible to adjust the spectral positions of two defect modes in two separate bandgaps in order to achieve such a coincidence. Among the various parameters governing the precise position of transmittivity windows of the filter, we establish the strong influence of the thickness of the defect layer. We also show that a strong localization of the optical field in the plane of the nanoparticle array is essential to enhance the efficiency of plasmonic excitation and obtain the desired control of the defect modes. Our study opens up possibilities for the further development of polarization-controlled nanophotonic devices.

Liquid crystal integrated metalens with dynamic focusing property.

Metalenses are developing fast towards versatile and integrated terahertz (THz) apparatuses, while tunable ones are highly pursued. Here, we propose a strategy that integrates dielectric metasurfaces with liquid crystals (LCs) to realize the dynamic focal spot manipulation. The silicon pillar meta-units of the metasurface are properly selected to generate different phase profiles for two orthogonal linear polarizations, permitting a laterally or axially altered focal spot. After LCs integrated, polarization-multiplexed focusing can be achieved via electrically varying the LC orientations. We demonstrate two metalenses with distinct functions. For the first one, the uniformly aligned LC works as a polarization converter, and further switches the focal length by altering the bias. For the second one, an LC polarization grating is utilized for rear spin-selective beam deflection. Consequently, a THz port selector is presented. This work supplies a promising method towards active THz elements, which may be widely applied in THz sensing, imaging, and communication.

Model of a tunable hybrid Tamm mode-liquid crystal device.

A concept of an easily tunable device based on hybrid Tamm modes is proposed. The device can be controlled using a high-sensitivity chiral liquid crystal serving as a mirror. The coupling of the chiral optical Tamm state with the Tamm plasmons is predicted. The Tamm plasmons are excited at different frequencies for the orthogonal linear polarizations, while the chiral Tamm state is excited at only one frequency. The properties of the proposed model are analytically and numerically calculated. The possibility of creating a two- and three-mode laser with tunable characteristics on the basis of the proposed model is discussed.

Use of Orthogonally Linearly Polarized Waves Radiated from a Radio Beacon in the Modulation Methods for Measuring Aircraft Bearing and Roll

On the basis of using the Jones vectors and matrices, we develop the polarization-modulation method for determining the aircraft bearing and roll by the radio-beacon radiated waves with orthogonal linear polarization, which was proposed in [1]. The waves are simultaneously radiated from two points with the known coordinates, which are spaced in the measurement plane. The engineering realization of the method, which is based on using the polarization modulator placed in the single-channel microwave transmission line of an onboard receiving antenna of an aircraft, is considered. The polarization modulator has the form of the rotating segment of a circular waveguide with a built-in half-wave phase plate. Mathematical expressions, which provide a clear physical understanding of the aircraft bearing and roll relation to polarization and spectral characteristics of the resulting onboard-recorded wave field of the radio beacon in the linear polarization basis, are presented.

Shift of zero-field level-crossing resonance in the Cs D1 line and its use in vector magnetometry.

We examine the level-crossing resonance in a cesium vapor cell filled with a buffer gas under counterpropagating pump and probe light waves with orthogonal linear polarizations. An optical transition Fg=4→Fe=3 is excited in the D1 line. Probe-wave transmission is analyzed versus a static magnetic field applied along the wave vectors. This configuration can provide ultrahigh-contrast electromagnetically induced absorption resonances. We report here a new, to the best of our knowledge, magneto-optical effect in the resonance shift caused by a transverse magnetic field and discuss how it can be applied in vector magnetometry.

Null reconstruction in orthogonal elliptical polarization holography read by non-orthogonal reference wave

Based on the newly developed tensor holography theory, the null reconstruction in orthogonal elliptical polarization holography is reported. In the recording stage, the information is stored in the recording material by two orthogonal elliptical polarization waves. In the reconstructing stage, the variation of the power of reconstructed wave with the polarization state of reading wave is studied. Then the null reconstruction, the reconstructed wave being identical to zero, is observed when the reading wave is the non-orthogonal reference wave of recording stage. However, in those previously reported experiments, when and only when the recording material is illuminated by the orthogonal reference wave, the null reconstruction could be observed. Thus, our result is very different from the previously reported results and would change the perspective on the null reconstruction. Based on the tensor theory, we analyze the condition for null reconstruction in orthogonal polarization holography. For the null reconstruction in orthogonal linear polarization holography, the reading wave should be the orthogonal reference wave. However, for the null reconstructions in orthogonal circular and elliptical polarization holography, the reading wave may be the non-orthogonal reference wave. We think the result may enlarge our knowledge about the null reconstruction.

Gap-surface plasmon metasurfaces for linear-polarization conversion, focusing, and beam splitting

Gap-surface plasmon (GSP) metasurfaces have attracted progressively increasing attention due to their planar configurations, ease of fabrication, and unprecedented capabilities in manipulating the reflected fields that enable integrating diverse bulk-optic-based optical components into a single ultrathin flat element. In this work, we design and experimentally demonstrate multifunctional metalenses that perform simultaneous linear-polarization conversion, focusing, and beam splitting, thereby reproducing the combined functionalities of conventional half-wave plates, parabolic reflectors, and beam splitters. The fabricated single-focal metalens incorporates properly configured distinct half-wave-plate-like GSP meta-atoms and exhibits good performance under linearly polarized incidence in terms of orthogonal linear-polarization conversion ( > 75 % ) and focusing (overall efficiency > 22 % ) in the wavelength spectrum ranging from 800 to 950 nm. To further extend the combined functionalities, we demonstrate a dual-focal metalens that splits and focuses a linearly polarized incident beam into two focal spots while maintaining the capability of orthogonal linear-polarization conversion. Furthermore, the power distribution between two split beams can readily be controlled by judiciously positioning the incident beam. The demonstrated multifunctional GSP-based metalenses mimic the combined functionalities of a sequence of discrete bulk optical components, thereby eliminating the need for their mutual alignment and opening new perspectives in the development of ultracompact and integrated photonic devices.

Achieving broadband absorption and polarization conversion with a vanadium dioxide metasurface in the same terahertz frequencies.

We present the bifunctional design of a broadband absorber and a broadband polarization converter based on a switchable metasurface through the insulator-to-metal phase transition of vanadium dioxide. When vanadium dioxide is metal, the designed switchable metasurface behaves as a broadband absorber. This absorber is composed of a vanadium dioxide square, silica spacer, and vanadium dioxide film. Calculated results show that in the frequency range of 0.52-1.2 THz, the designed system can absorb more than 90% of the energy, and the bandwidth ratio is 79%. It is insensitive to polarization due to the symmetry, and can still work well even at large incident angles. When vanadium dioxide is an insulator, a terahertz polarizer is realized by a simple anisotropic metasurface. Numerical calculation shows that efficient conversion between two orthogonal linear polarizations can be achieved. Reflectance of a cross-polarized wave can reach 90% from 0.42 THz to 1.04 THz, and the corresponding bandwidth ratio is 85%. This cross-polarized converter has the advantages of wide angle, broad bandwidth, and high efficiency. So our design can realize bifunctionality of broadband absorption and polarization conversion between 0.52 THz and 1.04 THz. This architecture could provide one new way to develop switchable photonic devices and functional components in phase change materials.

Nanoscale Noncoplanar Beam Splitters With Tunable Split Ratio

Beam splitters, especially those with tunable split ratios, play significant role in interferometers, spectrometers, and communication systems. To this end, we proposed a polarization-controllable beam splitter based on dielectric metasurface composed of an array of dielectric pillars. The dielectric metasurface presents phase gradients along two orthogonal directions, say, x- and y- axis, with each phase gradient applicable to one of two orthogonal linear polarizations. Due to the orthogonality of the dual phase gradients in both position and polarization, an elliptically polarized incident beam can be diffracted into two refracted beams, one lies within xoz plane and the other in yoz plane. More importantly, the split ratio of the two refracted beams is continuously tunable by changing the ellipticity of incident beam. Under extreme case, x- or y- polarized incident beam is refracted into one beam, but in different planes for different kind of linear polarization. Besides, the refracted angle of each refracted beam in respective refracted plane can be easily set by adjusting the phase difference of adjacent rows or columns of metasurface. With same method, a polarization-controllable dual-wavelength beam splitter is also achieved on the basis of phase-gradient metasurface. Such a noncoplanar beam splitter with tunable split ratios may play significant role in novel miniature optical devices and systems.

Electromagnetically induced absorption resonances in Hanle-configuration prepared in a paraffin coated 87Rb cell

We present an experimental investigation of electromagnetically-induced absorption (EIA) at the D1 line of 87Rb contained in an anti-relaxation coated vacuum optical cell. The configuration includes a pump and a probe beam propagating in opposite directions and having mutually orthogonal linear polarizations; the probe beam absorption is registered depending on the value of a magnetic field scanned around zero and applied collinearly to the laser beams. The advantages of this scheme have been recently evidenced in vapor cells filled with a buffer gas. In the present work we studied the width and the contrast of the EIA resonances obtained in a coated cell for different values of the pump power. The results are compared with those obtained in a buffer gas cell for the same transition of 87Rb. The theoretical calculations are in good agreement with the experiment.

A tiled dual-polarized transmitarray with 1-bit quantization

An original approach of a transmitarray which consists of the tiled unit cells placed in a plastic holder is considered. Each unit cell represents a passive receiver-transmitter structure with integrated phase-shifter, which can take either of two coding states corresponding 180° phase difference between the states. The transmitarray design supports two orthogonal linear polarizations. An example of a 10x10 element 1-bit beam steering transmitarray operated in C-band is presented. The results of radiation pattern measurements with single and multifeed excitation are shown. The proposed structure represents a cost-efficient solution for scalable transmitarrays.