Circular polarization

About: Circular polarization is a research topic. Over the lifetime, 15201 publications have been published within this topic receiving 234418 citations.

Measurement of axial and transverse trapping stiffness of optical tweezers in air using a radially polarized beam.

Abstract: The trapping efficiency and stiffness of optical tweezers using radial polarization are evaluated; the ray-tracing method and a proposed measurement method are used for numerical and experimental analyses, respectively. The maximum axial trapping efficiency with radial polarization is 1.84 times that with linear polarization, while the maximum transverse trapping efficiency decreases by 0.58 times. Further, the axial and transverse trapping efficiencies are found to be 1.19 times larger and 0.83 times smaller, respectively, than the values with linear polarization. From the experiments, the axial and transverse stiffness values are 1.2 times larger and 0.8 times smaller, respectively, with radial polarization. Hence, radial polarization enhances the axial trapping properties while reducing the transverse trapping properties.

A Wideband Open-Slot Antenna With Dual-Band Circular Polarization

Abstract: A wideband microstrip-fed open-slot antenna with dual-band circular polarization (CP) has been presented. A bent feeding structure and three slots, including a T-shaped and two inverted-L topologies etched in the ground plane, are designed to excite two orthogonal $E$ vectors with equal amplitude and 90 $^\circ $ phase difference (PD) for a radiating right-hand circularly polarized (RHCP) wave at 1.57 GHz and left-hand circularly polarized (LHCP) wave at 2.33 GHz. The two bands are the operated bandwidth of the global positioning system (GPS) and satellite digital audio radio (SDAR) service system. To improve the impedance bandwidth at the low-frequency band, a parasitic rectangular patch is added on the top plane of the substrate. Several resonances are merged, and thus, a wide impedance bandwidth is obtained. The measured impedance bandwidth of a reflection coefficient $ ranges from 1.45 to 3.93 GHz, and thus covers most of the commercial wireless communication systems, such as GPS, DCS, PCS, IMT-2000, WLAN, LTE, and WiMAX. The axial-ratio bandwidths are 65 MHz at the lower band (1.57 GHz) and 107 MHz at the upper band (2.33 GHz).

Electromechanically tunable metasurface transmission waveplate at terahertz frequencies

Abstract: Dynamic polarization control of light is essential for numerous applications ranging from enhanced imaging to material characterization and identification. We present a reconfigurable terahertz metasurface quarter-wave plate consisting of electromechanically actuated microcantilever arrays. Our anisotropic metasurface enables tunable polarization conversion through cantilever actuation. Specifically, voltage-based actuation provides mode-selective control of the resonance frequency, enabling real-time tuning of the polarization state of the transmitted light. The polarization tunable metasurface has been fabricated using surface micromachining and characterized using terahertz time domain spectroscopy. We observe a ∼230 GHz cantilever actuated frequency shift of the resonance mode, sufficient to modulate the transmitted wave from pure circular polarization to linear polarization. Our CMOS-compatible tunable quarter-wave plate enriches the library of terahertz optical components, thereby facilitating practical applications of terahertz technologies.

Effect of laser polarization on quantum electrodynamical cascading

Abstract: Development of quantum electrodynamical (QED) cascades in a standing electromagnetic wave for circular and linear polarizations is simulated numerically with a 3D PIC-MC code. It is demonstrated that for the same laser energy the number of particles produced in a circularly polarized field is greater than in a linearly polarized field, though the acquiring mean energy per particle is larger in the latter case. The qualitative model of laser-assisted QED cascades is extended by including the effect of polarization of the field. It turns out that cascade dynamics is notably more complicated in the case of linearly polarized field, where separation into the qualitatively different “electric” and “magnetic” regions (where the electric field is stronger than the magnetic field and vice versa) becomes essential. In the “magnetic” regions, acceleration is suppressed, and moreover the high-energy electrons are even getting cooled by photon emission. The volumes of the “electric” and “magnetic” regions evolve periodically in time and so does the cascade growth rate. In contrast to the linear polarization, the charged particles can be accelerated by circularly polarized wave even in “magnetic region.” The “electric” and “magnetic” regions do not evolve in time, and cascade growth rate almost does not depend on time for circular polarization.

Single-fed Circularly Polarized Antenna Element With Reduced Coupling for GPS Arrays

Abstract: A single-fed circularly polarized stacked patch antenna is proposed to cover all GPS bands, including the E5a/E5b band for the Galileo system. The small aperture size (lambda/8 at 1176 MHz, the L5 band) makes this antenna attractive for small GPS arrays. Also, in contrast to previous GPS antennas, the presented design uses a single feed for circular polarization. In this paper, we present the design procedures and performance of the designed GPS antenna and discuss issues relating to coupling between array elements. Modifications to reduce coupling are then presented.