Circularly-polarized Beam Research Articles

Tailoring of Circularly Polarized Beams Employing Bound States in the Continuum in a Designed Photonic Crystal Metasurface Nanostructure.

We propose a photonic crystal (PC) nanostructure that combines bound states In the continuum (BIC) with a high-quality factor up to 107 for emitting circularly polarized beams. We break the in-plane inversion symmetry of the unit cell by tilting the triangular hole of the hexagonal lattice, resulting in the conversion of a symmetrically protected BIC to a quasi-BIC. High-quality circularly polarized light is obtained efficiently by adjusting the tilt angles of the hole and the thickness of the PC layer. By changing the hole's geometry in the unit cell, the Q-factor of circularly polarized light is further improved. The quality factor can be adjusted from 6.0 × 103 to 1.7 × 107 by deliberately changing the shape of the holes. Notably, the proposed nanostructure exhibits a large bandgap, which significantly facilitates the generation of stable single-mode resonance. The proposed structure is anticipated to have practical applications in the field of laser technology, particularly in the advancement of low-threshold PC surface emitting lasers (PCSELs).

Method for fabricating circular polarization beam splitters based on polarization holography.

Based on polarization holography, circular polarization beam splitters with separation angles of up to 100° have been fabricated. The left- and right-handed circularly polarized waves can be reconstructed by the two holograms that were designed by the tensor theory of polarization holography, respectively. In the fabrication of circular polarization beam splitters, two holograms were recorded only by the interference method in the same area of the polarization-sensitive material. This method is simple, inexpensive, and easy to adjust the separation angles and element size. The diffraction efficiency and the polarization state of the reconstructed waves were tested under different incident waves, and the experimental results are in good agreement with the theory. This work not only deepens our understanding of polarization holography but also expands the applications of polarization holography.

Bidirectional multi-beam with multi-polarizations tensor holographic metasurface using bilayer anisotropic elements.

In this paper, we present and design a tensor holographic metasurface (THMS) capable of radiating multiple beams with different polarizations in both forward and backward directions. The proposed THMS manipulates the fundamental TE mode surface waves (SWs) to produce bidirectional leaky-wave radiation using bilayer anisotropic metal patches. To achieve the independent control of the direction and polarization of bidirectional beams, the nature of the capacitive impedance element supporting TE mode SWs is exploited. A dual-feed scheme exciting orthogonal TE SWs is proposed for THMS generating circularly polarized beams with good performance. As a proof of concept, a bidirectional THMS integrated with two WR-28 waveguide sources based on the orthogonal-feeds scheme, which simultaneously radiate linear- and circular-polarized four beams, is designed, fabricated, and measured at 35 GHz. The experiment results are in good agreement with the simulated ones, achieving a peak gain of 19.2 (19.6) dBi, a -3 dB gain bandwidth of 9.14% (4.3%), for circularly-polarized (linearly-polarized) beams and a 3 dB axial ratio bandwidth of 13% for circularly-polarized beams. The sidelobe levels and cross polarization levels of all beams are below -15 dB and -22 dB, respectively.

Coherent manipulation of Brewster angles and phase shifts for both left right circularly polarized beams in chiral medium

The Brewster angles and phase shift of both left right circular polarization beams of the probe field is controlled and modified in this manuscript. Subluminal and superluminal propagation of light having group indices of ±200 has been reported. The group velocities of left circularly polarized (LCP) and right circularly polarized (RCP) beam varies to ±1.5×106 m/s while, delay times varies to ±5ns. The peak values of Brewster angles of LCP and RCP beams are calculated 0.786 radian. The maximum value phase shift of LCP and RCP is reported to 31.45 radian at length L=5λ. Strong oscillation in Brewster angles and phase variations of LCP and RCP beams are investigated with azimuthal quantum number of control field and increasing length of position coordinates. The modified results of this manuscript are useful for interferometry and lasers technology.

Independent control of circularly polarized light with exceptional topological phase coding metasurfaces

Exceptional points, as degenerate points of non-Hermitian parity-time symmetric systems, have many unique physical properties. Due to its flexible control of electromagnetic waves, a metasurface is frequently used in the field of nanophotonics. In this work, we developed a parity-time symmetric metasurface and implemented the 2π topological phase surrounding an exceptional point. Compared with Pancharatnam-Berry phase, the topological phase around an exceptional point can achieve independent regulation of several circular polarization beams. We combined the Pancharatnam-Berry phase with the exceptional topological phase and proposed a composite coding metasurface to achieve reflection decoupling of different circular polarizations. This work provides a design idea for polarimetric coding metasurfaces in the future.

Transformations of the transverse Poynting vector distribution upon diffraction of a circularly polarized paraxial beam.

Usually, the structure of paraxial light beams is characterized by the intensity associated with distribution of the longitudinal energy flow density (Poynting momentum) across the transverse plane. In this work, special attention is paid to the distribution of internal energy flows described by the transverse Poynting momentum (TPM) components. This approach discloses additional polarization-dependent features of the vector beam transformations; in application to the edge diffraction of a circularly polarized (CP) Gaussian beam, it reveals the helicity-dependent asymmetry of the diffracted-field TPM profile characterized by the shifts of the TPM singularity, maximum, etc. These phenomena are confirmed experimentally and interpreted in terms of the spin-orbit interaction (SOI) and spin Hall effect of light. In contrast to the known SOI manifestations in the CP beams' diffraction originating from the small longitudinal component of a paraxial field, the new TPM-related effects stem from the transverse field components and are thus much higher in magnitude.

Mid-Infrared Circularly Polarized Beam Splitter Based on Metasurfaces

Mid-Infrared Circularly Polarized Beam Splitter Based on Metasurfaces

Compact Mobile Terminal Antenna With Endfire Circularly Polarized Beam for Satellite Communications

Compact Mobile Terminal Antenna With Endfire Circularly Polarized Beam for Satellite Communications

Compact wideband printed antenna with circularly polarized tilted beam radiation using a Quasi-Radiator

This paper presents a new compact wideband printed antenna with circularly polarized (CP) tilted beam radiation using a quasi-radiator. To achieve size compactness and tilted CP performance, the radiation patch of a conventional monopole is loaded by a fork-slot, and a shorting via is used to connect the corners of rectangular patch and partial ground plane together. The fabricated prototype has an |S11| < −10 dB of 60.9% (1.2–2.25 GHz), an AR < 3 dB of 25.7% (1.55–2 GHz), a peak gain of 3.7 dBi, a compact size of 0.186λ0 × 0.186λ0 × 0.008λ0 at the lowest frequency with CP radiation, a right-handed CP beam at θ = −42°, and a left-handed CP radiation at θ = −134° in the elevation plane. The antenna is analyzed using characteristic mode analysis (CMA) to figure out the orthogonal modes and working principle of CP radiation. The antenna benefits include low-profile, simple structure, easy fabrication, large tilt angle, and stable radiation patterns over entire bandwidth.

Study of particle acceleration by Laguerre–Gaussian ultra intense laser plasma interactions

In this work, simulations of multi-petawatt lasers in the range of ∼0.2 PW–∼100 PW with varying Laguerre–Gaussian (LG) azimuthal modes as well as linearly polarized (LP) and circularly polarized (CP) laser beams striking near critical density targets were studied by using three-dimensional particle in cell (PIC) codes. Particle acceleration mechanisms have a dependence on laser polarization and it affects the energy gained by the particles. It is known that laser pulses can be polarized helically by applying the LG distribution function to the fundamental Gaussian laser profile. In this study, differently polarized laser beams with varying powers were employed to study laser driven particle acceleration and compares accelerated charged particles’ energy spectra and angular distribution. It is seen that LG laser beams can accelerate higher energetic particles due to higher conversion efficiency compared to LP and CP laser beams. It is also seen that LG laser beams can collimate ions with a narrower spread compared to LP and CP beams. Furthermore, ions can have a smaller divergence angle with increasing azimuthal mode index when the laser is LG polarized. We also studied the energy deposition of these particles in a water cell obtained by the PIC codes for different laser parameters by using Geant4 Monte Carlo simulations which suggests that LG laser beam can be useful for the future hadron therapy applications.

Photo-Excited Metasurface for Tunable Terahertz Reflective Circular Polarization Conversion and Anomalous Beam Deflection at Two Frequencies Independently.

In this paper, a photo-excited metasurface (MS) based on hybrid patterned photoconductive silicon (Si) structures was proposed in the terahertz (THz) region, which can realize the tunable reflective circular polarization (CP) conversion and beam deflection effect at two frequencies independently. The unit cell of the proposed MS consists of a metal circular-ring (CR), Si ellipse-shaped-patch (ESP) and circular-double-split-ring (CDSR) structure, a middle dielectric substrate, and a bottom metal ground plane. By altering the external infrared-beam pumping power, it is possible to modify the electric conductivity of both the Si ESP and CDSR components. By varying the conductivity of the Si array in this manner, the proposed MS can achieve a reflective CP conversion efficiency that ranges from 0% to 96.6% at a lower frequency of 0.65 THz, and from 0% to 89.3% at a higher frequency of 1.37 THz. Furthermore, the corresponding modulation depth of this MS is as high as 96.6% and 89.3% at two distinct and independent frequencies, respectively. Moreover, at the lower and higher frequencies, the 2π phase shift can also be achieved by respectively rotating the oriented angle (αi) of the Si ESP and CDSR structures. Finally, an MS supercell is constructed for the reflective CP beam deflection, and the efficiency is dynamically tuned from 0% to 99% at the two independent frequencies. Due to its excellent photo-excited response, the proposed MS may find potential applications in active functional THz wavefront devices, such as modulators, switches, and deflectors.

Large spatial shifts of reflected light beam off biaxial hyperbolic materials

Many optical systems that deal with polarization rely on the adaptability of controlling light reflection in the lithography-free nanostructure. In this study, we explore the Goos–Hänchen (GH) shift and Imbert–Fedorov (IF) shift in a biaxial hyperbolic film on a uniaxial hyperbolic substrate. This research statistically calculates and analyzes the GH shift and IF shift for the natural biaxial hyperbolic material (NBHM). We select the surface with the strongest anisotropy within the NBHM and obtain the complex beam-shift spectrum. By incorporating the NBHM film, the GH shift caused by a transversely magnetic incident-beam on the surface increases significantly compared with that on the uniaxial hyperbolic material. The maximum of GH shift can reach 86λ 0 at about 841 cm−1 when the thickness of NBHM is 90 nm, and the IF shift can approach 2.7λ 0 for a circularly-polarized beam incident on a 1700-nm-thick NBHM. It is found that the spatial-shift increases when a highly anisotropic hyperbolic polariton is excited in hyperbolic material, where the shift spectrum exhibits an oscillating behaviour accompanied with sharp shift peak (steep slope). This large spatial shift may provide an alternative strategy to develop novel sub-micrometric optical devices and biosensors.

Circularly Polarized Leaky-Wave Antennas Based on Periodically Arranged Rotated Right-Angle Triangular Microstrip Patches

In this paper, a scheme to realize the circularly polarized periodic leaky-wave antennas is prosed. A single-row model and a dual-row model are presented based on the series-fed periodically arranged rotated right-angle triangular (RAT) microstrip patches. For either of the two models, the antenna unit of one period occupies four RAT microstrip patches and the units are arranged repetitively on one side or on both side of a transmission line. The open-stopband is eliminated by adjusting the distances between the patches in each unit. The single-row model with 12 units on one side of a transmission line achieves a main beam sweeping angle range of 96° (-56°-40°). The model realizes the left-hand (LH) circular polarization as the main beam is scanning continually from -19° to 22°. The dual-row model includes 20 units of a different form of the rotated RAT microstrip patches arranged on both side of a transmission line. The main beam is able to scan from - 40° to 35° while the antenna is radiating. The model realizes the LH circular polarization while the main beam is scanning from -18° to 13°. The proposed two models can both realize circular polarization and continual beam scanning across the broadside.

A metal-only reconfigurable reflectarray antenna for generating diversified circular-polarization focused beams and mode-agile vortex beams

ABSTRACT In this article, a metal-only reconfigurable reflectarray antenna (RRA) is proposed for generation of diversified circular-polarization (CP) focused beams and mode-agile vortex beams in the X-band. The proposed RRA element has the 3-D metal-only configuration, which consists of three staircases with different heights, a turntable, a latch, and a base. By rotating the proposed RRA element in 45° steps, the ability of 1-bit phase quantization with orthogonal linear polarization (LP) reconfigurability can be realized. Then, a 26 × 26-elements reconfigurable reflectarray antenna feeding by a linear polarization horn antenna is designed to enable free conversion of line-to-circle polarization at the array level. Full-wave simulations show that the diversified circular-polarization beams can be synthesized by adjusting the aperture element distribution. Furthermore, a manually reconfigurable reflectarray antenna prototype is fabricated to obtain the actual performance of the synthetic LHCP focused beams. The measured maximum gain of the LHCP beams is 27.1 dBi, with the aperture efficiency of 24.2% where the beam point at 20°, and the 1-dB gain bandwidth is 18.0% (9.3 GHz − 11.1 GHz). Finally, mode-agile vortex beams can also be realized by using the proposed reconfigurable reflectarray antenna, and the simulated results show that the mode purity of vortex beams are all above 35% in different modes, and the maximum gain of the vortex beams is 21.1 dBi, with aperture efficiency of 6.1% where the mode of vortex beams is −1.

Localized Spontaneous Chiroptical Response in Disordered Plasmonic Nanoaggregates

Metamaterials exhibiting orders-of-magnitude enhanced artificial chiroptical response than natural counterparts have been intensely investigated. The underlying principle of these chiral responses heavily hinges on an elaborate nanostructure fabrication to generate either intrinsic geometry chirality or handedness-dependent mode interference. Here, we unveil that localized spontaneous chiroptical response can be leveraged by plasmonic nanoaggregates with a disordered coupling effect. The near-field coupling among disordered individual gold nanoparticles leads to localized hot spots that are sensitive to the handedness of light. As a consequence, the nearby nanoparticles showcase near-unity circular dichroism in linear absorption to left- and right-circularly polarized light. It directly leads to a subsequent selective photothermal deformation of plasmonic nanoparticles, which produces prominent nonlinear circular dichroism in two-photon fluorescence by circular polarization beams. Such localized spontaneous chirality is then experimentally evidenced by nanoscale multiplexing watermarks in polychromatic beams with left- and right-circular polarizations. Our results might open a new strategy to tailor the chiroptical response in disordered photonic systems and facilitate the study of chiral light–matter interactions at the deep-subwavelength regime.

Tight Focus Vector Light Field of Hybrid Double Circularly Polarized Beams

Based on the Richard-Wolf diffraction theory, we demonstrate the tightly focused optical field distribution with two beams circularly polarized light. We deduced the expression of the double-beam superimposed vortex light intensity of left-handed circularly polarized light and right-handed circularly polarized light under the focusing condition of a high numerical aperture objective lens. Based on the different vortex topological charge values, amplitudes and initial phases of the dual beams, we numerically simulated the light intensity distribution of the superimposed hybrid focused light field. It is found that a variety of peculiar vortex spots can be obtained through the tight focus stacking of the double beams. These complex hybrid focused light fields with different polarizations can be used in fields such as optical field micro-manipulation or nonlinear fluorescence microscopy imaging.

Chiral Dual-Core Photonic Crystal Fiber for an Efficient Circular Polarization Beam Splitter

As a function of a circular polarization beam splitter (CPBS), combining a linear polarization beam splitter with a quarter-wave plate results in a polarization error in a circular polarization fiber-optic circuit. To relieve the error, chiral dual-core photonic crystal fiber (DC-PCF) is investigated as a kind of an efficient circular polarization beam splitter by using the chiral plane-wave expansion (PWE) method. On the basis of the competitive effect in polarization and coupling length between the circular asymmetry of the structure and the chirality of the medium, the effects of the structure and the chirality are analyzed. The numerical results demonstrate that a CPBS needs the weak circular asymmetry in its structure and a relatively stronger chirality of the medium. Then, a kind of CPBS based on chiral DC-PCF is designed with weaker chirality, with a central wavelength of 1.55 μm. The simulation shows the superior performance of having a shorter coupling length and a higher extinction ratio. Furthermore, the dual-wavelength of 1.55 μm and 1.30 μm with left-circular polarization can further be separated by the corresponding chiral DC-PCF. The results show promising applications for the circular polarized multiplexer/demultiplexer in fiber laser communication systems.

Reflect–Transmit-Array Antenna With Independent Dual Circularly Polarized Beam Control

In this letter, we propose a dual circularly polarized reflect–transmit-array (RTA) antenna with independent beam control. It can transmit left-hand circularly polarized (LHCP) wave as transmitarray antenna and reflect right-hand circularly polarized (RHCP) wave as reflectarray antenna at 8.7–10.2 GHz. In addition, 360° phase shift for each circularly polarized wave can be achieved by rotating the top and bottom patches. A 20 × 20-unit cell RTA is designed, fabricated, and measured. For the LHCP radiation, the measured results show that the 3 dB gain bandwidth and axial ratio (AR) bandwidth are 13.7% (8.8–10.1 GHz) and 15.9% (8.7–10.2 GHz), respectively. For the RHCP radiation, the measured 3 dB gain bandwidth and AR bandwidth are 11.4% (9.1–10.2 GHz) and 12.6% (8.9–10.1 GHz). The peak aperture efficiencies for LHCP and RHCP radiations are 45.5% at 9.2 GHz and 41.8% at 9.6 GHz, respectively.

Spin-multiplexed full-space trifunctional terahertz metasurface [Invited

The widespread use of multifunctional metasurfaces has started to revolutionize conventional electromagnetic devices due to their unprecedented capabilities and exceedingly low losses. Specifically, geometric metasurfaces that utilize spatially varied single-celled elements to impart arbitrary phase modulation under circularly polarized (CP) waves have attracted more attention. However, the geometric phase has intrinsically opposite signs for two spins, resulting in locked and mirrored functionalities for the right-handed and left-handed CP beams. Additionally, the demonstrated geometric metasurfaces so far have been limited to operating in either transmission or reflection modes at a single wavelength. Here, we propose a double-layered metasurface composed of complementary elliptical and reversal ring resonator structures to achieve simultaneous and independent control of the reflection and transmission of CP waves at two independent terahertz frequencies, which integrates three functions of reflected beam deflection, reflected Bessel beam generation, and transmitted beam focusing on the whole space. The high efficiency and simple design of our metasurface will open new avenues for integrated terahertz metadevices with advanced functionalities.

Circular-polarized beam splitter based on dielectrically chiral dual-core photonic crystal fiber

A kind of circular polarization beam splitter (CPBS) based on dielectrically chiral dual-core photonic crystal fiber (DC-PCF) is proposed and investigated by a chiral plane-wave expansion method. The numerical results demonstrate the achievement of circular polarized beam splitter must introduce the circular asymmetry of structure and chirality of medium, where the former can shorten the coupling lengths for right- and left-handed beams and increase their difference, while the latter can decrease their difference. Then, according to the competing effect of the circular asymmetry of structure and chirality of medium in polarization and the difference of the paired coupling length, a CPBS based on chiral DC-PCF is designed. The simulation demonstrates that it possesses the high extinction ratios and wide bandwidth at the central wavelength of 1.55µm.