Pancharatnam-Berry Phase Research Articles

Breaking of reciprocity and the Pancharatnam-Berry phase for light scattered by a disordered cold-atom cloud

Breaking of reciprocity and the Pancharatnam-Berry phase for light scattered by a disordered cold-atom cloud

Spatial momentum separation for optical vortex via phase-assembled metasurfaces

Expanding the spatial degrees of freedom is regarded to be the most innovative and effective solution for optical vortex encoding/decoding technology. A phase-assembled metasurface is proposed here to separate the momentum of the optical vortex into different spatial locations, and the incident high-order optical vortex is encoded in 18 channels. By combining both the propagation phase and the Pancharatnam-Berry (PB) phase, the fundamental Gaussian mode (solid spot) positions and other higher-order orbital angular momentum modes (hollow mode spots) positions at different channels are used to achieve the encryption of all-optical information. The scheme of grouping the mode spots on different channels into solid and hollow points greatly reduces the difficulty of encoding/decoding a high-order optical vortex. In this way, the combination of 2 incident high-order optical vortexes can represent 256 hexadecimal numbers from 00 to FF. We envision this work will open avenues for information encryption, multidimensional data storage, wavefront manipulation, and advanced orbital angular momentum detection technologies.

Large-scale fabrication of meta-axicon with circular polarization on CMOS platform

Abstract Metasurfaces, consisting of arrays of subwavelength structures, are lightweight and compact while being capable of implementing the functions of traditional bulky optical components. Furthermore, they have the potential to significantly improve complex optical systems in terms of space and cost, as they can simultaneously implement multiple functions. The wafer-scale mass production method based on the CMOS (complementary metal oxide semiconductor) process plays a crucial role in the modern semiconductor industry. This approach can also be applied to the production of metasurfaces, thereby accelerating the entry of metasurfaces into industrial applications. In this study, we demonstrated the mass production of large-area meta-axicons with a diameter of 2 mm on an 8-inch wafer using DUV (Deep Ultraviolet) photolithography. The proposed meta-axicon designed here is based on PB (Pancharatnam–Berry) phase and is engineered to simultaneously modulate the phase and polarization of light. In practice, the fabricated meta-axicon generated a circularly polarized Bessel beam with a depth of focus (DoF) of approximately 2.3 mm in the vicinity of 980 nm. We anticipate that the mass production of large-area meta-axicons on this CMOS platform can offer various advantages in optical communication, laser drilling, optical trapping, and tweezing applications.

A Low-Profile and Ultra-Wideband Pancharatnam-Berry Coding Metasurface for High-Efficiency and Wide-Angle Circular Polarization Anomalous Reflection.

The manipulation of electromagnetic waves using metasurfaces is important in areas such as stealth and communication. In this paper, we reported on the use of an element-based polarizer for the first step, which enables the incident electromagnetic waves to integrate into the cross-polarized waves with a relative bandwidth of 88% within 15-37.1 GHz. Then, an eight-element coding metasurface based on the Pancharatnam-Berry phase is presented for circular polarization anomalous reflection. The simulated values show that our work can achieve a high-efficiency (94%) and wide-angle (70°) anomalous reflection under normal incidence. The simulated values present good agreement with the experimental values. Our work reveals the ability to manipulate the waves and electromagnetic stealth.

Influence of thermal bath on Pancharatnam-Berry phase in an accelerated frame

A uniformly accelerated atom captures Pancharatnam-Berry phase in its quantum state and the phase factor depends on the vacuum fluctuation of the background quantum fields. We observe that the thermal nature of the fields further affects the induced phase. Interestingly the induced phase captures the exchange symmetry between the Unruh and real thermal baths. This observation further supports the claim that the Unruh thermal bath mimics a real thermal bath. Moreover for certain values of system parameters and at high temperature, the phase is enhanced compared to zero temperature situation. However the required temperature to observe the phase experimentally is so high that the detection of Unruh effect through this is not possible within the current technology.

A tunable chiral metasurface useable in terahertz imaging and wavefront shaping

We proposed a tunable chiral metasurface comprising a reflective bottom layer of gold, a dielectric layer of polyimide, and a structural top layer of gold-graphene. Its main properties were studied via numerical simulations conducted using CST Studio Suite. The results indicate that, based on the chiral metasurface, we achieved dual-band circular dichroism of −0.5 and 0.77 at 0.9 THz and 1.06 THz, respectively, and complementary near-field imaging applications were realized by tuning the Fermi level (E f ) of graphene. Subsequently, exploiting the exceptional selective characteristics of circularly polarized waves using a chiral metasurface, eight chiral phase-gradient metasurfaces were constructed by rotating the chiral structure. Moreover, based on the Pancharatnam-Berry phase principle, tunable wavefront shaping applications were further realized, including anomalous reflection, vortex beams, and focusing. In anomalous reflection, the reflection angles for left-circularly polarized (LCP) and right-circularly polarized (RCP) incidences are opposite when adjusting the E f of graphene. For example, when the graphene E f is 0 eV and the LCP wave is incident at 0°, the reflection angle is −18°. Conversely, when the graphene E f is 1 eV and the RCP wave is incident at 0°, the reflection angle is 18°. In the application of vortex beams, by adjusting the E f of graphene, we achieved vortex beams with opposite topological charges under different circularly polarized incidences. In the focusing application, the incident LCP and RCP can achieve focusing and defocusing, respectively. And the graphene E f can dynamically control the focusing efficiency at the incident LCP, increasing it from 13.63% to 44.84%.

Simple and hybrid metalens with high polarization conversion efficiency for near-infrared spectrum

Thanks to their ability to control light, research on metalenses is developing rapidly. However, it is still quite difficult to design broadband metalenses with high polarization conversion efficiency. In this study, an alternative plasmonic material, aluminum-doped zinc oxide, is presented for metalens operating in near-infrared regime. We propose simple and hybrid metalenses with high polarization conversion efficiency and high transmission values that can focus efficiently in a wide near-infrared bandwidth (700–1000 nm). We design metalens consisting of subwavelength aluminum-doped zinc oxide nanoblocks based the Pancharatnam-Berry phase method and utilizing the finite-difference time-domain method. The polarization conversion efficiency (minimum 87 %) and transmission values (minimum 85 %) calculated for the metalens unit cell are higher than those previously obtained over the entire 300 nm bandwidth. In addition, we propose hybrid metalens to focus the incident beam in right and left handed circular polarized states in the studied frequency range. The presented aluminum-doped zinc oxide metalens with high polarization conversion efficiency and transmission values can find a place in the applications of near-infrared nanophotonic systems.

Design of Compact Dielectric Metalens Visor for Augmented Reality Using Spin-Dependent Supercells

Augmented reality overlays computer-generated virtual information onto real-world scenes, enhancing user interaction and perception. However, traditional augmented reality optical systems are usually large, bulky, and have limited optical performance. In this paper, we propose a novel compact monochrome reflective dielectric metalens visor with see-through properties, engineered using a periodic structure of spin-dependent supercells. The supercell, which is composed of staggered twin nanofins, provides spin-dependent destructive or constructive interference with different circularly polarized incidences. The design combines the principles of interference with the Pancharatnam–Berry phase to enhance reflection at a working wavelength of 650 nm while maintaining good transmission. Right circularly polarized light incident from the substrate side causes destructive interference, enabling the supercell to work in reflection mode, while left circularly polarized light causes constructive interference, enabling the supercell to work in transmission mode. Furthermore, the supercell-constructed metalens can achieve near-diffraction-limited reflective focusing and a broad diagonal field of view of approximately 96°. In addition, compared to transmissive metalens visors, the reflective design eliminates the need for a beam splitter, significantly reducing the size and weight of the system. Our work could facilitate the development of compact and lightweight imaging systems and provide valuable insights for augmented reality near-eye display applications.

Perfect vortex beams generation based on reflective geometric phase metasurfaces

Perfect vortex beam (PVB) is a propagating light field with radial intensity distribution independent of topological charge and carrying orbital angular momentum (OAM). PVBs can be generated through the Fourier transformation of a Bessel-Gaussian (BG) beam, which traditionally requires a precisely aligned optical setup consisting of a spiral phase plate, a conical lens, and a Fourier lens. However, such traditional schemes are usually bulky and unstable. Here, we have utilized a method that differs from conventional approaches, employing metasurfaces designed as planar Pancharatnam-Berry (PB) phase elements to substitute for all the required components. Unlike traditional methods based on reflective or refractive elements, metasurface elements can significantly reduce the system's footprint. Because the use of metallic metasurfaces allows for a more flattened design plane, in this paper, we have demonstrated the generation of PVB within the 8 GHz microwave frequency band based on a single-layer metallic metasurface. The metasurface is composed of a square ring metal structure, which can serve as a half wave plate to provide the required geometric phase distribution for incident circularly polarized light to generate PVB. By rigorously optimizing the parameters of the square-ring structures, we have generated vortex beams carrying OAM with different topological charges. These vortex beams exhibit a constant radial intensity distribution, which validates their "perfect" characteristics. In addition, we also extracted the mode purity of different vortex beams, so that the mode states of different vortex beams can be distinguished. These results provide broader value for the application of perfect vortex beams in communication.

Twisted Stacking Metasurface for Complete Amplitude and Phase Control of Circularly Polarized Terahertz Waves

AbstractTerahertz (THz) metasurfaces have emerged as a powerful tool for manipulating THz wavefronts, typically achieved by adjusting various geometric parameters. In this study, an approach is introduced by incorporating interlayer coupling into twisted stacking metasurface design to completely control the amplitude and phase of circularly polarized THz waves. By leveraging the interlayer coupling effect and the Pancharatnam–Berry phase, the study achieves efficient control over transmission phase and amplitude by simply adjusting the relative twist angle between paired C‐shaped split‐ring resonators. To validate the concept, a holographic metasurface is fabricated and characterized, providing experimental evidence of its THz wavefront manipulation capabilities. This design strategy presents a versatile and tunable solution for THz wave control, promising applications in a wide range of functional devices.

Broadband Spin-Selective Wavefront Manipulations with Generalized Pancharatnam–Berry Phase Metasurface

Broadband Spin-Selective Wavefront Manipulations with Generalized Pancharatnam–Berry Phase Metasurface

Broadband high-efficiency meta-holography from all-dielectric quasi-continuous metasurfaces

The compactness and particular optical design make metasurface a competitive candidate for holographic display and storage. Recently, the selection and optimization for the used metasurface structures and types have become research spots. Now the most researched and demonstrated meta-holograms are often based on discrete structures, which can achieve high efficiency but comparatively narrow working bandwidths or a wide wavelength range but low power efficiency. Therefore, contemporary meta-holograms struggle for realizing simultaneous broadband and high efficiency. In this paper, all-dielectric quasi-continuous metasurfaces composed of nanostrips are introduced to expand the operating bandwidth for high efficiency meta-holography. Benefiting from the associated Pancharatnam–Berry phase, the nanostrips with spatially orientation angles continuous changes can realize arbitrary phase modulation. For the first time, the average power efficiency of a meta-hologram is experimentally measured to be 56.63% over a broad wavelength band ranging from 500 to 1000 nm. In addition, based on this kind of all-dielectric quasi-continuous nanostrips, we also design and experimentally achieve multicolor three-dimensional (3D) holographic images. Actually, such all-dielectric quasi-continuous methodology proposed here can be used to design other functional meta-devices, including optical metalens, nanoprinting, and information encryption.

Quarter-wave Pancharatnam-Berry phase gradient liquid crystal-enabled dual-polarization optical edge detection.

Here, we present a novel, to the best of our knowledge, optical edge detection scheme that can be operated in both linear and circular polarization modes, leveraging an optical spatial differentiator constructed by quarter-wave Pancharatnam-Berry (P-B) phase gradient element. After explaining the theoretical mechanism, we utilize a quarter-wave P-B phase liquid crystal polarization grating to validate the dual-polarization optical edge detection capability. We demonstrate that the orientation of linear polarization and the spin of circular polarization dictate the transition between edge and bright-field images. Besides, the linear and circular polarization modes exhibit broadband and monochromatic responsive properties, respectively. This mechanism, dependent on wavelength and polarization, holds promise for applications in color image processing, chiral sensing imaging, and polarization-entangled quantum imaging.

Switchable Terahertz Metasurfaces for Spin-Selective Absorption and Anomalous Reflection Based on Vanadium Dioxide.

Conventional chiral metasurfaces are constrained by predetermined functionalities and have limited versatility. To address these constraints, we propose a novel chirality-switchable terahertz (THz) metasurface with integrated heating control circuits tailored for spin-selective anomalous reflection, leveraging the phase-change material vanadium dioxide (VO2). The reversible and abrupt insulator-to-metal phase transition feature of VO2 is exploited to facilitate a chiral meta-atom with spin-selectivity capabilities. By employing the Pancharatnam-Berry phase principle, complete 2π reflection phase coverage is achieved by adjusting the orientation of the chiral structure. At the resonant frequency of 0.137 THz, the designed metasurface achieves selective absorption of a circularly polarized wave corresponding to the state of the VO2 patches. Concurrently, it reflects the circularly polarized wave of the opposite chirality anomalously at an angle of 28.4° while maintaining its handedness. This chirality-switchable THz metasurface exhibits promising potential across various applications, including wireless communication data capacity enlargement, polarization modulation, and chirality detection.

An Electrochemically Programmable Metasurface with Independently Controlled Metasurface Pixels at Optical Frequencies.

Metasurfaces have revolutionized optical technologies by offering powerful, compact, and versatile solutions to control light. Conducting polymers, characterized by their conjugated molecular structures, facilitate charge transport and exhibit interesting electrical, optical, and mechanical properties. Integrating conducting polymers with optical metasurfaces can unlock new opportunities and functionalities in modern optics. In this work, we demonstrate an electrochemically programmable metasurface with independently controlled metasurface pixels at optical frequencies. Electrochemical modulation of locally conjugated polyaniline on gold nanorods, which are arranged on addressable electrodes according to the Pancharatnam-Berry phase design, enables dynamic control over the metasurface pixels into programmable configurations. With the same metasurface device, we showcase diverse optical functions, including dynamic beam diffraction and varifocal lensing along and off the optical axis. The synergy between flat optics and conducting polymer science holds immense potential to enhance the performance and function versatility of metasurfaces, paving the way for innovative optical applications.

Focus tunable vector autofocusing Airy vortex beams resist atmospheric turbulence

The rapid increase in orbital angular momentum (OAM) mode size with increasing modal order, given the limited-size of the receiver, is a major impediment to high-capacity OAM mode multiplexing in practice. Based on the Pancharatnam-Berry (PB) phase theory, we correlate the change of the polarization state with the curvature of the wavefront isophase line in the source plane and manipulate the focusing ability of vector autofocusing Airy vortex beam (AAVB) by combining the isophase line curvature and the intensity gradient of the beam, which are two independent degrees of freedom. The present method enables flexible on-demand focusing of vector AAVBs in free space and is more effective in focusing higher order OAM modes, which can reduce the full-width at half maximum (FWHM) of the AAVB with topological charge l= 25 to 1/5 of that of the conventional scalar type. And the modulated vector AAVB is superior to the conventional scalar one in terms of mitigating atmospheric turbulent disturbance. The work provides a potentially useful basis for improving the capability of future free-space OAM systems for large-scale dense communications.

Compound spin Hall plasmonic lens

The propagation phase and the Pancharatnam–Berry phase are two primary strategies to control surface plasmon polaritons (SPPs) wave, however, hampered by the spatial conjugation and the spin conjugation, respectively. Combining these two approaches together, the conjugations are broken and a compound spin Hall plasmonic lens (SHPL) is proposed and demonstrated numerically and experimentally in the visible frequency range. The proposed strategy can be utilized to realize both transversal and longitudinal deviations of SPP focus. The positions of the SPP focus can be dynamically modulated by switching the spin states of excitation light and adjusting the phase gradient encoded onto the lens. Promising applications of the proposed SHPL include on-chip communication and polarization detection.

Simultaneous Circular Dichroism and Wavefront Manipulation with Generalized Pancharatnam-Berry Phase Metasurfaces.

Simultaneous circular dichroism and wavefront manipulation have gained considerable attention in various applications, such as chiroptical spectroscopy, chiral imaging, sorting and detection of enantiomers, and quantum optics, which can improve the miniaturization and integration of the optical system. Typically, structures with n-fold rotational symmetry (n ≥ 3) are used to improve circular dichroism, as they induce stronger interactions between the electric and magnetic fields. However, manipulating the wavefront with these structures remains challenging because they are commonly considered isotropic and lack a geometric phase response in linear optics. Here, we propose and experimentally demonstrate an approach to achieve simultaneous circular dichroism (with a maximum value of ∼0.62) and wavefront manipulation using a plasmonic metasurface made up of C3 Archimedes spiral nanostructures. The circular dichroism arises from the magnetic dipole-dipole resonance and strong interactions between adjacent meta-atoms. As a proof of concept, two metadevices are fabricated and characterized in the near-infrared regime. This configuration possesses the potential for future applications in photodetection, chiroptical spectroscopy, and the customization of linear and nonlinear optical responses.

Infrared all-dielectric bifocal metasurface beam splitter based on the transflective structure

Based on the design concept of a transflective double-ended response structured metasurface and the Pancharatnam-Berry (PB) phase modulation mechanism, we have designed and numerically demonstrated a bifocal all-dielectric metasurface beam splitter. This device is constructed by arranging silicon nanocolumns on SiO2 substrates. The bifocal metasurface beam splitter developed in this study achieves double-ended deflected focusing beam splitting at a wavelength of 1.55 μm. The focusing efficiency at both ends exceeds 50%, the equivalent numerical aperture at both ends is greater than 0.85, and the beam splitting ratio is approximately 1.4:1. Furthermore, compared to most current single-ended response bifocal metasurfaces, the transflective bifocal metasurface beam splitter, with equal phase modulation at both ends, is anticipated to be integrated into compact optical systems that require real-time signal feedback.

A tunable terahertz chiral metasurface with circular dichroism and Pancharatnam-Berry phase characteristics

A dual-mode reflective chiral metasurfaces, consisting of the photosensitive semiconductors germanium (Ge), vanadium dioxide (VO2), silicon dioxide (SiO2), and gold, is proposed, and the chirality of the metasurfaces is theoretically investigated by using CST Studio suite. The metasurfaces was found to be capable of realizing two modes of operation by adjusting the conductivity of the photosensitive semiconductor germanium with pump light and the conductivity of VO2 by temperature. When Ge is in the dielectric state and VO2 is in the metallic state (Mode I) at 0.791 THz, right CD is 0.904, adjusting the VO2 conductivity can tune the CD in the range 0.1–0.904. When Ge is in the metallic state and VO2 is in the dielectric state (mode II) at 0.841 THz, left CD is 0.91, adjusting Ge conductivity can tune CD in the range 0.06–0.91. By adjusting the geometric parameters of germanium and VO2, the resonance frequency can be tuned. Based on this property, a near-field imaging application has been developed. In addition, based on the Pancharatnam-Berry (PB) phase, the reflection phase distribution of the metasurfaces was designed. By designing different reflection phase distributions, focusing and vortex beam generation were realized.