Ultrathin Polarization Research Articles

A high-efficiency and ultrathin transmission-type circular polarization converter based on surface structure

In this paper, we propose, design and fabricate a kind of ultrathin and high-efficiency circularly polarization converter based on artificially engineered surfaces in the transmission mode. The converter is composed of double-layer periodic surface structures with cross slots. The top and bottom layers are printed on both sides of the F4B substrate and connected by metallic via holes. The proposed converter can transform the right-handed circularly polarized incident electromagnetic (EM) wave to a left-handed circularly-polarized one with near-unity efficiency in the transmission mode, or vice versa. We explain the conversion mechanism based on numerical simulations and equivalent circuit (EC) theory. The measured result has a good agreement with the simulated one in the working frequency band. Such ultrathin polarization converters can be used in wireless microwave communication, remote sensing, and EM imaging where circularly polarization diversity is needed.

Transmission of layered nanoresonators including epsilon-near-zero metamaterials: interference-enabled opportunities to realize ultrathin polarization converters

Polarization conversion of electromagnetic waves transmitted through multilayer nanoresonators, including a main homogeneous layer made of a transparent uniaxial dielectric sandwiched between epsilon-near-zero and metallic spacer layers, has been analytically modeled. The numerical analysis, based on exact solutions of electromagnetic boundary problems, confirms opportunities to use such multilayers as utracompact polarization converters (in particular, zero-order quarter and half waveplates) of a new type. The proposed systems are characterized by much wider ranges of parameters and significantly reduced (nanometric) thicknesses in comparison with the conventional waveplates. The operation regimes, resulting from the features of amplification of proper wave phase differences under multibeam interference conditions, are considered. The concept can be realized for both metamaterial-dielectric-metamaterial and metal-dielectric-metal structures and used for the development of ultrathin, large area, and simple in fabrication polarization devices for photonic applications.

Ultrathin and Flexible Reflective Polarization Converter Based on Metasurfaces With Overlapped Arrays

In this letter, an ultrathin reflective polarization converter with the total thickness of 1/62 wavelengths is proposed to realize the high efficiency of cross-polarization conversion at 32 GHz. Two metasurfaces overlapped on the same layer with a displacement are designed to improve its polarization conversion performance, angular stability, and conformal adaptability. Due to the flexibility of the polyimide substrate, a planar and a conformal converter are conveniently fabricated by the printed circuit board technology. Experimental results show that the maximum conversion efficiency of the planar converter is higher than 94.3%, which is rather close to the simulation prediction. Meanwhile, a cross-polarization conversion efficiency of 88.1% can be obtained by the conformal converter with a 100 mm curvature radius, which demonstrates the validity of the overlapped array design. Due to the ultrathin thickness and flexibility, the proposed converter has great application potential in polarization control devices, on-chip antennas, and wearable antennas.

Chiral Bilayer All-Dielectric Metasurfaces

Three-dimensional chiral plasmonic metasurfaces were demonstrated to offer enormous potential for ultrathin circular polarizers and applications in chiral sensing. However, the large absorption losses in the metallic systems generally limit their applicability for high-efficiency devices. In this work, we experimentally and numerically demonstrate three-dimensional chiral dielectric metasurfaces exhibiting multipolar resonances and examine their chiro-optical properties. In particular, we demonstrate that record high circular dichroism of 0.7 and optical activity of 2.67 × 105 degree/mm can be achieved based on the excitation of electric and magnetic dipolar resonances inside the chiral structures. These large values are facilitated by a small amount of dissipative loss present in the dielectric nanoresonator material and the formation of a chiral supermode in a 4-fold symmetric metasurface unit cell. Our results highlight the mechanisms for maximizing the chiral response of photonic nanostructures and offer important opportunities for high-efficiency, ultrathin polarizing elements, which can be used in miniaturized devices, for example, integrated circuits.

Compound-eye metasurface optics enabling a high-sensitivity, ultra-thin polarization camera.

Polarization imaging is key for various applications ranging from biology to machine vision because it can capture valuable optical information about imaged environments, which is usually absent in intensity and spectral content. Conventional polarization cameras rely on a traditional single-eye imaging system with rotating polarizers, cascaded optics, or micropolarizer-patterned image sensors. These cameras, however, have two common issues. The first is low sensitivity resulting from the limited light utilization efficiency of absorptive polarizers or cascaded optics. The other is the difficulty in device miniaturization due to the fact that these devices require at least an optical-path length equivalent to the lens's focal length. Here, we propose a polarization imaging system based on compound-eye metasurface optics and show how it enables the creation of a high-sensitivity, ultra-thin polarization camera. Our imaging system is composed of a typical image sensor and single metasurface layer for forming a vast number of images while sorting the polarization bases. Since this system is based on a filter-free, computational imaging scheme while dramatically reducing the optical-path length required for imaging, it overcomes both efficiency and size limitations of conventional polarization cameras. As a proof of concept, we demonstrated that our system improves the amount of detected light by a factor of ∼2, while reducing device thickness to ∼1/10 that of the most prevalent polarization cameras. Such a sensitive, compact, and passive device could pave the way toward the widespread adoption of polarization imaging in applications in which available light is limited and strict size constraints exist.

High-efficiency ultra-thin polarization converter based on planar anisotropic transmissive metasurface

We present the design, simulation, and characterization of an ultrathin polarization converter based on planar anisotropic transmissive metasurface. The metasurface consists of two identical metallic structures printed on both sides of a dielectric substrate and possesses a nearly uniform transmittance with a π phase difference over the whole bandwidth for waves of orthogonal linear polarizations. It is demonstrated numerically and experimentally that the designed metasurface can high-efficiently change the polarization plane of a linearly polarized plane wave or convert the circularly polarized plane wave into the wave of opposite handedness in a wide frequency bandwidth. The polarization conversion ratios in both cases could reach almost 100% from 15.8 GHz to 16.7 GHz. The proposed metasurface converter may find uses in various applications combining highly efficient control of polarization with a low insertion loss.

Design and analysis of a compact ultrathin polarization‐ and incident angle‐independent triple band metamaterial absorber

AbstractThis article reports a compact ultrathin metamaterial absorber with three resonances in S‐band, X‐band, and Ku‐band. The geometry of the proposed absorber consists of a square ring, a splitted square ring, and a plus shaped resonating structure. The plus shaped structure is enclosed within a split ring resonator and it is further enclosed by an outer square ring. The proposed absorber is fabricated on a low cost FR4 substrate of thickness 1 mm that is, 0.011 λlowest (where, λ is the lowest resonating frequency). The size of unit cell is 10 × 10 mm2. It exhibits 99.6%, 99.1%, and 99.1% absorption at 3.4, 9.6, and 13 GHz, respectively. Moreover, the physical insight of the design is explained by surface current distribution and equivalent circuit analysis. Stability of the proposed design is validated with different incident (for transverse electric (TE) and transverse magnetic (TM) modes) angles and different polarization angles. Finally, a prototype of the absorber is fabricated and validated experimentally.

Chemo- and Thermomechanically Configurable 3D Optical Metamaterials Constructed from Colloidal Nanocrystal Assemblies.

Nanofabrication has limited most optical metamaterials to 2D or, often with multiple patterning steps, simple 3D meta-atoms that typically have limited built-in tunability. Here, with a one-step scalable patterning process, we exploit the chemical addressability and structural adaptability of colloidal Au nanocrystal assemblies to transform 2D nanocrystal/Ti bilayers into complex, 3D-structured meta-atoms and to thermally direct their shape morphing and alter their optical properties. By tailoring the length, number, and curvature of 3D helical structures in each meta-atom, we create large-area metamaterials with chiroptical responses of as high as ∼40% transmission difference between left-hand (LCP) and right-hand (RCP) circularly polarized light (ΔT = TRCP - TLCP) that are suitable for broadband circular polarizers and, upon thermally configuring their shape, switch the polarity of polarization rotation. These 3D optical metamaterials provide prototypes for low-cost, large-scale fabrication of optical metamaterials for ultrathin lenses, polarizers, and waveplates.

Broadband Bias-Magnet-Free On-Chip Optical Isolators With Integrated Thin Film Polarizers

Most on-chip optical isolators utilize nonreciprocal magneto-optic (MO) garnet-materials that require an external bias magnetic field to operate. The magnetic field is applied through incorporation of either a permanent magnet or an active electromagnet. Permanent magnets add significantly to device bulk and electromagnets increase fabrication complexity and power consumption. Hence, it is highly desirable to reduce or eliminate the magnetizing component in these devices. Here, we experimentally demonstrate a first of its kind bias-magnet-free (BMF) on-chip waveguide optical isolator with integrated Polarcor UltraThin polarizers. The BMF isolator device obviates the need for magnetizing components while possessing superior performance, relative to other on-chip isolators, with ≥25 dB of isolation ratio (IR), and ≤3.5 dB of insertion loss (IL) across the entire infrared optical C-band.

All-metal metasurface polarization converter in visible region with an in-band function

We propose an ultrathin and high-efficiency all-metal metasurface polarization converter, by which cross-polarization conversion in reflection mode is achieved for linearly-polarized lights. The simulated result shows that the polarization conversion ratio for normal incidence is nearly 100% in the visible region. Moreover, strong coupling between nanobars with metallic ground plane, make it possible to provide novel application of in-band switch function. The proposed all-metal polarization converter not only improves the feasibility of nanofabrication due to its simple nanostructure, but demonstrates a reflection-type avenue to design optoelectronic devices up to the visible spectrum.

Perfect terahertz-wave polarization rotator using dual Fabry–Perot-like cavity resonance metamaterial

A novel kind of terahertz ultrathin perfect polarization rotator (UPPR) based on the composite metamaterial is proposed and numerically demonstrated in this paper. The proposed UPPR is constructed by two electric dipole resonant polarization selectors on the two sides and a cross-shaped polarization converter in the center between two dielectric layers as spacers. This typical structure forms a dual Fabry–Perot cavity-like resonance, leading to an enhanced 90° polarization rotation with polarization conversion ratio reaching 99.9%. Quantitative analysis is given to reveal the underlying principle of the UPPR and the detailed design guidelines are also provided for the others to accomplish this kind of UPPR in other frequency bands at will, such as in microwave and infrared regions. In a way, we believe this kind of UPPR, i.e., the polarization selector–polarization converter–polarization selector type, can enrich the metamaterial community for achieving the perfect polarization rotation.

Ultrathin Dual-Band Metasurface Polarization Converter

Metamaterials offer the freedom to manipulate the polarization states of light at the subwavelength scale. However, previous designs generally made use of single resonance and, hence, only function for one specific incident polarization within a single-frequency band. In this paper, we present a dual-band metasurface based on a concentric rectangular arrangement to control the polarizations of both linearly and circularly polarized electromagnetic waves. We show that, on the one hand, the proposed metasurface structure can convert the polarization of linearly polarized waves to the cross direction in two broad frequency bands 4.40–5.30 GHz and 9.45–13.60 GHz. On the other hand, this design can also reflect circularly polarized waves without changing the handedness in two frequency bands 4.47–5.35 GHz and 9.57–13.57 GHz. For both cases, average polarization conversion efficiency larger than 86% was obtained in our experiment. The numerical simulations reveal that the dual-band cross-polarization coupling results from the strong electric and magnetic resonances between the top and bottom layers. The ultrathin polarization converter experimentally realized in this paper provides an important stepping stone for the future design of other dual-band metasurface devices and is believed to be extendable to higher frequency regimes.

Frequency dependent multi-functional polarization convertor based on metasurface

Controlling the polarization state of light is an important research region in optics due to its enormous potential. Conventional polarization converters inevitably express huge size and low efficiency, which run counter to the requirement of modern optics. Herein, a frequency-dependent multi-functional metasurface is proposed and researched to design a broad-band and high-efficiency reflective-type polarization converter at near-infrared band. Based on the simulation results, 90° polarization convertor and quarter wave plate can be realized at different wavelengths. The broad-band 90° polarization convertor will transform gradually to a broad-band quarter wave plate by increasing the ”coupling gap” at the long wavelength region, and the functionalities of 90° polarization convertor and quarter wave plate can always be kept at the short wavelength region. Our results can provide a guide to design the ultrathin optical polarization converters.

Fabrication of highly efficient coatable polarizer from tolane-based smectic reactive mesogen

This work is aimed to fabricate ultra-thin coatable polarizers on a single substrate based on “host-guest” effect between highly ordered smectic reactive mesogen (RM) and dichroic dye. We designed and synthesized a new tolane-based RM with a highly ordered smectic A phase at room temperature. Polymerizable “host-guest” mixture was formulated from the host RM, dichroic dye and additives, then spin-coated on a single substrate having an alignment layer. Subsequent in-situ photopolymerization by UV irradiation successfully resulted in a coatable polarizer with good polarizing properties. The fabricated coatable polarizer showed a dichroic ratio (DR) of 16.4 and a degree of polarization (DOP) of 99.3% with the thickness of 4 μm. The resulting coatable polarizer possessed a considerable solvent resistance, good thermal stability and robust mechanical properties. Moreover, we prepared a TN-mode LC cell by using the prepared coatable polarizers inside the cell (in-cell), in which the coatable polarizers acted as a polarizer and an alignment layer, simultaneously. The resulting TN cell with in-cell polarizers exhibited a decent electro-optical behavior. We believe that the coatable polarizer proposed in this study possesses practical application potential in ultra-thin LCDs or flexible OLEDs.

Wide band ultrathin polarization insensitive electric field driven metamaterial absorber

We demonstrate a novel wideband ultrathin polarization insensitive electric field driven metamaterial based dually stacked petal resonator (DSPR) perfect absorber for cloaking, THz imaging and sensing, solar cell, stealth technology, and remote sensing applications. The designed DSPR absorber is composed of a polyimide substrate and gold. The DSPR perfect absorber exhibits 98% absorption fractional bandwidth of 12.8% over a frequency range of 0.591 THz to 0.672 THz. The compact unit cell has 0.29λo∗0.29λo∗0.06λo size, where λo is the lower absorption peak wavelength. Owing to the symmetric geometry, the DSPR absorption response is polarization insensitive over an extensive range of 90° for both Transverse Electric (TE) and Transverse Magnetic (TM) polarizations. An excellent absorption behavior is perceived over a wide oblique angle of incidence of 75° for both TE and TM polarizations. For an oblique angle of incidence, the proposed structure has interesting features to TE and TM polarizations. A thorough parametric optimization is investigated which elucidates the DSPR response as a function of structural parameters. The physics behind the absorption mechanism is explored by examining the surface current distribution, magnetic field distribution, electric field distribution, power loss density and normalized impedance. Field distributions reveal the existence of Fabry–Perot reflections and electric dipole resonances.

Triple band ultrathin polarization insensitive metamaterial absorber for defense, explosive detection and airborne radar applications

AbstractWe demonstrate an ultrathin polarization insensitive metamaterial‐based Concentric Closed Circular Ring Resonator (CCCRR) perfect absorber for explosive detection, bolometer, indoor radar clear applications, thermal detection, defense applications, airborne and surveillance radar signal absorption applications. The unit cell incorporates three concentric closed circular ring resonators. A parametric optimization has been carried out in order to obtain three discrete absorption peaks at 5.57 GHz, 7.969 GHz, and 13.44 GHz exhibiting absorption intensities of 98.87%, 97.99%, and 99.28%, respectively. Owing to the geometrical symmetry, the structure is polarization insensitive for both TE and TM polarizations and has significant absorbance over a wide angle of incidence of 45° for TE and 75° for TM polarizations. The structure is very compact with physical dimensions of 0.185λo*0.185λo *0.01λo, λo is wavelength corresponding to lower absorption peak. The thickness of the proposed structure is λo/100, evidencing the ultrathin characteristic of the proposed structure. The insight of absorption mechanism has been illustrated by analyzing the electric field distribution, power loss density, and normalized impedance. An extensive parametric analysis has been exercised to examine the influence of parametric alterations.

Ultrathin dual-band polarization angle independent 90° polarization rotator with giant optical activity based on planar chiral metamaterial

An ultrathin dual-band planar chiral metamaterial (CMM) with giant optical activity using Fermat’s Spiral structure (FSs) was proposed, which could yield a near polarization angle independent 90° rotation characteristic. The proposed CMM can convert an incident linear polarization (y-/x-polarized) wave into its cross-polarization (x-/y-polarized) or experience a near 90° polarization rotation at 4.67 and 8.51 GHz, respectively. The experiment results are in agreement well with numerical simulation. The surface current distributions of unit-cell structure of the proposed CMM were analyzed to illustrate the physics mechanism of this giant optical activity with 90° polarization rotation. Good performances and compact design of the CMM suggest a promising application in 90° polarization rotator that need to be integrated with other compact devices.

Geometric metasurface enabling polarization independent beam splitting

A polarization independent holographic beam splitter that generates equal-intensity beams based on geometric metasurface is demonstrated. Although conventional geometric metasurfaces have the advantages of working over a broad frequency range and having intuitive design principles, geometric metasurfaces have the limitation that they only work for circular polarization. In this work, Fourier holography is used to overcome this limitation. A perfect overlap resulting from the origin-symmetry of the encoded image enables polarization independent operation of geometric metasurfaces. The designed metasurface beam splitter is experimentally demonstrated by using hydrogenated amorphous silicon, and the device performs consistent beam splitting regardless of incident polarizations as well as wavelengths. Our device can be applied to generate equal-intensity beams for entangled photon light sources in quantum optics, and the design approach provides a way to develop ultra-thin broadband polarization independent components for modern optics.

Perfect absorption of modified-molybdenum-disulfide-based Tamm plasmonic structures

The two-dimensional semiconductor materials of transition metal molybdenum disulfide display various special optical properties in the interaction of matter and light. In this work, we study the strong coupling between the two-dimensional materials’ excitons and Tamm plasmon polaritons (TPPs). To enhance the interaction between light and matter, we introduce the grating modulation in the traditional Tamm structure. By adjusting the structure parameters of the grating-modified Tamm system, we achieve perfect absorption in the visible region. Our research results will pave the way for the application of ultrathin polarization optical devices.

Investigation of black phosphorus as a nano-optical polarization element by polarized Raman spectroscopy

Manipulating the polarization of light at the nanoscale is essential for the development of nano-optical devices. Owing to its corrugated honeycomb structure, two-dimensional (2D) layered black phosphorus (BP) exhibits outstanding in-plane optical anisotropy with distinct linear dichroism and optical birefringence in the visible region, which are superior characteristics for ultrathin polarizing optics. Herein, taking advantage of polarized Raman spectroscopy, we demonstrate that layered BP with a nanometer thickness can remarkably alter the polarization state of a linearly-polarized laser and behave as an ultrathin optical polarization element in a BP-Bi2Se3 stacking structure by inducing the exceptionally polarized Raman scattering of isotropic Bi2Se3. Our findings provide a promising alternative for designing novel polarization optics based on 2D anisotropic materials, which can be easily integrated in microsized all-optical and optoelectronic devices.