Control Of Light Polarization Research Articles

Valley-Hybridized Gate-Tunable 1D Exciton Confinement in MoSe2.

Controlling excitons at the nanoscale in semiconductor materials represents a formidable challenge in the quantum photonics and optoelectronics fields. Monolayers of transition metal dichalcogenides (TMDs) offer inherent 2D confinement and possess significant exciton binding energies, making them promising candidates for achieving electric-field-based confinement of excitons without dissociation. Exploiting the valley degree of freedom associated with these confined states further broadens the prospects for exciton engineering. Here, we show electric control of light polarization emitted from one-dimensional (1D) quantum-confined states in MoSe2. Building on previous reports of tunable trapping potentials and linearly polarized emission, we extend this understanding by demonstrating how nonuniform in-plane electric fields enable in situ control of these effects and highlight the role of gate-tunable valley hybridization in these localized states. Their polarization is entirely engineered through either the 1D confinement potential's geometry or an out-of-plane magnetic field. Controlling nonuniform in-plane electric fields in TMDs enables control of the energy (up to five times its line width), polarization state (from circular to linear), and position of 1D confined excitonic states (5 nm V-1).

Recent Progress in Light Polarization Control Schemes for Silicon Integrated Photonics

AbstractLight polarization control is a target in photonics, and this paper provides a comprehensive review of research from various groups on the silicon‐on‐insulator (SOI) platform. It draws comparisons between devices such as polarization splitters (PS), polarizers, and polarization splitters/rotators (PSR). These devices are fabricated using various technologies, including silicon nanowires, ridge waveguides, hybrid plasmonic waveguides, and subwavelength grating (SWG) waveguides. A detailed review of polarizers used as cleanup filters in splitters is initiated. Subsequently, various polarization splitters utilizing asymmetric directional couplers (ADCs), which typically exhibiting low extinction ratios (ERs), are delved. To enhance ERs, a detailed comparison of methods outlined in the literature is provided. One notable method includes integrating on‐chip polarizers at both ports to eliminate unwanted light fractions and achieve exceptionally high ERs. Furthermore, SWG‐based polarizers and splitters commonly face issues with Bragg reflections that can affect other photonic devices and lasers and ways to minimize unwanted polarization back reflections in SWG‐designed polarization control devices are examined. Finally, emerging applications in mid‐infrared (MIR) sensing are explored, highlighting the necessity of polarization rotators for on‐chip transverse electric (TE) operation, since quantum cascade lasers, the primary sources in this range, emitting radiation in the (TM) mode.

Nanophotonics with Plasmonic Nanorod Metamaterials

AbstractTaking advantage of their unique and tuneable electromagnetic properties, plasmonic metamaterials constitute a versatile platform for a variety of applications ranging from high‐resolution imaging, sensing and spontaneous emission engineering to ultrafast nonlinear optics and light polarization control. Here, recent advances in the design and applications of plasmonic metamaterials based on aligned metallic nanorod assemblies are reviewed, and the fast‐developing trends in their exploitation in nanophotonics are outlined. The fabrication of the nanorod‐based metamaterials is introduced and their linear and nonlinear optical properties are presented from both microscopic and phenomenological considerations. Multiscale structuring allowing precise engineering of the electromagnetic modes supported by the nanorod metamaterials, as well as nonlocal spatial dispersion effects and their impact on nanophotonic performance are discussed. To illustrate the developing field of practical applications of these metamaterials, some of their main application domains in sensing, photochemistry and nonlinear optics are overviewed and novel designs of anisotropic metamaterials directly derived from the nanorod architecture are introduced.

Precise Crystal Orientation Identification and Twist-Induced Giant Modulation of Optical Anisotropy in 1T'-ReS2.

The ability to precisely identify crystal orientation as well as to nondestructively modulate optical anisotropy in atomically thin rhenium dichalcogenides is critical for the future development of polarization programmable optoelectronic devices, which remains challenging. Here, we report a modified polarized optical imaging (POI) method capable of simultaneously identifying in-plane (Re chain) and out-of-plane (c-axis) crystal orientations of the monolayer to few-layer ReS2, meanwhile, propose a nondestructive approach to modulate the optical anisotropy in ReS2 via twist stacking. The results show that parallel and near-cross POI are effective to independently identify the in-plane and out-of-plane crystal orientations, respectively, while regulating the twist angle allows for giant modulation of in-plane optical anisotropy from highly intrinsic anisotropy to complete optical isotropy in the stacked ReS2 bilayer (with either the same or opposite c-axes), as well modeled by linear electromagnetic theory. Overall, this study not only develops a simple optical method for precise crystal orientation identification but also offers an efficient light polarization control strategy, which is a big step toward the practical application of anisotropic van der Waals materials in the design of nanophotonic and optoelectronic devices.

Control of light polarization by optically-induced-chirality in photosensitive nematic fluids

Light polarization rotations, created by applied optical field, are examined experimentally and theoretically in a photosensitive chiral nematic fluid. The polarization rotation of the transmitted beam is initiated by illuminating the sample with uniform UV light. The operation is tunable and reversible, depending on the UV intensity. It was revealed that the rotations can be ascribed to the optical-field-induced chirality effect, where the helical structure in chiral nematics changes in accordance with the UV intensity. The evolution of the helical structure as well as its effect on the light polarization upon illumination by uniform UV light have been monitored experimentally and compared by calculations based on the continuum theory. Our results proved that a polarization field with specific characteristics can be achieved using the remote and precise optical control.

Pseudo coherent-perfect-absorption approach toward perfect polarization conversion

Polarization is one of the essential properties of light. Thereby, its manipulation is important for numerous applications. When employing a resonance in a mirror-symmetry system to manipulate polarization, non-zero residual light in the excited polarization channel leads to the shrink in the scope of the polarization manipulation, and a perfect polarization conversion cannot occur. In this work we show that the concept of coherent perfect absorption can be applied to perfect polarization conversion for circular polarization states. We find that the only requirement to achieve a perfect polarization conversion is that the working frequency is the resonant one. More importantly, the range of the output polarization states can be efficiently enlarged, and can span the entire Poincare sphere by combining the momentum dependent radiative coupling rate driven by the bound states in the continuum (BIC) and the phase delay. When applied to realistic design, we adopt a guided mode resonance driven from the symmetry protected BICs in a dielectric photonic crystal slab. Numerical results are in good agreements with our theoretical predictions. We believe this work can deliver important benefits for a variety of applications based on the efficiently light polarization control and management.

Advanced Light: Liquid Crystals-Based Ultra-Broadband Polarization Rotator for Functional Smart Devices.

A novel ultra-broadband polarization rotator with advanced angular adjustability is proposed for functional devices such as displays and smart windows. The new solution offers dynamic control of light polarization across a broad range of wavelengths, encompassing the complete visible spectrum, ultraviolet and near-infrared. Moreover, it boasts a smaller footprint, faster response times, and lower dispersion compared to conventional rotators. The findings are remarkable in that they show that as the viewing angle increases, the hybrid alignment takes on a twist-like configuration, with the polarization rotation angle determined by the spatial variation in the twist angle. This intriguing behavior leads to an improved range of angular adjustability, as the effective polarization rotation depth is extended. The improved angular adjustability of reconfigurable smart devices surpasses the limitations of traditional polarization rotators, unlocking new innovative possibilities. For example, the rotator plays a crucial role in display technologies, allowing for effective control of viewing angles and minimizing reflection from disturbing external light. Similarly, in smart windows, it optimizes energy conservation by regulating direct sunlight transmission while ensuring clear visibility in normal conditions. It is believed that the proposed advanced ultra-broadband polarization rotator is a significant step forward in the development of reconfigurable smart devices.

Complete light polarization control using a chiral-nematic cell with tangential-conical boundary conditions

Light polarization control by the chiral-nematic cell with hybrid tangential-conical boundary conditions has been studied by means of photo- and electrically induced transformations of the orientational structure. The polarization azimuth changes due to the power ratio of ultraviolet and blue radiations, at which the director twist angle in the chiral nematic varies smoothly. The light polarization ellipticity is controlled by an electric field applied perpendicular to the liquid crystal cell changing the effective anisotropy of the refractive index. The optical material under study is promising to develop the devices for the light polarization converter over the entire visible range, as well as for photo-controlled rotators of linear polarization of white light.

Dual‐Mode Polarization Control with Quasi‐Bound States in the Continuum

AbstractFull control of light polarization is one of the most sought‐after functionalities in nanophotonics since it allows the replacement of bulky optical components like wave retarders. Here, the study reports the theoretical and experimental demonstration of an ultra‐compact dual‐mode frequency selective polarization controller that leverages the topological features of symmetry protected quasi‐bound states in the continuum (q‐BICs) supported by a silicon‐based nanostructure. Thanks to q‐BIC resonances, arbitrarily polarized incoming light can be converted into linearly polarized light without resorting to the local phase tuning mechanisms that characterize optical metasurfaces. Moreover, the dual‐mode operating regime allows to select the transmitted polarization without modifying the device orientation, therefore overtaking the concept of the wire grid polarizer. The experimental findings show that the proposed meta‐polarizer possesses an extinction ratio of ≈40 dB for two linear cross‐polarization excitations. These results pave the way for a novel class of ultra‐compact devices that can be used to compensate unwanted birefringence in optical fibers or to control polarization in complex media environments.

Dielectric diatomic metasurface-assisted versatile bifunctional polarization conversions and incidence-polarization-secured meta-image.

Dielectric metasurface empowering efficient light polarization control at the nanoscale, has recently garnered tremendous research interests in the field of high-resolution image encryption and display, particularly at low-loss wavelengths in the visible band. Nevertheless, due to the single fixed polarization conversion function, the image (either positive or negative image) can always be decrypted in a host-uncontrollable manner as long as the user applies an analyzer to select the polarization component of the output light. Here, we resort to half-waveplate- and quarter-waveplate-like silicon nanopillars to form a metamolecule of a dielectric diatomic metasurface, which can yield versatile linearly polarized (LP) and circularly polarized (CP) light upon orthogonally linear-polarized incidences, providing new degrees of freedom for image display and encryption. We show both theoretically and numerically that versatile different paired LP and CP combinations could be achieved by simply adjusting the orientation angles of the two nanopillars. The bifunctional polarization conversion functions make possible that a meta-image can only be seen when incident light is linearly polarized at a specific polarization angle, whereas no image can be discerned for the orthogonal polarization incidence case, indicating the realization of incidence-polarization secured meta-image. This salient feature holds for all individual metamolecules, reaching a remarkable image resolution of 52,916 dots per inch. By fully exploiting all polarization conversions of four designed metamolecules, three-level incidence polarization-secured meta-image can also be expected.

32‐Symmetric Chiral Gold Nanoplates with Near‐Infrared Circular Dichroism

AbstractPlasmonic chiral nanostructures provide a novel route for extraordinary optical properties, such as light polarization control and enhancing chiroptical signals of molecules. The symmetry of chiral nanostructures, such as helices, gyroids, and irregular tetrahedrons, is strongly correlated to chiroptical responses; therefore, it is an important design parameter. In a previous study, a synthetic strategy is demonstrated for 432‐symmetric chiral gold nanoparticles by breaking the mirror symmetry of a 4/m 2/m‐symmetric crystal structure on a high‐index surface. Herein, the aim is to extend the chiral symmetry of gold nanoparticles and their chiroptical responses. The symmetry of gold nanoparticles can be modulated by inducing single or multiple twin planes in seed nanoparticles. The 32‐symmetric chiral gold nanoplates, referred to as 32 helicoids, are successfully synthesized using 3 2/m‐symmetric triangular and hexagonal plates. The growth mechanism of the 32 helicoids, which results in two different characteristic morphologies, is analyzed. The 32 helicoids are significantly important owing to their optical activity over a wide range from the visible to the near‐infrared region. This investigation provides an insight that symmetry control of the nanomorphology can represent an important research direction in chiral plasmonic applications.

All-optical polarization tuning based on an intensity-dependent nonlinear metasurface

Active control of light polarization at the nanoscale is essential for integrated photonic devices. Here, an all-optical approach is proposed to tune the polarization state of near-infrared light using a nonlinear metasurface. Based on the large intensity-dependent refractive index change of epsilon-near-zero (ENZ) materials, a phase difference between two orthogonal electric fields at ENZ wavelength can be continuously tuned in a range larger than 0.61π by varying the incident light power. The polarization state of the reflected light can thus be actively tuned from linear to circular state via an all-optical approach. Notably, abundant polarization states can be obtained by altering the polarization angle of incident light. The proposed all-optical approach is promising for tunable photonic functionalities of practical applications.

Nonlinear Chiral Metasurfaces Based on the Optical Kerr Effect

AbstractChiral nanostructures have immense potential for complete polarization control of light. Given the intrinsic 3D structure of circularly polarized light, nanoarchitectures with structural chirality in 3D space are usually required to achieve “full” chiroptical response. On the other hand, due to the lack of available active materials at optical wavelengths, examples of chiral photonic devices that can be tuned in an active manner remain rare. Here, based on the large Kerr nonlinearities of silicon, the nonlinear chiroptical response from a planar Si metasurface supporting high quality (Q)‐factor guided mode resonances (GMRs) at near‐infrared wavelengths, are numerically demonstrated. In the linear regime, the optical anisotropy of the C2‐symmetric structure associated with the observed GMRs leads to a pair of chiral resonance modes, enabling pronounced cross‐polarization transmission circular dichroism and a strong handedness‐dependent field enhancement effect. Owing to the nonlinear Kerr effect, such Si metasurfaces are seen to exhibit prominent chiral‐selective optical nonlinearity. Importantly, a pronounced co‐polarization transmission circular dichroism is observed, suggesting that the circularly polarized waves in the nonlinear regime possess asymmetric Jones matrices. Dielectric chiral metasurfaces with Kerr nonlinearities can be utilized to facilitate polarization‐state modulators with simple planar structures.

Ferroelectric Domain Control of Nonlinear Light Polarization in MoS2 via PbZr0.2Ti0.8O3 Thin Films and Free‐Standing Membranes (Adv. Mater. 9/2023)

Light Polarization Control In article number 2208825, Xia Hong and co-workers describe how heterostructures composed of noncentrosymmetric 2D MoS2 and free-standing ferroelectric oxide membranes provide a versatile material platform for realizing in operando programming of nonlinear light via nanoscale domain patterning, which can be used for developing flexible optoelectronics and smart optical information processing.

Correlation of Light Polarization in the Magnetic Media with Non-Spherical Point-Like Inclusions

Light propagation through magnetic media with ellipsoidal inclusions much smaller than the light wavelength was investigated theoretically. It is assumed that the ellipsoidal inclusions have the same orientation but are randomly distributed inside the magnetic medium by the Gaussian law. The theoretical model is based on the multiple-scattering theory in the ladder approximation. A new type of electromagnetic field correlation is found to appear in this case, while it is absent in isotropic magnetic nanocomposites and nonmagnetic anisotropic composites. This feature allows for the precise control of light polarization in anisotropic magnetic media.

Polarization Control in Integrated Graphene-Silicon Quantum Photonics Waveguides.

We numerically investigated the use of graphene nanoribbons placed on top of silicon-on-insulator (SOI) strip waveguides for light polarization control in silicon photonic-integrated waveguides. We found that two factors mainly affected the polarization control: the graphene chemical potential and the geometrical parameters of the waveguide, such as the waveguide and nanoribbon widths and distance. We show that the graphene chemical potential influences both TE and TM polarizations almost in the same way, while the waveguide width tapering enables both TE-pass and TM-pass polarizing functionalities. Overall, by increasing the oxide spacer thickness between the silicon waveguide and the top graphene layer, the device insertion losses can be reduced, while preserving a high polarization extinction ratio.

Ultrafast All-Optical Polarization Switch Controlled by Optically Excited Picosecond Acoustic Perturbation of Exciton Resonance in Planar Microcavities

All-optical switching of the polarization of exciton polaritons is studied using a picosecond acoustic perturbation of the exciton resonance in high-$Q$ planar $\mathrm{Ga}\mathrm{As}$/$\mathrm{Al}\mathrm{As}$ microcavities. An irreversible switching of the degree of circular polarization from $22\mathrm{%}$ up to $82\mathrm{%}$ is realized in a microcavity pumped by a laser with a photon energy slightly exceeding the lower polariton resonance. The polarization switch is performed by a short-term, about 30-ps-long, blueshift of the exciton energy of ($\mathrm{In},\mathrm{Ga}$)$\mathrm{As}$ quantum wells in the cavity active layer by a 10-ps strain pulse generated in the $\mathrm{Ga}\mathrm{As}$ substrate by a violet femtosecond laser pulse and injected into the microcavity. The proposed all-optical control of light polarization using acoustic modulation of a polariton resonance opens the way for fast and easily tunable optical polarization switches.

Optical control of light polarization in heliconical cholesteric liquid crystals

We show here that light polarization of a beam propagating through a heliconical cholesteric cell can be controlled by tuning the Bragg resonance of the structure. We demonstrate that this control is achieved by varying either the low-frequency electric field or the intensity of a pump beam impinging on the sample. The study confirms the recently reported phenomenon of optical tuning of the heliconical cholesterics and opens the door for the development of simple and efficient polarization modulators controlled electrically or optically.

Bidirectional Deep Learning of Polarization Transfer in Liquid Crystals with Application to Quantum State Preparation

Accurate control of light polarization represents a core building block in polarization metrology, imaging, and optical and quantum communications. Voltage-controlled liquid crystals offer an efficient way of polarization transformation. However, common twisted nematic liquid crystals are notorious for lacking an accurate theoretical model linking control voltages and output polarization. An inverse model, which would predict control voltages required to prepare a target polarization, is even more challenging. Here we report both the direct and inverse models based on deep neural networks, radial basis functions, and linear interpolation. We present an inverse-direct compound model solving the problem of control voltages ambiguity. We demonstrate one order of magnitude improvement in accuracy using deep learning compared to the radial basis function method and two orders of magnitude improvement compared to the linear interpolation. Errors of the deep neural network model also decrease faster than the other methods with an increasing number of training data. The best direct and inverse models reach the average infidelities of $4 \times 10^{-4}$ and $2 \times 10^{-4}$, respectively, which is the accuracy level not reported yet. Furthermore, we demonstrate local and remote preparation of an arbitrary single-photon polarization state using the deep learning models. The results will impact the application of twisted-nematic liquid crystals, increasing their control accuracy across the board. The presented bidirectional learning can be used for optimal classical control of complex photonic devices and quantum circuits beyond interpolation.

Circular Displacement Current Induced Anomalous Magneto‐Optical Effects in High Index Mie Resonators

AbstractDielectric Mie nanoresonators showing strong light–matter interaction at the nanoscale may enable new functionality in photonic devices, such as strong magneto‐optical effects. However, most reports so far have been focused on the enhancement of conventional magneto‐optical effects. Here, anomalous magneto‐optical effects are observed in high‐index‐contrast Si/Ce:YIG/YIG/SiO2 Mie resonators. In particular, giant modulation of light intensity in transverse magnetic configuration up to 6.4% under s‐polarized incidence appears, which is non‐existent in planar magneto‐optical thin films. A large rotation of transmitted light polarization in longitudinal magnetic configuration is also observed, which is two orders of magnitude higher than for planar magneto‐optical thin films. These phenomena are originated from the unique circular displacement current when exciting magnetic resonances in the Mie resonators, which change the electric field direction locally. This work indicates an uncharted territory of light polarization control based on complex modal profiles in all‐dielectric magneto‐optical Mie resonators and metasurfaces.