Linear Polarization Components Research Articles

LP-mode diversity method for the beating model of FM-EDFAs with comparison between different beat lengths

The mode beating effects can be considered for improving the modeling accuracy of few-mode erbium-doped fiber amplifiers (FM-EDFAs). A linearly polarized (LP) mode diversity method for the beating model of FM-EDFAs is proposed in the paper, in which each vector mode is always decomposed into the x- and y-polarized LP components in erbium-doped fibers and then the mode interference effects between the co-polarized LP modes associated with different vector modes act on the erbium-ion population profile. The power evolution of LP11e mode as an example is firstly analyzed for three cases of long, moderate and short beat lengths, in comparison with the intensity model. It is shown that the FM-EDFA with a moderate beat length has a potential advantage in gain control and the intensity model is equivalent to the case with the long beat length. The simultaneous amplification of LP01 and LP11e modes are then investigated for the moderate beat lengths and the modal gain can approximately be expressed by that of the intensity model and a cosine function of the beat length. The similar analysis process is also applied to other beating scenarios, such as the simultaneous amplification of LP01, LP11e and LP11o modes.

Learning‐Based Vectorial Reconstruction of Orthogonal Polarization Components in a Structured Vector Optical Field Passing Through Scattering Media

AbstractOptical imaging through scattering media has become important due to its fundamental physics interest and various applications. The reconstruction of a structured optical field with various states of polarization passing through a scattering medium with a speckle pattern behind the scattering medium remains challenging since existing restoring techniques only reconstruct the speckle in a single‐polarization state (scalar optical field). This work proposes a novel approach to simultaneously restore the initial orthogonally polarized components from a speckle pattern behind a scattering medium. The neural network Polarization‐DenseUnet (P‐DenseUnet) based on the vector transfer matrix is constructed to restore the two orthogonally linear (or circular) polarization components of a structured vector optical field from a speckle pattern behind the scattering medium. The generalization and effectiveness of this proposed method are tested for high fidelity with different phase distributions such as vortex, digits, and Fashion‐mnist.

Molecular Orientation-Dependent Photonic Polarization Engineering in Organic Single-Crystal-Filled Microcavities.

Designing the polarization degree of freedom of light is crucial in many fields and has widespread application in, for example, all-optical circuits. In this work, we find that in an organic microcavity filled with anisotropic single crystals the cavity modes can be modulated to be elliptically polarized, i.e., partially circularly polarized and partially linearly polarized. The circular polarization component originates from the Rashba-Dresselhaus spin splitting, while the linear polarization component is due to the dislocation of linearly polarized modes. The dislocation of the linear polarizations is ascribed to the orientation of individual molecules and the molecular packing arrangement; hence, the linear polarizations can be controlled by properly structuring the molecular distributions. Our results pave the way for enriching and engineering the polarization properties of individual optical cavity modes in organic microstructures, which may favor the development of polarized lasers with various polarizations.

Control of structured light beams focusing through anisotropic multiple-scattering media via multi-focus-based digital optical phase conjugation

A framework to focus structured light beams through an anisotropic multiple-scattering medium (AMSM) with multi-focus-based digital optical phase conjugation is proposed. In this work, the measured full vector transmission matrix (VTM) in conjunction with a well-designed multifocal target field can be used to calculate the required input field, which consists of two orthogonally linear polarization components. The polarization, amplitude and phase of the light before and after the AMSM are then shaped and controlled by encoding the input field into a double-channel computer generated hologram that is displayed on a vector spatial light modulator. The desired output field composed of multifocal spots can be obtained through the AMSM. We demonstrated several examples, generating vector beams, array vector beams and vortex beams, to experimentally validate the feasibility of our approach. Additionally, the peak to background ratio (PBR) of the generated multifocal structured light can be predicted theoretically by introducing the idea of critical focus number. The simulated and experimental results show that the generated structured light with a clear optical ring and high PBR can be realized through the AMSM. Consequently, our method provides an effective way to control and optimize structured light beams focusing through the AMSM.

Patterned Chiral Perovskite Film for Self‐Driven Stokes Photodetectors

AbstractPolarization detection plays an essential role in a wide range of fields, including target identification, 3D reconstruction, and robotic vision. Self‐driven on‐chip full‐Stokes photodetectors are urgently required to meet the trend of miniaturization and integration. Nevertheless, how to fulfill efficient circular and linear polarimetry simultaneously with sufficient recognition effectiveness in a compact device is a great challenge. Herein, a patterned chiral perovskite film is fabricated by imprinting strategy, and vertically‐structured self‐driven Stokes photodetector is demonstrated, which can recognize various polarization states at 0 V. Through patterned design of the chiral perovskite film by integrating circle and nanowire structure, flexible tuning of circular and linear polarization components within the detector is achieved, enabling the detector to strike a balance between circular and linear polarization detection ability when recognizing arbitrary polarization light. The maximum circular polarization sensitivity factor and linear polarization ratio can reach 0.125 and 1.5, respectively. By optimizing well‐defined patterned shape, the resultant detector can recognize polarized light with an average recognition error <7%. This work opens an avenue toward the fabrication of self‐driven filterless Stokes detectors based on patterned chiral perovskite film for accurate detection of arbitrary polarization states.

Polarization-separating Alvarez metalens.

The rapid advancements in optical communication technologies have highlighted traditional optical components' limitations, particularly in size, adaptability, and integration capabilities, underscoring the need for more compact and versatile solutions. Metalenses offer a promising pathway to address these challenges, with their ability to provide high-functionality, miniaturized optical components. We developed a varifocal metalens with a polarization separation function designed for the wavelength of 1550 nm for potential application for next-generation communication technologies. To integrate the varifocal and polarization separation functions, polarization-dependent phase profiles for an off-axis Alvarez lens were derived and encoded by amorphous silicon pillar meta-atoms with rectangular cross sections to provide independent 0-2π phase delays for both orthogonal linear polarization components. The fabricated metalens achieved a varifocal range of 0.75 mm to 10.65 mm and a polarization extinction ratio of 18.5 dB.

Manipulation of polarization conversion and dual foci in a twisted caustic vector optical field in free space

Manipulation of polarization states in a complex structured optical field during propagation has become an important topic due to its fundamental interest and potential applications. This work demonstrates the effect of the caustic and twisting phases on the polarization states of a vector beam experimentally and theoretically. The novel properties of polarization evolution, especially the conversions of different states of polarization (SoPs) in a twisted caustic vector beam, occur during propagation in free space because of the modulation of twisting and caustic phases. The orthogonal polarization components tend to appear on the beam centers of two foci, and the two focal distances are closely related to the caustic and twisting phases. The twisting and caustic phases can manipulate the conversions between linear and circular polarization components that occur during propagation. These results provide a new approach to more complex manipulations of a structured optical field, especially in tailoring the evolution of polarization states and two foci. They may find potential applications in the corresponding field.

Influence of High-Order Twisting Phases on Polarization States and Optical Angular Momentum of a Vector Light Field

This study investigates the influence of high-order twisting phases on polarization states and optical angular momentum of a vector light field with locally linear polarization and a hybrid state of polarization (SoP). The twisted vector optical field (TVOF) is experimentally generated based on the orthogonal polarization bases with high-order twisting phases. The initial SoP of a TVOF modulated by the high-order twisting phase possesses various symmetric distributions. The propagation properties of a high-order TVOF with locally linear polarization and hybrid SoP are explored, including the intensity compression, expansion, and conversion between the linear and circular polarization components. In particular, orbital angular momentum (OAM) appears in a high-order TVOF during propagation where no OAM exists in the initial field. The variation of OAM distribution in cross-section becomes more frequent with the increase of the twisting phase order. In addition, a non-symmetric OAM distribution appears in a non-isotropic TVOF, leading to the rotation of the beam around the propagation axis during propagation. The optical energy flow distribution of a high-order TVOF provides a more profound understanding of the propagation dynamics of high-order TVOF. These results provide a new approach for optical field manipulation in a high-order TVOF.

Controlling the polarization dependence of the complex transmission spectrum using the Brewster effect in metafilms.

We propose a method for controlling the polarization dependence of the complex transmission spectrum using the Brewster effect in a two-dimensional array of meta-atoms with finite thickness, which we refer to as a metafilm. We show that the complex transmission spectra of the orthogonal linear polarization components can be controlled independently without reflection by stacking multiple metafilms that exhibit only an electric dipole resonance. As a proof-of-concept numerical demonstration, we design several broadband waveplates with high transmission efficiency based on simple design principles. The proposed method would enable us to easily design anisotropic metamaterials with various complex transmission spectra.

A Low-RCS Circularly Polarized Reflectarray Antenna With a Linearly Polarized Feed

A low-radar cross section (RCS) circularly polarized (CP) reflectarray antenna with a linearly polarized (LP) feed is designed. The out-of-band RCS of the reflectarray for both the TE and TM polarized incident waves is reduced by replacing its ground with an absorptive frequency selective reflector (AFSR). A systematic methodology based on synthesis of the equivalent circuit model (ECM) is presented to expedite the design of the AFSR. The unit phasing element of the reflectarray is designed in such a way that it exhibits minimum coupling between the two orthogonal reflected LP-field components. Moreover, during the reflectarray construction, a novel phase synthesis is used which takes into account possible lowest of the existing mutual coupling while providing quadrature phase difference between the orthogonal LP components with minimum phase error. The proposed design is fabricated using 14×14 phasing elements to experimentally validate the numerically simulated results. The performance of the reflectarray is compared with a conventional reflectarray without the AFSR. It is observed that when the reflectarray is integrated with the AFSR, its gain is reduced only by 1.16 dB. However, its out-of-band RCS is reduced significantly. The 8-dB RCS reduction bandwidth can be observed from 3.55-7.2 GHz (67.9%) and from 11.85-14.21 GHz (18.11%). Moreover, it provides peak co-pol CP gain of 21.62 dBi, aperture efficiency of 41%, and 1-dB gain-bandwidth from 8.68-8.95 GHz, respectively.

Linear polarization-separating metalens at long-wavelength infrared.

We designed and fabricated a linear polarization-separation metalens (PSM) made of single-crystal silicon (sc-Si) for long-wavelength infrared (LWIR) imaging. The PSM comprises sc-Si dielectric waveguide pillar meta-atoms with rectangular cross-sections, providing a full 2π phase delay range for two orthogonal linear polarization components with high transmittances (>70%). Electron beam lithography and deep reactive ion etching were used to fabricate the PSM. Polarization-separation imaging of elevated and ambient temperature objects was demonstrated with high extinction ratios of 21.8 dB and 12.8 dB for the x- and y-polarizations, respectively. Additionally, polarization-sensitive imaging was demonstrated by distinguishing the surfaces of a hand and toy windows. Our work enables the visualization of invisible information in the LWIR region and has widespread applications.

Satellite retrieval of the linear polarization components of the water-leaving radiance in open oceans.

Atmospheric correction (AC) of polarized radiances acquired by polarization satellite sensors, remains a challenge due to the complex radiative transfer processes of the coupled ocean-atmosphere system. In this study, we proposed an innovative polarized AC algorithm built on the near-infrared band (PACNIR) with an emphasis on the retrieval of the linear polarization components of the water-leaving radiance in clear open oceans. This algorithm was based on the black ocean assumption in the near-infrared band and fitted polarized radiance measurements along multiple observation directions with nonlinear optimized processing. Our retrieval algorithm notably inverted the linearly polarized components of the water-leaving radiance and aerosol parameters. Compared with that of the simulated linear polarization components of the water-leaving radiance via the vector radiative transfer model for the studied sea regions, the mean absolute error of the PACNIR-retrieved linearly polarized components (nQw and nUw) exhibited a magnitude of 10-4, while the magnitude of that of the simulated nQw and nUw data was 10-3. Moreover, the PACNIR-retrieved aerosol optical thicknesses at 865 nm exhibited a mean absolute percentage error of approximately 30% relative to in situ values obtained from Aerosol Robotic Network-Ocean Color (AERONET-OC) sites. The PACNIR algorithm could facilitate AC of the polarized data provided by the next generation of multiangle polarization satellite ocean color sensors.

High-Efficiency Diagnosis of Antenna Radiation Characteristics Based on Scanning Optic-Induced Plasma Scattering Technology

This article presents an innovative quasi-real-time antenna near-field diagnosis method, by scanning a laser-induced plasma on a silicon wafer and imaging the field with the synchronously produced scattered signals. Several approaches have been devised to adapt to the antenna diagnosis scenarios. By using the multilayer matching approach, the issue of multiple reflection disturbance between the aperture and silicon wafer is avoided, especially for large aperture antennae at high frequencies. The accuracy of near-field distribution is improved, and far-field patterns can be transformed directly. The experimental results of a Ka-band 20 dB standard antenna agree well with the simulation results. Diagnosis of radiation states in the reactive near-field region is demonstrated, and the resonate modes of a 2.4 GHz Wi-Fi patch antenna at different frequencies are clearly observed. The experiments of a TM01 mode antenna verify the full polarization diagnosis ability of the method, and the linear polarization component is measured with the help of a polarization grid. The demonstrated diagnosis method has the advantages of high efficiency, ultraclose measurement distance, and superresolution and provides a highly promising and widely available method for antenna diagnosis.

The Polstar high resolution spectropolarimetry MIDEX mission

The Polstar mission will provide a space-borne 60 cm spectropolarimeter operating at ultraviolet (UV) wavelengths, capturing all four Stokes parameters (intensity, two linear polarization components, and circular polarization). Polstar’s capabilities are designed to meet its goal of determining how circumstellar gas flows alter and inform massive star evolution, affect the stellar remnant population, and stir and enrich the interstellar medium (ISM). These will be achieved by investigating the dynamical geometries in the winds and disks of hot stars, the composition and magnetic alignment of interstellar dust, and the star-forming accretion disks of UV-bright stars at an important transition boundary. Together these areas map out a kind of two-way interface between massive stars and their effect on our galaxy, wherein the stellar winds enrich the ISM with metals and kinetic energy, preconditioning their environment and the stellar endpoints prior to undergoing supernova. The ISM dust in turn reveals the composition and magnetic environment leading to new star formation, and the accretion disks of Herbig Ae/Be stars reveal how the ISM gas returns to make new massive stars. Polstar will combine high-resolution spectroscopy in the time domain with high-precision UV polarimetry. Doppler-shifted UV resonance line opacity will provide information about circumstellar kinematics, while polarization gives complementary geometric information about unseen structures. The composition and magnetic alignment of the smallest interstellar dust grains provides a probe of the ISM utilizing radiative alignment theory (RAT). Polstar will operate in the far-UV (FUV) at 122–200 nm at high spectral resolution of around \(R \sim 30k\), and at FUV and near-UV (NUV) wavelengths of 122–320 nm at lower spectral resolutions of \(0.1-1k\). Detection of polarization levels as weak as 0.1% are expected, with a temporal cadence ranging from 5–10 minutes for most wind variability studies, to hours or days for sampling rotation, to days or weeks for sampling binary orbits, to months to a year for sampling substructure in the inner regions of protoplanetary disks. Sub-meter-class aperture is well suited to access this wide array of time domain science, made possible by restricting to a few hundred bright, massive stars, necessarily extincted by a small to moderate column of interstellar dust, informing both the attributes of the stars and the ISM through which they are seen. As such, the focus is on our own galaxy and its evolutionary drivers, but a few targets in the Magellanic clouds offer the potential to extend this understanding to low-metallicity environments.

Optimal photon polarization toward the observation of the nonlinear Breit-Wheeler pair production

We investigate the optimization of the photon polarization to increase the yield of the Breit-Wheeler pair production in arbitrarily polarized plane wave backgrounds. We show that the optimized photon polarization can improve the positron yield by more than $20\%$ compared to the unpolarized case, in the intensity regime of current laser-particle experiments. The seed photon's optimal polarization is resulting from the polarization coupling with the polarization of the laser pulse. The compact expressions of the coupling coefficients in both the perturbative and nonperturbative regime are given. Because of the evident difference in the coupling coefficients for the linear and circular polarization components, the seed photon's optimal polarization state in an elliptically polarized laser background, deviates considerably from the orthogonal state of the laser polarization.

Discrete vector light bullets in coupled [formula omitted] nonlinear cavities

We consider coupled weakly birefringent cavities filled-in with nonlinear Kerr material and subject to linearly polarized optical injection. Light propagation in such a system is described by a system of discrete Lugiato–Lefever-type equations for each linear polarization component of the electric field into each cavity, coupled by the cross-phase modulation terms and the neighboring waveguides field overlap integrals. We demonstrate that this system supports stable three-dimensional vector localized structures often called discrete vector light bullets. We consider both anomalous and normal dispersion and show that it results in the generation of, respectively, bright and dark discrete vector light bullets. Due to the polarization multistability of the system, we demonstrated coexisting light bullets with polarization at the light bullets peaks as different as predominantly linear to predominantly circular. We have shown that chaotic spatio-temporal dynamics can be realized even for such an injection strengths for which the light bullets distribution in the system is stationary by increasing the coupling strength C between the cavities.

Atmospheric diffuse transmittance of the linear polarization component of water-leaving radiation.

The polarization characteristics of water-leaving radiation contain rich information on oceanic constituents. Determining the atmospheric diffuse transmittance is crucial for extracting the polarization information of water-leaving radiation from the radiation acquired by polarimetry satellites at the top of the atmosphere. However, there is still a lack of understanding of the atmospheric diffuse transmittance of the linear polarization component of water-leaving radiation. Here, we first evaluated the difference between the atmospheric diffuse transmittance of the linear polarization component (TQ, TU) and the intensity component (TI) of the water-leaving radiation based on the Ocean Successive Orders with Atmosphere Advanced radiative transfer model. As a consequence, there were apparent differences between TQ, TU and TI. In the case of a large solar zenith angle and a large viewing zenith angle, the difference between TQ, TU and TI will exceed 1. Meanwhile, compared with TI, the oceanic constituents had a prominent interference with TQ and TU, and the sediment concentration had little interference with TQ and TU in low- and medium-turbidity water with respect to the aerosol model, optical thickness, observation geometry, and phytoplankton. Moreover, TQ and TU lookup tables were generated for medium- and low-turbidity water, which laid the foundation for extracting the water-leaving radiation polarization information from the satellite observation polarization signal.

Broadband and high efficiency terahertz metasurfaces for anomalous refraction and vortex beam generation

The applications of metasurfaces are currently a highly active research field due to their extraordinary ability to manipulate electromagnetic waves. The ultra-thin characteristics of metasurfaces allow the miniaturization and integration of metasurface devices. However, these devices work typically under a low efficiency and narrow bandwidth condition. In this work, we design eight multilayered unit cells with similar amplitudes and a phase interval of π/4, which convert the polarization states of the terahertz (THz) waves between two orthogonal directions. The average cross-polarized transmission amplitudes of these cells are all around 0.9 in an ultra-broad frequency range from 0.5 THz to 1.4 THz. Furthermore, unit cells are used to construct both an ultra-thin anomalous refraction metalens and a vortex phase plate. Our simulation results show that the anomalous refraction for the transmitted linear polarization component is comparable to the theoretical prediction, and the maximum error is determined to be below 4.8%. The vortex phase plate can also generate an ideal terahertz vortex beam with a mode purity of 90% and more. The distributions of longitudinal electric field, intensity, and phase illustrate that the generated vortex beam has excellent propagation characteristics and a weak divergence. Simulations of the two types of metasurface devices, based on the eight unit cells, exhibit very high efficiencies in a wide bandwidth. Our research will assist in the improvement in the practical applications of metasurfaces. It also provides a reference for the design of high efficiency and broadband devices that are applied to other frequency ranges.

Experimental Study on Bottom-Up Detection of Underwater Targets Based on Polarization Imaging.

Previous studies on the polarization imaging of underwater targets mainly focused on top-down detection; however, the capacities of bottom-up detection were poorly known. Based on in situ experiments, the capability of bottom-up detection of underwater targets using polarization imaging was investigated. First, to realize the objective of bottom-up polarization imaging, a SALSA polarization camera was integrated into our Underwater Polarization Imaging System (UPIS), which was integrated with an attitude sensor. At Qiandao Lake, where the water is relatively clear, experiments were conducted to examine the capacity of the UPIS to detect objects from the bottom up. Simultaneously, entropy, clarity, and contrast were adopted to compare the imaging performance with different radiation parameters. The results show that among all the used imaging parameters, the angle of polarization is the optimal parameter for bottom-up detection of underwater targets based on polarization imaging, which may result from the different diffused reflectance of the target surface to the linear polarization components of the Stokes vector.

Engineering Photon Statistics in a Spinor Polariton Condensate.

We implement full polarization tomography on photon correlations in a spinor exciton-polariton condensate. Our measurements reveal condensate pseudospin mean-field dynamics spanning from stochastic switching between linear polarization components, limit cycles, and stable fixed points, and their intrinsic relation to the condensate photon statistics. We optically harness the cavity birefringence, polariton interactions, and the optical orientation of an incoherent exciton reservoir to engineer photon statistics with precise control. Our results demonstrate a smooth transition from a highly coherent to a super-thermal state of the condensate polarization components.