Orthogonal Polarization Research Articles

Efficiency enhancement of long-reach passive optical network using the polarization coding

Abstract This paper, propose a new passive optical network (PON) system structure based on the two orthogonal polarization states of the same wavelength. This method is usually applied to increase the number of simultaneous users in the network, it can double the number of potential users. The proposed technique utilized to increase split ratio and consequently increase the reach and the split ratio. This can be achieved by implementing technologies such as power splitter. In terms of bit rate, the proposed PON offers a bit rate of 10 Gbps for downstream transmissions. The results obtained in this work are shown that the proposed system can accommodate more users simultaneously for the typical Q factor is greater than 6.

All-Solid Single-Polarization Anti-Resonant Fiber Base on Anisotropic Glass

A single-polarization solid-core anti-resonant fiber is proposed, and the influence of the fiber core material anisotropy of the solid-core anti-resonant fiber on polarization characteristics is investigated using the finite element method. Single-polarization guidance is achieved by using the anisotropy of optical fiber materials, which also ensures high birefringence. The numerical simulation results indicate that there are two single-polarization intervals (1210–1440 nm and 1490–1560 nm), with a maximum bandwidth of up to 230 nm, when the confinement loss difference between the two orthogonal polarizations exceeds two orders of magnitude. Specifically, when the work wavelength is 1550 nm, a polarization extinction ratio (PER) of 108 is obtained by optimizing the structure parameters. Additionally, the y-polarization fundamental mode (YPFM) can be well confined in the fiber center with a low confinement loss of 0.04 dB/m, while the x-polarization fundamental mode (XPFM) has a huge confinement loss larger than 4.65 dB/m due to the coupling with the tube mode. The proposed single-polarization solid-core anti-resonant fiber has a huge potential in applications such as laser systems, fiber-optic gyroscopes, and optical fiber communications.

Joint Amplitude‐Phase Metasurface for Polarization‐Selective Dynamic Wavefront Manipulation and Broadband Absorption

AbstractWith modern science and technology developing towards large information capacity and high integration level, anisotropic metasurfaces have emerged as an advanced platform for integrating distinct functionalities and multitasking. Despite the significant progresses, most of the existing polarization‐controlled metasurfaces support phase‐only modulation for dual orthogonal polarization information channels. Herein, a reconfigurable anisotropic metasurface of 576 independent meta‐atoms embedded with diodes and resistors is proposed to enable polarization‐selective amplitude‐phase modulation, which further integrates dynamic wavefront control and broadband energy absorption for two polarization channels with high isolation. As exemplary demonstrations, a series of programmable functionalities have been realized for one polarization channel, including dual‐beam scanning, quad‐beam radiation, and diffusive scattering for far‐field scattering manipulation, as well as reconfigurable focusing for near‐field redistribution. Meanwhile, robust broadband energy absorption has been maintained for the other polarization channel, irrespective of the programmable functionalities. Experiments in the microwave region are carried out to verify the powerful wavefront tailoring ability, and all the measured results are in good consistency with simulated analysis.

Compact wideband FSS-absorber-based low-RCS reflectarray antenna

This paper presents a method to realize compact broadband low-RCS ReflectArray (RA) antenna based on a Frequency Selective Surface (FSS) absorber and a reflective metasurface. Such an FSS absorber consists of a resistance-loaded lossy layer and an FSS layer, which is utilized to reach an absorption-transmission response. The bottom reflective metasurface works as a phase array, reshaping the quasi-sphere wave from the feeding antenna into the quasi-plane wave. As a demonstration, the low-RCS RA antenna is simulated, fabricated, and measured. The simulated and measured results show that the developed low-RCS RA antenna has an aperture efficiency of 42.7% and a gain of 25.4 dBi in the X band. In the meantime, it simultaneously reaches the 10 dB RCS reduction for the orthogonal polarizations at the S and C bands, corresponding to a fractal bandwidth of 120%. Specifically, the adopted patch-feeding antenna makes the RA antenna more compact than the horn-feed conventional ones. Furthermore, the proposed RA antenna uses a few layers of substrates, making it lower in cost and easier for fabrication. The proposed design may have potential application in integrated stealth communication systems.

Continuous fabrication of polarization maintaining fibers via an annealing improved infinity additive manufacturing technique for THz communications.

We report the design and fabrication of a polarization-maintaining fiber for applications in fiber-assisted THz communications. The fiber features a subwavelength square core suspended in the middle of a hexagonal over-cladding tube by four bridges. The fiber is designed to have low transmission losses, high birefringence, high flexibility, and near-zero dispersion at the carrier frequency of 128 GHz. An infinity 3D printing technique is used to continuously fabricate a 5 m-long polypropylene fiber of ∼6.8 mm diameter. The fiber transmission losses are furthermore reduced by as high as ∼4.4 dB/m via post-fabrication annealing. Cutback measurements using 3 m-long annealed fibers show ∼6.5-11 dB/m and ∼6.9-13.5 dB/m losses (by power) over a 110-150 GHz window for the two orthogonally polarized modes. Signal transmission with bit error rates of ∼10-11-10-5 is achieved at 128 GHz for 1-6 Gbps data rates using a 1.6 m-long fiber link. The average polarization crosstalk values of ∼14.5 dB and ∼12.7 dB are demonstrated for the two orthogonal polarizations in fiber lengths of 1.6-2 m, which confirms the polarization-maintaining property of the fiber at ∼1-2 meter lengths. Finally, THz imaging of the fiber near-field is performed and shows strong modal confinement of the two orthogonal modes in the suspended-core region well inside of the hexagonal over-cladding. We believe that this work shows a strong potential of the infinity 3D printing technique augmented with post-fabrication annealing to continuously produce high-performance fibers of complex geometries for demanding THz communications applications.

Airborne HSRL-2 measurements of elevated aerosol depolarization associated with non-spherical sea salt

Airborne NASA Langley Research Center (LaRC) High Spectral Resolution Lidar-2 (HSRL-2) measurements acquired during the recent NASA Earth Venture Suborbital-3 (EVS-3) Aerosol Cloud Meteorology Interactions over the Western Atlantic Experiment (ACTIVATE) revealed elevated particulate linear depolarization associated with aerosols within the marine boundary layer. These observations were acquired off the east coast of the United States during both winter and summer 2020 and 2021 when the HSRL-2 was deployed on the NASA LaRC King Air aircraft. During 20 of 63 total flight days, particularly on days with cold air outbreaks, linear particulate depolarization at 532 nm exceeded 0.15–0.20 within the lowest several hundred meters of the atmosphere, indicating that these particles were non-spherical. Higher values of linear depolarization typically were measured at 355 nm and lower values were measured at 1,064 nm. Several lines of evidence suggest that these non-spherical particles were sea salt including aerosol extinction/backscatter ratio (“lidar ratio”) values of 20–25 sr measured at both 355 and 532 nm by the HSRL-2, higher values of particulate depolarization measured at low (< 60%) relative humidity, coincident airbornein situsize and composition measurements, and aerosol transport simulations. The elevated aerosol depolarization values were not correlated with wind speed but were correlated with salt mass fraction and effective radius of the aerosol when the relative humidity was below 60%. HSRL-2 measured median particulate extinction values of about 20 Mm−1 at 532 nm associated with these non-spherical sea salt particles and found that the aerosol optical depth (AOD) contributed by these particles remained small (0.03–0.04) but represented on average about 30%–40% of the total column AOD. Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) spaceborne lidar aerosol measurements during several cold air outbreaks and CALIOP retrievals of column aerosol lidar ratio using column AOD constraints suggest that CALIOP operational aerosol algorithms can misclassify these aerosols as dusty marine rather than marine aerosols. Such misclassification leads to ∼40–50% overestimates in the assumed lidar ratio and in subsequent retrievals of aerosol optical depth and aerosol extinction.

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

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

Study of Parallel-Plate Waveguides Bordered by Reactive Huygens Metasurfaces

Huygens metasurfaces (HMSs) are 2-D structures exhibiting both electric and magnetic responses. In this article, the properties of a parallel-plate waveguide (PPW) formed by two dispersive reactive HMSs are investigated analytically by deriving the dispersion relations for supported surface waves. In particular, the PPWs formed by nondispersive HMSs are studied thoroughly and it is shown that they can support a maximum of four modes with a variety of transverse electric (TE) and transverse magnetic (TM) degenerate modes, modes with the same cutoff frequencies, and modes with constant phase and group velocities. Such explored PPWs offer degenerate modes with orthogonal polarizations with potential applications in leaky wave antennas and holographs. Moreover, PPWs with either nondispersive or dispersive borders support modes with subluminal phase velocities which find applications in device miniaturization. The proposed analytical derivations are verified by full-wave numerical simulations.

Circularly Polarized Horn Antenna With Miniaturized Longitudinal Dimension for Vehicular Satellite Communications

A wideband circularly polarized (CP) horn antenna with miniaturized longitudinal dimension is proposed for satellite communications, by cutting a pair of antipodal tapered slots (ATSs) on the broad walls of the horn and loading simple metal blocks near the ATSs. By introducing a pair of ATSs, a linear cross polarization is generated with almost equal amplitude and quadrature phase relative to the original polarization, and a circular polarization is realized. Then the CP horn is longitudinally shortened by 33.3% for miniaturized dimension, but the circular polarization is deteriorated because the two linear polarizations are perturbed. Critically, three pairs of simple metal blocks introducing extra capacitances are loaded near the ATSs to enhance the cross polarization, so the two orthogonal linear polarizations are rebalanced and the circular polarization is reconstructed. Other two pairs of metal blocks are embedded on the throat of the horn to improve the impedance match on the operating band, achieving a 32.8% bandwidth of 11.35-15.8 GHz for both impedance and axial ratio bandwidths. The proposed antenna is easy to be fabricated by standard mechanical manufacture process, showing a compact and low-cost candidate for vehicular satellite communications.

Monocular depth sensing using metalens

Abstract3-D depth sensing is essential for many applications ranging from consumer electronics to robotics. Passive depth sensing techniques based on a double-helix (DH) point-spread-function (PSF) feature high depth estimation precision, minimal power consumption, and reduced system complexity compared to active sensing methods. Here, we propose and experimentally implemented a polarization-multiplexed DH metalens designed using an autonomous direct search algorithm, which utilizes two contra-rotating DH PSFs encoded in orthogonal polarization states to enable monocular depth perception. Using a reconstruction algorithm that we developed, concurrent depth calculation and scene reconstruction with minimum distortion and high resolution in all three dimensions were demonstrated.

Electrically tunable THz graphene metasurface wave retarders

Abstract Anisotropic materials with chirality or birefringence can be used to manipulate the polarization states of electromagnetic waves. However, the comparatively low anisotropy of natural materials hinders the miniaturization of optical components and devices at terahertz frequencies. In this study, we experimentally demonstrate that the relative phase retardation of a THz wave can be electrically controlled by integrating patterned mono- and bilayer graphene onto an otherwise isotropic metasurface. Specifically, we show that a refractive index for one of the orthogonal polarization states can be electrically controlled by modulating graphene’s conductivity, thereby weakening the capacitive coupling between adjacent meta-atoms in an anisotropic manner. With monolayer graphene, phase retardation of 15° to 81° between two orthogonal polarization states can be achieved. Maximum phase retardation of 90° through a metasurface with bilayer graphene suggests its use as a tunable quarter-wave plate. Continuous control from linear- to circular-polarization states may provide a wide range of opportunities for the development of compact THz polarization devices and polarization-sensitive THz technology.

Modulating anti-dark vector bisolitons

Theoretical simulations about modulating anti-dark vector bisolitons are reported in this manuscript. The modulation bases on an optical fiber modulation system, and four kinds of soliton parameters are considered for variation. The input central wavelengths in orthogonal polarization directions are assumed to be same or slightly different, corresponding to polarization locked state or group-velocity locked state. The modulated pulse shapes or optical spectra at output port will show their own characteristics, depending on different modulation parameters. For example, modulated bisolitons in orthogonal directions demonstrate obvious pulse oscillations when projection angle varies, in the condition of different central wavelengths. These simulations are useful to study modulating optical fiber vector bisolitons out of fiber laser oscillator, and have potential applications in optical fiber vector soliton communication, quantum information processing and so on.

Effects of neighboring transitions on electromagnetically induced absorption and transparency in Rb atoms in circular orthogonal polarization configuration

Effects of neighboring transitions on electromagnetically induced absorption and transparency in Rb atoms in circular orthogonal polarization configuration

A shared-aperture transmissive/reflective bi-functional metasurface for both transmitarray and reflectarray

In this paper, a shared-aperture transmissive/reflective bi-functional metasurface is proposed. On metasurfaces, antisymmetric dipole pairs as transmissive elements and symmetric dipole pairs as reflective elements are interleaved in orthogonal polarization. By utilizing Huygens’ resonance, the metasurface can achieve near full phase coverage for orthogonally polarized transmitted and reflected wave. Then the bi-functional metasurface is used for the design of transmitarray (TA)/reflectarray (RA) bi-functional antenna. The measured results show that, for TA, the maximum gain is 30.26 dBi with antenna efficiency of 45.6 % and the 3-dB gain bandwidth is 26.3–29.3 GHz (10.79 %), and for RA, the maximum gain is 30.29 dBi with antenna efficiency of 45.7 % and the 3-dB gain bandwidth entirely covers the frequency region of 26–30 GHz. The bi-functional metasurface has important applications in the field of antenna engineering.

Silicon metasurface-based infrared polarizing beam splitter with on-demand deflection angles.

Polarizing beam splitters (PBSs) play an important role in applications requiring polarization multiplexing or high polarization purity. Traditional prism-based PBSs usually have large volumes, which hampers their further applications in ultracompact integrated optical systems. Here, we demonstrate a single-layer silicon metasurface-based PBS with the ability to deflect two orthogonally linearly polarized infrared light beams to on-demand angles. The metasurface consists of silicon anisotropic microstructures, which can provide different phase profiles for the two orthogonal polarization states. In experiments, two metasurfaces designed with arbitrary deflection angles for x- and y-polarized light exhibit good splitting performance at an infrared wavelength of 10 μm. We envision that this type of planar and thin PBS can be used in a series of compact thermal infrared systems.

Evaluating Mixing Height Estimations in the Western United States Using Satellite Observations

Wildfire smoke can be transported far from its origin, adversely impacting human health. The height of the atmospheric mixing layer, the near-surface layer of the troposphere in which turbulent convection leads to vertical mixing, is called the mixing height. Mixing height is a critical input in the smoke dispersion and air quality models used by agencies that monitor wildfires and air pollution. These models, coupled with forecaster expertise, are also used to determine if it is safe to execute a prescribed burn. In this paper, we derive mixing heights from two satellite datasets in order to assess mixing height forecasts produced by the National Weather Service (NWS) Fire Weather Program. Namely, we use Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) Vertical Feature Masks (VFM) and vertical water vapor profiles from the Moderate Resolution Imaging Spectroradiometer (MODIS). Our comparison indicates that NWS forecasts tend to underestimate CALIOP mixing heights with a median relative error of –13% and a mean relative error of –3.34%. Although MODIS and NWS mixing heights showed some agreement below 3 km, the lower vertical resolution of the MODIS estimates hindered a full comparison. We examine the discrepancies among mixing heights over wildfire smoke plumes determined by these methods and discuss biases and limitations. This work provides insight into potential bias patterns present in current mixing height forecasts and provides directions for future improvements in both NWS mixing height forecasts and satellite-based measurements of mixing height.

Longitudinal evolution from scalar to vector beams assembled from all-dielectric metasurfaces.

Vector vortex beams (VVBs) with non-uniform polarization states have a wide range of applications, from particle capture to quantum information. Here, we theoretically demonstrate a generic design for all-dielectric metasurfaces operating in the terahertz (THz) band, characterized as a longitudinal evolution from scalar vortices carrying homogeneous polarization states to inhomogeneous vector vortices with polarization singularities. The order of the converted VVBs can be arbitrarily tailored by manipulating the topological charge embedded in two orthogonal circular polarization channels. The introduction of the extended focal length and the initial phase difference effectively guarantees the smoothness of the longitudinal switchable behavior. A generic design approach based on vector-generated metasurfaces can assist in the exploration of new singular properties of THz optical fields.

Low Threshold Current and Polarization-Stabilized 795 nm Vertical-Cavity Surface-Emitting Lasers

Low threshold current and polarization-stabilized 795 nm vertical-cavity surface-emitting lasers (VCSELs) are fabricated by integrating a surface grating of high polarization selectivity and high reflectivity. The rigorous coupled-wave analysis method is used to design the surface grating. For the devices with a grating period of 500 nm, a grating depth of ~150 nm, and a diameter of the surface grating region of 5 μm, a threshold current of 0.4 mA and an orthogonal polarization suppression ratio (OPSR) of 19.56 dB are obtained. The emission wavelength of 795 nm of a single transverse mode VCSEL is achieved at a temperature of 85 °C under an injection current of 0.9 mA. In addition, experiments demonstrate that the threshold and output power also depended on the size of the grating region.

Reset-free adaptive polarization controller on a silicon-photonic platform for a self-coherent communication system.

To give full play to the advantages of the self-coherent systems in the data center scene, the problem of the random walk of the polarization state of the delivered local oscillator must be solved. An adaptive polarization controller (APC) is an effective solution, with the characteristics of easy integration, low complexity, being reset-free, and so on. In this work, we experimentally demonstrated an endlessly APC based on a Mach-Zehnder interferometer on a silicon-photonic integrated circuit. The APC is thermally tuned with only two control electrodes. It endlessly stabilizes the arbitrary state of polarization (SOP) of the light to a state of equal power of the two orthogonal polarizations (X and Y). A polarization tracking speed of up to 800 rad/s is achieved.

Realizing efficient asymmetric transmission using optical activity of ultrathin chiral metasurfaces for K‐band applications

AbstractAn elliptical chiral split‐ring‐resonator‐based bilayer thin metasurface is introduced in this paper. The proposed metasurface realizes strong electromagnetic (EM) activity with asymmetric transmission in the K‐band of the microwave regime. The efficiency is more than 80% over a range of frequencies from 18.6 to 20.8 GHz. Angular stability up to 60° makes the structure robust for practical applications. The structure also exhibits a negative refractive index for circularly polarized wave due to the strong chirality factor. Polarization azimuth rotation angle of 90° and ellipticity of 0° reveal the pure EM/optical activity. Furthermore, the simulation and measured results also affirmed orthogonal pure linear polarization transformation. The proposed chiral metasurface finds applications in radar and satellite belonging to K‐band.