Broadband Polarization Research Articles

Experimental Performance of a Broadband Dual-Stage 1950 nm PM Single-Clad Tm-Doped Fiber Amplifier

We report the experimental performance of a packaged dual-stage all-single-clad broadband polarization maintaining (PM) Tm-doped silica fiber amplifier (TDFA) with a high signal output power of 2.2 W at 1909 and 1951 nm. Our novel design incorporates an uncooled 940 nm multimode semiconductor pump laser source. Combined high gain of >46 dB, wide operating bandwidth of 1875-2000 nm, low noise figure of 7 dB, high OSNR of >54 dB/0.1 nm, and a PER of >20 dB are achieved with our TDFA.

P‐154: New Carbon Nanotubes UV Polarizer for Photoalignment of Liquid Crystals

We propose a unidirectionally aligned multi‐layered carbon nanotubes (CNT) as a UV polarizer for LC photoalignment, which can replace wire‐grid‐polarizer (WGP) with high cost. A 12 multi‐layered CNT polarizer exhibits the degree of polarization up to 91%. The fringe‐field switching (FFS) LC device made by photoalignment with use of the proposed CNT polarizer exhibit uniform LC alignment in whole area and excellent electro‐optics. The work proposes not only cost‐effective novel polarizer replacing WGP for photoalignment of LC but also for photonic component of broadband polarizer from UV to IR.

Stable complex conjugate artifact removal in OCT using circularly polarized light as reference

In Fourier domain optical coherence tomography (FDOCT), the depth profile is mirrored about the zero delay between the sample and reference optical paths, limiting the imaging depth to half of the entire ranging space and undermining the optimal sensitivity window. We present a new method, to the best of our knowledge, to remove the complex conjugate artifact by using circularly polarized light as reference. Quadrature detection of the complex fringe is achieved by utilizing the intrinsic λ/4 delay between two polarization channels. We use passive broadband polarization optics to control the polarization state of the light in the reference and sample arms and a balanced polarization diversity detection unit to simultaneously detect phase-shifted fringes. We demonstrate a 40 dB artifact suppression ratio with a swept-source optical coherence tomography system. Our proposed method is immune to sample motion and laser phase noise, and imposes no restrictions to the source bandwidth, imaging speed, or computational power. In vivo images of the human finger, as well as the cornea and retina of a non-human primate, were demonstrated.

Broadband polarisation reconfigurable antenna based on crossed dipole and parasitic elements for LTE/sub‐6GHz 5G and WLAN applications

Broadband polarisation reconfigurable antenna based on crossed dipole and parasitic elements is proposed in this study, which can switch among three polarisation modes, i.e. linear polarisation, left-hand circular polarisation and right-hand circular polarisation. The proposed antenna consists of two crossed dipoles fed by a 3/4 square ring, two microstrip feeding elements etched at the centre of the upper and lower sides of the dielectric substrate, and three sets of microstrip parasitic elements helping broaden the axial-ratio (AR) bandwidth. Four PIN diodes are embedded between each crossed dipole and the microstrip feeding element, which enable the polarisation reconfigurability. The working principle of polarisation reconfigurability is analysed in detail. The measured results show that the proposed antenna has a −10 dB overlapped impedance bandwidth of 63.5% (2.04–3.94 GHz) and the 3 dB overlapped AR bandwidth is about 54.5% (2.4–4.2 GHz), resulting in a wide overall bandwidth of 48.6% (2.40–3.94 GHz). Besides, the measured peak gain of this antenna reaches up to 8.5 dBi. The proposed antenna can be a good candidate for 2.45 GHz WiFi, LTE 4G, and sub-6 GHz 5G applications.

A Broadband, Wide-Angle Scanning, Linear-to-Circular Polarization Converter Based on Standard Jerusalem Cross Frequency Selective Surfaces

A broadband and wide-angle scanning linear polarization (LP)-to-circular polarization (CP) converter based on a dual-layer structure is presented. The elementary cell is composed of conventional Jerusalem crosses (JCs). The design procedure is based on transmission line circuit model and on full-wave simulations. The proposed equivalent circuit has been generalized to include the oblique incidence in the model. Simulated results demonstrate a 24% axial ratio bandwidth for an incidence angle θ = ±50° in both xz and yz planes. The proposed converter provides a unique combination of wide bandwidth, thin profile, and stable response with respect to the angle of incidence. It can be integrated into any LP antenna system to generate CP without significantly affecting the antenna performances.

Design of an ultrabroadband and compact filter based on square-lattice photonic crystal fiber with two large gold-coated air holes

An ultrabroadband and compact square-lattice photonic crystal fiber polarization filter based on surface plasmon resonance is proposed. Four large air holes are introduced near the core to destroy the symmetry of the original fiber structure so that the resonance wavelengths of x- and y-polarized core modes can be well separated. The inner walls of two large air holes along the x polarization direction are coated with gold film to generate the surface plasmon mode. In addition, to further enhance the coupling resonance strength between the core mode and the surface plasmon polariton mode, the six air holes near the gold-coated air holes are replaced by solid glass rods. Then the dispersion characteristics and loss spectrum of the proposed polarization filter are studied by the finite-element method. The results show that when the fiber length of the proposed filter is only 700 μm, ultrawideband y-polarized light transmission with a bandwidth of up to 730 nm in the wavelength range from 0.97 to 1.70 μm can be achieved. The effective filtering range covers all optical fiber communication bands from O to U. Moreover, the filter has excellent structural tolerances. These excellent properties are expected to make it a good candidate for a broadband polarization filter.

The polarized spectral energy distribution of NGC 4151

ABSTRACT NGC 4151 is among the most well-studied Seyfert galaxies that does not suffer from strong obscuration along the observer’s line of sight. This allows to probe the central active galactic nucleus (AGN) engine with photometry, spectroscopy, reverberation mapping, or interferometry. Yet, the broad-band polarization from NGC 4151 has been poorly examined in the past despite the fact that polarimetry gives us a much cleaner view of the AGN physics than photometry or spectroscopy alone. In this paper, we compile the 0.15–89.0 μm total and polarized fluxes of NGC 4151 from archival and new data in order to examine the physical processes at work in the heart of this AGN. We demonstrate that, from the optical to the near-infrared (IR) band, the polarized spectrum of NGC 4151 shows a much bluer power-law spectral index than that of the total flux, corroborating the presence of an optically thick, locally heated accretion flow, at least in its near-IR emitting radii. Specific signatures from the atmosphere of the accretion structure are tentatively found at the shortest ultraviolet (UV) wavelengths, before the onset of absorption opacity. Otherwise, dust scattering appears to be the dominant contributor from the near-UV to near-IR polarized spectrum, superimposed on to a weaker electron component. We also identify a change in the polarization processes from the near-IR to the mid-IR, most likely associated with the transition from Mie scattering to dichroic absorption from aligned dust grains in the dusty torus or narrow-line region. Finally, we present and discuss the very first far-infrared polarization measurement of NGC 4151 at 89 μm.

Switching between the Functions of Half-Wave Plate and Quarter-Wave Plate Simply by Using a Vanadium Dioxide Film in a Terahertz Metamaterial**Supported by the Scientific and Technological Developing Scheme of Jilin Province (Grant No. 20180101281JC), “135” Research Project of Education Bureau of Jilin Province (Grant No. JJKH20190579KJ), and “111” Project of China (Grant No. D17017).

We propose a switchable THz metamaterial that can be switched between two functions of half-wave plate and quarter-wave plate. The two switchable functions can be simply achieved by inserting a VO2 film in the metamaterial design. Finite-difference time-domain (FDTD) simulation results show that the proposed metamaterial can convert x-polarized incident wave to y-polarized reflected wave when VO2 is at metal phase, and convert x-polarized wave to circularly polarized wave when VO2 is at insulator phase. The metamaterial performs well in the two functions, i.e., the same broad working frequency band and near perfect polarization conversion. The switching effect originates from the switchable Fabry–Pérot cavity length induced by the phase change of VO2. We believe that our findings provide a reference in designing switchable metamaterials.

Broadband Plasmonic Polarization Filter Based on Photonic Crystal Fiber with Dual-Ring Gold Layer.

Polarization filter is a very important optical device with extinction characteristics. Due to the design flexibility of photonic crystal fibers and the high excitation losses of the gold layer, the polarization filter based on the photonic crystal fiber and surface plasmonic resonance effect is widely studied. Considering these, we present a simple and high-performance polarization filter using the finite element method. Numerical simulations show that there is a large difference in energy between the two polarization directions by reasonable adjustment of the structural parameters, the confinement loss in the x-pol direction is less than that in the y-pol direction, which is suitable to realize a broadband polarization filter. When the fiber length is 2 mm, the extinction ratio peak can reach −478 dB, and the bandwidth with the extinction ratio better than −20 dB is 750 nm, which covers communication wavelengths of 1.31 μm and 1.55 μm (1.05–1.8 μm). It also has a low insertion loss of 0.11 dB at 1.31 μm and 0.04 dB at 1.55 μm. In addition, our design has high feasibility in fabrication and better tolerance. The proposed filter with compactness, high extinction ratio, broad bandwidth, and low insertion loss would play an important role in the sensing detection, bio-medical, and telecommunication field.

Achieving broadband absorption and polarization conversion with a vanadium dioxide metasurface in the same terahertz frequencies.

We present the bifunctional design of a broadband absorber and a broadband polarization converter based on a switchable metasurface through the insulator-to-metal phase transition of vanadium dioxide. When vanadium dioxide is metal, the designed switchable metasurface behaves as a broadband absorber. This absorber is composed of a vanadium dioxide square, silica spacer, and vanadium dioxide film. Calculated results show that in the frequency range of 0.52-1.2 THz, the designed system can absorb more than 90% of the energy, and the bandwidth ratio is 79%. It is insensitive to polarization due to the symmetry, and can still work well even at large incident angles. When vanadium dioxide is an insulator, a terahertz polarizer is realized by a simple anisotropic metasurface. Numerical calculation shows that efficient conversion between two orthogonal linear polarizations can be achieved. Reflectance of a cross-polarized wave can reach 90% from 0.42 THz to 1.04 THz, and the corresponding bandwidth ratio is 85%. This cross-polarized converter has the advantages of wide angle, broad bandwidth, and high efficiency. So our design can realize bifunctionality of broadband absorption and polarization conversion between 0.52 THz and 1.04 THz. This architecture could provide one new way to develop switchable photonic devices and functional components in phase change materials.

High extinction ratio terahertz broadband polarizer based on the aligned Ni nanowire arrays.

We present a broadband terahertz (THz) polarizer based on the stacks of aligned Ni nanowire (NW) arrays. We demonstrated that the polarizer has an extinction ratio of 58.8 dB and an average extinction ratio of 46.6 dB throughout a frequency range of 0.3-2.3 THz. Compared to carbon-nanotube and metallic wire-grid polarizers, our Ni-NW polarizers with rapid, reliable, low-cost fabrication processes are ideal candidates for emerging THz technologies.

Multifunction tunable broadband terahertz device for polarization rotation and linear asymmetric transmission based on Dirac semimetals

A three-layer complementary strip Dirac semimetal polarizer is proposed to achieve polarization rotation, perfect polarization conversion, and asymmetric transmission. This device can realize broadband polarization operation of linear polarized waves in the terahertz frequency domain. By changing the Fermi level of the Dirac semimetal, the polarization angle of linearly polarized light in the frequency range of 1.3 to 1.63 THz can be rotated from 0°to 90°, and the device has good robustness for linearly polarized light with different incident angles. When used as an asymmetric transmission device, its polarization conversion efficiency reaches more than 98% and the asymmetric transmission parameter reaches more than 50% in the range of 1.3–1.63 THz. The asymmetric transmission parameters, polarization conversion ratio, polarization rotation angle, and ellipticity are used to describe the performance of the converter.

High-precision polarimetry of nearby stars (d < 50 pc)

Context. We investigate the linear polarization produced by interstellar dust aligned by the magnetic field in the solar neighborhood (d < 50 pc). We also look for intrinsic effects from circumstellar processes, specifically in terms of polarization variability and wavelength dependence. Aims. We aim to detect and map dust clouds which give rise to statistically significant amounts of polarization of the starlight passing through the cloud, and to determine the interstellar magnetic field direction from the position angle of the observed polarization. Methods. High-precision broad-band (BV R) polarization observations are made of 361 stars in spectral classes F to G, with detection sensitivity at the level of or better than 10−5 (0.001%). The sample consists of 125 stars in the magnitude range 6–9 observed at the 2.2 m UH88 telescope on Mauna Kea, 205 stars in the magnitude range 3–6 observed at the Japanese (Tohoku) T60 telescope on Haleakala, and 31 stars in the magnitude range 4–7 observed at the 1.27 m H127 telescope of the Greenhill Observatory, Tasmania. Identical copies of the Dipol-2 polarimeter are used on these three sites. Results. Statistically significant (>3σ) polarization is found in 115 stars, and >2σ detection in 178 stars, out of the total sample of 361 stars. Polarization maps based on these data show filament-like patterns of polarization position angles, which are related to both the heliosphere geometry, the kinematics of nearby clouds, and the Interstellar Boundary EXplorer ribbon magnetic field. From long-term multiple observations, a number (~20) of stars show evidence of intrinsic variability at the 10−5 level. This can be attributed to circumstellar effects (e.g., debris disks and chromospheric activity). The star HD 101805 shows a peculiar wavelength dependence, indicating size distribution of scattering particles different from that of a typical interstellar medium. Our high signal-to-noise measurements of nearby stars with very low polarization also provide a useful dataset for calibration purposes.

Design of a compact and broadband terahertz polarization splitter based on gradient dual-core photonic crystal fiber

We report a broadband polarization splitter based on polyethylene photonic crystal fiber with microstructured dual refractive index gradient cores. These dual cores consist of a properly optimized arrangement of air holes such that for individual fibers $x$x-polarized modes have large effective indices difference, while this index difference is almost zero for their $y$y-polarized modes, leading to efficient coupling between the $y$y-polarized modes. We have shown that by proper optimization of gradience created in the arrangement of air holes, efficient polarization splitting can be achieved for a broad range of terahertz frequencies. Device length and extinction ratio have been calculated numerically for the proposed configuration. Device length of $\sim{1.96}$∼1.96 to $\sim {60}\;{\rm cm}$∼60cm was found to be appropriate for frequencies in the 0.4-1.0 THz range to have high extinction ratios: $ - {38}$-38 to $ - {49}\;{\rm dB}$-49dB and $ - {15}$-15 to $ - {23}\;{\rm dB}$-23dB for the $x$x and $y$y polarizations, respectively. The bending loss for the proposed design is quite low: $\sim{0.05}\;{\rm dB/m}$∼0.05dB/m at 1 THz for the bend radius of 1 cm. These results suggest that a compact, low-loss, and broadband polarization splitter with very high extinction ratios can be achieved by wrapping the fiber around a small mandrel.

Broadband Polarization Rotator With Tunable Rotation Angle Composed of Three Wave Plates

A simple scheme for a broadband polarization rotator with tunable rotation angle is proposed and verified experimentally. The rotator consists of only three wave-plates, one of which is a full-wave plate. The robust approach inspired by the composite pulses analogy allows to compensate the wave-plate dispersion in large extent.

Gold-coated photonic crystal fiber based polarization filter for dual communication windows

Future optical integrated circuits can be created by overcoming the diffraction limit of light that imposes a lower bound on the size limit of optical devices and plasmonics can meet the desired requirements of producing very compact optical devices. A plasmonic based compact and broadband polarizer, capable of producing single polarized ray concurrently around the two communication windows of 1.31μm and 1.55μm, based on hexagonal lattice photonic crystal fiber is proposed. The results show that the confinement loss of x- and y-polarized modes are 1014.05 dB/cm and 0.048 dB/cm, respectively, at the wavelength of 1.31μm meaning that x-polarized mode is 20812 times lossier than y-polarized mode. Similarly, the achieved loss ratio between two orthogonal polarized modes is 6439 at the wavelength of 1.55μm. In addition, the filter can also maintain a broad bandwidth of over 800 nm by keeping crosstalk greater than 20 dB for the device length of 100μm. The bandwidth and maximum crosstalk value can be extended by loosing compactness of the device. The simultaneous filtering performance around two communication windows with broad bandwidth and compact in length makes the proposed filter a suitable candidate for optical communication and sensing system.

Countering Single-Polarization Radar Based on Polarization Conversion Metamaterial

Based on polarization conversion metamaterial, a novel method to counter single-polarization radar is proposed and discussed in this paper. Due to the resonance feature in the polarization conversion, energy attenuation and waveform distortion dual functions can be achieved. For radar, that will strongly reduce the SNR (Signal-to-Noise Ratio) of the matched filter and the probability of detection. A broadband polarization conversion metamaterial structure was designed with multi resonance frequencies. To evaluate the effectiveness, a typical pulse compression radar model was established, the waveform property, correlation loss in the matched filter and probability of radar detection were simulated and calculated. It was found that the metamaterial achieved the function of passive signal modulation, the echo energy was reduced markedly and great distortion was generated near the resonance frequencies, also the correlation loss in the matched filter was significantly increased especially near the resonance frequencies. Finally the calculated probability of radar detection gave furthermore proof of the effectiveness of the method.

Reconfigurable Multifunctional Metasurface for Broadband Polarization Conversion and Perfect Absorption

A reconfigurable multifunctional metasurface is proposed to realize the switching between broadband polarization conversion and perfect absorption by integrating the PIN diodes into the structure. An appropriate feed plate is designed to provide the bias voltage that controls the state of the diodes. When the diodes are in off-state, the metasurface will work in polarization conversion mode, which can convert the co-polarization wave into its cross-polarization state with polarization conversion ratio (PCR) of over 90% in the range from 2.97 to 6.03 GHz; While the diodes are in on-state, the metasurface exhibits perfect absorption with absorptivity of over 90% from 2.56 to 7.62 GHz, and the relative absorption bandwidth (RAB) reaches 99.4%. In addition, the metasurface is fabricated and measured to confirm the multifunctional performance. The proposed metasurface is expected to be applied in electromagnetic detection, stealth technology and communication system.

A broadband radar cross section reduction metasurface based on integrated polarization conversion and scattering cancelation

In this paper, we proposed and demonstrated a broadband radar cross section (RCS) reduction metasurface by integrating polarization conversion and scattering cancelation. A broadband polarization conversion structure was designed based on split concentric ring. We used a 4 × 4 array of split ring structure and its mirror-symmetric structure as the super-cell units to construct a metasurface with chessboard structure. The metasurface can efficiently reduce the co-polarization RCS for all azimuth angles of incident wave. The metasurface sample with optimized structure parameters was fabricated and measured. The measured 10 dB RCS reduction band of the metasurface is from 8.6 to 17.7 GHz.

Ultrasmall broadband wavelength and polarization router based on hybrid waveguide of monolithic-LiNbO3

The nanoscale wavelength and polarization router, which can simultaneously separate wavelength and polarization modes, is an essential component of on-chip nanophotonic devices. Here, an on-chip wavelength and polarization router is realized experimentally based on a three-layer hybrid waveguide of Au-SiO2-LiNbO3 etched with asymmetric nano-cavities. The central area size of the device is only 1.60×1.96 μm2. A broad operation band covers from 500nm to 1150nm with low cross talk of under 10dB. The monolithic-LiNbO3is introduced for the first time, to the best of our knowledge, to on-chip multichannel wavelength and polarization routers. This work plays a key role for dense chip integration, visible light displays, and communications, and can inspire LiNbO3-based nanophotonic devices.