Broadband Polarization Research Articles

Broadband Reflective Polarization Rotator Built on Single Substrate

A broadband polarization rotator built on single substrate is presented in this work. The device is designed for operation in the K and Ka bands. A slant array is used to achieve polarization rotation by 90° in a reflective manner. Broadband has been obtained, with the operation frequency range covering 15–45 GHz for 3 dB criteria, which is almost 100% fractional bandwidth. In addition, the insertion loss is less than 0.3 dB over a moderate broad incident angle from 0°–20°. Furthermore, the polarization conversion ratio can be as high as 0.95. By using a bi-static method, the fabricated prototype is measured, and the measured results demonstrate satisfactory agreement with the simulation ones. In comparison with other reflective designs in the literature, this design provides good bandwidth as well as polarization conversion ratio. Miniaturization can be investigated to increase the angular stability.

High-efficiency asymmetric transmission of linear polarized waves based on tri-layered metamaterial structure

In this work, a broadband polarization converter in transmission mode based on tri-layered metamaterial structure is proposed to realize asymmetric transmission and linear polarization conversion simultaneously. The proposed design model consists of a hexapolar split ring structure and two orthogonal sub-wavelength gratings embedded in two dielectric substrates. The appropriate parameters of the unit cell are optimized and selected. Sequentially, a prototype is fabricated and measured in order to confirm performance of the proposed design structure. The simulation and measurement results consistently demonstrate that the conversion polarization transmission coefficient is greater than 0.9 within the frequency region of 4.516.7 GHz, which is equivalent to 115% of the relative bandwidth. Based on the Fabry–Perot-like cavity theory, the working mechanisms of this structure have been discussed in detail. Thus, the proposed design structure is expected high potential applications in irreversible electromagnetic devices.

Broadband terahertz polarization converter with anomalous reflection based on phase gradient metasurface

In order to expand the application situation of the polarization converter in terahertz band, a broadband polarization converter based on phase gradient metasurface is proposed for simultaneously manipulating the polarization and the wavefront of the reflected wave in terahertz region. Consisting of six different “H”-shaped resonators which can tune the phase and the polarization respectively, the polarization converter is able to deflect the normally incident terahertz wave with an anomalous reflection angle while changing the polarization. Geometric rotation and resonant frequency modulation constitute the phase variation of the unit, which can be superimposed on each other without interference. The simulation results show that the reflecting angle from 0.40 to 0.60 THz varies from 39° to 22° with side lobe level lower than −14 dB. Specific elucidation for high polarization conversion ratio is discussed through reflection phase and resonant branch analysis. Compared to the conventional polarization converter, the proposed one has an advantage in propagation manipulating, which reveals its potential application in THz detection, imaging and sensing, etc.

Photonic Image Rejection Mixer Based on Polarization Manipulation of a Broadband Optical Source

We propose a photonic mixer with image rejection capability using a broadband optical source (BOS) and polarization processing. Intermediate frequency (IF) signals with image rejection are generated from the local oscillator-modulated and the time-delayed radio frequency (RF)-modulated BOS light. The RF operating frequency is flexibly tunable over a wide range by simply adjusting the time delay. In addition, the proposed system is free from dispersion-induced mixing power fading and bias drift problem. Experimental results exhibit an image rejection ratio of more than 44.6 dB for RF signals from 2 to 18 GHz, while the IF signal is fixed at 800 MHz. Image rejection mixing operation at different IF frequencies and signal power is also confirmed.

Polarization modeling and predictions for Daniel K. Inouye Solar Telescope, part 7: preliminary NCSP system calibration and model fitting

Daniel K. Inouye Solar Telescope (DKIST) is designed to deliver accurate spectropolarimetric solar data across a wide wavelength range, covering a large field of view simultaneously using multiple facility instruments for solar disk, limb, and coronal observations. We show successful design and implementation of National Solar Observatory Coudé Laboratory Spectropolarimeter, a custom metrology tool for efficient continuous broadband polarization calibration of the telescope mirrors through a coudé laboratory focus. We compare multiple fitting techniques for the 10 to >140 variable DKIST system polarization models. We compare results with the first DKIST solar calibration observations and find small thermally forced retardance changes of ±0.2 deg and ±0.5 deg for two separate SiO2 retarders. Modulation matrices derived are stable to < ± 0.01 per element during the first on-Sun calibration tests. We achieve good fit agreement to our metrology-based model over a 390- to 1600-nm bandpass. The solutions are robust and efficient using only 10 input Stokes vectors from elliptical calibration retarders. We developed a custom polarizer assembly used with metrology tools to orient the DKIST polarization coordinates to better than 0.1-deg clocking angle.

Aberration‐free pupil steering Maxwellian display with wide‐view broadband polarization converters

AbstractA see‐through Maxwellian display with aberration‐free pupil steering is proposed and experimentally demonstrated. The system uses a polarization‐dependent off‐axis lens coupler set fabricated with cholesteric liquid crystal. Electrically addressable polarization converters are used to switch among pupils. A wide‐view broadband polarization converter is designed accordingly.

Low-Loss Broadband Transverse Electric Pass Hybrid Plasmonic Fiber Polarizers Using Metallic Nanomaterials

Metals were for decades perceived as devoid of interesting optical properties that could be harnessed for optical components and devices. However, with the development of accurate nanofabrication techniques and precise control over architectural parameters, metals can be structured and characterized on the nanoscale. Metallic plasmonic nanomaterials exhibit a number of unique structural and optical properties, which offer the potential for developing new types of plasmonic devices. Here, we demonstrate a low-loss broadband polarizer based on a hybrid plasmonic fiber structure using metals as polarization-selective absorption materials. The polarization mechanism, design, fabrication, and characteristics of the plasmonic polarizers are investigated theoretically, numerically, and experimentally. The theoretical analysis predicts that the polarization-selective absorption with insensitivity to wavelength enables hybrid plasmonic fibers to function as broadband polarizers. Numerical simulations give the comparison of the polarization-selective absorption of various metallic nanomaterials (Ag, Au, In, Al, Cr) and show that aluminum is regarded as the optimum absorption material for the plasmonic polarizer. Experimental results show that through precise control over geometrical parameters, this device is capable of offering a high polarization extinction ratio (PER) of over 40 dB and a low insertion loss (IL) of less than 1.3 dB in the wavelength region of 810.1-870.0 nm. Compared with commercial birefringent-crystal-fiber polarizers, the plasmonic fiber polarizer has a better PER and IL bandwidth. These merits, combined with a compact and robust configuration, enable the plasmonic polarizer to have great potential in a broad range of applications.

Polarization-resolved supercontinuum generated in a germania-doped photonic crystal fiber

We characterize the polarization properties of a supercontinuum (SC) generated in a GeO2-doped photonic crystal fiber (PCF) to reveal the interplay between nonlinear broadening mechanisms of a pulse propagating in two independent fundamental modes associated to the principal axes of the fiber. Notably, we resolve self-phase modulation, self-shifted Raman solitons and dispersive waves within a set of orthogonal polarization states as they contribute to generate a broad spectrum spanning from 450 to 2150 nm. Interestingly, our experimental results feature a high degree of polarization at the edges of the spectrum in comparison to the region near the pump wavelength. We show that this modulation is caused by nonlinear spectral broadening. We also identify an additional depolarization mechanism preferentially acting on shorter wavelengths, indicative of a Rayleigh-like scattering effect due to the presence of intrinsic sub-wavelength defects in the fiber. Experiments rely on a free-space grating-based monochromator and a broadband polarizer to monitor the output SC and its linear polarization components along the principal axes of the PCF. Our results and experimental technique pave the way toward an improved standard for the characterization of broadband optical spectra and more efficient implementation of highly nonlinear fibers in a large range of polarization-sensitive applications.

Research on filtering characteristics of asymmetric photonic crystal fiber based on gold coating

In this paper, an asymmetric photonic crystal fiber (PCF) polarization filter near the gold-clad hole based on surface plasmon resonance (SPR) is proposed. The outer walls of the two air holes in the y-direction are coated with a gold film, and the two kinds of cladding air holes are introduced near the coated holes to increase the difference in the coupling strength of x and y polarization modes and SPP modes, thus separating the two polarization states. The finite element method is used to study the characteristics of the polarization filter, and the result shows that the polarization loss in the y-direction is as high as 1565.98 dB/cm at 1.55μm, while the loss in the x-direction is relatively small. When the fiber length is 1 mm, the crosstalk peak reaches 1322.7 dB. From 1μm to 2μm (range: 1000 nm), the crosstalk is always greater than 20 dB. If four kinds of pores with different sizes are used in the cladding layer, the symmetry around the gold-coated holes will be destroyed, and a better filtering effect can be obtained. The excellent performance of the proposed polarization filter makes it a good candidate material for broadband polarization filters.

Cavity-Backed Dual-Sinuous Antenna Modeling

Recently, for Radio Frequency (RF) signal identification on air vehicles, it has become critical to not only be able to detect the direction and angle of arrival of signals, but to also properly identify the polarization of such signals. For decades, cavity-backed dual-spiral antennas were heavily used for this purpose. However, that required the placement of both right-hand and left-hand elements to perform this function. Due to limited space and other issues, an alternative type of broadband antenna had to be identified. The Cavity-Backed Dual-Sinuous (CBDS) antenna makes an excellent replacement for this function. With its elements rotated 45° about its center, each element exhibits slant linear performance. Such an antenna, paired with proper connections and detection hardware, allows the detector to determine the polarization of arriving RF signals. A CBDS antenna was developed in the WIPL-D CEM code. Its RHCP and LHCP performance was studied over a broad range of frequencies. Results did prove that CBDS antennas have excellent broadband performance and polarization extraction.

Broadband polarization filter based on hybrid silver-graphene coated pentagonal photonic crystal fiber

In this paper, a polarization filter based on hybrid silver-graphene coated pentagonal Photonic Crystal Fiber (PCF) is proposed. The finite element method is used to analyse the confinement loss characteristics of the proposed PCF. The proposed PCF based filter selects the desired X-polarization mode with a low confinement loss of 0.12 dB/cm and 0.59 dB/cm and rejects the unwanted Y-polarization mode with a very high confinement loss of 361.26 dB/cm and 1508.37 dB/cm at the mostly used wavelengths of 1.31 μm and 1.55 μm for optical communication. The proposed PCF with a length of 300 μm achieves the cross-talk of 216.68 dB and 904.67 dB at 1.31 μm and 1.55 μm. It also accomplishes a broad spectral width of 816 nm with the cross-talk value greater than 20 dB. The influence of the structural parameters of the proposed PCF is studied. The fabrication feasibility of the proposed PCF is also investigated. The proposed PCF based polarization filter will be an inevitable candidate for the integrated optical system.

Design and Performance Analysis of a Highly Efficient Polychromatic Full Stokes Polarization Modulator for the CRISP Imaging Spectrometer

Abstract We present the design and performance of a polychromatic polarization modulator for the CRisp Imaging SpectroPolarimeter (CRISP) Fabry–Perot tunable narrow-band imaging spectropolarimer at the Swedish 1 m Solar Telescope (SST). We discuss the design process in depth, compare two possible modulator designs through a tolerance analysis, and investigate thermal sensitivity of the selected design. The trade-offs and procedures described in this paper are generally applicable in the development of broadband polarization modulators. The modulator was built and has been operational since 2015. Its measured performance is close to optimal between 500 and 900 nm, and differences between the design and as-built modulator are largely understood. We show some example data, and briefly review scientific work that used data from SST/CRISP and this modulator.

Simple design of efficient broadband multifunctional polarization converter for X-band applications

A simple design of a broadband multifunctional polarization converter using an anisotropic metasurface for X-band application is proposed. The proposed polarization converter consists of a periodic array of the two-corner-cut square patch resonators based on the FR-4 substrate that achieves both cross-polarization and linear-to-circular polarization conversions. The simulated results show that the polarization converter displays the linear cross-polarization conversion in the frequency range from 8 to 12 GHz with the polarization conversion efficiency above 90%. The efficiency is kept higher than 80% with wide incident angle up to 45°. Moreover, the proposed design achieves the linear-to-circular polarization conversion at two frequency bands of 7.42–7.6 GHz and 13–13.56 GHz. A prototype of the proposed polarization converter is fabricated and measured, showing a good agreement between the measured and simulated results. The proposed polarization converter exhibits excellent performances such as simple structure, multifunctional property, and large cost-efficient bandwidth and wide incident angle insensitivity in the linear cross polarization conversion, which can be useful for X-band applications. Furthermore, this structure can be extended to design broadband polarization converters in other frequency bands.

Tunable broadband polarization converters based on coded graphene metasurfaces

In this paper, two optimization algorithms (randomly initialized hill climbing and genetic algorithms) are considered to design broadband polarization converters based on coded metasurfaces. A pixeled graphene patch with an elliptic structure is proposed for the initial solution. Each pixel can be 1 and 0 which represents the presence and absence of the graphene. The initial guess tends to the optimum configuration after several optimization processes. Four broadband polarization converters are designed utilizing the optimization algorithms. By changing the chemical potential of graphene, the operation frequency of the polarization converters can be adjusted. Furthermore, the effects of relaxation time of graphene and incident angle on the polarization conversion bandwidth of the four designed structures are investigated.

Broadband Spin-Dependent Directional Coupler via Single Optimized Metallic Catenary Antenna.

With the rapid development of on-chip optics, integrated optical devices with better performance are desirable. Waveguide couplers are the typical integrated optical devices, allowing for the fast transmission and conversion of optical signals in a broad working band. However, traditional waveguide couplers are limited by the narrow operation band to couple the spatial light into the chip and the fixed unidirectional transmission of light flow. Furthermore, most of the couplers only realize unidirectional transmission under the illumination of the linear polarized light. In this work, a broadband polarization directional coupler based on a metallic catenary antenna integrated on a silicon-on-insulator (SOI) waveguide has been designed and demonstrated under the illumination of the circularly polarized light. By applying the genetic algorithm to optimize the multiple widths of the metallic catenary antenna, the numerical simulation results show that the extinction ratio of the coupler can be maintained larger than 18 dB in a wide operation band of 300 nm (from 1400 to 1700 nm). Moreover, the coupler can couple the spatial beam into the plane and transmit in the opposite direction by modulating the rotation direction of the incident light. The broadband polarization directional coupler might have great potential in integrated optoelectronic devices and on-chip optical devices.

Broadband Rotary Joint Concept for High-Power Radar Applications

To allow antenna movements in azimuth and elevation in high-power radar applications, rotary joints are essential. They allow the rotation of a transmission line and therefore are important transmission line components. In the present paper, a broadband rotary joint concept for high-power W-band radar applications is proposed. To avoid a twist of the polarization plane of a linearly polarized mode, like HE11, a combination of two broadband polarizer is used. A cross polarization of Xpol ≤ − 20 dB can be achieved within the considered frequency range from 90 GHz to 100 GHz. This corresponds to a suitable value for radar applications.

Optoelectronic Device for Molecular Orientation of Functional Materials

A new approach to the development of an optoelectronic device for molecular orientation of functional materials is proposed. Results of the development of its main components are presented: a collimator for the light from an LED and a broad band polarizer with a large angular aperture. The problem of the collimation of a strongly diverging beam from an LED is examined. It is shown that the use of a modified conical lens offers promise for solving this problem. A broad-band polarizer with a large angular aperture, which is an important component of the optoelectronic device, is developed and fabricated on the basis of a multilayered structure.

A Broadband Polarized Metamaterial Absorber Driven by Strong Insensitivity and Proximity Effects

Artificial electromagnetic metamaterial produces exotic resonance, extra ordinary characteristics not available in nature, but engineers can inherit the characteristics by controlling and manipulating their structure. This research primarily the design and realization of dual-band, polarization, and incident angle insensitive metamaterial absorber (MA) is presented. By controlling and manipulating the electromagnetic design shape, artificial structure, periodic array pattern, and dielectric layer thickness a significant way to realize high absorption. In order to achieve high absorption a new shape of an octagonal ring (OR), cross-wires (CWs), and cut-off circle (CC) artificial structure have been sensibly selected. The special characteristics of this structure produce a dual resonance and its bandwidth rises compared that of classical absorber. The proposed artificial structure operation suits the Ku-band application, but possible to enhance in $C$ -band. The numerical and experimental results display a dual-band 99.8% at 12.2 GHz and 99.9% at 15.5 GHz resonance is an excellent agreement in theory and numerical analysis. The effects of the constitutive property parameters: dielectric constant ( $\varepsilon $ ), magnetic permeability ( $\mu$ ), and negative refractive index ( $n$ ) are also investigated. The investigation of symmetric design structure shows the polarization-insensitivity and high absorption initiated even in changing the incident angle. Numerical and experimental results confirmed the destructive interference of multiple penetrations are responsible for the near-unity absorption. An excellent agreement in the absorptivity rates that touches near perfection which is prominent for solar cells, detection, and imaging applications.

Design of two miniaturized and broadband polarization filters based on two types of square-lattice gold-filled photonic crystal fibers

Two ultra-broadband polarization filters based on Structure 1 and Structure 2 are reported and characterized in terms of attenuation, crosstalk, bandwidth, and polarization filtering properties by the finite element method. Structure 1 is formed by introducing partial elliptical air holes in the first layer of the square-lattice gold-filled photonic crystal fiber. Based on the design solution of Structure 1, Structure 2 is arranged by using circular air holes with the changed transverse pitch to replace elliptical ones. Numerical results show that high resonance intensities of 2265.07 and 1831.83 dB/cm for y polarization, together with the corresponding x polarization losses of 0.50 and 0.18 dB/cm at respective communication wavelengths of 1.55 and 1.31 μm can be achieved by varying the gold film thickness for Structure 1.Moreover, the design of Structure 2 with all circle holes can also realize a high resonance loss of 1942.54 dB/cm for y polarization with a low loss of 0.43 dB/cm for x polarization at 1.55 μm. Structure 1 and Structure 2 with the fixed fiber length of 300 μm can obtain the crosstalk values of −590.09 and −506.07 dB at 1.55 μm, together with the bandwidths of 1500 and 900 nm, respectively. Additionally, two types of designs represent good produce tolerances. These results show a high potential of the suggested fiber for application in polarization-dependent filtering and other polarizing devices.

Mid-infrared flat-topped broadband chiral helix metamaterials based on indium tin oxide and their chiral properties

We proposed a periodic mid-infrared broadband chiral structure. Its unit cell consists of four indium tin oxide (ITO) helix subunits with different radii. The simulation results show that the flat-topped broadband circular dichroism (CD) can be achieved in the mid-infrared band by optimizing the parameters of helix structures. The simulation results also show that compared with the metallic (Ag and Au) helix structures, the ITO helix structure proposed exhibits evidently better broadband CD and optical activity, which provides a new idea for the design of broadband polarization state control devices in the mid-infrared band.