A multi-functional polarization convertor based on chiral metamaterial for terahertz waves

We present the design, analysis, fabrication, and measurement of an ultrathin cross-polarization converter in the transmission mode with near unity conversion efficiency. The converter is constructed of a periodic array of the dielectric substrate sandwiched with simply artificial structures, in which the top layer and bottom layer are connected by metallic vias. The proposed polarizer can convert the linearly polarized incident electromagnetic wave to its orthogonal counterpart in the transmission mode. The conversion mechanism is explained by both equivalent circuit model and full-wave simulations. The simulation and measured results have a good agreement in the entire frequency range. Such a scheme of the ultrathin cross-polarization converter has simple geometry and can be used in microwave communications, remote sensing, and imaging.

An Ultrathin Cross-Polarization Converter With Near Unity Efficiency for Transmitted Waves

A novel linear polarization converter operating in C- and X-bands with high polarization conversion ratio is described and demonstrated based on frequency selective surface. The building element is a planar-dipole pair, which is orthogonally printed on a double-layer substrate and vertically connected by a pair of through-via holes functioning as a quasi-two-wire transmission line coupler. A perforated metal shielding layer is sandwiched between the double-layer structure to only support a transverse electric and magnetic (TEM) mode coupling between the top and bottom dipolar components. The front dipole responds to the incident transverse electric (TE) wave, and sends the induced current into the two-wire transmission line to feed the bottom dipole. The bottom dipole is orthogonal or oriented at an arbitrary angle with respect to the top one, and a resultant outgoing transverse magnetic (TM) wave or arbitrary orientation polarized wave can be achieved. In addition, a bidirectional orthogonal polarization converter is realized by using double orthogonally arranged planar-dipole pairs, which are also printed on the same double-layer substrate.

Dual-band transmission polarization converter based on planar-dipole pair frequency selective surface.

In this paper, we present a linear polarization converter in the reflective mode with near unity conversion efficiency. The converter is designed in an array form on the basis of a pair of orthogonally arranged three-dimensional split-loop resonators sharing a common terminal coaxial port and a continuous metallic ground slab. It converts the linearly polarized incident electromagnetic wave at resonance to its orthogonal counterpart upon the reflection mode. The conversion mechanism is explained by an equivalent circuit model, and the conversion efficiency can be tuned by changing the impedance of the terminal port. Such a scheme of the linear polarization converter has potential applications in microwave communications, remote sensing, and imaging.

A linear polarization converter with near unity efficiency in microwave regime

A new chiral spiral slot structure is proposed in THz region. The chiral properties of the new spiral configuration are examined on the basis of the cross polarization conversion. The linearly polarized wave can be converted completely into its cross-polarized wave in dual-band. A numerical study was carried out, followed by an explanation of the cross-polarization conversion mechanism in the structure proposed in this work. A strong chirality can be caused owing to the cross coupling between the magnetic field and incident electric field. These novel properties can lead to new possibilities and solution in many valuable applications, such as communication system, polarization-insensitive devices and 90° polarization rotator.

Cross polarization conversion based on a new chiral spiral slot structure in THz region

Optical activity and cross polarization conversion (CPC) of a rotated-arm-square chiral metamaterial (CMM) is reported in this work. Proposed CMM shows strong chirality owing to the cross coupling between the induced magnetic field and incident electric field of the applied electromagnetic wave. Mechanism of CPC functionality is explained based on the surface current distribution of CMM structure. Microwave experiment is performed to reveal the CPC utility of the proposed CMM. Among various designs on the CPC converters, possibility of near 99% efficiency is revealed in the proposed CMM.

Cross polarization converter formed by rotated-arm-square chiral metamaterial

Spatial beam compression of an electromagnetic wave is one of the fundamental techniques employed in microwaves and optics. As there are many ways to achieve this task using the combination of prisms and lenses, recent research suggests the parabolic gradient index photonic crystals (GRIN PC) for the design of spatial beam compressor owing to its functionalities. However, the fabrication of a graded media with the parabolic proflle is a di-cult challenge in practical realization. As an alternative, present work attempts this problem with respect to the triangular gradient index proflle. The performance and aspects of the beam compression are investigated experimentally using the pillar type GRIN PC at the microwave length-scales. The utility of the device for an efiective beam injection to the photonic-waveguide component is further demonstrated experimentally.

/pdf/spatial-beam-compression-and-effective-beam-injection-using-z3grv7fwgv.pdf

Spatial Beam Compression and Effective Beam Injection Using Triangular Gradient Index Profile Photonic Crystals

The field confinement aspect of a multilayer cavity resonator formed by a one-dimensional photonic crystal with prism wedge configuration is described in this paper. The prism wedge consists of alternating dielectric layers and is used for the construction of polygon multilayered structures with different symmetries like C4v-square and C6v-hexagon. Field confinement is studied by finding the resonant modes and quality factors (Q) of the proposed geometries. The computed Q factors for the two-dimensional geometries (the third dimension is taken to be infinity) are of the order of 103–107. On the other hand, for the finite height of the cavity, the estimated Q factor is found to be of the order of 104. An attempt has been taken to achieve the vertical confinement of light for a few of the resonant modes so that the proposed cavities may be implemented for microwave applications, especially in spectroscopic techniques.

Field confinement and quality factor of the multilayer cavity resonators

This paper investigates the near fleld focusing behavior corresponding to the hyperbolic dispersion regime at the second band of the square lattice photonic crystal (PC). Numerical studies reveal the in∞uence of the corner part negative refraction in the observed focusing efiect, though the major part of the refraction is divergent at this hyperbolic regime. It is further observed that the investigated dispersion shows the surface mode behavior when the efiective index of the PC slab is higher than the air medium. This aspect may be implemented for the excitation and transfer of near flelds for an evanescent wave microscopy.

Near Field Focusing Effect and Hyperbolic Dispersion in Dielectric Photonic Crystals

The use of microwave band gap structures for the non-destructive evaluation of material property is being probed in this paper. As a flrst step, we studied numerically, the appearance of a point defect mode within the band gap of a microwave band gap structure for the use as a tool to evaluate the dielectric constant of the material at the defect site. The simulations were carried out using the FEMLAB software. In a pure 10£10 square lattice constructed with a material of dielectric constant (") 5.5 (in the form of a right circular cylinder), a point defect is created by replacing one of the rods with a geometrically similar but with difierent dielectric constant material. The appearance of the defect mode is governed by the refractive index contrast (deflned as the ratio between the refractive index of the material at the defect site (nd) and the material of the lattice (nl). In this case, the refractive index contrast (nd=nl) was found to be between 0.85 and 1.28. Simulations were also done with the lattice material of dielectric constant 10 and the defect mode appeared for 1:18 < nd=nl < 0:84. For the contrast less than 1, defect creates the fundamental mode similar to TE01 mode whereas for the contrast greater than 1, next higher mode similar to TE11 appears. Once a defect mode appears, it moves towards lower frequency as the dielectric constant of the defect site is increased. In this paper, we propose to evaluate the dielectric constant of a material using the above procedure. This paper also proposes the construction of a novel frequency selector switch that has two line defects in a 10£20 square lattice structure constructed with material of dielectric constant 10.

https://www.piers.org/piersonline/pdf/Vol4No6Page631to634.pdf

N. Yogesh

Papers

Cross polarization converter formed by rotated-arm-square chiral metamaterial

Spatial Beam Compression and Effective Beam Injection Using Triangular Gradient Index Profile Photonic Crystals

Field confinement and quality factor of the multilayer cavity resonators

Near Field Focusing Effect and Hyperbolic Dispersion in Dielectric Photonic Crystals

Application of Defect Induced Microwave Band Gap Structure for Non-destructive Evaluation and the Construction of a Frequency Selector Switch