Polarization-selective Coupling Research Articles

A Monolayer Dually Polarized High-Order Space Harmonic Leaky-Wave SIW Antennas With Fixed and Scanning Beam Capability

In this work, the concept of high-order space harmonics (HSHs) applied to a hybrid form of nonradiative dielectric (NRD) waveguide and substrate-integrated square waveguide (SIW) involving both TE10 and TE01 modes is investigated with aim to develop multi-functional dually polarized leaky-wave antennas (DP-LWAs). A polarization-selective coupling (PSC) mechanism is used to guide the two orthogonally oriented modes in the hybrid structure to achieve a polarization diversity feature. The polarization effect on unit-cell geometrical structures is examined for different characteristics of LWA such as propagation constant behavior, leakage ratio, and scanning range variation. In addition, we demonstrate how the extrinsic characteristics of HSHs in a one-dimensional periodic LWA and its unit-cell analysis can provide design flexibility through two case studies. In the first case of demonstration, we show a dually polarized multi-beam LWA design with wide scanning capability in which we use both even and odd HSHs of n-1,-2). The second antenna design case is concerned with a DP-LWA having the capability of fixed and scanning beams operation by using a combinatory set of PSC and four HSHs of n-1,-2,-3,-4. Two DP-LWA prototypes are demonstrated as proofs of concept, and the obtained experimental results show a very good agreement with their simulation and analysis counterparts.

Theoretical investigation of surface plasmonic polariton-based electro-optical modulator with low polarization dependence

Plasmonic modulators essentially support only transverse magnetic mode. A plasmonic modulator consisting of hybrid plasmonic waveguides in both vertical and horizontal directions is proposed to reduce the polarization-dependence. In a combined waveguide, surface plasmon polariton (SPP) modes polarized in the vertical and horizontal directions exist in the correspondingly oriented hybrid plasmonic waveguide. The light modulation is investigated by tuning the carrier density of the accumulated layer where occurs at the dielectric-ITO interfaces. In an optimized structure, a ΔIER (a difference between the extinction ratios of two polarization modes) under 0.01 dB/μm is demonstrated at ITO ENZ-state by simulation. The energy flux clearly shows the polarization-selective coupling between the polarized guided modes in the feeding silicon waveguide and those in the combined waveguide. Coupling efficiency above 74% is obtained for both polarizations. The proposed plasmonic combined modulator has a potential application in guiding and processing of light from a fiber with a random polarization state.

A Dually Polarized Six-Port Junction Based on Polarization-Selective Coupling for Polarization-Inclusive Remote Sensing

Enabling the dual-polarization feature in microwave components is proposed and demonstrated based on polarization-selective coupling (PSC). The PSC structure consists of two waveguides which are fused together in parallel. When one of the waveguides is excited by dually polarized wave, the vertical polarization remains in the excited waveguide while the horizontal polarization is fully coupled to the other one. The six-port junction is the fundamental module for developing interferometric transceivers. This junction is presented in this paper in a new form. In the new form, the six-port junction applies its functionality on two orthogonal polarizations simultaneously. This allows the implementation of a polarization-inclusive remote sensing application. The dually polarized six-port junction is invented by adding the dually polarized feature to each of its constituent components, namely, the power dividers, the hybrid 3-dB couplers, and the circularly bent phase shifters. These components are analytically studied and reinvented to be dually polarized using the aforementioned PSC. The dually polarized six-port junction is prototyped and measured. The simulated and measured results are found to be in a good agreement.

Modeling Effective Anisotropy of Substrate Integrated Dielectric Waveguides for Polarization Diversity

A field-based analytical procedure is presented and developed for accurate modeling of the effective parameters of substrate integrated nonradiative dielectric (SINRD) waveguide. This modeling strategy is based on the eigenmode analysis of a dielectric substrate material perforated with air holes and enclosed between two horizontal metallic plates. From this model, it is found that the resulting effective dielectric constant of the periodic geometry of the SINRD waveguide is dependent on the direction of an electric field vector with respect to the material periodicity. In other words, the guiding parts of the SINRD waveguides act as anisotropic materials. A full demonstration for the proposed analysis is supported with simulation results using a full-wave finite-element method. The proposed model provides a scheme for the isotropization of anisotropic substrates. This is in addition to clarifying the exact regimes of operation inside the SINRD waveguide based on the guiding mechanism. Validation examples are studied based on polarization-selective coupling and effective polarization-independent coupling. A prototype is realized and measured where good agreement is achieved between simulation and measurement results.

Theory of Polarization-Selective Coupling and Its Application to Design of Planar Orthomode Transducers

With the rapid and continuous development of new generations of wireless technologies and networks, exploring the underutilized millimeter-wave (mm-wave) band becomes inescapable. Polarization diversity has been an essential factor in the performance and capacity enhancement of various wireless systems including cellular networks. Accordingly, the design and development of dual-polarized antenna feeding structures in the mm-wave band is a must. In this paper, a compact wideband orthomode transducer design in the Ka-band is proposed and explored. The proposed architecture and design are based on a forward mode polarization-selective coupling strategy between two unconventional waveguides. These special waveguides are a combination between two types of guiding structure, namely, nonradiative dielectric waveguide and substrate-integrated waveguide. Polarization-selective coupling can be achieved in these structures due to different mechanisms by which orthogonally oriented modes are guided. Theoretical coupling levels of 0 dB are possible in the designed structure. Analytical analysis and design steps are given in detail. This analysis facilitates a complete control on the single-mode operation for each polarization. This control, besides the structure being planar, represents the main advantages of the proposed structure. Finally, a prototype is implemented and measured where an excellent agreement is achieved with the simulation results.

Black phosphorus integrated tilted fiber grating for ultrasensitive heavy metal sensing

We report the sub-parts-per-billion (sub-ppb) level detection of lead using black phosphorus (BP) integrated tilted fiber grating (BP-TFG) configuration where the light-matter interaction is enhanced. We synthesized BP nanosheets by using a liquid-phase exfoliation method and developed an in-situ layer-by-layer (i-LbL) technique for BP deposition. These approaches secured high-quality BP coating on specific fiber cylindrical surface with strong adhesion as well as a prospective thickness control. By taking advantage of i-LbL deposition, the unique optical tunable features including coating thickness-dependent polarization and polarization-selective coupling have been experimentally observed. Furthermore, the BP-TFG was exploited as the first BP-fiber optic chemical sensor for heavy metal Pb2+ ions detection, demonstrating significant performance of ultrahigh sensitivity up to 0.5×10−3dB/ppb, lower limit of detection down to 0.25ppb, and wider concentration range from 0.1ppb to 1.5×107ppb. We believe that this BP-fiber optic architecture opens the path as an optical platform for superior chemical sensing and biomedical applications.

Polarization-Selective Out-Coupling of Whispering-Gallery Modes

Whispering gallery mode (WGM) resonators are an important building block for linear, nonlinear and quantum optical experiments. In such experiments, independent control of coupling rates to different modes can lead to improved conversion efficiencies and greater flexibility in generation of non-classical states based on parametric down conversion. In this work, we introduce a scheme which enables selective out-coupling of WGMs belonging to a specific polarization family, while the orthogonally polarized modes remain largely unperturbed. Our technique utilizes material birefringence in both the resonator and coupler such that a negative (positive) birefringence allows selective coupling to TE (TM) polarized WGMs. We formulate a new coupling condition suitable for describing the case where the refractive indices of the resonator and the coupler are almost the same, from which we derive the criterion for polarization-selective coupling. We experimentally demonstrate our proposed method using a lithium niobate disk resonator coupled to a lithium niobate prism, where we show a 22dB suppression of coupling to TM modes relative to TE modes.

Asymmetric directional couplers based on silicon nanophotonic waveguides and applications

Directional couplers (DCs) have been playing an important role as a basic element for realizing power exchange. Previously most work was focused on symmetric DCs and little work was reported for asymmetric directional couplers (ADCs). In recently years, silicon nanophotonic waveguides with ultra-high index contrast and ultra-small cross section have been developed very well and it has been shown that ADCs based on silicon-oninsulator (SOI) nanophotonic waveguides have some unique ability for polarization-selective coupling as well as mode-selective coupling, which are respectively very important for polarization-related systems and modedivision-mulitplexing systems. In this paper, a review is given for the recent progresses on silicon-based ADCs and the applications for power splitting, polarization beam splitting, as well as mode conversion/(de)multiplexing.

Polarization-selective coupling to long-range surface plasmon polariton waveguides.

We demonstrate polarization-selective coupling from an optical fiber to long-range surface plasmon polariton waveguide modes using plasmonic antenna arrays. The arrays allow the sorting of two distinct (not necessarily orthogonal) polarizations to counter-propagating waveguide modes. The polarization-selective behavior of the devices is described by a compact formalism based on Stokes vectors that offers a clear graphical representation of the response. We experimentally observe polarization-controlled switching and unidirectional coupling with extinction ratios greater than 30 dB and coupling efficiencies comparable to those of a conventional grating coupler.

Low Loss, High Extinction Ration and Ultra-Compact Plasmonic Polarization Beam Splitter

In this letter, an ultra-compact plasmonic polarization beam splitter (PBS) is proposed and investigated by numerical simulations using the finite element method. The PBS is based on a three-core plasmonic directional coupler, which uses a long range surface plasmon polaritons waveguide as the middle waveguide to achieve polarization selective coupling. The calculations show that with proper structural parameters, the PBS with low insertion losses of 0.17 and 0.25 dB for TE and TM polarizations, respectively, and high extinction ratios of 20.17 and 19.83 dB for TE and TM polarizations, respectively, can be realized at a telecommunication wavelength of 1550 nm. Furthermore, an insertion loss and an extinction ratio > 14 dB can be realized across the entire C-band for both TE and TM polarizations.

Plasmonic waveguides with low polarization dependence

Plasmonic waveguides essentially support only transverse magnetic modes. A novel plasmonic waveguide consisting of hybrid plasmonic waveguides in both vertical and horizontal directions is proposed to reduce the polarization dependence. In a combined waveguide, surface plasmon polariton (SPP) modes polarized in both vertical and horizontal directions exist in the correspondingly oriented hybrid plasmonic waveguide. In an optimized structure, anticrossing mode coupling is observed between these two SPP modes with a low birefringence by finite-difference time-domain simulation. The energy flux clearly shows the polarization-selective coupling between the polarized guided modes in the feeding silicon waveguide and those in the combined waveguide. Coupling efficiency above 65% is obtained for both polarizations. The proposed plasmonic combined waveguide has a potential application in guiding and processing of light from a fiber with a random polarization state.

A Novel Polarization Splitter Based on the Photonic Crystal Fiber With Nonidentical Dual Cores

A novel polarization splitter based on photonic crystal fibers (PCFs) with two nonidentical cores is proposed. The two highly birefringent cores are vertically arranged to obtain polarization selective coupling. The horizontal polarization exchanges its energy between the two cores. However, the vertical polarization shows little coupling between the two cores. This is achieved in single-material glass waveguides for the first time to our knowledge. The PCF-based polarization splitter exhibits many advantages such as shorter length, high extinction ratio, and wide bandwidth over its counterparts.