Transverse Magnetic Polarization Research Articles

Ultrabroadband and independent polarization of optical amplification with InGaAs-based indium-rich cluster quantum-confined structure

This Letter reports polarization-independent optical amplification over an ultrabroad spectral range by semiconductor optical amplifiers. The technique uses an InGaAs-based indium-rich cluster (IRC) quantum-confined structure as the active medium and obtains comparable optical gain for both transverse electric (TE) and transverse magnetic (TM) polarization modes in the spectral ranges of 905–1005 and 905–970 nm, respectively. The device thus provides independent optical amplification for TE and TM polarizations over a common bandwidth of 65 nm. The difference between the amplified intensities of TE and TM modes is <0.5 dB. These results are attributed to the special emission mechanism of the IRC quantum-confined structure, which differs from that of conventional quantum wells or quantum dots. A preliminary analysis of this mechanism is provided.

Polarization Selectivity of the Thin-Metal-Film Plasmon-Assisted Fiber-Optic Polarizer.

The interaction between light and metallic nanostructures leads to many impressive achievements and has a wide range of applications. The thin-metal-film plasmon-assisted fiber-optic polarizer is one of the essential applications. However, the polarization mechanism and the transmitted polarization of the plasmon-assisted polarizer have given rise to controversy over the past decade. Which of the polarizations is preferentially transmitted through the polarizer? The transverse electric polarization or the transverse magnetic polarization? Here, special emphasis is placed upon the polarization mechanism and the transmitted polarization of thin-metal-film plasmon-assisted fiber polarizers. We first investigate the polarization mechanism of the polarizers theoretically and numerically. Furthermore, a novel approach is proposed to demonstrate the transmitted polarization in the plasmon-assisted fiber polarizers experimentally. We demonstrate that the polarization mechanism is based on the polarization selective absorption of the metallic material, and the transverse electric polarization is the only transmitted polarization of the metallic plasmon-assisted polarizer. Moreover, the plasmon-assisted polarizer can offer a high polarization extinction ratio (33.1 dB) and a low insertion loss (1.1 dB) at room temperature and have excellent temperature stability in the range of -48 to 82 °C. Experimental results agree well with our theoretical and numerical analyses. The findings clarify the confusion about the polarization mechanism and the transmitted polarization of metallic plasmon-assisted fiber polarizers over the past decade, providing new ground for the exploration of polarization-sensitive optical systems, with good potential applications in the fields of optical sensors, plasmonic lasers, coherent optical communications, and biosensor systems.

Fabrication of an infrared wire-grid polarizer via anisotropical Si etching in KOH solution

An infrared wire-grid polarizer was fabricated using two-beam interference lithography, anisotropical etching of Si in KOH solution, and thermal evaporation of Al. Consequently, an infrared wire-grid polarizer with a 1-µm-pitch and 195-nm-thick Al grating could be fabricated on the Si grating. The transmittance of transverse magnetic polarization was greater than 48% at 10-µm wavelength, and the extinction ratio was over 22 dB at this wavelength. This polarizer can be fabricated at a much lower cost and using simpler fabrication processes compared to those for conventional infrared polarizers fabricated using dry etching.

Wide-Band/Angle Blazed Dual-Mode Metallic Groove Gratings

A simple approach to acquire wide-band/angle blazing operation in 1-D metallic gratings is investigated by means of mode-matching and equivalent circuit analysis. The gratings are single-groove perfectly conducting gratings that support two propagating guided modes (opposed to typical single-mode cases). It is shown under what conditions one can achieve blazing over a wide range of frequencies and angles. Most importantly, it is identified what governs blazing, in particular the true matching condition that needs to be satisfied, and how the structures' multiple resonances play role in achieving such matching and tailoring the bandwidth. Parameters of the proposed equivalent circuit model for the case of the transverse magnetic (TM) polarization are analytically derived. The accuracy of the models is verified through a comparison against the results of full-wave simulations. The procedure to achieve wide-band/angle blazing performance is delineated, and the design parameters are explicitly given. It is shown that this structure can strongly transfer the power of the TM polarized incident wave to the -1st diffraction order with a fractional bandwidth of ≈50% at working frequency $f_{0}=10$ GHz and for -10 dB specular reflection loss, thus realizing a broadband structure. From the circuit model, an insightful discussion is presented at various mechanisms at play when Bragg and off-Bragg blazing occurs and fully justifies the behavior of the device. The proposed technique opens up new vistas in a wide range of applications, such as spectroscopy, Littrow cavities, beam splitters, refractive index biosensors, and frequency scanned antenna reflectors.

Rapid large-scale fabrication of multipart unit cell metasurfaces.

Periodic diffractive elements known as metasurfaces constitute platform technology whereby exceptional optical properties, not attainable by conventional means, are attained. Generally, with increasing unit-cell complexity, there emerges a wider design space and bolstered functional capability. Advanced devices deploying elaborate unit cells are typically generated by electron-beam patterning which is a tedious, slow process not suitable for large surfaces and quick turnaround. Ameliorating this condition, we present a novel route towards facile fabrication of complex periodic metasurfaces based on sequential exposures by laser interference lithography. Our method is fast, cost-effective, and can be applied to large surface areas. It is enabled by precise control over periodicity and exposure energy. With it we have successfully patterned and fabricated one-dimensional (1D) and two-dimensional (2D) multipart unit cell devices as demonstrated here. Thus, zero-order transmission spectra of an etched four-part 1D grating device are simulated and measured for both transverse-electric (TE) and transverse-magnetic (TM) polarization states of normally incident light. We confirm non-resonant wideband antireflection (∼800 nm) for TM-polarized light and resonance response for TE-polarized light in the near-IR band spanning 1400-2200 nm in a ∼100 mm2 device. Furthermore, it is shown that this method of fabrication can be implemented not only to pattern periodic symmetric/asymmetric designs but also to realize non-periodic metasurfaces. The method will be useful in production of large-area photonic devices in the realm of nanophotonics and microphotonics.

Design and simulation of a compact and ultra-wideband polarization beam splitter based on sub-wavelength grating multimode interference coupler

A compact and ultra-wideband multimode interferometer (MMI)-based polarization beam splitter (PBS) is designed in a silicon-on-insulator (SOI) platform. A sub-wavelength grating (SWG) structure is employed in the multimode region to reduce the overall length of the structure and also increase its operating bandwidth. Instead of using the beat-length difference to separate the transverse electric (TE) and transverse magnetic (TM) polarized waves, the TM waves are directly coupled to the output bar port through an interconnecting waveguide, while the TE polarized waves are transmitted to the cross port by the self-imaging process. This substantially reduces the length of the PBS and the overall footprint can be as small as 4.8 × 21 µm2. The proposed device exhibits the extinction ratio of more than 15 dB in a 250 nm wavelength range (1.38–1.63 µm) and more than 12 dB in the 350 nm wavelength range (1.3–1.65 µm) for the TE and TM polarizations, respectively. In addition, the insertion loss remains below 1.2 dB for both the TE and TM polarization in a broad wavelength range from 1.38 to 1.54 µm. The proposed PBS can be fabricated by a single-step etching process on an SOI wafer. Moreover, our simulations show the robustness of the PBS performance to the fabrication errors’.

Perturbation of the scattering resonances of an open cavity by small particles. Part I: the transverse magnetic polarization case

This paper aims at providing a small-volume expansion framework for the scattering resonances of an open cavity perturbed by small particles. The shift of the scattering resonances induced by the small particles is derived without neglecting the radiation effect. The formula holds for arbitrary-shaped particles. It shows a strong enhancement in the scattering resonance shift in the case of subwavelength particles with dipole resonances. The formula is used to image small particles located near the boundary of an open resonator which admits whispering-gallery modes. Numerical examples of interest for applications are presented.

Analysis, Design, and Implementation of a New Extremely Ultrathin 2-D-Isotropic Flexible Energy Harvester Using Symmetric Patch FSS

Electromagnetic (EM) energy exists far and wide in the environment and can be harnessed and transferred to the desired load(s). The researchers mostly designed and implemented the planar metasurface energy harvester (MEH) offering a restricted look-angle. In this article, we propose an extremely ultrathin 2-D-isotropic flexible MEH using multipolarized patch frequency selective surface. This MEH, which has a curved shape, enjoys a relatively constant performance over a huge range of oblique incident waves. The final structure can be prepared by a small slice of a cylinder. A classic model inspired from the dipole antenna concept is used for impedance matching. Theoretical analyses, design, and fabrication of the structure are presented using a deep subwavelength PCB substrate having a thickness of $\sim 0.004~\lambda _{0}$ . EM energy harvesting is analyzed with an equivalent circuit model. The experimental results are acceptably in agreement with the simulation results. The design can be scaled to different RF bands; however, to provide the required energy for Internet-of-Things (IoT) instruments, we have used WiFi as a crowded frequency band. The simulation efficiency of the flat style extremely ultrathin MEH (EMEH) for normal incidence (at 5.81 GHz) and 60° oblique angle incidence with transverse magnetic (TM) and transverse electric (TE) polarizations are 87.35%, 93.26%, and 64.42%, respectively. In addition, half power bandwidth (HPBW) for these situations is 6.97%, 8.86%, and 5.61%, respectively.

Ultra-broadband and broad-angle absorbers with transition metal dichalcogenide monolayer using Thue–Morse quasi-photonic crystals

Because of their desirable optical absorption responses, two-dimensional transition metal dichalcogenides have potential applications in optoelectronic devices. However, whether optoelectronic devices based on these materials are capable of absorbing light in a wide optical range is debatable. In this paper, we suggest using Thue–Morse quasi-photonic crystals based on Si3N4, SiO2 layers and transition metal dichalcogenides monolayers for optoelectronic devices. Absorption was calculated on the basis of the transfer matrix method. Optical absorption as large as 90% in a broadband wavelength range was achieved for both transverse-electric and transverse-magnetic polarizations. Our results can be useful for designing photonic devices and perfect absorbers with high absorption efficiencies.

Broadband Plasmonic Nanopolarizer Based on Different Surface Plasmon Resonance Modes in a Silver Nanorod

Conventional polarizers including sheet, wire-grid, prism, and Brewster-angle type polarizers are not easily integrated with photonic circuits. Polarizing elements on the nanoscale are indispensable for integrated all-optical nanophotonic devices. Here, we propose a plasmonic nanopolarizer based on a silver nanorod. The polarization characteristics result from the excitation of different resonance modes of localized surface plasmons (LSPs) at different wavelengths. Furthermore, the polarization characteristics in near field regions have been demonstrated by the electric field distribution of the nanorod based on finite-difference time-domain (FDTD) simulation, indicating a strong local resonant cavity with a standing wave mode for transverse electric (TE) polarization and weak electric fields distributed for transverse magnetic (TM) polarization. The nanopolarizer can efficiently work in the near field region, exhibiting a nanopolarization effect. In addition, very high extinction ratios and extremely low insertion losses can be achieved. Particularly, the nanopolarizer can work in a broadband from visible to near-infrared wavelengths, which can be tuned by changing the aspect ratio of the nanorod. The plasmonic nanopolarizer is a promising candidate for potential applications in the integration of nanophotonic devices and circuits.

Full electromagnetic Green's dyadic of spherically symmetric open optical systems and elimination of static modes from the resonant-state expansion

A general analytic form of the full 6x6 dyadic Green's function of a spherically symmetric open optical system is presented, with an explicit solution provided for a homogeneous sphere in vacuum. Different spectral representations of the Green's function are derived using the Mittag-Leffler theorem, and their convergence to the exact solution is analyzed, allowing us to select optimal representations. Based on them, more efficient versions of the resonant-state expansion (RSE) are formulated, with a particular focus on the static mode contribution, including versions of the RSE with a complete elimination of static modes. These general versions of the RSE, applicable to non-spherical optical systems, are verified and illustrated on exactly solvable examples of a dielectric sphere in vacuum with perturbations of its size and refractive index, demonstrating the same level of convergence to the exact solution for both transverse electric and transverse magnetic polarizations.

Efficient asymmetric transmission for wide incidence angles using bi-layered chiral metasurface

An ultrathin bi-layered chiral metasurface manifesting asymmetric transmission for linear polarization is designed and experimentally demonstrated. By breaking certain symmetries of the chiral structure, the proposed design is enabled to convert a y-polarized wave into an x-polarized upon transmission in the forward direction with transmission coefficient 0.95 while an x-polarized wave is completely reflected. On the other hand, in the backward direction, an x-polarized wave is transformed into y-polarized with transmission coefficient magnitude of 0.95 while a y-polarized wave is reflected. More importantly, the proposed structure maintains asymmetric transmission characteristics for oblique incidence up to 60º both for transverse electric and transverse magnetic polarizations. It is shown that unlike linear polarization, the proposed metasurface shows no propagation direction-dependent characteristics for circular polarization. The ultrathin thickness (0.026λ at 10 GHz), efficiency and high angular stability qualifies the proposed metasurface to be a promising candidate for integration with numerous microwave devices.

Enhanced third harmonic generation from sinusoidal graphene gratings

We investigate the nonlinear optical third harmonic generation of sinusoidal curved graphene which is placed on the dielectric substrate. Under transverse magnetic polarization, the third harmonic generation (THG) from graphene is dramatically enhanced at fundamental-mode and several higher-order modes of surface plasmon of graphene. The enhancement factor of THG is up to106 compared to that from graphene on a planar dielectric. We study in detail THG intensity affected by the Fermi level of graphene, grating period and amplitude, and the angle of incidence of light. The tunable and enhanced THG response at multiple wavelengths show that the sinusoidal-shaped graphene grating has potential applications for graphene based broadband nonlinear photonics.

Fast optimal design of optical components using the cultural algorithm.

Design of the guided-mode resonance (GMR) grating filter, as one of the most important optical components, using the cultural algorithm (CA) is presented, for the first time. CA is an evolutionary algorithm (EA) which is easy-to-implement, flexible, inspired by the human cultural evolution, upon using the domain knowledge for reducing the search space as a metaheuristic optimization method. Reflection spectra of the designed GMR filter based on the CA is in good agreement with the previous simulation results. CA has both acceptable accuracy and enough high speed to optimize the complicated structures; therefore, a novel double-line asymmetrical transmitter (DLAT) is introduced and optimized as a complex grating-based optical component using the mentioned algorithm. The results show the transmittance at two different communication wavelengths (1.5039 and 1.6113 µm) using the combination of binary diffraction grating and customized photonic crystal (PhC) structure. Also, the DLAT shows the characteristics of a perfect transverse magnetic (TM) polarizer. Furthermore, we demonstrated the Talbot effect at the DLAT output which is so applicable in the optical usage, especially for the integrated optics.

An Ultrathin and Ultrawideband Metamaterial Absorber and an Equivalent-Circuit Parameter Retrieval Method

In this article, we propose an ultrathin and ultrawideband metamaterial (MTM) absorber based on periodically arranged metallic square spirals. The design, characterization, and measurement of the proposal are presented as its equivalent circuit. The lumped elements of the equivalent circuit are extracted using a proposed algorithm based on the least-square method, which presents a straightforward and promising approach and shows a good matching with the electromagnetic simulation. The unit cell of the proposed structure has the square spiral mounted on an FR-4 substrate in front of a conductive plate. The simulated results show an absorptivity of more than 90% from 11.4 to 20.0 GHz, covering the $Ku$ -band for transverse magnetic (TM) and transverse electric (TE) polarizations, and this broadband feature is confirmed by the experimental measurement. Furthermore, the proposed MTM absorber is $\lambda /16.4$ in thickness at the lowest frequency of absorption. The proposed MTM has proper response under oblique incidence from 0° to 50° and shows great performance with regard to the absorbers previously presented in the literature.

Numerical design of a high-performance polarization beam splitter assisted by composite subwavelength gratings.

We report a compact polarization beam splitter (PBS) consisting of slotted waveguides assisted by composite subwavelength gratings (CSWGs) on a silicon-on-insulator platform. By tailoring the material anisotropy of the CSWGs, coupling strengths of transverse-electric (TE) and transverse-magnetic (TM) polarization coupling strengths are respectively suppressed and enhanced significantly, achieving concurrent improvements in polarization extinction ratio (PER), device footprint, and working bandwidth (BW) compared with purely slotted waveguides. Differing in construction from mono-material SWGs, the CSWGs comprise silicon strips covered with a silicon dioxide (SiO2) layer of the same thickness as the slot layer of the slotted waveguides, simplifying the fabrication process and further reducing device length. Numerical simulations show significant improvement in PERTM from about 15 dB for the purely slotted waveguides to 28 dB for the proposed design, with a 40% reduction in device length at a wavelength of λ = 1550 nm. Within a BW of ∼60 nm, the proposed PBS achieves PERTM ∼25 dB, PERTE >15 dB, and insertion loss (ILs) <0.1 dB for TE and TM modes. Fabrication tolerance investigations are also described and discussed. The proposed idea paves the way for simultaneous improvements in PER, footprint, and working BW for PBSs comprising a variety of coupled-waveguide systems.

Scattering of a Gaussian beam by an anisotropic-coated eccentric conducting circular cylinder

AbstractA solution to the problem of Gaussian beam scattering by a circular perfect electric conductor coated with eccentrically anisotropic media is presented. The incident Gaussian beam source is expanded as an approximate expression in the simple form with Taylor's series. The transmitted field in the anisotropically coated region is expressed as an infinite summation of Eigen plane waves with different polar angles. The unknown coefficients of the scattered fields are obtained with the aid of the boundary conditions. The addition theorem for cylindrical functions is applied to transfer from the local coordinates to the global ones. The infinite series can be truncated under the prerequisite of achieving the solution convergence. Only the case of transverse-electric polarization is discussed. The similar formulation of transverse-magnetic polarization can be obtained by adopting a similar method. Some numerical results are presented and discussed. The result is in agreement with that available as expected when the eccentric geometry comes to the concentric one.

Asymmetric light transmission based on a 1D triangular metal grating

Here, we present a 1D isosceles triangle silver grating on the dielectric substrate. The grating performs asymmetric light transmission (ALT) characteristics for the light with both transverse magnetic (TM) and transverse electric (TE) polarization states over a waveband in the vicinity of 1.55 µm. By checking the efficiency of each diffraction order and the distribution of the electromagnetic field, we found that the ALT characteristics originate from the high transmitted or reflected diffraction channels excited by forward and backward direction incidence. The grating shows the ALT characteristics in a waveband where incident wavelengths are less and more than the period, so that the grating may be a candidate for the wideband ALT devices. It is worth stressing that the contrast ratio (CR) at a specific wavelength can exceed more than 29 dB (the incident angle is 5.6897°; the incident wavelength is 1.7759 µm) under oblique incidence.

Dual-controlled broadband terahertz absorber based on graphene and Dirac semimetal.

We proposed a dual-controlled broadband terahertz (THz) absorber based on graphene and Dirac semimetal. Calculated results show that the absorptance over 90% is achieved in the frequency range of 4.79-8.99 THz for both transverse electric (TE) and transverse magnetic (TM) polarizations. Benefiting from the advantage of the dielectric constant of these materials varying with chemical doping or gate voltage, the simulation results exhibit that the absorbance bandwidth can be controlled independently or jointly by varying the Fermi energy of the graphene or Dirac semimetal patterns instead of redesigning the absorbers. Impedance matching theory was introduced to analyze the absorption spectra changing with EF. The bandwidth and absorptivity of the proposed absorber are almost independent of changing the incident angle θ up to 35° and 40° for TE and TM modes, respectively. It works well even at a larger incident angle. Because of the symmetry of the structure, this designed absorber is polarization insensitive and almost the same absorptivity for both polarizations. Furthermore, the physical mechanisms were further disclosed by the electric field distributions. The proposed broadband and dual-controlled absorber may have potential applications in various fields of high-performance terahertz devices.

Dual-polarization Dirac cones in a simple 2D square lattice photonic crystal.

We report on dual-polarization Dirac cones in a simple square lattice two-dimensional (2D) photonic crystal (PC) based on transmission at accidental degeneracies centered at the $k = {0}$k=0 symmetry ($ \Gamma $Γ) point. Finite difference time domain simulations are used to identify the material and geometric parameters for Dirac-like dispersion. A configuration that produces a Dirac-like point for both transverse electric and transverse magnetic polarizations at the same frequency is presented. The PC dispersion shows the expected threefold degenerate linear branch crossings at the Dirac-like point. Full-field electromagnetic wave simulations exhibit some common behaviors of devices based on Dirac-like dispersion, such as cloaking and waveguiding. The configuration works for a considerable range of the parameter space, and thus is experimentally realizable with a wide range of materials.