Transverse Magnetic Polarization Research Articles

Tunable ultra-wideband graphene metasurface absorber: A mode merger design approach for terahertz applications

This paper presents a systematic approach for designing an ultra-wideband (UWB) absorber for terahertz (THz) applications. The metasurface consists of top patterned graphene (Gpat) and bottom continuous graphene (Gcont), each having a thickness of 0.335 nm and separated by a 3 μm thick silicon dioxide (SiO2) dielectric. Multiple absorbing modes have been generated by engraving rectangular, star-shaped, and circular ring slots on the top Gpat resonating at 3.22, 4.52, and 0.32 THz, respectively. A circular ring slot works as a coupling controller and helps to combine different slot resonances. The mode merger technique, along with the high plasmonic coupling between Gpat and Gcont controlled by Gcont help to attain an absorption bandwidth (BW) of 5.9 THz (193.44%) with absorptivity ≥ 90% ranging from 0.1 to 6 THz. The periodicity and thickness of the proposed polarization-insensitive metasurface are found to be λ0/300 and λ0/996.68, respectively, where λ0 is free space wavelength computed at 0.1 THz. Absorptivity ≥ 80% for incidence angle up to 60∘ under both transverse electric (TE) and transverse magnetic (TM) polarization has also been achieved. The absorber provides excellent frequency tunable characteristics over a UWB band and shows blue-shift with increased chemical potential (μc).

Casimir Effect Invalidates the Drude Model for Transverse Electric Evanescent Waves

We consider the Casimir pressure between two metallic plates and calculate the four contributions to it determined by the propagating and evanescent waves and by the transverse magnetic and transverse electric polarizations of the electromagnetic field. The range of interplate separations is considered where nearly the whole pressure has its origin in the electromagnetic response of conduction electrons. In the Casimir physics, this response is described either by the dissipative Drude model resulting in contradictions with the measurement data or by the experimentally consistent but dissipationless plasma model. It is shown that the total transverse magnetic contribution to the Casimir pressure due to both the propagating and evanescent waves and the transverse electric contribution due to only the propagating waves, computed by means of the Drude model, correlate well with the corresponding results obtained using the plasma model. We conclude that the disagreement between the theoretical predictions obtained using the Drude model and precision measurements of the Casimir force is not caused by the account of dissipation in itself, but arises from an incorrect description of the response of metals to the low-frequency transverse electric evanescent waves by this model. It is demonstrated that the Drude model has no supporting experimental evidence in the range of transverse electric evanescent waves, so that the above conclusion is consistent with all available information. The alternative test of the Drude model for the transverse electric evanescent waves suggested in the framework of classical electrodynamics is discussed.

Anomalous polarization-sensitive Fabry-Perot resonance in a one-dimensional photonic crystal containing an all-dielectric metamaterial defect.

Owing to polarization-independent property of propagating phases inside isotropic dielectric layers, Fabry-Perot resonances in metal-dielectric-metal sandwich structures and one-dimensional (1-D) photonic crystals (PhCs) with isotropic dielectric defects are polarization-insensitive. Herein, we introduce an all-dielectric elliptical metamaterial (EMM) defect into a 1-D PhC to realize an anomalous polarization-sensitive Fabry-Perot resonance empowered by the polarization-sensitive property of the propagating phase inside the all-dielectric EMM layer. The wavelength difference of the Fabry-Perot resonance between transverse magnetic and transverse electric polarizations is larger than 100 nm at the incident angle of 45 degrees. Enabled by the polarization-sensitive property of the Fabry-Perot resonance, high-performance polarization selectivity can be achieved in a broad angle range. Our work offers a viable recipe, well within the reach of current fabrication technique, to explore polarization-dependent physical phenomena and devices.

Wideband ultrathin and polarization insensitive metamaterial absorber for Ku-band applications

In this paper, wideband, and ultrathin metamaterial absorber is proposed, analyzed and fabricated for Ku-band applications. The reported absorber has a nearly perfect absorptivity above 90% covering the entire Ku band (12–20 GHz) at normal incidence for both transverse electric and transverse magnetic polarization. This is due to the supported electric and magnetic resonances simultaneously. Consequently, the effective permittivity and permeability can be designed to obtain impedance matching with free space. This leads to the absorption of the entire incident energy in the metamaterial absorber. The suggested structure also shows a good absorption response (above 80%) under oblique incidence (from 0 to 50°). Therefore, the proposed absorber represents a good potential for Ku-band applications.

Design of an ultra-wideband solar absorber based on tungsten

A solar absorber based on tungsten with an ultra-wide wavelength band is investigated numerically using the finite-difference time–domain method. The designed structure consists of a cross-shaped resonator on top of the absorber and a metal thin film on the bottom that are separated by an intermediate dielectric layer. The absorber demonstrates continuous high absorptivity (>90%) over the 514–1945 nm wavelength range, and the average absorptivity ranges up to 92.36% within the 200–2000 nm range. The excitation of propagating surface plasmon resonance (SPR) and localized SPR in combination with Fabry–Pérot resonance leads to the observed wideband absorption. We also demonstrate that the proposed absorber is insensitive to both transverse electric and transverse magnetic polarizations and study its absorptive performance at larger angles of incidence. The effects of the structural parameters and of different dielectric layer materials on the absorption performance have also been investigated. Furthermore, we explain the absorption mechanism using a power flow plot and impedance matching. The proposed absorber has promising prospects for applications, including solar cells, solar energy harvesting, and thermal emitters.

Design of single‐layer bandstop fractal frequency selective surface based on WLAN applications

AbstractIn this letter, we present a new frequency selective surface (FSS) for shielding 2.4–2.5 and 4.98–5.825 GHz wireless local area network (WLAN) bands. This FSS structure is based on the traditional Sierpinski octagon and we improve it. Compared with the traditional structure, the improved one has a smaller element size and better angular stability. The design is realized on float glass with a relative permittivity () of 8, and the unit cell size is 0.1152λ0 × 0.1152λ0 (λ0 is the free space wavelength at the first resonant frequency). Wide rejection bandwidths (−10 dB) of 910 and 1630 MHz are obtained at 2.4–2.5 and 4.98–5.825 GHz, respectively. The surface current distribution and the equivalent circuit model are illustrated to explain the resonance behavior of the proposed FSS. Furthermore, this FSS exhibits stable frequency response to incident angles of 0°–80° under transverse electric and transverse magnetic polarizations. Finally, this FSS structure was fabricated and measured. The measured results demonstrate that this FSS structure has good performance in WLAN applications.

CPW-fed dual-element metamaterial inspired multiband antenna using simple FSS for gain enhancement

This article presents a dual-element metamaterial-inspired co-planar waveguide (CPW) fed elliptical antenna using a simple compact frequency selective surface (FSS) for multiband wireless applications. The designed antenna is fabricated on a cheap FR-4 substrate (εr = 4.4) with 40 × 40×1.6 mm3 dimensions. Dual complementary split ring resonators (CSRRs) loaded in the CPW ground create multiband characteristics, which are analyzed using the quasi-static design equations and the ANSYS HFSS EM simulator. FSS has been proposed as a reflector for the antenna to increase its gain. The FSS unit cell's angular stability has been analyzed using transverse electric (TE) and transverse magnetic (TM) polarization, and it has been determined to be 60°. The FSS integrated antenna offers measured bandwidths of 2.67 – 3.38 GHz (23.66 %), 3.77 – 4.17 GHz (10.25%), 4.91 – 5.93 GHz (19.61 %), and 7.28 – 8.93 GHz (20.24 %). The FSS integrated antenna shows nearly omnidirectional radiation patterns in all resonating bands with the highest gain of 9.72 dBi and measured radiation efficiency greater than 91 % in all the bands. The reported 'antenna with FSS' is appropriate for multiband wireless technologies as it covers IEEE 802.16 WiMAX, n77 5G NR, 5G Wi-Fi, WLAN, ISM and satellite spectrums.

A functionality switchable meta-device: from perfect reflection to perfect absorption

Tunable meta-devices trigger immense interest in many applications like biosensing, thermal camouflage, radiative cooling, thermal emitting, infrared imaging, and energy harvesting. This paper presents a polarization-independent broadband tunable absorbing and reflecting meta-device using a phase change material Germanium-Antimony-Tellurium (GST). The proposed design manifests high absorptivity >80% over a broadband range of wavelength spanning the mid-IR regime. Furthermore, by changing the phase of GST material from crystalline to amorphous with the help of external stimuli, the absorbance of the device was reduced to almost zero in the range from 4 μm to 12 μm. To previse the angular constancy of the meta-absorber, the absorptivity was scrutinized under different incidence angles in both transverse magnetic (TM) and transverse electric (TE) polarizations which manifested the robustness of the proposed meta-absorber. As a result, the proposed absorber has tunable broadband absorbance and angular stability, which proclaim great potential in applications such as thermal camouflage, radiation detection, thermal emitter, and stealth technology, etc.

Miniaturization of a Fully Metallic Bandpass Frequency Selective Surface for Millimeter-Wave Band Applications

This article presents a miniaturized all-metallic bandpass frequency selective surface (FSS) for millimeter-wave (mmWave) applications. The designed FSS is realized as a slot-type element that can be easily incorporated into all-metallic device architectures. The miniaturization is achieved by a convoluted or meander slot structure, i.e., a miniaturization technique borrowed from conventional substrate-based FSS design. It is demonstrated that the proposed FSS element provides a stable and wide bandpass performance from 24.9 to 31.4 GHz for both the transverse electric (TE) and the transverse magnetic (TM) polarizations at the broadside direction ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\theta = 0^{\circ }$</tex-math></inline-formula> ). Adequate performance is maintained at oblique incidence angles up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\theta = \pm \,45^{\circ }$</tex-math></inline-formula> . A 25 × 25-elements FSS array prototype has been manufactured using the cost-effective chemical etching technique and experimentally characterized utilizing a free-space measurement setup. The results demonstrate a remarkably good correlation between simulations and measurements. Hence, the proposed miniaturized FSS represents an excellent potential to realize an all-metallic FSS with low insertion loss, low profile, and wideband performance at low fabrication costs for mmWave applications.

High performance and high yield sub-240 nm AlN:GaN short period superlattice LEDs grown by MBE on 6 in. sapphire substrates

We develop ultraviolet (UV) light emitting diodes (LEDs) that operate in the sub-240 nm (far UVC) regime. The traditional limitations of high Al content AlGaN—the low light extraction efficiency due to transverse magnetic polarization and the poor doping efficiency—were overcome by using AlN:GaN short period superlattices (SPSLs) of varying compositions throughout almost the entire device structure. The quality of our molecular beam epitaxy process for growing SPSL devices was verified via transmission electron microscopy and x-ray diffraction—together, these demonstrate our capacity for growing high quality interfaces with a great deal of control over the thicknesses of each individual layer. Resistivity measurements of our SPSL were three times smaller than bulk AlGaN of similar composition due to the improved doping efficiency. Devices fabricated on 6 in. sapphire substrates showed uniform performance, leading to over 10 000 functional devices per wafer. Packaged diodes exhibited a peak wall plug efficiency of 0.55% and an output power of 1.7 mW when operated at peak efficiency. The devices had an operating life (70% initial power) of 2800 h (at 20 mA continuous wave). Additionally, they could be driven as high as 1 A, which resulted in a record for radiant flux of a far UVC LED grown on sapphire (17.4 mW).

Polarization-insensitive metamaterial perfect absorber in near-infrared band based on trapezoidal silver array

In this article, we presented our proposal for a metamaterial perfect absorber (MPA) operating in the near-infrared band. Our MPA comprised a trapezoidal silver layer, a substrate layer, and an intermediate alumina layer. The transmission characteristics of MPA were analyzed by the three-dimensional (3D) finite difference time domain method. The simulation results were analyzed by equivalent circuit theory. The results show that the MPA achieved 100% absorption of transverse magnetic (TM) polarization and transverse electric (TE) polarization with resonance wavelength = 1492.5 nm. By varying the length of the bottom side of the trapezoid, the MPA’s resonance wavelength could be effectively tuned, and the absorption was maintained at above 99%. With the incidence angle of 0°–55°, the absorption remains above 90% at TE polarization and above 80% at 55°–70°. The absorption at the TM polarization remains above 99% when the incident angle is 0°–70°. A wide angle of incidence and good absorption were achieved. The sensitivity (S) and figure of merit were 228 nm/refractive index unit and 1378 RIU−1, respectively. The proposed absorber with excellent absorption in the range of infrared spectra has a promising application potential in fields such as energy harvesting and infrared sensors.

Silicon-based subwavelength grating polarization beam splitter with asymmetric directional coupler

In this paper, a novel polarization beam splitter (PBS) is proposed. The silicon-based subwavelength grating (SWG) is successfully applied to the asymmetric directional coupled PBS, and the research shows that its performance has improved in many aspects. By carefully optimizing structural parameters, the transverse electric (TE) polarization is in a reflected state in the SWG, which effectively weakens the coupling strength, while the transverse magnetic (TM) polarization is almost unaffected. Simulation results show that the bandwidths of TE polarization and TM polarization are 200 nm (1450–1650 nm) and 141 nm (1450–1650 nm) in the extinction ratio of >20 dB, respectively, while the insertion loss is <0.5 dB and <1.3 dB, respectively. The PBS is very robust to the process production. With the manufacturing error exceeding 20 nm, the performance is only reduced by 0.6 dB, effectively solving the problem of complex preparation process.

Plus-shaped dielectric grating for seven-channel transmission

A new seven-channel transmission grating with plus-shaped array under normal incidence is proposed and discussed in this paper. Through the simulated annealing (SA) algorithm and rigorous coupled-wave analysis (RCWA), the novel microstructure can split the incident energy into 0-th/±1-st/±2-nd/±3-rd orders evenly. The influence of incident angle, period, incident wavelength, and other parameters on the diffraction efficiency are also analyzed in this paper. For transverse magnetic (TM) polarization, the range of period is 3062–3246 nm and the bandwidth of incident angle and wavelength is 1.96° and 32.3 nm, respectively. It can be concluded that the TM-polarized light of the designed grating has a good performance in incident bandwidth and fabrication tolerance. In addition, the efficiency of transverse electric (TE) polarization has the satisfactory uniformity of 2.40%. Therefore, the proposed grating has a certain significance for the research of multi-port beam splitter, especially for the seven-channel polarization-independent beam splitter.

Fourier synthesis dispersion engineering of photonic crystal microrings for broadband frequency combs

Dispersion engineering of microring resonators is crucial for optical frequency comb applications, to achieve targeted bandwidths and powers of individual comb teeth. However, conventional microrings only present two geometric degrees of freedom – width and thickness – which limits the degree to which dispersion can be controlled. We present a technique where we tune individual resonance frequencies for arbitrary dispersion tailoring. Using a photonic crystal microring resonator that induces coupling to both directions of propagation within the ring, we investigate an intuitive design based on Fourier synthesis. Here, the desired photonic crystal spatial profile is obtained through a Fourier relationship with the targeted modal frequency shifts, where each modal shift is determined based on the corresponding effective index modulation of the ring. Experimentally, we demonstrate several distinct dispersion profiles over dozens of modes in transverse magnetic polarization. In contrast, we find that the transverse electric polarization requires a more advanced model that accounts for the discontinuity of the field at the modulated interface. Finally, we present simulations showing arbitrary frequency comb spectral envelope tailoring using our Fourier synthesis approach.

Compact topological polarization beam splitter based on all-dielectric fishnet photonic crystals.

Conventional polarization beam splitters (PBSs) suffer energy loss and signal distortion due to backscattering caused by disturbances. Topological photonic crystals provide backscattering immunity and anti-disturbance robustness transmission owing to the topological edge states. Here, we put forward a kind of dual-polarization air hole-type fishnet valley photonic crystal with a common bandgap (CBG). The Dirac points at the K point formed by different neighboring bands for transverse magnetic and transverse electric polarizations are drawn closer via changing the filling ratio of the scatterer. Then the CBG is constructed by lifting the Dirac cones for dual polarizations within a same frequency range. We further design a topological PBS using the proposed CBG via changing the effective refractive index at the interfaces which guide polarization-dependent edge modes. Based on these tunable edge states, the designed topological PBS (TPBS) achieves efficient polarization separation and is robust against sharp bends and defects, verified by simulation results. The TPBS's footprint is approximately 22.4 × 15.2 μ m 2, allowing high-density on-chip integration. Our work has potential application in photonic integrated circuits and optical communication systems.

The electromagnetic scattering from multiple arbitrarily shaped cavities with inhomogeneous anisotropic media

We study the electromagnetic scattering problem from multiple arbitrarily shaped cavities filled with inhomogeneous anisotropic media. A local-refined Petrov-Galerkin finite element interface (PGFEI) method is developed for solving the scattering problem. By introducing the transparent boundary condition, the unbounded scattering problem can be reduced into bounded domain problem with coupled boundary conditions on the apertures of multiple cavities. The multiple cavity scattering in transverse magnetic (TM) and transverse electric (TE) polarizations are both investigated based on uniform non-body-fitted meshes. We adopt the level-set functions to capture the irregular cavity wall and the interfaces of inhomogeneous media. The special basis is constructed to satisfy the jump conditions across the interfaces of different materials further. The local-refined algorithm is proposed to enhance the accuracy of the solutions around the discontinuous interfaces. The generation of the grid points facilitates a special numbering scheme which enables a stepwise Schur complement decomposition of the discrete linear system derived by the PGFEI method. It could be an alternative method for solving the scattering problems which have similar structures. The proposed method can handle matrix coefficients caused by the permittivity and permeability tensor of anisotropic media. Numerical experiments illustrate the validity and efficiency of the method for solving the scattering from multiple arbitrarily shaped cavities with inhomogeneous anisotropic media in TM and TE polarization.

A Compact Polarization MMI Combiner Using Silicon Slot-Waveguide Structures.

The study of designing a compact transverse electric (TE)/transverse magnetic (TM) polarization multimode interference (MMI) combiner based on silicon slot-waveguide technology is proposed for solving the high demands for high-speed ability alongside more energy power and minimizing the environmental impact of power consumption, achieving a balance between high-speed performance and energy efficiency has become an important consideration in an optical communication system. The MMI coupler has a significant difference in light coupling (beat-length) for TM and TE at 1550 nm wavelength. By controlling the light propagation mechanism inside the MMI coupler, a lower order of mode can be obtained which can lead to a shorter device. The polarization combiner was solved using the full-vectorial beam propagation method (FV-BPM), and the main geometrical parameters were analyzed using Matlab codes. Results show that after a short light propagation of 16.15 μm, the device can function as TM or TE combiner polarization with an excellent extinction ratio of 10.94 dB for TE mode and 13.08 dB for TM mode with low insertion losses of 0.76 dB (TE) and 0.56 dB (TM) and the combiner function well over the C-band spectrum. The polarization combiner also has a robust MMI coupler length tolerance of 400 nm. These attributes make it a good candidate for using this proposed device in photonic integrated circuits for improving power ability at the transmitter system.

Propagation of surface magnetoplasmon polaritons in a symmetric waveguide with two-dimensional electron gas

The properties of surface magnetoplasmon polaritons (SMPPs) in a symmetric structure, composed of two semi-infinite regions of high-density two-dimensional electron gas (2DEG) separated by a thin film in Voigt configuration, are investigated. The normal and absorption dispersion relations for the transverse magnetic polarization are derived by correlating Maxwell’s equation and the boundary conditions. It is demonstrated that the features of SMPPs are greatly influenced by the external magnetic field, collision frequency of 2DEG, the dielectric constant, and the thickness of the thin film, suggesting that the locations and propagation lengths of SMPPs can be governed accordingly. It is shown that the symmetry of the physical geometry preserves the symmetry of the dispersion relations of SMPPs. Furthermore, it is discovered that as the external magnetic field increases, the penetration depth of SMPPs decreases, while their energy loss reduces, implying that plasmons can propagate for longer distances. Additionally, it is observed that SMPPs in the symmetric configuration have a longer lifetime than those in the asymmetric configuration.

The impact of light polarization and the nature of modes in the formation of quasi-bound states in the continuum at near-normal incidence

Bound states in the continuum (BIC) is a peculiar resonant mode with an infinite radiative lifetime and quality factor (Q-factor) embedded within the radiation continuum, which find applications in sensing, lasing, and quantum photonics. While an ideal BIC with an infinite Q-factor can only occur in theory, observing quasi-BIC in realistic samples with finite sizes is possible. However, the robustness of quasi-BIC depends primarily on the trapped electromagnetic modes. Here, we discuss the polarization dependence and the nature of quasi-BIC mode in a two-dimensional array of gallium arsenide (GaAs) scatterers through finite difference time domain simulations and analytical calculations. The calculated angle- and polarization-dependent transmission spectra show quasi-BIC evolution with high Q-factor at near-normal incidence only for transverse magnetic polarization. The calculated total scattering cross-section implies the dominant contribution from electric dipole moments in generating the quasi-BIC. The evolution of quasi-BIC mode is discussed in terms of Mie or Fabry–Perot modes using geometry-dependent transmission and field intensity calculations. The proposed GaAs metasurfaces with quasi-BIC at 638 nm, corresponding to the zero phonon line of nitrogen-vacancy centers in diamond are useful for applications in photonic quantum technologies.

Polarization-insensitive epsilon-mu-near-zero effect in two-dimensional annular photonic crystals

We report polarization-insensitive epsilon-mu-near-zero (EMNZ) effect for both transverse-electric (TE) and transverse-magnetic (TM) polarizations in two types of two-dimensional (2D) annular PCs (APCs). The square-lattice air-ring (or dielectric-ring) type 2D APC can support non-accidental Dirac-like degeneracy for three low-energy TE (or TM) bands and accidental Dirac-like degeneracy for three higher-energy TM (or TE) bands at the same frequency. We rigorously demonstrate the polarization-insensitive EMNZ effect in 2D APCs based on the S-parameters inversion technique.