TM Polarization Research Articles

High-efficiency polarization-selective two-dimensional diffraction gratings based on silver cuboid arrays

A two-dimensional (2D) diffraction grating based on silver cuboid arrays is demonstrated. With the structural optimization by three-dimensional (3D) finite-difference time-domain method, the proposed grating exhibits favorable polarization selectivity. At wavelength 1550 nm, high diffraction efficiency and polarization correlation can be realized in the case of two-port output ((0, ±1) or (±1, 0)) under TE polarization, as well as five-port output ((0, 0), (0, ±1) and (±1, 0)) under TM polarization. Under the two-port output state, the diffraction efficiency is nearly 48% with the extinction ratio of 16.44 dB and insertion loss of 0.20 dB. Under the five-port output status, the efficiency is larger than 19% for each diffraction order, meanwhile, the total efficiency and uniformity are 97% and 0.58%, respectively. The proposed grating with positive implications has good potentials in polarization multiplexing and polarization-correlated grating interferometry.

PVDF/Al2O3/Gd2O3 layers splitter with first-order suppression functionality

In the realm of optical component design, the proposed multilayer grating splitter represents a significant breakthrough. For the triple-layered grating in this paper, it combines the outstanding optical properties of polyvinylidene fluoride (PVDF), aluminum oxide (Al2O3), and gadolinium oxide (Gd2O3) to achieve high-efficiency outputs for both the 0th and −2nd orders under secondary Bragg angle incidence conditions. The diffraction efficiencies for both TE and TM polarizations exceed 97%, with energy uniformity surpassing 99%. These results highlight the potential of this design in precision beam control applications. The splitter's performance benefits from the intrinsic material properties and optimally designed structural dimensions, which enhance transparency and thermal stability under operational conditions. Through rigorous design and optimization, including modal methods and simulated annealing algorithms, the device achieves exceptional uniformity in diffraction efficiency, which is crucial for high-resolution spectroscopy and precision optical measurement applications.

Ultra-broadband and high extinction ratio polarization splitter based on triple-tapered directional couplers

The design and numerically investigation of a silicon polarization splitter (PS) is proposed using triple-tapered directional couplers (DCs).The proposed device consists of a triple-tapered DC, a triple-bent DC at through port, and a tapered waveguide at cross port. The coupling length of the device is 20.5 µm. At the 1550 nm wavelength, the realized PS exhibits the extinction ratio (ER) values of 35.7 dB and 37.35 dB as well as the insertion loss values of < 0.58 dB and < 0.4 dB for the TE and TM polarization modes, respectively. Furthermore, the device’s bandwidth for ER > 20 dB and ER > 25 dB are 170 nm and 136 nm, respectively.

Open-source toolbox for photographic characterization of optical propagation.

An alternative method for characterizing optical propagation in waveguide structures based on scattered light imaging is presented and demonstrated for the spectral range of 450-980 nm. Propagation losses as low as 1.40 dB/cm are demonstrated in alumina spiral waveguides. AlGaAs-on-insulator waveguides are measured using a tunable laser and compared to cut-back measurements. On AlGaAs, a one-sigma uncertainty of 1.40 and 2.23 dB/cm for TE and TM polarizations is obtained for repetitions of measurements conducted on the same waveguide, highlighting the approach's reproducibility. An open-source toolbox is introduced, allowing for reliable processing of data and estimation of optical propagation losses.

Terahertz tunable three-dimensional photonic jets

Highly localized electromagnetic field distributions near the “shadow-side” surface of certain transparent mesoscale bodies illuminated by light waves are called photonic jets. We demonstrated formation of three-dimensional (3D) tunable photonic jets in terahertz regime (terajets, TJs) by dielectric micro-objects -including spheres, cylinders, and cubes-coated with a bulk Dirac semimetal (BDS) layer, under uniform beam illumination. The optical characteristics of the produced TJs can be modulated dynamically through tuning the BDS layer’s index of refraction via changing its Fermi energy. It is demonstrated that the Fermi energy of BDS layer has a significant impact on tuning the optical characteristics of the produced photonic jets for both TE and TM polarizations. A notable polarization dependency of the characteristics of the TJs was also observed. The impact of obliquity of the incident beam was studied as well and it was demonstrated that electromagnetic field distributions corresponding to asymmetric photonic jets can be formed in which the intensity at the focal region is preserved in a wide angular range which could find potential application in scanning devices. It was found that the maximum intensity of the TJ occurs at a non-trivial morphology-dependent source-angle.

Tunable wideband terahertz absorber based on single-layer patterned graphene

In this study, we propose and validate a broadband terahertz perfect absorber. The absorber has a simple structure, which consists of a gold (Au) substrate, a TOPAS dielectric layer and a patterned graphene layer. By the simulations, a broad absorption band can be obtained with a high absorption above 90% between 3.31 THz and 7.15 THz, and the relative bandwidth reaches 73.4%. Meanwhile, the absorption higher than 99% is between 3.81 THz and 6.6 THz with a relative bandwidth of 53.6%. The mechanism of the surface excited plasma (SPP) and electromagnetic dipole resonance are responsible for its almost perfect broadband absorption. By changing the Fermi energy level of the graphene layer, the flexible broadband absorption spectra can be acquired. By varying the geometrical parameters of the structure, a wider spectral range of absorption wavelengths can be realized. For both TE and TM polarization, the absorption can remain above 90% over a wide range of incidence angles. Due to the independent tunability and high absorption of the proposed device, it has great potential applications in terahertz imaging, smart absorption, detectors and communications.

Electromagnetic transmission of two-dimensional inhomogeneous plasma photonic crystal

A 2D tunable plasma photonic crystal (PPC) was constructed and implemented experimentally over a frequency range of 1 GHz–12 GHz within the electromagnetic spectrum. The PPC was simulated using an inhomogeneous model of a plasma tube based on microwave diagnostics and numerical simulations. The simulation results were found to be in good agreement with the experimental results. The data indicates that for TM polarization, localized plasmons will be excited at various positions within the tube, which does not rely on an interface with the medium, resulting in a broad forbidden band due to plasma inhomogeneity. The bandwidth of this band is consistent with the plasma frequency range. Furthermore, a lattice resonance band is observed, which is related to the incident angle. The cutoff effect of inhomogeneous PPC for TE polarization can be predicted by averaging the plasma parameters. The structure or plasma parameters can be adjusted to tune all the bands mentioned above. These findings can be used as a reference for applications in communication and microwave devices, and could potentially be utilized as a diagnostic tool for plasma parameters.

Chirality identification of Ibuprofen enantiomers by a terahertz polarization-sensitive metasurface sensor

Chirality plays an important role in medicine, biology, and chemistry. Molecules of different chirality could display dramatically different medical effects, pharmacological activities, and physiological impacts. Ibuprofen is an important anti-inflammatory drug in clinics. The anti-inflammatory effect is almost solely attributed to the (S)-(+)-Ibuprofen, while its enantiomer (R)-(-)-Ibuprofen plays a negative effect on increasing the metabolic burden. In this work, a terahertz (THz) polarization-sensitive metasurface sensor is proposed for qualitative and quantitative identification of the chiral Ibuprofen. The chirality parameters of Ibuprofen are extracted from the circular-polarized transmission coefficients. The parameters are further used to simulate the coupling mechanism between the Ibuprofen and the sensor to explain the principle of recognition. The sensitivities of (R)-(-)-Ibuprofen and (S)-(+)-Ibuprofen are found to be 1.5 THz/(mg/L) and 1.8 THz/(mg/L) for the TM polarization, respectively, and 1.7 THz/(mg/L) and 2.1 THz/(mg/L) for the TE polarization, respectively. The difference enables the chirality identification according to the different frequency shift at the same concentration. The exceptional specificity and sensitivity provide a new avenue for chiral molecular recognition.

Tunable plasmon-induced transparency in anisotropic graphene-black phosphorus photonic device for high-performance sensors and switchers

A novel photonic device composed of graphene and black phosphorus (G-BP) has been proposed, which achieves high-performance plasmon-induced transparency (PIT) effect within the THz range and maintains substantial tunability and anisotropy. The anisotropy of the PIT effect arises from the near-field coupling between two bright modes characterized by distinct effective electron masses of BP, resulting transparency window at 33.35 THz for TE polarization and at 26.92 THz for TM polarization. Through the modulation of Fermi energy in graphene, doping levels of BP and geometric parameters separately, a tunable transparency window is achieved. Notably, the convergence or divergence of the anisotropic transparency windows can be well manipulated with different BP doping levels. Furthermore, the proposed G-BP photonic device exhibits a high sensitivity to changes in the surrounding refractive index and substrates, with a maximum sensitivity of 12.04 THz/RI, rendering it suitable for sensor applications. Overall, the proposed photonic device exhibits notable PIT effects characterized by high anisotropic performance, substantial tunability, great sensitivity, and stability, making it a promising candidate for applications in sensors, polarizers, and switchers.

Ultra-wideband absorber based on multilayer lossy frequency selective surface

In this letter, a multilayer dielectric with a lossy frequency-selective surface (FSS) absorber is proposed, which is composed of three layers of resistive film-dielectric composite layer and a metal grounded plane. Particularly, each resistive film-dielectric composite layer consists of a polyethylene terephthalate (PET), polymethacrylimide foam (PMI), and resistive film layer. An equivalent circuit model is established to further understand the performance of the absorber based on the impedance matching approach and the transmission line theory. Experimental results reveal that the metamaterial absorber (MMA) covers -10 dB bandwidth of 1.96-21.8 GHz for normal incidence. Meanwhile, the absorption rate can retain more than 80% for both TE and TM polarizations within 55° incidence angles. Furthermore, the fractional bandwidth of the MMA is 167% and its thickness is only 0.108 ?L. The MMA has the characteristics of ultra-wideband, high absorption rate, and polarization stability, making it suitable for communication systems.

Frequency selective surface with quad-band absorption/transmission and angular stability for TE and TM polarizations

The proposed FSS structure employs two square annular rings for absorption functionalities and two square aperture slots for transmission properties. Through comprehensive simulations and analysis, the FSS structure demonstrates remarkable performance in selectively absorbing and transmitting electromagnetic waves across four distinct frequency bands. Moreover, the design exhibits excellent TE and TM polarizations angular stability, consistently maintaining constant absorption and transmission characteristics across varying incidence angles. A comprehensive analysis of the equivalent circuit model of the FSS structure has also been performed to understand the quad-band transmission and absorption properties. The measurement results underscore the effectiveness of the design of a 250*250 mm array, with absorption peaks notably occurring at 4.2 GHz and 7.23 GHz, boasting peak absorption rates of 92% and 85%, respectively. Moreover, the insertion loss within the pass band at 8.8 GHz and 12.2 GHz stands impressively low at 0.2 dB and 0.32 dB, respectively. Notably, the proposed quad-band FSS showcases polarization-insensitive behavior across a range from 0° to 60° and successfully undergoes conformal testing with a curvature radius up to 50 mm. The results of experimental testing on a quad-band FSS prototype demonstrate superior agreement with those obtained through simulations and analytically derived equivalent circuit model (ECM) results, validating its practical applicability in real-world scenarios.

Design of a low profile and ultraminiaturized frequency selective surface with dual band-stop response

In this paper, a miniaturized dual-band frequency selective surface (FSS) for electromagnetic shielding applications is presented. The FSS unit cell provides band-stop response at the resonant frequencies of 0.95 GHz and 2.52 GHz. The FSS element is constructed by employing convoluted metal stripes that are positioned on both sides of the substrate. The proposed configuration enhances the electrical length of the resonator while maintaining its physical dimensions. Moreover, the unit cell of the FSS exhibits rotational symmetry, which enables polarization independent operation. The designed FSS structure demonstrates excellent miniaturization characteristics, with a cell size and thickness of 0.019 λ0 × 0.019 λ0, and 0.00048 λ0, respectively. The cell size and thickness are calculated at the lower resonating frequency of 0.95 GHz. In addition, the stability of the proposed FSS structure is observed for both the TE and TM polarizations across an incident angle range of 0° to 80°. The resonating behavior of the structure is elucidated with the help of electric field and surface current distribution. Experimental verification of the dual-band FSS is conducted through the fabrication of a prototype on a FR4 substrate. The measured transmission coefficients are in good agreement with the simulated response for both TE and TM modes. Compared with the dual-band FSSs previously reported, the proposed FSS has the significant advantages of low profile and miniaturization.

Dual-polarization valley-like transport in dielectric photonic crystals

Valley photonic crystal (VPC) waveguides possess strong immunity to backward scattering and robust transmission, originating from topologically protected edge states. Here, we propose a VPC/air/VPC sandwiched structure, and VPC possesses the common valley band gaps for TM and TE polarizations. By modifying the radii of the cylinders on both sides of the air channel, finite element method (FEM) simulations show the valley-locked waveguide modes with high flux are achieved, for both polarizations. Based on VPC/air/VPC sandwiched structure, we further design waveguide couplers and zigzag waveguide bends, and immunity to backward scattering and robust transmission are also verified. Our work finds a new method of designing photonic crystal waveguides, which support valley-like transport with enhanced flux and dual-polarization, making topological photonic devices easily to be integrated with conventional optical waveguides.

Multi-functional metasurface as a transmissive/reflective FSS and an on-air frequency mixer

In this paper, a multi-functional metasurface is proposed, which can work as a narrowband transmissive/reflective frequency selective surface (FSS) and an on-air frequency mixer based on its switching response. The metasurface is made up of unit cells with square and circular metallic loops connected by PIN diodes controlled by a bias source. In contrast to typical wideband FSSs, the structure provides 0.55 GHz of narrow stopband (a fractional bandwidth of 22%) at 2 GHz in the OFF state bias. The bandstop response can be adjusted by varying the reverse bias voltage. The metasurface alternates between its functionalities when in forward bias by providing a passband at the operational frequency. The structure is compact and operates as a transmissive/reflective surface under two different bias conditions (ON and OFF). The design is angularly stable and polarization-insensitive for both TE and TM polarisation. A prototype of the designed structure is developed and the measured results correlate well with the simulated responses from the finite-difference time-domain (FDTD) method-based simulation of the circuit model. On-air frequency mixing for a wave propagating through the metasurface is demonstrated and the effects of different parameters affecting the mixing are parametrically studied through FDTD simulations and experiments.

Ultralow-loss polarization-insensitive silicon nitride-assisted double-etched silicon edge coupler with polarization splitting

High-performance silicon-based edge couplers for interfacing with standard single-mode fibers encounter significant challenges due to limitations imposed by the minimum fabrication width. Here, we propose a silicon nitride-assisted double-etched O-band silicon edge coupler with a minimum width of 180 nm. Notably, the polarization splitting function naturally integrates into this edge coupler. Through simulation, the proposed edge coupler, without a cantilever, demonstrates a minimum coupling loss of 0.53/0.82 dB with an average extinction ratio of 42/18 dB for TE/TM polarization. Additionally, this edge coupler exhibits weak polarization dependence with an average difference of only 0.24 dB in the O band. Leveraging a segmented taper shape design, the 0.5-dB bandwidth of coupling loss extends to approximately 100 nm for both TE and TM polarizations, despite the inclusion of two evanescent coupling parts.

Dynamic frequency switching of a bandstop reconfigurable frequency selective surface with PIN diodes for C/X and Ku-band shielding applications

This paper presents a reconfigurable bandstop frequency selective surface (R-FSS) design capable of switching across C, X and Ku-bands. The electronic switching mechanism is achieved in real-time through PIN diodes. The combination of rectangular loops is selected as unit-cell and PIN diodes are strategically placed to dynamically adjust the bandstop region. The device operates in three distinct modes corresponding to the activation status of the PIN-diodes. For TE polarization, Mode 1 encompasses the Ku-bandstop (12.64–14.75 GHz), Mode 2 corresponds to the C/X-bandstop (6.62–11.28 GHz), and Mode 3 involves the X-bandstop (9.82–11.63 GHz), whereas X-bandstop characteristic is observed for TM polarization (9.054–––11.29 GHz). In TE polarization, each configuration is defined by specific equivalent circuit models, featuring an inductance in parallel with series L-C resonant circuit, an L-C resonant circuit in parallel with the inductance, and two L-C resonant circuits in parallel, respectively. Additionally, for TM polarization, the configuration incorporates two parallel L-C resonant circuits. A prototype of the proposed R-FSS is fabricated and measured. The results demonstrated effective switching operation across the C, X and Ku-band stopbands, depending on the biasing of the PIN diodes. The experimental outcomes are consistent with the simulation results, affirming the compatibility and functionality of the proposed R-FSS design.

Tunable wave localization at the Dirac frequency in a metallic photonic crystal cavity

In this study, the two-dimensional (2D) triangular lattice metallic photonic crystals (PCs) in visible and infrared bands have been utilized to achieve light confinement at the Dirac frequency. Distinct from the traditional bandgap or total internal reflection cavity modes, the unique photonic localization mechanism leads to an unusual algebraic decay of state and a unique frequency located beyond any bandgaps. This investigation delves into the band structure analysis of 2D metallic PCs, specifically focusing on their distinctive features, such as photonic bandgaps and Dirac cones. The plane wave expansion (PWE) method, enhanced with a linearization technique, is employed for band structure calculations, considering both the frequency-dependent dielectric properties and the intrinsic lossy nature of metallic materials described by the Drude model. The study provides a comprehensive derivation of the PWE equations for metallic PCs and investigates their band characteristics under both TM and TE polarizations. Focusing on TM modes in triangular lattice metallic PCs, it reveals zero density of states (DOS) at K points of the Brillouin corner and the existence of Dirac cones with linearly dispersion and linearly vanishing DOS. The study extends to exploring localized modes at Dirac frequencies, employing a relativistic quantum mechanics approach analogous to graphene's charge carriers. Theoretical predictions are corroborated by numerical simulations, and the potential for tunable Dirac localized modes is highlighted. This research not only deepens the understanding of Dirac properties in graphene-like systems but also lays the groundwork for further exploration of the practical quasi-2D devices, which will provide assistance in the integration of micro- and nano- devices, especially in applications requiring long-range coupling, given the critical importance of optical cavities in contemporary optical technologies.

Two-dimensional grating metasurface for communication band under Littrow mounting

For communication, it is important to reduce the polarization-independence loss, especially for the stereoscopic incidence. A two-dimensional (2D) grating with the cylindrical hole array is presented. The grating structure can achieve polarization-independent, high-efficiency and broadband output at the (−1, 0) diffraction order in the communication band. The novel metasurface achieves a diffraction efficiency of over 98% for both TE and TM polarizations at the (−1, 0) diffraction order. In addition, the (0, 0) diffraction order is well suppressed, resulting in extinction ratio of 43.89 and 46.18 dB for TE and TM polarization, respectively. In particular, the diffraction efficiency of the structure at the (−1, 0) order of magnitude under two polarizations exceeds 90% in the 1533–1561 nm bandwidth, which is a significant improvement over recently reported 2D gratings of the same type. Furthermore, the proposed structure has good incidence angle bandwidth and fabrication process tolerance, which ensures stable and efficient output in applications and fabrication. These results enrich the research on 2D gratings in the field of communication bands, and the designed grating has great potential for applications in spectroscopy, grating measurement and interferometry.

Design of 2.5-D miniaturized frequency selective surface with enhanced oblique stability

This paper presents a miniaturized 2.5-D frequency selective surface (FSS) that exhibits a band stop response at frequency of 1.5 GHz. In the unit cell, the meander patterns on both side of the substrate are connected in series by four vias. Moreover, the meandered pattern in each quadrant is also connected with one of the meander patterns of the adjacent unit cell. In this manner, a 2.5-D closed loop is created with large perimeter. The enlarged perimeter amplifies the effective inductance and leads to a decrease in both the resonant frequency and the dimensions of unit cell. Subsequently, the proposed FSS demonstrates excellent miniaturization with an overall size of 0.038 λ 0 × 0.038 λ 0. Moreover, the frequency response is highly stable up to 86° for both TE and TM polarization. The resonance mechanism of the designed FSS is explicated through distribution of surface current and electric field. The testing board of the proposed FSS has been fabricated for the verification of the design. The measured frequency response of the prototype are congruent with the simulation results. The distinguished features of the constructed structure are enhanced angular stability, miniaturized unit cell, low profile, simple geometry and easy fabrication.

A Dual-Band Polarization-Insensitive Frequency Selective Surface for Electromagnetic Shielding Applications.

This paper presents a novel polarization-insensitive dual-band frequency-selective surface (FSS)-based electromagnetic shield. The miniaturized FSS unit cell consists of a modified Jerusalem crossed loop and a corner-modified square loop. These FSS elements are arranged in a co-planner configuration over a single-layer Rogers 5880 substrate and simultaneously offer effective shielding in the X- and Ku-bands. Moreover, the FSS manifests polarization-independent and angularly stable band-reject filter characteristics over various oblique angles of incidence for both the TE and TM polarizations with virtuous attenuation at both resonances. In addition, the FSS structure is modelled into an equivalent lumped circuit to better analyze the phenomenon of EM wave suppression. A finite prototype of FSS is fabricated and tested. The simulated and measured results are in good agreement, thus making it a potential candidate for RF shielding/isolation applications.