TM Modes Research Articles

Design of Filtering Coupler Based on Patch Resonator with High Selectivity

In this paper, a new approach for designing a planar high frequency selectivity filtering coupler based on a circular patch resonator is proposed. In order to explain the operating principle, the resonant property of the circular patch resonator has been investigated firstly. Two circular patch resonators connected by two microstrip lines are used in this design. A filtering coupler is achieved by adjusting the feeder position and the length and width of the microstrip line used to connect the two resonators. Without additional circuits, the desired 0° and 180° phase differences are realized by the inherent in-phase and out-of-phase characteristics of E-fields at the TM11 mode. To improve the passband selectivity, transmission zeros are created by introducing a coupling between the source and load through the coupling slots etched on the ground. Finally, a prototype of the filtering coupler centered at 2.12 GHz is designed, implemented, and tested, while the measured results coincide well with simulated ones, verifying the proposed design concept.

3D trapezoidal edge coupler with high efficiency and tolerance based on Silicon-on-Insulator

Edge couplers connecting the optical fiber and the on-chip waveguide are indispensable devices in integrated photonics. In this study, a 3D edge coupler with trapezoidal cross-section is proposed and designed. High coupling efficiencies of the edge couplers are verified by theoretical calculations. The 3D trapezoidal edge couplers are fabricated on the thick-silicon layer of a Silicon-on-Insulator (SOI) substrate by using 3D grayscale lithography. Over the communication band (C-band), the fiber-to-chip measured results indicate that the maximum coupling efficiency of the 3D edge coupler is 0.68/0.99 dB for the TE/TM mode. The misalignment tolerances are less than 0.65 dB and 0.90 dB for the TE and TM modes within ±5 μm in the horizontal direction. The same measured values are less than 0.60 dB for both the TE and TM modes within 4 μm in the vertical direction. The excellent coupling characteristics of the 3D edge coupler are attractive for the large-scale photonic integration.

A miniaturized quintuple-band frequency selective surface based on enclosed cross slots

Abstract This article presents a low-profile quintuple-band frequency selective surface (FSS) that is designed as a sub-reflector for applications including satellite systems (C band), EPR (electron paramagnetic resonance) spectrometers, motion and traffic light crossing detectors (X band), Direct Broadcast Satellite and broadcasting satellite service (Ku band), and shortrange applications (K band). The dimensions of the miniaturized unit cell 0.08λ0×0.08λ0×0.012λ0, where, λ0 is the free-space wavelength corresponding to the lower cut-off frequency. There are five stop bands, and frequencies at which they resonate are 6.3, 7.06, 9.30, 11.2, 14.0, and 18.64 GHz. The fractional bandwidths (FBW) of these bands are 62.6, 7.5, 9.2, 11, and 11.69%, respectively. Additionally, as a result of the structure’s four-fold symmetry, it exhibits a good polarization-insensitive response as well as a stable response in both the TE and TM modes. Full-wave simulation is performed on the structure, after which an equivalent circuit model is constructed.

Optimized unidirectional and angle-insensitive ultra-broadband absorber based on layered graphene photonic structure

Using a chaotic gray wolf optimization algorithm to drive the transfer matrix method, a nonreciprocal and angle-insensitive absorber with ultra-wide bandwidth absorption is realized in a layered photonic structure comprised of graphene, which is spliced of a periodic sequence and a quasi-periodic sequence on a normalized scale. Compared to the periodic sequence, the proposed cascading construction has more preponderance in terms of bandwidth and angular stability. The surface conductivity of the graphene layer, which manipulates the absorption effect, can be modulated by the Fermi level, causing the characteristics of the proposed absorber tuned. The Fermi level of graphene, dielectric constants, and thicknesses of ordinary media, are optimized by the chaotic gray wolf algorithm, contributing to the decent improvement of absorption with a relative bandwidth of up to 127 %. Most importantly, in the 1.5–4.5 THz, the angular stability reaches 86° under the TM mode and 70° in TE one. The impacts of sequence number N of periodic sequence and M of quasi-periodic sequence on absorption in both angle and frequency domains are investigated. Additionally, the impedance match theory is introduced to express excellent absorption performance.

Simulation of low loss metamaterial based hollow core fiber for guiding mid-infrared (MIR) light

There is a great deal of interest in mid-infrared (MIR) light in diverse fields including spectroscopy, biomedical-applications, medical surgery, and astronomy. Due to higher material absorption, MIR light transmission is generally more difficult than visible light or microwave radiation. Recently, hollow-core MIR fibers are one of the best possibilities among presented several innovations having low Transverse Magnetic (TM) mode losses, although they are many orders of magnitude than Transverse Electric (TE) modes. Studies also have found that metamaterial-based HCF offers excellent potential for transmitting MIR light because of its distinct and flexible optical properties. In this study, a metamaterial-based HCF with an optimized design that uses metal wires with subwavelength spacing embedded in dielectric host, and acts as an effective TM reflector is proposed. In the 3 to 12 μm wavelengths, the effects of the design parameters including shape, number, and spacing of metal wires, dielectric thickness, and the diameter of the core are extensively investigated using finite element method. It is observed that TM01 mode losses are the lowest and a noteworthy confinement loss of 4.69× 10−7 dB/m is found at 9.5 μm wavelength, with an average loss of 5.22× 10−5 dB/m found within the range 8–10 μm wavelength. As the wires are wrapped up in a dielectric, there is a preferred position of 4 μm from the core edge and a number of 40 metal wires that results in the least amount of losses. This analysis could help to design low-loss metamaterial based HCF for guiding MIR light.

A Dual-Polarized Antenna Array With High Port Isolation Through TM03/04 Modes Cancellation

A new dual-polarized microstrip patch antenna array (MPAA) with high port isolation through TM03/04 modes cancellation is designed and reported in this letter. By introducing branches etched with slots between the units, the resonant frequency and impedance of TM03 mode are adjusted to be consistent with that of TM04 mode. First, TM03/04 modes cancellation decoupling scheme is applied to a two-element MPAA. And then, the proposed decoupling method is expanded to the compact decoupled dual-polarized four-element MPAA through multi-layer distribution. The co-linear port coupling is below -27 dB within the impedance matching bandwidth (S11 < -10 dB from 3.35 to 3.53 GHz), which is reduced by 20 dB from the original coupling. The maximum gain of 6.4 dBi is achieved, and the radiation efficiency is above 80%. Through miniaturized design, the proposed decoupling scheme achieves high port isolation and a stable radiation pattern. The proposed method may be expanded and greatly improve the performance in future decisions.

Low-loss and broadband polarization-diversity edge coupler on a thin-film lithium niobate platform.

Fiber-to-chip coupling is an essential issue for taking high-performance integrated photonic devices into practical applications. On a thin-film lithium niobate platform, such a high-performance coupler featuring low loss, large bandwidth, and polarization independence is highly desired. However, the mode hybridization induced by the birefringence of lithium niobate seriously restricts a polarization-independent coupling. Here, we propose and experimentally demonstrate a high-performance and polarization-diversity cantilever edge coupler (EC) with the assistance of a two-stage polarization splitter and rotator (PSR). The fabricated cantilever EC shows a minimal coupling loss of 1.06 dB/facet, and the fully etched PSR structure shows a low insertion loss (IL) of -0.62 dB. The whole polarization-diversity cantilever EC exhibits a low IL of -2.17 dB and -1.68 dB for TE0 and TM0 mode, respectively, as well as a small cross talk of <-15 dB covering the wavelength band from 1.5 µm to 1.6 µm. A polarization-dependent loss <0.5 dB over the same wavelength band is also obtained. The proposed fiber-to-waveguide coupler, compatible with the fabrication process of popular thin-film lithium niobate photonic devices, can work as a coupling scheme for on-chip polarization-diversity applications.

Fiber-to-Chip Three-Dimensional Silicon-on-Insulator Edge Couplers with High Efficiency and Tolerance.

The edge coupler is an indispensable optical device for connecting an external fiber and on-chip waveguide. The coupling efficiency of the edge coupler affects the effective integration of optical circuits. In this study, three-dimensional (3D) edge couplers with high efficiency and tolerance are proposed. The high coupling efficiency of the 3D edge couplers is verified by theoretical calculations. Three couplers are fabricated on a thick-silicon platform via 3D grayscale lithography. At the 1550 nm band, the fiber-to-chip experimental data show that the maximum coupling efficiencies of the three edge couplers are 0.70 dB and 1.34 dB, 0.80 dB and 1.60 dB, and 1.00 dB and 1.14 dB for the TE and TM modes, respectively. At the 1550 nm band, misalignment tolerances measurement data reveal 0.8 dB/0.9 dB tolerance of ±5 μm in the horizontal direction, and 1.7 dB/1.0 dB tolerance of ±2 μm in the vertical direction for TE/TM mode. This study provides a new idea for the design of 3D edge couplers and demonstrates significant superiority in research and industrial applications.

Broadband co-polarized antenna using monolithic slotted dielectric patch for full-duplex system

This paper suggests a broadband co-polarized antenna utilizing monolithic slotted dielectric patch (DP) for the applications of in-band full-duplex (IBFD). Three slot pairs with different sizes in the center of the monolithic DP are constructed and reduce the effective dielectric constant at this region. As a result, the E-field distributions of the two employed modes (TM10 and TE12 modes) inside the DP are moved to the unetched part (apart from the center of the DP). In this way, a broadband co-polarized antenna using the TM10 and TE12 modes is constructed while the isolation between the two ports for transmitting (TX) and receiving (RX) can be enhanced significantly in a broadband. The measured results of the antenna prototype are quite consistent with the simulated results. The experimental results illustrate that within the operating bandwidth of about 18% (|S11|< −10 dB), an isolation measured greater than 28 dB is attained, with a maximum value of 49.8 dB. Overall, the proposed co-polarized antenna owns advantages of simple structure, broad bandwidth, high efficiency, and low profile.

Elimination of the fundamental mode hybridization on an x-cut lithium-niobate-on-insulator by using a densely packed bent waveguide array.

Lithium niobate (L i N b O 3, LN) is a promising material for integrated photonics due to its natural advantages. The commercialization of thin-film LN technology has revitalized this platform, enabling low-loss waveguides, micro-rings, and compact electro-optical modulators. However, the anisotropic birefringent nature of X-cut LN leads to mode hybridization of TE and TM modes, which is detrimental to most polarization-sensitive integrated optical waveguide devices. A novel structure, to the best of our knowldege, utilizing a densely packed bent waveguide array is presented in this paper to eliminate mode hybridization. The refractive index is modulated in a manner that eliminates the avoided crossing of the refractive index curves of the TE and TM fundamental modes; thus, mode hybridization is prevented. The structures are readily accessible in the full range of commercially available LN film thicknesses from 400 to 720nm and in any etching depth. The proposed structures give a polarization extinction ratio of -30d B across all bend radii, while simultaneously maintaining low excess loss of less than -1d B after reaching a 100µm bend radius.

A compact circularly polarized microstrip patch filtenna based on reusable dual‐mode substrate integrated waveguide cavity

AbstractIn this letter, a compact circularly polarized (CP) microstrip patch filtenna designed by reusing dual‐mode substrate integrated waveguide (SIW) cavity is proposed. The dual‐mode SIW cavity, operating at its TE120 and TE210 modes, can be used not only as the first stage resonator of the filtering network but also feeds the four microstrip patches working at their TM10 and TM01 modes. A pair of asymmetric perturbed posts is inserted in the SIW cavity to perturb the electric field distributions of TE120 and TE210 modes so as to achieve one axial ratio (AR) minima. The other AR minima is realized by sequentially exciting the four orthogonal microstrip patches via the four rectangular slots that are etched on the top surface of the SIW cavity. In addition, four metal posts penetrated the SIW cavity is employed to improve the impedance matching. For verification, a CP filtenna prototype centered at 5.13 GHz is designed, manufactured, and tested. The measured results agree well with the simulated ones, demonstrating a fractional impedance bandwidth of 6.9% (4.95–5.3 GHz), a 3 dB AR bandwidth of 4.2% (5–5.21 GHz), and a maximum boresight realized gain of 8.4 dBic.

Low‐profile and broadband microstrip antenna with pattern diversity

AbstractThis paper presents a low‐profile and broadband pattern diversity microstrip antenna with quasiperiodic radiating patches fed by two slots. The thickness of the whole design is only 0.044λ0 (λ0 is the free‐space wavelength of the center frequency), showing great potential in applications. The broadband property is realized by efficiently exciting TM10 mode and antiphase TM20 mode and forming two resonant frequencies in the target band. The antenna can generate a broadside or difference pattern by switching the input port of the broadband 180° hybrid coupling feed network. The measured results show that the coincident impedance bandwidth of the antenna working in the two pattern modes is 20.5% (3.20–3.93 GHz), and the maximum gain values are 6.85 dBi for the directional pattern and 5.80 dBi for the difference pattern.

Angle-Selective Photodetection in Ge/Si Quantum Dot Photodiodes Enhanced by Microstructured Hole Arrays

We report on the near-infrared (NIR) photoresponse of a micropatterned Ge/Si quantum dot (QD) pin photodiode at different angles of radiation incidence. The photon-trapping hole array was etched through the n+-type top contact layer to reach the buried QDs. The normal-incidence responsivity was observed to be resonantly increased at wavelengths of 1.4, 1.7, and 1.9 μm by factors of 40, 33, and 30, respectively, compared with the reference detector without holes. As the incident angle θ increases, the resonance peaks are disappeared and at θ&gt;40∘ a new resonance with a 25× enhancement arises at a wavelength of 1.8 μm. Simulation of the near-field intensity, Poynting vector distribution and wave polarization showed that at small θ, the strong electric field is primarily localized under the air holes (1.4 μm, TM mode) or between the holes (1.7 and 1.9 μm, TE modes) inside the region occupied by QDs, resulting in the strong NIR photocurrent. At large θ, the dominant resonance detected at 1.8 μm is the result of coupling between the TE and TM modes and formation of a mixed near-field state.

Influence of Ion Exchange Process Parameters on Broadband Differential Interference.

The paper presents theoretical analyses and experimental investigations of broadband differential interference in planar gradient waveguides made via K+-Na+ ion exchange in BK-7 glass. This technology, due to its large polarimetric dispersion, is especially useful for applications in differential interferometry. We discuss the influence of technological parameters on the operation characteristics of the structure in terms of sensor applications. The refractive index variation in the measured external surroundings affects the modal properties of TE and TM modes and the spectral distribution at the output of the differential interferometer. The optical system described in this work has been designed specifically for use in biological systems where variations in the index of refraction need to be measured.

A Formal Approach to the Extraction of Permittivity and Permeability of Isotropic and Anisotropic Media Using the TM11 Mode in Rectangular Waveguides

Based on our previous work on the propagation of electromagnetic waves in a layered medium placed in a rectangular waveguide, we present the theory of using the TE10 and TM11 modes to determine the complex parameters of isotropic and anisotropic media. The Nicolson–Ross–Weir method was used. The cases of isotropic, uniaxial, and biaxial materials were considered. It has been shown that the TM11 mode can be used to extract parameters of non-magnetic uniaxial anisotropy media by a single measurement, without changing the sample position. This is not possible with the previously used TE10 mode. It is also possible to use the TM11 mode to quickly determine whether a material is isotropic or not. Experimental results are presented for some isotropic materials.

Simulation study of coaxial virtual cathode oscillator as a THz source

In this paper, a coaxial virtual cathode oscillator (vircator) is simulated by the particle-in-cell method for the terahertz (THz) band. THz waves have many applications in human life, and many researchers work on related technologies, especially on THz sources like vacuum electronic devices (VEDs). A vircator is a kind of VED that is usually operated at a few GHz, but in this study, a coaxial vircator is proposed as a THz source for the first time. By adding a reflector and center rod to the base coaxial configuration and optimizing the parameters, an output power of about 29 W is achieved at 0.25 THz with the dominant mode of TM01. Working voltage and current are 26 kV and 100 mA, respectively. In addition, to indicate the scalability of the device, two other designs for higher and lower frequencies are simulated. Simplicity is one of the important advantages of the proposed THz coaxial vircator in comparison to other THz sources.

On the use of dielectric elements in axion searches with microwave resonant cavities

This study explores the primary effects of dielectric materials in a resonant cavity-based search for axion dark matter. While dielectrics prove beneficial in numerous cases, their incorporation may lead to less-than-optimal performance, especially for the lowest TM mode. Additionally, the stronger confinement of the electric field inside the dielectrics can exacerbate mode mixings, in particular for higher-order modes. Case studies have been carried out using a combination of analytical solutions and numerical simulations. The findings indicate dielectric cavities employing the TM010 mode experience a significant reduction in sensitivity when compared to a similar search conducted in a cavity at equivalent frequency using no dielectrics.

Numerical approximation based on a decoupled dimensionality reduction scheme for Maxwell eigenvalue problem

We present a high‐accuracy numerical method based on a decoupled dimensionality reduction scheme for Maxwell eigenvalue problem in spherical domains. Using the orthogonality of vector spherical harmonics and the variable separation approach, we decompose the original problem into two classes of decoupled one‐dimensional TE mode and TM mode. For the TE mode, we establish a variational formulation and its discrete scheme and give the error estimations of the approximate eigenvalues and eigenfunctions. For the TM mode, it is different from TE mode which naturally meets the divergence‐free condition and will not generate some spurious eigenvalues. We design a numerical algorithm based on a parameterized method to filter out the spurious eigenvalues. Finally, some numerical results are presented to confirm the theoretical results and validate the algorithms.

Polarization control investigation based on an integrated graphene-assisted microring cavity

In this paper, we propose and analyze an integrated polarization-selective structure of a graphene-assisted silica microring cavity to realize polarization control due to different optical distributions of whispering-gallery modes in the microring and polarization-dependent absorptions of graphene. A graphene stripe is partially side coupled with a silica microring to distinctly influence the propagations of a TE mode and TM mode in the microring. Especially, the appearance of the plasmonic mode in the groove between the graphene and the microring enhances light–matter interaction between the graphene and the TM-polarized mode, while without that for the case of TE mode propagation. By applying voltage on the graphene stripe along with its electro-optic modulation effect, the difference in the polarization extinction ratio of 20.6 dB is obtained between the cases of the polarized TM mode and TE mode in the microring. Furthermore, a second silica microring is added in this hybrid structure to couple the original microring along with a graphene stripe embedded in between finally realizing an electromagnetically induced transparency line shape because of the plasmonic coupling in both cavities with the condition of TM mode propagation, while without any line-shape change for the case of TE mode propagation. This compact hybrid structure offers a good integrated photonic platform to realize an excellent polarization-selective device.

High-speed polarization-independent plasmonic modulator on a silicon waveguide.

The electrical bandwidth of an electro-optic modulator plays a vital role in determining the throughput of an optical communications link. We propose a broadband plasmonic electro-optic modulator operating at telecommunications wavelengths (λ0 ∼ 1550 nm), based on free carrier dispersion in indium tin oxide (ITO). The ITO is driven through its epsilon-near-zero point within the accumulation layers of metal-oxide-semiconductor (MOS) structures. The MOS structures are integrated into a pair of coupled metal-insulator-metal (MIM) waveguides aligned on a planarized silicon waveguide. The coupled MIM waveguides support symmetric and asymmetric plasmonic supermodes, excited adiabatically using mode transformation tapers, by the fundamental TM0 and TE0 modes of the underlying silicon waveguide, respectively, such that the modulator can operate in either mode as selected by the input polarisation to the silicon waveguide. The modulator has an active section 1.5 to 2 µm long, enabling the modulator to operate as a lumped element to bandwidths exceeding 200 GHz (3 dB electrical, RC-limited). The modulators produce an extinction ratio in the range of 3.5 to 6 dB, and an insertion loss in the range of 4 to 7.5 dB including input/output mode conversion losses. The AC drive voltage is ±1.75 V. The devices comprise only inorganic materials and are realisable using standard deposition, etching and nanolithography techniques.