Fundamental TE Research Articles

Frequency Reconfigurable Filtering Dielectric Resonator Antenna With Harmonics Suppression

A filtering dielectric resonator (DR) antenna (DRA) that does not require any filtering circuits is investigated. It deploys a rectangular DR and three slots fabricated in the ground plane. The antenna is excited in the fundamental TE <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sup> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1δ1</sub> DRA mode and two slot modes. By making use of these three modes, two tunable radiation nulls near the edges of the passband can be obtained, giving filtering effects without the need for any filtering circuits. In this article, the design, with minor modifications of the slots, is extended to a frequency-reconfigurable filtering DRA by using varactors. Its stopband can be extended to the third harmonic. By varying the voltages of the varactors, the antenna has continuous frequency agility of 27.7% (2.15-2.84 GHz), with almost the same harmonics suppression level. The antenna has a gain of ~5.0 dBi and a rejection level of over 16.1 dB across the stopband. Its total antenna efficiency in the passband is ~81%, whereas it is generally lower than the average value of 1.8% in the stopband (up to 7.0 GHz). Compared with the reported frequency-reconfigurable filtering antennas, our design has better frequency agility, more stable filtering response, and weaker radiation in the stopband.

A Compact Phase-Controlled Pattern-Reconfigurable Dielectric Resonator Antenna for Passive Wide-Angle Beam Scanning

The function of passive wide-angle beam scanning is desired by the base station antenna to provide “green” cellular services. In this communication, such function is realized by designing a compact phase-controlled pattern-reconfigurable dielectric resonator antenna (DRA). The proposed DRA has a compact structure with a side length of 0.38 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> and excites the fundamental TE and TM modes by diverse ports. By assigning phase between diverse ports, E-plane tilted patterns are synthesized with ±66° scan angles. Its pattern-reconfigurable capability makes contributions for increasing array beam scanning angle and minimizing gain fluctuation. A passive four-element array is verified to have an enhanced beam scanning angle of ±81° with a gain fluctuation of 1.25 dB. The maximum gain of the scanning beam is located on the off-axis angle of ±66° and achieves a wide 3 dB scan coverage of ±105°. Good agreements have been shown between the measured and simulated results. The proposed phase-controlled pattern reconfigurable DRA and DRA arrays have an impedance bandwidth of 3.33% (2.95-3.05 GHz) for a sub-6 GHz wireless system. They enable the wide-angle beam scanning for base station antenna and provide a cost-effective passive system for “green” communications.

Guided-mode resonance-based bandpass filter operating at full conical mounting.

We propose a cost-effective narrow bandpass filter based on a guided-mode resonance (GMR) structure, operating at full conical mounting configuration. Two additional layers above the GMR structure with designed geometry is considered to create a large angle of incidence (AOI) on the GMR structure with an almost normal AOI on the entire structure. In the visible wavelength range, the transmission spectrum contains three peaks: two peaks that are due to the GMR effect and one that is due to thin-film interference. The modal characteristic of the two GMR peaks is identified using a matrix method for the n-layer waveguide structure. The two GMR peaks with bandwidths of ∼1nm and ∼0.5nm correspond to the fundamental TE and TM modes, respectively. The GMR peaks can be pushed away from the thin-film interference peak by modulating the grating depth.

Dual Band Notch, Compact, Low profile Hybrid Ultra Wideband RDRA

This paper presents a novel, compact Ultra Wide Band , Asymmetric Ring Rectangular Dielectric Resonator Antenna (ARRDRA), which is a unique combination of Thin Dielectric Resonator (DR), Fork shape patch and defective ground structure. The base of the proposed antenna is its Hybrid structure, which generates fundamental TM, TE and higher order modes that yields an impedance bandwidth of 119%. Proposed antenna provides a frequency range from 4.2 to 16.6 GHz with a stable radiation pattern and low cross polarization levels. Peak gain of 5.5 dB and average efficiency of 90% is obtained by the design. Antenna is elongated on a FR4 substrate of dimension 20 x 24x 2.168 mm3 and is particularly suitable for C band INSAT, Radio Altimeter, WLAN, Wi-Fi for high frequencies. Ease in fabrication due to simplicity, compactness, stable radiation pattern throughout the entire bandwidth are the key features of the presented design. Inclusion of Defective ground structure and asymmetric ring not only increases the bandwidth but also stabilize the gain and efficiency due to less surface current. Presented design launch an Ultra Wide Band antenna with sufficient band rejection at 4.48-5.34 and 5.64-8.33 GHz with stable radiation pattern and high gain.

Hybrid demultiplexer for mode and dense wavelength division multiplexing based on photonic crystal and nanowire waveguides

We propose a hybrid demultiplexer for mode and dense wavelength division multiplexing (DWDM) based on photonic crystal (PhC) and nanowire waveguides. The designed demultiplexer consists of DWDM module using PhC cavities that are defined by an effective Aubry-André-Harper (AAH) bichromatic potential and mode division multiplexing module constructing of asymmetric directional coupler using nanowire waveguides. The performance parameters of the demultiplexer are analysed by two-dimensional finite-difference time-domain method. The results show that the fundamental transverse electric (TE0) modes and first-order TE (TE1) modes of 1573.0 and 1572.2 nm can be demultiplexed simultaneously. The insertion loss is smaller than 0.6 dB, and the crosstalk is smaller than −18.6 dB. Besides, the demultiplexer has a large free spectral range up to 250 nm, which can almost cover the whole range of DWDM system.

Periodic printed semi-annular substrate loaded TM01–TE11 mode converter

AbstractA mode converter design using the concept of periodic substrates loading in a circular waveguide, to convert TM01 mode to TE11 mode is presented in this paper. The detailed design principle, simulation, and measurement results are included in this study. Simulation results show that the purity of output fundamental TE11 mode of the converter approaches 99.2% for an operating frequency of 3.2 GHz. The mode conversion efficiency is more than 90% over 3.07–3.25 GHz band and the relative bandwidth is 5.6% (180 MHz). The proposed TM01–TE11 mode converter has advantages, such as the compact, lightweight structure, high conversion efficiency, and proper bandwidth. The fabrication cost is relatively low and the structure is easy to fabricate. The power-handling capability is limited to 10 MW due to dielectric-based design. The compactness and portability of the system (e.g. Space applications, Accelerators, High Power Microwave) can be improved significantly using the proposed mode converter.

Micrometer-scale InP selectively grown on SOI for fully integrated Si-photonics

Practical applications of low-defect III–V materials grown on Si require large areas for patterning metal contacts and enhancing design flexibility. Here, we report selective area growth of bufferless and micrometer-scale InP on commercial (001)-oriented silicon-on-insulators. We obtained in-plane, centimeter-long and micrometer-wide InP single crystal stripes right atop the buried oxide layer through leveraging the lateral aspect ratio trapping (lateral ART) growth method. Using the extended InP grown by “lateral ART,” we inserted InGaAs quantum wells emitting at the telecom bands. Numerical simulation suggests that the micrometer-scale InP can support the fundamental TE mode with an ultra-low metal-induced propagation loss of 3.2 dB/cm when patterned into ridge waveguides and introducing metal contacts at both ends. Our results here represent a leap toward electrically driven III–V lasers seamlessly interfaced with Si-photonics.

Design of the Single-/Dual-Port Wideband Differential Dielectric Resonator Antenna Using Higher Order Mode

In this letter, a wideband differential hollow rectangular dielectric resonator antenna (DRA) designed using higher order mode is investigated. The fundamental TE111 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sup> and higher order TE113 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sup> modes of the rectangular DRA were employed for the design. To merge these two DRA modes together, the hollow DRA with its air region displaced from the center is employed. Both the single- and dual-port wideband differential DRAs are considered. For the dual-port version, a wide differential impedance bandwidth of ~46% was achieved. For the single-port version, a 180° hybrid coupler was designed to feed the differential DRA compactly. The measured result shows that its impedance bandwidth can be achieved as ~44%. In addition, the proposed differential DRA provides a stable broadside radiation pattern with lower cross-polarized field.

Design and Efficiency Enhancement Studies of Periodically Dielectric Loaded W-Band Gyro-TWT Amplifier

In this article, design, simulation, and efficiency improvement of W-band gyrotron traveling wave tube (gyro-TWT) amplifier operating at fundamental TE01 mode have been presented. A triode-type magnetron injection gun (MIG) has been designed and optimized for the desired quality of electron beam with a minimum spread 2% with velocity ratio 1.12 to improve the electronic efficiency of gyro-TWT. Parasitic modes in gyro-TWT have been suppressed by employing a periodic dielectric loading in the RF interaction circuit. The simulated amplifier developed an output power of ~203 kW in fundamental TE01 mode with an electronic efficiency ~29% and power gain ~57 dB for a nonspread gyrating electron beam. To improve the overall efficiency of gyro-TWT, a single-stage depressed collector has been designed as a spent electron beam recovery system. The proposed collector has enhanced the overall efficiency of gyro-TWT to ~48%.

A novel dual resonance long period waveguide grating based highly sensitive refractive index sensor with reduced temperature sensitivity

In this paper, we are proposing a novel structure to reduce the temperature cross sensitivity of a refractive index (RI) sensor based on dual resonance long period waveguide grating in a metal clad ridge waveguide, operating near the dispersion turning point. The core of the waveguide is considered to be made of two parts having opposite thermo-optic coefficients with grating written in one part only. Considering the coupling between the fundamental TE mode and a higher order TE mode, we have shown that by adjusting the thickness of the two parts of the core, it is possible to achieve blueshifts for both the resonance wavelengths with the increase in temperature unlike the case of a conventional dual resonance spectrum where two resonance wavelengths show opposite shifts. As a result, an extremely low temperature cross sensitivity ∼0.006 nm/0C has been achieved, whereas the dual resonance spectrum holds its conventional behavior with the change in ambient RI, showing an extremely high RI sensitivity ∼57,260 nm/RIU near water RI 1.33. Further, it has been observed that as we approach the dispersion turning point, temperature sensitivity decreases gradually whereas RI sensitivity increases, leading to a more accurate ambient RI measurement

Single TE01 Mode Cylindrical Vector Beams Transmission Based on Composite Gold Nanowire Embedded Photonic Crystal Fiber

A ring-core photonic crystal fiber (PCF) embedded composite gold nanowire is proposed to propagate single TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> mode cylindrical vector beam. The ring-core PCF mainly supports six low loss modes including x-polarized fundamental mode, y-polarized fundamental mode, TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> mode, TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> mode, HE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21-e</sub> and HE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21-o</sub> modes. By introducing the composite gold nanowire into the center of the ring-core PCF, only the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> mode can propagate through the fiber with a low loss; while the other modes suffer a high loss due to the surface plasmon resonance (SPR). Numerical results demonstrate that the ring-core PCF embedded with two-shell structured composite gold nanowire has large loss ratios of the other modes to TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> mode. The loss ratios are greater than or equal to 50 within the wavelength range from 1.3 to 1.39 μm. It indicates that single TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> mode cylindrical vector beam can be obtained by using the ring-core PCF based on SPR, which makes the fiber have a great potential in laser processing, nanotechnology, high resolution imaging and optical capture.

Ultra-broadband TE-pass polarizer based on hybrid plasmonic-assisted contra-directional couplers

An ultra-broadband and compact TE-pass polarizer assisted by contra-directional coupling is proposed, which consists of two identical hybrid plasmonic waveguides (HPWs) and a middle strip grating waveguide (SGW). The grating pitch of the SGW is properly designed to make TM polarization satisfy the phase-matching condition. Therefore, the launched TE mode passes through the middle SGW directly with a very low propagation loss, while the launched TM mode is contra-directionally coupled to the two HPWs evenly and finally absorbed by the top metal layers. Simulation results show that the proposed polarizer has a compact coupling length of ∼ 16.48 µ m , and the insertion loss, extinction ratio, and reflection loss are 0.269 dB, 27.7 dB, and − 16.5 d B for the fundamental TE mode at 1550 nm, respectively. In the wavelength range of 1430–1700 nm, the ER is more than 20 dB and the IL is less than 1 dB, extending the operating spectrum to 270 nm.

Ultra-Compact Coupling Structures for Heterogeneously Integrated Silicon Lasers

Heterogeneous integration of III-V lasers on Silicon on Insulator (SOI) is crucial for next-generation optical interconnects. However, reducing the footprint of the couplers between III-V laser sources and silicon chips has been a challenge for dense photonic integrated circuit (PIC). Here, we propose a slot coupler and a bridge-SWG coupler with coupling lengths of only 5.5 and 5 μm respectively, to heterogeneously integrate III-V lasers on silicon chips. For such compact coupling structures, they also show high coupling efficiencies. At the wavelength of 1550 nm, the coupling efficiencies of the fundamental TE mode can reach 93.7% and 95.5% for the slot coupler and the bridge-SWG coupler, respectively. Moreover, these coupling structures possess excellent fabrication tolerance. In addition, we optimize the taper adiabatic coupler with a total coupling length of only 4 μm.

Polarization-selective waveguide holography in the visible spectrum.

We propose and experimentally demonstrate a polarization-selective waveguide hologram at optical wavelengths, based on an all-dielectric metamaterial multilayer system. We show that two spatially separated or overlapped holographic images can be produced with two orthogonally polarized beams, incorporated into a binary computer generated hologram (CGH). These two images can be combined into a single 3D stereoscopic image observable using linearly or circularly polarized glasses. The two polarized beams can also be utilized to construct radially and azimuthally polarized "vortex" beams. The fundamental and first higher-order TM and TE modes of an optical waveguide are used to guide the two polarization states with distinct propagation constants. The two guided waves act as spatially distinct reference waves such that the integrated, on-chip hologram can distinguish the two and provide two independent images corresponding to the two polarizations. Polarization selective waveguide holograms can be used in a diverse set of applications, from chip-scale displays and augmented reality (AR) to optical trapping.

Linear Analysis of 2-D Sheet Beam Cyclotron Maser With Metallic Grating Structures

Based on a kinetic model, a linear theory of the 2-D sheet beam metallic grating cyclotron maser has been derived and analyzed numerically. The TE mode dispersion relation and the periodicity of the normalized amplitudes of spatial harmonics of the cyclotron maser with rectangular gratings are obtained. Through numerical calculations, the dependence of the growth rate on the gap distance between the metallic grating surface and the beam, the external magnetic field strength, the beam current, the transverse-to-axial velocity ratio, the axial velocity spread, and the beam voltage are analyzed. This article presents an analysis of interaction using the fundamental TE mode in the 2-D metallic grating sheet beam system. The fundamental TE mode in the 2-D metallic rectangular waveguide grating structure is the fundamental TMx mode in the 3-D rectangular waveguide grating structure and this method can be extended to the practical 3-D interaction system that operates at other TMx modes and has a good potential for the study of the combined resonances in cyclotron masers with grating structures.

A Theoretical Study on Rib‐Type Photonic Wires Based on LiNbO3 Thin Film on Insulator

AbstractA theoretical study on rib‐type photonic wires (PW) based on lithium niobate (LiNbO3)‐on‐insulator (LNOI) using finite element method is performed. Aiming at 1.55 µm wavelength, effective refractive indices of several lower‐order transverse‐electric/magnetic (TE/TM) modes in the central rib region and the fundamental mode in the slab waveguide in the side region are calculated as a function of geometric parameters of the PW. By comparing effective refractive index of the first‐order mode in the central rib region with that of the fundamental mode in the slab waveguide, single‐mode condition in the central rib region is determined in terms of geometric parameters of the PW. Electric field distributions of fundamental TE and TM modes are also simulated and discussed. In addition, dispersion relation of effective group refractive index of the fundamental mode in the central rib region is calculated and discussed in comparison with those of ridge‐type LNOI PW, traditional Ti‐diffused LiNbO3 strip waveguide, and bulk LiNbO3 single‐crystal. For a fundamental TE mode in a rib‐type LNOI PW with a LiNbO3 film thickness 700 nm, a rib width 1 µm and an etching depth 100–200 nm, nearly zero group index dispersion in the wavelength range 1.31.7 µm can be realized.

Polarization-insensitive one-dimensional guided-mode resonance filter operating at conical mounting.

We report the design and implementation of a one-dimensional guided-mode resonance filter (1D-GMRF) aiming to achieve polarization insensitivity at conical mounting. (The incident plane is aligned neither perpendicularly nor parallelly to the grating bars.) The design guideline indicates that, at conical mounting, polarization insensitivity of the 1D-GMRF can be achieved by optimizing the grating parameters to excite the fundamental TE and the fundamental TM waveguide modes simultaneously. Moreover, it is revealed that, at conical mounting, the polarization-insensitive GMR position in the angle-resolved resonance spectra is azimuthal angle ϕ-dependent. The experimental results demonstrate that polarization insensitivity of the fabricated 1D-GMRF occurs at the resonance wavelength of ∼673 nm for the conical mounting of azimuthal angle ϕ≈30° and incident angle θ≈11.2°, which agree with the simulated results.

Tilted subwavelength gratings: controlling anisotropy in metamaterial nanophotonic waveguides.

Subwavelength grating (SWG) structures are an essential tool in silicon photonics, enabling the synthesis of metamaterials with a controllable refractive index. Here we propose, for the first time to the best of our knowledge, tilting the grating elements to gain control over the anisotropy of the metamaterial. Rigorous finite difference time domain simulations demonstrate that a 45° tilt results in an effective index variation on the fundamental TE mode of 0.23 refractive index units, whereas the change in the TM mode is 20 times smaller. Our simulation predictions are corroborated by experimental results. We furthermore propose an accurate theoretical model for designing tilted SWG structures based on rotated uniaxial crystals that is functional over a wide wavelength range and for both the fundamental and higher order modes. The proposed control over anisotropy opens promising venues in polarization management devices and transformation optics in silicon photonics.

Compact Single-/Dual-Polarized Filtering Dielectric Resonator Antennas

A compact single-polarized filtering dielectric resonator (DR) antenna (DRA) with high selectivity is investigated. The DRA is fed by hybrid microstrip line/conformal strip, excited in its fundamental TE $_{1\delta 1}^{y} $ mode. Owing to different loading effects of the microstrip stub and conformal strip, the resonance frequency of TE $_{1\delta 1}^{y}$ mode excited by the two feed lines is slightly different. Such stepping resonances yield a wide bandwidth of 21.9% and a very flat gain of 5.1 dBi. The hybrid-feeding scheme also establishes a cross-coupled structure in the DRA, which introduces two radiation nulls right near the band edges. A compact wideband filtering DRA (FDRA) with quasi-elliptic bandpass response is, therefore, obtained without requiring any specific filtering circuit. This single-polarized design is also modified to realize a dual-polarized FDRA by adding another orthogonal port with the same feeding scheme. To reduce mutual coupling between the two ports, the microstrip stubs are folded to L shape, and four additional metal posts are inserted into the DR. As a result, the isolation is improved by 14 dB, from 7.2 to 21.2 dB.

Mode splitting induced by an arbitrarily shaped Rayleigh scatterer in a whispering-gallery microcavity

We investigate theoretically the mode splitting induced by an arbitrarily shaped Rayleigh scatterer attached to a whispering-gallery microcavity. The information including polar position, orientation, and polarizability tensor of the nanoparticle can be obtained through the mode-splitting signal. It is found that when the electric field of a pair of counterpropagating modes have different orientations and are not linearly polarized, both of the split modes experience frequency shift and linewidth broadening. The polar angle, at which a nanoparticle binds on the microsphere cavity, can be extracted by comparing frequency splittings of two fundamental TE modes. Moreover, the orientation and polarizability of the particle can be acquired by combining frequency splittings and linewidth broadenings of three modes which polarize the particle in different orientations. This work provides a comprehensive theory base for microcavity sensing of nanoparticles of arbitrary shape instead of nanospheres and could push nanoparticle detection towards quantitative characterization.