Higher-order TE Research Articles

Расчет фильтра для выделения излучения третьей гармоники циклотронной частоты сильноточного гиротрона Ka-диапазона

The calculation of a mode filter for a circular waveguide designed to isolate a high-order TE mode consistent with its field has been carried out. A theoretical justification and results of electrodynamic modeling are given using the example of identifying the third harmonic TE12,4 mode of the gyrotron against the background of predominant radiation at the fundamental cyclotron harmonic in the TE4,2 mode.

Design of Filtering Dielectric Resonator Antenna Arrays Using Simple Feeding Networks

A 1 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 3 filtering dielectric resonator antenna (DRA) array is investigated in this communication. The central DRA is excited by a microstrip-coupled slot, while the two side DRA elements are, respectively, excited by the central DRA via a low-profile patch-loaded dielectric bridge laid between them. In order to integrate the filtering function, the open stub of the microstrip feed line is elaborately designed to generate a radiation null at the upper band edge, while two vertical metallic strips are added onto the sidewalls of the central DRA to provide another radiation null at the lower band edge. On the other hand, in order to achieve an enhanced gain in the operating passband, the higher order TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">113</sub> mode of the DRA elements is excited. It is found that due to the loading effects of metallic patches and conformal strips, three stepping resonances of the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">113</sub> mode are generated in the passband, leading to a wide impedance bandwidth of 13.7% and a stable gain of 11.4 dBi. As a result, both good radiation and filtering performance are achieved without requiring complex filtering circuits. To demonstrate the extensibility of the array, a larger 3 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 3 filtering DRA array with a high peak gain of 14.7 dBi is further designed by just using a three-way power dividing network.

Numerical analysis of a grating embedded bidirectional integrated optical coupler pressure sensor.

A numerical analysis of a grating embedded bidirectional optical coupled waveguide structure is presented for the first time, to our knowledge. A finite difference method (FDM) based scheme is devised to extract the allowed eigen TE and TM modes of the structure. Sensing characteristics of the grating employed between two high refractive index couplers are then explored. The influence of strain on the composite structure is numerically analyzed for better understanding of guiding phenomena. A numerical method based on a three-point central finite difference scheme with proper boundary conditions at the point of discontinuity is developed. For an accurate sensitivity analysis, a large number of mesh points (N=1000) are used in the FDM algorithm, while the whole analysis is done on MATLAB software. To the best of the authors' knowledge, Bragg grating sensitivities of individual TE and TM modes have been estimated for the first time. It is found that higher order TE and TM modes show improved sensitivity performance. The physics behind the improved sensitivity of the proposed structure is correlated with existing cases. The proposed technique is based on effective refractive index theory, and hence it is easy to implement. This work can be easily extended to obtain temperature, humidity, and vibration sensitivities of other novel structures.

Differential-Fed Pattern-Reconfigurable Dielectric Patch Antenna and Array With Low Cross-Polarization

A novel differential-fed dielectric patch (DP) antenna with beam steering capability is investigated in this communication. The TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mn</sub> mode in the DP resonator is theoretically analyzed to provide guidance for the subsequent antenna design. The high-order TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> mode that can be differentially excited is selected as the operating mode to further enhance the gain. Based on this, three parallel coupling slots loaded with p-i-n diodes are used as a beam steering structure. By controlling the ON-/OFF-state of the p-i-n diodes to change the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E$ </tex-math></inline-formula> -field distribution of the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> mode, the main beam can be switched to five directions. The measured gain of each state is higher than 7 dBi, and the peak value reaches 8.1 dBi. The beam steering structure and differential-fed scheme show good coordination, which effectively suppresses the deterioration of cross-polarization caused by structural asymmetry. The cross-polarization of each state is lower than −26 dB. To further verify the scalability of the proposed ideal, a 1 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 4 array fed by two dual Marchand baluns is implemented, which well maintains the beam steering capability and low cross-polarization. Reasonable agreement is obtained between the simulated and measured results. The proposed DP antenna provides a suitable candidate for indoor wireless communication.

A novel kind of wideband low-profile dielectric resonator antenna suitable for beam-scanning applications

In this paper, a low-profile wideband dielectric resonator antenna (DRA) with a very compact planar size is investigated. The antenna consists of a high permittivity dielectric sheet on the top, a low permittivity substrate in the middle, and a probe feeding structure at the bottom. By digging an annular slot in the designated area of the square dielectric sheet, the resonant frequency of fundamental TE <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">111</inf> mode can be effectively increased to be close to the high-order TE <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">131</inf> mode. The two modes can be finally merged together, yielding a wide impedance bandwidth of 16.6%. Most importantly, the combination of the two modes is done on the premise of a fixed antenna planar size, which can be very compact and suitable for beam-scanning applications. A probe feeding structure is used to excite the DRA, making the antenna simple and practical to be integrated with other RF circuits. For verification, antenna prototypes with single-feed linear polarization and differential-feed dual polarization were fabricated and measured. Reasonable agreement between the measured and simulated results is observed.

Scalable silicon-based mode-order converters assisted by tapered metal strip layer

On-chip multimode applications require efficient mode sources with various different mode-orders, so the scalable mode-order converters would be preferred but they are still not available at present. Here, we propose a scalable silicon-based mode-order conversion scheme that can achieve the mode-order conversion from input fundamental TE mode to arbitrary output higher-order TE mode in a conversion length of only 2.5 μm. Four higher-order modes (TE1 ∼ TE4) are analyzed as examples with mode conversion efficiencies >90%, crosstalks <−12 dB and insertion losses <2.8 dB, respectively. Further, the working bandwidths are relatively broad and fabrication tolerances are calculated in detail. With these features, such device scheme would help generate a serious of higher-order modes in compact sizes which would address the requirements of on-chip multimode applications, e.g., improving the mode channel numbers of on-chip mode-division multiplexing.

Realistic Design Studies on a 300-GHz, 1-MW, DEMO-Class Conventional-Cavity Gyrotron

This article presents the realistic initial design studies of a 300-GHz, 1-MW, conventional-cavity gyrotron for its probable application in the next-generation thermonuclear fusion reactors. Keeping the design goals, parameters, and constraints in view, the very high-order TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">49,18</sub> mode is chosen as the operating mode after a careful mode-selection calculation considering realistic ohmic cavity losses. After mode selection and mode competition studies, the cold-cavity design and initial design of a triode-type magnetron injection gun (T-MIG) and a gyrotron magnet are carried out and an electron beam radius of 8.11 mm is obtained with 2.4% velocity spread. Furthermore, investigation on RF behavior of the cavity is performed with the T-MIG beam parameters. By varying the nominal beam parameters, single-mode self-consistent calculations are conducted and achieved the desired output power. Then, multimode time-dependent self-consistent calculations are carried out before and after space-charge neutralization (SCN) with realistic velocity spread (up to 6%) and different beam radii for the assessment of the start-up scenario. Before SCN without velocity spread, the beam voltage is depressed to 70.08 kV and 0.72-MW output power is obtained, whereas with velocity spread (6%), 0.69-MW output power is obtained with 8.11 mm of beam radius. After 60% of SCN in the start-up scenario with velocity spread (6%), the beam voltage increases to 74.83 kV, and thereby, an output power of 0.91 MW is obtained.

Integrated TM-through/TE-converted polarization beam splitter based on z-cut lithium niobate-on-insulator platform

Lithium niobate-on-insulator (LNOI) platform has been regarded as the new driving force to push the developments of integrated photonics, where efficient polarization management and mode conversion are the fundamental issues to be solved. In this work, we propose a triple waveguide-based TM-through/TE-converted polarization beam splitter (PBS) integrated on the z-cut LNOI platform, where the device works on the phase matching of optical mode. To improve the device performance and shorten the device size, we have added two cutting angles on both ends of the intermediate waveguide and optimized the length overlap between two evanescent coupling regions. From results, polarization extinction ratio 26.15 dB, insertion loss 0.47 dB for input TM0 mode, and mode conversion efficiency 99.6%, crosstalk − 22.82 dB, insertion loss 0.12 dB for input TE0 to output TE1 mode have been obtained, respectively. So, efficient polarization separation and mode conversion have been achieved simultaneously on-chip. Further, the proposed device scheme can be extended to output other higher-order TE modes via adding the width of the cross output waveguide. We hope such device scheme can make for the compact integration and capacity improvement of on-chip optical interconnects through multiplexing transmissions on the LNOI platform.

Phase-Locking of Second-Harmonic Gyrotrons for Providing MW-Level Output Power

We propose the method of providing megawatt (MW)-level output power in continuous wave (CW) or long-pulse second-harmonic (SH) gyrotrons using phase-locking by a weak external monochromatic signal. Typically, the power of harmonic gyrotrons is hindered due to excitation of spurious fundamental-harmonic modes at the front of the accelerating voltage and the beam current. Injection of a seeding signal at the operating SH mode (priming) can suppress the spurious generation during the startup process. Within the frame of a self-consistent multimode model, we demonstrate the applicability of this approach to provide &#x007E;1-MW radiation in a 230-GHz SH gyrotron with the high-order TE_34,14 operating mode which is standardly unattainable for harmonic operation.

Compact and Low-Profile Linear-/Circular-Polarization Dielectric Resonator Antennas With Extended Bandwidths

The dielectric resonator antenna (DRA) with wide bandwidth, compact size and low profile is considered as an attractive candidate for 5G wireless communications. However, most of the reported DRAs either have bulky volumes or have limited bandwidths. In this paper, a kind of compact and low-profile DRA with extended bandwidth is proposed. By observing the E-field distribution differences between the two target modes and modifying the dielectric characteristics (such as material and dimension) of the designated region where the E-field is very weak for fundamental TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">111</sub> mode but quite strong for high-order TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">131</sub> mode, the frequency of TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">131</sub> mode can be significantly affected and shifted down to merge with that of TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">111</sub> mode which is less affected. As a result, extended operating bandwidth can be obtained. This technique also benefits from not having to enlarge the planar size of the high permittivity DR, therefore making the antenna compact enough for 5G beam-scanning and low profile applications. For demonstration, linear- and circular- polarization antenna prototypes were designed and measured. The LP antenna has a −10 dB impedance bandwidth of 17.3% and a peak gain of 7.1 dBi while the CP antenna achieves a 3-dB axial ratio (AR) bandwidth of 12% and a peak gain of 6.6 dBic. Both the antennas have compact volumes of no larger than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.35{\lambda } _{0} \times 0.35{\lambda } _{0} \times 0.11{\lambda } _{0}$ </tex-math></inline-formula> . Based on the LP and CP antenna elements, two <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1\times5$ </tex-math></inline-formula> antenna arrays with the capability of beam scanning are designed and simulated. Wide scanning angles of ±45° and ±40° can be obtained for the LP and CP arrays, respectively.

A Wideband Filtering Dielectric Patch Antenna With Reconfigurable Bandwidth Using Dual-Slot Feeding Scheme

A wideband filtering dielectric patch (DP) antenna with reconfigurable bandwidth is investigated in this paper. Adjusting the aspect ratio of the DP resonator can make the high-order TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">121</sub> mode close to the dominate TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">101</sub> mode to facilitate the design of wideband filtering DP antenna. Meanwhile, the high-order TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">111</sub> mode is adjacent to the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">121</sub> mode and then used as a non-excitation and non-radiation mode for producing an upper band-edge radiation null. On this basis, two slots with different sizes in parallel are introduced into the ground plane to excite the DP resonator, resulting in a lower band-edge radiation null, which sharpens the lower band-edge roll off. A pair of slits between the two coupling slots are incorporated and the varactor diodes are loaded on the slits to tune the electrical distance of the coupling slots, thereby electrically controlling the frequency of the lower band-edge radiation null. In this way, the fractional bandwidth (FBW) of the resultant filtering antenna can be flexibly tuned from 21% to 15.3%. A prototype has been designed, fabricated, and measured. Reasonable agreement was obtained between the simulated and measured results.

Generation of High-Order Waveguide Modes with Reduced Symmetric Protection

Single-mode operation in a rectangular waveguide is very important, since the existence of multimodes may arouse distortions of carried signals due to the modal dispersion. High-order mode means multiple periods of field in the transverse cross section, with distinct electromagnetic properties from the dominant mode. Although numerous methods are proposed to achieve mode selection within the waveguide, they only permit specific high-order modes to survive in a frequency range. However, it still remains a great challenge to control the bandwidth freely for single-mode operation. Here, we propose an approach for high-order mode generation, in which the desired mode operates in the band gap of other modes, and the working bandwidth can be engineered independently by reducing the symmetry of the loaded periodic metallic ridges in the waveguide. Two examples are demonstrated, where only ${\mathrm{TE}}_{20}$ and ${\mathrm{TE}}_{30}$ modes are supported. The proposed method can also be applied to generate other high-order TE modes in the future.

Metal Strip Endfire Antenna Based on TE1 Leaky-Wave Mode

In this article, the guided-wave modes and leaky-wave characteristic of rectangular metal strips are investigated to realize endfire radiation. By strategically exciting the high-order TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> leaky-wave mode in the metal strip, a transverse in-phase E-field could be realized to generate an endfire radiation. An effective scheme is validated to manipulate the phase constant and leaky rate by altering the width of the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> mode metal strip. Then, to further tailor the phase constant and leaky rate for achieving an enhanced directivity, periodic grooves are etched on both edges of the metal strip to slowdown the phase velocity to a surface-wave mode. To verify this concept, an all-metal planar prototype of corrugated rectangular metal strip (CRMS) was fabricated and measured. Both the full-wave simulation and experimental results show that the CRMS could offer a high endfire gain of 14.2 dBi within a footprint of 3.0 × 0.5λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Moreover, a broad overlapping bandwidth of 27.7% is realized with S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> <; -10 dB, gain variation less than 3 dB, and total efficiency better than 90%. The proposed design scheme paves the way for the traveling-wave antenna with simple structure, wide bandwidth, high gain, and good platform accommodation.

RF Behavior of a Coaxial Interaction Structure for 0.24-THz, 2-MW Gyrotron

The coaxial interaction structure for a 0.24-THz, 2-MW gyrotron is designed, and its RF behavior is analyzed for the beam current of 60 A and the beam voltage of 90 kV. The searching of a suitable, very high-order TE mode, which satisfies all the technical conditions required to generate 2-MW RF power, is an important and critical step in the development of a coaxial-cavity (COCA) gyrotron. The detailed analysis of mode selection is described in this article. The geometry of the axially corrugated insert is optimized using an in-house code COCA. Based on the optimized geometry of the coaxial insert and the cylindrical cavity, the coupling coefficient and the start oscillation current are computed to analyze the mode competition for the operating mode TE42,28. The particle-in-cell (PIC) algorithm-based simulation tool is used for the beam–wave interaction computation. Very fine meshing is implemented in the simulations, considering the high frequency and fine geometry of the coaxial insert. The electron beam parameters and the cavity magnetic field are optimized first aiming at the RF power ≥2 MW and frequency 240 GHz. The final results of the cavity design confirm 2.2-MW RF power and 239.975-GHz frequency at 9.74-T magnetic field.

Continuous Characterization of Permittivity over a Wide Bandwidth Using a Cavity Resonator

We examine a rectangular cavity resonator method to accurately characterize the complex permittivity of dielectric materials over a wide frequency range of 1–5 GHz by exploiting the fundamental mode and higher-order TE&lt;sub&gt;(1,0,&lt;i&gt;l&lt;/i&gt;)&lt;/sub&gt; modes. For this purpose, a rectangular waveguide is coupled with a cavity resonator through a large inductive aperture. The permittivity characterization at both even and odd TE&lt;sub&gt;(1,0,&lt;i&gt;l&lt;/i&gt;)&lt;/sub&gt; modes enables continuous determination of the permittivity over operating frequencies. The characterization of the permittivity for even TE&lt;sub&gt;(1,0,&lt;i&gt;l&lt;/i&gt;)&lt;/sub&gt; modes suffers from potential errors due to the displacement of materials. This paper also proposes a method to compensate for these errors and improve the accuracy in the even modes. The experimental results of the fabricated cavity are presented using different materials (frequency-independent and frequency-dependent). The measured complex permittivity results show a good agreement with the reported results over a wide bandwidth available in the literature.

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.

Enhancement of the quadrupole interaction of an atom with the guided light of an ultrathin optical fiber

We investigate the electric quadrupole interaction of an alkali-metal atom with guided light in the fundamental and higher-order modes of a vacuum-clad ultrathin optical fiber. We calculate the quadrupole Rabi frequency, the quadrupole oscillator strength, and their enhancement factors. In the example of a rubidium-87 atom, we study the dependencies of the quadrupole Rabi frequency on the quantum numbers of the transition, the mode type, the phase circulation direction, the propagation direction, the orientation of the quantization axis, the position of the atom, and the fiber radius. We find that the root-mean-square (rms) quadrupole Rabi frequency reduces quickly but the quadrupole oscillator strength varies slowly with increasing radial distance. We show that the enhancement factors of the rms Rabi frequency and the oscillator strength do not depend on any characteristics of the internal atomic states except for the atomic transition frequency. The enhancement factor of the oscillator strength can be significant even when the atom is far away from the fiber. We show that, in the case where the atom is positioned on the fiber surface, the oscillator strength for the quasicircularly polarized fundamental mode HE$_{11}$ has a local minimum at the fiber radius $a\simeq 107$ nm, and is larger than that for quasicircularly polarized higher-order hybrid modes, TE modes, and TM modes in the region $a<498.2$ nm.

RF Behavior of Cylindrical Cavity Based 240 GHz, 1 MW Gyrotron for Future Tokamak System

In this paper, we present the RF behavior of conventional cylindrical interaction cavity for 240 GHz, 1 MW gyrotron for futuristic plasma fusion reactors. Very high-order TE mode is searched for this gyrotron to minimize the Ohmic wall loading at the interaction cavity. The mode selection process is carried out rigorously to analyze the mode competition and design feasibility. The cold cavity analysis and beam-wave interaction computation are carried out to finalize the cavity design. The detail parametric analyses for interaction cavity are performed in terms of mode stability, interaction efficiency and frequency. In addition, the design of triode type magnetron injection gun is also discussed. The electron beam parameters such as velocity ratio and velocity spread are optimized as per the requirement at interaction cavity. The design studies presented here confirm the realization of CW, 1 MW power at 240 GHz frequency at TE46,17 mode.

Design and Microwave Measurement of a Novel Compact TE $_{0n}$ /TE $_{1n'}$ -Mode Converter

A novel method to generate a TE $_{0n}^{{{(\mathrm {C})}}}$ ( $n = 1$ , 2, 3) ( $C$ is circular for short) or TE $_{1n'}^{{{(\mathrm {C})}}}$ ( $n' = 2$ , 3, 4) mode via a TE $_{m0}^{{{(\mathrm {R})}}}$ ( $m = 2n$ or $m = 2n' - 1$ ) ( $R$ is rectangular for short) mode generator is proposed in this paper. Two main components, including a TE $_{10}^{{{(\mathrm {R})}}}$ –TE $_{m0}^{{{(\mathrm {R})}}}$ mode converter with multiple coupling apertures and matching steps and a TE $_{m0}^{{{(\mathrm {R})}}}$ –TE $_{0n}^{{{(\mathrm {C})}}}$ or TE $_{1n'}^{{{(\mathrm {C})}}}$ mode converter, were, respectively, demonstrated. Two novel compact mode converters, respectively, exciting the TE $_{01}^{{{(\mathrm {C})}}}$ and TE $_{13}^{{{(\mathrm {C})}}}$ modes at $Q$ - and $W$ -band based on the aforementioned methodology were designed and analyzed. In the TE $_{01}^{{{(\mathrm {C})}}}$ mode converter design, symmetric cylindrical ridges were introduced to improve the mode purity and suppress the unwanted TE $_{21}^{{{(\mathrm {C})}}}$ mode by cutting off its surface current on the metal wall. Such a mode converter operating at $Q$ -band was manufactured and vector network analyzer measurements showed excellent S-parameter performance (port reflection 90%), which agreed very well with our simulation. Besides, as an expansion of the TE $_{01}^{{{(\mathrm {C})}}}$ mode converter, the designed results of a high-order TE $_{13}^{{{(\mathrm {C})}}}$ mode converter excited by a similar methodology were also presented.

Mode hybridization and conversion in silicon-on-insulator nanowires with angled sidewalls.

The mode property and light propagation in a tapered silicon-on-insulator (SOI) nanowire with angled sidewalls is analyzed. Mode hybridization is observed and mode conversion between the TM fundamental mode and higher-order TE modes happens when light propagates in a waveguide taper which is used very often in the design of photonic integrated devices. This mode conversion ratio is possible to be very high (even close to 100%) when the taper is long enough to be adiabatic, which might be useful for some applications of multimode photonics. When the mode conversion is undesired to avoid any excess loss as well as crosstalk for photonic integrated circuits, one can depress the mode conversion by compensating the vertical asymmetry in the way of reducing the sidewall angle or introducing an optimal refractive index for the upper-cladding. It is also possible to eliminate the undesired mode conversion almost and improve the desired mode conversion greatly by introducing an abrupt junction connecting two sections with different widths to jump over the mode hybridization region.