Asymmetric Waveguide Research Articles

Mid-infrared silicon photonic phase shifter based on microelectromechanical system.

Mid-infrared (MIR) photonic integrated circuits have generated considerable interest, owing to their potential applications, such as thermal imaging and biochemical sensing. A challenging area in the field is the development of reconfigurable approaches for the enhancement of on-chip functions, where a phase shifter plays an important role. Here, we demonstrate a MIR microelectromechanical system (MEMS) phase shifter by utilizing an asymmetric slot waveguide with subwavelength grating (SWG) claddings. The MEMS-enabled device can be easily integrated into a fully suspended waveguide with SWG cladding, built on a silicon-on-insulator (SOI) platform. Through engineering of the SWG design, the device achieves a maximum phase shift of 6π, with an insertion loss of 4 dB and a half-wave-voltage-length product (VπLπ) of 2.6 V·cm. Moreover, the time response of the device is measured as 13 µs (rise time) and 5 µs (fall time).

Racetrack microring resonator with improved quality factor based on asymmetric waveguide bend

Racetrack microring resonators with improved quality factors based on asymmetric Bezier waveguide bend for silicon nitride photonics integration platform have been proposed and demonstrated experimentally in this paper. The asymmetric Bezier waveguide bend can reduce bend loss which is one of the major limitations of the Q factor of racetrack microring resonators. The proposed racetrack microring resonator structure based on an asymmetric Bezier bend waveguide can significantly improve the Q factor while maintaining the same device area. Such racetrack microring resonators with superior performance can help improve the performance of on-chip devices and further promote the development of a photonic integration platform.

High-power distributed feedback lasers with high-order surface curved gratings.

A novel, to the best of our knowledge, broad-area distributed feedback laser with high-order surface curved gratings has been fabricated based on standard near ultraviolet lithography. The characteristics of increasing output power and mode selection are achieved simultaneously by using a broad-area ridge as well as an unstable cavity structure composed of curved gratings and a high-reflectivity coated rear facet. Suppression of high-order lateral modes is realized by setting current injection/non-injection regions and asymmetric waveguides. This DFB laser emitting around 1070 nm has achieved a spectral width of 0.138 nm and a maximum output power of 915 mW kink-free optical power. The threshold current and side-mode suppression ratio of the device are 370 mA and 33 dB, respectively. The simple manufacturing process and stable performance give this high-power laser broad application prospects in the fields of light detection and ranging, laser pumps, optical disk access, etc.

Semiconductor laser design with an asymmetric large optical cavity waveguide and a bulk active layer near p-cladding for efficient high-power red light emission

A semiconductor laser design for efficient, high power, high brightness red light emission is proposed, using a large optical cavity asymmetric waveguide and a bulk active layer (AL) positioned very close to the p-cladding. The low threshold carrier density associated with the broad AL, as well as the proximity of the AL to the p-cladding, ensure that the electron leakage current, the major detrimental factor in red lasers, stays modest in a broad range of excitation levels. This in turn promises high-power, efficient operation.

Two-Dimensional Hybrid Perovskitoid Micro/nanosheets: Colorful Ultralong Phosphorescence, Delayed Fluorescence, and Anisotropic Optical Waveguide.

Molecular persistent luminescence, such as room-temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF), have attracted broad attention in the fields of biological imaging, information security, and optoelectronic devices. However, the development of molecular micro/nanostructures combining both RTP and TADF properties is still in an early stage. Herein, a new type of organic metal hybrid perovskitoid (OMHP) two-dimensional (2D) microcrystal has been fabricated through a facile solution method. The long-lived TADF-RTP dual emission can be highly tuned by changing the excitation wavelength, temperature, and decayed time. Moreover, the 2D OMHP microsheet exhibits an asymmetric and anisotropic optical waveguide with low optical loss coefficient, together with extremely high linearly polarized fluorescence-phosphorescence emission (anisotropy = 0.96), which is promising for the development of polarization-sensitive luminescent materials. Therefore, this work not only demonstrates new OMHP showing colorful persistent luminescence under different modes (such as excitation wavelength, temperature, polarization, lifetime, and dimension) but also takes advantage of the 2D micro/nanostructure to provide potential applications as optical logic gates and for delicate multiple information encryption.

Waveguide-coupled heterodyne terahertz detector based on AlGaN/GaN high-electron-mobility transistor

We report a room-temperature, low output impedance, broad intermediate-frequency (IF) bandwidth field-effect terahertz detector based on an AlGaN/GaN high-electron-mobility transistor (HEMT) integrated in a metal waveguide. The waveguide detector equips a pair of quasi-Yagi antenna probes that are used to couple the terahertz energy to the HEMT channel. The gate is configured as an asymmetric edge-coupled coplanar waveguide transmission line. This terahertz electric field is asymmetrically distributed in the channel along the edges of the transmission lines. The responsivity and noise for direct and heterodyne detections are characterized and analyzed at different local oscillator (LO) powers. The noise-equivalent power in direct detection is below 189 pW/Hz1/2. Operated in a heterodyne mode with a LO power of −3 dBm, the detector offers a conversion loss less than 55 dB in a frequency band of 320–340 GHz. The channel in a form of transmission line performs the broad IF bandwidth, which is increased to gigahertz range (3 GHz), and reduces the output impedance to 377 Ω which is about 20 times lower than previously reported. The transmission-line impedance could be optimized together with the distribution of the terahertz electric field in the gated channel to reduce the conversion loss.

A defect detection method for topological phononic materials based on few-shot learning

Topological phononic materials have been widely used in many fields, such as topological antennas, asymmetric waveguides, and noise insulation. However, due to the limitations of the manufacturing process, topological protection is vulnerable to some severe defects that may affect the application effect. Therefore, the quality inspection of topological materials is essential to ensure reliable results. Due to the low contrast and irregularity of defects and the similarity of topological phononics, they are difficult to recognize by traditional image processing algorithms, so manual detection is still mainstream at present. But manual detection requires experienced inspectors, which is expensive and time-consuming. In addition, topological materials are expensive to produce, and there is no large publicly available dataset, but deep learning usually relies on large datasets for training. To solve the above problems, we propose an automatic deep learning topology structure defect detection method (ADLTSDM) in this work, which could classify not only the structure of topological materials but also detect the defects of topological phononics based on a small dataset. ADLTSDM exploits the prior knowledge of the topological material structure and achieves an augmentation factor of more than 100 times through the random and fixed interval screenshot algorithm, thus enabling the training of deep neural networks with only two raw data. For defect detection, ADLTSDM has an accuracy of more than 97% and improves detection speed by more than 38% compared with manual detection. For structure classification, ADLTSDM can achieve an accuracy of over 99% and seven times faster speed compared with manual classification. Besides, the detection standard of ADLTSDM is unified, so the accuracy will not be affected by the experience of the inspectors, which has more potential in high-throughput industrial applications.

A Miniaturized Wideband Planar Bow-Tie Slot Antenna with Asymmetric CPW

In this paper, a novel miniaturized wideband planar bow-tie slot antenna is proposed. For the purpose of miniaturization and wide bandwidth, the effects of the dimension and shape of the bow-tie slot and feed structure are analyzed. This antenna adopts a water droplet slot, fed by an optimized asymmetric coplanar waveguide (CPW). By adjusting the feeding line, the impedance characteristic of the antenna is greatly improved that leads to a broader bandwidth. The proposed antenna operates from 2.8 GHz to 5.25 GHz with a gain of 3.8 dB. Compared with the traditional triangle bow-tie antenna, the relative bandwidth of the proposed antenna is broadened to more than 61%, while the size is reduced by about 36%, which indicates the proposed antenna is suitable for a variety of wireless applications.

An Efficient Technique for Evaluating the Characteristics of a Polarization Converter Consisting of an Asymmetric Waveguide

An efficient and accurate technique for evaluating the characteristics of a polarization converter consisting of a dielectric waveguide with a single asymmetric section is proposed and discussed with the aid of the imaginary-distance beam-propagation method. Detailed consideration regarding the optical-axis rotation angle reveals the necessity and effectiveness of introducing the excitation efficiency of the two hybrid eigenmodes of the asymmetric section. This enables us to assess the incident mode dependence, which cannot be done by the conventional rotation angle. We derive concise formulas regarding the polarization extinction ratio and the insertion loss using the hybrid eigenmodes. It is found that the present formulas provide reasonable results, showing a good agreement with the results obtained from a time-consuming FDTD simulation.

Mathematical Model and Practical Implementation of Transformer Oil Humidity Sensor

The mathematical dependence of the integral dielectric constant of transformer oil on its humidity is obtained. It is shown that the increase in humidity in the range from 0% to 0.5%, which corresponds to its allowable change, is accompanied by a monotonic increase in the integral dielectric constant along the nonlinear dependence. The design of a high-frequency humidity sensor in the form of a band asymmetric waveguide is proposed, which transforms the latter into a phase shift of the information wave. The mathematical model is developed and the transformation equation is obtained. It has been experimentally established that the total relative error, which consists of the error of this model, the instrumental error of the hard-ware and the subjective error of removing the measured information does not exceed 2%. The article is devoted to solving the problem of reliability of technological equipment and is part of an interdisciplinary study on the development of a set of energy efficient equipment for feed preparation, which is performed on the basis of laboratories of Vinnytsia National Agrarian University.

Lamb Wave Propagation Control Based on Modified GSL

As a new kind of elastic materials, elastic wave metasurface has great research significance in the field of elastic wave regulation. However, most of the researches on elastic wave metasurface are guided by traditional Generalized Snell’s Law (GSL), and the effect of higher order diffraction waves caused by structural periodicity is not considered. Under the action of higher order diffraction wave, the incident wave will produce more complex transmission phenomenon when passing through the metasurface, and the angle of transmission does not conform to GSL in some cases. In order to verify whether the modified GSL theory considering the higher-order diffraction term is still applicable to the regulation of solid elastic waves, this paper designs a helical metasurface based on the elastic wave theory of plate-beam structure, which is composed of helical lines of different lengths, and uses this structure to explain the complex transmission phenomenon of elastic wave metasurface. Finally, the asymmetric transmission, modal separation and waveguide of Lamb waves in thin plates are realized by combining the theory with structural design, which proves that the structure has great application potential in ultrasonic detection and other fields.

Asymmetric CPW-fed hexagonal monopole antenna with Boomerang-shaped Fractals for ultra-wideband applications

Abstract In recent days, miniaturized antennas have gained significance in portable ultra-wideband (UWB) applications owing to its broad coverage spectrum. Fractal antennas have become popular in this context owing to the three properties: self-similarity, space-filling, and lacunarity, thereby producing miniaturization with a broad spectrum. Conventional Fractal antennas achieve a good impedance bandwidth, relatively high gain, at the cost of trade-off between compact size, radiation characteristics and broad spectrum. In this paper, an asymmetric coplanar waveguide–fed hexagonal monopole antenna with Boomerang-shaped Fractals is proposed for UWB characteristics with relatively high antenna gain and wide bandwidth. The miniaturization of the antenna is realized by the Fractal structure. The size of the antenna is to be 0.287 λ r × 0.287 λ r × 0.009 λ r, where λ r is the resonating wavelength at 3.45 GHz. The proposed antenna is printed on a 0.8-mm-thick FR-4 substrate with relative dielectric constant of 4.4 and a loss tangent of 0.02. From frequency-domain analysis, the experimental results reveal that the fractional bandwidth is 101.7% and the peak antenna gain detected is 5.1 dBi. The radiation performance of the antenna was nearly omnidirectional. From the time-domain analysis, group delay and three different Fidelity Factors i.e. Fidelity Factor (FF), System Fidelity Factor (SFF), and Fidelity Factor of System (FFS), the proposed antenna is found to have negligible distortion. As the bandwidth meets up to fractional bandwidth above 20% and absolute bandwidth greater than 500 MHz, the proposed antenna is suitable for 3.45–10.6 GHz UWB applications.

Nanoplasmonic Directional Coupler Using Asymmetric Parallel Coupled MIM Waveguides

This article presents the design and analysis of a nanoplasmonic directional coupler using an asymmetric parallel-coupled line metal insulator metal (MIM) waveguide. The proposed plasmonic directional coupler is designed by applying three wire transmission line (TL) model based on the basic TL characteristic parameters of the related asymmetric parallel coupled line structures. To this end, the effective refractive index, propagation length, and characteristic impedance of the related coupled line MIM waveguide structure are obtained by using fullwave simulation software CST microwave studio suite. Specifically, the dual-band nature can be obtained by exchanging the asymmetric coupled line MIM waveguide section with two asymmetric even mode step impedance resonators (SIRs) by adjusting the gap width (g <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> ). Subsequently, a side-coupled resonator is designed and analyzed. Hence, the designed coupler is more useful to exchange several plasmonic devices such as power splitters and mixers in photonic integrated circuits (PICs) at a subwavelength scale.

Modal gain characteristics of a two-section InGaAs/GaAs double quantum well passively mode-locked laser with asymmetric waveguide

Monolithic two-section InGaAs/GaAs double quantum well (DQW) passively mode-locked lasers (MLLs) with asymmetric waveguide, consisting of the layers of p-doped AlGaAs waveguide and no-doped InGaAsP waveguide, emitting at ~ 1.06 μm, with a fundamental repetition rate at ~ 19.56 GHz have been demonstrated. Modal gain characteristics, such as a gain bandwidth and a gain peak wavelength of the MLL, as a function of the saturable absorber (SA) bias voltage (Va) as well as the injection current of gain section (Ig), were investigated by the Hakki-Paoli method. With the increase of Va, the lasing wavelength and net modal gain peak of the MLL both exhibited red-shifts to longer wavelength significantly, while the modal gain bandwidth was narrowed. Both the net modal gain bandwidth and gain peak of the MLL followed a polynomial distribution versus the reverse bias at the absorber section. In addition, for the first time, it was found that Va had an obvious effect on the modal gain characteristics of the MLL.

High slope-efficiency quantum-dot lasers grown on planar exact silicon (001) with asymmetric waveguide structures

We report electrically pumped continuous-wave (CW) InAs/GaAs quantum dot lasers directly grown on planar exact silicon (001) with asymmetric waveguide structures. Surface hydrogen-annealing for the GaAs/ Si (001) templates and low-temperature growth for GaInP upper cladding layers were combined in the growth of the laser structure to achieve a high slope efficiency. For the broad-stripe edge-emitting lasers with 2-mm cavity length and 20-µm stripe width made from the above laser structure, a threshold current density of 203.5 A/cm2 and a single-facet slope efficiency of 0.158 W/A are achieved at ∼1.31 µm band under CW conditions. The extrapolated mean-time-to-failure reaches up to 21000 hours at room temperature, which is deduced from the data measured from C-mount packaged devices. Importantly, these results can provide a practical strategy to realize 1.3 µm wavelength band distributed feedback lasers directly on planar exact Si (001) templates with thin buffer layers.

Wideband asymmetric coplanar waveguide antenna using composite right/left‐handed transmission line

AbstractA broadband asymmetric coplanar waveguide antenna is designed. In this design, two periodical composite right/left‐handed transmission line (CRLH‐TL) unit cells were chosen to generate three resonating modes. The broadband characteristic of this antenna can be achieved by combining the first‐negative‐order resonance, zeroth‐order resonance, and first‐positive‐order resonance of CRLH‐TL. A prototype structure of our proposed antenna has been fabricated and tested. The dimensions of the antenna are 30.0 × 40.0 × 1.6 mm3, which corresponds to 0.19 × 0.25 × 0.01 , where is the free‐space wavelength at 1.88 GHz. The measured band in which S11 is below −10 dB ranges from 1.80 to 3.75 GHz with the fractional bandwidth of 70.27%. The radiation patterns of the proposed antenna are highly consistent throughout the operating band, which covers the band of WiMAX, with the measured average peak gain of 2.77 dBi and radiation efficiency of 86.63%.

Enhancing performance of GaN-based LDs by using GaN/InGaN asymmetric lower waveguide layers

The effects of GaN/InGaN asymmetric lower waveguide (LWG) layers on photoelectrical properties of InGaN multiple quantum well laser diodes (LDs) with an emission wavelength of around 416 nm are theoretically investigated by tuning the thickness and the indium content of InGaN insertion layer (InGaN-IL) between the GaN lower waveguide layer and the quantum wells, which is achieved with the Crosslight Device Simulation Software (PIC3D, Crosslight Software Inc.). The optimal thickness and the indium content of the InGaN-IL in lower waveguide layers are found to be 300 nm and 4%, respectively. The thickness of InGaN-IL predominantly affects the output power and the optical field distribution in comparison with the indium content, and the highest output power is achieved to be 1.25 times that of the reference structure (symmetric GaN waveguide), which is attributed to the reduced optical absorption loss as well as the concentrated optical field nearby quantum wells. Furthermore, when the thickness and indium content of InGaN-IL both reach a higher level, the performance of asymmetric quantum wells LDs will be weakened rapidly due to the obvious decrease of optical confinement factor (OCF) related to the concentrated optical field in the lower waveguide.

High-Efficiency Continuous-Flow Microwave Heating System Based on Asymmetric Propagation Waveguide

Continuous-flow microwave heating is widely used in chemical engineering and other fields. However, during microwave heating, the load’s electrical permittivity change will affect microwave heating efficiency. In this article, a WR430 asymmetric propagation waveguide is proposed based on gradient-index metasurfaces (GIMs), which can achieve high-efficiency continuous-flow heating with a large range of permittivity. First, asymmetric microwave propagation is realized in a WR430 3-D waveguide model, and the influence of metasurfaces index, thickness, and discrete element size is analyzed. Second, the asymmetric propagation waveguide is realized by fluted medium based on the permittivity equivalent method. The results show that the microwave inside the waveguide can only propagate along one direction at 2.4–2.6 GHz. Finally, the proposed waveguide is applied to a continuous-flow heating system. Compared with the single-mode cavity, multimode cavity, and waveguide water load, the proposed method can improve heating robustness and efficiency with different loads. Experiments show that the microwave absorption efficiency is stable and greater than 90% in the proposed system when the permittivity of the load changes drastically. The proposed system has a simple structure and strong applicability, which can replace the three-stub tuner and get rid of the circulator and water load for continuous-flow heating.

Bragg fiber with a doubly defect layer-based tunable multiband optical filter

A Bragg fiber waveguide having double-defect layers in its periodic cladding region is investigated and optimized for inline tunable multi-bandpass filter applications. The proposed waveguide is classified in terms of a symmetric waveguide and an asymmetric waveguide depending upon the refractive index of the defect layers. The required reflectance and confinement loss equations are obtained using the boundary matching technique and the transfer matrix method. Due to the presence of the double-defect layer, two sharp passbands in the bandgap region are observed. The separation of the passbands and their intensities can be controlled by introducing the number of unit cells between the defect layers. Our analysis shows that the passband’s intensity, bandwidth, and central wavelength can also be tuned by changing the refractive index of the core material. In addition, the central wavelength for both defect modes are blue shifted with the increase of the core refractive index. In all of our considered cases, the higher tunability with a core refractive index variation in the right defect mode is 25.38 nm/RIU for the symmetric cases having defect layer refractive indices of 1.45. Similarly, the higher tunability with a core refractive index variation in the left defect mode is 16.9 nm/RIU for the asymmetric cases having a refractive index of 1.45 in the first defect layer and 3.42 in the second defect layer. Hence, our proposed waveguide can work as a tunable multi-bandpass inline filter with a narrow bandwidth.

Narrow-spectrum enhanced multiparameter gas sensor based on Fano resonance in an asymmetric MDM waveguide

In this study, a highly sensitive and narrow–spectrum enhanced multiparameter gas sensor is proposed based on Fano resonance in an asymmetric metal–dielectric–metal (MDM) waveguide. A side-coupled MDM structure comprising an upright rectangular cavity is initially investigated under different gaps. An assumed junction model is used to analyze the physical mechanism of a through coupled system (gap = 0) with an ultralow minimum transmission coefficient and higher refractive index sensitivity compared to other cases. Becausethe transmission spectrum of through-coupled structure is relatively broad, a ring resonator was added on the upper side of straight waveguide to generate an ultranarrow resonant mode as a discrete state that interferes with the previous broad mode serving as a quasicontinuum state to afford Fano resonance. Consequently, its full width at half maximum decreases by 420% from 496 to 11.56 nm. The response rate and detection difficulty of detection of y-asymmetric plasmonic nanostructures used in this study are exceed those of x-asymmetric plasmonic nanostructures. A multiparameter gas sensor can be developed by filling hydrogen- and methane-sensitive films in corresponding cavities of the plasmonic nanostructure. The sensitivities of methane and hydrogen can reach −2.863 and −0.265 nm/%, respectively, after optimizing relevant structural parameters. The proposed method provides an effective approach for designing narrow-spectrum enhanced and multichannel nanophotonic devices.