Mode Field Distribution Research Articles

Heterogeneously integrated quantum-dot emitters efficiently driven by a quasi-BIC-supporting dielectric nanoresonator

Bound states in the continuum (BICs) can make subwavelength dielectric resonators sustain low radiation leakage, paving a new way to minimize the device size, enhance photoluminescence, and even realize lasing. Here, we present a quasi-BIC-supporting GaAs nanodisk with embedded InAs quantum dots as a compact bright on-chip light source, which is realized by heterogeneous integration, avoiding complex multilayered construction and subsequent mismatch and defects. The emitters are grown inside the nanodisk to match the mode field distribution to form strong light–matter interaction. One fabricated sample demonstrates a photoluminescence peak sustaining a quality factor up to 68 enhanced by the quasi-BIC, and the emitting effect can be further promoted by improving the epilayer quality and optimizing the layer-transferring process in the fabrication. This work provides a promising solution to building an ultracompact optical source to be integrated on a silicon photonic chip for high-density integration.

Signal propagation parameters estimation through designed multi layer fibre with higher dominant modes using OptiFibre simulation

Abstract The aim and scope of the paper is to simulate the signal propagation parameters estimation through designed multi-layer fibre with higher dominant modes by using OptiFibre simulation software. The multi-layer fibre profile has a length of 1000 m is designed and clarified with six layers. RI difference profile variations are clarified with radial distance variations. Modal/group index, group delay, dispersion, mode field diameter and total fibre losses are demonstrated with the fibre wavelength variations. All the dominant mode field distribution for multi-layer fibre are simulated and demonstrated. The other modes for designed multi-layer fibre with the theoretical fibre cutoff values for the different modes based the designed multi-layer fibre are analyzed and clarified clearly in details.

Implementing the single/multiport tunable terahertz circularly polarized dielectric resonator antenna

A tunable terahertz circularly-polarized dielectric resonator antenna is implemented and numerically studied. An aperture coupled terahertz rectangular dielectric resonator antenna operating with the fundamental magnetic dipole is designed. The modal field distribution is perturbed using the material-perturbation technique and the electric field vectors are aligned in the horizontal plane with their orthogonal components having quadrature phase difference between them. Consequently, the circular polarization is obtained in the operating passband. The proposed antenna provides the 10-dB impedance bandwidth of 12.94% (4.27–4.86 THz) and 3 dB axial ratio bandwidth of 3.77% (4.43–4.60 THz). Moreover, tunability is achieved by modulation in the chemical potential of graphene layer coated at the top of the dielectric resonator by applying an electrostatic bias voltage. In addition, antenna provides the gain of 6.45 dBic along with 98% radiation efficiency. The proposed antenna can also be used for the implementation of multi-port wireless THz communication systems with the advantage of tunable CP response with impeccably high radiation performance parameters. A two-port multi input, multi output (MIMO) antenna is implemented with the usage of the proposed metal strip coated DR. This antenna provides high isolation between both the ports along with polarization response and pattern diversity with the acceptable value of MIMO performance parameters like envelop correlation coefficient and diversity gain.

On-Fiber Multiparameter Sensor Based on Guided-Wave Surface Plasmon Resonances

We report an ultracompact on-fiber multiparameter sensor that employs multiple guided-wave surface plasmon resonances (GWSPRs) and machine learning based signal processing. The sensor structure entails a gold plasmonic crystal cavity covered with a planar dielectric waveguide on the end-face of a single-mode fiber. Incident light on the gold gratings of the plasmonic crystal cavity excites surface plasmon resonances, which are coupled into the waveguide and induce multiple, high-Q GWSPRs. Due to the difference in the field distributions of these resonance modes, the resonance dips in the sensor reflection spectrum have distinctive responses to external stimuli, which enables simultaneous measurement of multiple parameters. To enhance the sensing accuracy, a neural network model is used to demodulate the sensor responses. A proof-of-concept sensor using a UV-curable polymer as a waveguide material is demonstrated for simultaneous measurement of temperature and salinity of salt solutions. Although we only demonstrate the measurement of two parameters, the proposed sensor has the capability to measure more parameters if a multilayer waveguide structure made of different functional materials is used. The proposed sensor can benefit multifunctional analysis in a broad range of biological, chemical, and environmental monitoring applications.

Asymmetric Topological Valley Edge States on Silicon‐On‐Insulator Platform

AbstractValley‐Hall photonic topological insulators (VPTIs) provide an intriguing approach to suppress backscattering, enhance the robustness of transport, and shrink the footprints of the topological devices. However, previous works focused on the transmission characteristics of the symmetric topological waveguides with few reports on functional devices involving edge mode coupling, which hinders the implementation of various functional devices such as optical couplers/splitters, switches, filters, and etc. In this paper, a new method to manipulate the mode field distributions in topological waveguides is demonstrated by introducing asymmetric edge states, thus the mode coupling with an arbitrary coupling ratio can be achieved between topological waveguides. As an example, a topological power splitter with a 33:67 splitting ratio is demonstrated experimentally. In addition, to verify the robust transmission property of the topological photonic devices, a high‐speed data transmission experiment for a topological power splitter is performed and a high data rate of 128 Gb s−1 is achieved. These results promise a new method to manipulate the mode field distribution in topological waveguides and devices that may find wide applications in diverse fields such as optical communications, nanophotonics, and quantum information processing.

Parallel-Integrated Sapphire Fiber Bragg Gratings Probe Sensor for High Temperature Sensing

This paper reports the fabrication of parallel integrated sapphire fiber Bragg gratings (SFBGs) probe sensor by the femtosecond laser point by point (PbP) method. The SFBGs probe sensor transmits optical signals through quartz multimode fiber, and takes an 8.5 mm sapphire fiber as the sensing probe, which can work stably for a long time at 1200 °C. This method can not only quickly prepare and obtain SFBGs with small bandwidth, but also obtain gratings with high reflectivity, which is about 15%. The mode field distribution in sapphire fibers with different lengths is studied by the beam quality analyzer. High-order modes are easily excited as the length of sapphire fibers increases. In addition, a spherical lens is prepared at the end of sapphire fiber, which effectively improve the signal-to-noise ratio (SNR) to 22 dB. The good spectral quality can still be maintained after holding at 1200 °C for 24 hours, and the temperature sensitivity can reach 30.19 pm/°C in the high temperature range, which is more than 2 times higher than that of quartz FBGs sensors. This parallel integrated SFBGs probe sensor overcomes the problems of doped quartz fiber element diffusion at high temperature and the instability of microstructure caused by material softening, and can be developed for long-term stable operation at 1200 °C high temperature and harsh environments.

Coupling characteristics of laterally coupled gratings with slots

Laterally-coupled ridge-waveguide distributed feedback lasers fabricated without epitaxial regrowth steps have the advantages of process simplification and low cost. We present a laterally coupled grating with slots. The slots etched between the ridge and grating area are designed to suppress the lateral diffusion of carriers and to reduce the influence of the aspect-ratio-dependent-etching effect on the grating morphology in the etching process. Moreover, the grating height in this structure can be decreased to lower the aspect ratio significantly, which is advantageous over the conventional laterally coupled ridge waveguide gratings. The effects of five main structural parameters on the coupling characteristics of gratings are studied by MODE Solutions. It is found that varying the lateral width of the grating can be used as an effective way to tune the coupling strength; narrow slots (100 nm and 300 nm) and wide ridge (2 μm–4 μm) promote the stability of grating coupling coefficient and device performance. It is important to note that the grating bottom should be fabricated precisely. The comparative study of carrier distribution and mode field distribution shows that the introduction of narrow slots can strengthen the competitive advantage and stability of the fundamental mode.

An Optical Fiber Sensor for Axial Strain, Curvature, and Temperature Measurement Based on Single-Core Six-Hole Optical Fiber.

In this paper, the field distribution and effective refractive index of transmission modes in single-core six-hole optical fiber were researched by modeling and simulation experiments. Based on the simulation results, a new type of sensor for axial strain, curvature, and temperature applications measurement was designed and fabricated. The experimental results showed that the axial strain sensitivities at different dips were −0.97 pm/με and −1.05 pm/με in the range from 0 to 2000 με, and the temperature sensitivities were 35.17 pm/°C and 47.27 pm/°C in the range from 25 to 75 °C. In addition, the proposed sensor also detected the curvature change with sensitivities of 7.36 dB/m−1 and 20.08 dB/m−1 from −2.582 m−1 to −1.826 m−1, respectively. Finally, through theoretical analysis, it can be deduced that this has potential application in the field of simultaneous measurement of strain and temperature.

Directional emission in X-cut lithium niobate microresonators without chaos dynamics

We systematically investigate the field distribution of the transverse electric modes in X-cut lithium niobate disks as an example of circular microcavities with anisotropic refractive index. A conserved quantity is discovered, which indicates the absence of chaos that generally exists in deformed microcavities and leads to a nontrivial directional emission. The emission directionality was theoretically investigated and experimentally verified by exciting high-order modes of an X-cut lithium niobate microresonator assisted with second harmonics. The field distribution analysis can enrich the knowledge in designing photonic devices that need precise control of field distribution, such as phase matching in nonlinear processes. Furthermore, the discovered emission phenomenon is momentous in enhancing and controlling communications between on-chip photonic devices.

Compact FIN defected ground structure for improved cross polarisation in array antenna

ABSTRACT In this article, a 2 × 2 microstrip array antenna integrated with FIN defected ground structure (DGS) is investigated, which is designed for 3.24 GHz band operation. The FIN-DGS has been etched from the ground plane in the H-plane direction between two contiguous elements in a symmetric manner. Therefore, it suppresses the cross-polarisation (XP) radiation in the antenna without affecting its co-polarisation (CP) radiation characteristics. A proposed antenna has been designed and experimentally verified and shows <35 dB XP (±50º) radiation around boresight of the radiating elements in the H-plane with 10.7 dBi gain. The variation of XP fields has been investigated using the modal field distribution. The designed antenna provides a wide range of applications in adaptive arrays and space antennas, where 3D coverage with decreased XP values is the primary constraint.

Characterization of mode field distribution in optical Fabry-Perot cavity based on nanofiber

The composite cavity optomechanical system combining optical Fabry-Perot (F-P) cavities, particles, and micro/nano mechanical oscillators is becoming more significant in the researches and applications of the fundamental physics, quantum information processing, and precision measurement. Characterizing the mode field distribution of optical F-P cavity is significant prior to the application of optical F-P cavity. In this paper, we propose and demonstrate a method to measure the waist of an optical F-P cavity and to characterize the mode field distribution of the optical F-P cavity by using a nanofiber nondestructively. In experiment, a nanofiber is placed in the mode of the optical F-P cavity with a fineness of around 1500. The optical F-P cavity is composed of two mirrors each with high reflectivity of 99.8%. The radius of curvature of the each mirror is 50 mm. The cavity length is (&lt;inline-formula&gt;&lt;tex-math id="M1"&gt;\begin{document}$ 80 \pm 4 $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="23-20221538_M1.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="23-20221538_M1.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;) mm. The nanofiber is fabricated from a single-mode fiber by the flame-brush method. The nanofiber diameter is around 440 nm. The transmission spectra of the optical F-P cavity are measured by scanning the cavity length. The free spectrum ranges and the inner cavity losses can be obtained from the transmission spectra. First, the influence of the nanofiber on the optical F-P cavity fineness is investigated. The fineness as a function of nanofiber position along the radial direction of the optical F-P cavity is measured. The fineness caused by the nanofiber decreases to a minimum value of about 240. Second, it is investigated that the optical F-P cavity inner loss caused by the nanofiber as a function of the nanofiber position along the radial direction of the optical F-P cavity when the nanofiber is placed at the waist of the optical F-P cavity. The inner loss of the optical F-P cavity caused by the nanofiber is related to the intensity distribution of the optical F-P cavity mode field, which is predicted theoretically. Thus, by making the Gaussian fitting of the optical F-P cavity inner loss as a function of the nanofiber position, we can obtain a waist radius of the optical F-P cavity to be (&lt;inline-formula&gt;&lt;tex-math id="M2"&gt;\begin{document}$ 72 \pm 1 $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="23-20221538_M2.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="23-20221538_M2.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;) μm. This is in good agreement with the theoretical calculation. Finally, the mode field distribution of the optical F-P cavity along the cavity axis is characterized. This method can be used for precisely controlling the coupling between the particles on the surface of nanofiber and optical F-P cavity. Besides, this method provides a good platform for studying the hybrid optomechanical system combining cavities, photons and quantum emitters.

Active and selective manipulation of dual transparency windows in hybrid graphene-vanadium dioxide metamaterial

Active and selective manipulation of dual–spectral electromagnetically induced transparency (EIT) metamaterial constructed by three graphene strips and vanadium dioxide (VO2) layer is proposed and demonstrated numerically. Simulation results illustrate that the dual-spectral EIT-like effect are induced by adjacent graphene strips acted as bright and bright mode and excited opposite-phase electric field distributions. One or two of EIT-like windows can be modulated by selectively varying graphene strip’s Fermi energy. Meanwhile, the Fermi energies of three graphene strips are varying simultaneously, the position of dual transparency windows as a whole obviously exhibit blue shift. Moreover, the amplitude of dual–spectral EIT windows can be simultaneously manipulated while frequency remain rough constant during the phase transition process of VO2. The physical mechanism underneath the phenomenon of actively and selectively tunable EIT, which is revealed by theoretically calculated results based on the classical three-oscillator model, can be attributed to the variation of resonance frequency, coupling coefficient and losses of the resonators caused by varying Fermi energy of graphene strips and conductivity of VO2.

Design of a New Dual-Band Balanced-to-Balanced Filtering Power Divider Based on the Circular Microstrip Patch Resonator

A novel compact dual-band balanced-to-balanced (BTB) filtering power divider (FPD) based on the circular microstrip patch resonator is presented, for the first time in this brief. Firstly, in order to elucidate its principle of operation, the resonant property of the circular microstrip patch resonator is researched. After that, a prototype of the dual-band BTB FPD is developed. It is mainly constructed by two coupled circular patch resonators, two impedance matching ports, and three pairs of balanced ports. Its operating mechanism can be strictly illustrated by the field distributions of the concerned resonant modes. Hereinto, desired dual-band balanced filtering response is attained by elaborately exploiting TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> and TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">31</sub> modes while suppressing other modes from the patches. Ultimately, for validation, a dual-band BTB FPD centered at 4.2 GHz and 9.4 GHz is designed, fabricated, and tested. Good agreement between simulated and measured results validates that expected differential mode (DM) response, prominent DM isolation, nice common-mode (CM) suppression, high selectivity, and satisfactory harmonic suppression.

Wide-Beam Dielectric Resonator Antennas Based on the Fusion of Higher-Order Modes

Geometry-induced resonant modes with intrinsic broad beam coverage are synthesized within step-shaped dielectric resonator antennas (DRAs). Following the idea of mode fusion, a synthesized mode inherits and combines the modal features from several conventional ones of regular DRAs. Superior flexibility and design freedom in beam shaping are thus obtained, leading to a 3 dB beamwidth exceeding 200° in both main planes. To form such a broad-beam mode, three regular higher-order modes from rectangular DRAs are chosen and merged. Their modal radiation patterns have fine complementation, meanwhile, they are readily excited by a shared feed. To further demonstrate the mechanism of mode fusion, the modal field distribution of the presented DRAs is analyzed. A design guide is presented as well.

Full-Vector Analysis of Bending Waveguides by Using Meshless Finite Cloud Method in a Local Cylindrical Coordinate System

By using a meshless finite cloud method, a full-vector mode solver in terms of transverse-magnetic-field components for optical dielectric waveguide bends is developed in a local cylindrical coordinate system. To construct the interpolation function, both the point collocation and the fixed reproducing kernel technique are utilized, and then with the help of the continuity conditions of the longitudinal field components and the perfectly matched layer absorbing boundary conditions, a standard matrix eigenvalue is obtained. Compared with the conventional meshed numerical techniques, the distributions of solution points of the present meshless method can be applied to the area of complexity in a completely free manner. Consequently, excellent convergence with high accuracy can be realized. Moreover, the present method can be applied to both the uniform and non-uniform nodal distributions, thus the computational procedure is relatively flexible. To validate the proposed method, both fundamental and high-order leaky modes for a typical rib bending waveguide are analyzed and their modal field distributions and corresponding effective refractive indexes are presented. Results are in good agreement with those published earlier, showing the effectiveness of the present method.

Nanogap Enabled Trajectory Splitting and 3D Optical Coupling in Self-Assembled Microtubular Cavities.

We report the generation of multiple sets of 3D confined resonant modes in a single microtube cavity owing to nanogap induced resonant trajectory splits. The optical field largely overlaps in the split resonant trajectories, enabling strong optical coupling of 3D confined resonant light. The anticrossing feature and modes changing-over were demonstrated as direct evidence of strong coupling. In such an optical coupling system, the spatial optical field distribution of 3D coupling modes was experimentally mapped under the strong coupling regime, which allows direct observation of the energy transfer process between two hybrid states. Numerical calculations based on a quasi-potential model and the mode detuning process are in excellent agreement with the experimental results. The generation of multiple sets of 3D confined resonant modes and their efficient coupling in a single microcavity are of high interest for directional coupling with a higher degree of freedom to realize on-chip integration with elevated functionalities such as multiplexing, 3D lasing, and signal processing.

Angle-Resolved Hollow-Core Fiber-Based Curvature Sensing Approach

We propose and theoretically study a new hollow-core fiber-based curvature sensing approach with the capability of detecting both curvature radius and angle. The new sensing method relies on a tubular-lattice fiber that encompasses, in its microstructure, tubes with three different thicknesses. By adequately choosing the placement of the tubes within the fiber cross-section, and by exploring the spectral shifts of the fiber transmitted spectrum due to the curvature-induced mode field distributions’ displacements, we demonstrate a multi-axis curvature sensing method. In the proposed platform, curvature radii and angles are retrieved via a suitable calibration routine, which is based on conveniently adjusting empirical functions to the fiber response. Evaluation of the sensing method performance for selected cases allowed the curvature radii and angles to be determined with percentual errors of less than 7%. The approach proposed herein provides a promising path for the accomplishment of new curvature sensors able to resolve both the curvature radius and angle.

Ultrabroadband Power Coupling and Mode-Order Conversion Based on Trapezoidal Subwavelength Gratings

We propose and experimentally demonstrate the broadband power coupling and mode-order conversion based on the trapezoidal subwavelength grating (SWG) structures. The slowly varying trapezoidal SWGs alter the modal field distribution in two closely spaced waveguides and result in an enhanced and adiabatically changing coupling strength between them. As a result, high coupling efficiencies over broad bandwidths are obtained for the coupled-waveguide devices with small sizes. Simulations show that the complete power transfer and the mode-order conversion can be accomplished using the coupling structure. The power coupler has a 1-dB bandwidth of 708 nm spanning from 1353 nm to 2061 nm, while the mode-order converter has a conversion loss less than 1 dB and crosstalk below -12.5 dB over a 324-nm bandwidth from 1388 nm to 1712 nm. Both devices were fabricated and experimentally characterized. The power coupler shows a measured insertion loss of <; 0.25 dB and the mode-order converter exhibits a measured conversion loss of <; 1.2 dB and a crosstalk value of <; -10 dB, over a ~120-nm bandwidth from 1507.2 nm to 1627.8 nm that covers the whole C- and L-band. The coupling length and the total length of our devices are 12.5 μm and 62.5 μm, respectively, which are very compact for adiabatic coupling structures.

High-frequency electric field intensity sensor based on double-slot waveguides filled with electro-optical polymer

We consider the structure of a high-frequency external electric field sensor based on microring resonators using waveguides with two horizontal or vertical slots filled with an electro-optical polymer. The method of lines is used to calculate the propagation constants and mode field distributions of such waveguides. It is shown that double-slot waveguides filled with an electro-optical polymer exhibit higher optical radiation intensity in the slot region compared to single-slot waveguides, which makes it possible to increase the sensor sensitivity. The distances between the slots and the values of their widths at which a maximum sensor sensitivity is achieved are determined. The sensor allows alternating electric fields with frequencies up to 10 GHz to be measured in the range of 100−16 × 106 V m−1 with an accuracy of 150 V m−1.

Full-vectorial meshless finite cloud method for an anisotropic optical waveguide analysis.

By using the meshless finite cloud method, an efficient full-vectorial mode solver based on the transverse-magnetic-field components is developed to analyze the optical waveguides made of anisotropic materials, in which the waveguide cross-section enclosed by the perfectly matched layers is divided into an appropriate number of homogeneous clouds. The point collocation technique is utilized to create a scattered set of nodes over the cloud, and then the continuity conditions of the longitudinal field components are imposed to appropriately deal with the discrete nodes at the interfaces shared by the adjacent clouds. In comparison with conventional mesh-based numerical techniques, the distributions of solution nodes of the present method can be applied to the area of complexity in a completely free manner. Moreover, an interior nodal distribution adaptively updating along the propagation direction is adopted to accomplish higher computational efficiency while improving numerical accuracy. To validate the proposed method, an anisotropic square waveguide, a magneto-optical raised strip waveguide, and a nematic liquid-crystal channel waveguide are considered as numerical examples, and their modal field distribution and corresponding effective refractive indexes are presented. Results are in good agreement with those published earlier, showing the effectiveness of the present method.