Waveguide-based Structure Research Articles

Surface acoustic wave actuated plasmonic signal amplification in a plasmonic waveguide

Enhancement of nanoscale confinement in the subwavelength waveguide is a concern for advancing future photonic interconnects. Rigorous innovation of plasmonic waveguide-based structure is crucial in designing a reliable on-chip optical waveguide beyond the diffraction limit. Despite several structural modifications and architectural improvements, the plasmonic waveguide technology is far from reaching its maximum potential for mass-scale applications due to persistence issues such as insufficient confined energy and short propagation length. This work proposes a new method to amplify the propagating plasmons through an external on-chip surface acoustic signal. The gold–silicon dioxide (Au-SiO2) interface, over Lithium Niobate (LN) substrate, is used to excite propagating surface plasmons. The voltage-varying surface acoustic wave (SAW) can tune the plasmonic confinement to a desired signal energy level, enhancing and modulating the plasmonic intensity. From our experimental results, we can increase the plasmonic intensity gain of 1.08 dB by providing an external excitation in the form of SAW at a peak-to-peak potential swing of 3 V, utilizing a single chip.

Additively Manufactured Dual Circularly Polarized Antennas With Bidirectional Same-Sense Radiation and Wide Bandwidth Characteristics

This communication presents two additively manufactured bidirectional circularly polarized (CP) antennas. Each antenna radiates the same-sense CP waves in opposite directions and has the capability of altering the CP state to either right-hand CP (RHCP) or left-hand CP (LHCP) by switching the feeding ports. They adopt the same scheme of combining a linearly polarized (LP) bidirectional source and two polarizers of the same type. Different polarizers, a single-slab dielectric polarizer (Ant 1) and a linearly tapered slot polarizer (Ant 2), are proposed and applied for them, respectively. The LP source adopts a circular waveguide-based structure. By altering the orthogonal degenerate modes in the waveguide, the CP states can be switched correspondingly. To validate the design ideas, prototypes of the two antennas are fabricated and tested. Experimental results show that the axial ratio bandwidth (ARBW) of Ant 1 and Ant 2 is 30.3% (4.9–6.66 GHz) and 17.9% (5.26–6.3 GHz), respectively. Within the ARBW, their gain is 8.4± 0.8 and 7.2± 1 dBic, respectively. These results demonstrate that both antennas exhibit the advantages of wide band, high gain, and ease of fabrication over the conventional designs.

Surface roughness impact on the performance of the 3D metal printed waveguide coupler at millimeterwave band

This paper presents the impact of surface roughness on the performance of a three –dimensional (3D) metal printed waveguide coupler designed at 28 GHz. The surface roughness is a significant factor that may affect 3D printed structures and post processing may be needed. It may degrade the performance of the printed devices in term of the reflection coefficient and increases the insertion loss. Thus, this work analyses the surface roughness impact on the 3D metal printed coupler designed at 28 GHz. The hybrid coupler is a waveguide-based structure with coupled resonators and the coupling is controlled by tuning the iris dimensions. The measurement is done without any post processing procedure to ensure the validation of the printed coupler with simulation results. The surface roughness measurement is performed with six tested areas of coupler structure using advanced 3D optical microscope. Then, the measured surface roughness values are included in CST software to re-simulate and compare with the original and measured results. The analysis shows that the surface roughness has a moderate influence on the reflection coefficient with 7 dB loss and 0.7 dB increased in insertion loss at 28 GHz.

Plasmonic color filter based on a hetero-metal-insulator-metal grating.

Plasmonic color filters are expected to be candidates for application to complementary metal-oxide-semiconductor (CMOS) image sensor arrays with reduced pixel size, owing to the subwavelength mode volume of plasmons. Designs of metallic gratings based on the guided-mode resonance effect suffer from the sideband transmission issue due to high-order diffraction. Here, we propose a plasmonic color filter structure based on a hetero-metal-insulator-metal grating. The guided mode, in resonance with the second-order diffraction, is highly attenuated by the forbidden band, such that the sideband transmission can be suppressed. As calculated by using the transfer matrix method and the finite-difference time-domain method, the Al-ZnO-Ag waveguide-based structure presents a color filter characteristic with the peak transmittance greater than 70% and the peak wavelength tunable in the visible light band. It may find application in displays, image sensors, and biomedical imaging technologies.

Multilayered photonic integration on SOI platform using waveguide-based bridge structure

A waveguide based structure on silicon on insulator platform is proposed for vertical integration in photonic integrated circuits. The structure consists of two multimode interference couplers connected by a single mode (SM) section which can act as a bridge over any other underlying device. Two more SM sections acts as input and output of the first and second multimode couplers respectively. Potential application of this structure is in multilayered photonic links. It is shown that the efficiency of the structure can be improved by making some design modifications. The entire simulation is done using effective-index based matrix method. The feature size chosen are comparable to waveguides fabricated previously so as to fabricate the proposed structure easily.

Design data for quick development of folded H plane tee at high average power level

At high average power level, waveguide-based structures are indispensable in microwave systems due to their higher power handling capacity. These structures are often used to perform power division and combination operation. Folded H plane tee is one of the many components that can be used for the power division application. Its advantage is that the output arms and input arms are in a single plane along a single axis, thus taking less space in the overall system. However, their proper thermal management is indispensable for its use, as high surface temperature of the waveguide reduces its power handling capacity at high power level. This paper presents quick, easy design steps and methodology for obtaining the structure of a folded H plane tee at any given frequency of operation. Further, a scheme for the thermal management for high input power level (500 kW continuous wave) is presented. The proposed methodology is tested at various frequencies in COMSOL Multiphysics, CST Microwave Studio and HFSS with excellent results. A prototype structure was fabricated for use at 3.7 GHz, which exhibited good agreement with the simulation results.

INVITED] Coherent perfect absorption of electromagnetic wave in subwavelength structures

Electromagnetic (EM) absorption is a common process by which the EM energy is transformed into other kinds of energy in the absorber, for example heat. Perfect absorption of EM with structures at subwavelength scale is important for many practical applications, such as stealth technology, thermal control and sensing. Coherent perfect absorption arises from the interplay of interference and absorption, which can be interpreted as a time-reversed process of lasing or EM emitting. It provides a promising way for complete absorption in both nanophotonics and electromagnetics. In this review, we discuss basic principles and properties of a coherent perfect absorber (CPA). Various subwavelength structures including thin films, metamaterials and waveguide-based structures to realize CPAs are compared. We also discuss the potential applications of CPAs.

Development of a Wideband and High-Efficiency Waveguide-Based Compact Antenna Radiator With Binder-Jetting Technique

A multilayer waveguide-based antenna radiator is proposed to achieve a wide operational bandwidth of high gain and high efficiency in a compact size. It is a $2\times 2$ array, consisting of a feeding waveguide, a matching cavity, and a radiating aperture. The proposed design provides sufficient freedom for the radiator to achieve broadband impedance matching. In order to improve radiation efficiency and avoid drawbacks from the traditional machining techniques, a binder-jetting process using metallic particles is adopted to realize the relatively complicated structure. This 3-D metal-direct-printing technique is competent to fabricate waveguide-based structures with high precision. Experimental results are favorably compared to the results of the fabrication by the machining technique. The measured relative bandwidth with VSWR $\leq1.5$ is 23.7% (13.0–16.5 GHz). A high efficiency of 90% is obtained at the center frequency, and more than 80% efficiency can be maintained over a 2.3-GHz bandwidth. This paper shows that the binder-jetting printing technique is a promising manufacturing approach to realizing high-performance waveguide-based antennas and microwave components.

Extraordinary Optical Transmission in a Hybrid Plasmonic Waveguide

Extraordinary optical transmission in free space through nanohole arrays has been widely investigated over the past two decades. However, because of its intrinsic nature of periodicity, it suffers from poor integration with nano-/micro- systems. Here, by folding a periodic grating into a compact cavity, we propose a waveguide-based structure within subwavelength, which also exhibits extraordinary optical transmission. Thus, lots of promising applications realized in metallic films can now be migrated onto integrated waveguides in an ultracompact way. Comparing the characteristics of the proposed integrated device and the conventional periodic structure, we reveal the nature of the unexpected transmission spectrum. Based on this principle, a collinear broadband (∼500 nm) polarizer with extinction ratio of >17.8 dB is proposed, with an ultrashort length of 450 nm. Furthermore, this structure has the potential in biological applications when integrated into lab-on-a-chip or microfluidic system. As an example, a biosensor with enhanced sensitivity of 775 nm/RIU is presented.

Rigorous evaluation of propagation losses in arbitrarily shaped waveguide structures using boundary integral – resonant mode expansion and perturbation of boundary conditions

The accurate consideration of propagation losses in arbitrarily shaped waveguide-based structures is studied in this paper. For such a purpose, a software tool based on the perturbation of the boundary conditions on the waveguide metallic walls and on the boundary integral – resonant mode expansion method has been developed. To show the advantages of the proposed technique with respect to the classic power-loss method, the complex propagation wavenumbers of a double ridge and an elliptical waveguide have been first computed and compared with results of a commercial software based on the finite element technique. Next a circular, a sectorial shaped and a triangular shaped waveguide have been considered. Then, a computer-aided design software package based on this modal analysis tool has been applied to predict the propagation loss effects in complex waveguide structures, such as an evanescent mode ridge waveguide filter, a traditional dual mode filter with circular cavities and a twist component for K-band applications.

Numerical investigation of a nano-scale electro-plasmonic switch based on metal-insulator-metal stub filter

We present a nano-scale electro-plasmonic scheme operating at 1550 nm based on plasmonic Metal-Insulator-Metal waveguide and stub filter configuration. The linear dependency of the transmission spectra of the stub filter to the length of the stubs allows designing a switch that works as normally ON or OFF switch by selecting the length of the stubs 300 or 410 nm, respectively. In our proposed waveguide-based structure, the core is an electro-optic material known as 4-dimethyl-amino-Nmethyl-4-stilbazolium tosylate with the refractive index 2.2 while the metal cladding is silver. Three-dimensional Finite Element Method simulations demonstrated that by applying a 10 V voltage to the silver cladding, a red-shift in the transmission spectra of the filter leads to turn the switch OFF or ON with calculated extinction ratio \(-13.83\) and 11.81 dB, respectively. The calculation of the capacitance implies that the switching rise-time of the switch is less than 20 fs and the bandwidth is far beyond the 18 GHz. At the maximum dimension \(460\,\hbox {nm}\times 450\,\hbox {nm}\), the subwavelength size of the switch promises the potential for future compact integrated plasmonic circuitry. For the verification of three dimensional simulation results, we have tried it, using two-dimensional transmission line method for modeling the stub filter, which demonstrates a reasonable accuracy in comparison with three-dimensional finite element method.

Millimeter-Wave Broadband Transition of Substrate Integrated Waveguide on High-to-Low Dielectric Constant Substrates

For emerging millimeter-wave wireless applications at W- and E-bands, active components including LNA and power amplifier are preferably fabricated or surface-mounted on the materials of a high dielectric constant (such as CMOS and MHMIC). On the other hand, antennas or radiating elements should be developed on relatively low-dielectric constant substrates for the enhancement of gain and bandwidth. Therefore, the development of a wideband transition from high-to-low dielectric constant substrates becomes necessary because the use of wire bonding schemes brings up packaging, interconnects, and manufacturing problems at millimeter-wave frequencies. This paper presents a novel integrated wideband transition of substrate integrated waveguide (SIW) on high-to-low dielectric constant substrates. The transition is made of a single-layer structure, which consists of a tapered high-dielectric constant substrate that connects two SIWs. Because of the waveguide-based structure of the transition, it has a self-shielded configuration, and its interference is minimum. Simulated and measured results show that the bandwidth of the proposed transition covers almost the entire W- and E-bands with low insertion loss.

A low-cost millimeter-wave whispering gallery-mode-based sensor: design considerations and accurate analysis

A dielectric waveguide-based structure coupled to a whispering gallery mode (WGM) disc resonator is introduced as a low-cost integrable millimeter-wave (mm-wave) bio-sensor. An efficient variational analysis method is developed and applied to the WGM. Three sets of sensors, operating in different ranges of frequency from 85 to 220 GHz, are fabricated and tested. The performance of the fabricated bio-sensor is demonstrated for sensing different concentrations of glucose solution samples at D-band. Also, the sensitivity, selectivity, and repeatability of these sensors are examined.

Efficient 3D sensitivity analysis of surface plasmon waveguide structures

We present a novel analytical approach for efficient sensitivity analysis of surface plasmon polaritons (SPPs) waveguide-based structures using the beam propagation method (BPM). Our approach exploits the adjoint variable technique to extract the response sensitivities with respect to all the design parameters regardless of their number. No extra BPM simulations are required. The accuracy of the results are comparable to those obtained using the expensive central finite difference approximations applied at the response level. Our approach is successfully applied to different SPPs structures for different applications.

Effects of random and systematic perturbations in a one-dimensional photonic crystal wavelength converter.

We study the problem of the tolerance to fabrication errors in one-dimensional photonic crystal wavelength converters. In particular we consider the case of wavelength conversion obtained via quasiphase matching (QPM) based on a periodic amplitude modulation of the fundamental wave (Bloch-mode-QPM). Both numerical simulations of a waveguide-based structure and experimental results in an AlGaAs thin-film multilayer show that the proposed QPM mechanism is extremely tolerant to both systematic and random errors in the periodicity and duty cycle of the grating.

An atmospheric pressure waveguide-fed microwave plasma torch: the TIA design

We report theoretical and experimental investigations of an atmospheric pressure, microwave plasma torch with axial gas injection (torche a injection axiale design). It is a waveguide-based structure comprising both waveguide and coaxial elements serving the purpose of wavemode conversion and impedance-matching. The device includes features common to various waveguide-fed torches disclosed previously by other authors, but not yet modelled. Our paper provides a simple equivalent circuit description of the torch operation that accounts for its impedance-matching, power transfer to plasma and tuning characteristics, as verified experimentally. From the outcome of the model and using our experimental results, we introduce new features in the torch design that enable one to optimize its performance. We also examine ways of simplifying its structure and operation.