Reconfigurable Waveguide Research Articles

Reconfigurable coupled-resonator acoustoelastic waveguides in fluid-filled phononic metaplates

We study numerically and experimentally acoustoelastic wave propagation in a two-dimensional phononic metaplate consisting of a periodic array of cups sitting on a thin epoxy plate that is perforated with cross holes. When all cups are filled with water, the metaplate possesses a complete band gap. Reconfigurable coupled-resonator acoustoelastic waveguides (CRAEWs) are created by locally emptying certain cups, thus introducing local resonances that are evanescently coupled. Straight and 90° bent periodic waveguides are considered, together with an aperiodic chain of 11 coupled resonators. The aperiodic chain has no definite spatial periodicity but supports collective resonances resulting from the coupling of nearest resonators. Lamb waves are experimentally excited by a piezoelectric patch and received by a scanning optical vibrometer. Experimental results for acoustoelastic wave propagation along both periodic and aperiodic CRAEWs are compared to a three-dimensional finite element model taking fluid–structure interaction into account. The propagation of confined acoustoelastic waves in the 90° bent waveguides and the collective resonances of the aperiodic chain of defected resonators are observed experimentally. Reconfigurability are realized based on the coupling of acoustoelastic waves in a phononic metaplate. Our results show plenty of potential possibilities for the practical design of reconfigurable and programmable elastic wave devices.

Electrically reconfigurable waveguide Bragg grating filters.

We propose and demonstrate an electrically reconfigurable waveguide Bragg grating filters in silicon-on-insulator using a multiple-contact heater element. There are six electrical pads connected to the heater element in an equidistant manner. These electrical pads allow to create different heat, and corresponding refractive index, distributions across the grating so that the local Bragg wavelength corresponding to the heated segments can be controlled. In turn, this control over the heat distribution allows the device to be reconfigured to implement different filter spectral responses. These filters are applicable for both wavelength division multiplexing systems and optical signal processing applications. As a verification, we demonstrate the generation of two (or more) separate filter bands with a spacing up to 35 nm or a Fabry-Pérot cavity with a 1.6 nm free-spectral range. Moreover, we explain a firm and accurate simulation framework of the proposed device based on COMSOL Multiphysics and the transfer matrix method, which is in excellent agreement with our experimental measurements.

Thickness‐Dependent Reconfigurable Spin‐Wave Dynamics in Ni80Fe20 Nanostripe Arrays

AbstractFerromagnetic nanostripes have gained massive attention due to their intriguing magnetic properties associated with dimensional confinements and shape anisotropy leading toward potential applications in magnetic storage, memory, and spin‐wave‐based devices. Consequently, reconfiguration of their static and dynamic magnetic properties by the geometric parameters and external field is imperative. Here, a combined experimental and numerical study of the reconfigurable spin‐wave dynamics in arrays of ferromagnetic nanostripes by the stripe thickness and external magnetic field strength and orientation is presented. Different uniform, localized, and standing spin waves in the nanostripes and their monotonic and nonmonotonic variation, including mode merging with these parameters, are observed. The observed variations are interpreted with the aid of simulated spin configurations, magnetostatic field maps, and spin‐wave mode profiles. Further numerical study reveals anisotropic spin‐wave propagation in nanostripes for different thicknesses and in different bias‐field geometry opening potential applications in magnonic circuit components such as reconfigurable magnonic waveguides and omnidirectional spin‐wave emitters.

Reconfigurable InP waveguide components using the Sb2S3 phase change material

Reconfigurable waveguide components are promising building blocks for photonic neural networks and as an optical analogue to field-programmable gate arrays. By changing the effective index of the waveguide, reconfigurable waveguide components can achieve on-chip light routing and modulation. In this paper, we design and demonstrate an Sb2S3-reconfigurable InP membrane Mach–Zehnder interferometer (MZI) on a silicon substrate. Sb2S3, which has tunable refractive index and low absorption in the near-infrared spectrum, was patterned on the InP waveguide MZIs to make an optical switch in the telecoms conventional-band. By laser induced crystallisation of the Sb2S3, it was possible to control interference in the MZI and achieve 18 dB on/off switching at 1540 nm. Laser reamorphisation and reversible switching of the Sb2S3 layer resulted in damage to the waveguide structure. However, simulations show that transition metal di-chalcogenide two-dimensional crystal layers can act as efficient thermal barriers that prevent thermal damage to the waveguide during laser amorphisation. Therefore, combining Sb2S3 with InP waveguides seems to be a feasible approach to achieve low-loss reprogrammable waveguide components for on-chip photonics routing and neural networks.

Novel Hybrid Electric/Magnetic Bias Concept for Tunable Liquid Crystal Based Filter

This paper presents a novel hybrid bias concept for liquid crystal (LC) filter by using simultaneously electric and magnetic bias fields. It enables continuous tuning with a simplified electrode design, decreased number of electrodes and reduced bias voltage. Furthermore, the tuning efficiency is increased, since the homogeneous bias fields enable a full exploitation of the LC's anisotropy. To demonstrate this concept, a novel reconfigurable gap waveguide two-pole bandpass filter with tunable center frequency and coupling elements is designed at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$30 \,\mathrm{GHz}$</tex-math></inline-formula> . Liquid crystal technology is applied as tunable material, whereby tunability of the center frequency and coupling elements is obtained by controlling the LC's effective permittivity. The presented filter's center frequency can be tuned from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$28.88 \,\mathrm{GHz}\,\mathrm{to}\, 29.88 \,\mathrm{GHz}$</tex-math></inline-formula> with a maximum bias voltage of 100 V, with a return loss of 20 dB and low insertion loss of only 1.65 to 1.95 dB.

Defect-induced monopole injection and manipulation in artificial spin ice

Lithographically defined arrays of nanomagnets are well placed for application in areas such as probabilistic computing or reconfigurable magnonics due to their emergent collective dynamics and writable magnetic order. Among them are artificial spin ice (ASI), which are arrays of binary in-plane macrospins exhibiting geometric frustration at the vertex interfaces. Macrospin flips in the arrays create topologically protected magnetic charges, or emergent monopoles, which are bound to an antimonopole to conserve charge. In the absence of controllable pinning, it is difficult to manipulate individual monopoles in the array without also influencing other monopole excitations or the counter-monopole charge. Here, we tailor the local magnetic order of a classic ASI lattice by introducing a ferromagnetic defect with shape anisotropy into the array. This creates monopole injection sites at nucleation fields below the critical lattice switching field. Once formed, the high energy monopoles are fixed to the defect site and may controllably propagate through the lattice under stimulation. Defect programing of bound monopoles within the array allows fine control of the pathways of inverted macrospins. Such control is a necessary prerequisite for the realization of functional devices, e. g. reconfigurable waveguide in nanomagnonic applications.

Space-Time-Modulated Reconfigurable Metamaterial Based on a Field-Focused Cavity for Nonreciprocal Transmission Control and Frequency Conversion.

Lorentz reciprocity is a fundamental physical property limiting advanced wave propagation control. Previously, special materials and magnetic bias were used to break the reciprocity; however, the approaches are limited by the bulky and costly implementation. To achieve nonreciprocity without magnetic bias, space-time-modulated metamaterials have been investigated for far-field wave propagation control. The metamaterial can also support wave propagation based on near-field coupling between the periodically arranged unit cells, i.e., magneto-inductive waves (MIWs). Near-field wave propagation control via the metamaterial has various significant applications; nevertheless, the potential for near-field wave propagation control has not been fully explored. Therefore, it is necessary to investigate the potential of the space-time-modulated near-field metamaterial. This paper demonstrates nonreciprocal MIW propagation control using a space-time-modulated metamaterial. To achieve field manipulation, we propose a tunable unit cell suitable for creating a cavity mode at a deep subwavelength scale (∼λ/103). Spatial field modulation, achieved by breaking the translational symmetry of the unit cells, allows for the creation of reconfigurable waveguides on the metamaterial. Temporal field modulation, achieved by breaking the capacitive symmetry of the varactor, allows for direction-dependent transmission in the waveguide. This spatiotemporal modulation successfully achieves nonreciprocal wave propagation and frequency conversion, investigated under various conditions. The proposed space-time-modulated metamaterial may provide significant advances for a wide range of systems that require dynamic, nonreciprocal, near-field wave propagation control.

Design of Reconfigurable Spin-Wave Nanochannels Based on Strain-Mediated Multiferroic Heterostructures and Logic Device Applications

A method based on the magnetoelectric effect present in multiferroic heterostructures was used to design a reconfigurable waveguide (WG) channel for spin wave (SW) transmission. The multiferroic heterostructures consisted of a piezoelectric (PZT) layer and an adjacent ferromagnetic (CoFeB) layer within the WG region. By applying voltage to the PZT layer, a piezostrain would be generated and transferred to the ferromagnetic layer, leading to a magnetoelastic field in the latter, which could modulate SW dispersion, including propagation frequency and SW vector. Two applications based on these piezostrain-modulated SW dispersion parameters were explored. A piezostrain-modulated, multiple-shaped WG channel was first proposed to allow specific-frequency SW propagation via control of the applied strain. Then, piezostrain was used to perform a phase shift modulation in the multiferroic SW channel. A <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\pi }$ </tex-math></inline-formula> -phase shift in the propagation of SW was obtained by customizing the length of strain operation for a given frequency. A phase shifter was designed to build an interferometer to fulfill the destruct and construct logic functions based on strain-controlled SWs. These simulation results highlight the considerable potential of strain engineering to control logical and computational reconfigurable SW devices.

Mechanically Reconfigurable Waveguide Filter Based on Glide Symmetry at Millimetre-Wave Bands.

This paper presents the design and fabrication of a mechanically reconfigurable filter at W band based on the concept of glide symmetry. The tunability is achieved by breaking and regenerating the glide symmetry. The filters are made of two glide-symmetric pieces that can be displaced in a certain direction, and therefore, break the symmetry. The high filtering capacity of these designs is demonstrated by simulation and measurement and can also be adjusted mechanically. The transmission level in the manufactured filter varies from a value between −1 and −2 dB when the filter is in the glide symmetry position to values close to −40 dB in the stop-band when it is in the broken symmetry position. The transmission band obtained in the symmetrical mode is around 20%, but, after breaking the symmetry, it is split into two passbands of 6.5% and 11% separated by a stop-band of 6%. The position, bandwidth, filtering level and filter roll-off can be adjusted for both modes of operation by appropriately selecting the unit cell design parameters and the number of unit cells.

Terahertz Metamaterials for Free-Space and on-Chip Applications: From Active Metadevices to Topological Photonic Crystals

Terahertz (THz) waves have exhibited promising applications in imaging, sensing, and communications, especially for the next-generation wireless communications due to the large bandwidth and abundant spectral resources. Modulators and waveguides to manipulate THz waves are becoming key components to develop the relevant technologies where metamaterials have exhibited extraordinary performance to control free-space and on-chip propagation, respectively. In this review, we will give a brief overview of the current progress in active metadevices and topological photonic crystals, for applications of terahertz free-space modulators and on-chip waveguides. In the first part, the most recent research progress of active terahertz metadevices will be discussed by combining metamaterials with various active media. In the second part, fundamentals of photonic topological insulations will be introduced where the topological photonic crystals are an emerging research area that would boost the development of on-chip terahertz communications. It is envisioned that the combination of them would find great potential in more advanced terahertz applications, such as reconfigurable topological waveguides and topologically-protected metadevices.

A K/Ka-Band Reconfigurable Substrate Integrated Coaxial Line to Waveguide Transition Technology

In this article, the designs of the K/Ka-Band reconfigurable Substrate Integrated Coaxial Line (SICL)-to-waveguide transitions are presented. Two types of reconfigurable SICL-to-waveguide transitions, with stepped impedance transformers waveguide transitions and ridge waveguide transitions, are designed for two operation frequency modes (K/Ka-band). Both simulated and experimental results are presented for the demonstration. Results indicate that the reconfigurable waveguide structure has the advantages of broad bandwidth and low return loss for both K/Ka-band compared with the conventional dual-band waveguide transitions. The presented waveguide transition designs with high function flexibility will be significant to satellite communication applications and massive MIMO beamforming networks with an active phased antenna array.

Reconfigurable waveguides defined by selective fluid filling in two-dimensional phononic metaplates

We investigate two-dimensional phononic metaplates consisting of a periodic array of cups on a thin epoxy plate that is perforated with periodic cross holes. The cups are individually filled with water or remain empty, in view of creating reconfigurable phononic waveguides. Phononic band gaps exist for empty or filled epoxy cups, leading to waveguides defined with either positive or negative contrast. Straight and 90° bent waveguides are considered experimentally. Lamb waves are excited by a piezoelectric patch glued onto the metaplate and are imaged using a scanning laser vibrometer. Experimental results are compared to a three-dimensional finite element model of fluid–structure interaction. Passing and forbidden frequency ranges are identified for positive and negative contrast, and confined propagation is observed along the waveguides. Significantly, the propagation of acoustoelastic waves in the 90° bent waveguides is observed experimentally. Reconfigurability and reusability are thus realized based on the coupling of elastic waves in the solid and acoustic waves in the fluid. The results show plenty of potentiality for the practical design of multiplexed and programmable acoustic devices implemented with reconfigurable waveguides printed on demand in a phononic metaplate.

Bend losses in flexible polyurethane antiresonant terahertz waveguides.

One important shortcoming of terahertz technology is the relative absence of convenient, flexible, and reconfigurable waveguides with low attenuation and small bend losses. While recent years have been marked by remarkable progress in lowering the impact of material losses using hollow-core guidance, such waveguides often have centimeter-scale diameter and are therefore not flexible. Here we experimentally and numerically investigate antiresonant dielectric waveguides made of thermoplastic polyurethane, a commonly used dielectric with a low Young's modulus. The hollow-core nature of antiresonant fibers leads to low transmission losses using simple structures, whereas the low Young's modulus of polyurethane makes them extremely flexible. The structures presented enable millimeter-wave manipulation in the same spirit as conventional (visible- and near-IR-) optical fibers, i.e. conveniently and reconfigurably, despite their centimeter-thick diameter. We investigate two canonical antiresonant geometries formed by one- and six-tubes, experimentally comparing their transmission, bend losses and mode profiles. The waveguides under investigation have loss below 1 dB/cm in their sub-THz transmission bands, increasing by 1 dB/cm for a bend radius of about 10 cm. We find that the six-tube waveguide outperforms its one-tube counterpart for smaller bend radii (here: 10cm); for larger bend radii, coupling to cladding tube modes can lead to a drop in transmission at specific frequencies in the six-tube waveguide that does not occur in the one-tube waveguide.

Guided Lamb waves in reconfigurable phononic crystal waveguides

We demonstrate experimentally the manipulation of Lamb waves guided along reconfigurable phononic circuits created by defects composed of threaded rods held with nuts in a perforated solid phononic crystal slab. Adjusting the free length of the rod, the resonant frequency of the defect can be tuned, without any change in the supporting phononic crystal slab. Both straight and bent waveguides are fabricated and measured in an aluminum sample with a lattice constant of 20 mm and a complete bandgap extending from 50 to 70 kHz. Guidance of Lamb waves is clearly observed by a Doppler vibrometer, even after 90° bends. The eigenmodes of guided waves are obtained using finite element analysis to explain the tuning of resonances through a bending cantilever model. Numerical and experimental results are generally found to be in fair agreement. They also suggest that the guiding frequency is rather independent of the details of the waveguides. They are of significance for the design of reconfigurable phononic devices.

Bio-Inspired Origami Metamaterials With Metastable Phases Through Mechanical Phase Transitions

Abstract Structural instability, once a catastrophic phenomenon to be avoided in engineering applications, is being harnessed to improve functionality of structures and materials, and has been a catalyst of substantial research in the field. One important application is to create functional metamaterials that deform their internal structure to adjust performance, resembling phase transformations in natural materials. In this paper, we propose a novel origami pattern, named the Shrimp pattern, with application to multi-phase architected metamaterials whose phase transition is achieved mechanically by snap-through. The Shrimp pattern consists of units that can be easily tessellated in two dimensions, either periodically with homogeneous local geometry or non-periodically with heterogeneous local geometries. We can use a few design parameters to program the unit cell to become either monostable or tune the energy barrier between the bistable states. By tessellating these unit cells into an architected metamaterial, we can create complex yet navigable energy landscapes, leading to multiple metastable phases of the material. As each phase has different geometries, the metamaterial can switch between different mechanical properties and shapes. The geometric origin of the multi-stable behavior implies that, conceptually, our designs are scale-independent, making them candidates for a variety of innovative applications, including reprogramable materials, reconfigurable acoustic waveguides, and microelectronic mechanical systems and energy storage systems.

An acoustoelectric-induced tailorable coupled resonator surface acoustic waveguide

Here, we introduce a tailorable coupled resonator surface acoustic waveguide (CRSAW), based on a linear defect of elliptical cylinders inside a phononic crystal of ZnO pillars on a Si substrate. The designed elliptical resonators allow the emergence of a minimally dispersive, monomode shear-guiding band inside the local resonance bandgap, owing to their partially broken structural symmetry in comparison with their previously reported counterparts such as pillars and hollow cylinders. Moreover, by introducing reconfigurable waveguide behavior, we benefit from the acoustoelectric-induced elasticity modulation of ZnO, which is a semiconducting piezoelectric material. Switching the conductivity of ZnO structures between two limiting low and high values (0.01 S m−1 and 100 S m−1), a considerable waveguide modulation at full width at half maximum (FWHM) (ΔFWHM = −21%) and guiding frequency (Δfd = −2.81%) are achieved for the designed optimized elliptical cylinder CRSAW while maintaining an acceptable loss value. Benefiting from the proposed ZnO-based elliptical CRSAW, we have achieved simultaneous monomode and low-bandwidth surface acoustic waveguide behaviors, without involving significant fabrication complications. The designed structures open up new horizons toward the realization of promising building blocks for designing reconfigurable and miniaturized SAW RF-filters, demultiplexers, and Mach–Zehnder devices for wireless communications applications.

Fixed-Frequency Beam-Steering Using Slotted Waveguide With Tunable Impedance Walls

In this paper, we describe the development of a new beam-steerable antenna array using a reconfigurable waveguide with tunable impedance side walls. The array has 36 radiating elements placed on the top wall of the waveguide and a common biasing voltage for tuning the impedance walls. The antenna operates at 9.3 GHz and its beam can be steered from 22° to 65° by changing the bias voltage from 16 to 7 volts. The gain of the antenna remains within the 3 dB limit of the maximum gain of 11.8 dB throughout the steering range. The effective radiating length of the antenna is $13\lambda $ and its half-power beamwidth is 5°. For this frequency range and electrical length, this antenna has a high radiation efficiency. This is due to the phase-shifting mechanism used which results in the varactor loss being less than all other sources of loss throughout most of the steering range. This makes the antenna suitable for applications where the varactors should operate at high frequencies with relatively low quality factors.

Rib Waveguide Based Liquid Crystal EO Switch

We report electrically re-configurable liquid crystal core rib waveguide based electro-optic switch. It is proposed to use single side anchored in-plane switching (IPS) configuration for optical switching in view of its low threshold voltage and low switching voltage in comparison to that in a double-side anchored LC waveguide switch. Further, the proposed LC waveguide based switch has better response time than that in a double side anchored configuration at operating voltage close to threshold voltage of a double side anchored. The device has been realized on a BK7 glass substrate using E7 LC. We also show wavelength re-configurability of the switch over a wide wavelength range (1 - 3 μm) by externally applied voltage. Proposed work would be useful for optical signal processing on integrated optic platform.

Programmable coding photonic topological edge waveguide

In order to obtain reconfigurable topological photonic waveguides, we design a two-dimensional photonic crystal with compound triangular lattice. Through rotating the dielectric rods, we change the topological phase of the lattice and achieve the topological edge states. Through the rotation of rods, we divide the two-dimensional structure space into “0” and “1” blocks made of the topologically trivial and nontrivial lattices, respectively. Through programming the codes of “0” and “1,” we can realize diverse transport pathways of light flow. The controllable light pathways will play important role in the optical circuit. The programmable design results have been demonstrated through the simulations of electromagnetic wave transport.

Reconfigurable topologically protected wave propagation in metastable structure

In this paper, topologically protected wave propagation in metastable structure has been investigated by mimicking the quantum valley Hall effect. Reconfigurable topological waveguides are achieved by switching the metastable states of the structure. First, a K-point Dirac cone, which is guaranteed by the C6 rotational symmetry of the metastable unit cell, is identified in the band structure. Then, by reconfiguring the bistable elements, the space inversion symmetry of the unit cell is broken and a topological bandgap opened. The topological non-triviality of this bandgap is verified by the values assumed by the Berry curvature and valley Chern number. Next, the topological edge modes localized at the interface are studied by analyzing the dispersion relation of a finite strip. The analysis results show that reconfigurable topologically protected waveguides, which are immune to backscattering at sharp corners and local defects, can be achieved utilizing the edge modes.