Beam Waveguide Research Articles

Experimental demonstration of broadband reconfigurable mechanical nonreciprocity

Breaking reciprocity has recently gained significant attention due to its broad range of applications in engineering systems. Here, we introduce the first experimental demonstration of a broadband mechanical beam waveguide, which can be reconfigured to represent wave nonreciprocity. This is achieved by using spatiotemporal stiffness modulation with piezoelectric patches in a closed-loop controller. Using a combination of analytical methods, numerical simulations, and experimental measurements, we show that contrary to the conventional shunted piezoelectrics or nonlinearity based methods, our setup is stable, less complicated, reconfigurable, and precise over a broad range of frequencies. Our reconfigurable nonreciprocal system has potential applications in phononic logic, wave diodes, energy trapping, and localization.

Compact Mid‐Infrared Chalcogenide Glass Photonic Devices Based on Robust‐Inverse Design

AbstractMid‐infrared (mid‐IR) on‐chip photonic devices have attracted increasing attention because of their potential applications in chemical and biological sensing and optical communications. In particular, chalcogenide glasses (ChGs) have long been regarded as promising materials for mid‐IR integrated photonics, owing to their broad infrared transparency, high nonlinearity, and excellent processing capabilities. Here, an inverse design approach is introduced to ChG photonic device design with a new robust inverse design method. A high‐performance mid‐IR inverse design polarization beam splitter, waveguide polarizer, mode converter, and wavelength demultiplexer are demonstrated for the first time. They all have a footprint of only several micrometers. The robust inverse design method could improve the robustness of device performance against fabrication variations and would be a general approach for designing and optimizing miniaturized chalcogenide photonic devices.

Research on Beam Waveguide Focus Phase Calibration Method of Deep-space TT&C System

The angle auto-tracking capability is needed in the deep space system, but in the sum-differential dual channels tracking model, the deep-space TT&C system must calibrate its phase before tracking a satellite. Because of the big aperture and high frequency of the deep-space TT&C system antenna, it is impossible to build a calibrating tower which satisfy the far-field condition, and the traditional phase calibration method relies on the tower is not suitable. The radio star calibration method selects a appropriate satellite as the calibrating signal source, but the signal of which is very weak and is affected easily. In this paper, the principle of phase calibration is analyzed, and the beam waveguide focus calibration method is studied, the processes of antenna tracking and angle error signal demodulation are given. The beam waveguide focus calibration method simulates the far field signal through controlling the position of horn antenna which is at the focus of the beam waveguide. The method can be realized easily in engineering, and the limit of the traditional calibration tower and the affections of the weather in using radio star calibration method are avoided.

Nanoscale Waveguide Beam Splitter in Quantum Technologies.

Usually in quantum optics, the theory of large- and small-scale waveguide beam splitters is the same. In this paper, it is shown that the theory of the nanoscale waveguide beamsplitter has a significant difference from a similar device, but of a larger scale. It is shown that the previously known theory of the waveguide beam splitter is a particular case of the theory presented here. The wave function at the output ports of the nanoscale beam splitter is analyzed. The results obtained are sensitive to the size of the beam splitter, the coupling parameter of the two waveguides, and the degree of nonmonochromaticity of the photons entering the first and second ports of the beam splitter. The results are important for quantum technologies using a nanosized beam splitter.

Femtosecond laser writing of waveguides in zinc oxide crystals: fabrication and mode modulation.

We report for the first time on optical waveguides in zinc oxide (ZnO) crystals fabricated by femtosecond laser direct writing. The confocal Raman microscopy under 488 nm laser excitation is used to investigate the micro-modifications of the laser irradiation, and guiding properties are studied via the end-face coupling at 632.8 nm. The mode modulation has been achieved by the adjustment of laser writing parameters. A minimum propagation loss of ∼6 dB/cm is obtained for the double-line waveguide structures. A Y-branch waveguide beam splitter is also fabricated, reaching a splitting ratio of nearly 1:1. The original optical properties in the guiding region have been well preserved, according to the confocal Raman investigation, which suggests potential applications of the ZnO waveguides for integrated photonics and nonlinear optics.

Controlled acceleration of GeV electron beams in an all-optical plasma waveguide

Laser-plasma accelerators (LPAs) produce electric fields of the order of 100 GV m−1, more than 1000 times larger than those produced by radio-frequency accelerators. These uniquely strong fields make LPAs a promising path to generate electron beams beyond the TeV, an important goal in high-energy physics. Yet, large electric fields are of little benefit if they are not maintained over a long distance. It is therefore of the utmost importance to guide the ultra-intense laser pulse that drives the accelerator. Reaching very high energies is equally useless if the properties of the electron beam change completely from shot to shot, due to the intrinsic lack of stability of the injection process. State-of-the-art laser-plasma accelerators can already address guiding and control challenges separately by tweaking the plasma structures. However, the production of beams that are simultaneously high quality and high energy has yet to be demonstrated. This paper presents a novel experiment, coupling laser-plasma waveguides and controlled injection techniques, facilitating the reliable and efficient acceleration of high-quality electron beams up to 1.1 GeV, from a 50 TW-class laser.

Chinese Deep Space Stations: A brief review [Antenna Applications Corner

To meet the rapidly growing needs of current and future deep space exploration missions, China has developed three deep space stations: Jiamusi and Kashi, (China), and Argentina (South America), for providing continuous telemetry, tracking, and command (TT&C), reliable communication, and precise navigation services. Integrated with state-of-the-art technologies, these three deep space stations are not only powerful for transmission but also extremely sensitive for receiving. Many remarkable innovations and achievements were made during the construction process, including the beam waveguide (BWG), adjustable subreflector, high-power transmitter, cryogenic low-noise amplifier (LNA), antenna-arraying technique, digital baseband receiver, and interferometry. This article briefly reviews the system architecture, general performance, critical system design issues, and contributions made by these Chinese deep space stations (CDSSs) during Chang’e missions.

Quantum Entanglement of Monochromatic and Non-Monochromatic Photons on a Waveguide Beam Splitter.

It is well known that the waveguide beam splitter can be used as a source for the quantum entanglement of photons. The analysis of such quantum entanglement is a difficult problem even for monochromatic photons, since the system under study is multiparametric. This paper will show that quantum entanglement can be represented in a simple form not only for monochromatic photons but also for non-monochromatic ones. It will be shown that quantum entanglement for non-monochromatic photons can be very different from monochromatic photons, which can be used to create large quantum entanglement.

On the broadband vibration isolation performance of nonlocal total-internal-reflection metasurfaces

The concept of a nonlocal elastic metasurface has been recently proposed and experimentally demonstrated in Zhu et al. (2020). When implemented in the form of a total-internal-reflection (TIR) interface, the metasurface can act as an elastic wave barrier that is impenetrable to deep subwavelength waves over an exceptionally wide frequency band. The underlying physical mechanism capable of delivering this broadband subwavelength performance relies on an intentionally nonlocal design that leverages long-range connections between the units forming the fundamental supercell. This paper explores the design and application of a nonlocal TIR metasurface to achieve broadband passive vibration isolation in a structural assembly made of multiple dissimilar elastic waveguides. The specific structural system comprises shell, plate, and beam waveguides, and can be seen as a prototypical structure emulating mechanical assemblies of practical interest for many engineering applications. The study also reports the results of an experimental investigation that confirms the significant vibration isolation capabilities afforded by the embedded nonlocal TIR metasurface. These results are particularly remarkable because they show that the performance of the nonlocal metasurface is preserved when applied to a complex structural assembly and under non-ideal incidence conditions of the incoming wave, hence significantly extending the validity of the results presented in Zhu et al. (2020). Results also confirm that, under proper conditions, the original concept of a planar metasurface can be morphed into a curved interface while still preserving full wave control capabilities.

Tunable laser induced periodic surface structures in Ge2Sb2Te5 thin films

Planar photonic structures, such as gratings and metasurfaces, are routinely used for beam steering, waveguide coupling, and light localization. However, conventional fabrication techniques that involve lithography are demanding in terms of time and cost. Much cheaper and simpler methods for surface patterning and formation of periodic surface structures are enabled by direct laser processing. Here, we demonstrate low-cost rapid fabrication of high-quality phase gratings based on the formation of laser induced periodic surface structures (LIPSS, or ripples) in Ge2Sb2Te5 (GST) thin films. Due to unique phase change properties of GST, the structures demonstrate strong modulation of refractive index with period controlled by the wavelength of laser irradiation. We study the formation of phase change LIPSS in a broad range of excitation wavelengths and observe transition between regimes with different orientations of generated ripples with respect to laser polarization.

Recoverable and rewritable waveguide beam splitters fabricated by tailored femtosecond laser writing of lithium tantalate crystal

We report on an integrated 1 × 5 beam splitter based on optical waveguides with type I and type II modifications of femtosecond laser (fs-laser) writing in lithium tantalate (LiTaO3) crystal. The cladding waveguides consisting of type-II modified tracks are used for optical signal transmission, photon crosstalk reduction, and mode field regulation. The single-line waveguides with type I modification are utilized for light beam splitting. Type-I single-line waveguides are with relatively weak thermal stability, which are utilized to produce a recoverable and rewritable optical beam splitter, and the structure still possesses good transmission properties after the reconstruction. Especially, the type-I modified waveguides can be rewritten in very short time (1–2 min). The beam splitter shows good performance in outputting programmable optical signals, which provides a possible strategy for the development of erasable photonic data processors.

Controlled acceleration of GeV electron beams in an all-optical plasma waveguide

Controlled acceleration of GeV electron beams in an all-optical plasma waveguide

Asymmetric lateral sound beaming in a Willis medium

Willis coupling, also known as pressure-velocity cross coupling, in acoustic materials has received much attention in the past years. This effect has been found useful in acoustic metasurface designs for wave redirection. We find that Willis coupling in phononic crystals also provides rich physics to manipulate waves. Here, we report the extreme asymmetric lateral sound beaming effect in a two-dimensional phononic crystal composed of Willis scatterers. By matching the second-order Bragg scattering with two leaky guided modes (a quadrupole resonance and a cross-coupling-induced dipole resonance), a normally incident wave is redirected towards the positive and negative directions orthogonal to the incident wave with different amounts of energy. Simulation and experimental results demonstrate the extraordinary asymmetric lateral beaming effect in the Willis medium. The results presented here may find applications in the design of tunable beam splitters and waveguides.

Two-photon controlled-phase gates enabled by photonic dimers

Photons are appealing as flying quantum bits due to their low-noise, long coherence times, light-speed transmission, and ease of manipulation at the single-qubit level using standard optical components such as beam splitters and waveguides. The challenge in optical quantum information processing has been the realization of two-qubit gates for photonic qubits due to the lack of highly efficient optical Kerr nonlinearities at the single-photon level. To date, only probabilistic two-qubit photonic controlled-phase gates based on linear optics and projective measurement using photon detectors have been demonstrated. Here we show that a high-fidelity frequency-encoded deterministic two-photon controlled-phase gate can be achieved by exploiting the strong photon-photon correlation enabled by photonic dimers, and the unique nonreciprocal photonic propagation in chiral quantum nanophotonic systems.

Boundary revision of a beam model for a thin-walled waveguide at bending vibration

The paper discusses the problem of choosing a model type for a straight thin-walled waveguide with a rectangular cross-section during its vibrations. To do this, calculations were made of the first natural frequency of vibration for waveguides of different geometric sizes. The restraints of the waveguide were accepted by a cantilever, hinged, and fixed supports. The difference between the values of the first natural frequency of vibration for the beam and shell waveguide models was estimated. Calculations were carried out analytically on the theory of beam vibration and by the numerical method of finite elements. The results show that the boundary known in static calculations of the applicability of the beam model Rmax/L = 0.1 requires clarification at bending vibrations for the small thickness of the section wall. With small wall thicknesses, the error of calculating the first natural frequency of vibrations will increase sharply due to the effect of a beam section warping.

Exploring topology of 1D quasiperiodic metastructures through modulated LEGO resonators

We investigate the dynamics and topology of metastructures with quasiperiodically modulated local resonances. The concept is implemented on a LEGO beam featuring an array of tunable pillar-cone resonators. The versatility of the platform allows the experimental mapping of the Hofstadter-like resonant spectrum of an elastic medium, in the form of a beam waveguide. The non-trivial spectral gaps are classified by evaluating the integrated density of states of the bulk bands, which is experimentally verified through the observation of topological edge states localized at the boundaries. Results also show that the spatial location of the edge states can be varied through the selection of the phase of the resonator's modulation law. The presented results open new pathways for the design of metastructures with functionalities going beyond those encountered in periodic media by exploiting aperiodic patterning of local resonances and suggest a simple, viable platform for the observation of a variety of topological phenomena.

Gradient-index electron optics in graphene p−n junctions

We investigate the electron transport in smooth graphene pn junctions, generated by gradually varying electrostatic potentials. The numerically calculated coherent current flow patterns can be understood largely in terms of semi-classical trajectories, equivalent to the ones obtained for light beams in a medium with a gradually changing refractive index. In smooth junctions, energetically forbidden regions emerge, which increase reflections and can generate pronounced interference patterns, for example, whispering gallery modes. The investigated devices do not only demonstrate the feasibility of the gradient-index electron optics in graphene pn junctions, such as Luneburg and Maxwell lenses, but may have also technological applications, for example, as electron beam splitters, focusers and waveguides. The semi-classical trajectories offer an efficient tool to estimate the current flow paths in such nano-electronic devices.

Factorization of Antenna Efficiency of Aperture-Type Antenna: Beam Coupling and Two Spillovers

Antenna efficiency is one of the most important figures of merit of a radio telescope for observations, especially at millimeter wavelengths or shorter wavelengths, even for a multibeam radio telescope. To analyze a system with a beam waveguide, a lossless antenna consisting of two apertures in series is considered in the frame of the scalar wave approximation. We found that the antenna efficiency can be evaluated with the field distribution over the second aperture, and the antenna efficiency is factorized into three factors: efficiencies of beam coupling, transmission spillover, and reception spillover. The factorization is applicable to general aperture-type antennas with beam waveguides and can relate the aperture efficiency to the pupil function. We numerically confirmed our factorization with an optical simulation. This evaluation enables us to manage the aberrations and is useful in the design of multibeam radio telescopes.

Matrix representations for classical and quantum beam splitters

Matrices provide a practical and elegant tool for describing the transformation properties of beam splitters and waveguide couplers acting on single-mode optical fields. Using a systematic approach, we show how the application of various physical constraints determines the form of the matrix for both classical fields and quantum number states. The goal is to provide a clear explanation of the conditions under which various matrix forms are appropriate to represent four-port couplers and beam splitters. Examples of calculations using the matrices are provided.

Toroidal Metaphotonics and Metadevices

AbstractToroidal moments in artificial media have received growing attention and considered as a promising framework for initiating novel approaches to manage intrinsic radiative losses in nanophotonic and plasmonic systems. In the past decade, there has been substantial attention on the characteristics and excitation methods of toroidal multipoles—in particular, toroidal dipole—in 3D bulk and planar metaplatforms. The remarkable advantages of toroidal resonances have thrust the toroidal metasurface technology from relative anonymity into the limelight, in which researchers have recently centered on developing applied optical and optoelectronic subwavelength devices based on toroidal metaphotonics and metaplasmonics. In this focused contribution, the key principles of 3D and flatland toroidal metastructures are described, and the revolutionary tools that have been implemented based on this topology are briefly highlighted. Infrared photodetectors, immunobiosensors, ultraviolet beam sources, waveguides, and functional modulators are some of the fundamental and latest examples of toroidal metadevices that have been introduced and studied experimentally so far. The possibility of the realization of strong plexciton dynamics and pronounced vacuum Rabi oscillations in toroidal plasmonic metasurfaces are also presented in this review. Ultimate efficient extreme‐subwavelength scale devices, such as low‐threshold lasers and ultrafast switches, are thus in prospect.