Bent Waveguides Research Articles

Elastic wave transport in angularly selective valley topological metamaterials plate

The valley degree of freedom has attracted increasing attention in elastic wave systems owing to its energy extrema at valleys and great potential in energy transportation. This study investigated the transport of valley edge states by angularly selective excitation in elastic wave metamaterials plate and designed a bifunctional elastic wave device in the bent waveguide containing two different interfaces. The supercell analysis revealed that the valley edge states exhibit symmetrical and anti-symmetrical distributions at two different interfaces. The straight and bent waveguides containing a single interface are designed, and the selective transport of valley edge states is observed due to the symmetrical or anti-symmetrical distributions at the interfaces. The angularly selective excitation of valley edge states by external excitation is demonstrated at the straight and bent interfaces. Based on these transport characteristics of valley edge states and the valley conservation mechanism, a bifunctional elastic wave device composed of a bent waveguide containing both two interfaces is designed. It can realize both the functions of the diode and the backward diode. The designed elastic wave device has the advantages of being a single structure with bifunctions. This study of topological valley transport with angularly selective characteristic may also have practical applications such as energy harvesting and sensing.

Thermo-mechanical analysis on reflection characteristics of deformed coupling system of a helix traveling wave tube

This paper proposes a fast ANSYS Multiphysics-based system coupling approach to study the impact of structural deformation on the reflection coefficient (S11) of the helix travelling wave tube (TWT) output coupling system at varying output powers. The system, comprising a coaxial stepped impedance transformer, a coaxial-to-rectangular waveguide with a door-knob transition, and a double-mitered bend waveguide, is analysed under 200 W and 250 W RF power in the X-band. The analysis shows that S11 improves at lower frequencies (−17.43 dB to −17.58 dB) and deteriorates at higher frequencies (−10.62 dB to −10.53 dB) due to structural deformation. Thermal simulation results were validated experimentally using infrared thermographic imaging.

Measurements of the Effective Refractive Index of Bent Waveguide Based on Microring Resonators

Measurements of the Effective Refractive Index of Bent Waveguide Based on Microring Resonators

Reconfigurable topological gradient metamaterials and potential applications

Elastic topological metamaterials are innovative fields of the fusion of physics and mechanics. Through novel microstructural designs, elastic topological metamaterials provide a pioneering approach to precisely manipulate elastic waves, maintaining robustness and efficiency in wave propagation even within complex environments. Recent advancements in reconfigurability and gradient features have significantly enriched the mechanical phenomena of wave manipulation, broadening the application potential of elastic topological metamaterials. In this study, we design the local resonant phononic crystal, employing a spiral support structure to ensure low-frequency characteristics and adjustable mass for flexible configuration. By utilizing the designed lattices with distinct topological phases, the topological valley edge states are constructed. The frequency and group velocity variation of the topological edge states under different stiffness and mass parameters are analyzed. Furthermore, we further constructed the mass and stiffness gradient metamaterial to analyze the transmission law of elastic waves in topological metamaterials. Additionally, the fluctuation features of the wave transmittance under disordered and impurity defects were discussed, confirming the robustness of waveguides within low-frequency topological metamaterials. Finally, we explored the potential applications of the designed metamaterials in energy localization and low-frequency reconfigurable waveguides. Numerical analysis showed that the topological gradient metamaterials can enhance the vibration energy at a specific interface, and low-frequency bend waveguide paths can be adjusted flexibly by configurable mass. In summary, this paper focuses on the low-frequency and gradient features of elastic topological metamaterials, aiming to unlock their application potential in vibrational energy harvesting, vibration suppression, and information transmission, which accelerate the practical implementation of topological metamaterials.

Selecting robust silicon photonic designs after Bayesian optimization without extra simulations.

Optimization methods are frequently exploited in the design of silicon photonic devices. In this paper, we demonstrate that pushing the objective function to its minimum during optimization often results in devices that gradually become more sensitive to perturbations of design variables. The dominant strategy of selecting the design with the smallest objective function can lead to fabrication failure or yield loss due to manufacturing process variations. To address this issue, we propose an intuitive selection criterion that can identify designs not only possessing small objective functions but that are also robust to variations. Our simulation results on the Y-splitter, direction coupler, and bent waveguide designs demonstrate that the proposed method can achieve 2x higher coverage of robust designs with almost negligible run time, compared to the two baseline methods.

Reshaping compact waveguide bend for mode transmission and conversion.

Compact waveguide bends with functionalities of mode manipulation, including certain mode transmission, multimode transmission, and mode conversion, are highly desirable in photonic integrated circuits. In this paper, an inverse design scheme for reshaped waveguide bend is presented, in which mode manipulation is achieved without additional nanoscale structures. We adopt quasi-3D models in finite element method to simulate the optical field, Bernstein polynomials to describe the deformation of two Si/air boundaries, and a gradient-based algorithm to efficiently determine the optimal design from a strict circular arc with a radius of 3.5 µm. 3D FDTD simulations with SOI configuration are implemented to measure the performance of the proposed designs. Three designs for certain mode transmission (individual TE0, TE1 and TE2) are first demonstrated as a validation of the method. For multimode transmission, the simultaneous TE0, TE1 and TE2 mode transmission in the bend requires a multi-target optimization and the design is achieved after 26 iterations. The output mode purities are 0.996, 0.971 and 0.989 at the center wavelength of 1550 nm, respectively. Furthermore, designs for TE0-to-TE1, TE0-to-TE2 and TE1-to-TE2 mode conversions in 90° bends are realized within 30 iterations. The output mode purities reach 0.985, 0.981 and 0.965, respectively. The performances of all designs remain acceptable within an operational bandwidth of 60 nm.

Low-Loss Silicon Directional Coupler With Arbitrary Coupling Ratios for Broadband Wavelength Operation Based on Bent Waveguides

Low-Loss Silicon Directional Coupler With Arbitrary Coupling Ratios for Broadband Wavelength Operation Based on Bent Waveguides

Matrix analysis of high-density arrayed waveguides: Crosstalk suppression by bending

For many photonic devices, crosstalk between densely packed waveguides poses a major problem leading to unreliable or inefficient operation of the device. In this work, a general method for modeling the crosstalk, not only in straight waveguide arrays but also in curved ones, is introduced. The method is based on a matrix analysis of electromagnetic field coupling between closely spaced waveguides. As an example, we show how bending of waveguides in an array reduces the crosstalk. The approach can help overcome the crosstalk problem in a variety of photonic integrated devices, including phased waveguide arrays, arrayed waveguide gratings, optical multiplexers, and high-density interconnects between optical and electronic components. Published by the American Physical Society 2024

Mathematical analysis of bent optical waveguide eigenvalue problem

Abstract This work investigates a mathematical model of the propagation of lightwaves in bent optical waveguides. This modeling leads to a non-self-adjoint eigenvalue problem for differential operator defined on the unbounded domain. Through detailed analysis, a relationship between the real and imaginary parts of the complex-valued propagation constants was constructed. Using this relation, it is found that the real and imaginary parts of the propagation constants are bounded, meaning they are limited within certain region in the complex plane. The orthogonality of these bent modes is also proved. By the asymptotic analysis of these modes, it is proved that as r → ∞ the behavior of the eigenfunctions is proportional to 1 / r .

Broadband and Compact Silicon Multimode Waveguide Bends Based on Hybrid Shape Optimization

Broadband and Compact Silicon Multimode Waveguide Bends Based on Hybrid Shape Optimization

Polygon search algorithm for ultra-compact multifunctional integrated photonics design

Ultra-compact multifunctional integrated photonic modules have great practical significance to photonic integrated circuits (PICs). However, the design effect and efficiency of the existing mainstream inverse design algorithms are incompetent when designing these modules. We analyze their shortcomings in this task, and propose a new, to our knowledge, inverse design algorithm named polygon search (PS) algorithm to address these problems. We utilize the PS algorithm to design an integrated dual-channel mode-conversion-crossing waveguide module. This module integrates three functions: interconversion between TE0 and TE1, interconversion between TE0 and TE2, and channel crossing within only a 4 μm×4 μm footprint, and its performance is verified by experimental testing. It not only greatly reduces the total footprint of many PICs but also greatly improves their fabricating robustness. Furthermore, we propose a PS-designed mode mixer and a PS-designed bending waveguide, and connect them with the integrated modules to form a four-channel crossing-mode-division-multiplexing system. This system can provide multiple modes on the basis of channel crossing and transmit the output signal in the same direction in parallel within a single output waveguide, which significantly increases the communication bandwidth and decreases the footprint of PICs. At last, we demonstrate the effect and efficiency advantages of the PS algorithm over several mainstream inverse design algorithms by a comprehensive contrast experiment and explain these advantages in theory from several perspectives.

Optimal Design of a Novel Semi-Elliptical Bending Waveguide Slow Wave Structure via Multistage Collaborative Deep Learning and Differential Evolution Algorithm

Optimal Design of a Novel Semi-Elliptical Bending Waveguide Slow Wave Structure via Multistage Collaborative Deep Learning and Differential Evolution Algorithm

General Waveguide Bend Design Based on Cubic Spline Interpolation and Inverse Design

General Waveguide Bend Design Based on Cubic Spline Interpolation and Inverse Design

A broadband and compact TE01 mode bend with hexagonal section for high-power microwave applications

The conventional circular waveguide 90° TE01 bend makes it difficult to achieve broadband because of the serious interference from TM11 mode. To solve this problem, the mode coupling characteristics in the hexagonal waveguides are investigated in this paper, and it is found that when the deformation amplitude is appropriate, not only the degradation between TE01 and TM11 is broken but other parasitic modes can be efficiently suppressed. Based on the analysis, an oversized broadband TE01 waveguide bend with variable curvature is proposed, and its transmission efficiency is over 95% from 8.5 to 11 GHz, while its structure length is only 26.16 times wavelength. Measurement results indicate that the S21 of the bend is about −0.4 dB from 8.5 to 11 GHz, and it works stably under a microwave output power of 1 MW. The consistency between theoretical calculations, simulation, and experiments indicates the feasibility of this novel TE01 bend.

Bound states in bent soft waveguides

The aim of this paper is to show that a two-dimensional Schrödinger operator with the potential in the form of a ‘ditch’ of a fixed profile can have a geometrically induced discrete spectrum. This occurs if such a potential channel has a single or multiple bends, being straight outside a compact. Moreover, under stronger geometric restrictions, the claim remains true in the presence of a potential bias at one of the channel ‘banks.’

A low loss silicon waveguide bend based on width and curvature variations

A simple, low loss and compact 90° SOI waveguide bend constructed by using an inner circular curve and an outer Euler-circular curve was proposed, optimal designed and fabricated. By adopting this simple structure, the width and curvature of the waveguide bend can be varied simultaneously, which can effectively suppress both the mode mismatch loss and the radiation loss. Three-dimensional finite difference time domain simulation results indicate a very low excess loss of about 0.0056 dB can be achieved for equivalent bending radius of 2 μm. By using the cut-back method, a low loss of about 0.0175 dB at 1550 nm was measured, which is less than one quarter of the traditional circular bend. In addition, the wavelength dependence for the proposed SOI waveguide bend was investigated and 0.0088 dB–0.0247 dB was measured in the wavelength range of 1480∼1580 nm.

High performance polarizer on thin-film lithium niobate with width-tapered Euler bending.

In this Letter, we propose and demonstrate an integrated polarizer on thin film lithium niobate (TFLN). The polarizer consists of a width-tapered 180° Euler bending waveguide featuring thin thickness and bilevel mode convertors with silica cladding. Notably, the TE0 mode is efficiently confined in the waveguide, while the TM0 mode confronts significant bending losses. The measurements reveal that the excess loss remains below 1.5 dB, and the extinction ratio surpasses 19 dB within a working bandwidth spanning from 1480 to 1578 nm. The proposed polarizer holds considerable promise for enhancing polarization handling within TFLN photonic circuits.

Integrating inverse design and partially etched platform: an ultra-compact polarization splitter and rotator as an example

Silicon photonics devices benefit greatly from a partially etched platform and inverse design. Herein, we propose a bi-layer polarization splitter and rotator with a topology pattern and demonstrate it on a silicon-on-insulator platform. Our device exhibits a significantly reduced physical footprint of only 2µm×6µm, compared to traditional directional couplers and tapered waveguides. The device accomplishes the functions of polarization conversion and separation in such a compact design without redundant tapered or bending waveguides. The tested minimum insertion loss with the fabrication batch reaches 0.57 and 0.67 dB for TE and TM modes, respectively. The TE mode demonstrates a wider bandwidth and lower ILs than the TM modes, averaging around 1 dB from 1530 to 1565 nm. The M modes exhibit approximately 2 dB ILs at the same wavelength range, decreasing to about 1 dB between 1565 and 1580 nm. Improved designs and fabrication conditions strongly suggest the potential for further performance enhancement in the device. This successful initiative validates the exceptional performance resulting from the integration of the partially etched platform and inverse design, providing valuable insights for future photonic integrated device designs.

Ultra-Compact Inverse Designed Multimode Waveguide Bend Based on Levelset Method

Ultra-Compact Inverse Designed Multimode Waveguide Bend Based on Levelset Method

A Hybrid Organic‐Crystal‐Based Curved Waveguide Network for Producing, Splitting, and Transducing Multi‐Color Outputs

AbstractHybrid optical components and circuits that deal with multiple signal generation and processing are quintessential for neural networking systems. Herein, the study reports the fabrication of one such component, a hybrid directional coupler (HDC) from blue emissive (4,4′‐bis(2,6‐di(1H‐pyrazol‐1‐yl)pyridin‐4‐yl)biphenyl) (BPP) and green emissive (E)‐1‐(((5‐bromopyridin‐2‐yl)imino)methyl)naphthalen‐2‐ol (BPyIN) pseudo‐plastic molecular crystals. Initially, a BPyIN microcrystal optical waveguide (OW1) is shaped into a strained waveguide with five bends using an atomic force microscopy cantilever‐tip aided mechanophotonics approach. Later, a singly bent BPyIN waveguide (OW2) is integrated into one of the bends at the coupling region on a strained waveguide to produce a 2 × 2 monolithic directional coupler (DC). Later, this 2 × 2 DC is extended to a HDC by integrating a blue emissive BPP waveguide (OW3) at another bend on the deformed waveguide. The fabricated HDC can effectively split the incident light into three parts with different split ratios and deliver multi‐color outputs depending on the port receiving the input signal. The spontaneous generation and processing of various signals produced in the circuit helps in understanding the functioning of complex optical neural networks. The demonstration of such innovative optical components manifests their utility for diverse applications in neural networking and quantum computing systems.