Multichannel Waveguide Research Articles

Sub-GHz Broadband Multi-channel Waveguiding Based on Subwavelength Wire Media

The paper involves the development of a new type of image transfer. With this aim the multi-channel waveguide was considered in a novel representation – it was based on a wire media structure where each space between each four the closest wires is a single subchannel. The utilized wire media (WM) structure has 10-by-10 wires dimensions and 150 mm of the length, thus the first Fabry-Perot resonance appears around 0.9-1 GHz. The goal is to show the broadband multi-channel imaging at frequencies lower than the first Fabry-Perot resonance that means the considered structure tends to electrically short size that has not been studied previously. Taking into account the multi-channel principle of the wire media, the imaging can be performed as a binary one. For this reason, each single channel is fed by individual electromagnetic (EM) source that is a dipole antenna in the non-resonant mode. The reason is to use a weak source and match it with a single channel because in the other case the dipole is perfectly matched at the defined resonance frequency. It was found in the paper that the broadband transfer is possible in the frequency range-under-study and impossible at the region of the first Fabry-Perot resonance due to the perfect complex interaction between all wires of structure. As evidence, a simultaneous transfer of EM power from several independent EM sources shaped as R-letter was performed in the frequency range from 0.3 to 0.75 GHz by simulations and experimental investigations. The clear recovery of the transferred letter is possible in the case when it performs not at the frequency of Fabry-Perot and for the enough value of signal-to-noise ratio (SNR). The binary recovery of the transferred image became possible in the paper with an additional post-image processing with a threshold method involvement.

Frequency-selective valley-edge transmission and channeling in phononic-crystal plates with dual topological modulations

In this numerical study, we propose dual-modulated topological pillared phononic crystal (PnC) plates and demonstrate their application in achieving frequency-selective waveguiding of Lamb-wave valley-edge states. We show that both the radius and the height of the pillars in the honeycomb unit cell can be varied, allowing a generalized parameter space to obtain the complete topological bandgaps and two groups of distinct valley Hall phases for designing topological waveguides operating in different frequency ranges. Accordingly, we construct different types of phase domain walls to support valley-edge states using the dual-modulated PnC plates with a lattice constant of 2000 μm and with topological bandgaps opened around the Dirac cone frequency of 426 kHz. The numerical results show that the valley-edge states emerge to cover different frequency ranges and exhibit robust backscattering immunity when propagating along zigzag paths with sharp corners. Furthermore, the transport path of the valley-edge states can be designed to be highly dependent on the operating frequency in different domain walls. Consequently, we design a straight waveguide and three multichannel waveguides to demonstrate frequency-dependent switchable transmission and selective channeling of valley-edge states, respectively. The results of this study pave the way for the development and optimization of topological acoustic circuits using the generalized parameter space approaches and are expected to find promising applications in frequency-controlled and signal-division devices.

Reconfigurable topological wave routing based on tunable valley kink states and valley-polarized chiral edge states.

Valley kink states and valley-polarized chiral edge states, whose topologically protected one-way propagation property provides a promising solution for manipulating light waves, have recently attracted considerable attention in topological photonics. However, it remains a great challenge to realize flexibly tunable dispersion for two different topological states and to develop a dynamically controllable topological photonic platform for switching topological wave routing. In this work, we propose a reconfigurable topological wave routing structure in the telecommunication frequency range, where phase-change material Sb2S3 cylinders with tunable refractive index are embedded into each topological channel to dynamically tune the dispersion of topological edge states. Via switching the phase states of Sb2S3 between amorphous and crystalline, we numerically demonstrate some unique applications of the proposed topological photonic crystals, such as topological optical switches, dual-channel selective transport, and controllable multi-channel intersection waveguides. More importantly, by digitally encoding each waveguide channel without the requirement of controlling each unit cell in the bulk domain, the proposed topological photonic platform provides a convenient and easy-to-implement solution for achieving dynamically reconfigurable topological wave routing propagation. Besides, the unique features of immunity against bending interface with disorders demonstrate the robustness of the topological wave propagation. Our proposed topological photonic platform has potential applications for designing intelligent photonic devices and opens up an avenue for advanced integrated photonic systems with reconfigurability.

Controllable propagation of waveguide mode in multi-channel photonic crystal waveguide

In this paper, we introduce a new method to realize the separation of waveguide modes in photonic crystal waveguides by controlling the position and polarization of the dipole sources. Our study shows that the waveguide modes in the transversal channel and longitudinal channel can be manipulated, respectively, by the dipole sources placed within the corresponding channels. Based on this discovery, we may further adjust the dipole sources in the transversal (longitudinal) channel individually and separate the zeroth order and the first order modes to propagate towards the preassigned channels. Compared with the former schemes to realize the mode separation by changing the structure, our method is more intuitive, convenient, and flexible.

Inverse-designed ultra-compact multi-channel and multi-mode waveguide crossings.

In this work, we use the inverse design method to design three-channel and four-channel dual-mode waveguide crossings with the design regions of 4.32 µm-wide regular hexagon and 6.68 µm-wide regular octagon, respectively. Based on the highly-symmetric structures, the fundamental transverse electric (TE0) and TE1 modes propagate through the waveguide crossings efficiently. Moreover, the devices are practically fabricated and experimentally characterized. The measured insertion losses and crosstalks of the three-channel and dual-mode waveguide crossing for both the TE0 and TE1 modes are less than 1.8 dB and lower than -18.4 dB from 1540 nm to 1560 nm, respectively. The measured insertion losses of the four-channel and dual-mode waveguide crossing for the TE0 and TE1 modes are less than 1.8 dB and 2.5 dB from 1540 nm to 1560 nm, respectively, and the measured crosstalks are lower than -17.0 dB. In principle, our proposed scheme can be extended to waveguide crossing with more channels and modes.

Dynamic modulation of localized defect states in multichannel photonic crystal waveguides

The localized defect states (LDS) can usually be obtained by introducing dielectric defects or dielectric disorder into photonic crystals. Here, we introduce a new method to dynamically generate LDS, which can be realized in multichannel photonic crystal waveguides by modulating the position, polarization and phase of multiple dipole sources. We propose a general theory to obtain the localization conditions. When multiple dipole sources satisfy the localization condition, LDS can be generated. Unlike the traditional LDS, the size and position of the LDS in our method can be adjusted by the control of the dipole sources. In addition, the conversion of LDS and waveguide mode can be realized easily by the modulation of the dipole sources.

Slotted-Waveguide Antenna Array Development by Means of Complementarity оf CST Microwave Studio and Compass 3D Programs

The main steps of the methodology for complex slotted-waveguide antenna arrays development using the complementary application of the COMPASS 3D design program and electromagnetic modeling CST Microwave Studio are considered. The presentation of the technique steps is carried out on the example of a structurally complex slotted-waveguide antenna array of the Ka-band with dimensions (117 mm ´ 30 mm) and two-dimensional array of 64 (2 ´ 8 ´ 4) slotted emitters. To facilitate the synthesis of the design parameters of such grids, it is proposed to use a three-stage process: 1) design of slotted antenna emitting modules with adjustment to a given operation frequency range; 2) development of harmonized multichannel power divider for them; 3) combining the antenna modules and the branched power divider into an effective antenna array with additional adjustment of their coordination parameters. According to this sequence, in the illustrated example, on the first step, the antenna emitter module with four slits is designed in the CST Microwave Studio program. Afterwards, on the second stage, a complex multi-channel waveguide power divider was designed. It is first drawn in COMPASS 3D and then imported and analysed in CST Microwave Studio. On the final third stage, the entire slotted-waveguide antenna array was assembled and simulated in CST Microwave Studio. At the same time, the obtained radiation pattern of the antenna array, the functions of electromagnetic field distribution in the waveguide path and other electromagnetic characteristics corresponded to the required ones. Equally, there was a slight shift in the standing wave ratio (SWR) of the operating frequency matching, as well as some deterioration in the SWR. This is explained by the fact that the links between the models of antenna emitters and the waveguide power distributor were carried out 'in ideal ports'. Meanwhile, the real values of the input resistances in these planes of the assembled structure are somewhat different from the ideal ones. Therefore, to complete the process of structural synthesis of the antenna-slot array, two approaches should be used: 1) it is better to complete design parameter optimization according to the criterion of improving the harmonization, if required to shift the operating frequency, 2) to reduce the SWR value, it is better to improve the coordination of the antenna array at its input by adjusting the matching device.

Optical Control of the Localized Surface Plasmon Resonance in a Heterotype and Hollow Gold Nanosheet.

The remote excitation and remote-controlling of the localized surface plasmon resonance (LSPR) in a heterotype and hollow gold nanosheet (HGNS) is studied using FDTD simulations. The heterotype HGNS contains an equilateral and hollow triangle in the center of a special hexagon, which forms a so-called hexagon-triangle (H-T) heterotype HGNS. If we focus the incident-exciting laser on one of the vertexes of the center triangle, the LSPR could be achieved among other remote vertexes of the outer hexagon. The LSPR wavelength and peak intensity depend sensitively on factors such as the polarization of the incident light, the size and symmetry of the H-T heterotype structure, etc. Several groups of the optimized parameters were screened out from numerous FDTD calculations, which help to further obtain some significant polar plots of the polarization-dependent LSPR peak intensity with two-petal, four-petal or six-petal patterns. Remarkably, based on these polar plots, the on-off switching of the LSPR coupled among four HGNS hotspots could be remote-controlled simply via only one polarized light, which shows promise for its potential application in remote-controllable surface-enhanced Raman scattering (SERS), optical interconnects and multi-channel waveguide switches.

Near Infrared Light-Induced Self-Written Optical Waveguide and Its Application for Multi-Channel Waveguides

Near Infrared Light-Induced Self-Written Optical Waveguide and Its Application for Multi-Channel Waveguides

Hierarchical Integration of Organic Core/Shell Microwires for Advanced Photonics.

The combination of multiple components or structures into integrated micro/nanostructures for practical application has been pursued for many years. Herein, a series of hierarchical organic microwires with branch, core/shell (C/S), and branch C/S structures are successfully constructed based on organic charge transfer (CT) cocrystals with structural similarity and physicochemical tunability. By regulating the intermolecular CT interaction, single microwires and branch microstructures can be integrated into the C/S and branch C/S structures, respectively. Significantly, the integrated branch C/S microwires, with multicolor waveguide behavior and branch structure multichannel waveguide output characteristics, can function as an optical logic gate with multiple encoding features. This work provides useful insights for creating completely new types of organic microstructures for integrated optoelectronics.

Hierarchical Integration of Organic Core/Shell Microwires for Advanced Photonics

AbstractThe combination of multiple components or structures into integrated micro/nanostructures for practical application has been pursued for many years. Herein, a series of hierarchical organic microwires with branch, core/shell (C/S), and branch C/S structures are successfully constructed based on organic charge transfer (CT) cocrystals with structural similarity and physicochemical tunability. By regulating the intermolecular CT interaction, single microwires and branch microstructures can be integrated into the C/S and branch C/S structures, respectively. Significantly, the integrated branch C/S microwires, with multicolor waveguide behavior and branch structure multichannel waveguide output characteristics, can function as an optical logic gate with multiple encoding features. This work provides useful insights for creating completely new types of organic microstructures for integrated optoelectronics.

Fully controllable multichannel waveguides induced by counterpropagating Bessel beams

We theoretically analyze the waveguiding structures photo-induced by two incoherent counter-propagating Bessel beams (BBs) in a biased photorefractive crystal. We demonstrate that the cross-coupling of two BBs enables adressable channels and tunability of the forming guiding structures. The truncation parameter of the BBs, their Bessel orders and the misalignment between the two beams are all key parameters for tailoring the characteristics of the photo-induced waveguides such as the number of outputs, the output intensity levels and the distance between each output channel. Accordingly, we optimized the different parameters for designing not only a fully tunable Y-coupler but also optical splitters with up to five outputs and even more complex star couplers for all-optical interconnect applications. Finally, we report on the stability behavior of the photo-induced platform. The stability threshold depends on the nonlinearity parameter beyond which the beams display time-periodic, quasi-periodic and turbulent dynamics where spatially localized instabilities can be observed. All these results suggest more opportunities for fully controllable complex waveguiding structures and new all-optical solutions for active components in optical telecommunication and innovative ways of performing optical computing based on spatiotemporal chaos.

Tunable propagation of waveguide mode by incident spin states in multi-channel metal waveguide

The control of scattering light direction by incident spin state offers a desirable and novel development opportunity for the nano optics and integrated optical devices. Here, the controllable propagation of light in multi-channel metal waveguide is investigated by analyzing and applying the symmetry between the light source and the system based on the component wave interference theory. The composite electric and magnetic dipoles are used to drive the selective scattering in a four-channel structure. We found that it is a very convenient and intuitive method to obtain the selective propagation direction by considering the symmetry. We also reveal that the spin-momentum locking is only the eigen property of the optical system, instead of the origin of unidirectionality.

Series of ultra-low loss and ultra-compact multichannel silicon waveguide crossing.

Ultra-compact waveguide crossing (UC-WC) is a basic component in optoelectronic fusion chip solutions, as its footprint is smaller in the orders of magnitude than that of traditional photonic integrated circuits (PICs). However, a large loss of UC-WC (decibel level) becomes a barrier to scaling and practicality. Here, we propose a series of ultra-low loss UC-WC silicon devices using an advanced hybrid design that combines the adjoint method with the direct binary search (DBS) algorithm. Simulation results show that our 2 × 2 UC-WC has an insertion loss as low as 0.04 dB at 1550 nm, which is about ten times lower than the previous UC-WC results. In the valuable C-band (1530-1565 nm), the insertion loss of UC-WC is lower than -0.05 dB, and the channel crosstalk is lower than -34 dB. Furthermore, for the 3 × 3 UC-WC device, the highest insertion loss in the entire C-band is approximately -0.07 dB, and the highest channel crosstalk is lower than -33 dB. Additionally, the 4 × 4 and more complex 8 × 8 UC-WC devices were also analyzed. The highest insertion loss for 4 × 4 and 8 × 8 UC-WC in the C-band is only -0.19 dB and -0.20 dB, respectively, and the highest channel crosstalk is approximately -22dB and -28 dB, respectively. These results confirm that the designed devices possess two attractive features simultaneously: ultra-compactness and ultra-low insertion loss, which may be of great value in future large-scale optoelectronic fusion chips.

Multi-Channel SPAD Chip for Silicon Photonics With Multi-Photon CoIncidence Detection

We present the design and characterization of a microelectronic chip consisting of 32 independent single-photon counting and multi-photon time-coincidence channels, based on Single Photon Avalanche Diodes (SPADs). The chip aims at easing the assembly together with Silicon Photonics substrates and chips, for a broad spectrum of quantum applications. More specifically we targeted the Quantum Random Number Generation by exploiting the randomness in the optical path of single photons through multi-channel waveguides. To this purpose, the chip provides not only 32 independent pulse outputs for multi-channel single-photon counting, but it features other two operation modalities. For single-photon applications, the chip provides the single-hit digital address of the channel detecting the photon among the 32 ones. For multi-photon applications, the chip provides an event-driven pulse every time more than n photons (n selectable between 2 and 4) concurrently trigger different channels. Each detection channel consists of 4 independent SPADs with different diameter (5 m, 10 m, 20 m, and 50 m), in order to easily match the waveguides and collection efficiency.

On the amplitude dynamics of solitons in waveguide systems with the generic Kerr nonlinearity coefficient and nonlinear gain-loss

We study the transmission of optical solitons in a nonlinear waveguide with the generic Kerr nonlinearity coefficient, the frequency dependent linear gain-loss, and the Ginzburg-Landau (GL) gain-loss profile. We first derive the expression for the collision-induced amplitude dynamics of two fast single solitons in the presence of weak cubic loss and weak quintic loss. This expression is then used to study the amplitude dynamics of solitons in multichannel optical waveguide systems. We show that the dynamics of soliton amplitudes in two-sequence transmission with the GL gain-loss profile are described by a Lotka-Volterra (LV) model. The stability analysis for the LV model is used to obtain the simple conditions on the physical parameters and to calculate the linear amplifier gain-loss for the transmission stabilization of the soliton sequences. The theoretical calculations are then confirmed by numerical simulations with the corresponding nonlinear Schrödinger (NLS) models. Furthermore, the optimal value of the Kerr nonlinearity coefficient for the robust transmission stabilization of the soliton sequences with the GL gain-loss profile is also proposed.

Ultra-compact multichannel optical waveguide crossings designed by a particle swarm optimized method

Ultra-compact multichannel optical waveguide crossings are designed by a particle swarm optimized inverse-design method. The 2 × 2 TE (TM) device has an ultra-small footprint of 2 ×2μm2 and exhibits a high transmission efficiency of 69.1% (89.7%) and low crosstalk of −34.4 dB (−84.8 dB) at 1550 nm. The devices can work within a large range of pixel size and waveguide width, suggesting high process tolerance of the design method. To further extend the functionality, a 3 × 3 device with the same size is designed, which exhibits a remarkable transmission efficiency of 47.6%, 61.8%, 67.2%, and low crosstalk of −33.3 dB, −39.2 dB, and −49.9 dB, respectively, for the three transmission paths. In addition, by adjusting the structure, other types of 3 × 3 devices with different transmission paths are demonstrated. The ultra-compact broad-bandwidth high-process-tolerance optical waveguide crossings have great potential in high-integration photonic-integrated circuits.

Ultrasensitive detection of SARS-CoV-2 RNA and antigen using single-molecule optofluidic chip.

Nucleic acids and proteins are the two most important target types used in molecular diagnostics. In many instances, simultaneous sensitive and accurate detection of both biomarkers from the same sample would be desirable, but standard detection methods are highly optimized for one type and not cross-compatible. Here, we report the simultaneous multiplexed detection of SARS-CoV-2 RNAs and antigens with single molecule sensitivity. Both analytes are isolated and labeled using a single bead-based solid-phase extraction protocol, followed by fluorescence detection on a multi-channel optofluidic waveguide chip. Direct amplification-free detection of both biomarkers from nasopharyngeal swab samples is demonstrated with single molecule detection sensitivity, opening the door for ultrasensitive dual-target analysis in infectious disease diagnosis, oncology, and other applications.

Topologically protected edge states of elastic waves in phononic crystal plates

<sec> The topologically protected edge states of elastic waves in phononic crystal plates have the outstanding characteristics in wave manipulation such as the strong suppression of back-scattering and defect immunity, which can be used for controlling vibration and noise, detecting the structural damage, conducting the material nondestructive test and other engineering practices, and therefore have received much attention. But for plate structures, the propagation of elastic waves is complicated due to the coexistence and coupling of different types of wave modes, resulting in a challenge in designing topologically protected states. </sec><sec>In this paper, a simple phononic crystal plate with triangular holes is designed for elastic wave manipulation based on topologically protected edge states. The band structure characteristics of the unit cell are studied by varying the rotation angle <i>θ</i> of the triangular holes around their geometric centers from the initial positions. It is found that the band structure of the initial unit cell with rotation angle <i>θ</i> = 0° has two pairs of degenerate modes. At <inline-formula><tex-math id="M6">\begin{document}$ \theta = \pm 33^\circ $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20200542_M6.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20200542_M6.png"/></alternatives></inline-formula>, a double Dirac cone appears at the center <i>Γ</i> point of the Brillouin zone without requiring the lattices to fold, and a band inversion occurs on both sides of <inline-formula><tex-math id="M7">\begin{document}$ \pm 33^\circ $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20200542_M7.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20200542_M7.png"/></alternatives></inline-formula> which can be characterized as a topological phase transition. </sec><sec>The elastic band gap and two kinds of pseudospin states with clockwise or counterclockwise circulating mechanical energy flux patterns in the band structure are found by calculating the projected band structures of a supercell which is composed of phononic crystals with different topological phases. Based on this finding, different constructions of phononic waveguide are used for implementing the numerical analysis to demonstrate the back-scattering immunity of the edge states when disorder, tortuosity and cavity are introduced into the waveguide. Unidirectional robust propagation and multichannel waveguide switch due to the pseudospin-dependent one-way edge modes are also validated with numerical models. The phononic crystal plate presented in this paper provides a simple realizable method of designing the topologically protected elastic edge states. </sec>

Theoretical study of a multichannel plasmonic waveguide notch filter with double-sided nanodisk and two slot cavities

• First, by changing the structure parameters, the filtering effect can be realized on SPPs waves with specific wavelength, especially for the optical spectrum 450 nm–750 nm band selective filtering. • Second, the band rejection wavelength of our proposed selective notch filter increases in almost the same intervals of 30 nm when the radius of nanodisk cavity increases in intervals of 10 nm, and other factors are invariable. And the resonance trough wavelengths of the notch filter can be tuned by only changing the radius of the nano-disk, which is in good agreement with the results of the theoretical calculations. • Third, with the change of the geometric size parameters, such as the length and width of the rectangular cavity, and the distance between the resonators, the Plasma-induced transparency (PIT) have a blue shift of resonance transmittance trough satisfying the resonance conditions. *Finally, the PIT response is strongly dependent on the separation between the adjacent slot cavities. Additionally, the FOM * (figure of merit) and sensitivity of this structure can be as high as 99 and 750 nm/RIU, respectively. Based on the transmission characteristics of surface plasmonic subwavelength structure, a multichannel plasmonic notch filter comprising two slot resonators and a nano-disk cavity with the metal-insulator-metal waveguide is proposed and investigated numerically using the finite element method (FEM). It demonstrates that our proposed structure has the novel multichannel notch filter characteristics in optical regime. And the three resonance trough wavelengths of the notch filter can be tuned by changing the radius of the nano-disk and width of the slot, which is in good agreement with the results of the coupled mode theory (CMT). Moreover, the second resonance trough wavelength of the transmission spectrum increases in almost the same intervals of 30 nm when the radius of nano-disk cavity increases in intervals of 10 nm, showing a Fano line and an obvious red-shift. At the third resonance trough, the results show that the plasmon-induced transparency (PIT) is produced. And the PIT response is strongly influenced by the separation gap between the adjacent slot cavities. Additionally, the FOM * (figure of merit) and sensitivity of this structure can be as high as 99 and 750 nm/RIU, respectively. The results of this study not only present a tunable multichannel plasmonic notch filter, but also aid in developing ultra-compact refractive index sensor in optical highly integration circuits.