Characterization Of Waveguides Research Articles

Cross-talk-free, high extinction ratio, and ultra-compact all‑optical 4 × 2 encoder using graphene-based plasmonic waveguides

This paper presents an all-optical 4 × 2 encoder based on graphene-plasmonic waveguides for operation in the wavelength range of 8–12 μm. The basic plasmonic waveguide consists of a silicon (Si) strip and a graphene sheet supported by two dielectric ridges. Surface plasmon polaritons (SPPs) are stimulated in the spatial gap between the graphene sheet and the Si strip. The effect of geometric parameters and chemical potential of the graphene sheet changes on the suggested waveguide’s waveguiding behavior is meticulously investigated using the three-dimensional finite-difference time-domain (3D-FDTD) method. The encoder comprises a straight waveguide to detect the state of the In0 input and two Y-combiners with outputs Out0 and Out1 to detect the state of the In1, In2, and In3 inputs. The encoder exhibits a minimum extinction ratio (ERmin) of 19 dB at a wavelength of 10 μm. In addition, the cross-talk (CT) and insertion loss (IL) values are −21.3 and −1.31 dB, respectively. The encoder offers an ultra-compact structure with a total footprint of 4.25 μm2. Due to its exceptional waveguiding features, low CT and IL values, and high ERmin, the proposed encoder holds promise for various communication and signal processing applications.

Investigation of Modal Characteristics of Silicon Nitride Ridge Waveguides for Enhanced Refractive Index Sensing

This paper investigates the wavelength-dependent sensitivity of a ridge waveguide based on a silicon nitride (Si3N4) platform, combining numerical analysis and experimental validation. In the first part, the modal characteristics of a Si3N4 ridge waveguide are analyzed in detail, focusing on the effective refractive index (neff), evanescent field ratio (EFR), and propagation losses (αprop). These parameters are critical for understanding the interplay of guided light with the surrounding medium and optimizing waveguide design for sensing applications. In the second part, the wavelength-dependent sensitivity of a racetrack ring resonator (RTRR) based on the Si3N4 waveguide is experimentally demonstrated. The results demonstrate a clear increase in the sensitivity of the RTRR, rising from 116.3 nm/RIU to 143.3 nm/RIU as the wavelength shifts from 1520 nm to 1600 nm. This trend provides valuable insights into the device’s enhanced performance at longer wavelengths, underscoring its potential for applications requiring high sensitivity in this spectral range.

Comparative autofluorescence analysis of silicon nitride and tantalum pentoxide waveguides at 532 nm.

In this paper, we quantitatively compare the autofluorescence of stoichiometric low pressure chemical vapor deposition (LPCVD) silicon nitride and sputtered tantalum pentoxide waveguides at a pump wavelength of 532 nm. Through a direct quantitative characterization of comparable waveguides formed from the two films, we find no observable autofluorescence for tantalum pentoxide waveguides. Our experimental sensitivity is limited by Raman scattering of the pump into our detection band and our measurements indicate that the autofluorescence of the tantalum pentoxide waveguides is more than 600 × smaller than that of silicon nitride waveguides. This finding holds promise for visible technologies such as biosensors and quantum devices that require strong optical pumping and minimal background noise.

On-chip cryogenic low-pass filters based on finite ground-plane coplanar waveguides for quantum measurements.

Quantum technology exploits fragile quantum electronic phenomena whose energy scales demand ultra-low electron temperature operation. The lack of electron-phonon coupling at cryogenic temperatures makes cooling the electrons down to a few tens of millikelvin a non-trivial task, requiring extensive efforts on thermalization and filtering high-frequency noise. Existing techniques employ bulky and heavy cryogenic metal-powder filters, which prove ineffective at sub-GHz frequency regimes and unsuitable for high-density quantum circuits such as spin qubits. In this work, we realize ultra-compact and lightweight on-chip cryogenic filters based on the attenuation characteristics of finite ground-plane coplanar waveguides. These filters are made of aluminum on sapphire substrates using standard microfabrication techniques. The attenuation characteristics are measured down to a temperature of 500 mK in a dilution refrigerator in a wide frequency range of a few hundred kHz to 8.5GHz. We find their performance is superior by many orders compared to the existing filtering schemes, especially in the sub-GHz regime, negating the use of any lumped-element low-pass filters. The compact and scalable nature makes these filters a suitable choice for high-density quantum circuits such as quantum processors based on quantum dot spin qubits.

Mode-informed complex-valued neural processes for matched field processing.

A complex-valued neural process method, combined with modal depth functions (MDFs) of the ocean waveguide, is proposed to reconstruct the acoustic field. Neural networks are used to describe complex Gaussian processes, modeling the distribution of the acoustic field at different depths. The network parameters are optimized through a meta-learning strategy, preventing overfitting under small sample conditions (sample size equals the number of array elements) and mitigating the slow reconstruction speed of Gaussian processes (GPs), while denoising and interpolating sparsely distributed acoustic field data, generating dense field data for virtual receiver arrays. The predicted field is then integrated with the matched field processing (MFP) method for passive source localization. Validation on the SWellEx-96 waveguide shows significant improvements in localization performance and reduces sidelobes of ambiguity surface compared to traditional MFP and GP-based MFP. Moreover, the proposed kernel based on MDFs outperforms the Gaussian kernel in describing ocean waveguide characteristics. Because of the feature representation of multi-modal mapping, this kernel enhances acoustic field prediction performance and improves the accuracy and robustness of MFP. Simulated and real data are used to verify the validity.

Comments on “Characteristics of a Slotted Parallel-Plate Waveguide Filled With a Truncated Dielectric”

Comments on “Characteristics of a Slotted Parallel-Plate Waveguide Filled With a Truncated Dielectric”

Grazing emission X-ray fluorescence characterization of a thin-film waveguide with laboratory equipment

Grazing emission X-ray fluorescence characterization of a thin-film waveguide with laboratory equipment

Miniaturized Arrow-Shaped Flexible Filter-Embedded Antenna for Industrial and Medical Applications

This paper presents the design and characterization of a coplanar waveguide (CPW) fed, low-profile, and flexible arrow-shaped filtenna for ISM band applications at 2.45 GHz. The antenna design involves an innovative approach incorporating etching slots to achieve miniaturization by 34%, contrasting with a traditional quadrilateral-shaped antenna. After the attainment of desired miniaturization, the unwanted harmonics are also mitigated by deploying simple filtering methodology. A perpendicular rectangular stub is strategically introduced to the feedline, effectively minimizing harmonics across a broad frequency range of 3.3–11.0 GHz. Through simulations and measurements, the results indicate that the antenna’s operational band spans from 2.276 to 2.75 GHz, encompassing the entire ISM band (2.4–2.5 GHz). Notably, the antenna demonstrates promising radiation characteristics, including omnidirectional gain of approximately 2.2 dBi and a radiation efficiency exceeding 95%. With a compact overall size of 0.24λ × 0.20λ × 0.0005λ (where λ is the free-space wavelength at 2.45 GHz), coupled with wide harmonic rejection property, the proposed arrow-shaped flitenna emerges as a compelling candidate for ISM band applications.

The effect of time-varying characteristics of shallow-sea waveguides on low-frequency acoustic signal transmission

The time-varying characteristic of shallow sea channel plays one of the most important role in the exploration of ocean. However, there is still lack of estimation model to describe the time-varying characteristics of shallow water low-frequency acoustic channels. This paper proposes a low-frequency channel model based on wave equation and ray theory to estimate the time-varying characteristics of shallow sea. Firstly, for the actual characteristics of shallow sea, suitable boundary conditions are designed to solve the wave equation. Secondly, the constraint conditions of shallow sea wave equation are optimized by combining ray theory. Then, based on the physical characteristics of shallow sea, time-delay variation and phase variation are solved by shallow wave equation. Combining bellhop propagation model with ocean disturbance model, the simulation is designed to verify the time-varying characteristic model of low-frequency shallow sea in this paper. Finally, with different propagation distance measurement experiment of sea, estimation value of time-delay variation and phase variation are confirmed, which is significant to shallow sea channel.

Pseudospin-polarized slow light waveguides with large delay-bandwidth product

Delay-bandwidth product (DBP) is a key metric in slow light waveguides, requiring a balance between a large group index and broad bandwidth—two parameters that often involve a trade-off. Here, we propose and demonstrate a slow light waveguide with large DBP using a pseudospin-polarized transverse electromagnetic mode. This waveguide features a folded edge configuration that supports a 200% relative bandwidth from quasistatic limit (zero frequency) and an arbitrarily large group index. Owing to the pseudospin-polarized design, the dense folding would not introduce backscattering and the associated group velocity dispersion (GVD). The resulting gapless linear dispersion and pulse transmission behavior in folded edge waveguide are observed in microwave experiments. Our scheme provides a way to overcome the trade-off between group index and working bandwidth in slow light waveguide, which has potential applications in broadband optical buffering, light-matter interaction enhancement, terahertz radiation source and time domain processing.

Speed of Light in Hollow-Core Photonic Bandgap Fiber Approaching That in Vacuum.

A Fresnel mirror is introduced at a hollow-core photonic bandgap fiber end by fusion splicing a short single-mode fiber segment, to reflect the light backward to an optical frequency domain reflectometry. The backward Fresnel reflection is used as a probe light to achieve light speed measurement with a high resolution and a high signal-to-noise ratio. Thus, its group velocity is obtained with the round-trip time delay as well as the beat frequency at the reflection peak. Multiple Fresnel peaks are observed from 2180.00 Hz to 13,988.75 Hz, corresponding to fusion-spliced hollow-core fiber segments with different lengths from 0.2595 m to 1.6678 m, respectively. The speed of light in the air guidance is calculated at 2.9753 × 108 m/s, approaching that in vacuum, which is also in good agreement with 2.9672 × 108 m/s given by the numerical analysis with an uncertainty of 10-3. Our demonstration promises a key to hollow-core waveguide characterization for future wide-bandwidth and low-latency optical communication.

PTFE-Based Circular Terahertz Dielectric Waveguides

This paper presents the transmission characteristics of flexible solid circular dielectric waveguides in the terahertz frequency band. In this paper, we measured the electrical properties of certain polymers within 325–500 GHz. Through simulation and measurement, the transmission loss, bending loss, and electric field distribution of solid-core polymer dielectric waveguides were analyzed and discussed. Additionally, we considered the surrounding cladding of the dielectric waveguide, the signal-feeding mode transmitter, and the interconnection of the dielectric waveguide. Ultimately, in the operating frequency range of 325–500 GHz, we selected PTFE rods with diameters of 0.5 mm and 1 mm as the dielectric waveguides, with measured transmission loss of less than 30 dB/m and 33 dB/m, respectively, and bending loss of less than 1 dB/m. The described dielectric waveguide has engineering significance for short-distance connections in complex geometric environments and provides a reference for subsequent research.

Epitaxial Growth of Two-Dimensional Organic Crystals with In-Plane Heterostructured Domain Regulation.

Complex organic lateral heterostructures (OLHs) with spatial distribution of two or more chemical components are crucial for designing and realizing unique structure-dependent optoelectronic applications. However, the precise design of well-defined OLHs with flexible domain regulation remains a considerable challenge. Herein, we present a stepwise solution self-assembly method to synthesize two-dimensional (2D) OLHs with a central rhombus domain and a lateral region featuring tunable blue and green emission based on the sequential nucleation and growth of 2D crystals. By controlling the initial crystallization time of 2,6-diphenylanthracene, the rhombic length ratio (α) of the multicolor-emissive part of the 2D OLHs is precisely modified. Furthermore, a third lateral layer is constructed on the resulting OLHs, demonstrating scalable lateral regulation. Significantly, these prepared 2D OLHs exhibit great excitation position-dependent waveguide characteristics and enable a 0.06 dB/μm low-loss waveguiding, which are conducive to photon transport and conversion for photonic integrated circuits. This work provides a stepwise strategy for the accurate fabrication of 2D OLHs, fabricating the developments of next-generation optoelectronics devices.

Dispersion and Attenuation Estimation of Ultrasonic Guided Waves using Multi-Subarrays Matrix Pencil Method

Abstract Dispersion and attenuation estimation of ultrasonic guided waves is important for waveguide characterization. Matrix pencil (MP) method has been proposed for multimode complex wavenumber estimation, but its performance highly depends on the signal to noise ratio (SNR), which still brings challenges for high attenuation waveguide evaluation. In addition, the model order, i.e., matrix size in MP method, significantly impacts the dispersion curve extraction. In this study, to avoid the model order interference and compensate the SNR sensitivity of the classical MP algorithm, a multi-subarrays MP method is proposed for accurate dispersion and attenuation estimation. Considering with different Hankel matrix sizes, the multi-subarrays MP method estimates the complex wavenumbers from each pair of submatrices to filter uncertain results. A soft threshold strategy is applied to compensate the noise sensitivity of the estimation. Simulated results prove the proposed method can improve the dispersion and attenuation curve estimation.

Arctic-Type Seismoacoustic Waveguide: Theoretical Foundations and Experimental Results

The results of theoretical analysis and practical implementation of seismoacoustic methods developed for monitoring ice-covered regions in the Arctic are presented and discussed. Special attention is paid to passive seismoacoustic tomography as a unique method of studying the deep structure of the lithosphere and hydrosphere without the use of powerful sources. One of the distinctive features of the considered approach is the use of receivers located on the ice surface to recover characteristics of Arctic-type seismoacoustic waveguide “lithosphere-hydrosphere-ice cover”. In passive monitoring, special attention is paid to reducing the noise signal accumulation time required to obtain seismoacoustic wave propagation times, as well as expanding the analyzed frequency bandwidth. The presented results can be used to develop technologies for seasonal and long-term monitoring of the currently observed variability of large areas of the Arctic region due to climatic changes.

Optimized hybrid plasmonic waveguide-based ring resonator for advanced refractive index sensing

In this study, we conducted a comprehensive numerical analysis employing the finite element method to explore the characteristics of a hybrid plasmonic waveguide (HPWG)-based ring resonator (RR) structure. Our investigation reveals that the device’s sensitivity can be significantly augmented through strategic geometric modifications. The device exhibits sensitivities of approximately 176 nm RIU−1 and 238 nm RIU−1 when utilizing WG widths of 300 nm and 270 nm, respectively, in forming the ring structure. Through optimization efforts aimed at enhancing the overlap between the dielectric and plasmonic modes, the device’s sensitivity reaches an optimized level of around 316 nm RIU−1 by reducing the ring width to 250 nm. Overall, our findings underscore the potential for leveraging geometric adjustments to enhance the sensitivity and functionality of HPWG-based RRs, thereby advancing their utility in diverse sensing applications.

Dispersion characteristics of arc-axis waveguides

Ultrasonic single mode excitation methods, mode separation algorithms and damage detection applications all require the calculation of the dispersion characteristics of the waveguide. However, existing dispersion calculation methods are mainly applicable to straight-axis waveguides. Therefore, in this paper, a novel semi-analytical finite element method in cylindrical coordinates (SAFEM-CC) is established and we focus on the dispersion characteristics of arc-axis waveguides. The cross-section of the waveguide can have arbitrary complex shapes, and the correctness of this method is verified by the finite element eigenfrequency method. At the same time, this paper takes the example of an arc-axis structure with a square cross-section and investigates the convergence of SAFEM-CC under different numbers of elements, element types, and element orders. This paper also establishes a finite element simulation model to study the waveform transmission law over a wide frequency range and the wave amplitude distribution law within the cross-section of arc-axis waveguides. The dispersion characteristics of arc-axis waveguides at different radii are also investigated. Finally, the correctness of the proposed method and the dispersion characteristics of arc-axis waveguides are verified by a large number of experiments. The main conclusions are as follows: the waveform transmission laws of the guided wave in arc-axis waveguides at each frequency agree with the dispersion curve; the theoretical wavestructure gives the distribution law of the amplitude within the cross-section; when the axis is arc, the displacement of the wavestructure on the inner and outer sides does not have symmetry, and the difference between the left and right sides gradually increases as the radius decreases.

Characterisation of optical waveguides for photonic integrated circuits

Fast signal processing at the speed of light is the main advantage of photonic integrated circuits. Therefore, these circuits have good prospects for the implementation of mathematical calculations, including matrix to vector multiplication. The purpose of the research was to create and investigate a technique for automatic measurement of brightness distribution along optical waveguides of analogue photonic integrated circuits. Empirical methods (observation, measurement, comparison, experiment) and a complex method (analysis and synthesis) have been used during the research. The proposed technique uses a digital camera that captures images of optical waveguide illuminated by light emitting diodes and image processing software to calculate brightness distribution. This technique determines the best approximation of this distribution, calculates parameters of brightness non-uniformity and losses of optical radiation. Measurements of a set of optical waveguides help to identify the best candidates for photonic integrated circuits. It has been found that optical waveguides with grinded surfaces acting as diffusive scattering have good combination of smooth brightness distribution and small losses of optical radiation. Due to multiple diffuse reflection and scattering within waveguide material, these waveguides are promising candidates for analogue photonic integrated circuits. All other waveguides with non-processed surface, with grooves or grinded with a large grain have sufficient losses of optical radiation. These losses are usually caused by the exit of optical radiation from waveguide surface. The obtained results are necessary for accurate design of circuits that takes into account scattering and losses in optical waveguides. The proposed technique can be applied in automatic technological process of manufacturing a fast and economical photonic matrix to vector multiplication, which does not require expensive electron-beam, optical or laser lithographic equipment

Study on fs-laser machining of optical waveguides and cavities in ULE® glass

The potential of ultrafast laser machining for the design of integrated optical devices in ULE® glass, a material known for its low coefficient of thermal expansion (CTE), is addressed. This was done through laser direct writing and characterization of optical waveguides and through the fabrication of 3D cavities inside the glass by following laser irradiation with chemical etching. Type I optical waveguides were produced and their internal loss mechanisms at 1550 nm were studied. Coupling losses lower than 0.2 dB cm−1 were obtained within a wide processing window. However, propagation loss lower than 4.2–4.3 dB cm−1 could not be realized, unlike in other glasses, due to laser-induced photodarkening. Selective-induced etching was observed over a large processing window and found to be maximum when irradiating the glass with a fs-laser beam linearly polarised orthogonally to the scanning direction, akin to what is observed in fused silica laser-machined microfluidic channels. In fact, the etching selectivity and surface roughness of laser-machined ULE® glass was found to be similar to that of fused silica, allowing some of the already reported microfluidic and optofluidic devices to be replicated in this low CTE glass. An example of a 3D cavity with planar-spherically convex interfaces is given. Due to the thermal properties of ULE® glass, these cavities can be employed as interferometers for wavelength and/or temperature referencing.

ANN-based estimation of dispersion characteristics of slotted photonic crystal waveguides

ANN-based estimation of dispersion characteristics of slotted photonic crystal waveguides