Characterization Of Waveguides Research Articles

Tunable elastic wave modulation via local phase dispersion measurements of a piezoelectric metasurface with signal correlation enhancement

Tunable piezoelectric metasurfaces have been proposed as a means of adaptively steering incident elastic waves for various applications in vibration mitigation and control. Bonding piezoelectric material to thin structures introduces electromechanical coupling, enabling structural dynamics to be altered via tunable electric shunts connected across each unit cell. For example, by carefully calibrating the inductive shunts, it is possible to implement the discrete phase shifts necessary for gradient-based waveguiding behaviors. However, experimental validations of localized phase shifting are challenging due to the narrow bandgap of local resonators, resulting in poor transmission of incident waves and high sensitivity to transient noise. These factors, in combination with the difficulties in experimental circuitry synthesis, can lead to significant variability of data acquired within the bandgap operating region. This paper presents a systematic approach for extracting localized phase shifts by taking advantage of the inherent correlation between the incident and transmitted wavefronts. During this procedure, matched filtering greatly reduces noise in the transmitted signal when operating in or near bandgap frequencies. Experimental results demonstrate phase shifts as large as −170° within the locally resonant bandgap, with an average 28% reduction in error relative to a direct time domain measurement of phase, enabling effective comparison of the dispersive behavior with corresponding analytical and finite element models. In addition to demonstrating the tunable waveguide characteristics of a piezoelectric metasurface, this technique can easily be extended to validate localized phase shifting of other elastic waveguiding metasurfaces.

Numerical analysis of the propagation modes of photo-switching PDMS-arylazopyrazole optical waveguide and thin-film spectroscopic characterization

Numerical analysis of the propagation modes of photo-switching PDMS-arylazopyrazole optical waveguide and thin-film spectroscopic characterization

A Novel Approach to Realize Plasmonic Sensors via Multimode Optical Waveguides: A Review

In recent decades, the Surface Plasmon Resonance (SPR) phenomenon has been utilized as an underlying technique in a broad range of application fields. Herein, a new measuring strategy which harnesses the SPR technique in a way that is different from the classical methodology was explored by taking advantage of the characteristics of multimode waveguides, such as plastic optical fibers (POFs) or hetero-core fibers. The sensor systems based on this innovative sensing approach were designed, fabricated, and investigated to assess their ability to measure various physical features, such as magnetic field, temperature, force, and volume, and to realize chemical sensors. In more detail, a sensitive patch of fiber was used in series with a multimodal waveguide where the SPR took place, to alter the mode profile of the light at the input of the waveguide itself. In fact, when the changes of the physical feature of interest acted on the sensitive patch, a variation of the incident angles of the light launched in the multimodal waveguide occurred, and, as a consequence, a shift in resonance wavelength took place. The proposed approach permitted the separation of the measurand interaction zone and the SPR zone. This meant that the SPR zone could be realized only with a buffer layer and a metallic film, thus optimizing the total thickness of the layers for the best sensitivity, regardless of the measurand type. The proposed review aims to summarize the capabilities of this innovative sensing approach to realize several types of sensors for different application fields, showing the high performances obtained by exploiting a simple production process and an easy experimental setup.

Electromagnetic deactivation spectroscopy of human coronavirus 229E

An investigation of the deactivation of pathogens using electromagnetic waves in the microwave region of the spectrum is achieved using custom-built waveguide structures. The waveguides feature sub-wavelength gratings to allow the integration of an air cooling system without disturbing the internal propagating fields. The waveguides are tapered to accommodate an experimental sample internally with sufficient surrounding airflow. The proposed methodology allows for precise control over power densities due to the well-defined fundamental mode excited in each waveguide, in addition to temperature control of the sample due to microwave exposure over time. Human coronavirus (HCoV-229E) is investigated over the 0–40 GHz range, where a peak 3-log viral reduction is observed in the 15.0–19.5 GHz sub-band. We conclude HCoV-229E has an intrinsic resonance in this range, where nonthermal structure damage is optimal through the structure-resonant energy transfer effect.

Metasurfaces integrated with a single-mode waveguide array for off-chip wavefront shaping.

Integration of metasurfaces and SOI (silicon-on-insulator) chips can leverage the advantages of both metamaterials and silicon photonics, enabling novel light shaping functionalities in planar, compact devices that are compatible with CMOS (complementary metal-oxide-semiconductor) production. To facilitate light extraction from a two-dimensional metasurface vertically into free space, the established approach is to use a wide waveguide. However, the multi-modal feature of such wide waveguides can render the device vulnerable to mode distortion. Here, we propose a different approach, where an array of narrow, single-mode waveguides is used instead of a wide, multi-mode waveguide. This approach tolerates nano-scatterers with a relatively high scattering efficiency, for example Si nanopillars that are in direct contact with the waveguides. Two example devices are designed and numerically studied as demonstrations: the first being a beam deflector that deflects light into the same direction regardless of the direction of input light, and the second being a light-focusing metalens. This work shows a straightforward approach of metasurface-SOI chip integration, which could be useful for emerging applications such as metalens arrays and neural probes that require off-chip light shaping from relatively small metasurfaces.

Artificial Gauge Field Enabled Low‐Crosstalk, Broadband, Half‐Wavelength Pitched Waveguide Arrays

AbstractDense waveguide arrays with half‐wavelength pitch, low‐crosstalk, broadband, and flexible routing capability are essential for integrated photonics. However, achieving such performance is challenging due to the relatively weaker confinement of dielectric waveguides and the increased interactions among densely packed waveguides. Here, leveraging the artificial gauge field mechanism, half‐wavelength‐pitched dense waveguide arrays, consisting of 64 waveguides, in silicon with −30 dB crosstalk suppression from 1480 to 1550 nm are demonstrated. The waveguide array features negligible insertion loss for 90° bending. This approach enables flexibly routing a large‐scale dense waveguide array that significantly reduces on‐chip estate, leading to a high‐density photonic integrated circuit, and may open up opportunities for important device performance improvement, such as half‐wavelength‐pitch optical phased array and ultra‐dense space‐division multiplexing.

Oriented Self-Assembly of Hierarchical Branch Organic Crystals for Asymmetric Photonics.

Organic hierarchical branch micro/nanostructures constituted by single crystals with inherent multichannel characteristics exhibit superior potential in regulating photon transmission for photonic circuits. However, organic branch micro/nanostructures with precise branch positions are extremely difficult to achieve due to the randomness of the nucleation process. Herein, by taking advantage of the dislocation stress field-impurity interaction that solute molecules deposit preferentially along the dislocation line, twinning deformation was introduced into microcrystals to induce oriented nucleation sites, and ultimately organic branch microstructures with controllable branch sites were fabricated. The growth mechanism of these controllable single crystals with an angle of 140° between trunk and branch is attributed to the low lattice mismatching ratio (η) of 4.8%. These as-prepared hierarchical branch single crystals with asymmetrical optical waveguide characteristics have been demonstrated as an optical logic gate with multiple input/out channels, which provides a route to command the nucleation sites and offers potential applications in the organic optoelectronics at the micro/nanoscale.

High-efficiency and easy-to-fabricate integrated plasmonic grating couplers for the telecommunication wavelength range

The paper describes results of the numerical simulation and experimental characterization of plasmonic gratings and waveguides in the optical range of 1520 – 1630 nm. Gold structures were coated with a 630-nm thick tetraethylorthosilicate layer to achieve higher coupling efficiency for plasmonic gratings using lensed optical probes. We experimentally demonstrated gold input/output plasmonic gratings with an efficiency of about – 3.8 ± 0.2 dB per grating. The measured loss of the plasmonic mode propagating over the surface of the gold waveguide was 0.14 ± 0.02 dB / μm. The work was carried out with the aim of studying integrated plasmonic structures for the development of a hybrid photonic-plasmonic integrated technology.

Widely tunable 2 µm hybrid laser using GaSb semiconductor optical amplifiers and a Si3N4 photonics integrated reflector

Tunable lasers emitting in the 2-3 µm wavelength range that are compatible with photonic integration platforms are of great interest for sensing applications. To this end, combining GaSb-based semiconductor gain chips with Si3N4 photonic integrated circuits offers an attractive platform. Herein, we utilize the low-loss features of Si3N4 waveguides and demonstrate a hybrid laser comprising a GaSb gain chip with an integrated tunable Si3N4 Vernier mirror. At room temperature, the laser exhibited a maximum output power of 15 mW and a tuning range of ∼90 nm (1937-2026 nm). The low-loss performance of several fundamental Si3N4 building blocks for photonic integrated circuits is also validated. More specifically, the single-mode waveguide exhibits a transmission loss as low as 0.15 dB/cm, the 90° bend has 0.008 dB loss, and the 50/50 Y-branch has an insertion loss of 0.075 dB.

Supercontinuum in integrated photonics: generation, applications, challenges, and perspectives.

Frequency conversion in nonlinear materials is an extremely useful solution to the generation of new optical frequencies. Often, it is the only viable solution to realize light sources highly relevant for applications in science and industry. In particular, supercontinuum generation in waveguides, defined as the extreme spectral broadening of an input pulsed laser light, is a powerful technique to bridge distant spectral regions based on single-pass geometry, without requiring additional seed lasers or temporal synchronization. Owing to the influence of dispersion on the nonlinear broadening physics, supercontinuum generation had its breakthrough with the advent of photonic crystal fibers, which permitted an advanced control of light confinement, thereby greatly improving our understanding of the underlying phenomena responsible for supercontinuum generation. More recently, maturing in fabrication of photonic integrated waveguides has resulted in access to supercontinuum generation platforms benefiting from precise lithographic control of dispersion, high yield, compact footprint, and improved power consumption. This Review aims to present a comprehensive overview of supercontinuum generation in chip-based platforms, from underlying physics mechanisms up to the most recent and significant demonstrations. The diversity of integrated material platforms, as well as specific features of waveguides, is opening new opportunities, as will be discussed here.

Efficient optical waveguiding and lasing in needle crystals of thiophene/phenylene co-oligomers grown in solution

Needle organic single crystals of light-emitting π-conjugated compounds are superior platforms for photonic circuits. Thiophene/phenylene co-oligomers have been ideal laser media, however, a facile crystal growth method that controls crystal morphologies and optical waveguiding characteristics has not yet been developed. Here, 2,5-bis(4′-cyanobiphenyl-4-yl)thiophene (BP1T-CN) and 5,5′-bis(4′-cyanobiphenyl-4-yl)-2,2′-bithiophene (BP2T-CN) are crystallized with needle morphologies in solution. The attenuation coefficients estimated via spatially resolved PL measurements were 0.012 ± 0.006 μm−1 for a BP1T-CN crystal and 0.027 ± 0.003 μm−1 for a BP2T-CN crystal. Furthermore, both exhibited lasing in a Fabry–Pérot mode via self-cavity effects.

Acoustic Splitter Waves Based on Ramified System Made of Waveguides

In this paper, we studied the propagation of acoustic waves in an acoustic ramified system. Our proposed system contains an input waveguide of length d0 and three output lines (three channels), each output line contains a semi-infinite waveguide. The theoretical analysis is based on the Transfer Matrix Method (TMM), which allows us to calculate the three transmission rates T1, T2, T3 and the reflection rate R. We demonstrate that our proposed three-output channels system can be used to design a multifunctional device that functions as an amplitude splitter: an incident sound wave is splited to three output channels. This system is capable of achieving various waveguiding characteristics with perfect channels transmissions.

Characteristics of Plasma Waveguide Based on Anchored Cavity

Characteristics of Plasma Waveguide Based on Anchored Cavity

Propagation Characteristics in a Circular Waveguide for Feasibility Study of Terabit DSL

Due to the demand for higher data rates and greater download speeds by users and increasing number of deployed devices providing content-rich data, new cost-effective technologies which utilizes the concept of waveguides over copper that can enable the realization ofterabit DSL need to be explored to meet the required demands. This paper presents the propagation characteristics of circular waveguide which include reflection/transmission coefficient, attenuation coefficient and surface current. The design and simulation process have been carried out using CST Microwave Studios at the frequency of 100GHz to 300GHz. The circular waveguide is varied for various radius and length to observe for the respective propagation characteristics. Based on the result, it is shown that the reflection coefficient decreases with the increase in radius and length and it is below -50dB. Besides, with the increase in frequency, the transmission coefficient shows that the waveguide is able to achieve 100% transmission (0dB) at 200GHz with the increase in radius and length. Moreover, the attenuation coefficient of the waveguide is low which is about 0.0022dB/mm and maximum surface current intensity of 81.5556A/m. The results obtained can be considered the first step on understanding the propagation characteristics of waveguide at terahertz frequency range towards the realization of Terabit DSL.

Mathematical Model of the On-Board Antenna of Reentry Spacecraft Taking into Account Surface Waves

Introduction. The onboard antennas of the returned hypersonic aircraft are weakly directional, which is achieved by radiation from the open end of the waveguide. When passing through dense layers of the atmosphere, they are exposed to aerodynamic heating, for protection from which a heat-resistant radio-transparent thermal protection is used. The case of uniform thermal protection of the antenna can be interpreted as the absence of heating or heating uniform in the thickness of the thermal protection.Aim. The problem of obtaining an analytical description of the radiation characteristics of a circular waveguide closed by a flat homogeneous dielectric plate is solved. Since in such a formulation it is necessary to consider the resonant domain, a strict solution of Maxwell's equations is required.Materials and methods. Of the known analytical methods of solution, it is possible to use the method of integral transformations and the method of eigen functions. Both of these methods are used in the work. In this case, the assumption is used that the electrical parameters of the dielectric plate (thermal protection) and the geometric dimensions do not depend on time.Results. The relations describing the directional pattern of a circular waveguide with dielectric thermal protection and taking into account the electrical parameters of thermal protection and its thickness are obtained. Expressions are also obtained for the fields of lateral, surface and outflow waves, from which it is possible to calculate the power output by these fields. Relations for the separation of singular points of integrand expressions into poles corresponding to surface, outflow and lateral waves are obtained. Surface, outflow and lateral waves can have a certain effect on the radiation pattern. To determine this conclusion, analytical relations are obtained for determining the poles of integrand expressions that fully describe surface, outflow and side waves. All the analytical results obtained correspond to Numerical calculations were carried out on some of the obtained ratios.Conclusion. The results showed that the power of the side waves is zero. It also follows from the calculations carried out that there is no radiation field of surface and outgoing waves, i.e. there is no contribution of them to the radiation pattern.

Waveform inversion for wavenumber extraction and waveguide characterization using ultrasonic Lamb waves

Wavenumber dispersion of ultrasonic Lamb waves associating with the thickness and material property of plates plays an important role in waveguide characterization and non-destructive testing. Classical waveguide characterization with wavenumber estimation methods is performed based on a large amount of Lamb wave signals or sensitive to wave mode overlapping and noise. A genetic algorithms-based waveform inversion method is developed for wavenumber extraction of one Lamb wave signal and characterization of plate in this work. The individual chromosome is encoded in real number by the thickness and material properties of the structure. The elastic formula of Lamb waves is solved by the bisection method to further derive the wavenumber curves; then the wave mode signals are generated based on the propagation function, and are linearly combined to form the individual signal. The signal with the minimum residual ratio to the analysis signal is iteratively searched by the genetic algorithm. Finally, the plate properties and wavenumber of Lamb waves are identified with the chromosome of searched individual. Numerical and experimental studies prove the developed waveform inversion method can realize accurate wavenumber extraction of a Lamb wave signal, even though its time–frequency representation has low sparsity, and characterization of plate. The residual ratio between the inversion wavenumber and theory curves is around 1%; and the estimation deviation of material properties of plate is around 6%.

Numerical analysis of the highly non-linear and ultra-sensitive modified core of a photonic crystal fiber sensor for detection of liquid analytes

A design of the highly non-linear and ultra-sensitive modified core of a photonic crystal fiber (PCF) sensor is reported for the detection of various liquid analytes. The sensor design comprises three rings of a hexagonal lattice around the liquid-infiltrated hollow core. A steric-shaped hollow core design in PCF effectively optimizes the sensor’s sensitivity and performance. The design is analyzed numerically by using the full vector finite element method with perfectly matched layers to find a rigorous solution. The proposed PCF sensor exhibits ultra-high relative sensitivity, a high power fraction, high non-linearity coefficient, low confinement loss, ultra-low chromatic dispersion, compact effective mode area, and single-mode operation in a wider wavelength range, i.e., within visible and infrared wavelength regimes. At an operating wavelength of 1.0 µm, optimum relative sensitivities of 96.37%, 97.40%, and 99.82% with high non-linear coefficients of 78.0 W − 1 k m − 1 , 66.09 W − 1 k m − 1 , and 62.57 W − 1 k m − 1 and extremely low confinement loss of ∼ 10 − 10 d B / m are obtained for water, ethanol, and benzene analytes, respectively. Further, waveguiding characteristics of the PCF sensor endorse its usage for a range of liquid analyte detections. It is a simple design and can be fabricated using existing manufacturing technologies.

Efficient Optical Waveguiding Enabled by Focused Proton Beam Writing in Nd:YCOB Crystal

We report on microfabrication and optical characterization of buried channel waveguides defined in Nd:YCOB crystal by focused proton beam writing (PBW). In the fabrication process, the focused proton beam irradiation creates a local material modification region with geometrically symmetric positive index changes at the end of the proton trajectory, where efficient optical waveguiding can be locally supported within a fiber-like channel structure. The impact of the proton fluence (with different values ranging from 1015 to 1016 cm−2) on the optical waveguiding performance is well studied. The experimental results of the optical waveguide properties are in fairly good agreement with the simulation results.

One-dimensional and two-dimensional Er3+-doped germanate glass waveguides by combination of He+ ion implantation and precise diamond blade dicing

Compact and miniaturized Er3+-doped waveguide structure is an important research direction in integrated optics. In this work, the Er3+-doped germanate glass was bombarded by a 400-keV He+ ion beam with a fluence of 6.0 × 1016 ions/cm2 for the formation of the one-dimensional waveguide in a vacuum. Subsequently, the precise diamond blade with a rotating velocity of 20,000 rpm and a cutting speed of 0.1 mm/s was applied to dice the surface of the one-dimensional waveguide for the fabrication of the two-dimensional structure. The formation mechanism and the refractive index profile of the one-dimensional waveguide were studied by the SRIM 2013 and the RCM, respectively. The electromagnetic field profiles for the fundamental modes of both one-dimensional and two-dimensional waveguides were measured by the end-face coupling method. It presents some useful information in the field of fabrication and characterization of optical waveguides for active photonic applications.

Influence of Thermal Pretreatment of Lithium Niobate Plates on the Characteristics of Proton-Exchange Waveguides

Influence of Thermal Pretreatment of Lithium Niobate Plates on the Characteristics of Proton-Exchange Waveguides