Properties Of Waveguides Research Articles

Electrodynamic properties of a rectangular waveguide with a dielectric plate located in the center of its wide wall

A rectangular waveguide with a dielectric plate located in the E-plane is the basic element of devices for microwave heat treatment of sheet materials. In this regard, it is relevant to study the processes of propagation and transformation of electromagnetic waves in such a system. The purpose of the work is to study the influence of the transformation of the electromagnetic field in the air medium of a rectangular waveguide in the zone of propagation of the slow wave H10 on the distribution of electric field energy in the dominant wavelength range and determining the wavelength, at which its maximum value is reached. The range properties of the intrinsic electrodynamic parameters and the field structure of a rectangular waveguide with a dielectric plate located in the E-plane in the middle of its wide wall have been studied. The wavelength at which the maximum energy level of the electric field in the dielectric plate is achieved is determined. The results obtained can be used in the design of microwave heating devices for dielectric materials.

Effects of germanium content on the optical properties of GeO2-based organic-inorganic composite films doped with azobenzene

Organic-inorganic composite materials have great applications in integrated optics due to their good optical performance. In this study, GeO2-based organic-inorganic composite films doped with azobenzene were prepared by combining the solgel technique and the spin-coating method. The optical waveguide properties including the refractive index and film thickness and the optical response properties of the composite films with different germanium contents have been investigated. The results indicate that the refractive index of the film increases, but the film thickness decreases as the germanium content increases. The composite film with 0.2 mol of germanium exhibits the best optical response properties. Further, the optical switching characteristics of the optimal composite film shows good stability and reversibility. The photochemical and structural properties of the film were also investigated by using Fourier transform infrared spectroscopy and thermo-gravimetric analysis. Finally, hexagonal microlens arrays were built in the film by using the UV nanoimprint technique, resulting in neatly arranged structures with good optical imaging performance.

The elastic stiffness tensor of cellulosic viscose fibers measured with Brillouin spectroscopy

Brillouin light scattering spectroscopy is applied to study the micromechanics of cellulosic viscose fibers, one of the commercially most important, man-made biobased fibers. Using an equal angle scattering geometry, we provide a thorough description of the procedure to determine the complete transversely isotropic elastic stiffness tensor. From the stiffness tensor the engineering-relevant material parameters such as Young’s moduli, shear moduli, and Poisson’s ratios in radial and axial fiber direction are evaluated. The investigated fiber type shows that, at ideal conditions, the material exhibits optical waveguide properties resulting in spontaneous Brillouin backscattering which can be used to obtain additional information from the Brillouin spectra, enabling the measurement of two different scattering processes and directions with only one scattering geometry.

Guiding light with surface exciton–polaritons in atomically thin superlattices

Abstract Two-dimensional materials give access to the ultimate physical limits of photonics with appealing properties for ultracompact optical components such as waveguides and modulators. Specifically, in monolayer semiconductors, a strong excitonic resonance leads to a sharp oscillation in permittivity from positive to even negative values. This extreme optical response enables surface exciton–polaritons to guide visible light bound to an atomically thin layer. However, such ultrathin waveguides support a transverse electric (TE) mode with low confinement and a transverse magnetic (TM) mode with short propagation. Here, we propose that realistic semiconductor–insulator–semiconductor superlattices comprising monolayer WS2 and hexagonal boron nitride (hBN) can improve the properties of both TE and TM modes. Compared to a single monolayer, a heterostructure with a 1-nm hBN spacer separating two monolayers enhances the confinement of the TE mode from 1.2 to around 0.5 μm, while the out-of-plane extension of the TM mode increases from 25 to 50 nm. We propose two simple additivity rules for mode confinement valid in the ultrathin film approximation for heterostructures with increasing spacer thickness. Stacking additional WS2 monolayers into superlattices further enhances the waveguiding properties. Our results underscore the potential of monolayer-based superlattices as a platform for visible-range nanophotonics with promising optical, electrical, and magnetic tunability.

Femtosecond-laser-inscribed cladding waveguides in KTiOPO4 crystal for second-harmonic generation and Y-branch splitters

In this study, the fabrication of straight- and Y-branch-cladding waveguides in KTiOPO4 crystals using femtosecond laser-direct writing is described. The second-harmonic generation (SHG) of green light through the cladding waveguides was realized using a pulsed-wave pump at 1,064 nm. The guiding properties of straight-cladding waveguides fabricated by varying the laser-writing conditions were investigated. The minimum insertion loss was approximately 2.0 dB at 1,064 nm. Confocal micro-Raman spectroscopy was used to investigate the lattice micro-modifications. The maximum SHG conversion efficiency of the straight-cladding waveguide reached 31.4% with a maximum output power of 79.29 mW from an input power of 252.6 mW. The performances of the Y-branch splitters with splitting angles ranging from 0.5° to 2.6° were characterized at 1,064 nm, showing excellent properties, including symmetrical output ends and approximately equal splitting ratios. An SHG conversion efficiency of 13.4% and maximum output power of 33.63 mW were achieved in the Y-branch splitter with a splitting angle of 1.0°. These findings support potential applications in constructing compact-frequency converters by using femtosecond laser-written KTiOPO4 depressed-cladding waveguides.

Flexible organic crystal with dual mechanical bending capabilities and optical waveguiding directionality

The study of organic luminescent crystal material has become a hot topic in the field of flexible optoelectronics. In this context, we report a crystal of 2,5-dihydro-3,6-bis (pentanamine) dimethyl terephthalate, which exhibits the unique property of self-doping, coupled with dual mechanical bending capabilities. Notably, the crystal exhibits optical waveguide properties, which highlights its potential application in flexible optoelectronics. In this work, through a simple "self-doping” process and controlled morphology, we obtained the synthesis of high-quality bulk organic crystals of varied sizes that not only bend elastically but also bend plastically as the molecular layer undergoes slippage. Subsequent, analysis of the crystal structure was conducted to investigate the reason for its dual mechanical bending capabilities. Our findings suggested that the optical waveguide is not only available in linear shape, elastic bending shape, and plastic bending shape, but also in large-size flake crystals. More importantly, the propagation of light in this crystal is directional owing to the anisotropy of the crystals. It is also proven that organic crystals have the potential to be applied in advanced optoelectronic devices, offering the possibility of their application as directional waveguide materials.

A comparative investigation into the impact of Cd and Mg on the optoelectronic properties of ZnO thin films by spray pyrolysis for waveguide applications

This study examines the impact of Mg and Cd on ZnO waveguide properties using CdxZn1−xO and CdxZn1−xO thin films (x=0, 0.03, 0.05). X-ray diffraction confirms successful Mg incorporation in the ZnO wurtzite, while CdO segregates, increasing lattice parameters. UV–Vis measurements show opposing trends in band gap energy, increasing for Mg doping and decreasing for Cd doping. Photoluminescence data reveals varying defect characteristics consistent with band gap energy behavior. Through SEM, Mg increased grain size and slightly decreased the surface density. Cd-doped films exhibit no significant morphology change by AFM measurements. Hall measurements show both Cd and Mg doping increase resistivity tenfold. Cd causes a 94.5% decrease in mobility, whereas Mg leads to a substantial 2190 times increase. Charge carrier density decreases by 105 in Mg0.05Zn0.95O and increases threefold in Cd0.05Zn0.95O. M-lines measurements demonstrate birefringent behavior, positive for Mg doping and negative for Cd doping, and a decreasing refractive index.

Spatially Resolved Anion Diffusion and Tunable Waveguides in Bismuth Halide Perovskites.

Bismuth halide perovskites are widely regarded as nontoxic alternatives to lead halide perovskites for optoelectronics and solar energy harvesting applications. With a tailorable composition and intriguing optical properties, bismuth halide perovskites are also promising candidates for tunable photonic devices. However, robust control of the anion composition in bismuth halide perovskites remains elusive. Here, we established chemical vapor deposition and anion exchange protocols to synthesize bismuth halide perovskite nanoflakes with controlled dimensions and variable compositions. In particular, we demonstrated the gradient bromide distribution by controlling the anion exchange and diffusion processes, which is spatially resolved by time-of-flight secondary ion mass spectrometry. Moreover, the optical waveguiding properties of bismuth halide perovskites can be modulated by flake thicknesses and anion compositions. With a unique gradient anion distribution and controllable optical properties, bismuth halide perovskites provide new possibilities for applications in optoelectronic devices and integrated photonics.

Optoelectronic Material Characterization Platform using RF Topological Edge States

AbstractEfficient characterization of optoelectronic material properties represents a crucial step in the development of next‐generation infrared (IR) materials and devices. For the first time, a sensitive, contact‐free optoelectronic material characterization platform is demonstrated that exploits the unique properties of radio frequency (RF) topological edge states implemented in a topological microstrip waveguide. The topological device is compatible with standard printed circuit board (PCB) processes with no additional materials, stubs, or resonators. The waveguide and topological properties computationally are designed and then experimentally the results are validated with S‐parameter and near‐field measurements. Finally, as a proof of principle, the room temperature spectral response of a micron‐scale thick mid‐wave infrared (MWIR) mercury cadmium telluride (Hg0.70Cd0.30Te) is measured using the topological microstrip and a five‐fold and 20‐fold increase is demonstrated in response when compared to a plain microstrip and trivial bandgap device, respectively. These results open the door to straightforward, low‐cost characterization of optoelectronic films.

Unveiling the in-plane anisotropic dielectric waveguide modes in α-MoO3 flakes

Abstract The unique in-plane and out-of-plane anisotropy of α-MoO3 has attracted considerable interest for potential optoelectronic applications. However, most research has focused on the mid-infrared spectrum, leaving its properties and applications in the visible and near-infrared light spectrum less explored. This study advances the understanding of waveguiding properties of α-MoO3 by near-field imaging of the waveguide modes along the [100] and [001] directions of α-MoO3 flakes at 633 nm and 785 nm. We investigated the effects of flake thickness and documented the mode's dispersion relationship, which is crucial for tailoring α-MoO3's optical responses in device applications. Our findings enhance the research field of α-MoO3, highlighting its utility in fabricating next-generation optoelectronic devices for its unique optically anisotropic waveguide.

The impact of various factors on the surface of X-cut lithium niobate and properties of proton-exchanged waveguides

This work describes the effects of various impacts (thermal, plasma, chemical) on X-cut lithium niobate surface and on the structure and optical characteristics of proton-exchanged waveguides. Pre-annealing at 500 °C improved the structural homogeneity of congruent lithium niobate and thus enabled fabricating waveguides of a higher quality. Ar-plasma pretreatment damaged crystal surface and increased lattice deformations. Chemical treatment influenced the surface composition of lithium niobate and the refractive index in annealed proton exchange waveguides. The results provide better understanding of the role of crystal surface in the fabrication of diffusion waveguides and photonic integrated circuits.

Illegal food chemicals sensing with photonic crystal fiber sensor in the terahertz spectrum

The method by which a photonic crystal is manufactured fiber is detailed throughout the subsequent undertaking, containing a hexahedron core and hazardous dietary additives using a hexagonal cladding. Saccharine, sorbitol, and butyl acetate are used as analytes for sensing purposes. The sensor contains five tiers of circular ventilation holes within the hexagonal framework, as well as two tiers of hexahedron circles in the central area. FEM (Finite Element Method) is implemented in the sensor design of COMSOL software version 4.2. We noticed the response of the PCF sensor to the specific substances. We examined key optical metrics encompassing specifications including V-parameter, Relational sensitivity, effective refractive index, and power fraction to assess the suitability of the sensor for precisely and effectively detecting various food additives. The revised model attains sensitivity values of 90.10%, 91.30%, and 86.60%, respectively, at a frequency of 1 THz, the identification of saccharine (1.550 in the index of refraction), sorbitol (1.375 in the index of refraction), and butyl acetate (1.394 in the index of refraction) is performed. Furthermore, the compositions of saccharine (1.550 in the index of refraction), sorbitol (1.375 in the index of refraction), and butyl acetate (1.394 in the index of refraction) demonstrate losses from confinement of 6.15 × 10−8 dB/m, 7.25 × 10−8 dB/m, and 6.35 × 10−8 dB/m, which are comparatively minimal, and 0.0235 cm−1 is an insignificant effective material loss. These structures are studied at the terahertz frequency spectrum. Owing to its superior wave-guiding properties, this proposed sensor can be used for polarization-preserving terahertz wave applications and detecting dangerous food additives. Besides, because of simple fabrication, high sensitivity, and low confinement loss, we strongly believe this optimized geometrical structure will contribute to real-life applications that lead to safer food and support a circular economy in developing countries.

Minimum intensity projection of embossed quadrant-detection images for improved photoreceptor mosaic visualisation.

Non-confocal split-detection imaging reveals the cone photoreceptor inner segment mosaic in a plethora of retinal conditions, with the potential of providing insight to ageing, disease, and response to treatment processes, in vivo, and allows the screening of candidates for cell rescue therapies. This imaging modality complements confocal reflectance adaptive optics scanning light ophthalmoscopy, which relies on the waveguiding properties of cones, as well as their orientation toward the pupil. Split-detection contrast, however, is directional, with each cone inner segment appearing as opposite dark and bright semicircles, presenting a challenge for either manual or automated cell identification. Quadrant-detection imaging, an evolution of split detection, could be used to generate images without directional dependence. Here, we demonstrate how the embossed-filtered quadrant-detection images, originally proposed by Migacz etal. for visualising hyalocytes, can also be used to generate photoreceptor mosaic images with better and non-directional contrast for improved visualisation. As a surrogate of visualisation improvement between legacy split-detection images and the images resulting from the method described herein, we provide preliminary results of simple image processing routines that may enable the automated identification of generic image features, as opposed to complex algorithms developed specifically for photoreceptor identification, in pathological retinas.

Love waves propagation in layered viscoelastic waveguides characterized by a Zener model

This paper describes a theory of surface Love waves propagating in lossy waveguides consisting of a viscoelastic layer deposited on a semi-infinite elastic substrate. The Zener model to describe the viscoelastic behavior of a medium is used. This simple model captures both the relaxation and retardation. A new form of the unsteady momentum equation for viscoelastic waveguides has been established. By using appropriate boundary conditions, an analytical expression for the complex dispersion equation of Love waves has been deduced. The influence of the loss factor and the ratio of shear moduli of the surface layer on the dispersion curves of Love waves velocity and attenuation is analyzed numerically. The numerical solutions show the dependence of the velocity change and the wave attenuation in terms of the loss factor and the ratio of shear moduli. The obtained results show that the change in the ratio of shear moduli can represent a hardening or softening effect of the surface layer. These effects depend on the loss factor value of the surface layer. In addition, these results are novel, fundamental and can be applied in the characterization of the viscoelastic properties of soft biomaterials and tissues, in nondestructive testing of materials, in geophysics and seismology. Thus, the obtained complex dispersion equation can be very useful to interpret the experimental measurements of Love waves properties in viscoelastic waveguides.

Pyroelectric influence on lithium niobate during the thermal transition for cryogenic integrated photonics

Lithium niobate has emerged as a promising platform for integrated quantum optics, enabling efficient generation, manipulation, and detection of quantum states of light. However, integrating single-photon detectors requires cryogenic operating temperatures, since the best performing detectors are based on narrow superconducting wires. While previous studies have demonstrated the operation of quantum light sources and electro-optic modulators in LiNbO3 at cryogenic temperatures, the thermal transition between room temperature and cryogenic conditions introduces additional effects that can significantly influence device performance. In this paper, we investigate the generation of pyroelectric charges and their impact on the optical properties of lithium niobate waveguides when changing from room temperature to 25 K, and vice versa. We measure the generated pyroelectric charge flow and correlate this with fast changes in the birefringence acquired through the Sénarmont-method. Both electrical and optical influence of the pyroelectric effect occur predominantly at temperatures above 100 K.

Lattice Damage, Optical and Electrical Properties Induced by H and C Ions Implantation in Nd:YLF Crystals

Neodymium-doped yttrium fluoride crystal has emerged as one of the most valuable functional materials, and has thus become a research hotspot and shown promising application value in recent years. In this work, utilizing 460 keV H and 6.0 MeV C ions implantation, the damage behavior, lattice structure change, spectral, and electrical characteristics of the Nd:YLF crystal induced by electronic and nuclear energy loss were investigated, utilizing complementary characterization techniques (X-ray diffraction, hardness and elastic (Young’s) modulus, micro-Raman, absorption, fluorescence spectra, and I–V characteristic curve). Thus, the annealing effect on the waveguide properties and the surface damage of the samples was discussed. The fabricated waveguide structure shows potential application in highly sensitive optoelectronic sensors.

Near‐Field Nanoimaging of Colloidal Transition Metal Dichalcogenide Waveguides

AbstractBulk transition metal dichalcogenide (TMDC) nanostructures are regarded as promising material candidates for integrated photonics due to their high refractive index at the near‐infrared wavelengths. In this work, colloidal TMDC waveguides with tailorable dimensions are prepared by a scalable synthetic approach. The optical waveguiding properties of colloidal nanowires are studied by the near‐field nanoimaging technique. In addition to dependence on thickness and wavelength, the excitonic responses and resultant waveguide modes in TMDC nanowires can be modulated by the environmental temperature. With the high‐throughput production and tunable optical properties, colloidal TMDC nanowires highlight the potential for active optical components and integrated photonic devices.

Elastic Guanine-Based Single Crystals with Optical Waveguiding Properties: Toward Tailored Bioinspired Materials

Elastic Guanine-Based Single Crystals with Optical Waveguiding Properties: Toward Tailored Bioinspired Materials

Large transmittance contrast via 90-degree sharp bends in square lattice glide-symmetric photonic crystal waveguides.

We demonstrate an intriguing transmittance contrast in a glide-symmetric square-lattice photonic crystal waveguide with a 90-degree sharp bend. The glide-symmetry gives rise to a degeneracy point in the band structure and separates a high-frequency and a low-frequency band. Previously, a similar large transmittance contrast between these two bands has been observed in glide-symmetric triangular- or honeycomb-lattice photonic crystals without inversion symmetry, and this phenomenon has been attributed to the valley-photonic effect. In this study, we demonstrate the first example of this phenomenon in square-lattice photonic crystals, which do not possess the valley effect. Our result sheds new light onto unexplored properties of glide-symmetric waveguides. We show that this phenomenon is related to the spatial distribution of circular polarization singularities in glide-symmetric waveguides. This work expands the possible designs of low-loss photonic circuits and provides a new understanding of light transmission via sharp bends in photonic crystal waveguides.

Laser Glass deposition of single-mode glass fibers for the fabrication of chip-scale photonic circuits

The use of glass, particularly fused silica (FS), instead of polymers or semiconductors as optical waveguide material is advantageous due to broadband transmission, reduced propagation losses, and enhanced thermal and mechanical stability. In this contribution, laser glass deposition for the chip-scale fabrication of FS-based optical waveguides is investigated. We use a CO2 laser with emission at a wavelength of 10.6 µm to weld conventional single-mode glass fibers onto a FS substrate, with the aim of maintaining the waveguide properties of the fibers. Synchronized translational and rotational axis movements allow for positioning of the waveguides in arbitrary geometries. Furthermore, a CO2 laser-based cleaving method is introduced, which facilitates on-chip creation of waveguide end facets for optical coupling. An analysis of the cleave geometry in dependence on process parameters as well as optical coupling losses are presented. Coupling losses of 0.88 dB for a laser-cleave and propagation losses of 0.56 dB/cm for a 10 cm on-chip welded fiber were achieved. The results pave the way for on-chip integration of fiber-based systems like lasers, sensing devices or optical communication networks.