Three-layer Waveguide Research Articles

Models of symmetric three-layer waveguide structures with graded-index core and nonlinear optical liners

Models of symmetric three-layer waveguide structures with graded-index core and nonlinear optical liners

Transverse electric waves in three-layered waveguide structure with a parabolic spatial profile of the dielectric constant, optical linear and nonlinear layers

A three-layered waveguide structure containing the Kerr nonlinear medium separated by an optical linear interlayer from a parabolic graded-index layer is considered. Exact solutions of the wave equation corresponding to several types of transverse electric waves existing in different ranges of values of the effective refractive index are found. The types of waves differ from each other by the presence or absence of oscillations in the interlayer and in the graded-index layer, as well as the form of attenuation in a nonlinear medium. The wave types obtained can be divided into two main groups. The first group includes such waves that can propagate with an arbitrarily varying effective refractive index in the allowable range of values. The second one includes such waves that can propagate at certain discrete values of the effective refractive index. Such values of the effective refractive index of waveguide modes are determined by the wavelength of the incident ray, difference between the dielectric constants of a parabolic graded-index layer, and its width. Even and odd waveguide modes are described separately. Field oscillations can be observed only in the interlayer for waves of the first group. Field oscillations can also be observed in the graded-index layer for waves of the second group. The field profile is a self-focusing nonlinear medium flatter than in a defocusing one for all types of waves. An increase in the same parameters has a different effect on the profiles of the different types of waves. The possibility of controlling the distribution of the wave energy between the layers of the waveguide structure by changing the angle of incidence is shown.

Synthesis and characterization of fluorinated polyimide doped with NaYF4 nanocrystals for optical waveguide applications

Fluorinated polyimide materials were selected for their exceptional flexibility, high thermal stability, and minimal absorption loss. These materials were subsequently employed in the production of single-mode polymer optical waveguide devices using photolithography. In this study, a fluorinated polyimide material doped with NaYF4 nanocrystals was prepared and confirmed to exhibit low absorption loss near 1550 nm, which is within the common communication window. The refractive index of the fluorinated polyimide films was precisely adjusted by the NaYF4 doping, the adjustable ranges for the refractive index were 1.95% and 1.72% for doped and undoped, respectively. Secondly, utilizing the NaYF4 nanocrystals doped-fluorinated polyimide materials, a three-layer single-mode polymer optical waveguide device for C-band (near 1550 nm) optical interconnection was fabricated by etching the underlying cladding and employing silicon nitride as a mask. The transmission performance of the device was excellent, with a total waveguide coupling and transmission loss of 1.502 dBm.

Low-loss 3-dimensional waveguide crossing with a parabolic taper interlayer coupler based on a SiN-SiN-Si three-layer platform.

We demonstrated a SiN-SiN-Si three-layer silicon waveguide crossing with low-loss crossings and interlayer couplers. The underpass and overpass crossings exhibited ultralow loss (<0.82/1.16 mdB) and cross talk (<-56/-48 dB) in the wavelength range of 1260-1340 nm. To reduce the loss and length of the interlayer coupler, a parabolic interlayer coupling structure was adopted. The measured interlayer coupling loss was less than 0.11 dB from 1260 to 1340 nm, which is, to the best of our knowledge, the lowest loss reported for an interlayer coupler based on a SiN-SiN-Si three-layer platform. The total interlayer coupler length was only 120 µm.

SYMBOLIC-NUMERICAL IMPLEMENTATION OF THE GALERKIN METHOD FOR APPROXIMATE SOLUTION OF THE WAVEGUIDE DIFFRACTION PROBLEM

In this paper, we construct a symbolic-numerical implementation of the Galerkin method for approximate solution of the waveguide diffraction problem at the junction of two open planar three-layer waveguides. The Gelerkin method is implemented in the Maple computer algebra system by symbolic manipulations; its software implementation is based on the scprod symbolic-numerical procedure, which enables the numerical calculation of scalar products for the Galerkin method based on symbolic expressions. The use of symbolic manipulations makes it possible to speed up the calculation of integrals in the Galerkin method owing to single-run symbolic calculation of integrals typical for the problem, rather than multiple numerical integration.

Theoretical analysis of mode evolution in a tapered double clad fiber based on the coupled local mode theory

Mode characteristics of a tapered double clad fiber should be analyzed based on three-layer waveguide model, so it is more complicated than that of a single clad fiber. In this paper, a method based on coupled local mode theory is introduced to calculate the mode evolution process in a tapered double clad fiber. Mode field characteristics of double clad fiber are calculated analytically with weak guidance approximation, and the expression of mode coupling coefficient is derived. Based on this, the local mode characteristics and mode coupling characteristics in a tapered double clad fiber are analyzed. The mode evolution characteristics of tapered double clad fibers with different parameters are simulated. As an example, the structure optimization process of a tapered double clad fiber is introduced. High efficiency coupling with a six-mode single clad fiber is realized, and the theoretical transmission loss is less than 0.3 dB.

Optical propagation of exciton polaritons in ultrathin van der Waals microcrystals down to few monolayers

The exciton polariton is a kind of quasiparticles and provides a promising opportunity to explore fundamental quantum phenomena for photonic applications. Transition-metal dichalcogenide (TMD) materials provide the platform of nanophotonics that supports the propagative exciton polaritons even at room-temperature. Previously, real space studies on thin flakes of TMDs by scattering-type scanning nearfield optical microscopy (s-SNOM) were limited to waveguide thickness down to 30 nm. In this work, we present the nano-optical imaging of ordinary transverse electric modes of exciton polaritons in MoS2 and WSe2 down to a few atomic layers, measured by atomic force microscope-based s-SNOM. Surprisingly, the interference fringe patterns can be observed clearly at the prepared ultrathin TMD flakes with thickness down to ~3 nm (4 ML) and ~8 nm (12 ML) for MoS2 and WSe2, respectively, which breaks greatly the previous measurement limitation. The wavevectors stay around 1.6k0−1.7k0 constantly when the thickness approaching to a few MLs, instead of 1k0 according to the theory. These modes are supported by the nearly-freestanding TMD microflakes in the form of three-layer symmetric waveguide to confine the exciton polaritons. Our results provide in-depth understanding and open new avenues to explore the polaritonic devices operating at the near infrared region based on ultrathin TMD materials.

Adiabatic guided modes of a three-layer integral optical waveguide

The numerical solution of the problem of guided propagation of polarized light in a smooth junction of a planar waveguide is considered. Within the framework of the model of adiabatic guided modes, the system of Maxwell equations is reduced to a system of four ordinary differential equations and two algebraic equations for six components of the electromagnetic field in the zeroth approximation and the same number of equations in the first approximation. The multilayer structure of waveguides makes it possible to reduce the problem to a homogeneous system of linear algebraic equations, whose nontrivial solvability condition yields the dispersion equation. Auxiliary eigenvalue problems for describing the adiabatic modes of the waveguide are solved. Keywords: smoothly irregular integrated-optical multilayer waveguides, eigenvalue and eigenvector problems, single-mode propagation of adiabatic waveguide modes.

Optical Field Transmission Analysis of an All-Fiber Signal Combiner With a Dumbbell Shape

In this paper, the optical field transmission characteristics of an all-fiber signal combiner with a dumbbell shape and its application in laser beam combining are analyzed theoretically. Based on the three-layer waveguide model, the mode characteristics of a tapered multi-core fiber and a tapered single core fiber are analyzed respectively. On this basis, the working principle of an all-fiber signal combiner with a dumbbell shape is introduced from the perspective of mode evolution. The finite-difference beam propagation method is used to numerically analyze optical field envolution process in the combiner. Influences of the waist diameter, taper length and geometric arrangement are analyzed in detail. The calculation results show that an all-fiber signal combiner with a dumbbell shape can realize high brightness laser beam combining and the beam quality can reach the theoretical limit.

Radiation forces on a Mie particle in the evanescent field of a resonance waveguide structure.

Evanescent waves of a guided mode carry both momentum and energy, which enables them to move small objects located on a waveguide surface. This optical force can be used for optical near-field manipulation, arrangement, and acceleration of particles. In this paper, using arbitrary beam theory, the optical force on a dielectric particle in the evanescent wave of a resonance waveguiding structure is investigated. Using Maxwell's equations and applying the boundary conditions, all the field components and a generalized dispersion relation are obtained. An expression for the evanescent field is derived in terms of the spherical wave functions. Cartesian components of the radiation force are analytically formulated and numerically evaluated by ignoring the multiple scattering that occurs between the sphere and plane surface of the structure. Our numerical data show that both the horizontal and vertical force components and the forward particle velocity are enhanced significantly in the proposed resonance structure compared to those reported for three-layer conventional waveguides. Exerting stronger force on macro- and nanoparticles can be very useful to perform advanced experiments in solutions with high viscosity and experiments on biological cells. In addition, this resonance planar structure can be mounted on an inverted optical microscope stage for imaging the motion of nanoparticles especially when the particle collides and interacts with objects.

Cladding mode characteristics simulation of an excessively tilted fiber grating coated with gold nanoshells.

The cladding mode characteristics simulation of an excessively tilted fiber grating (ExTFG) coated with gold nanoshells was conducted in this study. First, the effective refractive indices of the core and cladding mode before coating were obtained by solving the eigenvalue equation of the three-layer waveguide structure, and the coupling characteristics were briefly analyzed. Then HE1,m and EH1,m modes were selected as the research objects, and the spectral characteristics of ExTFG coated with gold nanoshells were simulated by the finite element method. The simulated refractive index sensitivity of HE1,29 and EH1,29 modes is 160.16 and 185.03 nm/RIU, respectively. Compared with the non-localized surface plasmon resonance (LSPR) effect, it increased by 10.76 nm/RIU (7.2%) and 19.53 nm/RIU (11.8%), respectively. Thus, the LSPR effect was verified to be beneficial to improve the refractive index sensitivity of ExTFG.

Dispersion properties of a slab waveguide with a graded-index core layer and a nonlinear cladding using the WKB approximation method

Graded-index waveguides deserve investigation because they are more practical than those of step-index profiles. In this communication, a three-layer slab waveguide in which the core film has an exponentially graded refractive index is assumed. In this case, the film and substrate layers merge smoothly to form one layer of refractive index n ( x ) which is equal to n f at the cladding–film boundary and n s deep in the substrate layer. The cladding layer is made of a Kerr-type nonlinear material. An exact solution to such a waveguide structure is not possible. Approximation techniques are usually used in these cases. We employ the WKB approximation method to find an approximate dispersion relation of the proposed waveguide in terms of the asymmetry parameters a , b , and V . The universal dispersion curves are studied in detail. A number of interesting features are observed, such as the lack of a cutoff thickness related to the symmetric waveguide structure of a = 0 . The b -values are all less than one, which corresponds to guided modes.

Fast light propagating waveguide composed of heterogeneous metamaterials

A symmetrical three-layer fast light waveguide based on photonic crystal heterostructure is proposed in this article. Two types of photonic crystal where their effective optical parameters such as permittivity and permeability are variable from negative to positive at vicinity of the “Dirac-like” point frequency, are designed. Then the symmetrical three-layer light waveguide composed of these two different photonic crystals (heterogeneous structure at the junction between the cladding and the core) are constructed. By analyzing the anomalous dispersion mode of this waveguide, numerically calculated the group velocity to be negative. The light propagation effect of the waveguide is simulated, and it shows that the waveguide can confine light to the core layer well. In addition, observing the backward moving behavior of the wave packet by incident modulated gaussian pulses envelope, further verifying the generation of fast light. These numerical simulation results agree well the analytical analysis. The proposed waveguide structures in this article may improve the sensitivity of optical instruments and offer potential applications in the fields of integrated photonic circuits, on-chip optical interconnect, and fast optical communication and transmission.

Modes Characteristics in Slab Waveguide with Noble Metal Interfaces

In this paper, a three-layer chip waveguide with ordinary materials was analyzed with the introducing of metal interfaces among the layers, where three types of metals were used: Au, Ag and Cu. The problem has been analyzed theoretically by deriving the characteristic equations as well as solving them numerically in the COMSOL environment. The results showed that the two methods are identical in the absence of metal, but the presence of metal will cause differences between the two methods that decrease for modes with lower orders, and the use of a small thickness of metal will increase the difference between the two methods. Field distributions vary with normalized frequency, metallic interface thickness, and little change with metal type.

Slab dielectric waveguide with randomly fluctuating refractive indices

The three-layer slab dielectric waveguide is perhaps the most basic structure for designing optical and electronic devices. Deterministic results, assuming constant refractive indices, on the propagation of an electromagnetic wave within this structure are well known and they are reported in papers and textbooks, however to the best of the authors knowledge, there are no works reported in the literature on the stochastic propagation. In order to describe the stochastic propagation, we propose a model in which the refractive indices are variables fluctuating randomly. Our main objective is to show the student the significant difference between the deterministic and stochastic response of the system, when constant or random refractive indices are considered. In particular the dispersion curves, the distribution of the fields and the energy flow are presented and discussed. Our results show that the asymmetry factor associated with the dispersion curves can be easily modified by means of the magnitude of the induced fluctuation. Another interesting property shows that both TE0 and TM0 fundamental modes propagate only for small fluctuations. In the core of the guide, the amplitude of the electric and magnetic fields exhibits damped oscillations due to the randomness of the system. The energy flow is high in the substrate region, but it is vanishing in the cladding region. We conclude that those deterministic results are a particular case of our stochastic results.

Design methodology of a surface plasmon resonance-based affinity biosensor using instantaneous Poynting vector analysis

We deduce mathematical equations for instantaneous optical power density (instantaneous Poynting vector) of three-layer lossy optical waveguide consisting of metal-dielectric interfaces. We propose new equations which can be exploited to compute the thicknesses and refractive indices of various optical layers engaged in the evanescently coupled optical and nano-photonic devices. We then propose the design of a plasmonic sensor to be used in the detection of biological entities such as the concentration of a specific bacteria E. coli. We then use the new equations to determine the best value of the thickness of the dielectric layer to be used as the affinity layer for immobilizing the specific bacteria population on the surface of the sensor, which in our sensor design is taken to be silica, and examine its performance. Thereafter we discuss how to apply our derived equations to determine the best thickness of a thin dielectric layer (having high value of its refractive index) that can be added into any traditional SPR-based sensor to improve its sensitivity and other parameters. The calculated best values of the thickness of the dielectric is seen to be highly correlated with previously published experimental data by other researchers.

Radiation Characteristics of Cranial Leaky Lamb Waves.

We numerically and experimentally investigate the dispersion properties of leaky Lamb waves in the cranial bone. Cranial Lamb waves leak energy from the skull into the brain when propagating at speeds higher than the speed of sound in the surrounding fluid. The understanding of their radiation mechanism is significantly complicated by the geometric and mechanical characteristics of the cortical tables and the trabecular bone (diploë). Toward such understanding, we here analyze the sub-1.0 MHz radiation angle dispersion spectrum of porous bone phantoms and parietal bone geometries obtained from μ CT scans. Our numerical results show that, when diploic pores are physically modeled, leakage angles computed from time transient finite-element analyses correspond to those predicted by an equivalent three-layered fluid-loaded waveguide model. For the bone geometries analyzed, two main leaky branches are observed in the near-field dispersion spectrum: a fast wave radiated at small angles, which is related to the fastest fundamental Lamb mode supported by the cranial bone, and a slower wave radiated at larger angles. This observation is also confirmed by experimental tests carried out on an immersed parietal bone.

A novel application of ultrasonic Lamb waves: studying adhesive effects on the inspection of coating debonding in a three-layer waveguide

ABSTRACT In this research, a thorough experimental and numerical study is conducted to investigate a novel application of the ultrasonic Lamb waves which is its capability to detect the coating disbond in a double-layer waveguide (aluminium-adhesive) and a triple-layer waveguide (aluminium-adhesive-coating). The experimental tests are set up and implemented to evaluate how the attenuation of Lamb waves is affected by the adhesive bonding beside the contribution of the coating layer to the behaviour of Lamb waves. In the presence of additive white Gaussian noise (AWGN), a range of important indices including energy index (EI), amplitude index (AI), pulse width index (PWI), and the time of flight index (ToFI) are worked out in association with the disbond length. It is inferred that a) even in the very noisy environment of 0 dB SNR, the Lamb waves are effectively able to identify debonding defects particularly using the EI, giving sensitivity rates 105% and 30% for triple-layer and double-layer, respectively; b) the contribution of adhesive to the absorption of the guided wave energy is 30%, 40%, and 50% in EI, AI, and PWI, respectively, corroborating the value of the features to distinguish the debonding between each layer of bonded structures.

Dispersion properties of slab waveguides with a linear graded-index film and a nonlinear substrate

Three-layer slab waveguide with a graded-index film and a nonlinear substrate is investigated. The nonlinear substrate is considered of Kerr-type and the film index is assumed to change linearly as we move from the film-clad to the film-substrate interfaces. The solutions of the fields in the guiding film contains Airy functions which can be written as Bessel functions of order 1/3. The dispersion relation is derived in terms of three well-known normalized parameters V, a and b and the dispersion properties are plotted and studied. Many interesting features are obtained such as the nonexistence of cut-off thickness due to the nonlinear substrate and the value of the normalized guide index does not exceed unity which means they correspond to guided modes.

Double Electromagnetically Induced Transparency and Its Slow Light Application Based On a Guided-Mode Resonance Grating Cascade Structure.

In recent years, the achievement of the electromagnetically induced transparency (EIT) effect based on the guided-mode resonance (GMR) effect has attracted extensive attention. However, few works have achieved a double EIT-like effect using this method. In this paper, we numerically achieve a double EIT-like effect in a GMR system with a three-layer silicon nitride waveguide grating structure (WGS), using the multi-level atomic system model for theoretical explanation. In terms of slow light performance, the corresponding two delay times reach 22.59 ps and 8.43 ps, respectively. We also investigate the influence of wavelength detuning of different GMR modes on the transparent window and slow light performance. Furthermore, a wide-band flat-top transparent window was also achieved by appropriately adjusting the wavelength detuning between GMR modes. These results indicate that the EIT-like effect in the WGS has potential application prospects in low-loss slow optical devices, optical sensing, and optical communications.