Heterogeneous Waveguides Research Articles

Polymer-Embedding Germanium Nanostrip Waveguide of High Polarization Extinction.

Germanium (Ge) nanostrip was embedded in a polymer and studied as a waveguide. The measurements reveal that this new type of semiconductor/polymer heterogeneous waveguide exhibits strong absorption for the TE mode from 1500 nm to 2004 nm, while the propagation loss for the TM mode declines from 20.56 dB/cm at 1500 nm to 4.89 dB/cm at 2004 nm. The transmission characteristics serve as an essential tool for verifying the optical parameters (n-κ, refractive index, and extinction coefficient) of the strip, addressing the ambiguity raised by spectroscopic ellipsometry regarding highly absorbing materials. Furthermore, the observed strong absorption for the TE mode at 2004 nm is well beyond the cut-off wavelength of the crystalline bulk Ge (~1850 nm at room temperature). This redshift is modeled to manifest the narrowing of the Tauc-fitted bandgap due to the grain order effect in the amorphous Ge layer. The accurate measurement of the nanometer-scale light-absorbing strips in a waveguide form is a crucial step toward the accurate design of integrated photonic devices that utilize such components.

Heterogeneous optomechanical crystal cavity coupled by a wavelength-scale mechanical waveguide

Integrated optomechanical crystal (OMC) cavities provide a vital device prototype for highly efficient microwave to optical conversion in quantum information processing. In this work, we propose a novel heterogeneous OMC cavity consisting of a thin-film lithium niobate (TFLN) slab and chalcogenide (ChG) photonic crystal nanobeam coupled by a wavelength-scale mechanical waveguide. The optomechanical coupling rate of the heterogeneous OMC cavity is optimized up to 340 kHz at 1.1197 GHz. Combined with phononic band and power decomposition, 17.38% energy from the loaded RF power is converted into dominant fundamental horizontal shear mode (SH0) in the narrow LN mechanical waveguide. Based on this fraction, as a result, 3.51% power relative to the loaded RF energy is scattered into the fundamental longitudinal mode (L0) facing the TFLN-ChG heterogeneous waveguide. The acoustic breathing mode of the heterogeneous OMC is successfully excited under the driving of the propagating L0 mode in the heterogeneous waveguide, demonstrating the great potentials of the heterogeneous piezo-optomechanical transducer in high-performance photon–phonon interaction fields.

Monolithic integration of polymer waveguide phase modulators with silicon nitride waveguides using adiabatic transition tapers.

Polymer waveguide phase modulators (PMs) demonstrate high thermal confinement with outstanding thermo-optic properties and can provide stable low-power phase modulation in optical phased arrays (OPA). On the other hand, silicon nitride (SiN) waveguides produce stronger optical confinement with smaller waveguide core sizes than polymer waveguides and can handle high optical power without nonlinear effects. In this work, a high-performance PM was achieved by monolithic integration of a polymer waveguide and tapered SiN input and output waveguides. The integration of heterogeneous waveguide materials on a single substrate will enable the fabrication of efficient OPAs for advanced imaging, display, sensing, and communications applications.

The Generalized Routh Equations in the Plate Theory of $$\boldsymbol{N}$$th Order and their Use in Problems of Normal Wave Dispersion in Heterogeneous Waveguides

The Generalized Routh Equations in the Plate Theory of $$\boldsymbol{N}$$th Order and their Use in Problems of Normal Wave Dispersion in Heterogeneous Waveguides

A Computationally Efficient Rayleigh–Ritz Model for Heterogeneous Oceanic Waveguides Using Fourier Series of Sound Speed Profile

The normal mode method is widely used in ocean acoustic propagation. Usually, finite difference and finite element methods are used in its solution. Recently, a method has been proposed for heterogeneous layered waveguides where the depth eigenproblem is solved using the classical Rayleigh–Ritz approximation. The method has high accuracy for low to high frequency problems. However, the matrices that appear in the eigenvalue problem for radial wavenumbers require numerical integration of the matrix elements since the sound speed and density profiles are numerically defined. In this paper, a technique is proposed to reduce the computational cost of the Rayleigh–Ritz method by expanding the sound speed profile in a Fourier series using nonlinear least square fit so that the integrals of the matrix elements can be computed in closed form. This technique is tested in a variety of problems and found to be sufficiently accurate in obtaining the radial wavenumbers as well as the transmission loss in a waveguide. The computational savings obtained by this approach is remarkable, the improvements being one or two orders of magnitude.

Enhancing Si3N4 Waveguide Nonlinearity with Heterogeneous Integration of Few-Layer WS2.

The heterogeneous integration of low-dimensional materials with photonic waveguides has spurred wide research interest. Here, we report on the experimental investigation and the numerical modeling of enhanced nonlinear pulse broadening in silicon nitride waveguides with the heterogeneous integration of few-layer WS2. After transferring a few-layer WS2 flake of ∼14.8 μm length, the pulse spectral broadening in a dispersion-engineered silicon nitride waveguide has been enhanced by ∼48.8% in bandwidth. Through numerical modeling, an effective nonlinear coefficient higher than 600 m–1 W-1 has been retrieved for the heterogeneous waveguide indicating an enhancement factor of larger than 300 with respect to the pristine waveguide at a wavelength of 800 nm. With further advances in two-dimensional material fabrication and integration techniques, on-chip heterostructures will offer another degree of freedom for waveguide engineering, enabling high-performance nonlinear optical devices, such as frequency combs and quantum light sources.

Use of the higher-order plate theory of I. N. Vekua type in problems of dynamics of heterogeneous plane waveguides

The dynamics of elastic plane waveguides is studied on the basis of the extended formulation of the plate theory of N th order. The plate model is based on the Lagrangian formalism of analytical dynamics combined with the dimensional reduction approach and the biorthogonal expansion of the spatial distribution of the displacement. The boundary conditions shifted from the faces onto the base plane are interpreted as constraints for the variational formulation of two-dimensional plate models. The normal wave dispersion in plates is modelled, the convergence of the approximate solutions is studied using the known exact solution for a plane layer as a reference. The proposed plate theory is used to analyse the normal wave dispersion in power graded waveguides of both symmetric and asymmetric structures, the locking phase frequencies for various power indices are computed.

Bound states in weakly deformed waveguides: numerical versus analytical results

We study bound states in weakly deformed and heterogeneous waveguides, and compare analytical predictions using a recently developed perturbative method with precise numerical results for three different configurations: a homogeneous asymmetric waveguide, a heterogenous asymmetric waveguide and a homogeneous broken strip. We have found excellent agreement between the analytical and numerical results in all the examples; this provides a numerical verification of the analytical approach. doi:10.1017/S1446181117000293

BOUND STATES IN WEAKLY DEFORMED WAVEGUIDES: NUMERICAL VERSUS ANALYTICAL RESULTS

We study bound states in weakly deformed and heterogeneous waveguides, and compare analytical predictions using a recently developed perturbative method with precise numerical results for three different configurations: a homogeneous asymmetric waveguide, a heterogenous asymmetric waveguide and a homogeneous broken strip. We have found excellent agreement between the analytical and numerical results in all the examples; this provides a numerical verification of the analytical approach.

Weakly Bound States in Heterogeneous Waveguides: A Calculation to Fourth Order

We have extended a previous calculation of the energy of a weakly heterogeneous waveguide to fourth order in the density perturbation, deriving its general expression. For particular configurations where the second and third orders both vanish, we discover that the fourth order contribution lowers in general the energy of the state, below the threshold of the continuum. In these cases the waveguide possesses a localized state. We have applied our general formula to a solvable model with vanishing second and third orders reproducing the exact expression for the fourth order.

Effect of Cu2+ Ion Irradiation on Microstructure of Er2O3 Coating Layer Formed by MOCVD Method

We have extended a previous calculation of the energy of a weakly heterogeneous waveguide to fourth order in the density perturbation, deriving its general expression. For particular configurations where the second and third orders both vanish, we discover that the fourth order contribution lowers in general the energy of the state, below the threshold of the continuum. In these cases the waveguide possesses a localized state. We have applied our general formula to a solvable model with vanishing second and third orders reproducing the exact expression for the fourth order.

Weakly bound states in heterogeneous waveguides

We study the spectrum of the Helmholtz equation in a two-dimensional infinite waveguide, containing a weak heterogeneity localized at an internal point, and obeying Dirichlet boundary conditions at its border. We prove that, when the heterogeneity corresponds to a locally denser material, the lowest eigenvalue of the spectrum falls below the continuum threshold and a bound state appears, localized at the heterogeneity. We devise a rigorous perturbation scheme and derive the exact expression for the energy to third order in the heterogeneity.

Hybrid Photonic Integration on a Polymer Platform

To fulfill the functionality demands from the fast developing optical networks, a hybrid integration approach allows for combining the advantages of various material platforms. We have established a polymer-based hybrid integration platform (polyboard), which provides flexible optical input/ouptut interfaces (I/Os) that allow robust coupling of indium phosphide (InP)-based active components, passive insertion of thin-film-based optical elements, and on-chip attachment of optical fibers. This work reviews the recent progress of our polyboard platform. On the fundamental level, multi-core waveguides and polymer/silicon nitride heterogeneous waveguides have been fabricated, broadening device design possibilities and enabling 3D photonic integration. Furthermore, 40-channel optical line terminals and compact, bi-directional optical network units have been developed as highly functional, low-cost devices for the wavelength division multiplexed passive optical network. On a larger scale, thermo-optic elements, thin-film elements and an InP gain chip have been integrated on the polyboard to realize a colorless, dual-polarization optical 90° hybrid as the frontend of a coherent receiver. For high-end applications, a wavelength tunable 100Gbaud transmitter module has been demonstrated, manifesting the joint contribution from the polyboard technology, high speed polymer electro-optic modulator, InP driver electronics and ceramic electronic interconnects.

Widely tunable grating-assisted heterogeneous silicon nitride/polymer waveguide coupler

A grating-assisted heterogeneous waveguide coupler is designed, fabricated, and demonstrated on a polymer platform. The parallel silicon nitrite core and polymer core are horizontally placed with vertical center alignment accuracy of ±5 nm. The coupler is differentially thermally tunable. The temperature gradient distribution, introduced by offset micro-heaters, is studied by thermal simulations. A total tuning range of 82 nm is demonstrated experimentally.

Manipulation of Light Flows in Organic Color‐Graded Microstructures towards Integrated Photonic Heterojunction Devices

Organic color-graded optical waveguides permit low-power photonic analogies of diode/transistors based on the energy-transferred conversion of exciton species. The donor-acceptor junction can asymmetrically output blue/red colors due to the mono-directional energy transfer during light propagation. The switching function of transistors is achieved with an additional gate input by altering the ground state density of acceptors. These organic heterogeneous waveguides are further cascaded together to steer the guided light flows for potential applications in photonic integrations.

Optical Crossing and Integration Using Hybrid Si-Wire/Silica Waveguides

We studied the feasibility of an integrated optical circuit consisting of Si-wire waveguides and silica-based waveguides. In order to realize such a hybrid waveguide optical circuit, we investigated a waveguide junction structure based on adiabatic mode conversion with tapered Si and a waveguide crossing structure of heterogeneous waveguides by numerical analysis and measurements. We estimated the optical coupling loss between the waveguides to be 0.39 dB from the measurements. We also estimated the insertion loss of the waveguide crossing to be less than 0.7 dB, and the crosstalk between the waveguides to be less than -35 dB by numerical analysis.

Optical Crossing and Integration Using Hybrid Si-Wire/Silica Waveguides

We studied the feasibility of an integrated optical circuit consisting of Si-wire waveguides and silica-based waveguides. In order to realize such a hybrid waveguide optical circuit, we investigated a waveguide junction structure based on adiabatic mode conversion with tapered Si and a waveguide crossing structure of heterogeneous waveguides by numerical analysis and measurements. We estimated the optical coupling loss between the waveguides to be 0.39 dB from the measurements. We also estimated the insertion loss of the waveguide crossing to be less than 0.7 dB, and the crosstalk between the waveguides to be less than -35 dB by numerical analysis.

Slow Light Propagation in Liquid-Crystal Infiltrated Silicon-On-Insulator Photonic Crystal Channel Waveguides

An SOI-based liquid-crystal (LC)-infiltrated photonic-crystal channel waveguide having rectangular air holes in a Silicon core is proposed-and has an average group index of 43 over a bandwidth of 1.02 THz, with vanishing group velocity dispersion, as well as reduced higher-order dispersion. The possible propagation losses due to coupling inefficiency are also investigated for the proposed structure. It is found that high transmission is obtained for a broad bandwidth from the output of the heterogeneous waveguide finally designed, which consists of an LC-infiltrated PhC slow waveguide surrounded by fast PhC regions on either side. The LC-infiltrated W0.7 PhC waveguide that has been designed for slow light propagation should be highly tolerant to fabrication errors-and has enhanced sensitivity in comparison with conventional PhC waveguides.

Optical properties of new wide heterogeneous waveguides with thermo optical shifters

We present analysis and simulation of novel silicon-on-insulator (SOI) heterogeneous waveguides with thermo-optic phase shifters. New structure design contains a p-n junction on both sides of SOI ridge waveguide with 220 nm x 35 microm silicon core. Strongly mode-dependent optical losses (by additional free charge absorption) provide quasi-singe-mode behavior of wide waveguide with mode size approximately 10 microm. Local heater produces an efficient phase shifting by small temperature increase (DeltaT approximately 2K), switching power (< 40 mW) and switching time (< 10 micros). Mode optical losses are significantly decreased at high heating (DeltaT approximately 120 K).

2.5D SH Wave Propagation in Heterogeneous Crustal Wave Guides Using the Phase Screen Method

Abstract One-way approximations for regional phases slice the half-space crustal wave guide into a number of slabs perpendicular to the propagation direction; the Moho discontinuity can be easily treated as a perturbation from the crustal background. The advantage of one-way propagation methods is their great saving of computing time and memory compared to full-waveform numerical methods, especially for 3D simulations. In this article, we present general 2.5D SH formulas for the thin-slab method and a generalized screen propagator (GSP) for simulating SH wave propagation in the heterogeneous half-space crustal wave guide. Comparisons of numerical results with a finite-difference (FD) algorithm for a standard flat crustal model show excellent agreement, demonstrating the validity and accuracy of the 2.5DGSP for the half-space problem. We then compare the curves of energy attenuation calculated by the 2D and 2.5D formulas. The comparison shows that the energy attenuation of the 2.5D case is about 1.5–3 times greater than that of the 2D case when the trapped mode is formed. The SH screen propagator is also used to simulate two laterally unvarying (in the y direction) crustal models, showing the path effects on regional wave propagation.