Two-dimensional Optical Waveguide Research Articles

Integrating Full-Color 2D Optical Waveguide and Heterojunction Engineering in Halide Microsheets for Multichannel Photonic Logical Gates.

Ensuring information security has emerged as a paramount concern in contemporary human society. Substantial advancements in this regard can be achieved by leveraging photonic signals as the primary information carriers, utilizing photonic logical gates capable of wavelength tunability across various time and spatial domains. However, the challenge remains in the rational design of materials possessing space-time-color multiple-resolution capabilities. In this work, a facile approach is proposed for crafting metal-organic halides (MOHs) that offer space-time-color resolution. These MOHs integrate time-resolved room temperature phosphorescence and color-resolved excitation wavelength dependencies with both space-resolved ex situ optical waveguides and in situ heterojunctions. Capitalizing on these multifaceted properties, MOHs-based two-dimensional (2D) optical waveguides and heterojunctions exhibit the ability to tune full-color emissions across the spectra from blue to red, operating within different spatial and temporal scales. Therefore, this work introduces an effective methodology for engineering space-time-color resolved MOH microstructures, holding significant promise for the development of high-density photonic logical devices.

Two-Dimensional Optical Waveguides at Telecom Wavelengths Based on Organic Single-Crystal Microsheets of a Charge Transfer Complex.

Organic charge transfer (CT) cocrystals open a new door for the exploitation of low-dimensional near-infrared (NIR) emitters by a convenient self-assembly approach. However, research about the fabrication of sheet-like NIR-emitting microstructures that are significant for structural construction and integrated application is limited by the unidirectional molecular packing mode. Herein, via regulation of the biaxial intermolecular CT interaction, single-crystalline microsheets with remarkable NIR emission from 720 to 960 nm were synthesized via the solution self-assembly process of dithieno[3,2-b:2',3'-d]thiophene and 7,7,8,8-tetracyanoquinodimethane. The expected sheet-like structure is conducive to achieving a two-dimensional (2D) optical waveguide with an ultralow optical loss rate of 0.250 dB/μm at 860 nm. More significantly, these as-prepared organic microsheets with tunable thicknesses (h) from 100 to 1100 nm exhibit thickness-dependent NIR optical transportation performance. These findings could pave the way to a new class of low-dimensional NIR emitters for 2D photonics at telecom wavelengths.

A collocation-based spectral element method for computing nonlinear optical waveguide

Computation of nonlinear optical waveguide needs to solve nonlinear eigenvalue/ eigenfunction problem mathematically. However, usually the refractive index profiles in the nonlinear optical waveguide are discontinuous, which makes solution of nonlinear eigenvalue/eigenfunction problem not smooth enough. In this work, we mainly discuss how to use high-order collocation-based spectral element method (SEM) to discretize such problem and propose an iterative algorithm for computing nonlinear optical waveguide with discontinuous refractive index profiles. Starting from the linear eigenvalue/eigenfunction problem, we adopt SEM to discretize it and solve the resulting discretized system with Matlab eigen solver; for the nonlinear problem, we first change the nonlinear problem into corresponding linear problems, and then solve the linear problems by usage of the iterative method. The proposed method has advantage of high-order accuracy and lower-order cost. The accuracy and efficiency of the method are tested by several one-dimensional and two-dimensional linear optical waveguide structures. Numerical results for some nonlinear optical waveguide are also presented.

Directed self-assembly of organic crystals into chip-like heterostructures for signal processing

Organic single crystals show broad application prospects in the field of optical confinement and waveguides due to their low optical transmission loss and tunable optical properties. Individual one- or two-dimensional (1D or 2D) optical waveguide crystals have the limitations of a single function in organic photonics. In this work, a chip-like organic heterostructure was fabricated using an elaborately designed, sequential growth method. By regulating the concentration of each organic component, the processes of solution self-assembly, etching, and epitaxial self-assembly are successively performed to complete the directional growth of organic micro/nanostructures. Notably, the as-prepared chip-like organic heterostructure is composed of 1D/2D optical waveguide crystals, which can realize multidimensional photon transportation and multi-terminal directional optical signal output. Furthermore, the unique 2D optical waveguide properties of the chip-like heterostructures offer opportunities for constructing the encoding form of the output optical signal at the micro/nanoscale.

Volume Integral Equations Combined with Orthogonality of Modes for Analysis of Two-Dimensional Optical Slab Waveguide

Volume Integral Equations Combined with Orthogonality of Modes for Analysis of Two-Dimensional Optical Slab Waveguide

Bound states in the continuum in asymmetrical quantum-mechanical and electromagnetic waveguides

We study transport properties and the formation of bound states in the continuum (BIC) in asymmetric quantum mechanical and electromagnetic waveguides. An analytical model for an arbitrary asymmetric two-terminal quantum mechanical waveguide is proposed, and conditions of BIC formation are formulated. We show that the Friedrich-Wintgen mechanism of BIC formation in a system coupled to two continua takes place regardless of the symmetry of the system as long as the proportionate coupling condition is fulfilled. This result is illustrated by numerical simulation of two-dimensional quantum billiard and optical waveguide with a cavity. Due to the universal wave nature of BIC, the proposed BIC formation mechanism allows one to obtain BICs in the broader class of quantum mechanical, electromagnetic, acoustic, and other types of structures.

Boundary Integral Equations Combined with Orthogonality of Modes for Analysis of Two-Dimensional Optical Slab Waveguide: Single Mode Waveguide

Boundary Integral Equations Combined with Orthogonality of Modes for Analysis of Two-Dimensional Optical Slab Waveguide: Single Mode Waveguide

Ultracompact low-pass modal filters based on shortcuts to adiabaticity

A versatile approach to the design of photonic ultracompact low-pass modal filters is proposed. The idea stems from the shortcut to adiabaticity protocol, originally developed for quantum-mechanical systems and recently introduced in full-wave optics. This method allows one to achieve efficient rejection of higher order modes in a broad wavelength range for any two-dimensional multimode optical waveguide in an ultracompact configuration of the filter. A study case, corroborated by finite-element method numerical simulations, is reported for slab waveguides.

Sharp bend in two-dimensional optical waveguide based on gradient refractive index structure.

In this work, we propose the design of a sharp bend in a two-dimensional optical waveguide which has super-ellipse curve boundaries and a gradient refractive index structure in its core. Numerical simulations are presented to show the efficient light propagation in the waveguide bend, as well as the efficient light coupling between the proposed waveguide bend and a straight waveguide, for TE0 and TM0 modes. The proposed design strategy is also useful for designing other compact optical and photonic components.

Rational Design of Charge-Transfer Interactions in Halogen-Bonded Co-crystals toward Versatile Solid-State Optoelectronics.

Charge-transfer (CT) interactions between donor (D) and acceptor (A) groups, as well as CT exciton dynamics, play important roles in optoelectronic devices, such as organic solar cells, photodetectors, and light-emitting sources, which are not yet well understood. In this contribution, the self-assembly behavior, molecular stacking structure, CT interactions, density functional theory (DFT) calculations, and corresponding physicochemical properties of two similar halogen-bonded co-crystals are comprehensively investigated and compared, to construct an "assembly-structure-CT-property" relationship. Bpe-IFB wire-like crystals (where Bpe = 1,2-bis(4-pyridyl)ethylene and IFB = 1,3,5-trifluoro-2,4,6-triiodobenzene), packed in a segregated stacking form with CT ground and excited states, are measured to be quasi-one-dimensional (1D) semiconductors and show strong violet-blue photoluminescence (PL) from the lowest CT1 excitons (ΦPL = 26.1%), which can be confined and propagate oppositely along the 1D axial direction. In comparison, Bpe-F4DIB block-like crystals (F4DIB = 1,4-diiodotetrafluorobenzene), packed in a mixed stacking form without CT interactions, are determined to be insulators and exhibit unique white light emission and two-dimensional optical waveguide property. Surprisingly, it seems that the intrinsic spectroscopic states of Bpe and F4DIB do not change after co-crystallization, which is also confirmed by theoretical calculations, thus offering a new design principle for white light emitting materials. More importantly, we show that the CT interactions in co-crystals are related to their molecular packing and can be triggered or suppressed by crystal engineering, which eventually leads to distinct optoelectronic properties. These results help us to rationally control the CT interactions in organic D-A systems by tuning the molecular stacking, toward the development of a fantastic "optoelectronic world".

Asymmetric wave propagation in planar chiral fibers

We demonstrate the realization of a two-dimensional chiral optical waveguide with an infinite translational symmetry that exhibits asymmetric wave propagation. The low-symmetry geometry of the cross-section that lacks any rotational and mirror symmetries shows in-principal directional asymmetric polarization rotation. We use general symmetry arguments to provide qualitative analysis of the waveguide's eigenstates and numerically corroborate this using finite element simulation. We show that despite the only perturbative break of time-reversal symmetry via small modal losses, the structure supports a non-degenerate pair of co-rotating elliptical modes. We fabricated meters long fiber with a spiral structure and studied its optical properties.

Anderson cross-localization

We report Anderson localization in two-dimensional optical waveguide arrays with disorder in waveguide separation introduced along one axis of the array, in an uncorrelated fashion for each waveguide row. We show that the anisotropic nature of such disorder induces a strong localization along both array axes. The degree of localization in the cross-axis remains weaker than that in the direction in which disorder is introduced. This effect is illustrated both theoretically and experimentally.

Study on Omnidirectional Reflection Bands of Two-Dimensional Photonic Crystals and Optical Waveguides Based on This Effect

The omnidirectional reflection bands of several typical 2-D photonic crystals are presented. Numerical results show that there are omnidirectional reflection bands in photonic crystals without bandgaps. Furthermore, photonic crystal waveguides based on omnidirectional reflection bands can be constructed by using photonic crystals without bandgaps. Like conventional photonic crystal waveguides based on bandgaps, the novel waveguides can also achieve high-efficient transmission through waveguide bends with near-zero radii of curvature. This waveguide is expected to be applied to highly dense photonic integrated circuits after further research. The aforementioned results are helpful to widen the research field of photonic crystal waveguides.

Optical waveguide simulations for the optimization of InGaN-based green laser diodes

Two-dimensional optical waveguide mode simulations have been employed to investigate the optimized device structures for ridge-waveguide (Al, In, Ga) N-based green (520nm) laser diodes (LDs). The effects of thicknesses, alloy compositions, and doping densities of each epitaxially grown layers as well as ridge geometries on optical confinement factors (Γ) and waveguide absorption (α) were comprehensively surveyed. InyGa1−yN (y=0.07–0.1) guiding layers (GLs) with thickness more than 50nm were effective for realizing high Γ and low α. To minimize the absorption by the anode metal, p-cladding layer (p-CL) was required to be more than 500nm. At the same time, low index insulator such as SiO2 was preferable for the narrow ridge, where the thickness at the sidewall had to be more than 60nm. We also found that InGaN barriers layers between the quantum wells (QWs) were superior to GaN barriers to increase Γ and reduce α. Moreover, a thicker last barrier between the topmost QW and the electron blocking layer was also effective to reduce α. Regarding the effect of Mg doping concentration on the absorption, the reduction in Mg in the p-CL and the p-GL was significant to reduce α. Generally, it was confirmed the design for typical 405nm LDs can be applied for 520nm LD with the inclusion of InGaN GLs and barriers for the QWs.

High-accurate computation of wave propagation in complex waveguides for microchip optical interconnections

In two-dimensional optical waveguides with the varied refractive index along the transverse direction, the wave propagation is accurately computed. The asymptotic mode solutions are taken as initial guesses for Rayleigh Quotation iteration. More accurate solutions by considering leaky modes and both wave propagation in the transverse electric (TE) and transverse magnetic (TM) are obtained. Numerical simulations demonstrate that the results from Rayleigh Quotation iteration with the asymptotic solutions are better than ones from Lapack solver when the norms of modes are large enough. Thus, it is the best way to combine the two solvers together. This method is particularly useful to the design and simulation of micro waveguide with core layer refractive index fluctuation.

Wide-angle beam propagation method without using slowly varying envelope approximation

A new wide-angle (WA) beam propagation method (BPM) is developed whereby the exact scalar Helmholtz propagator is replaced by any one of a sequence of higher-order (m,n) Pade approximant operators. Unlike the previous well-known WA-BPM proposed by Hadley [Opt. Lett.17, 1426 (1992)], the resulting formulations allow one a direct solution of the second-order scalar wave equation without having to make slowly varying envelope approximations so that the WA formulations are completely general. The accuracy and improvement of this approximate calculation of the propagator is demonstrated in comparison with the exact result and existing approximate approaches. The method is employed to simulate two-dimensional (2D) and three-dimensional (3D) optical waveguides and compared with the results obtained by the existing approach.

LAYER-MODE TRANSPARENT BOUNDARY CONDITION FOR THE HYBRID FD-FD METHOD

We combine the analytic eigen mode expansion method with the flnite-difierence, frequency-domain (FD-FD) method to study two-dimensional (2-D) optical waveguide devices for both TE and TM polarizations. For this we develop a layer-mode based transparent boundary condition (LM-TBC) to assist launching of an arbitrary incident wave fleld and to direct the re∞ected and the transmitted scattered wave flelds back and forward to the analytical regions. LM- TBC is capable of transmitting all modes including guiding modes, cladding modes and even evanescent waves leaving the FD domain. Both TE and TM results are compared and verifled with exact free space Green's function and a semi-analytical solution.

Construction of Two-Dimensional Waveguides in Insulating Optical Materials by Means of Ion Beam Implantation for Photonic Applications: Fabrication Methods and Research Progress

Ion beam implantation has been used not only to modify some properties of the bulk materials but also to construct waveguide structures in many optical substrates by accurate control the refractive index in selected regions. This paper reviews the recent development of ion beam implantations on fabrication of two-dimensional (2D) optical waveguides, i.e., in cases of channel or ridge configurations, in diverse insulating optical materials by giving detailed fabrication methods and research progress obtained to date. Future prospects of practical applications in photonics are also discussed briefly. Another aim of this work is to show the challenging task of this field, that is, to create practical 2D waveguide devices applicable in any existing insulating optical materials.

Enhancement of two-photon excited fluorescence in two-dimensional nonlinear optical polymer photonic crystal waveguides

We examined two-photon excited fluorescence (TPEF) in two-dimensional highly nonlinear optical polymer photonic crystal waveguides with metallic cladding. A large TPEF enhancement of approximately two orders of magnitude was observed, originating from resonance between the external pump laser field and a photonic band mode. The results for TPEF enhancement are in good agreement with experimental photonic band resonances obtained by angle-resolved reflectivity measurements and the theoretical photonic band structure generated by three-dimensional finite-difference time-domain calculations, indicating that it is possible to use band dispersion control to design artificial nonlinear two-photon excitation processes.

Leaky modes of optical waveguides with varied refractive index for microchip optical interconnect applications – Asymptotic solutions

In two-dimensional optical waveguides with the varied refractive index, approximate analytic solutions of the leaky modes are derived by using an asymptotic analysis for both transverse electric (TE) and transverse magnetic (TM) modes. Numerical simulations show that the asymptotic solutions of the leaky modes are quite close to the exact ones. The results are useful in the eigenmode method, where the leaky modes appear if a perfectly matched layer (PML) is used to terminate the transverse directions of optical waveguides.