Slab Waveguide Research Articles

Light diffraction in slab waveguide lenses simulated with the stepwise angular spectrum method.

A stepwise angular spectrum method (SASM) for curved interfaces is presented to calculate the wave propagation in planar lens-like integrated optical structures based on photonic slab waveguides. The method is derived and illustrated for an effective 2D setup first and then for 3D slab waveguide lenses. We employ slab waveguides of different thicknesses connected by curved surfaces to realize a lens-like structure. To simulate the wave propagation in 3D including reflection and scattering losses, the stepwise angular spectrum method is combined with full vectorial finite element computations for subproblems with lower complexity. Our SASM results show excellent agreement with rigorous numerical simulations of the full structures with a substantially lower computational effort and can be utilized for the simulation-based design and optimization of complex and large scale setups.

Guided Modes in Slab Waveguide with Central Anisotropic Metamaterial Layer

This work studies the characteristics of TE modes in a three layers slab waveguide that contains an anisotropic metamaterial as a central layer. The results show that all modes except TE 1 achieved forward propagation and then turned backwards. The effective refractive index value at which the propagation type is reversed increases with the mode order and the thickness of the middle layer. In addition, an anisotropic property in the metamaterial layer shift the modes curves (exept TE 1 ) to left or right with respect to the isotropic case. Furthermore, the mode TE 1 is abnormal and inconsistent with the behavior of other modes. Except TE 1 mode, the confinement factor is small in the forward propagation region and reaches large values in the backward propagation region.

Theory of intrinsic propagation losses in topological edge states of planar photonic crystals

Using a semi-analytic guided-mode expansion technique, we present theory and analysis of intrinsic propagation losses for topological photonic crystal slab waveguide structures with modified honeycomb lattices of circular or triangular holes. Although conventional photonic crystal waveguide structures, such as the W1 waveguide, have been designed to have lossless propagation modes, they are prone to disorder-induced losses and backscattering. Topological structures have been proposed to help mitigate this effect as their photonic edge states may allow for topological protection. However, the intrinsic propagation losses of these structures are not well understood and the concept of the light line can become blurred. For four example topological edge state structures, photonic band diagrams, loss parameters, and electromagnetic fields of the guided modes are computed. Two of these structures, based on armchair edge states, are found to have significant intrinsic losses for modes inside the photonic band gap, more than 100 dB/cm, which is comparable to or larger than typical disorder-induced losses using slow-light modes in conventional photonic crystal waveguides, while the other two structures, using the valley Hall effect and inversion symmetry, are found to have a good bandwidth for exploiting lossless propagation modes below the light line.

Polariton relaxation and polariton nonlinearities in nonresonantly cw-pumped III-nitride slab waveguides

Polariton lasers are mostly based on planar cavities. Here we focus on an alternative configuration with slab waveguide modes strongly coupled to excitons confined in GaN/AlGaN quantum wells. We study experimentally and theoretically polariton relaxation at temperatures ranging from 4 to 200 K. We observe a good robustness of the lower polariton population peak energy position against temperature changes due to a balance between the shift of the exciton energy and the change in the normal mode splitting, a promising feature for future applications such as lasers and amplifiers where a small temperature drift in the emission wavelength is a desired asset. Finally, at $T=4\phantom{\rule{4pt}{0ex}}\mathrm{K}$ we observe the signature of polariton nonlinearities occurring in the continuous wave regime that are assigned to an optical parametric oscillation process.

Hybrid coupled mode modelling of the evanescent excitation of a dielectric tube by semi-guided waves at oblique angles

A dielectric step-index optical fiber with tube-like profile is considered, being positioned with a small gap on top of a dielectric slab waveguide. We propose a 2.5-D hybrid analytical/numerical coupled mode model for the evanescent excitation of the tube through semi-guided waves propagating in the slab at oblique angles. The model combines the directional polarized modes supported by the slab with analytic solutions for the TE-, TM-, and orbital-angular-momentum (OAM) modes of the tube-shaped fiber. Implementational details of the scheme are discussed, complemented by finite-element simulations for verification purposes. Our results include configurations with resonant in-fiber excitation of OAM modes with large orbital angular momentum and strong field enhancement.

Chip scale GaAs optical phased arrays for high speed beam steering.

High speed photoelectronic optical phased arrays are demonstrated by vertically arranged GaAs-AlGaAs slab waveguides. The optical phased arrays are composed of 15-channel independently tuned waveguide with end-fire emission. We achieve a very fast beam steering step response of 0.34 µs, beam divergence of 4.7°, and beam steering ranges of around 30°with side lobe level better than 8 dB. The presented optical phased arrays provide a superior approach for high speed beam steering on a nano-photoelectronic integrated chip.

Power conversion with complete photonic band gap in magneto-photonic crystal slab based on cerium-substituted yttrium iron garnet

Abstract In this work, we propose a slab waveguide structure based on a magneto-photonic crystal, formed by a triangular lattice of circular air holes in a cerium-substituted yttrium iron garnet (Ce-YIG) medium grown on a silica (SiO2) substrate; in this structure, we have studied the width of the photonic band gap (PBG) using the expansion plane waves method in three dimensions to reach and optimize the complete PBG, centered at the telecommunication wavelength, also a theoretical study of the conversion mode, reported and studied the effect of some parameters such as the radius and the thickness using a beam propagation method in two dimensions. In our proposed structure, the maximum conversion modes ratio equal to 98% with a low coupling length LC = 15 µm is obtained for gyrotropy g = 0.36 and Faraday rotation FR = 1500 × 104 deg/cm.

Theoretical study of a pure LinbO3/Quartz waveguide coated gold nanorods using supercontinuum laser source

Abstract In this study, we explore by simulation the dependency of the LinbO3/Quartz on the waveguide design for filter and sensor applications using COMSOL multi-physics 4.4. LinbO3/Quartz was used to design slab waveguide for filter applications due to the variation of the core refractive indices and the laser beam incident angles. Three different diameters of gold nanorods 5, 10, and 15 nm and three acceptance angles 0°, 27°, and 36° were used to study the Lithium niobate/Quarts material in slab waveguide design as surface plasmon sensor applications. A set of refractive indices of Lithium niobate (2.83, 2.63, 2.43, 2.23, 2.03, and 1.83) were varied for slab waveguide core using supercontinuum laser within the range from 420 nm to 1900 nm. The waveguide power transmission with respect to wavelength is calculated under various parameters, such as slab core refractive index and incident angles. The results of resonance wavelength dip with variations of the nanorods diameters and acceptance angles were obtained. The resonance dip was not recognized in most transmission curves at 0° acceptance angle and has different behavior at 27° and 36°. The best SPR dip for nclad = 1.5 was found at 5 nm diameter, 27° acceptance angle, and ncore = 2.43. The best resonance dip was discovered at d = 5 nm, 27° incident angle, and refractive index n = 2.43. To the best of our knowledge, the use of gold nanorods multi diameters with the best core of Lithium niobate/Quartz material supported at the best incident angle for SPR phenomenon has not previously been reported.

Integrated Gires-Tournois interferometers based on evanescently coupled ridge resonators.

We propose integrated Gires-Tournois interferometers (GTIs) for guided modes of dielectric slab waveguides. The proposed GTIs consist of one or several dielectric ridge resonators separated by subwavelength-width grooves patterned into an abruptly terminated slab waveguide and operate at oblique incidence of the fundamental transverse-electric-polarized mode. The grooves act as partially reflective mirrors, whereas the end facet of the last ridge works in the total internal reflection regime and reflects all the incident radiation. We show that the single-ridge structure provides a nonlinear staircase-like phase response characteristic for GTIs. By using several properly arranged ridges, one can engineer group delay or group delay dispersion in a required spectral range. As an example, we design a three-ridge GTI providing an almost constant group delay dispersion in a 50-nm-wide wavelength range. The proposed planar GTIs may find application in integrated optical circuits for introducing or compensating for chromatic dispersion.

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.

Numerical modeling and analysis of a TM mode-division (de)multiplexer based on grating assisted couplers

In this paper, a mode-division (de)multiplexer capable of multiplexing three transverse magnetic modes simultaneously at the operating wavelength of 1550 nm has been proposed. The device structure is designed using slab waveguides with Si and SiO2 as core and cladding materials, respectively. Grating assisted couplers have been employed to couple the fundamental modes of two single-mode waveguides with the two higher-order modes of a multimode waveguide in the opposite direction. The fundamental mode of the multimode waveguide keeps propagating in the same waveguide without any power coupling to other modes. Using perturbation approach and coupled-mode theory, the proposed structure is theoretically analyzed. 2D Finite Difference Time Domain numerical simulation technique has been used to simulate and analyze the proposed mode division (de)multiplexer. During the demultiplexing operation, the proposed device exhibits insertion loss ranging from − 2.01 to − 0.01 dB, return loss ranging from − 31.07 to − 9.17 dB, and crosstalk in the range of − 41.76 to − 13.58 dB. Whereas for the multiplexing operation, insertion loss, return loss, and crosstalk range from − 1.59 to − 0.01 dB, − 31.07 to − 10.17 dB, and − 41.76 to − 8.05 dB respectively.

Analytical study of hybrid surface plasmon polaritons in a grounded chiral slab waveguide covered with graphene sheet

In this paper, we propose a new analytical model for grounded chiral slab waveguides covered with graphene sheets. The general waveguide is constructed of a graphene sheet sandwiched between two different chiral layers (as substrate and cover layers), each one has the permittivity, the permeability and the chirality of $$ \varepsilon_{c} ,\mu_{c} ,\gamma_{c}$$ , respectively. The substrate is supposed to be a perfect electromagnetic conductor, which is able to easily convert to a perfect electric conductor or a perfect magnetic conductor. A novel matrix representation is obtained for the general structure to find its dispersion relation and other propagating parameters. To show the richness of the proposed waveguide, two new structures have been introduced and investigated. It has been shown that the modal properties of these exemplary structures are tunable by changing the chemical potential of the graphene and the chirality. The proposed general structure and its analytical model can be utilized for designing tunable plasmonic devices in THz frequencies.

On-chip second-order spatial derivative of an optical beam by a periodic ridge.

In this paper, a very simple periodic ridge on a symmetric slab waveguide is used for implementing an on-chip CMOS-compatible second-order spatial differentiator. The reflection and transmission coefficients of this structure show that the second derivative is performed in the transmission when the optical beam normally incidents on the periodic ridge. Simulations confirm that the reason behind the second-order spatial differentiation of the incoming beam is the excitation of the guided mode of the periodic ridge. A Maxwell's equation solver that utilizes the finite element method (FEM) is used to simulate this structure, and an eigenmode solver is utilized for the validation. The results of both methods have a very good agreement with each other.

Fabrication of ion-sliced yttrium-aluminum-garnet thin films on silica by He+ implantation and Cu–Sn bonding

The fabrication of sub-micron-thickness ion-sliced yttrium-aluminum-garnet thin films on silica is performed by He + implantation and the Cu–Sn bonding. The formation of blisters on He-ion-implanted YAG crystals caused by thermal annealing is investigated. YAG thin films with an area of approximately 6 mm × 5 mm are produced. The implanted YAG crystals and fabricated YAG thin films are investigated using optical, transmission electron, and scanning electron microscopy, as well as prism-coupling methods. A YAG thin film with a low-refractive-index silica cladding can be used as a waveguide to manufacture photonic components with high refractive index contrast. • We report the fabrication of ion-sliced YAG thin films on SiO 2 for the first time. • The blistering behavior is investigate. • A sub-micron-thickness YAG thin film with an area of 6 × 5 mm is fabricated. • A YAG thin film on SiO 2 cladding layer can act as a slab waveguide.

Zinc Sulfide Waveguide Analysis

The Maxwell equations are considered as fundamental formulation of wave propagation for a dielectric slab waveguide at frequencies in the IR region. In this article, the theoretical analysis of electromagnetic waves propagating through the zinc sulfide (ZnS) semiconductor planar waveguide at wavelength of 1 µm is reported using 2013 MATLAB software. Additionally, a comparison of the waveguide parameters using two modes namely transvers electric (TE) and transvers magnetic (TM) is demonstrated in details. This could be attributed to the interference of effective refractive index value. In particular, the penetration depth has demonstrated values of 0.2419 and 0.2445 µm for TE0 and TM0 modes at thickness of 2.69 µm, respectively. Subsequently, the effect of temperature on the effective reflective index has been elaborated. Furthermore, the propagation angles in TM modes exhibited lower values than TE modes with respect to the core thickness; and lower wavelength resulted in higher cutoff frequency with respect to the number of modes. While, the relation between neff and temperature for both TE and TM modes showed that TE mode exhibited advanced values as compared to TM mode. This work demonstrates a short pathway for a theoretical analysis of electromagnetic waves through ZnS planer waveguide using both TE and TM modes.

Coupling of quantum-well emission to waveguide–plasmon polaritons in rolled-up microtubes

We study the coupling of GaAs quantum wells to waveguide–plasmon polaritons supported by a thin InAlGaAs-based slab waveguide and a Ag grating. The hybrid photon–plasmon modes are excited in a freestanding emitter–waveguide–plasmon structure realized by rolling-up strained InAlGaAs-based layers and nanopatterned Ag structures. By varying the grating’s bar width, we tune the plasmonic resonance of the system. We observe by means of spatially, spectrally, and temporally resolved photoluminescence measurements, a coupling of the quantum-well emission to the waveguide–plasmon system for a specific grating’s bar width. Supported by finite-element simulations, we can assign the coupling to the excitation of a waveguide–plasmon polariton.

Edge modes in two-dimensional electromagnetic slab waveguides: Analogs of acoustic plasmons

We analyze planar electromagnetic waves confined by a slab waveguide formed by two perfect electrical conductors. Remarkably, 2D Maxwell equations describing transverse electromagnetic modes in such waveguides are exactly mapped onto equations for acoustic waves in fluids or gases. We show that interfaces between two slab waveguides with opposite-sign permeabilities support 1D edge modes, analogous to surface acoustic plasmons at interfaces with opposite-sign mass densities. We analyze this novel type of edge modes for the cases of isotropic media and anisotropic media with tensor permeabilities (including hyperbolic media). We also take into account `non-Hermitian' edge modes with imaginary frequencies or/and propagation constants. Our theoretical predictions are feasible for optical and microwave experiments involving 2D metamaterials.

Numerical modeling of integrated electro-optic modulators based on mode-gap shifting in photonic crystal slab waveguides containing a phase change material

This paper presents novel designs and simulation results of electro-optic modulators in integrated silicon photonics platforms. The electro-optic modulators described in this paper are based on the modulation of the photonic bandgap in a silicon photonic crystal slab waveguide, consisting of a phase change material (germanium selenide) sandwiched in between silicon layers. Three-dimensional finite difference time domain (FDTD) modeling is employed to simulate two configurations of electro-optic modulators based on mode-gap shifting in photonic crystal slab waveguides—one that is designed for operation with the transverse electric (TE) polarization of light and the other for the transverse magnetic (TM) polarization. When the electric field is applied across the germanium selenide layer surrounded by doped silicon layers, there is a change of phase of the germanium selenide layer. A large refractive index contrast between the two phases of the germanium selenide layer—i.e., between the amorphous phase and the crystalline phase—on application of the electric field is responsible for shifting of the mode gap in the dispersion characteristics of the PhC slab waveguide. Our results show excellent performance of the electro-optic modulators in terms of the high On/Off extinction ratio ( > --> 37 d B in the TE configuration and > --> 28 d B in the TM configuration), broadband switching capability ( ∼ 100 n m ), low insertion loss in the On state ( < 2 d B ), high range of tunability (by changing the lattice constant and radius of air holes), and low operating voltage ( < 4 V ). The proposed devices can be used as electro-optic modulators in future nanoscale photonic integrated circuits.

Second-harmonic generation and manipulation in lithium niobate slab waveguides by grating metasurfaces

Nonlinear optical processes in waveguides play important roles in compact integrated photonics, while efficient coupling and manipulations inside the waveguides still remain challenging. In this work, we propose a new scheme for second-harmonic generation as well as beam shaping in lithium niobate slab waveguides with the assistance of well-designed grating metasurfaces at λ = 1064 nm . By encoding the amplitude and phase into the holographic gratings, we further demonstrate strong functionalities of nonlinear beam shaping by the metasurface design, including dual focusing and Airy beam generation. Our approach would inspire new designs in the miniaturization and integration of compact multifunctional nonlinear light sources on chip.

Highly sensitive electro-optic detection of terahertz waves in a prism-coupled thin LiNbO3 layer

Electro-optic sampling of pulsed terahertz radiation by femtosecond laser pulses in noncollinear geometry in a 40 μm thick layer of LiNbO3 attached to a Si prism is experimentally demonstrated. Terahertz radiation is prism-coupled into the layer through its surface and modulates the frequency and angular spectra of the optical radiation propagating along the layer as a fundamental mode of a dielectric slab waveguide. The modulation results in the optical intensity variations in the optical beam transmitted through the layer. By measuring the intensity variations, we achieved 38 and 216 times enhancement in the sensitivity of electro-optic detection as compared to the conventional collinear ellipsometric technique with 1 mm thick ZnTe and 0.2 mm thick GaP crystals, respectively.