Modes In Slab Waveguide Research Articles

Characteristic frequencies of transverse electric modes in a double negative slab waveguide with Kerr-type nonlinearity

The evolution equation for guided transverse electrical modes in a slab waveguide having a double negative core is derived for the electrical field. Special solutions of the dispersion equation for the case with double positive symmetric cladding are searched for. Relevant eigenmodes are formulated in terms of characteristic frequencies as a new method, and these frequencies corresponding to the oscillating guided modes are found for different wave numbers and core widths assuming the lossless Drude model can be used for the core medium with a Kerr-type nonlinearity. Results show that normalized characteristic frequencies increase with increasing wave numbers and mode numbers.

Room Temperature Emission Line Narrowing and Long‐Range Photon Transport in Colloidal Quantum Wells Coupled to Metasurface Resonance

AbstractHighly efficient and spectrally pure single photon sources are desirable in fundamental studies of quantum physics and in many varied applications like in quantum metrology and quantum cryptography. 2D semiconductor colloidal quantum wells (CQWs) are quite appropriate as nanoscale photon sources because of their giant oscillator strengths and large absorption cross sections. The integration of such sources with dielectric metasurfaces exhibiting narrow resonances provides an excellent platform for highly efficient light‐matter interactions and the development of on‐chip light sources with high spectral purity. Here details on the use of capillary filling method are reported to achieve photonic coupling of CQWs to a metasurface resonator (MSR) featuring a square‐lattice geometry of holes on a slab‐waveguide to achieve strongly enhanced and almost spectrally pure emission of ≈3% of the original out‐of‐plane emission line‐width of the quantum emitters at room temperature. Long‐range exciton‐mediated photon transport facilitated by in‐plane slab waveguide modes is demonstrated and a theoretical basis to explain all the experimental data including that in terms of the MSR‐modified Lamb shifts and Purcell decays is provided. The results demonstrate a new platform with emergent photonic properties and suggest possibility of their use in on‐chip photonic quantum information processing.

Ultrahigh efficiency plasmonic mode conversion between symmetric and antisymmetric modes in metal slab waveguides by introducing a gyration-managed waveguide link

Ultrahigh efficiency plasmonic mode conversion between symmetric and antisymmetric modes in metal slab waveguides by introducing a gyration-managed waveguide link

Impact of film thickness in laser-induced periodic structures on amorphous Si films

We report self-organized periodic nanostructures on amorphous silicon thin films by femtosecond laser-induced oxidation. The dependence of structural periodicity on the thickness of silicon films and the substrate materials is investigated. The results reveal that when silicon film is 200 nm, the period of self-organized nanostructures is close to the laser wavelength and is insensitive to the substrates. In contrast, when the silicon film is 50 nm, the period of nanostructures is much shorter than the laser wavelength, and is dependent on the substrates. Furthermore, we demonstrate that, for the thick silicon films, quasi-cylindrical waves dominate the formation of periodic nanostructures, while for the thin silicon films, the formation originates from slab waveguide modes. Finite-difference time-domain method-based numerical simulations support the experimental discoveries.Graphical abstract

Gain measurements on VCSEL material using segmented contact technique

We report direct measurements of the optical gain on vertical-cavity surface-emitting laser (VCSEL) material using a stripe-length method featuring segmented contacts. We utilise the similarity of the in-plane transverse electric (TE) polarised matrix element and that of the VCSEL lasing mode and a simple method to reduce round trip effects. The confinement factor is determined from cold-cavity simulations of the in-plane TE polarised slab waveguide mode and used to convert the measured in-plane modal gain into the vertical-cavity modal gain, as required for the VCSEL structure. This gives a threshold material gain of 1440 ± 140 cm−1 at 30 °C for this structure. A comparison with the threshold material gain values determined from the lasing condition, where internal optical losses due to doping induced absorption is included using parameters taken from the literature, indicates the presence of an additional source of optical loss in the experiment which increases the threshold material gain by ∼450 cm−1. A best fit is obtained by increasing the optical loss in the n-DBR (distributed Bragg reflectors) layers to 40 cm−1, which is consistent with previous work on additional scattering losses due to interface roughening in the n-DBR layers. To further demonstrate the utility of this method for rapid optimisation, the gain-peak wavelength is measured directly, and its temperature dependence is compared to the lasing wavelength.

Nodal degeneracy of guided modes in uniaxial crystal slabs

We study the dispersions of the guided modes in the continuous uniaxial crystal slab waveguide and engineer their degeneracies through dielectric anisotropy. By switching the uniaxial positivity and negativity, we can obtain distinctive nodal types, point and line, for the lowest degeneracy in frequency. The mirror symmetry protections, Mx and My, are pointed out, and the degeneracy properties are intuitively analyzed through comparing the approximate slopes of the guided modes. Our results reveal a link between the lowest nodal types and the positivity/negativity of the uniaxial crystal, and provide a new approach to regulate the topology of degeneracy in two-dimensional photonic bands.

Total absorption and coherent perfect absorption in metal-dielectric-metal resonators integrated into a slab waveguide.

We propose and investigate integrated metal-dielectric-metal (MDM) resonators operating with semi-guided waves (guided modes of dielectric slab waveguides). The MDM resonators are constituted by two metal strips "buried" in the waveguide core layer and separated by a dielectric waveguide segment. We theoretically prove and numerically demonstrate that by a proper choice of the mode incidence geometry, the widths of the metal strips, and the distance between them, it is possible to achieve either total absorption of the incident wave or coherent perfect absorption (in the case of symmetric incidence of two modes on the structure). The proposed planar MDM resonators may find application as absorbers or filters in integrated optical circuits.

Nonlinear coupling and modulation of the guided modes in photorefractive slab waveguide

Owing to its excellent electro-optic, ferroelectric and nonlinear optical properties, photorefractive crystal (PRC) provides a versatile platform for developing nonlinear waveguides, which has a great potential in integrated optics components. In this paper, we theoretically study nonlinear coupling of optical guided modes in photorefractive waveguides by the spatial-partition fast Fourier transform beam propagation method (SP FFT-BPM). The modulation of applied external electrical field on the guided modes is investigated, and demonstrated as a new method to modulate the guided modes without artificially refabricating physical configuration or structure of the waveguide.

Bound State in the Continuum in Nanoantenna-Coupled Slab Waveguide Enables Low-Threshold Quantum-Dot Lasing.

Colloidal quantum dots (CQDs) are a promising gain material for solution-processed, wavelength-tunable lasers, with potential application in displays, communications, and biomedical devices. In this work, we combine a CQD film with an array of nanoantennas, made of titanium dioxide cylinders, to achieve lasing via bound states in the continuum (BICs). Here, the BICs are symmetry-protected cavity modes with giant quality factors, arising from slab waveguide modes in the planar CQD film, coupled to the periodic nanoantenna array. We engineer the thickness of the CQD film and size of the nanoantennas to achieve a BIC with good spatial and spectral overlap with the CQDs, based on a second-order transverse-electric (TE)-polarized waveguide mode. We obtain room-temperature lasing with a low threshold of approximately 11 kW/cm2 (peak intensity) under 5-ns-pulsed optical excitation. This work sheds light on the optical modes in solution-processed, distributed-feedback lasers and highlights BICs as effective, versatile, surface-emitting lasing modes.

Mode coupling at avoided crossings in slab waveguides with comparison to optical fibers: tutorial

Avoided crossings are important in many waveguides and resonators. That is particularly the case in modern-day solid-core and air-core optical fibers that often have a complex geometry. The study of mode coupling at avoided crossings often leads to a complicated analysis. In this tutorial, we aim to explain the basic features of avoided crossings in a simple slab waveguide structure so that the modes can be found analytically with simple sinusoidal and exponential forms. We first review coupled-mode theory for the guided mode in a slab waveguide, which has a higher index in the core. We study the effective index of the guided true mode for a five-layer slab waveguide including two core layers with higher indices compared to the indices in the three cladding layers. Then, we study the same structure by using the overlap between approximate modes confined in the two individual core slabs. When the two individual core slabs are not near each other, the avoided crossing using the true modes within the two-slab waveguide agrees well with the results using the overlap between the two approximate modes. We also study coupled-mode theory and avoided crossings for leaky modes in an antiresonant slab waveguide. We obtain good agreement between the results using the true leaky mode and the results using the overlap between approximate modes. We then discuss examples of avoided crossings in solid-core and air-core optical fibers. We describe the similarities and differences between the optical fibers and simple slab waveguides that we have analyzed in detail.

Reversed Hyperbolic Plasmonic Responses in Phosphorene Under Uniaxial Strain

In this paper, hyperbolic plasmonic responses of phosphorene under uniaxial strains have been explored within density functional theory. In the hyperbolic regime, plasmonic slab waveguide modes are found only along armchair direction. Then, uniaxial strains up to 10% have been applied along zigzag and armchair directions, which can significantly modify its plasmonic responses. Under appropriate strain, the signs of permittivities along two in-plane directions can be even reversed, causing switching of the propagating direction of the plasmonic modes into zigzag direction. Our investigations may give a general idea about how to control the hyperbolic plasmonic modes in phosphorene via strain.

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.

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.

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.

Guided Optical Modes in Metal-Cladded Tunable Hyperbolic Metamaterial Slab Waveguides

We have theoretically investigated metal-cladded waveguides of tunable hyperbolic metamaterial (THMM) cores, employing graphene sheets as a tunable layer, in terms of guided waves propagation over near- to mid-infrared range, following the effective medium approximation. We have proven that these subwavelength guiding structures offer a number of effects usually not found in other types of waveguides, including controllable propagation gap and number of modes, inversion of power flow direction with respect to phase velocity, TM mode propagation, and absence of the fundamental mode, which occur as a result of controlled change of the guiding layer dispersion regime. This is the first time that the above-mentioned effects are obtained with a single, voltage-controlled waveguiding structure comprising graphene sheets and a dielectric, although the presented methodology allows us to incorporate other tunable materials beyond graphene equally well. We believe that such or similar structures, feasible by means of current planar deposition techniques, will ultimately find their practical applications in optical signal processing, controlled phase matching, controlled coupling, signal modulation, or the enhancement of nonlinear effects.

Nonlinear, tunable, and active optical metasurface with liquid film

Optical metamaterials and metasurfaces, which emerged in the course of the last few decades, have revolutionized our understanding of light and light–matter interaction. While solid materials are naturally employed as key building elements for construction of optical metamaterials mainly due to their structural stability, practically no attention was given to study of liquid-made optical two-dimensional (2-D) metasurfaces and the underlying interaction regimes between surface optical modes and liquids. We theoretically demonstrate that surface plasmon polaritons and slab waveguide modes that propagate within a thin liquid dielectric film trigger optical self-induced interaction facilitated by surface tension effects, which leads to the formation of 2-D optical liquid-made lattices/metasurfaces with tunable symmetry and can be leveraged for tuning of lasing modes. Furthermore, we show that the symmetry breaking of the 2-D optical liquid lattice leads to phase transition and tuning of its topological properties, which allows the formation, destruction, and movement of Dirac-points in the k-space. Our results indicate that optical liquid lattices support extremely low lasing threshold relative to solid dielectric films and have the potential to serve as configurable analogous computation platform.

An efficient plasmonic waveguide mode solution using rational function fitting of Green’s function

A novel approach to find plasmonic waveguide modes is presented in this paper. The method is based on rational function fitting of spectral Green’s function (RFF-SGF) of slab waveguide with the use of modified VECTFIT algorithm. Dispersion equation solutions including complex modes of structures with material/metal loss can be obtained with no extra complexity during the poles and residues extraction in the fitting approach. Moreover, this method can be used in multilayered plasmonic waveguides straightforwardly which are widely utilized in nanophotonic devices. The main advantage of this method lies in its simple implementation, speed as well as controllable accuracy. Surface plasmon and also surface wave modes of various plasmonic slab waveguides are investigated, and excellent agreements with rigorous methods are shown.

High-Q resonances supported by a single dielectric ridge on the surface of a slab waveguide

Diffraction of slab waveguide modes on a dielectric ridge located on the waveguide surface is studied. Calculations, based on aperiodic rigorous coupled-wave analysis, demonstrate the existence of sharp resonant features in the reflectance and the transmittance spectra occurring at oblique incidence of TE-polarized waveguide mode on the ridge. Angular widths of the resonant peaks and dips vary from units to less than a thousandth of a degree. Using the effective index method, we explain the resonances by the excitation of cross-polarized modes of the ridge. The existence of high-Q resonances makes this structure promising for filtering, sensing and all-optical signal processing.

TE振荡模在左手材料劈形平面波导中的传输

TE振荡模在左手材料劈形平面波导中的传输

Hybrid mode tunability in metamaterial nanowaveguides

We employ the properties of metamaterials to tailor the modes of metamaterial-dielectric waveguides operating at optical frequencies. We survey the effects of three-dimensional isotropic metamaterial structural parameters on the refractive index of metamaterials and on the hybrid modes in slab metamaterial-dielectric waveguides. Hybrid modes refer to hybrid ordinary-surface plasmon polariton modes in the waveguide structures. We investigate how robust metamaterials are to fluctuations in their structural parameters; specifically, we examine the effects of Gaussian errors on the metamaterials electromagnetic behavior. Our survey enables us to determine the allowable fluctuation limits and from this to identify appropriate unit-cell structure for further applications of metamaterials in waveguide technologies.