Greatly enhanced Kerr nonlinearity in hyperbolic slot waveguides

In an on-chip silicon-organic hybrid electro-optic (EO) modulator, the mode overlap with EO materials, in-device effective r33, and propagation loss are among the most critical factors that determine the performance of the modulator. Various waveguide structures have been proposed to optimize these factors, yet there is a lack of comprehensive consideration on all of them. In this Letter, a one-dimensional (1D) photonic crystal (PC) slot waveguide structure is proposed that takes all these factors into consideration. The proposed structure takes advantage of the strong mode confinement within a low-index region in a conventional slot waveguide and the slow-light enhancement from the 1D PC structure. Its simple geometry makes it robust to resist fabrication imperfections and helps reduce the propagation loss. Using it as a phase shifter in a Mach-Zehnder interferometer structure, an integrated silicon-organic hybrid EO modulator was experimentally demonstrated. The observed effective EO coefficient is as high as 490 pm/V. The measured half-wave voltage and length product is less than 1 V·cm and can be further improved. A potential bandwidth of 61 GHz can be achieved and further improved by tailoring the doping profile. The proposed structure offers a competitive novel phase-shifter design, which is simple, highly efficient, and with low optical loss, for on-chip silicon-organic hybrid EO modulators.

Hyperbolic metamaterials possess unique optical properties owing to their hyperbolic dispersion. As hyperbolic metamaterials can be constructed just from periodic multilayers of metals and dielectrics, they have attracted considerable attention in the nanophotonics community. Here, we review some of our recent works and demonstrate the benefits of using hyperbolic metamaterials in plasmonic waveguides and light scattering. We also discuss nonlocal topological transitions in the hyperbolic metamaterials that effectively induce a zero refractive index.

A very recent paper [1] focuses on linear hyperbolic metamaterials. The latter have uniaxial symmetry and are the basis of elegant outcomes concerning a new generalized theory about their structural topology. The broad assertion, developed here, is that the current hyperbolic metamaterial world is only partially served by investigations that incorporate only some limited version of anisotropy. It is emphasised that a strong emphasis must be placed upon the orientation of the optic axis, which can, for example, be at a polar angle θ to the z-axis and possess a projection angle φ to x-axis in the (x,y) plane. These are significant elements in the optical properties of uniaxial hyperbolic metamaterials. Indeed, it is shown that, quite differently from conventional anisotropic waveguides, for a hyperbolic metamaterial, a critical angle exists for which the guided waves are homogeneous for all the values of the polar angle. This remarkable effect facilitates the achievement of propagating modes in meta-waveguides and leads to resulting structures that are more tolerant to optic axis misalignment. It is shown, using graphene as an example, that tilting the optic axis of a uniaxial metamaterial produces beautiful new effects in the linear domain [2]. Both leaky and surface waves are supported. Critical orientation angles are derived for the optic axis. In more detail, for the linear domain, it is the propagation of TM-polarized surface waves and leaky waves for a finite-thickness slab of hyperbolic metamaterial, with the optic axis, tilted with respect to slab interfaces, that is fully investigated, for the first time‥ It is only in the low frequency range that backward waves occur. For an optic axis perpendicular to the slab interfaces, the hyperbolic nature of the metamaterial is destroyed above a certain frequency window. For a tilted optic axis mode, changes occur at lower frequencies and a negative permittivity is maintained.

Berry’s discovery of a topological phase in quantum mechanics has led to a unified view of many seemingly disconnected topological phenomena in physics, both at the quantum and classical levels.1 Here we review some recent optical manifestations of this Aharonov-Bohm-like phase. There are now four distinct manifestations of topological phases in optics. All these phases can be thought of as anholonomies. An anholonomy can arise whenever a system is processed through a sequence of changes such that it is returned to its original state; most of the variables characterizing the system obviously return to their original values, but surprisingly certain ones may not. An example is the phase anholonomy which an electron exhibits when it returns to its original state after encircling a solenoid in the Aharonov-Bohm effect. Another example is the age anholonomy which a travelling twin experiences relative to the nontravelling twin when he returns to the Earth after a rocket trip in the twin paradox. When light is cycled through a sequence of states such that it returns to its original state, it can also acquire anholonomies at both the classical and quantum levels.

Highly sensitive Mach–Zehnder interferometer biosensor based on silicon nitride slot waveguide

This paper presents a novel nanosource of continuous terahertz (THz) wave radiation based on difference frequency generation (DFG). Both the optical and THz waves are confined in a nanoscale plasmonic waveguide. The results of theoretical investigations indicate that the appropriate geometry of the plasmonic waveguide has a relatively long optical and THz propagation distance (on the order of several tens of wavelengths). Phase matching is obtained using the dispersive properties of the waveguide for generating 0.8 THz at the central optical wavelength of 1.52 μm. Our numerical calculation shows that the conversion efficiency in this waveguide structure can be achieved up to 5 times as large as the micron scale dielectric waveguides and almost 10 times as large as the metallic micron scale waveguides.

Transmission properties of circular dielectric- coated metallicwaveguides for infrared transmissionMitsunobu Miyagi, Kazuhide Harada, Yoshizo Aizawa, and Shojiro KawakamiResearch Institute of Electrical Communication, Tohoku University,2 -1 -1 Katahira, Sendai, 980 JapanAbstractSeveral kinds of dielectric- coated metallic waveguides such as germanium- coated nickelor silicon- coated aluminum hollow waveguides are fabricated by using a method based on rfsputtering, plating, and etching techniques. Transmission losses of 0.34 dB /m are achievedfor straight waveguides at 10.6 pm. Measurements of bending losses of several kinds ofhollow waveguides are conducted, which reveal that dielectric- coated metallic waveguideshave smaller bending losses than conventional metallic waveguides. Edge -guided modes orwhispering gallery modes in circular metallic waveguides are also observed. A design theoryfor reducing bending losses of circular dielectric- coated waveguides has been presented byusing a new theory' different from that used previously.2 Theoretical and experimentalresults have been compared.IntroductionDevelopment of low -loss flexible waveguides is of great concern for transmitting infraredCO2 laser light in medical and industr_al applications. Although significant progress hasbeen made for dielectric fibers as cited in our previous paper,' hollow -core waveguides seemto be potential media from the viewpoint of high power operation. So far there have beenproposed and fabricated several types of hollow -core waveguides for practical use.3 -7 Amongthem, there are two types of circular waveguides which can transmit the HE1, mode with low

Plasmonic waveguides are promising in nonlinear optical applications because of their subwavelength field confinement, which can strongly enhance light-matter interactions and greatly reduce the device footprint. We investigate the Kerr nonlinear characteristics of two typical plasmonic waveguides and compare their relative merits to a conventional all-dielectric silicon slot waveguide. This work provides useful guidance on designing ultra-compact nonlinear optical devices.

Conventional rectangular metallic waveguides are seldom used at frequencies higher than twice the cutoff frequency because of higher mode propagation. Single-mode propagation is available for a metallic waveguide using two arrayed dielectric rods. Although coaxial-waveguide converters are generally used for the introduction of electromagnetic wave to metallic waveguides, impedances cannot be matched by only one converter, because of the narrow bandwidth. Accordingly a frequency multiplexer or demultiplexer that connects to two coaxial-waveguide converter is necessary for impedance matching in each frequency range. S-parameters for three waveguide ports were calculated using Ansoft's HFSS. Although the frequency width for the reflection coefficient of each port is not so wide, port isolation is above 20 dB from 14 GHz to 17.5 GHz between two output ports.

Dielectric singularities (DSs) constitute one of the most exotic features occurring in the effective permittivity of artificial multilayers called hyperbolic metamaterials (HMMs). Associated to DSs, a rich phenomenology arises that justifies the ever-increasing interest profuse by the photonic community in achieving an active control of their properties. As an example, the possibility to “canalize” light down to the nanoscale as well as the capability of HMMs to interact with quantum emitters, placed in their proximity, enhancing their emission rate (Purcell effect), are worth mentioning. HMMs, however, suffer of an intrinsic lack of tunability of its DSs. Several architectures have been proposed to overcome this limit and, among them, the use of graphene outstands. Graphene-based HMMs recently shown outstanding canalization capabilities achieving λ/1660 light collimation. Despite the exceptional performances promised by these structures, stacking graphene/oxide multilayers is still an experimental challenge, especially envisioning electrical gating of all the graphene layers. In this paper, we propose a valid alternative in which indium-tin-oxide (ITO) is used as an electrically tunable metal. Here we have numerically designed and analyzed an ITO/SiO2 based HMM with a tunable canalization wavelength within the range between 1.57 and 2.74 μm. The structure feature light confinement of λ/8.8 (resolution of about 178 nm), self-focusing of the light down to 0.26 μm and Purcell factor of approximately 700. The proposed HMM nanoarchitecture could be potentially used in many applications, such as ultra-fast signal processing, high harmonic generation, lab-on-a-chip nanodevices, bulk plasmonic waveguides in integrated photonic circuits and laser diode collimators.

Slot-based plasmonic waveguides have attracted significant attention owing to their unique ability to confine light within nanometer-scale. In this context, enhanced localized light-matter interaction and control have been exploited to demonstrate novel concepts in data communication and sensing applications revealing the immense potential of plasmonic slot waveguides. However, inherent light absorption in the metallic parts included is such structures hampers the scaling of plasmonic devices and limits their application diversity. A promising solution of such issues is the use of hybrid plasmo-photonic configurations. Hybrid slot waveguides have been introduced as the means to reduce such propagation losses while maintaining their functional advantages. In addition, their co-integration with low-loss photonic waveguides can enable the development of more complex structures with acceptable overall losses. In such scenario, light needs to be efficiently transferred from the photonic to the plasmonic components and/or backwards. Based on this rationale, in this work a hybrid slot-based structure is adopted to achieve highly efficient light transfer between photonic and plasmonic slot waveguides in the near-infrared spectrum region (λ=1550 nm). This transition is realized with the aid of a directional coupling scheme. For this purpose, a Si3N4 bus waveguide (photonic branch) is located below an Aubased metallic slot (plasmonic branch) forming a hybrid waveguide element. The combined configuration, as it is shown with the aid of numerical simulations , is capable of supporting two hybrid guided modes with quasi-even and odd symmetry allowing the development of a power exchange mechanism between the two branches. In this context, a new directional coupling structure has been designed which can achieve power transmission per transition over 68% within a coupling length of the order of just several microns.

Our purpose in this paper is to analyze the Pais-Uhlenbeck (PU) oscillator using complex canonical transformations. We show that starting from a Lagrangian approach we obtain a transformation that makes the extended PU oscillator, with unequal frequencies, to be equivalent to two standard second order oscillators which have the original number of degrees of freedom. Such extension is provided by adding a total time derivative to the PU Lagrangian together with a complexification of the original variables further subjected to reality conditions in order to maintain the required number of degrees of freedom. The analysis is accomplished at both the classical and quantum levels. Remarkably, at the quantum level the negative norm states are eliminated, as well as the problems of unbounded below energy and non-unitary time evolution. We illustrate the idea of our approach by eliminating the negative norm states in a complex oscillator. Next, we extend the procedure to the Pais-Uhlenbeck oscillator. The corresponding quantum propagators are calculated using Schwinger's quantum action principle. We also discuss the equal frequency case at the classical level.

Screening outstanding mechanical properties and low lattice thermal conductivity using global attention graph neural network

Total internal reflection (TIR) is a ubiquitous phenomenon used in photonic devices ranging from waveguides and resonators to lasers and optical sensors. Controlling this phenomenon and light confinement are keys to the future integration of nanoelectronics and nanophotonics on the same silicon platform. We introduced the concept of relaxed total internal reflection in 2014 to control evanescent waves generated during TIR. These unchecked evanescent waves are the fundamental reason photonic devices are inevitably diffraction-limited and cannot be miniaturized. Our key design concept is the engineered anisotropy of the medium into which the evanescent wave extends thus allowing for skin depth engineering without any metallic components. In this article, we give an overview of our approach and compare it to key classes of photonic devices such as plasmonic waveguides, photonic crystal waveguides and slot waveguides. We show how our work can overcome a long standing issue in photonics nanoscale light confinement with fully transparent dielectric media.

Subwavelength conductor-gap-silicon plasmonic waveguides along with compact S-bends and Y-splitters were theoretically investigated and experimentally demonstrated on a silicon-on-insulator platform. A thin SiO2 gap between the conductor layer and silicon core provides subwavelength confinement of light while a long propagation length of 40 microm was achieved. Coupling of light between the plasmonic and conventional silicon photonic waveguides was also demonstrated with a high efficiency of 80%. The compact sizes, low loss operation, efficient input/output coupling, combined with a CMOS-compatible fabrication process, make these conductor-gap-silicon plasmonic devices a promising platform for realizing densely-integrated plasmonic circuits.