Photonic skin-depth engineering

The extremely local electric field enhancement and light confinement is demonstrated in dielectric waveguide with corner and gap geometry. The numerical results reveal the local electric field enhancement in the vicinity of the apex of fan-shaped waveguide. Classical electromagnetic theory predicts that the field enhancement and confinement abilities increase with decreasing radius of rounded corner ($r$) and gap ($g$), and show singularity for infinitesimal $r$ and $g$. For practical parameters with $r=g=10\,\mathrm{nm}$, the mode area of opposing apex-to-apex fan-shaped waveguides can be as small as $4\times10^{-3}A_{0}$ ($A_{0}=\lambda^{2}/4$), far beyond the diffraction limit. This way of breaking diffraction limit with no loss outperforms plasmonic waveguides, where light confinement is realized at the cost of huge intrinsic loss in the metal. Furthermore, we propose a structure with dielectric bow-tie antenna on a silicon-on-insulator waveguide, whose field enhancement increases by one order. The lossless dielectric corner and gap structures offer an alternative method to enhance the light-matter interaction without metal nano-structure, and will find applications in quantum electrodynamics, sensors and nano-particle trapping.

Based on the concept of transformation optics and complementary media, a hexagonal shaped reciprocal external cloak is proposed which hides an object inside it perfectly. The hexagonal shape has been sub-divided into regions of rectangular and triangular shapes. The rectangular sub-regions have diagonal material properties whereas the triangular sub-regions have complete anisotropic tensor properties. The advantage of proposed cloak is that the material properties are homogeneous within all sub-regions. The other advantage is that its cloaked area can be increased without any change in material parameters. Full-wave simulations reveal that the proposed cloak has good performance even for hiding multiple objects of different shapes and sizes inside it.

Complex media have gained interest in microwave and millimeter-wave devices. They display some interesting characteristics such as, for instance, tunability and controlled filtering capacity. However, such media are generally very complex as they can be fully nonhomogeneous; frequency dependent, anisotropic, time dependent, or chiral. This requires simulation techniques capable of solving Maxwell’s equations accounting for such media. Also, apart comparison with rather difficult measurement, canonical solutions are not available for validation. In this paper, the concept of transformation optics (TO) is presented as a systematic tool to construct computational problems involving complex media for which the analytical solution is known. Several examples are shown for validation of a new transmission-line matrix (TLM) cell that model complex media.

The concept of transformation optics is extended to nonlinear electrodynamics. It is shown that transformation optics favors implicit constitutive relations in terms of energy densities D.E and B.H rather than E^2 and H^2. The Kerr nonlinearity is studied in detail and the transformation optics based engineering of self-interaction effects is discussed. As a specific example we introduce transformation optics applied on a self-focusing field configuration.

A new, rigorous theory is presented for analyzing radiation and transmission of electromagnetic waves in uniformly curved sections of slab waveguides. General fields are expressed, in this theory, in terms of a spectral integral of eigenmodes with continuous eigenvalues. The theory is applied to the investigation of mode transmission characteristics of a circularly bent, finite‐length dielectric slab waveguide, sandwiched between the two straight sections. It is demonstrated that the analysis method is also applicable, though approximately, to the study of radiation and transmission of electromagnetic fields in a uniform bend of a three‐dimensional dielectric waveguide.

The emerging field of nanophotonics1 addresses the critical challenge of manipulating light on scales much smaller than the wavelength. However, very few feasible practical approaches exist at present. Surface plasmon polaritons2,3 are among the most promising candidates for subwavelength optical confinement3,4,5,6,7,8,9,10. However, studies of long-range surface plasmon polaritons have only demonstrated optical confinement comparable to that of conventional dielectric waveguides, because of practical issues including optical losses and stringent fabrication demands3,11,12,13. Here, we propose a new approach that integrates dielectric waveguiding with plasmonics. The hybrid optical waveguide consists of a dielectric nanowire separated from a metal surface by a nanoscale dielectric gap. The coupling between the plasmonic and waveguide modes across the gap enables ‘capacitor-like’ energy storage that allows effective subwavelength transmission in non-metallic regions. In this way, surface plasmon polaritons can travel over large distances (40–150 µm) with strong mode confinement (ranging from λ2/400 to λ2/40). This approach is fully compatible with semiconductor fabrication techniques and could lead to truly nanoscale semiconductor-based plasmonics and photonics. Xiang Zhang and colleagues from the University of California, Berkeley, propose a new approach for confining light on scales much smaller than the wavelength of light. Using hybrid waveguides that incorporate dielectric and plasmonic waveguiding techniques, they are able to confine surface plasmon polaritons very strongly over large distances. The advance could lead to truly nanoscale plasmonics and photonics.

The mid-infrared (MIR) region is one of the most thriving spectral regions as it contains the vibrational resonances of several molecules of interest, as well as the absorption bands for hot bodies. In this work, we propose a novel dielectric waveguide that confines the light in a nanoscale air gap. This dielectric waveguide is a suitable candidate for on-chip sensing. Detailed dispersion analysis of this 3D waveguide is also provided. The effect of the refractive index change in the gap is studied and shows very high sensitivity and causes significant changes in the modal parameters. We also show that these waveguide modes exhibit plasmonic-like characteristics at the MIR region with controllable plasma frequency, without the inclusion of any metals. This waveguide is also utilized in various on-chip applications with nanoscale confinement at the MIR region.

In this work, we proposed a technique in which two-dimensional (2-D) confinement of light is achieved in one-dimensional (1-D) planar waveguide by loading it with a low refractive index material. A waveguide design is based on ZnO/Al2O3 dielectric materials for integrated photonics. These waveguides are capable of propagating TE and TM polarization at 0.633 µm visible light. Based on these waveguide structures, many optical elements such as S-bend, Y-splitter can be realized which will provide a compact platform for integrated optics.

Nanoscale amplification of non-linear processes in solid-state devices opens novel applications in nano-electronics, nano-medicine or high energy conversion for example. Coupling few nano-joules laser energy at a nanometer scale for strong field physics is demonstrated. We report enhancement of high harmonic generation in nano-structured semiconductors using nanoscale amplification of a mid-infrared laser in the sample rather than using large laser amplifier systems. Field amplification is achieved through light confinement in nano-structured semiconductor 3D waveguides. The high harmonic nano-converter consists of an array of zinc-oxide nanocones. They exhibit a large amplification volume, 6 orders of magnitude larger than previously reported [1] and avoid melting observed in metallic plasmonic structures. The amplification of high harmonics is observed by coupling only 5-10 nano-joules of a 3.2 µm high repetition-rate OPCPA laser at the entrance of each nanocone. Harmonic amplification (factor 30) depends on the laser energy input, wavelength and nanocone geometry [2]. [1] Vampa et al., Nat. Phys. 13, 659–662 (2017). [2] Franz et al., arXiv:1709.09153 [physics.optics] (2017)

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.

This work is devoted to calculation of constitutive parameters and numerical simulation of anisotropic metamaterial lens via transformation optics concept. The possibility to use this lens as a device for imitation of an antenna radiation out its real location is shown in this work.

Surface plasmon polaritons (SPPs) are the electromagnetic excitations that evaporate when confined in a direction perpendicular to the interface and propagate along the interface between two different media with opposite dielectric constants in a wave-like pattern [1]. It gives a strong light confinement power in integrated photonic circuit [2]. In this paper, by using SoI technology light confinement for the plasmonic slot rectangular waveguide is studied. The most promising dimension of the recommended design is represented by the values of d3 and d4, which are 180 nm and 220 nm, respectively, for the waveguide's width and height [3]. The slot rectangular waveguide confinement power and mode effective area are studied by applying a Gold (Au) layer around the core at a distance Mg.

Photonic devices integrated in Si optoelectronic circuits offer less power dissipation and larger bandwidth than those of electronic components, but suffer from a larger footprint due to the fundamental diffraction limit of light in dielectric waveguides and the weak optical response of Si. These two limitations may be overcome by utilizing plasmonics owing to the tight optical mode confinement in plasmonic waveguides. Besides the capability of miniaturization of photonic devices on the nanometer scale, plasmonics also provides the potential to design novel photonic devices due to the incorporation of metal and dielectrics. In this chapter, we present Si-based active plasmonic devices developed in our laboratory, including modulators and detectors. These active plasmonic devices can be seamlessly integrated into existing Si optoelectronic circuits using standard CMOS technology. Introduction Silicon photonics, in which photonic devices are fabricated on silicon-on-insulator (SOI) platforms using mature CMOS technology, has been well developed recently for high-performance Si electronic-photonic integration circuits (EPICs) [1]. In particular, integrated Si modulators and Ge-on-Si detectors with performances competitive with those of their counterparts based on III–V semiconductors have been demonstrated [2, 3]. However, due to the fundamental diffractive limit of light in dielectric waveguides as well as the weak optical response of Si, the Si photonic devices suffer from large footprints. For example, Mach–Zehnder-based Si modulators, which are mostly implemented in Si EPICs, require a millimeter–scale length to reach π phase shift.

Using eddy power-flow formulation of electromagnetic fields, a very simple derivation is presented of the relationship between phase index N = c/νp and group index M = c/νg of guided modes in dielectric waveguides, where νp and νg are the phase and group velocities of the mode, and c is the velocity of light in free space.

Physical conductors (metals) that model adequately the behavior of a perfect conductor at microwave frequencies are too lossy at optical frequencies to provide low-loss enclosures. The same holds for reflectors. Whereas a metallic reflector is perfectly adequate at microwave frequencies, at optical frequencies reflectors have to be constructed using layered dielectrics of the proper thickness and dielectric constant. Total internal reflection is utilized in the construction of dielectric waveguides at microwave frequencies as well as at optical frequencies. At optical frequencies these dielectric waveguides are realized as fibers. Optical beams can also be contained in free space, if periodically refocused by lenses or mirrors. Optical resonators can be built with two or more curved mirrors that balance the diffraction of the beam bouncing back and forth and maintain a resonance mode in the space between the mirrors. The modes in dielectric waveguides and the modes of optical resonators share many of the properties of microwave waveguides and resonators discussed in the preceding chapter.KeywordsGaussian BeamPropagation ConstantKerr EffectDeterminantal EquationDielectric WaveguideThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.