The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

http://ieeexplore.ieee.org/iel5/6354/16969/00781867.pdf

Photonic crystals

Graphene plasmons were predicted to possess ultra-strong field confinement and very low damping at the same time, enabling new classes of devices for deep subwavelength metamaterials, single-photon nonlinearities, extraordinarily strong light-matter interactions and nano-optoelectronic switches. While all of these great prospects require low damping, thus far strong plasmon damping was observed, with both impurity scattering and many-body effects in graphene proposed as possible explanations. With the advent of van der Waals heterostructures, new methods have been developed to integrate graphene with other atomically flat materials. In this letter we exploit near-field microscopy to image propagating plasmons in high quality graphene encapsulated between two films of hexagonal boron nitride (h-BN). We determine dispersion and particularly plasmon damping in real space. We find unprecedented low plasmon damping combined with strong field confinement, and identify the main damping channels as intrinsic thermal phonons in the graphene and dielectric losses in the h-BN. The observation and in-depth understanding of low plasmon damping is the key for the development of graphene nano-photonic and nano-optoelectronic devices.

Highly confined low-loss plasmons in graphene-boron nitride heterostructures

We describe the history, guiding mechanism, recent advances, applications, and future prospects for hollow-core negative curvature fibers. We first review one-dimensional slab waveguides, two-dimensional annular core fibers, and negative curvature tube lattice fibers to illustrate the inhibited coupling guiding mechanism. Antiresonance in the glass at the core boundary and a wavenumber mismatch between the core and cladding modes inhibit coupling between the modes and have led to remarkably low loss in negative curvature fibers. We also summarize recent advances in negative curvature fibers that improve the performance of the fibers, including negative curvature that increases confinement, gaps between tubes that increase confinement and bandwidth, additional tubes that decrease mode coupling, tube structures that suppress higher-order modes, nested tubes that increase guidance, and tube parameters that decrease bend loss. Recent applications of negative curvature fibers are also presented, including mid-infrared fiber lasers, micromachining, and surgical procedures. At the end, we discuss the future prospects for negative curvature fibers.

Negative curvature fibers

종격동 종양 및 낭종 27례에 대한 임상적 고찰

The application of topology in optics has led to a new paradigm in developing photonic devices with robust properties against disorder Although considerable progress on topological phenomena has been achieved in the classical domain, the realization of strong light-matter coupling in the quantum domain remains unexplored We demonstrate a strong interface between single quantum emitters and topological photonic states Our approach creates robust counterpropagating edge states at the boundary of two distinct topological photonic crystals We demonstrate the chiral emission of a quantum emitter into these modes and establish their robustness against sharp bends This approach may enable the development of quantum optics devices with built-in protection, with potential applications in quantum simulation and sensing

A topological quantum optics interface

Compact and robust waveguide chips are crucial for new integrated terahertz applications, such as high-speed interconnections between processors and broadband short-range wireless communications. Progress on topological photonic crystals shows potential to improve integrated terahertz systems that suffer from high losses around sharp bends. Robust terahertz topological transport through sharp bends on a silicon chip has been recently reported over a relatively narrow bandwidth. Here, we report the experimental demonstration of topological terahertz planar air-channel metallic waveguides which can be integrated into an on-chip interconnect. Our platform can be fabricated by a simple, cost-effective technique combining 3D-printing and gold-sputtering. The relative size of the measured topological bandgap is ~12.5%, which entails significant improvement over all-silicon terahertz topological waveguides (~7.8%). We further demonstrate robust THz propagation around defects and delay lines. Our work provides a promising path towards compact integrated terahertz devices as a next frontier for terahertz wireless communications.

3D-Printed Terahertz Topological Waveguides

We propose a novel M-shaped single mode fiber (M-SMF) sensor based on stimulated Brillouin scattering of higher-order acoustic modes for simultaneous temperature and strain measurement. Numerical investigation of longitudinal acoustic modes in the M-SMF shows that multi-peak Brillouin spectrum in M-SMF is contributed by the couplings between the LP01 optical mode and multiple acoustic modes. The Brillouin characteristics in the M-SMF are compared with those of standard single mode fiber. Utilizing the multi-peak feature of Brillouin gain spectrum, sensing characteristics of the M-SMF under different temperature and strain conditions were studied. Thanks to the widely spaced $L_{01}$ and $L_{02}$ acoustic mode peaks in the Brillouin spectrum of M-SMF, the proposed fiber enables discriminative sensing of temperature and strain at an accuracy of 0.47 °C and $12.3~{\mu \varepsilon }$ , respectively.

Simultaneous Temperature and Strain Sensing Based on M-Shaped Single Mode Fiber

We design a hollow-core terahertz (THz) waveguide guiding a single linearly polarized mode. This is achieved using a hybrid cladding, where we introduce a ring of subwavelength structures, including metal wires and air-holes. The wire-based cladding is extremely anisotropic, reflecting only transverse magnetic (TM) modes. The polarization of TM modes is further manipulated by replacing some wires with air-holes. Numerical simulations confirm the guidance of only an x-polarized TM2 mode over 0.36–0.46 THz in a wavelength-scale core (diameter of 1 mm). The propagation losses are of the order 0.25  dB/cm, with low bend losses <0.3  dB/cm at 0.4 THz for a bend radius of 5 cm.

Linearly polarized single TM mode terahertz waveguide.

In this Letter, we investigate the nanofocusing of hybrid plasmons-phonons-polaritons (SPP-HPhPs) in a graphene-hexagonal boron nitride (h-BN) heterostructure with a graphene coating on a tapered h-BN slab. Compared with the hyperbolic phonon polariton (HPhP) in h-BN, the hybrid SPP-HPhP in a heterostructure exhibits much smaller losses, which is validated through both analytical and numerical methods. Furthermore, the thickness dependent dispersions of a hybrid SPP-HPhP enable the tapered heterostructure to achieve a function of focusing electromagnetic waves. Compared with the tapered h-BN slab, the field enhancement in a tapered heterostructure is improved evidently with a maximum enhancement of the amplitude of normalized electric field over 60. This nanofocusing scheme may have potential in applications such as nonlinear optics.

Nanofocusing of hybrid plasmons-phonons-polaritons in a graphene-hexagonal boron nitride heterostructure.

We propose and numerically analyze a tunable nanomechanical plasmonic filter based on Bragg-grating-assisted gold–air–gold gap plasmon (GP) waveguide. Bragg grating is formed by introducing periodical grooves on lower gold layers, and the air-gap size is mechanically changeable by electrostatically actuating the upper gold layer. Using the sensitivity of the GP mode to the gap size, the tunability of the proposed filter is realized by changing the gap size. By introducing a phase shift in the Bragg grating, sharp transmission peak with a quality factor of 35 is achieved within the stopband, which could be tuned over a wide wavelength range by a small change in the gap size. The proposed filter can be applied in the tunable plasmonic devices for future integrated optical circuits.

Haisu Li

Papers

3D-Printed Terahertz Topological Waveguides

Simultaneous Temperature and Strain Sensing Based on M-Shaped Single Mode Fiber

Linearly polarized single TM mode terahertz waveguide.

Nanofocusing of hybrid plasmons-phonons-polaritons in a graphene-hexagonal boron nitride heterostructure.

Nanomechanical Plasmonic Filter Based on Grating-Assisted Gap Plasmon Waveguide