One terahertz (THz) waveguide based on 3D printed metallic photonic crystals is experimentally and numerically demonstrated in 0.1-0.6 THz, which consists of periodic metal rod arrays (MRAs). Results demonstrated that such waveguide supports two waveguide modes such as fundamental and high-order TM-modes. The high-order TM-mode shows high field confinement, and it is sensitive to the geometry changes. By tuning the metal rod interspace, the spectral positions, bandwidths, and transmittances of the high-frequency band can be optimized. The investigation shows that a mode conversion between high-order modes occurs when the MRAs symmetry is broken via change the air interspace.
Optical waveguide segments based on geometrically unbound photonic crystal fibers (PCF) designs could be exploited as building blocks to realize miniaturized complex devices which implement advanced photonic operations. Here, we show how to fabricate optical waveguide segments with PCF designs by direct high-resolution 3D printing and how the combination of these segments can realise complex photonic devices. We demonstrate the unprecedented precision and flexibility of our method by fabricating the first-ever fiber polarising beam splitter based on PCFs. The device was directly printed in one…
A Bragg waveguide-based resonant fluidic sensor operating in THz band is studied. A fused deposition modeling 3D printing technique is employed to fabricate the sensor where the liquid analyte is flowing in the microfluidic channel integrated into the waveguide cladding. The analyte refractive index-dependent resonant defect state supported by the fluidic channel is probed by tracking the resulting absorption dip and phase change of the core-guided mode on waveguide transmission spectra. The proposed fluidic sensor can open new opportunities in applied chemical and biological sensing as it off…
Mechanical tuning of a 3D-printed, polymer-based one-dimensional photonic crystal was demonstrated in the terahertz spectral range. The investigated photonic crystal consists of 13 alternating compact and low-density layers and was fabricated through single-step stereolithography. While the compact layers are entirely polymethacrylate without any intentional internal structures, the low-density layers contain sub-wavelength sized slanted columnar inclusions to allow the mechanical compression in a direction normal to the layer interfaces of the photonic crystal. Terahertz transmission spectros…
Quantum-dot (QD) nanolasers integrated on a silicon photonic circuit are demonstrated for the first time. QD nanolasers based on one-dimensional photonic crystal nanocavities containing InAs/GaAs QDs are integrated on CMOS-processed silicon waveguides cladded by silicon dioxide. We employed transfer-printing, whereby the three-dimensional stack of photonic nanostructures is assembled in a simple pick-and-place manner. Lasing operation and waveguide-coupling of an assembled single nanolaser are confirmed through micro-photoluminescence spectroscopy. Furthermore, by repetitive transfer-printing,…
Invisibility cloak capable of hiding an object can be achieved by properly manipulating electromagnetic field. Such a remarkable ability has been shown in transformation and ray optics. Alternatively, it may be realistic to create a spatial cloak by means of confining electromagnetic field in three-dimensional arrayed waveguides and introducing appropriate collective curvature surrounding an object. We realize the artificial structure in borosilicate by femtosecond laser direct writing, where we prototype up to 5000 waveguides to conceal millimeter-scale volume. We characterize the performance…
In this paper we describe an application of the finite difference method to obtain the transverse magnetic photonic band gap diagram of a photonic crystal. The strategy of this method is to formulate the Maxwell equations in finite differences in order to write a computational code. We present experiments that confirm the validity of the calculations of the photonic band diagram as well as the refraction indix of such structure. All calculations were made for two dimensional metallic photonic crystal.
We investigate numerically Fano resonances excited in periodic arrays of dielectric, metallic and left-handed cylinders. Of particular interest are Fano resonances excited in the linear array of cylin- ders. We analyze spatial distribution and symmetry of electromagnetic field and discuss the relation between observed Fano resonances and frequency spectra of two-dimensional arrays of cylinders.
A metamaterial with a negative effective index of refraction is made from a three-dimensional hexagonal lattice photonic crystal with a metallic basis embedded in foam. It has been simulated with Ansoft HFSSTM in a frequency range from 7.0 to 12.0 GHz. Simulated results tested experimentally and negative refraction verified in some frequencies. Experimental results are in excellent agreement with simulations.
Complex photonic band structures (CPBS) of transmission metallic gratings with rectangular slits are shown to exhibit strong discontinuities that are not evidenced in the usual energetic band structures. These discontinuities are located on Wood's anomalies and reveal unambiguously two different types of resonances, which are identified as horizontal and vertical surface-plasmon resonances. Spectral position and width of peaks in the transmission spectrum can be directly extracted from CPBS for both kinds of resonances.
Compact and low-loss photonic crystal waveguides are critical in integrated terahertz (THz) applications. Compared with pure metal or dielectric photonic crystal waveguides, hybrid (metal-dielectric) integrated waveguides provide a simple way to further improve the field confinement and the propagation loss. In this work, we investigate a hybrid waveguide consisting of metallic photonic crystals and dielectric films in 0.1-1.0 THz. Photonic crystal waveguides based on metal pillar arrays (MPAs) support two resonance modes including the fundamental and high-order transverse magnetic (TM) modes …
We develop a theory to compute and interpret the photonic band structure of a periodic array of metallic helices for the first time. Interesting features of band structure include the ingenuous longitudinal and circularly polarized eigenmodes, the wide polarization gap [Science 325, 1513 (2009)], and the helical symmetry guarantees the existence of negative group velocity bands at both sides of the polarization gap and band crossings pinned at the zone boundary with fixed frequencies. A direct proof of negative refraction via a chiral route [Science 306, 1353 (2004)] is achieved for the first …
Multi-photon lithography allows to complement planar photonic integrated circuits (PIC) by in-situ 3D-printed freeform waveguide structures. However, design and optimization of such freeform waveguides using time-domain Maxwell's equations solvers often requires comparatively large computational volumes, within which the structure of interest only occupies a small fraction, thus leading to poor computational efficiency. In this paper, we present a solver-independent transformation-optics-(TO-) based technique that allows to greatly reduce the computational effort related to modeling of 3D free…
We theoretically study the interactions between plasmonic and photonic modes within a structure that is composed of two thin corrugated metallic plates, embedded in air. We show that the interactions depend upon the symmetry of the interacting modes. This observation is explained by the phase difference between the Fourier components of the two gratings. The phase can be controlled by laterally shifting one grating with respect to the other. Therefore, this relative shift provides an efficient "knob" that allows to control the interaction between the various modes, resulting in an efficient mo…
Photonic components based on structured metallic elements show great potential for device applications where field enhancement and confinement of the radiation on a subwavelength scale is required. In this paper we report a detailed study of a prototypical metallo-dielectric photonic structure, where features well known in the world of dielectric photonic crystals, like band gaps and defect modes, are exported to the metallic counterpart, with interesting applications to infrared science and technology, as for instance in quantum well infrared photodetectors, narrow-band spectral filters, and …
Frequency and transmission spectrum of two-dimensional array of metallic rods is investigated numerically. Based on the recent analysis of the band structure of two-dimensional photonic crystal with dielectric rods [P. Markoš, Phys. Rev. A 92 043814 (2015)] we identify two types of bands in the frequency spectrum: Bragg (P) bands resulting from a periodicity and Fano (F) bands which arise from Fano resonances associated with each of the cylinders within the periodic structure. It is shown that the existence of Fano band in a certain frequency range is manifested by a Fano resonance in the tran…
Ordinary metallic photonic crystals (PCs) have photonic band gaps in which the density of states (DOS) is strongly modified. Thermal emission of photons can be suppressed and enhanced accordingly. We consider the thermal emission characteristics of a metallic photonic crystal slab with a tunable thickness which in the thick limit approaches that of a photonic crystal and in the thin limit approaches that of a textured surface. We find that a thick photonic crystal suppresses emission in a specific range while a thin slab suppresses low frequency emission.
The rings, spots and stripes found on some butterflies, Pachyrhynchus weevils, and many chameleons are notable examples of natural organisms employing photonic crystals to produce colorful patterns. Despite advances in nanotechnology, we still lack the ability to print arbitrary colors and shapes in all three dimensions at this microscopic length scale. Commercial nanoscale 3D printers based on two-photon polymerization are incapable of patterning photonic crystal structures with the requisite ~300 nm lattice constant to achieve photonic stopbands/ bandgaps in the visible spectrum and generate…
The light propagation through a stack of two media with different refractive indices, which are aligned according to different quasiperiodic sequences determined by metallic means, is studied using the transfer matrix method. The focus lies on the investigation of the influence of the underlying quasiperiodic sequence as well as the dependence of the transmission on the frequency, the incidence angle of the light wave and different ratios of the refractive indices. In contrast to a periodically aligned stack we find complete transmission for the quasiperiodic systems for a wide range of differ…
Recent numerical studies have demonstrated the possibility of achieving substantial enhancements in the transmission of transverse-electric-polarized electromagnetic fields through subwavelength slits in a thin metallic screen by placing single or paired metallic cut-wire arrays at a close distance from the screen. In this Letter, we report on the first experimental evidence of such extraordinary transmission phenomena, via microwave (X/Ku-band) measurements on printed-circuit-board prototypes. Experimental results agree very well with full-wave numerical predictions, and indicate an intrinsic…
We have calculated the photonic band structures of metallic inverse opals and of periodic linear chains of spherical pores in a metallic host, below a plasma frequency $ω_{\text{p}}$. In both cases, we use a tight-binding approximation, assuming a Drude dielectric function for the metallic component, but without making the quasistatic approximation. The tight-binding modes are linear combinations of the single-cavity transverse magnetic (TM) modes. For the inverse-opal structures, the lowest modes are analogous to those constructed from the three degenerate atomic p-states in fcc crystals. For…
Dense and efficient circuits with component sizes approaching the physical limit is the hallmark of high performance integration. However, current fabrication technology is mostly constraint to 2D lithography, and thermal energy dissipation induced by switching electronic signal lines presents a fundamental challenge for truly 3D electronic integration. Photonics reduces this problem, and direct laser writing of a photoresin is a promising high-resolution tool for 3D photonic integration. Here, we combine one and two-photon polymerization (TPP) for waveguide integration for the first time, dra…
Due to their large electric conductivity, stand-alone metallic films are highly reflective at microwave frequencies. For this reason, it is nearly impossible to observe Faraday rotation in ferromagnetic metal layers, even in films just tens of nanometers thick. Here, we show using numerical simulations that a stack of cobalt nano-layers interlaced between dielectric layers can become highly transmissive and display a large Faraday rotation in a finite frequency band. A 45-degree Faraday rotation can be achieved with metallic ferromagnetic layers as thin as tens of nanometers.
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 …
Weyl points are point degeneracies that occur in momentum space of periodic materials, and are associated with a quantized topological charge. We experimentally observe in a 3D micro-printed photonic crystal that a charge-2 Weyl point can be split into two charge-1 Weyl points as the protecting symmetry of the original charge-2 Weyl point is broken. Moreover, we use a theoretical analysis to confirm where the charge-1 Weyl points move within the Brillouin zone as the strength of the symmetry breaking increases, and confirm it in experiments using Fourier-transform infrared spectrometry. This m…
Photonic waveguides are prime candidates for integrated and parallel photonic interconnects. Such interconnects correspond to large-scale vector matrix products, which are at the heart of neural network computation. However, parallel interconnect circuits realized in two dimensions, for example by lithography, are strongly limited in size due to disadvantageous scaling. We use three dimensional (3D) printed photonic waveguides to overcome this limitation. 3D optical-couplers with fractal topology efficiently connect large numbers of input and output channels, and we show that the substrate's f…
Here, the frequency degree of freedom is introduced into valley photonic crystals with dual band gaps. Based on the high-order plane wave expansion model, we derive an effective Hamiltonian which characterizes dual band gaps. Metallic valley photonic crystals are demonstrated as examples in which all four topological phases are found. At the domain walls between topologically distinct valley photonic crystals, frequency-dependent edge states are demonstrated and a broadband photonic detouring is proposed. Our findings provide the guidance for designing the frequency-dependent property of topol…
We propose a new paradigm for realizing bound states in the continuum (BICs) by engineering the environment of a system to control the number of available radiation channels. Using this method, we demonstrate that a photonic crystal slab embedded in a photonic crystal environment can exhibit both isolated points and lines of BICs in different regions of its Brillouin zone. Finally, we demonstrate that the intersection between a line of BICs and line of leaky resonance can yield exceptional points connected by a bulk Fermi arc. The ability to design the environment of a system opens up a broad …
Optical cavities, plasmonic structures, photonic band crystals, interfaces, as well as, generally speaking, any photonic media with homogeneous or spatially inhomogeneous dielectric permittivity (including metamaterials) have local densities of photonic states, which are different from that in vacuum. These modified density of states environments are known to control both the rate and angular distribution of spontaneous emission. In the present study, we ask the question whether the proximity to metallic and metamaterial surfaces can affect other physical phenomena of fundamental and practical…
We discuss optical forces exerted on particles, either dielectric or metallic, near a subwavelength slit illuminated by a photonic nanojet. We compare those cases in which the Mie resonances are or are not excited. The configurations on study are 2D, hence those particles are infinite cylinders and, in order to obtain extraordinary transmission, the illuminating beam is p-polarized. We show the different effects of these particle resonances on the optical forces: while whispering gallery modes under those illumination conditions weaken the force strength, this latter is enhanced by localized p…
Most dielectric materials have very weak electro-optic properties, whereas the optical properties of some plasmonic materials may be greatly tuned, especially around their plasma frequency, where dielectric constant is transiting between positive ("dielectric state") and negative ("metallic state") values. In this report, we will review some of our recent work on electro-optical modulation and introduce a new concept, photonic MOS based on "optical property inversion". This concept may provide inspiration for the development of nanophotonic devices. Some of the material was adapted from unfund…
We propose an efficient multiband absorber comprising a truncated one-dimensional periodic metal-dielectric photonic crystal and a reflective substrate. The reflective substrate is actually an optically thick metallic film. Such a planar device is easier to fabricate compared with the absorbers with complicated shapes. For a 4-unit cell device, all of the four absorption peaks can be optimized with efficiencies higher than 95%. Moreover, those absorption peaks are insensitive to both polarization and incident angle. The influences of the geometrical parameters along with the refractive index o…
Optical properties of metallic nanoparticles are most often considered in terms of plasmons, the coupled states of light and quasi-free electrons. Here we predict that confinement of electrons inside the nanostructure leads to another, very different, type of resonance, which determines the optical properties in the frequency range significantly below the plasmonic resonance. We demonstrate that closely placed confinement-induces resonances typically join into a single composite "super-resonance" which produces giant nonlinearity at low frequencies. Our simulations show how such nonlinearities…
A localized defect mode in a photonic-layered structure develops nodal points. Placing a thin metallic layer at such a nodal point results in the phenomenon of induced transparency. We demonstrate that if this nodal point is not a point of symmetry, then even a tiny alteration of the permittivity in the vicinity of the defect suppresses the localized mode along with the resonant transmission; the layered structure becomes highly reflective within a broad frequency range. Applications of this hypersensitive transport for optical limiting and switching are discussed.
Thermo-optic microheater is indispensable in silicon photonic devices for smart and reconfigurable photonic networks. Much efforts have been made to improve the metallic microheater performance in the past decades. However, because of the metallic nature of light absorption, placing the metallic microheater very close to the waveguide for fast response is impractical and has not been done experimentally. Here, we experimentally demonstrate a metallic microheater placed very close to the waveguide based on parity-time (PT) symmetry breaking. The intrinsic high loss of metallic heater ensures th…
Implementation of topology on photonics has opened new functionalities of photonic systems such as topologically protected boundary modes. We present polarization-dependent topological properties in 2D Su-Schrieffer-Heeger lattice by using a metallic nanoparticle array and considering the polarization degree of freedom. We demonstrate that when eigenmodes are polarized parallel to the plane of the 2D lattice, it supports isolated longitudinal edge modes and transverse modes that are hidden from the projected bulk states. Also, the in-plane polarized modes support a second-order topological pha…
We propose a design of two-dimensional bi-anisotropic meta-waveguide exhibiting topologically nontrivial photonic phase and robust photonic transport. The structure proposed represents a waveguide formed by a periodic array of metallic cylinders placed inside parallel metal plates and is designed to support two pairs of Dirac cones thus allowing emulation of the spin of the electrons in condensed matter systems. It is shown, that by making the meta-waveguide bi-anisotropic one can mimic the spin-orbital interaction in topological insulators and open a complete photonic topological band gap. Fi…
In this paper we study numerically and experimentally the possibility of using metallic photonic crystals (PCs) of different geometries (log-piles, direct and inverse opals) as visible light sources. It is found that by tuning geometrical parameters of a direct opal PC one can achieve substantial reduction of the emissivity in the infrared along with its increase in the visible. We take into account disorder of the PC elements in their sizes and positions, and get quantitative agreement between the numerical and experimental results. We analyze the influence of known temperature-resistant refr…
Because surface plasmons can be confined below the diffraction limit, metallic lasers that support plasmonic modes can provide miniaturized sources of electromagnetic waves. Such devices often exploit a multilayer design, in which a semiconductor gain layer is placed near a metallic interface with a gap layer in between. However, despite many experimental demonstrations, key considerations for these planar metallic lasers remain understudied, leading to incorrect conclusions about the optimal design. Here, we pursue a detailed experimental and theoretical study of planar metallic lasers to exp…
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 eng…
Controlled integration of metallic nanoparticles (NPs) onto photonic nanostructures enables realization of complex devices for extreme light confinement and enhanced light-matter interaction. This can be achieved combining Nanoparticle-on-Mirror (NPoM) nanocavities with the light manipulation capabilities of micron-scale metallic antennas and/or photonic integrated waveguides. However, metallic nanoparticles are usually deposited via drop-casting, which prevents their accurate positioning. Here we present a methodology for precise transfer and positioning of individual NPs onto different photo…
We present here the transmission of electromagnetic waves through layered structures of metallic and left-handed media. Based on the theory of finite periodic systems, we show that besides the strong influence of the incidence angle, the low transmission characteristic of a single conductor slab, for frequencies $ω$ below the plasma frequency $ω_p$, becomes in this domain highly oscillating. Similarly, the well-established transmission coefficient of a single left-handed slab becomes highly resonant with superluminal effects in superlattices with more than one unit cell. We determine the space…
The Single Gyroid, or srs, nanostructure has attracted interest as a circular-polarisation sensitive photonic material. We develop a group theoretical and scattering matrix method, applicable to any photonic crystal with symmetry I432, to demonstrate the remarkable chiral-optical properties of a generalised structure called 8-srs, obtained by intergrowth of eight equal-handed srs nets. Exploiting the presence of four-fold rotations, Bloch modes corresponding to the irreducible representations E- and E+ are identified as the sole and non-interacting transmission channels for right- and left-cir…
We investigated on the interface modes in a heterostructure consisting of a semi-infinite metallic layer and a semi-infinite Fibonacci quasi-periodic structure. Various properties of the interface modes, such as their spatial localizations, self-similarities, and multifractal properties are studied. The interface modes decay exponentially in different ways and the modes in the lower stable gap possess highest spatial localization. A localization index is introduced to understand the localization properties of the interface modes. We found that the localization index of the interface modes in t…
Emerging technology based on artificial materials containing metallic structures has raised the prospect for unprecedented control of terahertz waves through components like filters, absorbers and polarizers. The functionality of these devices is static by the very nature of their metallic or polaritonic composition, although some degree of tunability can be achieved by incorporating electrically biased semiconductors. Here, we demonstrate a photonic structure by projecting the optical image of a metal mask onto a thin GaAs substrate using a femtosecond pulsed laser source. We show that the re…
We developed a technique that enables to replace a metallic waveguide cladding with a low-index (n $\sim$ 1.4) material - CaF2 or BaF2 - that in addition is transparent from the mid-IR up to the visible range: elevated confinement is preserved while introducing an optical entryway through the substrate. Replacing the metallic backplane also allows double-side patterning of the active region. Using this approach, we demonstrate strong light-matter coupling between an intersubband transition (lambda $\sim$ 10 microns) and a dispersive resonator, at 300 K and at 78 K. Finally, we evaluate the pot…
Inspired by complete graph theory, we demonstrate that a metallic claw "meta-atom" structure can carry a high number of nearly degenerate resonant modes. A photonic meta-crystal composing of a lattice of such meta-atoms exhibits a large number of flat bands that are squeezed into a narrow frequency window, and these flat bands can be designed to locate in a wide complete 3D bandgap. The degeneracy dimension (Nf) of the flat bands is determined by the number of branches (Nb) of the metallic claw with Nf=Nb-3, which is geometrically related to the complete graph theory. Different from those flat…
The phenomenon of trapping broad spectrum of light is known as `rainbow trapping' and achieved using all-dielectric, hybrid metallo-dielectric or all-metallic configurations. In the latter cases, unavoidable ohmic losses result in sub-picosecond trapped-mode lifetimes. For all practical purposes, novel strategies are required to be devised for trapping and subsequently, releasing broadband electromagnetic (em) field with lifetime > 1 ps. We present a rainbow trapping configuration using the excitation of multiple optical Tamm (OT) modes in an one-dimensional chirped photonic crystal (PC) desig…
We have studied spectral properties of a cholesteric liquid crystal with a combined defect consisting of a nanocomposite layer and a twist. The nanocomposite layer is made of metallic nanoballs dispersed in a transparent matrix and featuring effective resonant permittivity. A solution has been found for the transmission spectrum of circularly polarized waves in the structure. We have analyzed spectral splitting of the defect mode in the bandgap of the cholesteric when its frequency coincides with the nanocomposite resonant frequency. Defect modes have characteristics strongly dependent on the …
