A rod-type photonic crystal (PC) with a rectangular lattice shows a large-angle quasi-self-collimation (quasi-SC) effect by changing the symmetry of its rectangular lattice to straighten one of the isofrequency contours. To investigate the straightness of the isofrequency contour as well as the quasi-SC effect, we propose a straightness factor L based on the method of least squares. With L smaller than L0 (L0 = 0.01 is the critical value), the isofrequency contour is sufficiently straight to induce quasi-SC effect with the beam quasi-collimating in the structure. Furthermore, the efficiency of light coupling to the quasi-SC PC is studied, and can be greatly improved by applying a carefully designed antireflection layer.
I studied experimentally the beam self-collimation and splitting in two-dimensional microwave photonic crystals. Using a microwave photonic crystal fabricated from alumina rods, I present an experimental proof of principle for an earlier theoretical proposal [A. Matthews et al., Opt. Commun. 279, 313 (2007)] of a photonic crystal beam splitter based on the self-collimation effect.
We demonstrate a mesoscopic self-collimation effect in photonic crystal superlattices consisting of a periodic set of all-positive index 2D photonic crystal and homogeneous layers. We develop an electromagnetic theory showing that diffraction-free beams are observed when the curvature of the optical dispersion relation is properly compensated for. This approach allows to combine slow light regime together with self-collimation in photonic crystal superlattices presenting an extremely low filling ratio in air.
We investigate the optical properties of a photonic crystal composed of a quasi-one-dimensional flat-band lattice array through finite-difference time-domain simulations. The photonic bands contain flat bands (FBs) at specific frequencies, which correspond to compact localized states as a consequence of destructive interference. The FBs are shown to be nondispersive along the $Γ\rightarrow X$ line, but dispersive along the $Γ\rightarrow Y$ line. The FB localization of light in a single direction only results in a self-collimation of light propagation throughout the photonic crystal at the FB f…
We report the observation of a large-angle self-collimation phenomenon occurring in photonic crystals composed of nanorods. Electromagnetic waves incident onto such photonic crystals from directions covering a wide-range of incident angles become highly localized along a single array of rods, which results in narrow-beam propagation without divergence. A propagation length of 0.4 mm is experimentally observed over the wavelength range of 1540 nm to 1570 nm, even in the large incident angle case, which is a very considerable length scale for on-chip optical interconnection.
We suggest a novel type of photonic structures where the strength of diffraction can be managed in a very broad frequency range. We introduce optimized arrays of curved waveguides where light beams experience wavelength-independent normal, anomalous, or zero diffraction. Our results suggest novel opportunities for efficient self-collimation, focusing, and reshaping of beams produced by white-light and super-continuum sources. We also show how to manipulate light patterns through multicolor Talbot effect, which is possible neither in free space nor in conventional photonic lattices.
Metasurfaces provide the disruptive technology enabling miniaturization of complex cascades of optical elements on a plane. We leverage the benefits of such a surface to develop a planar integrated photonic beam collimator for on-chip optofluidic sensing applications. While most of the current work focuses on miniaturizing the optical "detection" hardware, little attention is given to develop on-chip hardware for optical "excitation". In this manuscript, we propose a flat metasurface for beam collimation in optofluidic applications. We implement an inverse design approach to optimize the metas…
Three-dimensional complete photonic bandgap materials or photonic crystals block light propagation in all directions. The rod-connected diamond structure exhibits the largest photonic bandgap known to date and supports a complete bandgap for the lowest refractive index contrast ratio down to $n_{high}/n_{low} \sim 1.9$. We confirm this threshold by measuring a complete photonic bandgap in the infrared region in Sn--S--O $(n\sim1.9)$ and Ge--Sb--S--O $(n\sim2)$ inverse rod-connected diamond structures. The structures were fabricated using a low-temperature chemical vapor deposition process via …
We show that it is possible to confine light in a volume of order 10^-3 cubic wavelengths using only dielectric material. Low-index (air) cavities are simulated in high index rod-connected diamond (RCD) photonic crystals. These cavities show long storage times (Q-factors >10^6) even at the lowest volumes. Fabrication of such structures could open up a new field of photon level interactions.
We present the simulation, fabrication, and optical characterization of low-index polymeric rod-connected diamond (RCD) structures. Such complex three-dimensional photonic crystal structures are created via direct laser writing by two-photon polymerization. To our knowledge, this is the first measurement at near-infrared wavelengths, showing partial photonic bandgaps for this structure. We characterize structures in transmission and reflection using angular resolved Fourier image spectroscopy to visualize the band structure. Comparison of the numerical simulations of such structures with the e…
We measured and calculated transmission spectra of two-dimensional quasiperiodic photonic crystals (PCs) based on a 5-fold (Penrose) or 8-fold (octagonal) symmetric quasiperiodic pattern. The photonic crystal consisted of dielectric cylindrical rods in air placed normal to the basal plane on vertices of tiles composing the quasiperiodic pattern. An isotropic photonic band gap (PBG) appeared in the TM mode, where electric fields were parallel to the rods, even when the real part of a dielectric constant of the rod was as small as 2.4. An isotropic PBG-like dip was seen in tiny Penrose and octag…
Interface states in photonic crystals (PCs) have attracted attention for the special properties, such as high transmission efficiency in bend waveguides, and their generation related to the topological phase. Previous works on interface states in PCs were mainly based on the square lattice, the honeycomb lattice or the triangular lattice, but with different materials, shapes, or sizes of rods resulting in the complicated structure. In this paper, an interface is constructed by two 2D PCs with different rectangular lattices, but the same materials, shapes, and sizes of dielectric rods, which ge…
Micro-/nanocavities that combine high quality factor ($Q$) and small mode volume ($V$) have been used to enhance light-matter interactions for cavity quantum electrodynamics (cQED). Whispering gallery mode (WGM) geometries such as microdisks and microrings support high-$Q$ and are design- and fabrication-friendly, but $V$ is often limited to tens of cubic wavelengths to avoid WGM radiation. The stronger modal confinement provided by either one-dimensional or two-dimensional photonic crystal defect geometries can yield sub-cubic-wavelength $V$, yet the requirements on precise design and dimensi…
The PhD thesis is devoted to the study of second harmonic generation of narrow beams in photonic crystals. The basic idea is that if both frequencies, the fundamental and second harmonics are in the region of self-collimation, then the second harmonics of narrow beams can be very efficient. The beams do not spread diffractively during propagation and interaction. The phase matching is ensured for all components of the interacting beams. This allows to enhance the nonlinear interaction efficiency several times. The thesis rewises the theory of self-collimation of narrow beams in photonic crysta…
The optical transmission of resonant guided-mode gratings patterned on suspended silicon nitride thin films and illuminated at normal incidence with a Gaussian beam are investigated both experimentally and theoretically. Effects due to the beam focusing and its finite size are accounted for by a phenomenological coupled mode model whose predictions are found to be in very good agreement with the experimentally measured spectra for various grating structures and beam sizes, and which allow for a detailed analysis of the respective magnitude of these effects. These results are highly relevant fo…
Using an extended plane-wave-based transfer-matrix method, the photonic band structures and the corresponding transmission spectrum of a two-dimensional left-handed photonic crystal are calculated. Comparisons between the periodic structure with a single left-handed cylindric rod are made, and many interesting similarities are found. It is shown that, due to the localized surface polaritons presented by an isolated left-handed rod, there exist many exciting physical phenomena in high-dimensional left-handed photonic crystals. As direct results of coupling of the localized surface polaritons of…
We study the bandgap properties of two-dimensional photonic crystals created by a lattice of rods or holes conformed in a symmetric or asymmetric triangular structure. Using the plane-wave analysis, we calculate a minimum value of the refractive index contrast for opening both partial and full two-dimensional spectral gaps for both TM and TE polarized waves. We also analyze the effect of ellipticity of rods and holes and their orientation on the threshold value and the relative size of the bandgap.
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…
Defect cavities in 3D photonic crystal can trap and store light in the smallest volumes allowable in dielectric materials, enhancing non-linearities and cavity QED effects. Here, we study inverse rod-connected diamond (RCD) crystals containing point defect cavities using plane-wave expansion and finite-difference time domain methods. By optimizing the dimensions of the crystal, wide photonic band gaps are obtained. Mid-bandgap resonances can then be engineered by introducing point defects in the crystal. We investigate a variety of single spherical defects at different locations in the unit ce…
We study theoretically light propagations at the zigzag edge of a honeycomb photonic crystal consisting of dielectric rods in air, analogous to graphene. Within the photonic band gap of the honeycomb photonic crystal, a unimodal edge state may exist with a sharp confinement of optical fields. Its dispersion can be tuned simply by adjusting the radius of the edge rods. For the edge rods with a graded variation in radius along the edge direction, we show numerically that light beams of different frequencies can be trapped sharply in different spatial locations, rendering wideband trapping of lig…
In this paper, we propose an all-optical high-speed half adder based on linear defects in a photonic crystal (PhC) structure composed of silicon rods. The proper design of half adder results in no need to increase the intensity of the input optical signal for the appearance of the nonlinear Kerr effect, which leads to diverting the incoming light toward the desired output. The proposed device consists of four optical waveguides and a defect in a square lattice PhC. Two famous plane wave expansion and finite difference time domain methods are used to study and analyze photonic band structure an…
We consider meta materials made from a two-dimensional dielectric rod-type photonic crystal. The magnetic response is studied within the recently developed homogenization theory and we in particular study the effects of topology and inhomogeneous broadening. While topology itself mainly affects the Mie resonance frequency we find that the dispersion in the topological radius R of the dielectric rods may lead to significant inhomogeneous broadening and suppression of the negative-mu phenomena for dR/R0 >> epsilon''/epsilon', with epsilon=epsilon'+i*epsilon'' being the relative dielectric functi…
We have measured the photonic bandgap in the transmission of microwaves through a two-dimensional photonic crystal slab. The structure was constructed by cementing acrylic rods in a hexagonal closed-packed array to form rectangular stacks. We find a bandgap centered at approximately 11 GHz, whose depth, width and center frequency vary with the number of layers in the slab, angle of incidence and microwave polarization.
Thermophotovoltaic systems in principle enable utilization of heat that is usually regarded as wasted energy. However, the wavelength selectivity of the thermal emitter required for high efficiencies is rather difficult to control with conventional designs. Here, we design a thermophotovoltaic system comprising silicon rods as thermal emitter with a relatively narrow emission spectrum and a photovoltaic cell with a band gap corresponding to 1.76 $μ$m, and verify efficient power generation. By accurately measuring the heat flux that enters the emitter, the emitter temperature, and the electrica…
We study experimentally the Goos-Hanchen effect observed at the reflection of a self-collimated beam from the surface of a two-dimensional photonic crystal and describe a method for controlling the beam reflection through surface engineering. The microwave photonic crystal, fabricated from alumina rods, allows control of the output position of a reflected beam undergoing an internal Goos-Hanchen shift by changing the rod diameter at the reflection surface. The experimental data is in good agreement with the results of the finite-difference time-domain numerical calculations.
We propose a method to directly visualize the photonic band-structure of micron size photonic crystals using wide angle spectroscopy. By extending Fourier Imaging Spectroscopy sensitivity into the infrared range we have obtained accurate measurements of the band-structures along the high-symmetry directions (X-W-K-L-U) of polymeric three-dimensional rod-connected diamond photonic crystals. Our implementation also allows us to record single-wavelength reflectance far field patterns showing a very good agreement with simulations of the same designs. This technique is suitable for the characteriz…
We demonstrate that multiple higher-order topological transitions can be triggered via the continuous change of the geometry in kagome photonic crystals composed of three dielectric rods. By tuning a single geometry parameter, the photonic corner and edge states emerge or disappear with the higher-order topological transitions. Two distinct higher-order topological insulator phases and a normal insulator phase are revealed. Their topological indices are obtained from symmetry representations. A photonic analog of fractional corner charge is introduced to distinguish the two higher-order topolo…
In this study, we propose the application of non-Hermitian photonic crystals (PCs) with anisotropic emissions. Unlike a ring of exceptional points (EPs) in isotropic non-Hermitian PCs, the EPs of anisotropic non-Hermitian PCs appear as lines symmetrical about the $Γ$ point. The non-Hermitian Hamiltonian indicates that the formation of EPs is related to the non-Hermitian strength. The real spectrum appears in the $Γ$Y direction and has been validated as the complex conjugate medium (CCM) by effective medium theory (EMT). But for the $Γ$X direction, EMT indicates that the effective refractive in…
We propose a scheme for coupling 2D materials to an engineered cavity based on a defective rod type photonic crystal lattice. We show results from numerical modelling of the suggested cavity design, and propose using the height profile of a 2D material transferred on top of the cavity to maximise coupling between exciton recombination and the cavity mode. The photonic structure plays a key role in enhancing the launch efficiency, by improving the directionality of the emitted light to better couple it into an external optical system. When using the photonic structure, we measured an increase i…
We predict the existence of surface gap modes, known as Tamm states for electronic systems, in truncated photonic crystals formed by two types of dielectric rods. We investigate the energy threshold, dispersion, and modal symmetries of the surface modes, and also demonstrate the existence and tunability of nonlinear Tamm states in binary photonic crystals with nonlinear response.
We present a two-dimensional photonic crystal design with a microcavity of four defect dielectric rods with eigenfrequencies residing in the propagating band of directional waveguide. In the linear case for tuning of material parameters of defect rods the nonrobust bound state in the continuum (BSC) might occur. The BSC is a result of full destructive interference of resonant monopole and quadrupole modes with the same parity. % to trap light interior of the microcavity. A robust BSC arises in a self-adaptive way without necessity to tune the parameters of the microcavity with the Kerr effect.…
We present the key results from a comprehensive study of the refraction and focusing properties of a two-dimensional dodecagonal photonic ``quasicrystal'' (PQC), carried out via both full-wave numerical simulations and microwave measurements on a slab made of alumina rods inserted in a parallel-plate waveguide. We observe anomalous refraction and focusing in several frequency regions, confirming some recently published results. However, our interpretation, based on numerical and experimental evidence, differs substantially from the one in terms of ``effective negative refractive-index'' that w…
We report on the formation and development of the photonic band gap in two-dimensional 8-, 10- and 12-fold symmetry quasicrystalline lattices of low index contrast. Finite size structures made of dielectric cylindrical rods were studied and measured in the microwave region, and their properties compared with a conventional hexagonal crystal. Band gap characteristics were investigated by changing the direction of propagation of the incident beam inside the crystal. Various angles of incidence from 0 \degree to 30\degree were used in order to investigate the isotropic nature of the band gap. The…
The great interest to the two and three dimensionally periodic structures, called photonic crystals (PCs), has begun with the pioneer works of Yablonovitch and John as one can efficiently control the propagation of the electromagnetic (EM) waves in the same manner with semiconductors that affect the electron conduction. One of the main peculiar properties of PCs is that they have photonic band gap in the transmission spectrum similar to electronic band gap and hence, they are able to prevent the light to propagate in certain frequency regions irrespective of the propagation direction in space.…
We develop a model for the coupling of quasi-normal modes in open photonic systems consisting of two resonators. By expressing the modes of the coupled system as a linear combination of the modes of the individual particles, we obtain a generalized eigenvalue problem involving small size dense matrices. We apply this technique to dielectric rod dimmer of rectangular cross section for Transverse Electric (TE) polarization in a two-dimensional (2D) setup. The results of our model show excellent agreement with full-wave finite element simulations. We provide a convergence analysis, and a simplifi…
We present the controlled creation of single nitrogen-vacancy (NV) centers via ion implantation at the center of a photonic crystal cavity which is fabricated in an ultrapure, single crystal diamond membrane. High-resolution placement of NV centers is achieved using collimation of a 5keV-nitrogen ion beam through a pierced tip of an atomic force microscope (AFM). We demonstrate coupling of the implanted NV centers' broad band fluorescence to a cavity mode and observe Purcell enhancement of the spontaneous emission. The results are in good agreement with a master equation model for the cavity c…
In recent years, there have been rapid advances in the parallel fields of electronic and photonic topological crystals. Topological photonic crystals in particular show promise for coherent transport of light and quantum information at macroscopic scales. In this work, we apply for the first time the recently developed theory of "Topological quantum chemistry" to the study of band structures in photonic crystals. This method allows us to design and diagnose topological photonic band structures using only group theory and linear algebra. As an example, we focus on a family of crystals formed by…
In this paper we analyze theoretically how the introduction of the third component into the two-dimensional photonic crystal influences the photonic band structure and the density-of-states of the system. We consider the periodic array of cylindrical air rods in a dielectric, and the third medium is introduced as a ring-shaped intermediate layer between the air pores and the dielectric background. Using the plane wave method, we have obtained the band structures for the 2D triangular lattice photonic crystals. The dependencies of TE and TM band gaps' widths and gaps' edges position on the inte…
In a recent investigation, we studied two-dimensional point-defected photonic bandgap cavities composed of dielectric rods arranged according to various representative periodic and aperiodic lattices, with special emphasis on possible applications to particle acceleration (along the longitudinal axis). In this paper, we present a new study aimed at highlighting the possible advantages of using hybrid structures based on the above dielectric configurations, but featuring metallic rods in the outermost regions, for the design of extremely-high quality factor, bandgap-based, accelerating resonato…
We study the distribution of eigenfrequency spacings (the so-called level spacing statistics) for light in a two-dimensional (2D) disordered photonic crystal composed of circular dielectric (silicon) rods in air. Disorder introduces localized transverse-magnetic (TM) modes into the band gap of the ideal crystal. The level spacing statistics is found to approach the Poisson distribution for these modes. In contrast, for TM modes outside the band gap and for transverse-electric (TE) modes at all frequencies, the level spacing statistics follows the Wigner-Dyson distribution.
Transformation optics is used to design a gateway that can block electromagnetic waves but allows the passage of other entities. Our conceptual device has the advantage that it can be realized with simple materials and structural parameters and can have a reasonably wide bandwidth. In particular, we show that our system can be implemented by using a magnetic photonic crystal structure that employs a square ray of ferrite rods, and as the field response of ferrites can be tuned by external magnetic fields, we end up with an electromagnetic gateway that can be open or shut using external fields.…
University of Namur（南纳慕尔大学）；Institute of Condensed Matter and Nanosciences (IMCN), Université Catholique de Louvain (UCLouvain)（天主教鲁汶大学凝聚态与纳米科学研究所）；Cenaero（塞纳罗）
This study reports on the design of small footprint, integrated polarization filters based on engineered photonic lattices. Using a rods-in-air lattice as a basis for a TE filter and a holes-in-slab lattice for the analogous TM filter, we are able to maximize the degree of polarization of the output beams up to 98 % with a transmission efficiency greater than 75 %. The proposed designs allow not only for logical polarization filtering, but can also be tailored to output an arbitrary transverse beam profile. The lattice configurations are found using a recently proposed parallel tabu search alg…
We introduce a weakly coupled photonic crystal waveguide as a promising and realistic model for all-optical amplification. A symmetric pillar type coupled photonic crystal waveguide consisting of dielectric rods periodically distributed in a free space is proposed as all-optical amplifier. Using the unique features of the photonic crystals to control and guide the light, we have properly chosen the frequency at which only one mode (odd mode) becomes the propagating mode in the coupled photonic crystal waveguide, whereas another mode (even mode) is completely reflected from the guiding structur…
This study presents active beam steering and afocal zooming of light by incorporating liquid crystals (LCs) with graded index photonic crystal (GRIN PC). The GRIN PC structures are composed of low refractive index polymer annular rods having gradually varied radii of holes. To actively manipulate incident light, the annular rods are infiltrated with nematic LCs. By applying an external voltage to the infiltrated LCs, the effective index profile of the low-index GRIN PC structure is modulated without introducing any mechanical movement. The incident beam deflection and corresponding focal dista…
In this Letter, we present a study of the confinement properties of point-defect resonators in finite-size photonic-bandgap structures composed of aperiodic arrangements of dielectric rods, with special emphasis on their use for the design of cavities for particle accelerators. Specifically, for representative geometries, we study the properties of the fundamental mode (as a function of the filling fraction, structure size, and losses) via 2-D and 3-D full-wave numerical simulations, as well as microwave measurements at room temperature. Results indicate that, for reduced-size structures, aper…
We numerically study amorphous analogues of a two-dimensional photonic Chern insulator. The amorphous lattices consist of gyromagnetic rods that break time-reversal symmetry, with the lattice sites generated by a close-packing algorithm. The level of short-range order is adjustable, and there is no long-range order. The topologically nontrivial gaps of the photonic Chern insulator are found to persist into the amorphous regime, so long as there is sufficient short-range order. Strongly nonreciprocal robust transmission occurs via edge states, which are shown to propagate ballistically despite …
We present a detailed analysis of a coupler based on the Luneburg lens to couple a silica waveguide to a photonic crystal waveguide. The dependence of coupling efficiency on the lens's truncation, cut position of the photonic crystal structure, coupler tip width, and misalignment are investigated with two-dimensional finite element method. We implement the lens with a concentric ring-based multilayer structure. We also present a method to replace layers with very narrow widths by layers of predetermined minimum widths in the structure of the lens. The coupling loss of the designed 2.7 $μm$-lon…
Photonic crystal is a dielectric material which has a refractive index or permittivity which vary periodically, thus preventing the propagation of light with specific frequency and direction. The frequency range is called a photonic bandgap (PBG). If the structure of photonic crystals is modified by taking one line of rod in a photonic crystal is obtained a waveguide. Giving structures with symmetrical defects around the waveguide channel with the parameters given occurs coupling between the waveguide and cavity. Coupling indicates transfer part or all of the EM field depends on the frequency …
It has recently been predicted that a conical singularity (= Dirac point) in the band structure of a photonic crystal produces an unusual 1/L scaling of the photon flux transmitted through a slab of thickness L. This inverse-linear scaling is unusual, because it is characteristic of radiative transport via diffusion modes through a disordered medium -- while here it appears for propagation of Bloch modes in an ideal crystal without any disorder. We present a quantitative numerical test of the predicted scaling, by calculating the scattering of transverse-electric (TE) modes by a two-dimensiona…
