Showing papers on "Photonic crystal published in 2010"

Three-Dimensional Invisibility Cloak at Optical Wavelengths

Abstract: We have designed and realized a three-dimensional invisibility-cloaking structure operating at optical wavelengths based on transformation optics. Our blueprint uses a woodpile photonic crystal with a tailored polymer filling fraction to hide a bump in a gold reflector. We fabricated structures and controls by direct laser writing and characterized them by simultaneous high-numerical-aperture, far-field optical microscopy and spectroscopy. A cloaking operation with a large bandwidth of unpolarized light from 1.4 to 2.7 micrometers in wavelength is demonstrated for viewing angles up to 60 degrees.

Coherent perfect absorbers: Time-reversed lasers

Abstract: An arbitrary body or aggregate can be made perfectly absorbing at discrete frequencies, if a precise amount of dissipation is added under specific conditions of coherent monochromatic illumination. This effect arises from the interaction of optical absorption and wave interference, and corresponds to moving a zero of the S-matrix onto the real wavevector axis. It is thus the time-reversed process of lasing at threshold. The effect may be demonstrated in a Si slab illuminated in the 500–900nm range. Coherent perfect absorbers form a novel class of linear optical elements—absorptive interferometers—which may be useful for controlled optical energy transfer.

Sub-femtojoule all-optical switching using a photonic-crystal nanocavity

Abstract: Although high-speed all-optical switches are expected to replace their electrical counterparts in information processing, their relatively large size and power consumption have remained obstacles. We use a combination of an ultrasmall photonic-crystal nanocavity and strong carrier-induced nonlinearity in InGaAsP to successfully demonstrate low-energy switching within a few tens of picoseconds. Switching energies with a contrast of 3 and 10 dB of 0.42 and 0.66 fJ, respectively, have been obtained, which are over two orders of magnitude lower than those of previously reported all-optical switches. The ultrasmall cavity substantially enhances the nonlinearity as well as the recovery speed, and the switching efficiency is maximized by a combination of two-photon absorption and linear absorption in the InGaAsP nanocavities. These switches, with their chip-scale integratability, may lead to the possibility of low-power, high-density, all-optical processing in a chip. All-optical switching energies as small as 0.42 fJ — two orders of magnitude lower than previously reported — are demonstrated in small photonic crystal cavities incorporating InGaAsP. These devices can switch within a few tens of picoseconds, and may therefore have potential for low-power high-density all-optical processing on a chip.

Tunable Colors in Opals and Inverse Opal Photonic Crystals

Abstract: Colloidal photonic crystals and materials derived from colloidal crystals can exhibit distinct structural colors that result from incomplete photonic band gaps. Through rational materials design, the colors of such photonic crystals can be tuned reversibly by external physical and chemical stimuli. Such stimuli include solvent and dye infiltration, applied electric or magnetic fields, mechanical deformation, light irradiation, temperature changes, changes in pH, and specific molecular interactions. Reversible color changes result from alterations in lattice spacings, filling fractions, and refractive index of system components. This review article highlights the different systems and mechanisms for achieving tunable color based on opaline materials with close-packed or non-close-packed structural elements and inverse opal photonic crystals. Inorganic and polymeric systems, such as hydrogels, metallopolymers, and elastomers are discussed.

Structure, function, and self-assembly of single network gyroid (I4132) photonic crystals in butterfly wing scales

Abstract: Complex three-dimensional biophotonic nanostructures produce the vivid structural colors of many butterfly wing scales, but their exact nanoscale organization is uncertain. We used small angle X-ray scattering (SAXS) on single scales to characterize the 3D photonic nanostructures of five butterfly species from two families (Papilionidae, Lycaenidae). We identify these chitin and air nanostructures as single network gyroid (I4132) photonic crystals. We describe their optical function from SAXS data and photonic band-gap modeling. Butterflies apparently grow these gyroid nanostructures by exploiting the self-organizing physical dynamics of biological lipid-bilayer membranes. These butterfly photonic nanostructures initially develop within scale cells as a core-shell double gyroid (Ia3d), as seen in block-copolymer systems, with a pentacontinuous volume comprised of extracellular space, cell plasma membrane, cellular cytoplasm, smooth endoplasmic reticulum (SER) membrane, and intra-SER lumen. This double gyroid nanostructure is subsequently transformed into a single gyroid network through the deposition of chitin in the extracellular space and the degeneration of the rest of the cell. The butterflies develop the thermodynamically favored double gyroid precursors as a route to the optically more efficient single gyroid nanostructures. Current approaches to photonic crystal engineering also aim to produce single gyroid motifs. The biologically derived photonic nanostructures characterized here may offer a convenient template for producing optical devices based on biomimicry or direct dielectric infiltration.

Manipulating light with strongly modulated photonic crystals

Abstract: Recently, strongly modulated photonic crystals, fabricated by the state-of-the-art semiconductor nanofabrication process, have realized various novel optical properties. This paper describes the way in which they differ from other optical media, and clarifies what they can do. In particular, three important issues are considered: light confinement, frequency dispersion and spatial dispersion. First, I describe the latest status and impact of ultra-strong light confinement in a wavelength-cubic volume achieved in photonic crystals. Second, the extreme reduction in the speed of light is reported, which was achieved as a result of frequency dispersion management. Third, strange negative refraction in photonic crystals is introduced, which results from their unique spatial dispersion, and it is clarified how this leads to perfect imaging. The last two sections are devoted to applications of these novel properties. First, I report the fact that strong light confinement and huge light–matter interaction enhancement make strongly modulated photonic crystals promising for on-chip all-optical processing, and present several examples including all-optical switches/memories and optical logics. As a second application, it is shown that the strong light confinement and slow light in strongly modulated photonic crystals enable the adiabatic tuning of light, which leads to various novel ways of controlling light, such as adiabatic frequency conversion, efficient optomechanics systems, photon memories and photons pinning.

Engineering the Photonic Density of States with metamaterials

Abstract: The photonic density of states (PDOS), like its' electronic coun- terpart, is one of the key physical quantities governing a variety of phenom- ena and hence PDOS manipulation is the route to new photonic devices. The PDOS is conventionally altered by exploiting the resonance within a device such as a microcavity or a bandgap structure like a photonic crystal. Here we show that nanostructured metamaterials with hyperbolic dispersion can dramatically enhance the photonic density of states paving the way for metamaterial based PDOS engineering.

Deterministic Coupling of a Single Nitrogen Vacancy Center to a Photonic Crystal Cavity

Abstract: We describe and experimentally demonstrate a technique for deterministic, large coupling between a photonic crystal (PC) nanocavity and single photon emitters. The technique is based on in situ scanning of a PC cavity over a sample and allows the precise positioning of the cavity over a desired emitter with nanoscale resolution. The power of the technique is demonstrated by coupling the PC nanocavity to a single nitrogen vacancy (NV) center in diamond, an emitter system that provides optically accessible electron and nuclear spin qubits.

Photonic crystal nanobeam cavity strongly coupled to the feeding waveguide

Abstract: A deterministic design of an ultrahigh Q-factor, wavelength-scale photonic crystal nanobeam cavity is proposed and experimentally demonstrated. Using this approach, cavities with Q>106 and on-resonance transmission T>90% are designed. The devices, fabricated in silicon and capped with a low refractive index polymer, have experimental Q=80 000 and T=73%. This is, to the best of our knowledge, the highest transmission measured in deterministically designed, wavelength-scale high-Q cavities.

Engineering photonic density of states using metamaterials

Abstract: The photonic density of states (PDOS), like its electronic counterpart, is one of the key physical quantities governing a variety of phenomena and hence PDOS manipulation is the route to new photonic devices. The PDOS is conventionally altered by exploiting the resonance within a device such as a microcavity or a bandgap structure like a photonic crystal. Here we show that nanostructured metamaterials with hyperbolic dispersion can dramatically enhance the photonic density of states paving the way for metamaterial-based PDOS engineering.

Mimicking the colourful wing scale structure of the Papilio blumei butterfly

Abstract: The brightest and most vivid colours in nature arise from the interaction of light with surfaces that exhibit periodic structure on the micro- and nanoscale. In the wings of butterflies, for example, a combination of multilayer interference, optical gratings, photonic crystals and other optical structures gives rise to complex colour mixing. Although the physics of structural colours is well understood, it remains a challenge to create artificial replicas of natural photonic structures. Here we use a combination of layer deposition techniques, including colloidal self-assembly, sputtering and atomic layer deposition, to fabricate photonic structures that mimic the colour mixing effect found on the wings of the Indonesian butterfly Papilio blumei. We also show that a conceptual variation to the natural structure leads to enhanced optical properties. Our approach offers improved efficiency, versatility and scalability compared with previous approaches.

On the use of Purcell factors for plasmon antennas.

Abstract: The Purcell factor is the standard figure of merit for spontaneous emission enhancement in microcavities and has also been proposed to describe emission enhancements for plasmonic resonances. A comparison of quality factor, mode volume, and Purcell factor for single and coupled plasmon spheres to exact calculations of emission rates shows that a Purcell factor derived from quality factor and mode volume does not describe emission changes due to plasmon antennas.

Colloquium : Looking at a soliton through the prism of optical supercontinuum

Abstract: A traditional view on solitons in optical fibers as robust particlelike structures suited for information transmission has been significantly altered and broadened over the past decade when solitons have been found to play the major role in generation of octave broad supercontinuum spectra in photonic crystal and other types of optical fibers. This remarkable spectral broadening is achieved through complex processes of dispersive radiation being scattered from, emitted, and transformed by solitons. Thus solitons have emerged as the major players in nonlinear frequency conversion in optical fibers. Unexpected analogies of these processes have been found with dynamics of ultracold atoms and ocean waves. This Colloquium focuses on recent understanding and new insights into physics of soliton-radiation interaction and supercontinuum generation.

Three-Dimensional Nanostructures for Photonics

Abstract: Recent progress in direct laser writing of three-dimensional (3D) polymer nanostructures for photonics is reviewed. This technology has reached a level of maturity at which it can be considered as the 3D analogue of planar electron-beam lithography. Combined with atomic-layer deposition and/or chemical-vapor deposition of dielectrics-the 3D analogues of planar evaporation technologies, the 3D polymer templates can be converted or inverted into 3D high-refractive-index-contrast nanostructures. Examples discussed in this review include positive and inverse 3D silicon-based woodpile photonic crystals possessing complete photonic bandgaps, novel optical resonator designs within these structures, 3D chiral photonic crystals for polarization-state manipulation, and 3D icosahedral photonic quasicrystals. The latter represent a particularly complex 3D nanostructure.

High-speed ultracompact buried heterostructure photonic-crystal laser with 13 fJ of energy consumed per bit transmitted

Abstract: The ability to directly modulate a nanocavity laser with ultralow power consumption is essential for the realization of a CMOS-integrated, on-chip photonic network, as several thousand lasers must be integrated onto a single chip. Here, we show high-speed direct modulation (3-dB modulation bandwidth of 5.5 GHz) of an ultracompact InP/InGaAsP buried heterostructure photonic-crystal laser at room temperature by optical pumping. The required energy for transmitting one bit is estimated to be 13 fJ. We also achieve a threshold input power of 1.5 µW, which is the lowest observed value for room-temperature continuous-wave operation of any type of laser. The maximum single-mode fibre output power of 0.44 µW is the highest output power, to our knowledge, for photonic-crystal nanocavity lasers under room-temperature continuous-wave operation. Implementing a buried heterostructure leads to excellent device performance, reducing the active region temperature and effectively confining the carriers inside the cavity. Advanced on-chip photonic networks require integrated nanoscale lasers with low power consumption. Researchers have now demonstrated high-speed modulation of a compact heterostructure photonic crystal laser at room temperature with an unprecedented low required energy of ∼13 fJ per bit transmitted.

Dye-sensitized solar cell based on a three-dimensional photonic crystal.

Abstract: We present a material assembly route for the manufacture of dye-sensitized solar cells, coupling a high-surface mesoporous layer to a three-dimensional photonic crystal (PC). Material synthesis aided by self-assembly on two length scales provided electrical and pore connectivity at the mesoporous and the microporous level. This construct allows effective dye sensitization, electrolyte infiltration, and charge collection from both the mesoporous and the PC layers, opening up additional parameter space for effective light management by harvesting PC-induced resonances.

Subwavelength grating periodic structures in silicon-on-insulator: a new type of microphotonic waveguide.

Abstract: We report on the experimental demonstration and analysis of a new waveguide principle using subwavelength gratings. Unlike other periodic waveguides such as line-defects in a 2D photonic crystal lattice, a subwavelength grating waveguide confines the light as a conventional index-guided structure and does not exhibit optically resonant behaviour. Subwavelength grating waveguides in silicon-on-insulator are fabricated with a single etch step and allow for flexible control of the effective refractive index of the waveguide core simply by lithographic patterning. Experimental measurements indicate a propagation loss as low as 2.1 dB/cm for subwavelength grating waveguides with negligible polarization and wavelength dependent loss, which compares favourably to conventional microphotonic silicon waveguides. The measured group index is nearly constant n(g) ~1.5 over a wavelength range exceeding the telecom C-band.

Nanomanipulation Using Silicon Photonic Crystal Resonators

Abstract: Optical tweezers have enabled a number of microscale processes such as single cell handling, flow-cytometry, directed assembly, and optical chromatography. To extend this functionality to the nanoscale, a number of near-field approaches have been developed that yield much higher optical forces by confining light to subwavelength volumes. At present, these techniques are limited in both the complexity and precision with which handling can be performed. Here, we present a new class of nanoscale optical trap exploiting optical resonance in one-dimensional silicon photonic crystals. The trapping of 48 nm and 62 nm dielectric nanoparticles is demonstrated along with the ability to transport, trap, and manipulate larger nanoparticles by simultaneously exploiting the propagating nature of the light in a coupling waveguide and its stationary nature within the resonator. Field amplification within the resonator is shown to produce a trap several orders of magnitude stronger than conventional tweezers and an order of magnitude stiffer than other near-field techniques. Our approach lays the groundwork for a new class of optical trapping platforms that could eventually enable complex all-optical single molecule manipulation and directed assembly of nanoscale material.

3D microlasers from self-assembled cholesteric liquid-crystal microdroplets.

Abstract: We demonstrate a tunable and omnidirectional microlaser in the form of a microdroplet of a dye-doped, cholesteric liquid crystal in a carrier fluid. The cholesteric forms a Bragg-onion optical microcavity and the omnidirectional 3D lasing is due to the stimulated emission of light from the dye molecules in the liquid crystal. The lasing wavelength depends solely on the natural helical period of the cholesteric and can be tuned by varying the temperature. Millions of microlasers can be formed simply by mixing a liquid crystal, a laser dye and a carrier fluid, thus providing microlasers for soft-matter photonic devices.

Enhancement of the zero phonon line emission from a single nitrogen vacancy center in a nanodiamond via coupling to a photonic crystal cavity

Abstract: Using a nanomanipulation technique a nanodiamond with a single nitrogen vacancy center is placed directly on the surface of a gallium phosphide photonic crystal cavity. A Purcell-enhancement of the fluorescence emission at the zero phonon line (ZPL) by a factor of 12.1 is observed. The ZPL coupling is a first crucial step toward future diamond-based integrated quantum optical devices.

Optical Metamaterials—More Bulky and Less Lossy

Abstract: Usually, investigators in materials science have asked: “What properties does a certain new material or structure have?” Now, the inverse problem arises: “I want to achieve certain—possibly unheard-of—material properties. How should the corresponding micro- or nanostructure look?” Examples could be: efficiently blocking acoustic noise due to a highway from a nearby village by a tailored wall, concentrating electromagnetic energy into as-tight-as-possible spaces, or avoiding reflections from a material's surface. The underlying common scheme is wave physics. Material properties that were otherwise unachievable, e.g., negative refraction and cloaking, may eventually be designed into optical metamaterials and photonic crystals. Both require tailoring of the properties (i.e., phase velocity and impedance) of an electromagnetic wave moving through the substance at the local level. In photonic crystals, the phase velocity of an electromagnetic wave moving through the crystal is controlled by tuning the photonic band structure; the impedance is determined by the electromagnetic field distributions throughout the material. In metamaterials, this amounts to tailoring the effective electric permittivity and magnetic permeability. In either case, introducing resonances is the key to controlling the local wave properties. The recent development of advanced fabrication techniques being applied to metamaterials and photonic crystals may lead to realization of such designer materials.

Review of long period fiber gratings written by CO2 laser

Abstract: This paper presents a systematic review of long period fiber gratings (LPFGs) written by the CO2 laser irradiation technique. First, various fabrication techniques based on CO2 laser irradiations are demonstrated to write LPFGs in different types of optical fibers such as conventional glass fibers, solid-core photonic crystal fibers, and air-core photonic bandgap fibers. Second, possible mechanisms, e.g., residual stress relaxation, glass structure changes, and physical deformation, of refractive index modulations in the CO2-laser-induced LPFGs are analyzed. Third, asymmetrical mode coupling, resulting from single-side laser irradiation, is discussed to understand unique optical properties of the CO2-laser-induced LPFGs. Fourthly, several pretreament and post-treatment techniques are proposed to enhance the efficiency of grating fabrications. Fifthly, sensing applications of the CO2-laser-induced LPFGs are investigated to develop various LPFG-based temperature, strain, bend, torsion, pressure, and biochemical sensors. Finally, communication applications of the CO2-laser-induced LPFGs are investigated to develop various LPFG-based band-rejection filters, gain equalizers, polarizers, and couplers.

Nonlinear optical properties of core-shell nanocavities for enhanced second-harmonic generation.

Abstract: A nonlinear optical plasmonic core-shell nanocavity is demonstrated as an efficient, subwavelength coherent light source through second-harmonic generation. The nonlinear optical plasmonic nanocavity incorporates a noncentrosymmetric medium, which utilizes the entire mode volume for even-order nonlinear optical processes. In previous plasmonic nanocavities, enhancement of such processes was only possible at the interface but symmetry prohibited in the body. We measured an enhancement of over 500 times in the second-harmonic radiation power. Calculations show that an enhancement of over 3500 times is achievable.

Coherent mixing of mechanical excitations in nano-optomechanical structures

Abstract: The combination of the large per-photon optical force and small motional mass achievable in nanocavity optomechanical systems results in strong dynamical back-action between mechanical motion and the cavity light field. In this Article, we study the optical control of mechanical motion within two different nanocavity structures, a zipper nanobeam photonic crystal cavity and a double-microdisk whispering-gallery resonator. The strong optical gradient force within these cavities is shown to introduce significant optical rigidity into the structure, with the dressed mechanical states renormalized into optically bright and optically dark modes of motion. With the addition of internal mechanical coupling between mechanical modes, a form of optically controlled mechanical transparency is demonstrated in analogy to electromagnetically induced transparency of three-level atomic media. Based upon these measurements, a proposal for coherently transferring radio-frequency/microwave signals between the optical field and a long-lived dark mechanical state is described.

Dispersion engineered slow light in photonic crystals: A comparison

Abstract: We review the different types of dispersion engineered photonic crystal waveguides that have been developed for slow light applications. We introduce the group index bandwidth product (GBP) and the loss per delay in terms of dB ns −1 as two key figures of merit to describe such structures and compare the different experimental realizations based on these figures. A key outcome of the comparison is that slow light based on photonic crystals performs as well or better than slow light based on coupled ring resonators.

Chemical Aspects of Three-Dimensional Photonic Crystals

Abstract: Three-dimensional (3D) photonic crystals (PCs) are crystalline materials where the refractive index is periodically modulated on a length scale comparable to the light wavelength of interest. Interference of the light waves scattered from the dielectric lattice (i.e., Bragg scattering) leads to omnidirectional stop bands or photonic band gaps (PBGs), which are analogous to the electronic energy band gaps in a semiconductor.1,2 The bandwidth and the frequency of the PBG are determined by the refractive index contrast between the high and low (typically air) dielectric materials, the structural symmetry and periodicity, and the filling fraction and morphology of high-refractive-index materials. Photonic crystals with a large, complete PBG are highly desired, which act like an optical trap to reflect incident light from any direction at a certain frequency range of light. Thus, controlled functional structures can be engineered into the 3D structures to confine or guide photons of specific wavelengths. Therefore, PCs potentially offer revolutionary advances in the next-generation microphotonic devices and the integration of existing optoelectronic devices, including integrated optical circuits, lasers, sensing, spectroscopy, and pulse shaping. In the last two decades, there has been much interest in exploring new PC structures and studying the related new phenomenon. Existing techniques for the largescale fabrication of microstructures with submicrometer features mainly rely on the use of optical projection lithography developed for silicon IC manufacturing. This method is inherent 2D patterning and requires laborious layer-by-layer photolithography and etching processes or stacking and fold-up of the 2D layers to generate the continuous 3D structures.2-4 A promising 3D fabrication technique should be able to do the following: •produce submicrometer periodicity for PBGs in the visible to infrared (IR) spectral range •access a large number of structures with tailored shapes, functionalities, and sizes of motifs •allow for mass-production over a large area •provide fine control of defects for photonic device applications •construct structures from materials with high refractive indices for complete PBGs.

Photonic Crystal Geometry for Organic Solar Cells

Abstract: We report organic solar cells with a photonic crystal nanostructure embossed in the photoactive bulk heterojunction layer, a topography that exhibits a 3-fold enhancement of the absorption in specific regions of the solar spectrum in part through multiple excitation resonances. The photonic crystal geometry is fabricated using a materials-agnostic process called PRINT wherein highly ordered arrays of nanoscale features are readily made in a single processing step over wide areas (approximately 4 cm(2)) that is scalable. We show efficiency improvements of approximately 70% that result not only from greater absorption, but also from electrical enhancements. The methodology is generally applicable to organic solar cells and the experimental findings reported in our manuscript corroborate theoretical expectations.

Photon scattering by a three-level emitter in a one-dimensional waveguide

Abstract: We discuss the scattering of photons from a three-level emitter in a one-dimensional waveguide, where the transport is governed by the interference of spontaneously emitted and directly transmitted waves. The scattering problem is solved in closed form for different level structures. Several possible applications are discussed: the state of the emitter can be switched deterministically by Raman scattering, thus enabling applications in quantum computing such as a single-photon transistor. An array of emitters gives rise to a photonic band gap structure, which can be tuned by a classical driving laser. A disordered array leads to Anderson localization of photons, where the localization length can again be controlled by an external driving.

Optimal light trapping in ultra-thin photonic crystal crystalline silicon solar cells

Abstract: Crystalline silicon is an attractive photovoltaic material because of its natural abundance, accumulated materials and process knowledge, and its appropriate band gap. To reduce cost, thin films of crystalline silicon can be used. This reduces the amount of material needed and allows material with shorter carrier diffusion lengths to be used. However, the indirect band gap of silicon requires that a light trapping approach be used to maximize optical absorption. Here, a photonic crystal (PC) based approach is used to maximize solar light harvesting in a 400 nm-thick silicon layer by tuning the coupling strength of incident radiation to quasiguided modes over a broad spectral range. The structure consists of a double layer PC with the upper layer having holes which have a smaller radius compared to the holes in the lower layer. We show that the spectrally averaged fraction of photons absorbed is increased 8-fold compared to a planar cell with equivalent volume of active material. This results in an enhancement of maximum achievable photocurrent density from 7.1 mA/cm(2) for an unstructured film to 21.8 mA/cm(2) for a film structured as the double layer photonic crystal. This photocurrent density value approaches the limit of 26.5 mA/cm(2), obtained using the Yablonovitch light trapping limit for the same volume of active material.