Photonic crystal

About: Photonic crystal is a research topic. Over the lifetime, 43424 publications have been published within this topic receiving 887083 citations.

Ultracompact and low-power optical switch based on silicon photonic crystals

Abstract: Switching light is one of the most fundamental functions of an optical circuit. As such, optical switches are a major research topic in photonics, and many types of switches have been realized. Most optical switches operate by imposing a phase shift between two sections of the device to direct light from one port to another, or to switch it on and off, the major constraint being that typical refractive index changes are very small. Conventional solutions address this issue by making long devices, thus increasing the footprint, or by using resonant enhancement, thus reducing the bandwidth. We present a slow-light-enhanced optical switch that is 36 times shorter than a conventional device for the same refractive index change and has a switching length of 5.2

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.

Photonic Glass: A Novel Random Material for Light**

Abstract: From medieval stained glass windows to future photonic chips, understanding light interaction with complex dielectric media has been the key to design and tailor the optical properties. From random to periodic media, the engineered internal microstructure of a dielectric is at the basis of many new optical properties which are unexpected in homogeneous dielectric media. Very promising examples are represented by “left-handed” materials which show negative values of permeability and permittivity, and for which light propagation, Doppler effect, Cherenkov radiation, and even Snell’s law are found to be strongly affected. Another important example is given by photonic crystals, where the dielectric function (e) varies periodically on the length scale of the light wavelength, and which exhibits anomalous refraction, super-refraction (superprism effect), small group velocity, and, for certain structures, even the opening of a complete photonic bandgap (PBG). In both cases, the nanometer and micrometer sized building blocks are arranged periodically to induce the required properties. Usually, defects in photonic crystals are regarded as undesirable features that spoil optical quality and performances. However, they can also be viewed as an enriching factor since, when controlled, they can be used to build up cavities, waveguides etc. being the base of future circuits of light. This only happens when a strict control is exerted on defects amount, position, shape, and other morphological characteristics. The amount of defects in photonic crystals produced by self-assembly is partly out of control and the achievement of the highest quality possible is a common goal of the colloidal community, for which many routes have been tested. Disordered microstructured dielectrics, which are based on an opposite assembly strategy, are a rich and novel photonic medium. Random packing of hard spheres has been focus of considerable attention for the last decades as a model to pack objects efficiently. Nevertheless, the packing of spheres is, apparently, the exception rather than the rule showing the highest possible filling fraction. A number of interesting new optical phenomena have also been studied in random media such as coherent backscattering enhancement, Anderson localization of light, random lasing only to mention a few. Three-dimensional random systems have been mainly achieved by the use of very polydisperse distributions of different materials powders or clusters. A random distribution of monodisperse building blocks forming a solid phase has not yet been achieved. Using spheres, which has been tried in colloidal suspensions, offers a very interesting advantage as they are the simplest object for which light resonances. Moreover, the interaction between light and a dielectric sphere can be described completely by Mie theory, an exact solution of the Maxwell’s equations. Some experiments have been already performed in a single or a small group of micro-spheres. A new range of interesting phenomena will be affected by monodispersity of spheres, giving rise to a resonant behaviour of diffusion constant, transport mean free path and energy velocity or random lasing action in macroscopic arrangements of this kind of scatters. In this work, we present a new material that we call “photonic glass”. This new three dimensional system is composed by monodisperse polymer spheres arranged in a completely disordered (random) way. Due to the resonant behaviour of the spheres, discrete light states exist, and therefore every sphere acts as a meta-atom for light. We describe two different approaches to grow completely random distributions of monodisperse polymeric spheres with diameters from 200 nm to 2300 nm. The first method is based on rheology and takes advantage from the two-body interaction between polymeric spheres in colloidal suspensions. Very thick (from a few hundred microns to millimetres) and uniform samples can be grown attenuating the sphere-sphere repulsive potential by dissolving a low concentration of electrolytes (ions) in the colloidal suspension. The second method is based on vertical deposition, which is commonly used to grow colloidal photonic crystals providing extremely high quality structures. By combining a binary colloidal suspension composed by polymethyl methacrylate (PMMA) and polystyrene (PS) spheres and by selective etching of one of them, thin disordered films can be grown. Contrary to intuition, the introduction of arbitrarily high amounts of disorder is an unsuspected equally difficult task as obtaining defects-free systems. Few methods were tested here to get a completely disordered arrangement of monodisperse spheres such as rapid sedimentation or modified vertical deposition, being completely unsuccessful. Only the two methods presented here after were found to be fruitful. C O M M U N IC A IO N

Single quantum-dot Purcell factor and β factor in a photonic crystal waveguide

Abstract: A theoretical formalism to calculate the spontaneous emission rate enhancement (Purcell factor) and propagation mode $\ensuremath{\beta}$ factor from single quantum dots in a planar-photonic-crystal waveguide is presented. Large Purcell factors for slow light modes, and enormous $\ensuremath{\beta}$ factors ($g0.85$) over a broadband (10 THz) spectral range are subsequently predicted. The local density of photon states is found to diverge at the photonic band edge, but we discuss why this divergence will always be broadened in real samples, most notably due to structural disorder. Applications towards ``on-chip'' single photon sources are highlighted.

Fabrication of Photonic Wire and Crystal Circuits in Silicon-on-Insulator Using 193-nm Optical Lithography

Abstract: High-index contrast silicon-on-insulator technology enables wavelength-scale compact photonic circuits. We report fabrication of photonic circuits in silicon-on-insulator using complementary metal-oxide-semiconductor processing technology. By switching from advanced optical lithography at 248 to 193 nm, combined with improved dry etching, a substantial improvement in process window, linearity, and proximity effect is achieved. With the developed fabrication process, propagation and bending loss of photonic wires were characterized. Measurements indicate a propagation loss of 2.7 dB/cm for 500-nm photonic wire and an excess bending loss of 0.013 dB/90deg bend of 5-mum radius. Through this paper, we demonstrate the suitability of high resolution optical lithography and dry etch processes for mass production of photonic integrated circuits.