There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Inorganic semiconductor light-emitting diodes (LEDs) are environmentally benign and have already found widespread use as indicator lights, large-area displays, and signage applications. In addition, LEDs are very promising candidates for future energy-saving light sources suitable for office and home lighting applications. Today, the entire visible spectrum can be covered by light-emitting semiconductors: AlGaInP and AlGaInN compound semiconductors are capable of emission in the red to yellow wavelength range and ultraviolet (uv) to green wavelength range, respectively. Currently, two basic approaches exist for white light sources: The combination of one or more phosphorescent materials with a semiconductor LED and the use of multiple LEDs emitting at complementary wavelengths. Both approaches are suitable for high efficiency sources that have the potential to replace incandescent and fluorescent lights. In this article, the properties of inorganic LEDs will be presented, including emission spectra, electrical characteristics, and current-flow patterns. Structures providing high internal quantum efficiency, namely, heterostructures and multiple quantum well structures, will be discussed. Advanced techniques enhancing the external quantum efficiency will be reviewed, including resonant-cavities, die shaping (chip shaping), omnidirectional reflectors, and photonic crystals. Different approaches to white LEDs will be presented and figures-of-merit such as the color rendering index, luminous efficacy, and luminous efficiency will be explained. Finally, the packaging of low power and high power LED dies will be discussed.


Keywords:

light-emitting diodes (LEDs);
solid-state lighting;
compound semiconductors;
device physics;
reflectors;
resonant cavity LEDs;
white LEDs;
packaging

Light Emitting Diodes

Review of Charged Particle Dynamics. Beam Optics and Focusing Systems Without Space Charge. Linear Beam Optics with Space Charge. Self-Consistent Theory of Beams. Emittance Variation. Beam Physics Research from 1993 to 2007. Appendices. List of Frequently Used Symbols. Bibliography. Index.

Theory and Design of Charged Particle Beams

Anti-reflective coatings (ARCs) have evolved into highly effective reflectance and glare reducing components for various optical and opto-electrical equipments. Extensive research in optical and biological reflectance minimization as well as the emergence of nanotechnology over the years has contributed to the enhancement of ARCs in a major way. In this study the prime objective is to give a comprehensive idea of the ARCs right from their inception, as they were originally conceptualized by the pioneers and lay down the basic concepts and strategies adopted to minimize reflectance. The different types of ARCs are also described in greater detail and the state-of-the-art fabrication techniques have been fully illustrated. The inspiration that ARCs derive from nature (‘biomimetics’) has been an area of major research and is discussed at length. The various materials that have been reportedly used in fabricating the ARCs have also been brought into sharp focus. An account of application of ARCs on solar cells and modules, contemporary research and associated challenges are presented in the end to facilitate a universal understanding of the ARCs and encourage future research.

Anti-reflective coatings: A critical, in-depth review

This book treats nonlinear dynamics in both Hamiltonian and dissipative systems. The emphasis is on the mechanics for generating chaotic motion, methods of calculating the transitions from regular to chaotic motion, and the dynamical and statistical properties of the dynamics when it is chaotic. The book is intended as a self consistent treatment of the subject at the graduate level and as a reference for scientists already working in the field. It emphasizes both methods of calculation and results. It is accessible to physicists and engineers without training in modern mathematics. The new edition brings the subject matter in a rapidly expanding field up to date, and has greatly expanded the treatment of dissipative dynamics to include most important subjects. It can be used as a graduate text for a two semester course covering both Hamiltonian and dissipative dynamics.

Regular and Chaotic Dynamics

A design criterion that permits truly omnidirectional reflectivity for all polarizations of incident light over a wide selectable range of frequencies was used in fabricating an all-dielectric omnidirectional reflector consisting of multilayer films. The reflector was simply constructed as a stack of nine alternating micrometer-thick layers of polystyrene and tellurium and demonstrates omnidirectional reflection over the wavelength range from 10 to 15 micrometers. Because the omnidirectionality criterion is general, it can be used to design omnidirectional reflectors in many frequency ranges of interest. Potential uses depend on the geometry of the system. For example, coating of an enclosure will result in an optical cavity. A hollow tube will produce a low-loss, broadband waveguide, whereas a planar film could be used as an efficient radiative heat barrier or collector in thermoelectric devices.

https://science.sciencemag.org/content/sci/282/5394/1679.full.pdf

A Dielectric Omnidirectional Reflector

The emergence of a dielectric omnidirectional multilayer structure opens new opportunities for low loss broad-band guiding of light in air We demonstrate the effectiveness of such an approach by fabricating a broad-band, low-loss hollow waveguide in the 10-/spl mu/m region and measuring its transmission around a 300 bend The generality of the solution enables the application of the method to many wavelengths of interest important in telecommunication applications as well as for guiding high-power lasers in medical and other fields of use

Guiding optical light in air using an all-dielectric structure

We have derived the global band gaps for general two-dimensional (2D) photonic band gap (PBG) structures formed by square or triangular arrays of metal posts. Such PBG structures have many promising applications in active and passive devices at microwave, millimeter wave, and higher frequencies. A coordinate-space, finite-difference code, called the photonic band gap structure simulator (PBGSS), was developed to calculate complete dispersion curves for lattices for a series of values of the ratio of the post radius (r) to the post spacing (a). The fundamental and higher frequency global photonic band gaps were determined numerically. These universal curves should prove useful in PBG cavity design. In addition, for very long wavelengths, where the numerical methods of the PBGSS code are difficult, dispersion curves were derived for the transverse-magnetic (TM) mode by an approximate, quasi-static approach. Results of this approach agree well with the PBGSS code for r/a<0.1. The present results are compared with experimental data for transverse-electric (TE) and TM mode PBG resonators built at Massachusetts Institute of Technology (MIT) and the agreement is found to be very good.

/pdf/simulation-of-photonic-band-gaps-in-metal-rod-lattices-for-3k02hp4gtn.pdf

Simulation of photonic band gaps in metal rod lattices for microwave applications

A device having at least one dielectric inner core region in which electromagnetic radiation is confined, and at least two dielectric outer regions surrounding the inner core region, each with a distinct refractive index. The outer regions confine electromagnetic radiation within the inner core region. The refractive indices, the number of outer regions, and thickness of the outer regions result in a reflectivity for a planar geometry that is greater than 95% for angles of incidence ranging from 0° to at least 80° for all polarizations for a range of wavelengths of the electromagnetic radiation. In exemplary embodiments, the inner core region is made of a low dielectric material, and the outer regions include alternating layers of low and high dielectric materials. In one aspect of the invention, the device is a waveguide, and in another aspect the device is a microcavity.

Omnidirectional multilayer device for enhanced optical waveguiding

Non-neutral plasmas, like electrically neutral plasmas, exhibit a broad range of collective properties, such as plasma waves and instabilities, and the ability to support long-lived, large-amplitude coherent structures. This paper reviews the equilibrium and stability properties of intense non-neutral electron flow in crossed electric and magnetic fields. Following a description of equilibrium properties for magnetically insulated electron flow in planar geometry, extraordinary-mode stability properties are investigated for relativistic non-neutral electron flow between planar conductors. Particular emphasis is placed on the magnetron and diocotron instabilities, and detailed stability behavior is shown to exhibit a sensitive dependence on the self field intensity (as measured by the dimensionless parameter ${s}_{e}=\frac{{\ensuremath{\gamma}}_{e}^{0}{\ensuremath{\omega}}_{\mathrm{pe}}^{2}}{{\ensuremath{\omega}}_{\mathrm{ce}}^{2}}$) as well as on the shape of the equilibrium profiles. The influence of cylindrical effects (such as the centrifugal and Coriolis accelerations of an electron fluid element) on stability behavior is then investigated for rotating electron flow in cylindrical geometry. Finally, the properties of large-amplitude coherent structures in non-neutral plasmas with circulating electron flow are investigated. Topics covered in this area include particle-in-cell computer simulations of dense (${s}_{e}\ensuremath{\sim}1$) electron flow in relativistic magnetrons which show large-amplitude spoke formation in the circulating electron density, and application of a cold-fluid guiding-center model to investigate large-amplitude vortex structures in low-density (${s}_{e}\ensuremath{\ll}1$) non-neutral plasma. The accessibility and stability of such stationary structures (in the rotating frame) remain important topics for future investigation.

Chiping Chen

Papers

A Dielectric Omnidirectional Reflector

Guiding optical light in air using an all-dielectric structure

Simulation of photonic band gaps in metal rod lattices for microwave applications

Omnidirectional multilayer device for enhanced optical waveguiding

Equilibrium and stability properties of intense non-neutral electron flow