The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

http://ieeexplore.ieee.org/iel5/6354/16969/00781867.pdf

Photonic crystals

Two-photon excitation provides a means of activating chemical or physical processes with high spatial resolution in three dimensions and has made possible the development of three-dimensional fluorescence imaging, optical data storage, and lithographic microfabrication. These applications take advantage of the fact that the two-photon absorption probability depends quadratically on intensity, so under tight-focusing conditions, the absorption is confined at the focus to a volume of order λ3 (where λ is the laser wavelength). Any subsequent process, such as fluorescence or a photoinduced chemical reaction, is also localized in this small volume. Although three-dimensional data storage and microfabrication have been illustrated using two-photon-initiated polymerization of resins incorporating conventional ultraviolet-absorbing initiators, such photopolymer systems exhibit low photosensitivity as the initiators have small two-photon absorption cross-sections (δ). Consequently, this approach requires high laser power, and its widespread use remains impractical. Here we report on a class of π;-conjugated compounds that exhibit large δ (as high as 1, 250 × 10−50 cm4 s per photon) and enhanced two-photon sensitivity relative to ultraviolet initiators. Two-photon excitable resins based on these new initiators have been developed and used to demonstrate a scheme for three-dimensional data storage which permits fluorescent and refractive read-out, and the fabrication of three-dimensional micro-optical and micromechanical structures, including photonic-bandgap-type structures.

Two-photon polymerization initiators for three-dimensional optical data storage and microfabrication

Thirty years ago, Coullet et al. proposed that a special optical field exists in laser cavities bearing some analogy with the superfluid vortex. Since then, optical vortices have been widely studied, inspired by the hydrodynamics sharing similar mathematics. Akin to a fluid vortex with a central flow singularity, an optical vortex beam has a phase singularity with a certain topological charge, giving rise to a hollow intensity distribution. Such a beam with helical phase fronts and orbital angular momentum reveals a subtle connection between macroscopic physical optics and microscopic quantum optics. These amazing properties provide a new understanding of a wide range of optical and physical phenomena, including twisting photons, spin-orbital interactions, Bose-Einstein condensates, etc., while the associated technologies for manipulating optical vortices have become increasingly tunable and flexible. Hitherto, owing to these salient properties and optical manipulation technologies, tunable vortex beams have engendered tremendous advanced applications such as optical tweezers, high-order quantum entanglement, and nonlinear optics. This article reviews the recent progress in tunable vortex technologies along with their advanced applications.

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Optical vortices 30 years on: OAM manipulation from topological charge to multiple singularities

Optical imaging through and inside complex samples is a difficult challenge with important applications in many fields. The fundamental problem is that inhomogeneous samples such as biological tissue randomly scatter and diffuse light, preventing the formation of diffraction-limited images. Despite many recent advances, no current method can perform non-invasive imaging in real-time using diffused light. Here, we show that, owing to the ‘memory-effect’ for speckle correlations, a single high-resolution image of the scattered light, captured with a standard camera, encodes sufficient information to image through visually opaque layers and around corners with diffraction-limited resolution. We experimentally demonstrate single-shot imaging through scattering media and around corners using spatially incoherent light and various samples, from white paint to dynamic biological samples. Our single-shot lensless technique is simple, does not require wavefront-shaping nor time-gated or interferometric detection, and is realized here using a camera-phone. It has the potential to enable imaging in currently inaccessible scenarios. Diffraction-limited imaging in a variety of complex media is realized based on analysis of speckle correlations in light captured using a camera phone.

Non-invasive single-shot imaging through scattering layers and around corners via speckle correlations

High-performance photovoltaic cells use semiconductors to convert sunlight into clean electrical power, and transparent dielectrics or conductive oxides as antireflection coatings. A common feature of these materials is their high refractive index. Whereas high-index materials in a planar form tend to produce a strong, undesired reflection of sunlight, high-index nanostructures afford new ways to manipulate light at a subwavelength scale. For example, nanoscale wires, particles and voids support strong optical resonances that can enhance and effectively control light absorption and scattering processes. As such, they provide ideal building blocks for novel, broadband antireflection coatings, light-trapping layers and super-absorbing films. This Review discusses some of the recent developments in the design and implementation of such photonic elements in thin-film photovoltaic cells.

/pdf/light-management-for-photovoltaics-using-high-index-2u8o7699oo.pdf

Light management for photovoltaics using high-index nanostructures.

A one-step fabrication of a photonic crystal (PC) with functional defects is demonstrated. Using multi-beam phase-controlled holographic lithography with a diffracting optical element, large area one dimensional (1D) and two dimensional (2D) PCs with periodic defects were fabricated. The uniform area is up to $2mm^2$ , and tens of defect channels have been introduced in the 1D and 2D PC structure. This technique gives rise to substantial reduction in the fabrication complexity and significant improvement in the spatial accuracy of introducing functional defects in photonic crystals. This method can also be used to design and fabricate three dimensional (3D) PCs with periodic defects.

/pdf/fabrication-of-large-area-photonic-crystals-with-periodic-szoznktip9.pdf

Fabrication of Large Area Photonic Crystals with Periodic Defects by One-Step Holographic Lithography

A novel Gaussian profile filter and reflector that uses a capillary and a lens are proposed and experimentally demonstrated. The experimental results are in agreement with theory.

Gaussian profile filter and reflector employing capillary and lens

We propose a periodic SiNx/SiO2 microstructure to effectively extract light from quantum-dot light emitting diodes (QLEDs). The FDTD simulation results show that direct emitting efficiency can be doubled while keeping an indistinguishable color shift. This approach can also be applied to optimize the performances of green and blue QLEDs.

P-164L: Late-News Poster: Enhancing the Light Outcoupling Efficiency of Quantum-Dot Light Emitting Diodes with Periodic Microstructures

Efficient excitation of gap plasmon polaritons (GPPs) in an aluminum tapered gap is numerically investigated. Surface plasmon polaritons (SPPs) are efficiently excited via higher-order propagating modes by fabricating a pair of grooves on the internal surface of the tapered gap and the SPPs then be coupled into GPPs in the tip region. The physical mechanism and influence of the critical structure parameters such as groove location, groove depth, groove width and the taper angle are discussed. Based on the compression of the GPPs, a field enhancement of about 5000-fold is obtained at a 5 nm aperture.

Efficient Excitation of Gap Plasmon Polaritons via Higher-Order Propagating Modes

In this article, we propose a quantitative evaluation for the display uniformity in a directional backlight system. Display uniformity is divided into two research aspects - static uniformity and motional uniformity. Factors influencing uniformity deterioration are then discussed in our evaluation. Furthermore, a visualized simulation based on ray-tracing model is proposed to analyze this display uniformity in quantitative depth. Optical distribution on the screen is obtained in this simulation to provide visualized results compared with the experimental results. Our work helps to fill the vacancy for the evaluation of display uniformity on directional backlight type 3D display.

Jianying Zhou

Papers

Fabrication of Large Area Photonic Crystals with Periodic Defects by One-Step Holographic Lithography

Gaussian profile filter and reflector employing capillary and lens

P-164L: Late-News Poster: Enhancing the Light Outcoupling Efficiency of Quantum-Dot Light Emitting Diodes with Periodic Microstructures

Efficient Excitation of Gap Plasmon Polaritons via Higher-Order Propagating Modes

Simulation based quantitative evaluation for display uniformity in a directional backlight auto-stereoscopic display