Photonic crystal

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

Zero dispersion at small group velocities in photonic crystal waveguides

Abstract: Modes of photonic crystal (PC) line-defect waveguides can have small group velocity away from the Brillouin zone edge. This property can be explained by the strong interaction of the modes with the bulk PC. An anticrossing of “index guided” and “gap guided” modes should be taken into account. To control dispersion, the anticrossing point can be shifted by the change of the PC waveguide parameters. An example of a waveguide is presented with vanishing second- and third-order dispersion.

Conversion of broadband to narrowband thermal emission through energy recycling

Abstract: Converting from a broadband to a narrowband thermal emission spectrum with minimal loss of energy is important in the creation of efficient environmental sensors and biosensors1,2 as well as thermo-photovoltaic power generation systems3,4. Here, we demonstrate such thermal emission control by manipulating photonic modes with photonic crystals as well as material absorption with quantum-well intersubband transitions. We show that the emission peak intensity for our device can be more than four times greater than that of a blackbody sample under the same input power and thermal management conditions due to an increase in the temperature compared to the blackbody reference, and the emission bandwidth and angular spread are narrowed by a factor of 30 and 8, respectively. These results indicate that the energy saved by thermal emission control can be recycled and concentrated to enhance the narrow peak emission intensity. By constructing a thermal emission control device based on a multiple-quantum-well layer embedded in a two-dimensional photonic crystal, researchers demonstrate that they can convert a broadband thermal emission spectrum into a narrowband spectrum with minimal loss of energy.

Stimulated Brillouin scattering from multi-GHz-guided acoustic phonons in nanostructured photonic crystal fibres

Abstract: Wavelength-scale periodic microstructuring dramatically alters the optical properties of materials. An example is glass photonic crystal fibre1 (PCF), which guides light by means of a lattice of hollow micro/nanochannels running axially along its length. In this letter, we explore stimulated Brillouin scattering in PCFs with subwavelength-scale solid silica glass cores. The large refractive-index difference between air and glass allows much tighter confinement of light than is possible in all-solid single-mode glass optical fibres made using conventional techniques. When the silica-air PCF has a core diameter of around 70% of the vacuum wavelength of the launched laser light, we find that the spontaneous Brillouin signal develops a highly unusual multi-peaked spectrum with Stokes frequency shifts in the 10-GHz range. We attribute these peaks to several families of guided acoustic modes each with different proportions of longitudinal and shear strain, strongly localized to the core2,3. At the same time, the threshold power for stimulated Brillouin scattering4 increases fivefold. The results show that Brillouin scattering is strongly affected by nanoscale microstructuring, opening new opportunities for controlling light—sound interactions in optical fibres.

Tunable Block Copolymer/Homopolymer Photonic Crystals

Abstract: Interest in the photonic properties of dielectrically struc-tured materials is growing rapidly. This is fueled by the potential application of such materials in a broad range of fields. Much recent work has focused on lithographically fabricated photonic materials, [1,2] and on self-assembled colloidal crystals [3,4] and inverse opal structures. [5±7] The former need to be fabricated on small-area flat surfaces, the latter tend to have long timescales inherent in the fabrication and both have limited tunability with respect to the precursor materials. Our recent work [8,9] has shown that self-assembled block copolymer systems can exhibit a one-dimensionally periodic lamellar structure with component domains having widths large enough (l/4n) to act as visible light photonic materials. Their use in photonics would bring many advantages in terms of materials properties, process-ability, as well as cost, and would enable the fabrication of large-area conformable photonic materials. In this communication we show that multilayer photonic crystals active within a broad range of wavelengths in the visible spectrum can easily be produced from a simple system comprised of a block copolymer and two homopolymers. Ternary blends of a poly(styrene-b-isoprene) (S/I) di-block copolymer, polystyrene, and polyisoprene were solution cast from cumene. As the samples begin to dry they selectively reflect light, giving the appearance of green or red color. After drying, each sample showed a single well-defined peak in reflectivity in the visible wavelength range (350±600 nm) and a corresponding drop in the transmission profile. This implies that the reflection was fairly efficient and that the color observed in the samples was not due to significant absorption. In Figure 1a, we show typical reflec-tivity curves for several blend samples. The relative width of the reflectivity peaks (or transmission dips), Dl/l, varies approximately from 0.15 to 0.25, widening as the fraction of homopolymer in the blend increases. The wavelength of the reflectivity peak versus the homopolymer composition is plotted in Figure 1b. There is a monotonic increase in the peak reflective wavelength with the fraction of homopoly-mer. Scanning electron microscopy (SEM) of the samples confirmed that a lamellar morphology was present in the samples , with typical grain sizes of the order of several micro-meters. The backscattered electron imaging (BEI) image of a sample containing 40 % homopolymer is shown in Figure 2a. The bright regions correspond to the OsO 4 stained polyisoprene domains and the dark regions are the un-stained polystyrene. The lamellar repeat from the …

Chalcogenide Glass-Fiber-Based Mid-IR Sources and Applications

Abstract: The Naval Research Laboratory (NRL) is developing chalcogenide glass fibers for applications in the mid-and long-wave IR wavelength regions from 2 to 12 mum. The chalcogen glasses (i.e., glasses based on the elements S, Se, and Te) are transparent in the IR, possess low phonon energies, are chemically durable, and can be drawn into fiber. Both conventional solid core/clad and microstructured fibers have been developed. Chalcogenide glass compositions have been developed that allow rare earth doping to enable rare-earth-doped fiber lasers in the IR. Also, highly nonlinear compositions have been developed with nonlinearities ~1000times silica that enables nonlinear wavelength conversion from the near IR to the mid-and long-wave IR. In this paper, we review rare-earth-doped chalcogenide fiber for mid-and long-wave IR lasers, and highly nonlinear chalcogenide fiber and photonic crystal fiber for wavelength conversion in the mid-and long-wave IR.