This PDF file contains the front matter associated with SPIE Proceedings Volume 6901, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

We review experimental studies performed on left-handed metamaterials (LHM) at microwave frequencies. The metamaterial structure is composed of periodic arrays of split-ring resonators and wire meshes and exhibits a left-handed propagation band at frequencies of negative permittivity and negative permeability. Negative refraction is verified using prism shaped LHM and also by beam-shifting method. Subwavelength focusing of a point source is achieved with a resolution of 0.13λ through a flat LHM superlens.

The opportunity to manipulate optical properties of materials through fabrication is the unique capability offered by photonic crystals. Among different directions to exploit the possibilities in this field, there have been recent research activities to engineer the dispersive properties of photonic crystals to change the propagation properties of waves passing through these periodic structures. To provide an efficient way to implement such devices, an approximate modeling technique will be used to simplify the analysis and design process for dispersive photonic crystal devices. Furthermore, the issue of efficient coupling to dispersive photonic crystal modes which is crucial for practical implementation of these devices will be addressed. Here, in particular, we will focus on employing the dispersive properties of photonic crystals to realize compact optical spectrometers and wavelength demultiplexers. We will show that by combining multiple dispersive properties (i.e., negative diffraction and the superprism effect) it is possible to enhance the performance of devices targeted for such applications. The potentials of these photonic crystal devices to meet the requirements of current and future applications in optical information processing and integrated optical sensing will be discussed.

We analyze the spatial coherence of thermal field emitted from a lossy dielectric slab using fluctuation-dissipation theorem.¹ For a given wavelength λ, the coherence property varies drastically with the distance from the slab surface. The coherence length is roughly λ / 2 in the far-field zone, but in the extreme near-field zone, it is many orders of magnitude smaller than λ, due to spatially fluctuating surface charges at the air-dielectric interface. On the other hand, in the intermediate near-field zone, the coherence length can be much longer than λ / 2 if the loss is small, because of the presence of waveguide modes of the slab. Such long-ranged coherence falls off approximately as 1/√x , in contrast to 1/x for a blackbody radiator, where x refers to displacement parallel to the slab surface. Furthermore, at a point of fixed distance from the slab surface, the frequency spectrum of the local energy density exhibits distinct fluctuation pattern, which is shown to be closely related to the waveguide dispersion relation.

Surface waves have been shown to play a key role in spontaneous thermal emission in the near-field as well as the coherence and the polarization properties of the nonradiative field. The near-field coherence of the delocalized nonradiative surface waves can be transferred into radiative fields by introducing a shallow grating on the surface. We show that the coherency of the thermal radiation can be enhanced by an order of magnitude compared with the coherency imposed by the delocalized surface waves. The enhanced coherency is due to coherent coupling between resonant cavities obtained by surface standing waves, where each cavity supports localized field that is attributed to coupled surface waves. We realized coupled resonant cavity structure on amorphous SiO₂ and crystalline SiC, both support surface phonon-polaritons, to demonstrate extraordinary coherent thermal emission with a high quality factor of 600 and a spatial coherence length of 760λ (8.8mm).

We report on the experimental and theoretical investigation two kinds of acoustic waves in two dimensional phononic crystal: bulk acoustic waves and surface acoustic waves. For bulk acoustic waves, the work focuses on the experimental observation of full acoustic band gaps in a two-dimensional lattice of steel cylinders immersed in water as well as deaf bands that cause strong attenuation in the transmission for honeycomb and triangular lattices. For surface acoustic waves, complete acoustic band gaps found experimentally in a two-dimensional square-lattice piezoelectric phononic crystal etched in lithium niobate will be presented. Propagation in the phononic crystal is studied by direct generation and detection of surface waves using interdigital transducers. The complete band gap extends from 203 to 226 MHz, in good agreement with theoretical predictions. Near the upper edge of the complete band gap, it is observed that radiation to the bulk of the substrate dominates. This observation is explained by introducing the concept of sound line.

In this paper we analyze a disk-like quantum dot embedded in an engineered two-dimensional (2D) photonic crystal cavity as an artificial atom. In this quantum dot electron and hole form an exciton where photon and electron-hole bound state can interact. Within the engineered electromagnetic vacuum of the PBG material, the exciton can emit and reabsorb a virtual poton. If the exciton energy lies near in the photonic band gap edge the exciton level splits into two levels. The dressed state exciton exhibits a lower energy than that of bare exciton. Here energy associated with dressed exction is evaluated.

We report spectrally selective IR absorption enhancement in the defect-free photonic crystal cavities, via Fano resonances. For a symmetric slab structure (air-slab-air membrane) with an absorptive layer in the center of the slab, enhanced absorption can be observed with enhancement factor ~180 for certain range of r/a values at wavelength of 4 µm. Similar results can also be achieved in an asymmetric slab structure (air-slab-semiconductor substrate), where higher index substrate is feasible for the proposed IR detectors, with optimized design. This important feature ensures flexible design for infrared photodetectors incorporating photonic crystal cavities. Detailed simulations were carried out to understand the design trade-offs on the key parameters, such as the substrate index, the absorption layer thickness, and the air hole radius.

We have recently demonstrated a number of functional photonic crystals devices and circuits, including an ultrafast, roomtemperature, low threshold, nanocavity laser with the direct modulation speed approaching 1THz, an all-optical switch controlled with 60 fJ pulses and with the speed exceeding 20GHz, and a local, reversible tuning of individual quantum dots on a photonic crystal chip by up to 1.8nm, which was then used to tune single quantum dots into strong coupling with a photonic crystal cavity and to achieve a giant optical nonlinearity.

The predictive simulation of the microcavity emission spectra is still a complex and challenging task although the physics of spontaneous emission in active microcavities is well understood. This becomes even more important because emerging technologies such as quantum cryptography and biological sensing applications rely on efficient micro-LEDs. In this work we present an efficient multilevel simulation approach for the emission spectra which takes into account the spatially and spectrally varying local density of optical states in a microcavity, loss due to free carrier absorption, and the coupling efficiency to an external optical system. The foundation of this approach is a three-dimensional finite element Maxwell solver that facilitates the computation of the cavity modes. The cavity modes complemented by a semi-analytic model for the radiative modes yield the emission spectra of the microcavity by means of an efficient mode expansion scheme. The effect of substrate reflection on the performance of photonic crystal microcavities is presented in a design study.

We propose and demonstrate reconfigurable microfiber-coupled photonic crystal (PhC) lasers. In this generic configuration, the position of a PhC resonator can be defined (and redefined) repeatedly by simply relocating a curved microfiber along the linear PhC waveguide. In the proximity of the PhC waveguide in contact with the microfiber, the cutoff frequency (effective index) of the PhC waveguide becomes smaller (larger) than that of a bare PhC waveguide. Accordingly, when a curved microfiber is in contact with the PhC waveguide, a linear PhC resonator having Gaussianshaped potential well is formed. Experimentally we confirm the formation of the reconfigurable resonator by observing laser operation slightly below three available band edges.

We present analytical results that shed new light on the properties of photonic-crystal fibers (optical fibers with periodic structures in their cladding). First, we discuss a general theorem, applicable to any periodic cladding structure, that gives rigorous conditions for the existence of cutoff-free guided modes-it lets you look at a structure, in most cases without calculation, and by inspection give a rigorous guarantee that index-guiding will occur. This theorem especially illuminates the long-wavelength limit, which has proved diffcult to study numerically, to show that the index-guided modes in photonic-crystal fibers (like their step-index counterparts) need not have any theoretical cutoff for guidance. Second, we look in the opposite regime, that of very short wavelengths. As previously identified by other authors, there is a scalar approximation that becomes exact in this limit, even for very high contrast fibers. We show that this "scalar" limit has consequences for practical operation at finite wavelengths that do not seem to have been fully appreciated: it tells you when band gaps arise and between which bands, reveals the symmetry and "LP" degeneracies of the modes, and predicts the scaling of cladding-related losses (roughness, absorption, etc.) as the size of a hollow core is increased.

A strongly anisotropic photonic crystal structure was made exploiting form birefringence. It was designed to have a low group velocity close to a degenerate band edge (DBE) which is also associated with large field enhancements proportional to the fourth power of the number of periods. Numerical results are presented illustrating the expected properties and these are compared with experimental data. There are interesting discrepancies in behavior and possible reasons are discussed which include the nature of the anisotropy and fabrication-related structural disorder. At microwave frequencies, unexpected field enhancements at specific frequencies and locations outside the structure have been observed which have potential applications

The transfer matrix formalism has proven to be a powerful tool for analyzing one-dimensional photonic bandgap structures, whether their multilayers are perfectly periodic or randomized in some fashion. In the randomized structure, as the number of layers tends to infinity, Furstenberg's formula can be used, at least theoretically, to find the deterministic Lyapunov exponent (localization factor, sometimes called the inverse localization length) governing the confinement of energy transmission in the model. The challenge in using Furstenberg's formula is that it requires the calculation of the invariant probability measure of the direction of the vector propagated by the chain of random matrices. This invariant measure is usually impossible to find analytically, and so one must resort to numerical simulation or some other approximating assumption. To aid in the numerical determination of this invariant probability measure, we consider matrix similarity transformations based on the average plane wave transfer matrix at a given frequency. These transformations, like the original transfer matrix, are elements of SU(1,1), the special pseudo-unitary group, and are obtained by moving the fixed points of the bilinear (or Mobius) transformation of the original transfer matrix to the corresponding fixed points of the canonical forms known from the Iwasawa decomposition. Amazingly, in some situations, including a quarter-wave stack, such a transformation can cause the invariant probability measure to become a nearly uniform probability density function, making the Furstenberg formula more readily useable.

We present a theoretical analysis of propagation losses in photonic crystal waveguides due to fabrication imperfections. The analysis is performed using a Green's function-based technique with the layer Korringa-Kohn-Rostoker method. This approach requires only the calculation of the complex mode behavior of the photonic crystal structure, from which the loss of a given mode is directly deduced. The accuracy and applicability of the method is discussed. The method will be demonstrated using two-dimensional photonic crystals with line-defect waveguides having a single fabrication defect.

By applying a low level of disorder, in the range of 10 to 20 %, to a translationally symmetric photonic crystal one can obtain the dielectric profile of a rotationally symmetric quasi-crystal. Through the use of a morphing algorithm we study the effects of incrementally applying the disorder to a triangular lattice photonic crystal, converting it to a 12-fold quasi-crystal. Through FDTD simulation, band gap maps and defect states are computed and presented as a function of the morphing process.

When the periodic permittivity of two-dimensional (2D) photonic crystal (PC) can be separated in x- and y- coordinates, one can consider the structure as two separate 1D photonic crystals, one of them being periodic in x coordinate and the other in y coordinate. If it is possible to find a proper separable permittivity function, we can approximate a 2D PC with two distinct 1D structures. One of the advantages is rapid calculation the density of state of a 2D PC. In this article an analytical calculation of the density of states for such a 2D PC has been done with the aim of taking this advantage. For calculating the density of states we use the effective resonance approach to analyze the 1D PC.

We review recent progress on the understanding of optical guidance mechanisms in hollow-core photonic crystal fibers. Two classes of hollow-core photonic crystal fiber are identified, one guides via a photonic bandgap and the other guides by virtue of an inhibited coupling between core and cladding mode constituents. For the former fiber type, we explore how the bandgap is formed using a photonic analogue of the tight-binding model and how it is related to the antiresonant reflection optical wave-guidance. For the second type of fiber, which can guide over a broad wavelength range, we examine the nature of the inhibited coupling.

Hollow fibers can be used for compact infrared gas sensors. The guided light is absorbed by the gas introduced into the hollow core. High sensitivity and a very small sampling volume can be achieved depending on fiber parameters i.e. attenuation, flexibility, and gas exchange rates. Different types of infrared hollow fibers including photonic bandgap fibers were characterized using quantum cascade lasers and thermal radiation sources. Obtained data are compared with available product specifications. Measurements with a compact fiber based ethanol sensor are compared with a system simulation. First results on the detection of trace amounts of the explosive material TATP using hollow fibers and QCL will be shown.

Metallo-dielectric photonic crystals (MDPCs) can exhibit intriguing and potentially useful optical properties, including ultra-wide photonic bandgaps, engineered thermal emission, and negative refractive index. But access to such materials has been limited by the lack of suitable methods for their preparation. We have developed a route to three-dimensional (3D) MDPCs that involves fabricating a polymeric pre-form by multi-photon direct laser writing and then conformally depositing metal onto the pre-form by electroless metallization. We use the approach to prepare silver- and copper-plated "woodpile" PCs having face-centered tetragonal symmetry and unit-cell period of several micrometers. The resulting 3D metallized structures exhibit mid-infrared reflectance that is consistent with theory and experimental observations obtained for MDPCs prepared by other routes. These data indicate that multi-photon direct laser writing coupled with electroless metallization is a viable route to complex 3D MDPCs of many symmetries and basis sets and provides a path for integrating such structures with other micron-scale optical elements.

Observation of defects inscribed in 3D photonic band gap opal templates has been investigated by means of fluorescence of solidified photo polymer. The defects, or breaks in periodicity, have been inscribed inside the structure by two-photon polymerization (2PP) of an infiltrated hybrid polymer from the type ORMOCER^®. In-situ and ex-situ observation of the inscribed defects has been achieved with fluorescence microscopy.

Infiltration of planar 2D silicon photonic crystals with nanocomposites using a simple melt processing technique is presented. The nanocomposites that were developed by evenly dispersing functionalized TiO₂ nanoparticles into a photoconducting polymer exhibit high optical quality and tunable refractive index. The infiltrated photonic crystals show tuning of the photonic band-gap that is controllable by the adjustment of the nanoparticle loading level. These results may be useful in the development of tunable photonic devices, hybrid light emitting diodes and photovoltaics.

Using soft lithography technology, the 2D photonic crystal superprism structures with a triangle array of air holes on the polymer slab were designed, simulated and fabricated successfully. The profile of the molded structures with 450nm in diameter and 900nm in lattice constant was obtained and observed by SEM. By means of optical experiment and measurement, when the input incident angle varied from 15° to 11°, we observed the beam propagation angle change from positive to negative and the superprism effect was demonstrated effectively at near-infrared wavelength 1550nm.

Photonic crystal waveguides (PCW) on silicon-on-insulator (SOI) are considered as a promising guiding platform with flexible guiding properties for dense photonics integration. Although SOI is a versatile material for photonics integration, PCWs fabricated on SOI substrates suffer from small guiding bandwidth due to the coupling to leaky TM-like modes. The purpose of this work is to present a systematic approach to increase the low-loss guiding bandwidth of PCWs on SOI. This has been achieved by reducing the interaction of low-group-velocity modes with the surrounding photonic crystal. By this method the low-loss bandwidth of a W1 PCW is increased from 2.5 nm to 12 nm which is the highest reported for this type of waveguide. We also present a detailed analysis of transmission properties of W1 PCWs and elaborate on the coupling to TM-like guided modes present in the low-loss transmission bandwidth of this device.

The Cu-based interconnect is a major bottleneck for sustaining technological advances in semiconductor integrated circuits. Matured optics technology may be able to resolve this challenge. Optics can provide high-speed, wavelengthdivision- multiplexing signals with the capability of interfacing optics with electronics through EO and OE conversion- directly-modulated laser, external modulator, and photodiode. An optical waveguide is a major building block for optical interconnects technology. A three-dimensional photonic crystal may provide single-mode, low-loss, group-velocitydispersionless, and compact waveguides. We report designs of double-heterojunction optical waveguides in a threedimensional photonic crystal. Compact optical waveguide modes are induced by modulating unit cells onedimensionally or two-dimensionally. One way to do this is to modulate the unit cell size. A well-type waveguide structure is formed by modulating the lattice constant of woodpile in one direction. For some 1D double-heterojunction geometries, light propagation becomes non-dispersive in the space domain, i.e. light is self-collimated along certain directions within the well plane. Next, two-dimensional unit-cell-modulation is applied to a 3D photonic crystal for exciting wire-type waveguide modes, for which light propagates along the horizontal or vertical wire. As a result, light may be guided in the same level or into different levels. The propagation properties, such as group velocity, and waveguide group velocity dispersion, are also analyzed in this work.

We present methods for systematic design of couplers for efficient coupling of light into the slow group velocity modes of photonic crystal waveguides (PCW).

A low loss refractive waveguided mode can be efficiently coupled to Bloch modes in two dimensional array of nanopillars, in a two-level high index membrane structure, according to a numerical study. More specifically, when using a slow Bloch mode above the light line, a wavelength selective, directional extraction can occur from the waveguide to the free space. The main conditions to be achieved, such as phase matching, strength of the coupling, photon lifetime in the photonic crystal, influence of embedding... will be discussed.

Ultrathin Ag films (2-10 nm thick) were fabricated on clean glass microslides by thermal evaporation. XRD shows them to be X-ray amorphous implying absence of long range order. AFM pictures show the presence of 2D triangular nanoplatelets arranged in a random manner, the sizes of the platelets grow with increasing film thickness Optical absorption spectra in the UV-visible give evidence for the presence of Mie particles through surface plasmon resonance whose peak positions and intensities depend sensitively upon thickness of Ag films. Surface plasmon resonance(SPR) features occur with maxima at 440, 457 and 484nm for the films of thickness 2, 5 and 10nm respectively with 5nm films showing properties characteristic of a optimally matched dielectric and electronic properties of the substrate and sample respectively.

The new term "Perfectly Periodic Photonic Quasi-Crystals" (P³QC) applies to 2-D and 3-D dielectric arrangements that posses a high rotational order about a central pivot point (standard photonic quasi-crystal) and in the same pattern posses a radial periodicity as viewed from the same central pivot point. These structures display no translational symmetry as associated with standard photonic crystals. In a 2-D structure, P³QC periodicity is observed for the polar coordinates (r, φ) and a unit cell of surface dS =rdrd θ serves as the building block of the pattern at each of the radial "Lattice Points". A generating algorithm based on orthogonal functions is used to produce many different types of P³QC patterns for latter analysis through FDTD simulations. The presence of bandgaps in the transmission spectrum for these structures is observed when the dielectric fill factor, rotational order and dielectric contrast are carefully selected. Central localized light states are commonly observed in these structures.