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As engineers and scientists, we use a variety of techniques to concisely represent information. The ubiquitous equations and plots found in the pages of this journal demonstrate this well; however, nothing rivals the power of an image to convey information. As a result, in our relentless pursuit to explore and exploit the information available in all parts of the electromagnetic spectrum, imaging is often the end goal for the systems we develop. Terahertz and millimeter wavelengths have been no exception to this pursuit, and since we first began sensing at these wavelengths, we have constantly developed and improved systems for forming images.

A technique is described for displaying polarization information from passive millimeter-wave (mmW) sensors. This technique uses the hue of an image to display the polarization information and the lightness of an image to provide the unpolarized information. The fusion of both images is done in such a way that minimal information is lost from the unpolarized image while adding polarization information within a single image. The technique is applied to experimental imagery collected in a desert environment with two orthogonal linear polarization states of light and the results are discussed. Several objects such as footprints, ground textures, tire tracks, and shrubs display strong polarization features that are clearly visible with this technique, while materials with low polarization signatures such as metal are also clearly visible in the same image.

We demonstrate experimentally the ability to shape the point spread function of a distributed-aperture millimeter-wave imaging system by modifying its aperture phase. We consider distributions on a regular hexagonal array and a nonredundant array. We also show how to exploit this capability to perform low-resolution analog image processing. A preliminary investigation of system performance reveals nonuniformity in amplitude response across the array is a major contributor to deviations from predicted point spread functions (PSFs).

Spatial coherence in optical processing can be exploited to implement a wide variety of image processing functions. While fully coherent systems tend to receive the most attention, spatially noncoherent systems can often provide equivalent functionality while offering significant advantages over coherent systems with regard to noise performance and system robustness. The term noncoherent includes both partially coherent and fully incoherent illumination. In addition to the noise immunity advantage, noncoherent diffraction-based processors have relaxed requirements on pupil plane spatial light modulator characteristics. In this paper we provide a discussion of the tradeoffs between coherent and noncoherent processing, taking into account the limited performance characteristics of commercially available spatial light modulators. The advantages of noncoherent processing are illustrated with numerical and experimental results corresponding to three different noncoherent architectures.

We report on the development of a digital-micromirror-device (DMD)-based multishot snapshot spectral imaging (DMD-SSI) system as an alternative to current piezostage-based multishot coded aperture snapshot spectral imager (CASSI) systems. In this system, a DMD is used to implement compressive sensing (CS) measurement patterns for reconstructing the spatial/spectral information of an imaging scene. Based on the CS measurement results, we demonstrated the concurrent reconstruction of 24 spectral images. The DMD-SSI system is versatile in nature as it can be used to implement independent CS measurement patterns in addition to spatially shifted patterns that piezostage-based systems can offer.

In this paper we present the design and implementation of a Compressive Sensing Microscopy (CSM) imaging system, which uses the Compressive Sensing (CS) method to realize optical-sectioning imaging. The theoretical aspect of the proposed system is investigated using the mathematical model of the CS method and an experimental prototype is constructed to verify the CSM design. Compared to conventional optical-sectioning microscopes (such as Laser Scanning Confocal Microscopes (LSCMs) or Programmable Array Microscopes (PAMs)), the CSM system realizes optical-sectioning imaging using a single-pixel photo detector and without any mechanical scanning process. The complete information of the imaging scene is reconstructed from the CS measurements numerically.

Free-carrier absorption (FCA) has proven to be an important obstacle in the development of a silicon-based laser; however, FCA may serve as a potential advantage in active silicon-based switches or modulators. In this work, we present FCA modulation in slot waveguides with silicon nanocrystals (Si-ncs) embedded in SiO(2) as the low-index slot material. Slot waveguides were fabricated with and without Si-ncs, and the presence of Si-ncs was shown to increase the pump-induced FCA loss in the waveguides by a factor of 4.5. We modeled the Si-nc material using a four-level rate equation analysis to estimate the excited population of Si-ncs, allowing us to extract a value of 2.6 × 10(-17) cm(2) for the FCA cross section of the Si-nc material.

In this letter, we propose a high speed and ultralow driving voltage traveling wave electro-optic (EO) modulator based on a dual horizontal slot waveguide. The proposed design harnesses the unique properties of ferroelectric materials such as LiNBO3 and exotic, organic EO polymers to tightly confine both the optical and rf modes in a nanoscale slot maximizing the nonlinear interaction with the electric field. Larger electrode separation allows for significant reduction in rf propagation loss. Simulations of the half-wavelength voltage-length product and electro-optic response of the proposed device reveal ultrabroadband operation, up to 250 GHz, and subvolt driving voltage for a 1 cm long modulator.

Typical silicon nanocrystal light emitting devices (LEDs) operate under direct current (DC) biasing conditions that require high electric fields or high current densities. The electroluminescence (EL) under these conditions relies on impact excitation that can be damaging to the material. In this work, we present bipolar injection into silicon nanocrystal LEDs using a pulsed pumping scheme. We measured the frequency dependence of the integrated and time-resolved EL of the LEDs. The frequency dependent behavior of the time-resolved characteristics is used to explain the integrated EL measurements. In addition, the light output of the device was measured under pulsed excitation and was found to increase by a factor of 18 as compared to the case of DC excitation.

Far-infrared outdoor imagery has a lower contrast in the morning/afternoon relative to the highest contrast, which is observed at 14:00. Millimeter-wave (mmW) imagery can also follow this pattern. However, in this paper, we show that the opposite can occur for mmW imagery, wherein a higher contrast can occur in the morning/afternoon and lower contrast at 14:00. To this end, we show that a wood and rubber sample are observed to have a difference in mmW radiometric temperature of 17 degrees C at 9:00 and a difference of only 7 degrees C at 14:00. Details of our observations are presented.

We demonstrate a process to fabricate highly uniform large-area polymer 3-D "woodpile" photonic crystal structures with nanometer-scale features. This fabrication process utilizes the SU-8 resist's enhanced absorption of deep-UV wavelengths to achieve resist exposure confinement to a desired depth. It also uses the high resistance of cross-linked SU-8 resist to solvents for layer-upon-layer resist application and processing. This fabrication method affords the flexibility of incorporating arbitrary design patterns for the different layers. Depending on the exposure mask area and the size of exposure window available in the mask aligner, this fabrication process can provide such devices over wafer-scale areas. This fabrication method is highly compatible with standard semiconductor processing methods and is thus well suited for mass fabrication.

We compare the two prevailing raised-microdisk whispering-gallery-mode (WGM) characterization techniques, one based on coupling emission to a tapered fiber and the other based on collecting emission in the far field. We applied both techniques to study WGMs in Si nanocrystal raised microdisks and observed dramatically different behavior. We explain this difference in terms of the radiative bending loss on which the far-field collection technique relies and discuss the regimes of operation in which each technique is appropriate.

We examined a concentric Si nanocrystal (Si-nc) and Er doped SiO 2 (Er:SiO 2 ) microdisk structure supporting high-Q whispering gallery modes (WGMs) at both visible and telecom wavelengths. This structure provides a means to utilize Si-nc luminescence as an optical pump for an Er:SiO 2 cavity without subjecting a telecom-wavelength, Er:SiO 2 -based mode to loss mechanisms associated with the Si-nc material. After fabricating a concentric microdisk consisting of an inner Si-nc disk and an outer Er:SiO 2 ring, we characterize visible wavelength WGMs excited by the Si-nc photoluminescence and observed spectrometer limited quality factors as high as 10 3 . Telecom wavelength photoluminescence from the Er:SiO 2 ring was measured to have a quality factor as high as 10 4 in the erbium luminescence region using a passive pulled fiber setup.

In some optical computing architectures [1] array generators are used to establish an array of fixed, regular interconnects between two planes. Because system programmability is achieved elsewhere, the ability to reconfigure the array is not a requirement and the array generator can be fabricated as a fixed phase filter. In contrast, for optical processing applications such as optical morphology [2] reconfigurability and programmability of the spot array are essential, for which purpose magneto-optic spatial light modulators [3] and acoustooptic (AO) modulators [4] have been employed.

In this paper we describe an acousto-optic morphological image processor used to implement a morphological hit-or-miss transform. Morphology is an image algebra technique whereby the shape and structure of an input object is transformed by a smaller object referred to as a structuring element. The two most fundamental morphological operations, erosion and dilation, can be implemented as a convolution followed by a threshold. We perform the convolution optically and the threshold digitally. The input to the system is displayed on an Epson 1020 LCTV, and the system utilizes an acousto-optic Bragg cell in the Fourier plane of a coherent optical correlator to generate the desired structuring element. The hit-or-miss transform is the intersection of two eroded images. One image is the input object eroded by the desired structuring element, and the second image is the erosion of the complement of the input by the complement of the structuring element. This transform is useful for extracting specified features from images, as is necessary in automatic target recognition. Experimental results are presented.

We describe the fabrication and characterization of a compressive-sampling multispectral imaging (CS-MSI) system that uses single-pixel detectors to capture multiple spectral images concurrently, without mechanical scanning. In particular, we pay special attention to the hardware/software characterization of the CS-MSI system, wherein we discuss the optical realization of the proposed system, measure the effective sensitivity range, and investigate the relationship between the digital micromirror device frame rate and the reconstruction quality. We also compare the imaging performance of the Hadamard-pace variable-density sampling method, which is the CS method implemented with our hardware architecture, with the conventional random sampling method. We propose a compressive-sampling modulation transfer function (CS-MTF) to measure the amplitude response of different spatial frequencies by using different CS methods.

Based on coupled quantum electrodynamics the light propagation in active silicon nanocrystals was reported in this paper. The classical electron oscillator model was employed to bridge the link between the rate equations of the four-level atomic system of the active medium and the electromagnetic interaction. With the assistance of auxiliary differential equations we numerically solved the system by using the Finite-difference Time-domain (FDTD) method. Both stimulated and spontaneous emissions were taken into account in the active medium system. Light amplification characteristics due to stimulated emission were investigated under various pumping rates. To enhance the spontaneous emission, microcavities based on one-dimensional photonic crystals were designed to maximize the nonlinear interaction between the active medium and electromagnetic waves. Preliminary experimental investigation of the cavity-enhanced luminescence was performed to demonstrate the validation of the proposed simulation scheme.

In this paper, we studied phase modulation numerically using metamaterials such as stacked structures of dual split ring resonators (DSRRs). To demonstrate the modulation, a vertical and a planar design were considered, where the wave vectors were parallel and perpendicular to the proposed structures creating 70 degrees and 80 degrees of phase change, respectively. In both of the designs modulation was brought about by changing the effective index of the structure through switching between the open and short states of the DSRRs while maintaining high transmission. One of the attractive features of our design was the thin layers of DSRRs, where for the vertical and planar models the DSRRs layers were 5 mm and 2.28 mm respectively. The numerical results obtained by simulation matched well with the theoretical prediction.

Morphology is an image algebra technique whereby the shape and structure of an input object is transformed by a smaller object called the structuring element. The two most fundamental morphological operations, erosion and dilation, are usually defined in terms of set operations. Alternatively they can be understood in terms of a convolution followed by a threshold. In this paper we describe an iterative acoustooptic (AO) morphological image processor. The input to the system is displayed on a 128 × 128 magnetooptic spatial light modulator, and the system utilizes an AO Bragg cell in the Fourier plane of a coherent optical correlator to generate the desired structuring element. Thresholding is performed electronically in an image processing system. The feedback necessary for multiple erosions and dilations is provided electronically via a single computer that controls both an image processing system in the output image plane and the MOSLM.

Morphological image processing based on binary set representation of an image has been receiving increasing attention as a viable alternative to the linear image processing based on Fourier domain filtering [1], The fundamental morphological filtering operations of erosion and dilation are nonlinear operations from which more complex operations (opening, closing, pattern spectra) suitable for shape extraction and analysis can be synthesized. The morphological operations are defined between a working image and a much smaller image called the structuring element. In most cases the structuring element is binary while the working image can be binary, analog with binary threshold decomposition representation or analog with weighted binary representation. For the first two representations, the dilation and erosion operations consist of a superposition of several shifted replicas of the working image followed by a point-wise threshold operation at different levels; 1 for dilation and (m-1) for erosion, where "m" is the number of images superposed. With the third representation, the minimum/maximum value (for dilation/erosion, respectively) for the superposed pixels is detected and assigned as the pixel value in the output image. In either case, the processing operations are of low complexity. The number of shifted replicas of the working image and the amount of shift corresponds to the number and position, respectively, of bright pixels in the structuring element. For large and irregularly shaped structuring elements the morphological processing operation complexity is dominated by data communication.

In this paper we present novel light trapping designs applied to multiple junction thin film solar cells. The new designs incorporate one dimensional photonic crystals as band pass filters that reflect short light wavelengths (400 - 867 nm) and transmit longer wavelengths(867 -1800 nm) at the interface between two adjacent cells. In addition, nano structured diffractive gratings that cut into the photonic crystal layers are incorporated to redirect incoming waves and hence increase the optical path length of light within the solar cells. Two designs based on the nano structured gratings that have been realized using the scattering matrix and particle swarm optimization methods are presented. We also show preliminary fabrication results of the proposed devices.

We present a fiber-to-waveguide coupling structure, the so-called vertical J coupler, based on the parabolic reflector. The device addresses the multiple objectives of high coupling efficiency, large bandwidth operation, polarization insensitivity, and compact footprint. The optical mode emanating from a fiber arranged normal to the plane of the substrate is incident underneath the parabolic reflector, turned through 90 degrees and focused into a dielectric waveguide. The viability of the coupler is demonstrated by finite-difference time-domain electromagnetic simulation as well as preliminary fabrication and optical testing of the device.

The size of infrared camera systems can be reduced by collecting low-resolution images in parallel with multiple narrow-aperture lenses rather than collecting a single high-resolution image with one wide-aperture lens. We describe an infrared imaging system that uses a three-by-three lenslet array with an optical system length of 2.3 mm and achieves Rayleigh criteria resolution comparable with a conventional single-lens system with an optical system length of 26 mm. The high-resolution final image generated by this system is reconstructed from the low-resolution images gathered by each lenslet. This is accomplished using superresolution reconstruction algorithms based on linear and nonlinear interpolation algorithms. Two implementations of the ultrathin camera are demonstrated and their performances are compared with that of a conventional infrared camera.

We consider the eigen-fields of a two-dimensional negative-refraction photonic crystal and obtain negative effective permittivity and negative effective permeability. Effective permittivity, permeability, and surface impedance are calculated by averaging the eigen-fields. The value of the surface impedance is shown to be location-dependent and is validated by finite-difference time-domain simulations. The unique power propagation mechanism in the photonic crystal is demonstrated through time-evolution of eigen-fields.

In this work, we present for the first time a new and realistic application of the "perfect lens", namely, electromagnetic traps (or tweezers). We combined two recently developed techniques, 3D negative refraction flat lenses (3DNRFLs) and optical tweezers, and experimentally demonstrated the very unique advantages of using 3DNRFLs for electromagnetic traps. Super-resolution and short focal distance of the flat lens result in a highly focused and strongly convergent beam, which is a key requirement for a stable and accurate electromagnetic trap. The translation symmetry of 3DNRFL provides translation-invariance for imaging, which allows an electromagnetic trap to be translated without moving the lens, and permits a trap array by using multiple sources with a single lens. Electromagnetic trapping was demonstrated using polystyrene particles in suspension, and subsequent to being trapped to a single point, they were then accurately manipulated over a large distance by simple movement of a 3DNRFL-imaged microwave monopole source.

In this paper, we demonstrate a 2-bit optical analog-to-digital (A/D) converter. This converter consists of three cascaded splitters constructed in a self-guiding photonic crystal through the perturbation of the uniform lattice. The A/D conversion is achieved by adjusting splitting ratios of the splitters through changing the degree of perturbation. In this way, output ports reach a state of '1' at different input power levels to generate unique states desired for an A/D converter. To validate this design concept, we first experimentally characterize the relation between the splitting ratio and the degree of lattice perturbation. Based on this understanding, we then fabricate the 2-bit A/D converter and successfully observe four unique states corresponding to different power levels of input analog signal.

The first AlGaAsSb/InGaAsSb phototransistors with a cutoff wavelength (50% of peak responsivity) of 2.4 µm operating in a broad range of temperatures are reported. These devices are also the first AlGaAsSb/InGaAsSb heterojunction phototransistors (HPT) grown by molecular beam epitaxy (MBE). The new MBE-grown HPT exhibited both high responsivity R (up to 2334 A/W for λ=2.05 µm at−20°C) and specific detectivity D* (up to 2.1×1011 cmHz1/2/W for λ=2.05µm at −20°C).

We present an auxiliary differential equation Finite-difference Time-domain (ADE-FDTD) approach to numerically model the wave propagation within a gain or absorbing medium such as quantum well structures. Start from traditional quantum electronics theory, the macroscopic susceptibility of the semiconductor is derived and expressed by a multiple-Lorentz-like model based on Prony's method. With the auxiliary differential equation method each Lorentz-like model can be simulated in the time domain and the induced polarization is then determined by summing all the models. By incorporating the induced polarization into the time-domain Maxwell's equations, electromagnetic wave propagation in the quantum well medium can be accurately modeled using the FDTD method.

We demonstrate the use of silicon photonic crystal based microcavity structures to perform light modulation at potentially giga-Hertz speeds through the use of optically induced plasma dispersion. The cavity configurations considered have the potential to operate at low pump power when the Q of the cavity involved is maximized.

We demonstrate nondefect mid-infrared waveguides based on the self-collimation effect in photonic crystals (PhCs). Due to the spatial dispersion properties serving to confine and route light, propagation loss as low as 2.56 dB/mm is obtained in a silicon-on-insulator (SOI)-based waveguide. The efficiency, together with their ability of arbitrary and structureless routing of electromagnetic beams, of these self-collimation devices provide a potential candidate for miniaturizing devices.

We demonstrate an efficient prism coupling method to couple nonplanar infrared waves into a 2-D planar photonic-crystal PhC de- vice, such as a PhC waveguide PhCW. A coupling efficiency of 31.1% is obtained experimentally. Results from finite-difference time-domain FDTD modeling are shown to closely match the results measured in a fabricated sample. © 2005 Society of Photo-Optical Instrumentation Engineers.

This paper focuses on the integration of InGaAsSb photodetectors along with micro-optics in order to realize a prototype system that can achieve a stronger response during atmospheric profiling and spectroscopy measurements. The integration of the detector was executed using a novel conductive-adhesive-based flip-chip integration process. The design, fabrication, and integration of the constituent technologies and experimental results from their characterization are presented.

We demonstrate a guided resonance filter based on photonic crystals (PhCs), which are fabricated in a high-permittivity material. The resulting spectra from a three-dimensional analysis of the structure and experimental measurement results show sharp dips and flattop transmissions. These provide promising properties in constructing sensitive and compact wavelength-selective devices, such as wavelength-division multiplexers.

We experimentally demonstrate subwavelength imaging by a “flat cylindrical” lens using negative refraction. A two-dimensional photonic crystal whose dispersion at the second band provides group velocity opposite to the phase velocity for electromagnetic waves is employed to realize the flat lens, and the working frequency is chosen so that the effective refractive index is approximately equal to −1.0. Experiment demonstrated the imaging of a point source in both amplitude and phase in the millimeter-wave regime. By measuring the field distributions in the object plane and image plane, we observed amplification of evanescent waves and subwavelength size image. The image of two incoherent sources with subwavelength distance showed two resolvable spots, which served to further verify subwavelength resolution.

We present a promising coupling device, namely, a terahertz (THz) planar photonic crystal (PhC) lens based on the effective refractive-index contrast between the PhC and the surrounding unpatterned area. Three-dimensional finite-difference time-domain calculations show a 90% power transfer from a 100-microm silicon waveguide to a 10-microm waveguide, and 45% coupling efficiency is confirmed experimentally. These results demonstrate the utility of the PhC lens as an effective approach to coupling into PhC THz circuits.

In this letter we present a revised formulation of the plane wave method (PWM) for the band structure calculation of photonic crystals. In comparison to the conventional PWM, the formulation in this letter allows for modeling of dispersive material. One application of the presented method is for band structure calculations of photonic crystal slabs. While a thin photonic crystal slab is considered, a full three-dimensional (3D) problem can be reduced to a two-dimensional one by using the effective index method. However, the obtained effective index of such a slab is frequency dependent. The revised PWM is then applied to solve this problem. The results obtained using this algorithm have been compared with those using a full 3D finite-difference time-domain method and found to agree very well.

We demonstrate that guided resonant modes can be readily observed in asymmetrical photonic crystal slabs on high-index substrates. In spite of the high radiative loss associated with all optical modes in these cases, the guided resonant modes are found to give rise to strong high-Q features in the transmission spectra. Since these photonic crystal structures are far more robust and easier to fabricate than the free-standing photonic crystal membranes used in previous studies of guided resonant modes, detailed studies of relevant optical phenomena and the implementation of proposed applications are greatly simplified.

We describe a design methodology for synthesizing polarization-sensitive diffractive optical elements based on two-dimensional form-birefringent microstructures. Our technique yields a single binary element capable of producing independent phase transformations for horizontally and vertically polarized illumination. We designed two elements for operation at 10.6 microm and fabricated them in silicon. Qualitative experimental results agree with design predictions.

Micro-optics offers the ability to realize massively parallel, surface-normal interconnects at the chip scale. In this context, we investigate the integration of a 10-Gbytes/s, 850-nm vertical-cavity surface-emitting laser (VCSEL) with a 2×2 array of continuous surface profile, diffractive optical elements to demonstrate a prototype system that incorporates 3-D, highly dense, parallel optical interconnects. The integration is achieved using a novel conductive polymer-based flip-chip process, which is implemented using conventional fabrication techniques. We present experimental results from the design, fabrication, integration, and characterization of the prototype system.

For highest efficiency optical devices, it is desirable to form continuously graded device features. We describe a technique to produce such features through the fabrication of a continuous-tone grayscale mask and subsequent grayscale photolithography. The design of the mask fabrication process is outlined, including the high-energy-beam-sensitive (HEBS) glass electron-beam exposure response characterization, and the generation of an exposure profile with inherent proximity effect correction. Application of the process is demonstrated through fabrication of smooth-facet retroreflectors, with features that are not possible to produce either by a grayscale process that employs discreet gray levels or by anisotropic wet etch techniques.

We present a new algorithm for calculation of the band structure of photonic crystal slabs. This algorithm combines the plane-wave expansion method with perfectly matched layers for the termination of the computational region in the direction out of the plane. In addition, the effective-medium tensor is applied to improve convergence. A general complex eigenvalue problem is then obtained. Two criteria are presented to distinguish the guided modes from the PML modes. As such, this scheme can accurately determine the band structure both above and below the light cone. The convergence of the algorithm presented has been studied. The results obtained by using this algorithm have been compared with those obtained by the finite-difference time-domain method and found to agree very well.

We present a method for parallel coupling from a single-mode fiber, or fiber ribbon, into a silicon-on-insulator waveguide for integration with silicon optoelectronic circuits. The coupler incorporates the advantages of the vertically tapered waveguides and prism couplers, yet offers the flexibility of planar integration. The coupler can be fabricated by use of either wafer polishing technology or gray-scale photolithography. When optimal coupling is achieved in our experimental setup, the coupler can be packaged by epoxy bonding to form a fiber-waveguide parallel coupler or connector. Two-dimensional electromagnetic calculation predicts a coupling efficiency of 77% (- 1.14-dB insertion loss) for a silicon-to-silicon coupler with a uniform tunnel layer. The coupling efficiency is experimentally achieved to be 46% (-3.4-dB insertion loss), excluding the loss in silicon and the reflections from the input surface and the output facet.

We present the design and electromagnetic analysis of an all-diffractive millimeter-wave imaging system having a field of view of +/- 15 degrees. This system consists of two 16-level diffractive lenses, with the stop in contact with the first lens. By considering the Seidel aberrations for a diffractive lens and applying the corresponding stop shift formula, we established the expressions of third-order wave aberrations for this system. By setting all primary Seidel aberrations to zero and solving the corresponding system of equations, we obtained two sets of solutions for this two-element all-diffractive system, which totally compensate for all Seidel aberrations. To assess image system performance, we apply the finite-difference time-domain technique and a vector plane-wave spectrum method, in combination, to validate the performance of the system. To reduce the computational cost and thereby enable the complete electromagnetic analysis of the system, a four-step analysis procedure has been developed and applied as an electromagnetic system model.

This paper presents the implementation of a parallelized Finite- Difference Time-Domain method, based on the Message Passing Interface (i.e. MPI), which is used to study the modal properties of three-dimensional (3D) dielectric waveguide structures. To this end, we also use the leastsquare method to obtain the wave vector, beta, along the axis of propagation. Lastly, bending losses in arbitrary-angle waveguides are also discussed.

A terahertz-scale two-dimensional photonic-crystal waveguide based on a silicon-on-insulator was fabricated, and the optical transmission spectrum was measured. Terahertz beam propagation characteristics were observed using a thermal imaging camera, with incident light in the 10.1-10.7 microm range. The measured transmission spectrum was in good agreement with a three-dimensional finite-difference time-domain calculation.

We describe a simple and effective method, based on a combination of centrifugation and spin coating, developed for the fabrication by self-assembly of photonic crystal structures. The process produces compact 3-D arrays of polystyrene microspheres (opals) that are organized into crystalline lattices with single-crystal regions up to several hundred micrometers in size. These arrays are subsequently used as templates for infiltration with polyurethane. The resulting inverse opals are characterized by Fourier transform IR reflection spectroscopy and exhibit strong reflectivity for a band of wavelengths in excellent agreement with band structure calculations. This process offers the ability to rapidly form 3-D photonic crystals using inexpensive instrumentation, which makes it attractive for an array of applications. Process parameters, fabricated structures, and their experimental characterization are presented.

We propose and demonstrate a process for fabricating large-area photonic-crystal slabs with designed defects. The process takes advantage of a property we have observed in certain photoresists. These resists, which under ultraviolet illumination exhibit positive tone, behave as negative resists under electron-beam exposure. Electron-beam exposure is used first to expose defect structures, which renders them insensitive to further exposure. Subsequently, a large area is exposed with a photonic-crystal structure consisting of a regular pattern of holes defined by the interference between several ultraviolet laser beams. Upon chemical developing, a large photonic-crystal region with local patterned defects is created in the resist. The patterned resist is used as an etch mask for etching a slab of high-refractive-index material. In this article, we describe the fabrication process and present fabricated structures.

A photonic crystal (PhC) horn is presented. Using the finite- difference time-domain method with the perfectly matched layer (PML) absorbing boundary condition (ABC) in inhomogeneous media, we opti- mize the mismatch factor between a PhC horn and waveguide to achieve high radiation efficiency. The optimized PhC horn is then used to construct an horn array of 25 elements, whose element weights and element positions are optimized using simulated annealing (SA) to acheive continuous beam steering in the range between 215 and 15 deg with the maximum side lobe of less than 210 dB. © 2004 Society of Photo