KEYWORDS: Atmospheric propagation, Microchannel plates, Radio propagation, Data modeling, Image segmentation, Principal component analysis, Hyperspectral imaging, 3D modeling, Solid modeling, Systems modeling
In this paper, we present a set of numerical tools, namely principal component analysis, clustering methods, and a covariance propagation model, that when appropriately assembled, form what we refer to as the mean-class propagation (MCP) method. The MCP method generates clusters of similar class materials in hyperspectral imaging (HSI) scenes while preserving scene spectral clutter information for radiometric transport modeling. We will demonstrate how various implementations of the MCP method can be employed to generate unique HSI products with varying levels of statistical realism across regions in the scene. Such implementations of the MCP method, compared with traditional pixel-based methods, may allow for faster generation of HSI scene data, better insight on how environmental conditions alter the statistical properties of measured scene clutter, and lays a foundation for the formulation of more robust spectral matched filter operations. To quantify the differences between the MCP method and a pixel-based method, we present a comparison computational processing time for each method.
We investigate methods for actively tuning two-dimensional photonic crystal devices by modulating the index of refraction of the constituent materials. The index of refraction is modulated by infiltrating liquid crystals into a photonic crystal lattice of air cylinders in silicon. Moreover, the orientation of the liquid crystal molecules within the cylinders is actively modulated in order to induce a change in the dielectric tensor; thereby, tuning the optical properties of the photonic crystal. We validate and characterize the tunability of these devices both experimentally and with three-dimensional finite-difference time-domain method simulations. Furthermore, we integrate these tunable devices to demonstrate their enhancement of WDM photonic crystal applications.
A novel implementation of a variable beam splitter using a photonic crystal (PhC) is proposed. The beam splitter consists of two periodic structures: a non-channel dispersion guiding region and a band gap based splitting structure. The dispersion guiding PhC structure is used to route the optical wave by exploiting the dispersion properties of the lattice. Arbitrary power ratio between output beams can be achieved by varying the parameters of the splitting structure. Within the studied range of splitting structures, high output power was observed and verified experimentally.
In this paper, we review the confinement mechanism of self-collimation in planar photonic crystals. In this mechanism, an approximately flat equi-frequency contour (EFC) below the light cone of the planar photonic crystal can be used to laterally confine the light and total internal reflection (TIR) provides vertical confinement. To this end, self-collimation in both low-index and high-index planar photonic crystals are investigated using the three-dimensional (3D) finite-difference time-domain (FDTD) method and the 3D iterative plane wave method (PWM). It is found that low-loss self-guiding is achievable in both the valence and conduction bands for high-index planar photonic crystals. However, for low-index planar photonic crystals, low-loss self-guiding can be only observed in the valence band. Experimental results show a propagation loss of as low as 1.1 dB/mm for the self-guiding in a high-index planar photonic crystals.
We present a method for coupling from a single mode fiber, or fiber ribbon, into an SOI waveguide for integration with silicon opto-electronic circuits. The coupler incorporates the advantages of the tapered waveguides and prism couplers, yet offers the flexibility of planar integration. The coupler can be fabricated on a double polished silicon wafer using direct polishing or grayscale photolithography. Tapered waveguides or J-couplers are then used as lateral mode converters. An experimental setup with a rotational stage and a pneumatic plunger has been built for adjusting the incident angle and tunnel layer thickness, which are key factors in determining the coupling efficiency. When optimal coupling is achieved on the setup, the coupler can be packaged using epoxy bonding. Thus, a fiber-waveguide parallel coupler or connector can be easily constructed. Electromagnetic calculation predicts a coupling efficiency of 77%(-1.14dB insertion loss) for a silicon-to-silicon coupler with a uniform tunnel layer. The coupling efficiency is experimentally achieved to be 46%(-3.4dB insertion loss) excluding the loss in silicon and the reflections from the input surface and output facet.
We investigate methods for actively tuning two-dimensional photonic crystal devices by modulating the index of refraction of the constituent materials. The index of refraction is modulated by infiltrating liquid crystals into a photonic crystal lattice of air cylinders in silicon. Moreover, the orientation of the liquid crystal molecules within the cylinders is actively modulated in order to induce a change in the dielectric tensor; thereby, tuning the optical properties of the photonic crystal. We validate and characterize the tunability of these devices both experimentally and with three-dimensional finite-difference time-domain method simulations. Furthermore, we integrate these tunable devices to demonstrate their enhancement of WDM photonic crystal applications.
In this paper we discuss the design and implementation of integrated planar optical devices realized by exploiting the unique dispersion properties of photonic crystal (PhC) devices. In particular, we demonstrate the ability to focus and spatially route optical beams in the absence of channelized structures. By this we mean that these devices do not contain any form of lateral confinement, in the sense of a physical structure, other than the dispersion properties of the crystal lattice. To this end, lateral control is imposed on the propagating wave by virtue of engineering the band structure of the photonic crystal lattice. Our approach to this effort is based on engineering the dispersion diagram of a given periodic structure outside of its band gap. As such, this allows for the determination of unique propagation characteristics and corresponding devices, as we show in theoretical simulations and experimental results.
Techniques for analyzing symmetric and asymmetric polarized modes in coupled photonic crystal waveguides are presented. The techniques employed include the plane wave method (PWM) and the finite-difference time-domain (FDTD) method. Two variants of a photonic crystal directional coupler consisting of air holes in silicon are discussed. Additionally, fabricated photonic crystal directional couplers are characterized and experimental results are presented. Applications for photonic crystal directional couplers include frequency-selective filters, dispersion compensators, and optical switches.
In this paper we present the development of several new and novel fabrication methods for the realization of two-dimensional photonic crystal devices in silicon slab waveguides. We begin by presenting a process for the fabrication of high fill-factor devices in silicon-on-insulator wafers. Next, we present a grayscale fabrication process for the realization of three-dimensional silicon structures, such as tapered horn couplers. We then present the fabrication of suspended silicon slabs using a co-polymer process based on direct write electron beam lithography and silicon sputtering. And lastly, we conclude by presenting an alternate method for realizing PhC devices in a silicon slab based on a combination of wet and dry etching processes in bulk silicon wafers.
In this paper we present the design and characterization of a micro 4f optical imaging system for the purpose of characterizing mesoscopic diffractive optical elements. To this end, we demonstrate the systems' ability to measure very small variation sin diffraction intensity with high resolution. Because the system is illuminated by both coherent and incoherent sources, we characterize the cutoff frequency and modulation transfer function to determine the spatial resolution of the system. The system is validated by comparing measured results to theoretical predictions.
In this paper, we employ a wavelet-based electromagnetic optimization algorithm to enhance multilevel diffractive lens performance. As we show in this paper, the optimized performance and iteration time is very much a function of the initial lens profile. To demonstrate this we analyze various types of initial profiles ranging from scalar-based lenses to flat and random structures. Additionally, we characterize the performance of replicated multilevel lenses fabricated using a soft lithographic technique known as nanoimprint lithography ( NIL) . Experimentalresults are presented.
In this paper we present a study on the performance of diffractive lenses as a function of their f/#. To this end, we study two- and three-dimensional lenses that consist of binary, four-, eight-, and sixteen-level diffractive profiles over a range of f/#s. Lens performance is characterized in terms of diffraction efficiency for lenses of different number of levels and f/#.
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