Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session J41: Photonics/Optoelectronics |
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Sponsoring Units: FIAP Chair: Donald Morelli, Michigan State University Room: Colorado Convention Center 504 |
Tuesday, March 6, 2007 11:15AM - 11:27AM |
J41.00001: Chemically and Electrically Tunable Block Copolymer Photonic Gels: Exceptionally Large Tunability via Uniaxial Swelling Youngjong Kang, Joe Walish, Taras Gorishnyy , Edwin L. Thomas Many potential applications of photonic band gap (PBG) materials have been limited by their insufficient tunability and sensitivity as well as their difficulty of fabrication. Self-assembly of block copolymers could provide an unraveling route for addressing these problems. Here we report the preparation of chemically and electrically tunable PBG materials from self-assembly of PS-b-P2V. Because of the unique meso-lamellar gel structures, where the swellable P2VP gel layers are bound on the glassy PS layers, our photonic gels expand only uniaxially normal to the substrate, and which gives extremely large tunability from UV-VIS to NIR region. Using the osmotic deswelling, we demonstrate dynamically and reversibly tunable photonic gels in aqueous salt solution. We also demonstrate the electrical tunability for the same system by using electrophoretic control of domain spacing. We anticipate our material can be applicable to many novel applications including an active component of display devices, electrically tunable lasers, and electrically controlled photonic switches. [Preview Abstract] |
Tuesday, March 6, 2007 11:27AM - 11:39AM |
J41.00002: Polarization conversion in a silica microsphere Pablo Bianucci, Chris Fietz, John W. Robertson, Gennady Shvets, Chih-Kang Shih Light transmitted through a waveguide coupled to a whispering gallery mode (WGM) resonator will experience a non-linear phase shift. Microsphere WGMs can be of two orthogonal polarizations, and they are non-degenerate. We can exploit the non-degeneracy of the modes and the induced phase shift to convert the incoming polarization to its orthogonal one with high efficiency. We have experimentally demonstrated a conversion efficiency of 75\% on a silica microsphere. [Preview Abstract] |
Tuesday, March 6, 2007 11:39AM - 11:51AM |
J41.00003: Light Propagation in Colloidal Glass: enhancement of scattering at reduced coordination number Xiaotao Peng, A.D. Dinsmore We measure the propagation of light through random films of strongly-scattering microspheres as a function of the mean number of contacts per particle (the coordination number, $Z)$. Two kinds of colloidal spheres are mixed to prepare dried films with random structure. Latex spheres coated with a high-index ZnS are mixed in various ratios with PMMA spheres and the PMMA spheres are then dissolved by acetone. The transport mean-free path of light $l$* is then extracted from measurements of coherent backscattering of light from the films. We found a minimum of $l*$ (maximum of scattering) occurs around $Z$=4, not in a close-packed film (Z$\sim $11), which is counterintuitive. In a simple mean field model, decreasing $Z$ reduces the local average refractive index and enhances the optical contrast of each scattering sphere with the effective background, thus reducing $l$*. These results may guide our understanding of the propagation of waves in random media in general and may lead to new photonic materials. This work is supported by the NSF-sponsored UMASS MRSEC. A.D.D is a Cottrell Scholar of the Research Corporation. [Preview Abstract] |
Tuesday, March 6, 2007 11:51AM - 12:03PM |
J41.00004: Bio-functional subwavelength optical waveguides for chemical detection. Donald Sirbuly, Olgica Bakajin, Aleksandr Noy Compact, reusable biochemical sensors are highly desirable for rapid on-site analytical analysis of gas and liquid mixtures in the field. A key to miniaturizing devices and providing reliable quantitative chemical identification of small sample volumes hinges on the development of novel materials capable of multiple complementary sensing modalities. Here we build a bio-functional optical sensing platform that utilizes the evanescent field of a subwavelength nanowire waveguide to detect single biochemical molecules. The optical cavities are integrated into polymeric flow cells for rapid chemical functionalization, multiplex sensing and reusability. The biocompatibility of the waveguide is assured by assembling fluid lipid membranes tagged with receptor molecules within the evanescent field. With the advantage of carrying out multiple spectroscopy techniques such as absorbance, fluorescence and surface enhanced Raman spectroscopy (SERS) on sub-picoliter probe volumes, these evanescent field sensors offer a unique design for portable all-optical detection systems. This work was performed under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under Contract W-7405-Eng-48. [Preview Abstract] |
Tuesday, March 6, 2007 12:03PM - 12:15PM |
J41.00005: Focused Surface Plasmons for Enhanced Raman Scattering Alexandra Imre, John T. Bahns, Liaohai Chen, John E. Pearson, Jon M. Hiller, Vitalii K. Vlasko-Vlasov, Ulrich Welp Surface plasmon polaritons launched at concentric arcs can be focused into a sub-wavelength wide focal spot of high near-field light intensity. When increasing the number of arcs from one to eight the focused intensity increases by a factor of 30. The focused plasmons give raise to enhanced Raman scattering from R6G molecules placed in the focal area. By exploiting the polarization dependence of the focusing we establish an enhancement of the Raman signal by a factor of three. Our results show that focusing of propagating surface plasmons on flat metal surfaces may be an alternative to localized plasmons on metal nanostructures for achieving enhanced Raman scattering. In particular, a flat metal substrate enables better control over the local electric fields and the placement of analyte molecules, and, therefore, ultimately better fidelity of Raman spectra. [Preview Abstract] |
Tuesday, March 6, 2007 12:15PM - 12:27PM |
J41.00006: Evanescent field response to small patterned features on a planar waveguide biosensor Guangwei Yuan, R. Yan, M. Stephens, D. Dandy, K. Lear A novel optical sensor is developed on the concept that the evanescent field surrounding the core of an appropriately designed waveguide can be very sensitive to the local refractive index of the cladding surrounding the core. The formation of a protein- or ssDNA-based adlayer via specific binding of an analyte target to one of several localized patches of immobilized biological molecule probes can be detected by measuring the change in the evanescent field of the waveguide. The biosensor studied is based on a waveguide fabricated from a high refractive index silicon nitride thin film surrounded by a lower cladding of silicon dioxide and an upper cladding of air or water. To detect small features, the thickness of the waveguide core is optimized to be a fraction of a micrometer. In this study, the response of the sensor to small polymer features (1$\times $1 $\mu $m$^{2}$, 20 to 80 nm thick) with indices of refraction comparable to biological material is evaluated using near field scanning optical microscopy (NSOM). The results have significant implications for the density of a sensor array, particularly in two-dimensional arrays. Issues such as transient interference and positional dependency are addressed. [Preview Abstract] |
Tuesday, March 6, 2007 12:27PM - 12:39PM |
J41.00007: Surface-plasmon-polariton band structure of nanostructured multi-layer systems Erich Runge, Stephan Schwieger, Parinda Vasa We calculate the optical response of multi-layer systems where at least one layer contains arrays of metalic substructures of nanometer size. The dependence on lattice constant and excitation energy is studied systematically. An - at first glance non-intuitive - dependence of the plasmon intensity on the geometry of the metalic substructures is observed numerically. Generalizing the work of Park and Lee [PRL 95, 103902 (2005)], the results are interpreted in terms of plasmon-plasmon and plasmon-radiation couplings of different strength. A rich surface-plasmon-polarition bandstructure with ``gaps'' due to avoided crossings is seen. Super- and subradiant modes are found in the vicinity of those features. [Preview Abstract] |
Tuesday, March 6, 2007 12:39PM - 12:51PM |
J41.00008: Photonic bandgap properties of gradient-index thin films with one-dimensional periodicity and anisotropic structure. Matthew Hawkeye, Michael Brett Glancing angle deposition is a single-step fabrication technique providing \textit{in-situ} control over the internal columnar structure of the deposited thin film. Using this technique, the density of thin TiO$_{2 }$films are varied sinusoidally along the substrate normal direction with a physical periodicity equivalent to wavelengths in the visible spectrum. As radiation propagates in the film, constructive and destructive interference effects lead to the observation of photonic bandgap properties. Optical characterizations of the films are performed to examine the properties of the photonic stopband. These results examine stopband behavior for light at non-normal incidence and of different polarization states. The incorporation of structural defects in the film to introduce and control optical states within the stopband is also studied. The observed properties are related to the structure of the films using effective medium theory and solution of Maxwell's equations in anisotropic media. [Preview Abstract] |
Tuesday, March 6, 2007 12:51PM - 1:03PM |
J41.00009: Periodically bent porous metal oxide nanostructures as linear polarization selective Bragg filters Nicholas Wakefield, Kyrylo Tabunshchyk, Michael Brett, Andriy Kovalenko, Jeremy Sit The periodically bent nematic liquid crystal (LC) phase is a theoretical arrangement characterized by uniaxial rod shaped mesogens in an s-shaped configuration. The periodically bent phase is predicted to yield strong linear polarization selective Bragg effects due to the modulation of the extraordinary refractive index throughout the sample. Unlike the analogous selective circular Bragg effects obtained from the readily achievable chiral nematic LC phase, the periodically bent nematic phase is comparatively more difficult to realize. Glancing angle deposition is a physical vapour deposition technique which allows for the fabrication of isolated columnar nanostructures, suitable for LC infiltration. Using advanced substrate motion control, s-shaped films and other designs that incorporate a modulated extraordinary index are easily fabricated. Experimental transmittance and reflectance spectra are presented to examine the strength and polarization selectivity of the stopband for as-deposited metal oxide films. The dependencies on film material and deposition angle are investigated. The observed results are compared to simulations obtained using a frequency domain electromagnetic mode solver and to earlier results obtained for the periodically bent nematic LC phase. [Preview Abstract] |
Tuesday, March 6, 2007 1:03PM - 1:15PM |
J41.00010: Extraordinary optoconductance in InSb-Au thin film hybrid structures K.A. Wieland, Yun Wang, S.A. Solin Extraordinary optoconductance (EOC)\footnote{K. A. Wieland \textit{et al}., Appl. Phys. Lett. {\bf88}, 52105 (2006).} is the third reported effect following extraordinary magnetoresistance (EMR) and extraordinary piezoconductance (EPC) that is based on the geometric enhancement of the conductivity of a metal semiconductor hybrid structure (MSH). Using a Van der Pauw plate setup, the voltage of the bare sample is compared directly to that of the MSH to determine the EOC, defined as $\{V_{MSH}-V_{bare}\}/V_{bare}$. In GaAs-In at 30K EOC $\approx$500\% has been observed. Bulk InSb-In structures have a room temperature EOC $\approx$50\%. Prior research\footnote{K. A. Wieland \textit{et al}., Phys. Rev. B., \textbf{73} 155305 (2006).} has shown that the one may increase the EOC by using a semiconductor with a large differential e-h mobility. Te doped $n$-type InSb thin films (n$= 2.11\times10^{22}$ m$^{-3}$ and $\mu_{e} =4.02$ m$^2/$Vs) are therefore prime candidates for room temperature EOC. Thin film Au shunts were chosen because of their coefficient of thermal expansion and non-magnetic properties. These MSHs were illuminated with Ar focused 488.0nm light and studied as a function of the position of the laser spot and temperature.\\ [Preview Abstract] |
Tuesday, March 6, 2007 1:15PM - 1:27PM |
J41.00011: 200 nm deep ultraviolet photodetectors based on AlN R. Dahal, J. Li, Z.Y. Fan, M.L. Nakarmi, J.Y. Lin, H.X. Jiang Aluminium nitride possesses the widest direct bandgap ($\sim $6.1 eV) among all semiconductors and appears to be promising material for the development of deep ultraviolet (DUV), vacuum UV and extreme UV (EUV) detectors. Detectors based on AlN would overcome many limitations imposed by Si technology. The 6.1 eV bandgap not only permits the intrinsic solar blindness but also allows the room temperature operation, which relives the requirements of optical filters and cooling system. We report the fabrication and characterization of Metal-Semiconductor-Metal (MSM) deep ultraviolet photodetectors based on high quality AlN epiyayers grown on sapphire substrate using metal organic chemical vapor deposition. The fabricated detectors have 80 $\mu $m x 80 $\mu $m as an active area with interdigital fingers for Schottky contact with 2 $\mu $m/2 $\mu $m to 4 $\mu $m/ 4 $\mu $m finger width/spacing. The photodetectors exhibit lowest cutoff wavelength at 207 nm with peak responsivity at 200 nm. The AlN MSM detectors possess outstanding features such as extremely low dark current, high breakdown voltage, high responsivity, and high UV to visible rejection ratio. These results demonstrate the high promise of AlN as an active material for DUV opto-electronic device applications. [Preview Abstract] |
Tuesday, March 6, 2007 1:27PM - 1:39PM |
J41.00012: ABSTRACT WITHDRAWN |
Tuesday, March 6, 2007 1:39PM - 1:51PM |
J41.00013: ABSTRACT WITHDRAWN |
Tuesday, March 6, 2007 1:51PM - 2:03PM |
J41.00014: Microlens Fabrication by Fluid Deposition of Curable Optical Polymers Paul Rugheimer, Cameron Chen, Yves Idzerda We utilize a Fluid Microplotter instrument to produce microlenses fabricated from UV-curable polymers with a variety of focal lengths and diameters. The diameters are as small as 10 microns and focal lengths range controllably from 25 microns to several hundred microns. Microlenses such as these are of interest to optics companies for use with diode laser products, for coupling light into waveguides, fiber optics, and other optical components. In addition to precise and repeatable control of the position, size, and focal length of the lenses, we are able to produce them in moderately large arrays consisting of hundreds of lenses, each with a user-defined location. We dispense fluid from a piezoelectrically driven glass micropipette attached to a robotic positioner. Through electronic and positional control of the pipette we are able to precisely vary the position, size, and volume of the lenses. By varying the temperature and surface coatings on the substrate we are able to alter the wetting properties and further control the size and focal length of the lenses. Fabrication and physical properties of the lenses will be discussed as well as preliminary results of the lenses in a prototype device scheduled for future production by a commercial optics company. [Preview Abstract] |
Tuesday, March 6, 2007 2:03PM - 2:15PM |
J41.00015: Efficient calculations of the dielectric response in semiconductor nanostructures for optical metrology Hugh Wilson, Giulia Galli, Francois Gygi, Sebastien Hamel, Andrew Williamson, Ed Ratner, Dan Wack The ability to predict the optical and dielectric properties of semiconductor nanostructures is highly desirable, in order to efficiently couple theory and experiment in the characterization and design of nanostructured materials. For example, in designing optimal procedures for optical metrology, the knowledge of the full dielectric matrix of nanostructures as a function of size and shape would be desirable. However, methods based on Density Functional Theory (DFT) are only computationally feasible for sizes below 2 nm and it is still difficult to extend them to the 5 - 25nm size regime of interest to many experiments. In order to make contact between theory and experiment for this important class of systems, we have developed computational techniques based on the empirical pseudopotential method (EPM). Here we compare EPM and DFT results for small nanostructures and we then use EPM results to discuss the properties of Si spheres and rods in the larger size regime. [Preview Abstract] |
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