Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session Y16: Optics and Optoelectronics |
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Sponsoring Units: FIAP Chair: Stuart A Solin, Washington University Room: Baltimore Convention Center 312 |
Friday, March 17, 2006 8:00AM - 8:12AM |
Y16.00001: Investigations of Carbon Nanotube Networks for use as Transparent Conductors Mark Topinka Recently there has been increasing interest in the physics of conduction through carbon nanotube networks and the possibility of using carbon nanotube networks as transparent conducting layers for solar cells and other optoelectronic applications(1). Conductivities as high as 30 ohm/square with transparencies of about 80{\%} have been reported(2). Here we present results of our work on understanding the underlying physics behind the real-world behavior of these systems and identifying the bottlenecks which are currently limiting their performance. We focus in particular on their possible use in solar cells as a low-cost alternative to more expensive transparent conductor technologies such as Indium Tin Oxide (ITO). We include numerical simulations of conduction through nanotube networks and scanning probe microscopy studies of transport through these systems. (1) L.Hu, D.S.Hecht, G.Gruner, \textit{NanoLetters} \textbf{4}, 2513 (2) Z.Wu, et al, \textit{Science} \textbf{305}, 1273 [Preview Abstract] |
Friday, March 17, 2006 8:12AM - 8:24AM |
Y16.00002: Theoretical model of extraordinary optoconductance in GaAs-In hybrid structures A.M. Girgis, L.R. Ram-Mohan, K.A. Wieland, Yun Wang, S.A. Solin We have recently demonstrated extraordinary optoconductance (EOC) of order 500\% in GaAs-In metal semiconductor hybrid structures (MSHs).\footnote{ K.A. Wieland \textit{et al.}, Applied Physics Letters, submitted.} This is the third example of a geometry driven ``EXX'' phenomenon, the first example of which was extraordinary magnetoresistance (EMR).\footnote{ S.A. Solin \textit{et al.}, Science {\bf289}, 1530 (2000).} However, EOC is the first example of an EXX effect in which the bulk properties of the semiconductor and not the interfacial properties are modified by the external perturbation. Here we describe a Gaussian broadened point charge theoretical model which quantititavely accounts for the dependence of the optocondutance on the position of a focussed Ar laser beam. We also account quantitatively for the temperature dependence of the EOC. Our theoretical model incorporates the Dember effect\footnote{ H. Dember, Phys. Z. {\bf32}, 544 (1931).} directly via the differential mobilities of the electrons and holes. Using these mobilities and a third variable corresponding to the net charge, a good fit to the positional dependence of the voltage is achieved. The strengths and limitations of this theory will be highlighted. [Preview Abstract] |
Friday, March 17, 2006 8:24AM - 8:36AM |
Y16.00003: Extraordinary optoconductance in InSb-In hybrid structures K.A. Wieland, Yun Wang, S.A. Solin, A.M. Girgis, L.R. Ram-Mohan Previously reported extraordinary optoconductance (EOC)\footnote{ K.A. Wieland \textit{et al.}, Applied Physics Letters, submitted.} in degenerate Si-doped $(n\sim 1 \times 10^{18}$ cm$^{-3})$ GaAs-In metal-semiconductor hybrid structures (MSHs) is compared to new experimental results on intrinsic Te-doped $(n\sim4 \times 10^{14}$cm$^{-3})$ InSb-In MSHs. Using a shunted van der Pauw plate, DC and AC voltage measurements of InSb MSHs were acquired. The sample was illuminated with a focused Ar ion laser and studied as a function of wavelength $(457-526$nm$)$, bias current $(\pm100$mA$)$, lateral position (transverse to the beam), and at 300K and 10K. Whereas the optimal room temperature position sensitivity in the case of GaAs is 137 mV/mm for 100mW of 488.0 nm illumination, the corresponding sensitivity of InSb is found to be 1.2 mV/mm for 10 mW of 514.5 nm illumination. The magnitude of the InSb result is surprisingly large given the relative values of band gaps, mobility, carrier concentration, and laser illumination.\footnote{O. Madelung, editor, Data in Science and Technology: Semiconductors - Group IV Elements and III-V Compounds (Springer, New York, 1991).} The origin of this large position sensitive photovoltage will be discussed. [Preview Abstract] |
Friday, March 17, 2006 8:36AM - 8:48AM |
Y16.00004: All-Epitaxial Microcavity for Cavity-QED with Quantum Dots Andreas Muller, Dingyuan Lu, Jaemin Ahn, Deepa Gazula, Sonia Quadery, Sabine Freisem, Dennis Deppe, Chih-Kang Shih We report on the optical characterization of a novel type of optical microcavity that forms a fully-buried semiconductor heterostructure and offers numerous technological advantages such as chemical/mechanical stability, good thermal heat-sinking, and compatibility with electrical injection. Based on epitaxial re-growth over a lithographically-defined, quantum dot-containing mesa, this approach leads to self-alignment of single dots with the field anti-node while simultaneously providing quality factors exceeding 10,000 that support lasing with only a single quantum dot layer. Time-resolved measurements reveal the most basic cavity-QED effect in this structure, namely the Purcell spontaneous emission enhancement. A strong spectral and spatial dependence of this effect is observed using photoluminescence imaging, highlighting in particular the importance of the spatial overlap. [Preview Abstract] |
Friday, March 17, 2006 8:48AM - 9:00AM |
Y16.00005: Ultra-high-Q Microcavities for D$_{2}$O Detection Andrea Armani, Deniz Armani, Sean Spillane, Kerry Vahala Ultra high Q optical microcavities (Q $>$ 10$^{6})$ provide a method for boosting detection sensitivity over conventional detection methods. In a recently published work, the difference between quality factors (Q) of microcavities immersed in D$_{2}$O and H$_{2}$O was measured and calculated. Due to the higher absorption of H$_{2}$O, resonators immersed in H$_{2}$O have lower Q's than those immersed in D$_{2}$O. This difference in absorption can be exploited to use the resonator as a D$_{2}$O detector. The effect on Q is most noticeable at 1300nm, where the Q in water is 10$^{6}$ and the Q in D$_{2}$O is 10$^{7}$. At longer wavelengths, both Q(D$_{2}$O) and Q(H$_{2}$O) are further degraded, reducing the efficacy of detection, and at shorter wavelengths, Q(D$_{2}$O) and Q(H$_{2}$O) become similar, reducing the effect that the presence of D$_{2}$O alone has on Q. By monitoring the quality factor, .01 M concentration of D$_{2}$O in water (10$^{17}$ molecules of D$_{2}$O) has been detected; however, the actual sensitivity limit is far better than this concentration value. Detection has also been demonstrated by cyclic introduction and flushing of D$_{2}$O, leading to cyclic degradation and improvement of the Q, thereby demonstrating reversible detection. [Preview Abstract] |
Friday, March 17, 2006 9:00AM - 9:12AM |
Y16.00006: Radiation-pressure-induced regenerative mechanical oscillations in optical microcavities Hossein Rokhsari, Mani Hossein-Zadeh, Tobias Kippenberg, Tal Carmon, Kerry Vahala A silica microcavity is shown to allow both circulation of long lived cavity photons as well as mechanical vibrations at characteristic radio frequencies. Radiation pressure or the force due to impact of photons can couple the mechanical modes of an optical cavity structure to its optical modes, leading to regenerative RF mechanical oscillations of the micro structure with only micro-Watts of optical threshold power. Embodied within a microscale, chip-based device, this mechanism can benefit both research into macroscale quantum mechanical phenomena and improve the understanding of the mechanism within the context of Laser interferometer gravitational-wave observatory (LIGO). This novel class of oscillators that acquire gain directly from CW optical fields may also find applications in all-optical photonic systems. Through a detailed study of the short-term stability of these optomechanical oscillators we demonstrate that thermo-mechanical noise also referred to as Brownian noise, is the dominant noise mechanism at room temperatures. Preliminary calculations show that lowering the temperature in a vacuum environment may enable the observation of quantum back action noise in microtoroidal resonators. [Preview Abstract] |
Friday, March 17, 2006 9:12AM - 9:24AM |
Y16.00007: Optimizing planar waveguide design for multi-wavelength and nonlinear quantum cascade lasers Scott Howard, Fatima Toor, Anthony Hoffman, Claire Gmachl, Deborah Sivco High performance and novel multi-wavelength quantum cascade (QC) lasers present unique challenges in designing waveguides. We present a computational approach that uses the projected threshold current densities and mode overlaps to iteratively optimize the waveguide design. This program has been used to solve three specific problems by designing: (1) two dual wavelength QC laser structures (a 7.5 and 13.5 $\mu $m, and a 9.5 and 11.5 $\mu $m structure) with the goal of minimizing the threshold current of each pair of lasers simultaneously below the continuous wave threshold while maintaining an operating voltage less than 10 V; (2) a waveguide for high performance QC lasers with the goal of minimizing input electrical power at high operating temperatures; and (3) waveguides for nonlinear QC lasers designed for difference frequency generation with the goal of minimizing the threshold currents of the two integrated pump lasers, maximizing the overlap of the pump light with the monolithically-integrated nonlinear mixing region, and reducing the loss of the non-linear guided mode. [Preview Abstract] |
Friday, March 17, 2006 9:24AM - 9:36AM |
Y16.00008: Distributed Bragg reflectors on quantum cascade lasers fabricated by focused ion beam milling Afusat Dirisu, Claire Gmachl, Deborah Sivco The use of Focused Ion Beam (FIB) milling to fabricate custom gratings on Quantum Cascade (QC) lasers for single mode operation is reported. Using the FIB, gratings that fit specific laser wavelength requirements can be fabricated after all other laser processing is completed. This has the advantage that the processed lasers can be fully characterized before milling to determine the laser gain spectrum and its alignment with the desired emission wavelength, hence allowing the proper choice of the grating parameters, such as period and strength to be tailored to the final device. We have been able to mill gratings onto QC laser ridges using the FIB method to significantly narrow the emission spectrum without compromising other properties, such as output power or threshold, of the working device. We fabricated distributed Bragg reflector gratings approximately 1.2 $\mu $m deep, 250 $\mu $m long, with square profile, and with a period of 1.2 $\mu $m; these were processed on top of 2.7-3 mm long QC laser ridges emitting at 7.7 $\mu $m. We observed single mode operation with a side mode suppression ratio of about 12dB. [Preview Abstract] |
Friday, March 17, 2006 9:36AM - 9:48AM |
Y16.00009: Light propagation in random colloidal films with varying coordination number Xiaotao Peng, Anthony Dinsmore We measure the propagation of light through a random film of strongly-scattering microspheres as a function of the mean number of contacts per particle (the coordination number, Z). Decreasing Z reduces the local average refractive index and enhances the optical contrast of each scattering sphere with the effective background. In our experiments, we mix two kinds of colloidal spheres and prepare a dried film with random structure. Latex spheres coated with a high-index ZnS and poly(methylmethacrylate) spheres are used, as well as SnS$_{2}$ core-shell spheres for the near infrared. The transport mean-free path is then extracted from measurements of coherent backscattering of light from the films; its value is sensitive to Z. The 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] |
Friday, March 17, 2006 9:48AM - 10:00AM |
Y16.00010: Calculations of the Photonic Properties of Two Dimensional QuasiCrystals Weining Man, Orion Crisafulli, Paul Steinhardt, Paul Chaikin Quasicrystals have higher point group symmetry than ordinary crystals, and hence are good candidates for complete photonic bandgaps. Our model system consists of infinite long cylinder dielectric (or air) rods at each Penrose lattice point We took three different approaches in using periodic approximants for these calculations. Our first approach uses a rectangular section of a Penrose tiling of different sizes and at different positions. In the second set of calculations, we generate a series of periodic approximants of the Penrose lattice via an inflation method. Our third approach, a rational number approximation, has the fewest number of defects. The rational number approximant is the best since there are no modes localized along the defects and no artificial modes appear in the gap frequency region. In each case we increased the approximant size until the results converged. Our calculations on 2-D Penrose quasicrystals show very isotropic sizeable complete photonic bandgaps which can be identified with known Bragg scattering peaks. We predict the best Bragg scattering spot and optimize the cylinder size for the widest over all band gap for a given dielectric contrast. We also discuss experimental results on 3D icosahedral quasicrystals in the microwave regime and show that 3D icosahedral quasicrystals are better photonic bandgap candidates than crystalline structures. [Preview Abstract] |
Friday, March 17, 2006 10:00AM - 10:12AM |
Y16.00011: A Magnus Expansion Analysis of Frequency-Dependent Mueller Matrices Michael Reimer, David Yevick We have recently demonstrated that, for any physical system characterized by a non-singular, frequency dependent Jones matrix, the frequency evolution of the corresponding Mueller matrix is described by a differential equation whose general solution can be compactly formulated through the Magnus expansion [M. Reimer, D. Yevick, and D. Dumas, submitted to J. Opt. Soc. Am. A, Photon. Technol. Lett.]. [D. Yevick, T. Lu, W. Huang and W. Bardyszewski to be published in J. Opt. Soc. Am. A]. We subsequently applied our analytic results to optical compensators for communications networks and to the estimation of a system's frequency dependent Mueller matrix based on repeated measurements of the output state of polarization for randomly generated input polarization states [M. Reimer, D. Yevick and D. Dumas, submitted to Photon. Technol. Lett.]. We have also incorporated the Magnus expansion into a Clifford algebra description of polarization evolution. This procedure reformulates numerous physical transformations in a simple and transparent manner [M. Reimer and D. Yevick, submitted to Photon. Technol. Lett.]. [Preview Abstract] |
Friday, March 17, 2006 10:12AM - 10:24AM |
Y16.00012: Nanoscale Motion Detection by Diffraction of Evanescent Waves P. Scott Carney, Devrez Karabacak, Stephen B. Ippolito, M. Selim Unlu, Kamil L. Ekinci Conventional optical techniques such as Michelson interferometry and Fabry-Perot interferometry have been widely used for ultrasensitive motion detection in micro- and nanoscale mechanical devices. Here, we propose a novel motion detection scheme based upon the diffraction of evanescent waves. In this scheme, an evanescent field is formed within the vicinity of a moving device surface. The motion of the surface results in an enhanced scattering of the evanescent field into propagating states. This novel detection scheme appears to have several advantages over conventional techniques: it lowers the background optical signal; if implemented using a solid immersion lens, the effective spot size is reduced. We shall describe a possible implementation of a darkfield microscope for motion detection in a nanomechanical resonator and present numerical analyses. [Preview Abstract] |
Friday, March 17, 2006 10:24AM - 10:36AM |
Y16.00013: High Sensitivity Electro-Optic Field Sensors Anthony Garzarella, Dong Ho Wu, Terence Wieting, Syed Qadri, Randal Hinton The use of electro-optic (EO) crystals for electric field detection has recently gained considerable interest, due to their nonperturbative method of detecting both field amplitude and phase over a wide range of frequencies. One of the technical challenges facing this detection technique is to improve the detection sensitivity. Since the sensor responsivity is proportional to the EO coefficient of the crystal ($r_{33})$, utilizing materials with a large $r_{33}$ values, such as Sr$_{0.75}$Ba$_{0.25}$Nb$_{2}$O$_{6}$ (SBN-75), is the most straightforward approach. However, it was found that in spite of its large EO coefficient, sensors utilizing SBN-75 ($r_{33}^{\exp t} \sim $700 pm/V) showed similar or weaker responsivities than sensors utilizing LiNbO$_{3}$ ($r_{33}^{\exp t} \sim $30 pm/V). The detailed data indicate that the responsivity losses in SBN-75 are produced by optically-induced incoherence in the birefringence of the crystal. In this report, we measure this incoherence, and demonstrate its direct impact on the sensitivity and stability of the EO sensor. [Preview Abstract] |
Friday, March 17, 2006 10:36AM - 10:48AM |
Y16.00014: Characterization of triangular-structured two-dimensional photonic crystals designed for visible wavelengths. Jeffrey Clark, Michael Marciniak, Robert Nelson, James Lott The growing number of fabrication techniques of photonic crystals (PhC) is increasing the number of applications for these devices. This work focuses on the fabrication and characterization of triangular-structured, two-dimensional PhC designed for visible wavelengths. The fabrication processes studied for this PhC are focused ion beam, electron lithography, photolithography, and holographic photo-polymerization/lithography. The fabrication techniques and materials used to create the PhC in part determine the characterization technique required to investigate the PBG. Techniques examined here include the coupling of a beam by means of a prism into a wave-guiding medium in which the PhC has been fabricated, and the guiding of a beam to a PhC through a cylindrical glass container filled with an index matching medium. Analyses of the transmission and reflectance properties of a PhC for various incident angles confirm the presence of a PBG. The design of the PhC was based on a program created to display gap maps for triangular structures. The PBG of the structure, designed from the gap maps, was modeled using another program created to display band diagrams for triangular structures. Finally, FDTD modeling and simulation results are compared to the experimental results. [Preview Abstract] |
Friday, March 17, 2006 10:48AM - 11:00AM |
Y16.00015: Dynamics of lasers coupled by nearest-neighbor interaction Alexandra Landsman, Ira Schwartz The dynamics of arrays of nonlinear oscillators with diffusive coupling are investigated. The types of coupling needed to achieve synchronization are explored. The effects of time-delayed coupling are also considered. The results have implications for the production of coherent radiation in lasers and with suitable modification of the equations may be extended to biological networks. [Preview Abstract] |
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