Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session H31: Photonics and Optoelectronics |
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Sponsoring Units: DPOLY FIAP Chair: Adam Fontecchio, Drexel University Room: LACC 503 |
Tuesday, March 22, 2005 8:00AM - 8:12AM |
H31.00001: Analysis of the diffraction properties of volume holograms written with spherical object beams Michael Ermold, Adam Fontecchio Currently, large area primary mirror technology relies on thin layers of metal to serve as the reflecting surface for light collection. As these mirrors become large, they suffer from structural instabilities requiring complex and expensive support systems to maintain excellent reflected wavefront quality. Thin film holographic optical elements (HOEs) present a unique advantage over traditional optics. Holographic thin films are lightweight and are recorded in a one step process. A large range of focal length mirrors can be realized in these devices; however we expect that the reflected wavefront quality is ultimately limited by the optics used to record the holograms. In lieu of the inherent limitations, our analysis will consist of holograms written with idealized recording wavefronts. These holograms are typically formed by a planar reference beam interfering with a spherical object wave. A closed form function for the volume refractive index modulation for these phase gratings is also derived. Diffraction theory is applied and the diffracted field expression is derived. Through this analysis we are able to describe the spectral response, diffraction efficiency, focusing and imaging properties. [Preview Abstract] |
Tuesday, March 22, 2005 8:12AM - 8:24AM |
H31.00002: Development of High Refractive Index Poly(thiophene) for 3-D Organic Photonic Crystals Stephen Cheng, Shi Jin, Matthew Graham, Timothy Bunning Currently, no polymers have a sufficiently high refractive index to open a complete photonic band gap (PBG) in the commonly used inverse opal structure. Poly(thiophene) (PT) is predicted to have a high enough refractive index, but experimental values have been significantly less then those predicted. To reconcile this discrepancy, the electro-polymerization of thiophene has been optimized. The resulting poly(thiophene) (PT) films had improved structural regularity, and conjugation length. This translated into an elevated refractive index, as measured by Variable Angle Spectrographic Ellipsometry, which was sufficient to open a complete PBG. The next step to realizing an organic 3-D PC was to create high quality opal templates through which the PT could be polymerized. Colloidal crystallization of monodisperse spheres was used to fabricate the templates, while a novel nano-mechnical annealing technique was used to perfect the crystal structure. Taken together these developments offer the opportunity for the first time to make an organic 3-D PC with a complete PBG. [Preview Abstract] |
Tuesday, March 22, 2005 8:24AM - 8:36AM |
H31.00003: Self-Assembly of Conjugated Block Copolymers for Optoelectronic Applications Rachel Segalman, Bradley Olsen, Yuefei Tao Recent breakthroughs in the device physics of organic optoelectronics have demonstrated that the interfaces between two conducting organics of different work function play an integral role in the separation of electrons and holes to generate energy in a photovoltaic cell or conversely in the recombination necessary to generate light. Organic optoelectronics can benefit from interfacial design on the 10nm length-scale of an exciton diffusion length, prompting an extension of controlled block copolymer self-assembly techniques to more complex, conjugated backbone polymers. We synthesize a model poly(phenylene vinylene) (PPV) derivative joined to a polyisoprene or poly(ethylene oxide) coil to prepare a series of rod-coil block copolymers. We demonstrate that by careful tuning of sidechain chemistry and block interactions, we can gain insight into the complex self-assembly of these materials. The interplay between the liquid crystallinity of the rod-like PPV block with the microphase separation of the block copolymer and morphological effects on light emitting diodes and luminescent electrochemical cells will be discussed. [Preview Abstract] |
Tuesday, March 22, 2005 8:36AM - 8:48AM |
H31.00004: Nanomechanical Characterization of Finite-Size Constrained Relaxation Processes in Optoelectronic and Photonic Thin Films Tomoko Gray, Rene Overney, Marnie Haller, Jingdong Luo, Alex Jen In this talk, macroscopically determined optoelectronic phenomena will be linked to nanorheologically deduced structural conformation and molecular dynamics in polymer thin films. We explore molecular relaxation properties of structurally constraint electronic materials using two recently developed scanning force microscopy (SFM) based methods; (i) a method that explores local transition temperatures in ultrathin films [1], and (ii) a method that deduces energy values and critical time scales from inter- and intra-molecular relaxation processes [2]. In particular, the two techniques have provided insight into the molecular reorientation process of dendronized nonlinear optical (NLO) polymers, and finite-size effects on the photoluminescent efficiency of a blue light emitting poly(9, 9-dioctylfluorene) (PFO). [1] T. Gray et al., \textit{Nanorheological Approach for Characterization of Electroluminescent Polymer Thin Films}, Appl. Phys. Lett. \textbf{83}, 2563-2565 (2003). [2] S.E. Sills et al., \textit{Creeping friction dynamics and} \textit{molecular dissipation mechanisms in glassy polymers}, Phys. Rev. Lett. \textbf{91}(9), 095501 (1-4), (2003). [Preview Abstract] |
Tuesday, March 22, 2005 8:48AM - 9:00AM |
H31.00005: Quadratic Electro-Optic Effect and Electroabsorption in a Novel Nano-Optical Material based on the Nonconjugated Conductive Polymer, Poly(ethylenepyrrolediyl) Derivative R. Swamy, P. Vippa, H. Rajagopalan, J. Titus, M. Thakur, A. Sen We report quadratic electro-optic effect and electroabsorption measurements in a novel nano-optical material based on the nonconjugated conductive polymer, iodine-doped poly(ethylenepyrrolediyl) derivative. Such effect has been recently reported in doped polyisoprene [1]. The measurement was made at 633 nm using field-induced birefringence. A modulation of 0.1{\%} was observed for a field of 0.66 V/micron (film thickness 0.3 micron). The change in refractive index, $\Delta $n, is 3.35x10$^{-4}$ and the Kerr constant is 1.2x10$^{-9 }$m/V$^{2}$ which is about 125 times that of nitrobenzene. Modulation due to electroabsorption was 0.05{\%}. The exceptionally large electro-optic effect is most likely due to the specific structure and quantum confinement within a nanometer volume. In contrast, nonlinearity in a conjugated polymer is known to decrease upon iodine doping. [1] Thakur, Swamy and Titus, \textit{Macromolecules}, Vol.37, 2677, (2004). [Preview Abstract] |
Tuesday, March 22, 2005 9:00AM - 9:12AM |
H31.00006: Single- and Two-photon Pumped Defect-Mode Lasing in Dye-doped One-Dimensional Photonic Crystal Jongseung Yoon, Wonmok Lee, Steven Kooi, Jean-Michel Caruge, Moungi Bawendi, Robert Field, Przemyslaw Markowicz, Paras Prasad, Edwin Thomas We have developed a novel dye-doped organic/inorganic hybrid one-dimensional photonic crystal system for single-and two-photon pumped defect- mode lasing. The multilayer laser structure consists of alternating layers of titania nanoparticles and polymethylmethacrylate with an active emission layer of organic dyes. Single-mode lasing actions under one- and two- photon excitation have been observed at a defect-mode wavelength. Effective gain enhancement and low threshold one-and two photon pumped lasing of the photonic bandgap structure will be discussed. [Preview Abstract] |
Tuesday, March 22, 2005 9:12AM - 9:24AM |
H31.00007: Electro-optic Modulation Using a DAST Single-crystal Film in a Fabry-Perot Cavity S.P. Kutty, M. Thakur In this paper, we report a multiple-pass electro-optic modulator using a single- crystal film of 4'-dimethyamino-N-methyl-4-stilbazolium tosylate (DAST) placed inside a Fabry-Perot cavity. The single-crystal film was prepared using the modified shear method. Electro-optic modulation was achieved at 633 nm using field-induced birefringence in the cross polarized geometry including the Fabry-Perot cavity. The modulation due to the electro-optic effect was recorded as a function of phase while the phase was controlled by moving one of the mirrors in the cavity. The observed modulation was high (80 percent) for a low field (0.5V/micron) applied along the charge transfer axis on the film. Similar modulation using the Fabry-Perot cavity with a lower modulation depth was observed involving electroabsorption at 633 nm. Electroabsorption in the DAST film has been recently reported [1]. These are important results considering applications in photonics. [1] ``Electroabsorption in single-crystal film of a second-order optical material,'' R. K. Swamy, S. P. Kutty, J. Titus, S. Khatavkar, and M. Thakur, APL, Vol. 85, 4025, (2004). [Preview Abstract] |
Tuesday, March 22, 2005 9:24AM - 9:36AM |
H31.00008: Investigation of the self-pumped two-beam coupling in a photorefractive material using beam propagation simulation Mohammad Saleh, Partha Banerjee, Gary Cook, Shekhar Guha, Dean Evans Self-pumped contra-directional two-beam coupling is simulated in a photorefractive medium for arbitrary shaped beams using a split-step beam propagation method. When the photovoltaic effect is added to the model that is first developed for diffusion dominated materials, the simulation shows enhancement of the two-beam coupling efficiency, in agreement with published experimental observations. Simulation results including the effects of absorption and dark conductivity will be presented also. [Preview Abstract] |
Tuesday, March 22, 2005 9:36AM - 9:48AM |
H31.00009: Demonstration of Wavelength Tunable Silicon Raman Laser Ozdal Boyraz, Bahram Jalali The need for low cost photonic devices has stimulated significant amount of research in silicon photonics. One approach that has been pursued for light generation and amplification is the utilizing high Raman gain coefficient in silicon. However, free carrier generation due to two photon absorption limited the achieving high Raman gain. Pulsed pumping technique has been utilized to mitigate free carrier accumulation and achieve high gain. We report the demonstration of a Raman laser in silicon waveguide by pulsed pumping technique. A pump laser with 25 MHz repetition rate at 1540 nm and with 30 ps pulses is used to obtain Raman laser in silicon. Lasing is measured at 1675 nm. A clear lasing threshold is observed at 9W peak pulse power along with a slope efficiency of 8.5{\%} above threshold. Temporal and spectral profiles of the silicon Raman laser are studied experimentally. We also demonstrated wavelength tunability of the silicon Raman laser by varying pump wavelength and modifying the cavity resonance. Experimentally we measure lasing from 1667 nm to 1700 nm in silicon. [Preview Abstract] |
Tuesday, March 22, 2005 9:48AM - 10:00AM |
H31.00010: Silicon light emission from {113} rodlike defects Grant Z Pan, Roman Ostroumov, Yaguang Lian, K. N. Tu, Kang L Wang We studied the electroluminescence of p-n junction Si LEDs in correlation with the type of implant-induced defects formed during the post implant anneal. The LEDs were fabricated by boron implantation at an energy of 30 keV with a dose of 1.0 x 10$^{15}$ cm$^{-2}$ into an n-type Si substrate. By varying the post implant annealing conditions to tune the type of defects and by using plan-view transmission electron microscopy to identify them, we found that {\{}113{\}} rodlike defects precipitated along the $<$110$>$ Si before the formation of dislocation loops are the light-emitting centers of the p-n junction Si LEDs. The peak intensity of electroluminescence from {\{}113{\}} rodlike-defect-engineered LEDs is about twenty-five times higher than that from dislocation-loop-engineered LEDs. This finding, for the first time, is highly significant in the development of high efficient defect engineered Si LEDs for all optic monolithic Si microphotonics. [Preview Abstract] |
Tuesday, March 22, 2005 10:00AM - 10:12AM |
H31.00011: Effect of Photovoltaic Induced Instabilities in Photorefractive Reflection Gratings in LiNbO$_{3}$:Fe Jennifer Gibson, Mohammad Saleh, Gary Cook, Dean Evans In LiNbO$_{3}$:Fe, photovoltaic induced instabilities are observed as sudden increases in transmitted power when recording photorefractive reflection gratings for contra-directional two-beam coupling applications. A beam diffracted off the grating while it forms will determine if the phase difference between the space-charge field and interference pattern temporarily changes or if the grating is briefly destroyed. [Preview Abstract] |
Tuesday, March 22, 2005 10:12AM - 10:24AM |
H31.00012: Development of a new photorefractive and photovoltaic potassium niobate crystal D.R. Evans, G. Cook, J.L. Gibson, M.A. Saleh, S.A. Basun, J.M. Seim, G.J. Mizell Photovoltaic measurements have been made on a new doped potassium niobate crystal that yields significantly larger photovoltaic fields than other doped potassium niobate crystals. Contra-directional two-beam coupling efficiencies and Raman spectroscopy measurements have also been conducted, which show major differences with respect to the published results for other doped potassium niobate materials. [Preview Abstract] |
Tuesday, March 22, 2005 10:24AM - 10:36AM |
H31.00013: Reduction of Dark Current in Germanium Quantum Dot Infrared Photodetector Siguang Ma, Song Tong, Hyung-Jun Kim, Joo-Young Lee, K. L. Wang We present theoretical and experimental studies aimed for the reduction of dark current of self-assembled Ge/Si quantum dot infrared photodetector. P-i-p structures were grown with p-type doped Ge dots embedded in the intrinsic Si region using p$^{+}$-type Si (100) substrates. A Si$_{1-x}$Ge$_{x}$ thin layer with high Ge content was inserted in the active region and the quantum well formed in the valence band acts as a current barrier layer (CBL). In simulation, the modification of the hole masses due to strain effects was determined by a k$\cdot $p band structure calculation. Quantum confinement, thermionic emission and scattering process were taken into consideration for carrier transport model in the quantum well region. Simulation study showed that the leakage current can be reduced up to three orders of magnitude. Experiments were carried out to verify the simulation results. The photocurrent to dark current ratio with respect to bias was examined to show the impact of CBL on device performance. [Preview Abstract] |
Tuesday, March 22, 2005 10:36AM - 10:48AM |
H31.00014: EXAFS Study of the Electroluminescence Materials ZnS:Cu,Cl and ZnS:Cu,Mn,Cl, and EL devices Frank Bridges, M. Warkentin, S. A. Carter, M. Anderson When a high-frequency AC voltage is applied to ZnS:Cu,Cl and ZnS:Cu,Mn,Cl devices, optical fluorescence, known as electroluminescence (EL) is observed which depends on both the Cu and Mn dopants. The local structure of these compounds was studied using the EXAFS technique to understand the role of Cu and Mn. Data were taken at the K-edge of Zn, Cu and Mn, for powder material and for both new and aged (degraded) devices. The EXAFS data show that Mn substitutes for Zn in the ZnS lattice, whereas Cu has a different local structure (it cannot be fit to the ZnS structure). For all the Cu edge data, the first shell of neighbors is best fit using an experimental standard obtained from CuS suggesting that almost all of the Cu resides in tiny CuS-like clusters. Since these clusters are dominant in both the new and degraded samples and do not change with aging, they likely do not contribute directly to the luminescence. Consequently, our results indicate that a very small fraction of the Cu atoms are EL active, possibly isolated defects (substitutional in ZnS) or pairs. Annealing at high T shows that degraded samples can be rejuvenated. Thus, one possible explanation for the rapid degradation of a device is that the isolated Cu ions electro-diffuse to the CuS-like clusters, at which point they no longer produce EL. [Preview Abstract] |
Tuesday, March 22, 2005 10:48AM - 11:00AM |
H31.00015: Anomalous space-charge field enhancement in Fe:KNbO3 Gary Cook, Dean Evans, Sergei Basun, Jennifer Gibson, Mohammad Saleh Photorefractive measurements on Fe:KNbO$_{3}$ using self-pumped two-wave mixing have revealed the formation of a large bulk electric field with characteristics similar to those arising from the photovoltaic effect. The magnitude of the field necessary to account for the observed optical effects is much greater than the directly measured photovoltaic field. [Preview Abstract] |
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H31.00016: Microbeam HRXRD and Photoluminescence characterization of selective area grown (SAG) optoelectronic waveguide arrays A.A. Sirenko, S. O'Malley, A. Kazimirov, D.H. Bilderback, Z.-H. Cai, B. Lai, A. Ougazzaden We present microbeam high-resolution x-ray diffraction (HRXRD) and micro-Photoluminescence analysis of the InGaAlAs-based MQW ridge-waveguide arrays for monolithically integrated optoelectronic devices. Waveguide arrays have been produced by the MOVPE technique in the Selective Area Growth (SAG) regime with the waveguide width varied from 1.6 to 60 $\mu$m and the distance between the waveguides of 5 $\mu$m. Synchrotron Radiation-based HRXRD measurements with the angular resolution of 3 arcsec were carried out at CHESS (beamsize of 10 $\mu$m) and APS (beamsize of 0.35 $\mu$m). Strain, thickness, and composition variation in the active region of the ridge waveguides have been measured and compared for the regimes of the selective growth controlled by the gas-phase diffusion and surface migration of the metal-organic precursors from the masked regions. Strong contribution of the surface migration from the oxide mask into the SAG growth process has been observed for the waveguides with the width $<$ 10 $\mu$m. Strain-induced relaxation effects in the active regions have been studied using micro-beam reciprocal space mapping analysis. [Preview Abstract] |
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