... PROGRAM ELEMENT NUMBER 6. AUTHOR(S) Kelvin H. Wagner, University of Colorado, Boulder Dana An... more ... PROGRAM ELEMENT NUMBER 6. AUTHOR(S) Kelvin H. Wagner, University of Colorado, Boulder Dana Anderson,University of Colorado, Boulder Zoya Popovic, University of Colorado, Boulder Randall W. Babbitt, Montana State University Andre Knoesen, University of ...
Alternatives to the Perfectly Matched Layer for Waveguide Simulation Using the FDFD Method
Electromagnetics, 2005
One of the most widely utilized absorbing boundaries for the finite difference frequency domain (... more One of the most widely utilized absorbing boundaries for the finite difference frequency domain (FDFD) method is the perfectly matched layer (PML); however, this boundary is not ideal, as it significantly increases the computational complexity of a simulation. We compare three alternatives to the PML for modal solution using the FDFD method: the Higdon absorbing boundary condition, the complementary operators
Synthesis and Nonlinear Optical Properties of a Peripherally Functionalized Hyperbranched Polymer by DR1 Chromophores
ACS Applied Materials & Interfaces, 2009
The first peripheral postfunctionalization of a hyperbranched polyimide by nonlinear optic chromo... more The first peripheral postfunctionalization of a hyperbranched polyimide by nonlinear optic chromophores (DR1 derivative) was achieved using two different routes. The first one consists in the esterification of the terminal carboxylic acid groups, whereas the second is based on copper-catalyzed Huisgen reaction of the terminal propargylic ester groups. The resulting polymers display good solubility in classical organic solvents and good filmability because thick films can be prepared (up to 2.7 mum). The second-order nonlinear optical properties were measured by SHG at 1064 nm and we show that these hyperbranched polymers exhibit good poling efficiency and good thermal stability since the electro-optic activity remains stable up to 130 degrees C. These results illustrate the potential of hyperbranched polymers to host second-order nonlinear optical chromophores to replace dendrimers or classical linear polymers generally used in this area.
Most wine fermentations are completed in successive batches during a 2 month harvest period. Red ... more Most wine fermentations are completed in successive batches during a 2 month harvest period. Red wine fermentations are usually completed in 10 to 14 days, while white wine fermentations are completed in 21 to 24 days. The demand for resources-equipment, water, energy, labor, etc.-in a short time motivates the precise, automated control of the fermentation process. While the effects of temperature on wine chemistry are well studied, few advanced control strategies have been developed for the precise control of temperature for wine chemistry research. In this study, a nonlinear model predictive controller (NMPC) was developed to determine the temperature to achieve the desired fermentation rate. The controller was combined with a pulse cooling and heating strategy to improve the energy efficiency of temperature control. The feasibility of this approach is demonstrated by simulations and experiments in 15 L fermentations.
Characterization of Nonlinear Polymers for High-speed Photonic Response and Nonlinear Dispersion
Abstract : High-frequency instrumentation was acquired to perform: (a) high-frequency dielectric ... more Abstract : High-frequency instrumentation was acquired to perform: (a) high-frequency dielectric measurements on poled electro-active polymers and to determine the stability when exposed to microwave radiation, and (b) electro-optic measurements of the resonant enhancement of nonlinear polymers with demonstrated photochemical stability. In particular, the equipment was used to investigate large-bandwidth, traveling wave polymeric in-line fiber (PILF) modulator that is being co-developed by UC Davis and Optivision. This PILF amplitude modulator consists of a fiber half-coupler substrate evanescently coupled to a multimode electro-optic waveguide. PILF modulators are intrinsically rugged, exhibit low third order intermodulation nonlinearity and can be produced at lower cost than fiber pigtailed modulators. The equipment consisted of a high-frequency probe station, high-frequency amplifier and signal generator, 15 GHz photodetector, low relative intensity noise fiber coupled 1330 nm laser, and a 1064 diode pumped laser. The deviations from the original budget are that the $30K in UC cost sharing was used towards a laser ablation accessory for the probe station (instead of the thermal evaporator), the elimination of the 1550 nm laser source and the purchase with fund remaining a high-frequency signal generator.
An efficient finite-diference frequency domain-method for waveguiding structures including thin curved layers
Microwave and Optical Technology Letters, 2006
Absorption of polymers for optical waveguide applications measured by photothermal deflection spectroscopy
Linear and Nonlinear Optics of Organic Materials, 2001
A technique based on photothermal deflection spectroscopy has been developed for measuring the ab... more A technique based on photothermal deflection spectroscopy has been developed for measuring the absolute absorption of polymers. The technique utilizes the frequency dependence measurement of the deflection signals to retrieve polymers' thermal properties and experimental parameters that are necessary to convert the deflection signals to the absolute absorption coefficients. All the measurements are done on the same experimental setup and the same sample without the need of obtaining either the materials' thermal properties or the reference absorption coefficients from other sources. This technique has been applied to several polymers and the results are reported.
Frontiers in Optics 2007/Laser Science XXIII/Organic Materials and Devices for Displays and Energy Conversion, 2007
ABSTRACT Polysiloxane and conductive polymers were integrated onto a side-polished optical fiber ... more ABSTRACT Polysiloxane and conductive polymers were integrated onto a side-polished optical fiber to implement a variable optical attenuator. A conductive polymer thermo-optically altered the refractive index of elastomer placed in close proximity to a fiber core.
<title>Absolute absorption measurements in polymer films using photothermal deflection spectroscopy</title>
Organic Photorefractives, Photoreceptors, Waveguides, and Fibers, 1999
ABSTRACT
Transit time coplanar probe for biomolecular interactions at an aqueous–solid interface
Sensors and Actuators A: Physical, 2007
The displacement of water from a solid–aqueous interface by a low-dielectric constant film that i... more The displacement of water from a solid–aqueous interface by a low-dielectric constant film that is a few nanometers thick can be detected as a change in the transit time of a baseband electrical pulse, of picosecond duration, propagating in a coplanar transmission line. The results of an electromagnetic analysis are experimentally verified by depositing polyelectrolyte monolayers on the probe surface and measuring changes in the pulse transit time of a short baseband electrical pulse.
RF Photonics for Array Processing MURI 5th Year Summary
... wide-bandwidth and multidimensional analog signal processing, GOMAC 03, Tampa, FL, Apr. 2003.... more ... wide-bandwidth and multidimensional analog signal processing, GOMAC 03, Tampa, FL, Apr. 2003. 13. Kelvin H. Wagner, Zoya Popovic, Dana Z. Anderson, Randall W, Babbitt, Lloyd Grif-fiths, Andre Knoesen, &quot;RF Photonic Systems for Array Control and Processing,&quot; In-...
Methods for calculating the optical properties as a function of wavelength for second-order nonli... more Methods for calculating the optical properties as a function of wavelength for second-order nonlinear optical polymers are presented. By combining the optical properties of the individual components, that is, those of the polymer and those of the chromophore, one can determine the real and the imaginary parts of the index of refraction and the second hyperpolarizability as a function of wavelength for a composite polymer, for either a guest-host or a side-chain system. These properties are important for characterizing and applying nonlinear optical polymers to devices. The methods allow for an accuracy in index of 3%, if the wavelength range includes the main absorption band (with absorption maximum at max ) of the chromophore, and of 0.2% for wavelengths 400 nm and more to the long-wavelength side of max . In addition, if the index of the composite polymer is known at one specific wavelength on the long-wavelength side of max , the dispersion in the index in this wavelength range can be predicted to within 0.1%.
Iterative calculation of complex propagation constants of modes in multilayer planar waveguides
IEEE Journal of Quantum Electronics, 1992
A Newton-Raphson complex root-finding algorithm, based on the thin-film transfer matrix analysis,... more A Newton-Raphson complex root-finding algorithm, based on the thin-film transfer matrix analysis, is described. This second-order convergent algorithm, which requires only O(n) calculations per iteration, was presented to find the complex propagation constants of any mode in an n-layer planar waveguide. The number of calculations per iteration is reduced below those required by competitive schemes through application of the Cauchy-Riemann relations. The method demonstrates higher accuracy and improved efficiency over other iterative techniques, making this approach highly suitable for the analysis and design of planar structures consisting of a large number of layers
A general, convergent approach to the synthesis of a series of stilbene-and azo-based donor-accep... more A general, convergent approach to the synthesis of a series of stilbene-and azo-based donor-acceptor, second-order nonlinear optical (NLO) chromophores is reported. The synthetic strategy enables preparation of both acid-and base-reactive structures, yielding protected, diamine-functionalized chromophores which can be liberated using either acidic or alkaline regents for incorporation into polyimide backbones. Three such chromophores, bis(4-aminophenyl all having high thermal stabilites, were synthesized, characterized, and condensed with hexafluoroisopropylidene diphthalic anhydride or 2-(1,3dioxoisobenzofuran-5-ylcarbonyloxy)ethyl 1,3-dioxoisobenzofuran-5-carboxylate to yield six high glass transition temperature polyimides (T g as high as 313 °C) for use as poled NLO materials. After casting as thin films, curing, and electric field corona poling, these materials exhibit χ (2) (1064 nm) responses as high as 82.0 pm/V and negligible decay in response upon aging in air at 100 °C for over 1000 h.
Unification of azo-polymer systems by photo-induced molecular movement
SPIE Proceedings, 1997
We review our recent research in the field of photochromic polymeric structures for optical data ... more We review our recent research in the field of photochromic polymeric structures for optical data storage and nonlinear optics. We unify some of the sub-themes of azopolymer structures in the light of photo-induced movement of azobenzene molecules. In particular, we discuss photo-induced effects in supramolecular assemblies containing azobenzene molecules (e.g. Langmuir-Blodgett-Kuhn structures and ultrathin silane layers). Reorientation of azobenzenes in these structures will be compared to that observed in spin-cast films. Photoisomerization and photo-induced orientation of azobenzene molecules is also studied at the molecular level by means of azosilane molecules chemisorbed on Silicon Oxide substrates. We establish a correlation between polymer architecture and sub-glass transition temperature (Tg) light-induced molecular movement in high Tg nonlinear optical azo-polyimide polymers. We show that the isomerization reaction itself depends on the polymer molecular structure, and we present evidence of light-induced molecular movement 325 °C below Tg of a rigid NLO azopolyimide polymer containing no flexible connector or tether.
Ultrashort pulse photochemical decay of nonlinear optical polymers
LEOS '95. IEEE Lasers and Electro-Optics Society 1995 Annual Meeting. 8th Annual Meeting. Conference Proceedings, 1995
ABSTRACT Our group has pursued the utilization of poled polymeric films in ultrashort pulse secon... more ABSTRACT Our group has pursued the utilization of poled polymeric films in ultrashort pulse second harmonic generation (USP-SHG). In particular, we have been interested in chromophores derived from tricyanovinylaniline (TCVA). These chromophores have large dipole moments, are relatively easy to prepare, and provide a “blue window” of low absorption at the harmonic wavelength of the modelocked Ti:Al2O3 laser. We expect that our investigations of ultrashort pulse induced photochemical degradation will also be relevant to degradation problems in electro-optic devices
Summary form only given. We have designed, modeled, and fabricated a polymeric in-line fiber modu... more Summary form only given. We have designed, modeled, and fabricated a polymeric in-line fiber modulator capable of high-speed, low-distortion operation. This device is based an evanescent coupling from a fiber half-coupler to a nonlinear polymer waveguide and the low-distortion characteristics are a direct result of the nonperiodic optical transfer function.
High bandwidth traveling wave polymeric in-line fiber modulator
CLEO '97., Summaries of Papers Presented at the Conference on Lasers and Electro-Optics
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Papers by André Knoesen