Proceedings Volume 8983

Organic Photonic Materials and Devices XVI

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Proceedings Volume 8983

Organic Photonic Materials and Devices XVI

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Volume Details

Date Published: 26 March 2014
Contents: 12 Sessions, 30 Papers, 0 Presentations
Conference: SPIE OPTO 2014
Volume Number: 8983

Table of Contents

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Table of Contents

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  • Front Matter: Volume 8983
  • Nonlinear Optics I
  • Nonlinear Optics II
  • OLED and OLET
  • Fiber and Waveguide
  • Nano Photonic
  • Pattern Formation
  • Absorption and Excitation
  • OPV
  • EO-Polymer Devices
  • Biophotonics
  • Poster Session
Front Matter: Volume 8983
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Front Matter: Volume 8983
This PDF file contains the front matter associated with SPIE Proceedings Volume 8983 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.
Nonlinear Optics I
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Optimization of the electronic third-order nonlinearity of cyanine-like molecules for all optical switching
Honghua Hu, Trenton R. Ensley, Matthew Reichert, et al.
All optical switching (AOS) applications require materials with a large nonlinear refractive index (n2) but relatively small linear and nonlinear absorption loss. The figure-of-merit (FOM), defined as the ratio between the real and imaginary parts of the second hyperpolarizability (γ), is widely used to evaluate the operating efficiency of AOS materials. By using an essential-state model, we describe the general dispersion behavior of γ of symmetric organic molecules and predict that the optimized wavelength range for a large FOM is near its linear absorption edge for cyanine-like dyes. Experimental studies are normally performed on organic solutes in solution which becomes problematic when the solvent nonlinearity dominates the total signal. This has been overcome using a Dual-arm Z-scan methodology to measure the solution and solvent simultaneously on two identical Z-scan arms and discriminating their small nonlinear signal difference. This technique significantly reduces the measurement uncertainty by correlating the excitation noise in both arms, leading to nearly an order-of-magnitude increase in sensitivity. Here we investigate the n2 and two-photon absorption (2PA) spectra of several classes of cyanine-like organic molecules and find that the results for most molecules agree qualitatively and quantitatively with the essential-state model. Many cyanine-like molecules show a relatively small FOM due to the presence of large 2PA bands near the linear absorption edge; however, an exception is found for a thiopyrylium polymethine molecule of which the maximum FOM can be < 400, making it an excellent candidate for AOS.
Second-order nonlinear susceptibilities in nonelectrically poled DR1PMMA guest-host polymers
A. Sugita, Y. Sato, K. Ito, et al.
The presentation will report nonelectrical poling behaviors of guest-host polymers, consisting of Disperse Red1 (DR1) and poly (methyl methacrylate) and related second-order nonlinear optical susceptibilities. Our present experimental results found the emissions of the second harmonic generations from the polymer thin films on SiO2 glass substrates after annealing the materials at the temperatures higher than the glass transition temperatures of the PMMA even in the absence of applying the external electric fields. The hydrogen bonds between the hydroxyl groups of the DR1 and the silanols of the substrate surely played essential roles for breaking the centrosymmetry in the alignments of the guests. The optimized conditions of the nonelectrical poling procedures were examined from the standpoints of the polymer film thickness and the concentrations of the guest chromophores.
Surface-plasmon-enhanced third-order harmonic generation of organic materials
Fanghui Ren, Xiangyu Wang, Zhong-An Li, et al.
We design and fabricate metallic photonic crystals that are integrated with highly-efficient third-order nonlinear polymers. Compared with nanoparticle-doped composite materials, metallic photonic crystals are favorable due to the presence of Bragg-grating-modulated surface plasmon polaritons (SPPs) with strong light localization in large spatial volumes to uniformly enhance the harmonic signals. We experimentally observed extraordinary emission of THG signals from the surface-plasmon-enhanced organic thin film using telecommunication wavelength pulsed laser. This hybrid organic-plasmonic nanostructure opens a new avenue to develop innovative nonlinear optical devices.
Nonlinear Optics II
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Second harmonic generation at liquid interface: molecular organization, supramolecular assemblies, and chirality
Emmanuel Benichou, Pierre-Marie Gassin, Gaëlle Gassin-Martin, et al.
Second Harmonic Generation (SHG) was used to study the optical properties of molecular films formed at liquid interfaces (air-water or dodecane-water interfaces). The technique was applied to a two-dimensional film of hemicyanine molecules: dye (4-(4-dihexadecylaminostyryl)-N-methylpyridinium iodide) (DiA) and 4-(4-(diethylamino)styryl)-Nmethylpyridinium iodide (sDiA). First, at the air-water interface, the SHG intensity was measured as a function of the incident fundamental and outgoing harmonic wave polarization. The orientation of the molecules was determined by the analysis of the polarization plots. Secondly, the adsorption of sDiA at the dodecane-water interface was characterized by the SHG technique. Finally, in the case of DiA molecules, the formation of aggregates at the air-water interface was monitored by the analysis of SHG intensity fluctuations.
OLED and OLET
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Progress of OLED devices with high efficiency at high luminance
Carmen Nguyen, Grayson Ingram, Zhenghong Lu
Organic light emitting diodes (OLEDs) have progressed significantly over the last two decades. For years, OLEDs have been promoted as the next generation technology for flat panel displays and solid-state lighting due to their potential for high energy efficiency and dynamic range of colors. Although high efficiency can readily be obtained at low brightness levels, a significant decline at high brightness is commonly observed. In this report, we will review various strategies for achieving highly efficient phosphorescent OLED devices at high luminance. Specifically, we will provide details regarding the performance and general working principles behind each strategy. We will conclude by looking at how some of these strategies can be combined to produce high efficiency white OLEDs at high brightness.
Fiber and Waveguide
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Optical properties of sulfur copolymers for infrared applications
Soha Namnabat, Jared J. Gabriel, Jeffrey Pyun, et al.
The development of organic polymers with high refractive indices has been widely investigated, as a possible alternative to inorganic metal oxide, semiconductor, or chalcogenide-based materials for a variety of optical devices and components, such as waveguides, anti-reflective coatings, charge-coupled devices and fiber optic cables. In principle, organic-based polymers are attractive for these applications because of their low weight, ease of processing, mechanical toughness, and facile chemical variation using commercially available precursors. However, one of the fundamental challenges associated with organic polymers is their generally low refractive indices in comparison to their inorganic counterparts. Herein we report on the optical characterization of a new class of sulfur copolymers that are readily moldable, transparent above 500nm, possess high refractive index (n < 1.8) and take advantage of the low infrared absorption of S‒S bonds for potential use in the mid-infrared at 3-5 microns. These materials are largely made from elemental sulfur by an inverse vulcanization process; in the current study we focus on the properties of a chemically stable, branched copolymer of poly(sulfur-random-1,3-diisopropenylbenzene) (poly(S-r-DIB). Copolymers with elemental sulfur content ranging from 50% to 80% by weight were studied by UV-VIS spectroscopy, FTIR, and prism coupling for refractive index measurement. Clear correlation between material composition and the optical properties was established, confirming that the high polarizability of the sulfur atom leads to high refractive index while also maintaining low optical loss. Applications of the materials for bulk optics, high-density photonic circuits, and infrared components will also be discussed.
Multidirectional waveguide arrays in a planar architecture
Ian D. Hosein, Hao Lin, Matthew R. Ponte, et al.
We previously showed that large populations (<10, 000 cm-3) of self-induced cylindrical multimode waveguides spontaneously form when an incoherent white light field suffers modulation instability in a photopolymerizable medium. By deliberately modulating the optical field and employing multiple beams, we then generated a diverse range of waveguide lattices with 1-D, 2-D and 3-D geometries. Here, we describe the potential of this technique - optochemical organization – to provide an inexpensive, single-step, room temperature route to waveguide-inscribed planar architectures, which could serve as light-collecting, steering and focusing elements.
Longitudinal versus transversal excitation in doped graded-index polymer optical fibers
M. A. Illarramendi, J. Arrue, I. Ayesta, et al.
In this work we perform a detailed experimental and theoretical analysis of the properties of amplified spontaneous emission (ASE) in a rhodamine-6G-doped graded-index polymer optical fiber when the fiber is pumped either longitudinally or transversally with respect to the fiber axis. The dependence of the ASE threshold and efficiency on fiber length has been compared for both schemes of excitation. A theoretical model for longitudinal excitation has been carried out by means of the laser rate equations as functions of time, distance traveled by light and wavelength. The analysis takes into account that the fiber is a typical graded-index POF in which the radial distributions of light power density and dye concentration are not uniform. The theoretical calculations agree satisfactorily with the experimental results. The photodegradation of the ASE intensity has also been measured for both pumping schemes.
Proteins detection by polymer optical fibers sensitised with overlayers of block and random copolymers
Alexandros El Sachat, Anastasia Meristoudi, Christos Markos, et al.
A low cost and low complexity optical detection method of proteins is presented by employing a detection scheme based on electrostatic interactions, and implemented by sensitization of a polymer optical fibers' (POF) surface by thin overlayers of properly designed sensitive copolymer materials with predesigned charges. This method enables the fast detection of proteins having opposite charge to the overlayer, and also the effective discrimination of differently charged proteins like lysozyme (LYS) and bovine serum albumin (BSA). As sensitive materials the block and the random copolymers of the same monomers were employed, namely the block copolymer poly(styrene-b-2vinylpyridine) (PS-b- P2VP) and the corresponding random copolymer poly(styrene-r-2vinylpyridine) (PS-r-P2VP), of similar composition and molecular weights. Results show systematically different response between the block and the random copolymers, although of the same order of magnitude, drawing thus important conclusions on their applications' techno-economic aspects given that they have significantly different associated manufacturing method and costs. The use of the POF platform, in combination with those adaptable copolymer sensing materials could lead to efficient low cost bio-detection schemes.
Nano Photonic
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Laser inscription of surface structures and induction of optical anisotropy in azo-benzene substituted photochromic polymers and other systems
Andrzej Miniewicz, Lech Sznitko, Ewa N. Szlapa, et al.
We present trial calculations of surface light-induced patterns in photochromic azo-substituted polymers. Using microscope with nanopositioning stage various birefringence and surface structures have been recorded in photochromic azo-functionalized polymers. By systematic approach to the inscription experiment and controlling cw or pulsed laser light intensity, its polarization and beam scan speed we observed the dynamics of molecular photoorientation and its relation to mass transport. We discuss properties of holographically inscribed polarization gratings and analyze them spatially by monitoring of microscopic local diffraction efficiency. We report how azo-benzene molecules can work in other systems, i.e. azobenzene functionalized POSS molecules embedded in nematic liquid crystal.
Epitaxial growth of a methoxy-functionalized organic semiconductor on dielectric surfaces
Frank Balzer, Rong Sun, Horst-Günter Rubahn, et al.
Functionalization of small, rod like organic molecules can be used to optimize organic devices. Here we report on nanofiber formation and thin film growth of a methoxy-functionalized para-quaterphenylene (1,4'''-Dimethoxy- 4,1':4',1'':4'',1'''-quaterphenylene, MOP4) on prototypical dielectric substrates such as muscovite mica, phlogopite mica, highly ordered pyrolytic graphite (HOPG), and on the alkali halide NaCl. The nanofibers consist of lying molecules, the films of upright standing ones. The grown samples are characterized by polarized optical microscopy (fluorescence, birefringence, bireflectance), by atomic force microscopy (AFM), and by Kelvin probe force microscopy (KPFM) to gain insight into their structure and epitaxial relation with the substrates.
Pattern Formation
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Fully updatable holographic stereogram display device based on organic monolithic compound
Naoto Tsutsumi, Kenji Kinashi, Kazuhiro Tada, et al.
Following former report in Optics Express 21, 19880, (2013), we present here a prototype mobile updatable holographic display system using a holographic stereographic technique with a transparent optical device of PMMA doped organic monolithic compound. 50 or 100 elemental holograms which are a series of pictures of object took from different angles can completely reproduce updatable entire hologram of object. Immediately after recording one holographic stereogram, another holographic stereogram can be over-recorded without erasing. Recorded updatable 3D hologram can be viewable for up to a couple of hours directly on a device without any eye glasses and other tools to magnify images. Hologram can be easily refreshed by overwriting without erasing process. Large size and improved holographic device is also presented.
Numerical studies on self-organized liquid crystal micro photonic systems
Tatsunosuke Matsui, Masahiro Kitaguchi, Akiko Okajima
The liquid crystals (LCs) form various types of nano- and micro- structures in a self-organized manner. In recent years, numerous studies have been carried out to develop novel types of optical functional materials and devices utilizing such self-organizing characteristics of the LCs. Based on the finite-difference time-domain (FDTD) method or its extended version, auxiliary differential equation FDTD (ADE-FDTD) method, we have been numerically studying on the optical characteristics and functionalities of the self-organized LCs such as: (1) lasing from the cholesteric LCs (CLCs) and (2) photonic nanojet (PNJ) from LC micro-systems. Based on the ADE-FDTD method incorporating the equation of motion of the macroscopic polarization and the rate equations at the four level energy structures, we have successfully reproduced circularly polarized lasing from CLC at the edge energy of the stop band. It has also been clarified that the introduction of the defect is effective to lower the lasing threshold. Our technique can be utilized to design the CLC laser devise architecture for much lowered lasing threshold. The PNJ from LC micro-systems are uniquely polarized reflecting birefringence of LCs, which cannot be obtained using optically isotropic microdroplets or microcylinders. A small degree of birefringence drastically changes the optical characteristics of the obtained PNJ. Our findings may open the way for the development of the novel optical functional materials and devices.
Photorefractive device using self-assembled monolayer coated indium-tin-oxide electrodes
Kenji Kinashi, Kento Masumura, Wataru Sakai, et al.
We present here the optimized photorefractive (PR) device based on methyl-substituted poly(triarylamine) (PTAA). The PR performance of PTAA-based PR device was demonstrated using chemically modified electrodes (CMEs) of selfassembled monolayer (SAM) coated indium-tin-oxide (ITO) electrodes. The SAM-ITO electrodes successfully suppressed dark current which blocks the formation of space-charge field and also causes the dielectric breakdown, which result in the remarkable response time faster than video rate of 16 ms. Our approach will widen the usage of higher mobility materials to photorefractive field and give us more favorable materials to achieve the best performance of photorefractivity in the future.
Absorption and Excitation
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Two-photon solvatochromism of 4-dimethylamino-4'-nitrostilbene (DANS)
Variation of two-photon absorption (2PA) of organic chromophores as a function of the environment such as different solvent polarity has important implications for practical applications of nonlinear optical (NLO) materials but could be also used as a sensitive probe of local inter- and intra-molecular interactions. We report measurement of the 2PA spectrum in the broad wavelength range 700-1000 nm of a benchmark NLO chromophore 4-Dimethylamino-4’-nitrostilbene (DANS) in a series of solvents with varying polarity by using a femtosecond nonlinear-optical transmission method with a nearly-collimated laser beam. The 2PA peak of DANS shifts systematically from 834 nm in a low dielectric constant solvent isobutyl isobutyrate (dielectric constant = 4) to 892 nm in a highly polar solvent DMSO (dielectric constant = 48), which quantitatively follows the corresponding solvatochromic shift of the S0→S1 transition peak in the linear absorption spectrum, and indicates that DANS has a significant ground state permanent electric dipole moment that interacts with the solvent environment. The corresponding change of the S0→S1 transition peak 2PA cross section in solvents with different polarity is quite large, ranging from 160 GM in isobutyl acetate to 240 GM in 1,3-Dioxolane. However, this variation exhibits no direct correlation with the solvent polarity. This effect may be tentatively attributed to the change of the excited state permanent electric dipole moment due to the instantaneous S0→S1 transition. Our results confirm that accurate measurement of 2PA spectra may serve as a probe of local molecular-level interactions.
Random lasing in liquid and solid solutions oversaturated with organic laser dye
Lech Sznitko, Konrad Cyprych, Adam Szukalski, et al.
We present the results of studies carried out for oversaturated solutions with common laser dye 4- (Dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM) and 3-(1,1-Dicyanoethenyl)-1-phenyl-4,5- dihydro-1H-pyrazole (DCNP) nonlinear chromophore. We show that oversaturating the solution leads to formation of crystals suspension resulting in strong Mie scattering and thus random laser operation can be observed. The formation of aggregates can be induced be oversaturating the solution or by injection of non-solvent to the dye solution, leading to reduction of solubility limit. Similar situation can be obtained for polymeric matrices for which small crystals are precipitated during layer formation (solvent evaporation) when film is casted from the solution.
Polymeric waveguide Fabry Perot resonators
Optical microcavities are used in variety of applications ranging from sensors to lasers and signal routing in high volume communication networks. Achieving a high quality factor (Q) is necessary for achieving the higher sensitivity in sensing applications and for narrow linewidth light emission in most lasing applications. In this work, we propose a new way for achieving a higher quality factor in thin film, Fabry-Perot polymeric optical resonators. We show that lateral photon confinement in a vertical Fabry-Perot microcavities can be achieved by optical writing of a refractive index profile utilizing our UV-sensitive polymer. This method can improve the quality factor by one or more orders of magnitudes. In order to demonstrate this improvement, the device has been fabricated. The fabricated device consists of two dielectric Bragg reflectors with a layer of 100 μm thick polymer layer between them. The polymer is a thiol-ene/methacrylate photopolymer whose optical index can be modified utilizing standard photo-lithography processes. The refractive index of this polymer can be modified utilizing standard photo-lithography processes. The measured finesse of the fabricated device was 692 and the quality factor was 55000. The achieved finesse combined with the flexible polymer layer allows this device to be used as an ultrasound detector in optical micromachined ultrasound transducers (OMUT).
OPV
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Efficient small-molecule photovoltaic cells using nanostructured template
Tetsuya Taima, Ying Zhou, Takayuki Kuwabara, et al.
We report a simple method to achieve efficient nanostructured organic photovoltaics via patterning copper iodide (CuI) nano-rod template on indium tin oxide. The CuI nano-rod sheet was fabricated by glancing angle deposition method. The strong interfacial interaction between zinc phthalocyanine (ZnPc) and CuI leads to the formation of nano-pillar arrays with lying-down crystalline order, which greatly improve absorption efficiency and surface roughness for exciton dissociation. Optimized ZnPc/C60 bilayer cell has a power conversion efficiency of 4.0 ± 0.1%, which is about three-fold larger than that of conventional planar cell.
In addition, we also reported the new type of nano-structured template based on organic semiconductor. As the template material, diindenoperylene (DIP) was introduced into bilayer photovoltaic cells using based on tetraphenyldibenzoperifl anthene (DBP) and C60. While the basic molecular structure of DIP is similar to that of DBP, DIP shows higher crystallinity than DBP one. We obtained power conversion efficiency of 5.2% and high fill factor of 0.72 due to high crystallinity of DIP nano-structured template.
EO-Polymer Devices
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All-Polymer modulator for high frequency low drive voltage applications
David L. K. Eng, Stephen Kozacik, Shouyuan Shi, et al.
Organic electro-optic material based optical modulators have been fervently pursued over the past two decades. The material properties of organic materials over crystalline electro-optic materials such as LiNbO3 have yielded devices with record low drive voltages and significant promise for high frequency operation that are ideal for implementation in many developing telecommunication technologies. This paper will discuss a TM electro-optic phase modulator based on a recently developed material IKD-1-50. A simple fabrication process that is compatible with wafer scale manufacturability using commercially available cladding materials, spin processing, standard photolithography, and dry etching will be presented. Non-centrosymmetric order is induced in the core material via a thermally enabled poling process that was developed based on work in simple slab waveguide material characterization devices, and optimized for polymer stack waveguide architectures. Basic phase modulators are characterized for half wave voltage and optical loss. In device r33 values are estimated from a combination of measured and simulated values. Additional work will be discussed including amplitude modulation and high frequency applications. The design for a Mach-Zehnder interferometer amplitude modulator that implements a multi mode interference cavity splitter will be presented along with plans for a microstrip transmission line traveling wave modulator.
Dual slot modulator for millimeter wave photonics
Matthew R. Konkol, Stephen T. Kozacik, David L. K. Eng, et al.
Silicon slot waveguides leverage the field enhancement provided by the continuity of normal electric flux density across a dielectric boundary to confine an optical mode to a void between two proximal silicon strips. Silicon-organic hybrid slot modulators make use of this mode profile by infiltrating the slot region with a non-linear organic electro-optic material (OEOM) for modulation. The dual slot modulator takes this idea a step further by similarly confining a propagating RF mode to the same slot region to increase modal overlap for improved modulation efficiency. This effect is achieved by aligning a titanium dioxide RF slot along a conventional silicon slot waveguide. The TiO2 has an optical refractive index lower than silicon, but a significantly higher index in the RF regime. As a result of the large modal overlap and high electro-optic activity of the OEOM this design can produce measured phase modulated VπL of less than 1.40 V•cm. Furthermore, as the modulator operates without the introduction of a doping scheme it can potentially realize high operational bandwidth and low loss. We present work towards achieving various working prototypes of the proposed device and progress towards high frequency operation.
Biophotonics
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Latest advances in biomaterials: from deoxyribonucleic acid to nucleobases
Fahima Ouchen, Eliot Gomez, Donna Joyce, et al.
This paper is a review of the recent research in bio-based materials for photonics and electronics applications. Materials that we have been working with include: deoxyribonucleic acid (DNA)-based biopolymers and nucleobases. We will highlight work on increasing the ionic conductivity of DNA-based membranes, enhancing the direct (DC) current and photoconductivity of DNA-based biopolymers, crosslinking of DNA-based biopolymers and promising applications for DNA nucleobases. Key
Bio-hybrid integrated system for wide-spectrum solar energy harvesting
Kathleen Martin, Matthew Erdman, Hope Quintana, et al.
An integrated hybrid photovoltaic-thermoelectric system has been developed using multiple layers of organic photosensitizers on inorganic semiconductors in order to efficiently convert UV-visible and IR energy into electricity. The hot anode of n-type ZnO nanowires was fabricated using a thermal process on pre-seeded layer and results to be crystalline with a transmittance up to 92 % and a bandgap of 3.32 eV. The visible-UV light-active organic layer was deposited between the anode and cathode at room temperature using a layer-by-layer deposition onto ITO and ZnO and Bi2Te3 nanowires from aqueous solution. The organic layer, a cooperative binary ionic (CBI) solid is composed of oppositely charged porphyrin metal (Zn(II) and Sn(IV)(OH‑)2) derivatives that are separately water soluble, but when combined form a virtually insoluble solid. The electron donor/acceptor properties (energy levels, band gaps) of the solid can be controlled by the choice of metals and the nature of the peripheral substituent groups of the porphyrin ring. The highly thermoelectric structure, which acts as a cold cathode, is composed of p-type Bi2Te3 nanowires with a thermoelectric efficiency (ZT) between ~0.7 to 1, values that are twice that expected for bulk Bi2Te3. Efficiency of the integrated device, was found to be 35 at 0.2 suns illumination and thermoelectric properties are enhanced by the charge transfer between the CBI and the Bi2Te3 is presented in terms of photo- and thermogenerated current and advantages of the low cost fabrication process is discussed.
Poster Session
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Triphenylamine-based acrylate polymers for photorefractive composite
Ha N. Giang, Kenji Kinashi, Wataru Sakai, et al.
Two kinds of triphenylamine (TPA)-based acrylate polymer are applied to photorefractive (PR) composite. Poly(4- (diphenylamino)benzyl acrylate) (PDAA) have TPA moiety attached to acrylate main chain. Poly(4-((4- methoxyphenyl)(phenyl)amino)benzyl acrylate) (PMPAA) has a similar structure with a side chain of TPA derivative modified with a methoxy group at para position. PMPAA shows even more readily ionized than PDAA. TPA plasticizer is used instead of the conventional N-ethylcarbazole plasticizer to improve the photoconductivity. A series of composite based on two kinds of acrylate polymer have been prepared and investigated by degenerate four-wave mixing. With the polymer concentration of 55 and 50 wt%, the composite using modified-TPA-polymer of PMPAA shows significant improvement in diffraction efficiency and response time. When polymer concentration is reduced to 45 wt%, the PDAA composite shows a large PR enhancement. With 532 nm laser, diffraction efficiency reaches 70% and 40% for PDAA and PMPAA composites, respectively.
FDTD analysis of photonic nanojet from self-organized liquid crystal microsystems
Akiko Okajima, Tatsunosuke Matsui
Since Chen et al. reported on the photonic nanojet (PNJ), many researches have been carried out from various viewpoints such as fundamental physics and device applications. We have numerically analyzed, based on the finite-difference time-domain (FDTD) method, generation of PNJ from microcylinders incorporating the liquid crystals (LCs) with radial hedgehog and tangential alignments, in which the director of LC molecules is perpendicular or parallel to the LC/matrix interface. For the radial hedgehog alignment of LC molecules, the PNJ from LC microcylinders is separated into two beams. For the tangential alignment of LC molecules, we show that the PNJ from LC microcylinders are uniquely polarized reflecting birefringence of LCs, which cannot be obtained using optically isotropic microdroplets or microcylinders. By using the LC micro-systems, we may obtain a rich variety of PNJ with electrical tunability.
Diffraction can mimic saturation in multiphoton absorbers
Many traditional investigations of saturation in multiphoton absorbers with the z-scan method use an approximate analytical formula that assumes a steady-state approximation. Using a numerical simulation for Maxwell’s equations for laser propagation including diffraction and coupled electron population dynamics, we show that the commonly used analytical formula for determining saturation in multiphoton absorbers is often incorrect, even when the sample thickness is only one diffraction length. Using published experimental data on an organic chromophore, we show that saturation, in fact, does not occur at the laser intensity values predicted for these two and three photon absorbers. We numerically fit the published experimental z-scan data and obtain new absorption coefficients for multiphoton absorbers that accurately reflect their intrinsic values. The new values are from three to ten times larger than the published values. Because multiphoton absorbers are being used more extensively in many applications such as optical limiter, medical diagnostics and two photon microscopy, it is important to have accurate values for the two and three-photon absorption coefficients. Knowing the real value of the multiphoton absorber coefficients, even for a single diffraction length, is therefore of the utmost importance. In particular, the laser intensity at which the absorber saturates can determine which absorber is useful for a particular application.
Surface charge measurements and (dis)charging dynamics of organic semiconductors in various media using optical tweezers
Rebecca R. Grollman, Kyle Peters, Oksana Ostroverkhova
An exciting application of optical tweezers is the measurement of the surface charge on a trapped particle, as well as its time evolution with a single charge resolution. We report on an optical tweezer-based method to measure the effective surface charge on an organic semiconductor film at microscopic scales, which offers opportunities for investigations of ion and electron transfer between organic molecules and surrounding medium. Effective charge densities of 13±5 elementary charges per μm2 were observed in anthradithiophene-coated silica microspheres suspended in water, with a more than an order of magnitude reduction in charge densities upon replacing water with the 50% wt/wt glycerol/water mixture.
Sustainable UV-curable low refractive index resins with novel polymers for polymer cladding materials
Hiroki Tokoro, Takako Ishikawa, Nobuyuki Koike, et al.
Low refractive index polymers are used as cladding materials for high numerical aperture (NA) fibers. Since transparent fluoro polymers are ideal for this application, they have been used over many years. However, some fluoro chemicals face an issue related to perfluoro octanoic acid (PFOA) which is caused by its longtime persistence in the environment and human body. In this research, non-PFOA type UV curable fluoro resins suitable for cladding were developed with novel materials. The cured films showed high transparency, good adhesion to glass and low refractive index of 1.359 and 1.386 at 850 nm. Optical fibers prepared with those cladding showed almost equivalent attenuation to a fiber with commercially available material.
Synthesis and electro-optic properties of the chromophore-containing NLO polyarylate polymers
Haohui Ren, Chengcheng Peng, Shuhui Bo, et al.
Base on the same two monomers, diphenolic acid (DPA) and isophthaloyl chloride (IPC), three chromophore-containing nonlinear optical (NLO) polyarylate polymers were prepared. A tricyanofuran (TCF)-acceptor type chromophore group was in main-chain (mPAR-chr1), side-chain (sPAR-chr1) and side-chain with a 1,1-bis(4-hydroxyphenyl)-1-phenyl-2,2,2-trifluoroethane (BPAPF) group (sPAR-F-chr1), respectively. The obtained polymers were characterized and evaluated by UV-Vis, 1H NMR, DSC and TGA. All the polymers exhibited good electro-optic (EO) activity. The relationship between EO coefficients (r33) and the chromophore concentration of the three polymers were also characterized and discussed. There were no obvious differences found in EO activity between mPAR-chr1 and sPAR-chr1 polyarylates with the same chromophore. The fluorinated block polyarylate sPAR-F-chr1 has the largest r33 value in these three polyarylates which is 52 pm/V at the wavelength of 1310 nm (which is almost twice the r33 value of normal polymers contained the same chormophore at the same content), when the concentration of chromophore 1 is 18wt.%. 85% of the r33 value was retained in the sPAR-F-chr1 after being heated at 85°C for 600 hours. The polymer sPAR-F-chr1, with good solubility, high Tg (above 200 °C) and side functional group at the same time, may probably be a practical NLO material. These properties make the new polyarylates have potential applications in EO devices such as EO modulators and switches.
Design of Mach-Zehnder interference modulators composed of enhanced electro-optic active polymers
Organic electro-optic polymer has low dielectric constant and high electro-optic coefficient, which is one of the perfect materials for making modulators with low loss and high bandwidth. In this paper, we synthesized a novel chromophore based on the 4-(diethylamino) salicylaldehyde electron donor and the rigid isolated benzyl group. Based on the innovative chormophore, we designed low loss Mach-Zehnder interference modulators with 3dB bandwidth 50GHz using tapered waveguides and coplanar waveguide electrodes as well as micro-strip electrodes. Performance parameters of the modulators were detailed analyzed and two microwave driven electrodes were compared.