Second International Conference On Applications Of Optics .
PROCEEDINGS OF SPIESecond International Conference onApplications of Optics and PhotonicsManuel Filipe P. C. Martins CostaRogério Nunes NogueiraEditors26–30 May 2014Aveiro, PortugalOrganized bySPOF—Portuguese Society for Research and Development of Optics and Photonics (Portugal)Supported byIT—Instituto de Telecomunicações (Portugal) OSA Student Chapter of University of AveiroICO—International Commission for Optics SPIE EOS—European Optical SocietyThe Optical Society RIAO—Red Iberoamericana de Óptica Photonics21—EuropeanTechnology Platform for Photonics SEDOPTICA—Sociedad Española de ÓpticaAMO—Academia Mexicana de Óptica RCO—Red Colombiana de ÓpticaSTO—Société Tunisienne d'Optique OPSS—Optics and Photonics Society of SingaporeCVO—Comité Venezolano de Optica Fábrica-Centro Ciência Viva de AveiroUniversity of Porto SPIE Student Chapter University of Aveiro University of MinhoEFTA—Esc. F.P. Turismo de Aveiro City of Aveiro Innova Scientific Quantel LaserMicron Optics, Inc. M.T. Brandão Spectra-Physics FiberSensing, Sistemas Avançados deMonitorização, S.A. MWTechnologies, Ltd. Espectral Telecomunicações, S. A.Tektronix, Inc Keithley Instruments, Inc.Volume 9286Proceedings of SPIE 0277-786X, V. 9286SPIE is an international society advancing an interdisciplinary approach to the science and application of light.Second International Conference on Applications of Optics and Photonics, edited byManuel Filipe P. C. Martins Costa, Rogério Nunes Nogueira, Proc. of SPIE Vol. 9286,928601 · 2014 SPIE · CCC code: 0277-786X/14/ 18 · doi: 10.1117/12.2075361Proc. of SPIE Vol. 9286 928601-1Downloaded From: http://proceedings.spiedigitallibrary.org/ on 11/13/2014 Terms of Use: http://spiedl.org/terms
The papers included in this volume were part of the technical conference cited on the cover andtitle page. Papers were selected and subject to review by the editors and conference programcommittee. Some conference presentations may not be available for publication. The paperspublished in these proceedings reflect the work and thoughts of the authors and are publishedherein as submitted. The publisher is not responsible for the validity of the information or for anyoutcomes resulting from reliance thereon.Please use the following format to cite material from this book:Author(s), "Title of Paper," in Second International Conference on Applications of Optics andPhotonics, edited by Manuel Filipe P. C. Martins Costa, Rogério Nunes Nogueira, Proceedings ofSPIE Vol. 9286 (SPIE, Bellingham, WA, 2014) Article CID Number.ISSN: 0277-786XISBN: 9781628413618Published bySPIEP.O. Box 10, Bellingham, Washington 98227-0010 USATelephone 1 360 676 3290 (Pacific Time)· Fax 1 360 647 1445SPIE.orgCopyright 2014, Society of Photo-Optical Instrumentation Engineers.Copying of material in this book for internal or personal use, or for the internal or personal use ofspecific clients, beyond the fair use provisions granted by the U.S. Copyright Law is authorized bySPIE subject to payment of copying fees. The Transactional Reporting Service base fee for thisvolume is 18.00 per article (or portion thereof), which should be paid directly to the CopyrightClearance Center (CCC), 222 Rosewood Drive, Danvers, MA 01923. Payment may also be madeelectronically through CCC Online at copyright.com. Other copying for republication, resale,advertising or promotion, or any form of systematic or multiple reproduction of any material in thisbook is prohibited except with permission in writing from the publisher. The CCC fee code is0277-786X/14/ 18.00.Printed in the United States of America.Publication of record for individual papers is online in the SPIE Digital Library.SPIEDigitalLibrary.orgPaper Numbering: Proceedings of SPIE follow an e-First publication model, with papers publishedfirst online and then in print and on CD-ROM. Papers are published as they are submitted andmeet publication criteria. A unique, consistent, permanent citation identifier (CID) number isassigned to each article at the time of the first publication. Utilization of CIDs allows articles to befully citable as soon as they are published online, and connects the same identifier to all online,print, and electronic versions of the publication. SPIE uses a six-digit CID article numbering systemin which:The first four digits correspond to the SPIE volume number.The last two digits indicate publication order within the volume using a Base 36 numberingsystem employing both numerals and letters. These two-number sets start with 00, 01, 02, 03, 04,05, 06, 07, 08, 09, 0A, 0B 0Z, followed by 10-1Z, 20-2Z, etc.The CID Number appears on each page of the manuscript. The complete citation is used on thefirst page, and an abbreviated version on subsequent pages. Numbers in the index correspond tothe last two digits of the six-digit CID Number.Proc. of SPIE Vol. 9286 928601-2Downloaded From: http://proceedings.spiedigitallibrary.org/ on 11/13/2014 Terms of Use: http://spiedl.org/terms
THURSDAY POSTER SESSION9286 4WReinforced adaboost face detector using support vector machine [9286-230]9286 4XResolution analysis in computational imaging with patterned illumination and single-pixeldetection [9286-117]9286 4ZDesign and optimization of a spectrometer for spectral domain optical coherencetomography [9286-167]9286 50Experimental research of methods for clustering and selecting image fragments usingspatial invariant equivalent models [9286-238]9286 54SLM-based optical simulator for dynamic speckle analysis [9286-123]9286 58Optical non-invasive 3D characterization of pottery of pre-colonial Paranaiba valley tribes[9286-219]9286 5BFill-factor and performance optimization in bulk-heterojunction organic solar cells[9286-162]9286 5CInfluence of a bleaching post-exposure treatment in the performance of H-PDLC deviceswith high electric conductivity [9286-97]FR.1.A9286 5IOn the impact of fiber-delay-lines (FDL) in an all-optical network (AON) bottleneck withoutwavelength conversion (Invited Paper) [9286-34]9286 5JEnergy-aware RWA for IP transport over WDM networks [9286-218]9286 5KEfficiency analysis on platform over the top (OTT) to deploy content and applications(edutainment) in digital television on optical network link [9286-143]FR.1.B9286 5MOptical response of fractal aggregates of polarizable particles [9286-28]xProc. of SPIE Vol. 9286 928601-10Downloaded From: http://proceedings.spiedigitallibrary.org/ on 11/13/2014 Terms of Use: http://spiedl.org/terms
Influence of a bleaching post-exposure treatment in the performance ofH-PDLC devices with high electric conductivityManuel Ortuñoa,b,*, Andrés Márqueza,b, Sergi Gallegoa,b, Roberto Fernándeza,b, Víctor NavarroFustera,b, Augusto Beléndeza,b and Inmaculada Pascuala,caInstituto Universitario de Física Aplicada a las Ciencias y las Tecnologías, Universidad de Alicante,P.O. Box 99, E-03080, Alicante, Spain;bDepartamento de Física, Ingeniería de Sistemas y Teoría de la Señal, Universidad de Alicante, P.O.Box 99, E-03080, Alicante, SpaincDepartamento de Óptica, Farmacología y Anatomía, Universidad de Alicante, P.O. Box 99, E03080, Alicante, SpainABSTRACTHolographic polymer dispersed liquid crystals (H-PDLC) are made by holographic recording in a photo-polymerizationinduced phase separation process in which the liquid crystal molecules diffuse to dark zones in the diffraction grating.The devices with H-PDLC materials develop a dynamic behavior that may be modified by means of an electric field. Westudy a photopolymer formulation with high diffraction efficiency but with the problem of high electric conductivity. Weuse a bleaching post-exposure treatment to obtain devices with a better electro-optical performance.Keywords: Holographic polymer dispersed liquid crystals, holographic recording materials, photopolymer formulation,electro-optical polymer devices.1. INTRODUCTIONHolographic polymer dispersed liquid crystals (H-PDLC) are made by holographic recording in a photo-polymerizationinduced phase separation process in which the liquid crystal molecules diffuse to dark zones in the diffraction grating.Afterwards they can be oriented by means of an electric field. The reorientation of the liquid crystal produces a refractiveindex variation which changes the diffraction efficiency. Therefore, the grating develops a dynamic behavior that may bemodified by means of an electronic device. In this manner, it is possible to make dynamic devices such as tunable-focuslenses, sensors, phase modulators or prism gratings [1-7].The objective of a H-PDLC material is to act as a support for an electro-optical dynamic device. Bearing this in mind,the material must have a low thickness in order to use a low electric field with the device. In this work, we study aphotopolymer formulation with high diffraction efficiency [8]. We have identified a problem related to the high electricalconductivity of the formulation which implies a low voltage for the H-PDLC devices and therefore the electro-opticalresponse is very poor. We have identified several ionic components of the photopolymer formulation that could berelated to the high electric current intensity obtained when the voltage is increased. We use a bleaching post-exposuretreatment in order to improve the electro-optical performance.*mos@ua.es; phone 34 965 90 34 00; www.ua.esSecond International Conference on Applications of Optics and Photonics, edited byManuel Filipe P. C. Martins Costa, Rogério Nunes Nogueira, Proc. of SPIE Vol. 9286,92865C · 2014 SPIE · CCC code: 0277-786X/14/ 18 · doi: 10.1117/12.2063540Proc. of SPIE Vol. 9286 92865C-1Downloaded From: http://proceedings.spiedigitallibrary.org/ on 11/13/2014 Terms of Use: http://spiedl.org/terms
2. EXPERIMENTAL SECTIONThe photopolymer is composed of dipentaerythritol penta/hexa-acrylate (DPHPA) as monomer, N-vinyl-2-pyrrolidone(NVP) as crosslinker, N-phenylglycine (NPG) as radical generator and octanoic acid (OA) as surfactant and cosolvent[9]. We used ethyl eosin (YEt) as dye and N-methyl-2-pyrrolidone (NMP) to control the overmodulation during thehologram recording. This composition was optimized in a previous work [10]. Table 1 shows the composition of thematerial.Table 1. Composition of the ation (wt%)46.5229.3115.800.084.223.130.94We used the nematic liquid crystal CL036 from Qingdao Intermodal Co., Ltd. It is a mixture of 4-cyanobiphenyls withalkyl chains of different lengths. It has an ordinary refractive index n0 1.520, and a difference between extraordinaryand ordinary index Δn 0.250. Figure 1 shows the molecular structure of the components of the material.Dipentaerythritol ile (CL036)Ethyl 2-pyrrolidone(OCH2Octanoic acidFigure 1. Molecular structure of the components of the material.Proc. of SPIE Vol. 9286 92865C-2Downloaded From: http://proceedings.spiedigitallibrary.org/ on 11/13/2014 Terms of Use: http://spiedl.org/terms
The material was made by mixing the components under red light where they are not sensitive. The solution wassonicated in an ultrasonic bath, deposited between two conductive ITO glass plates 1 mm thick and separated using 13µm hollow glass microspheres as spacers (Figure 2). The device was exposed to a laser beam (λ 532 nm) in aholographic set-up in order to record a diffraction grating in the photopolymer layer (Figure 3). A photopolymerizationreaction takes place in the bright zones of the diffraction grating and a highly reticulated polymer network is generated.The liquid crystal molecules diffuse to the unexposed region where they remain as droplets.After recording, the diffraction grating in the H-PDLC is reconstructed (λ 633 nm) and the diffraction efficiency isobtained. The device with the optimized composition is exposed to a variable electric field in order to evaluate theelectro-optical properties induced by the liquid crystal. We consider a bipolar square waveform, generated by awaveform generator connected to a voltage amplifier [9], whose voltage amplitude is modified. Figure 2 shows a schemeof the H-PDLC device. The polymer rich zone and liquid crystal rich zone are separated in the graph but the polymernetwork penetrates into the liquid crystal rich zones.:.634.:I A-14-2Figure 2. Scheme of the H-PDLC device: 1 glass plate, 2 ITO coating on glass plate, 3 electric connection zone, 4 glass microspheres,5 polymer rich zone, 6 liquid crystal rich zone.2.1 Holographic set-upWe obtained diffraction gratings using a holographic setup to study the behaviour of these photopolymers as aholographic recording material. The experimental device is shown in Figure 3. A Nd:YAG laser tuned at a wavelength of532 nm was used to record diffraction gratings by means of continuous laser exposure. The laser beam was split into twosecondary beams with an intensity ratio of 1:1. The diameter of these beams was increased to 1 cm by means of a lens,while spatial filtering was ensured. The object and reference beams were recombined at the sample at an angle of 16degrees to the normal with an appropriate set of mirrors, and the spatial frequency obtained was 1036 lines/mm. Theworking intensity at 532 nm was 7 mW/cm2. The diffracted and transmitted intensity were monitored in real time with aHe-Ne laser positioned at Bragg’s angle (19.1 ) tuned at 633 nm, where the material does not polymerize. Thediffraction efficiency was calculated as the ratio of the diffracted beam (ID) to the incident power (I0).Proc. of SPIE Vol. 9286 92865C-3Downloaded From: http://proceedings.spiedigitallibrary.org/ on 11/13/2014 Terms of Use: http://spiedl.org/terms
M1Nd:YAG laser (532 nm)01SampleMotioncontrolM6ID3PCIM7L3He -Ne laser (633 nm)SF3Figure 3. Experimental set-up. BS: Beamsplitter, Mi: mirror, SFi: spatial filter, Li: lens, Di: diaphragm, Oi: optical power meter, PC:data recorder.2.2 Electro-optical responseThe devices are exposed to an electrical field in order to evaluate the electro-optical response. Figure 4 shows theelectro-optical set-up. It includes a Tektronik TDS1012B oscilloscope (A), Tektronic AFG3022B dual channel arbitraryfunction generator (B), N4L voltage amplifier (C), and an impedance control circuit designed in our laboratory (D). Thesignal applied to the device is adjusted to AC, 1 kHz bipolar square waveform. The impedance control circuit attenuatesthe high intensity spikes associated with capacitance effects produced by the steep voltage changes in the applied voltage.These intensity spikes reach values higher than the ones allowed by the amplifier protection circuit, thus switching it offand limiting the range of the applicable high voltage amplitude values. The capacitance is due to the capacitor structureof the H-PDLC cell, composed of the two ITO electrodes and the H-PDLC dielectric layer in between.Proc. of SPIE Vol. 9286 92865C-4Downloaded From: http://proceedings.spiedigitallibrary.org/ on 11/13/2014 Terms of Use: http://spiedl.org/terms
tvPFigure 4. Electro-optical set-up: the upper arrow shows the diffraction when the hologram is reconstructed. The bottom arrow showsthe H-PDLC device plate with the electric connections.When the voltage is applied, the liquid crystal molecules are reoriented in the direction of the electric field. Due to theliquid crystal fraction the refraction index of the dark zones decreases to values closer to that of the bright zones.Therefore the index modulation decreases when the voltage increases.3. RESULTS3.1 Experiment without post-exposure treatmentAfter recording of the hologram, the device is placed into an electrical field in order to evaluate the electro-opticalresponse. Figure 5 graph A shows the diffraction efficiency (DE) as a function of the applied RMS voltage. The deviceA without post-exposure treatment reaches a DEmin 59% at 22 V. At this voltage, the electrical current intensitythrough the device reaches 100 mA (RMS value) and the protection circuit of the amplifier switches off the electricpower (the impedance control circuit only affects the transient intensity values). Therefore is not possible to increasemore the voltage. But this voltage is still very small to obtain changes of the diffracted intensity.The relatively high value of electric intensity is due to the characteristics of the components in the photopolymer solution(Table 1). The molecular structure of each component can be seen in Figure 1. YEt, NPG and OA are ionic moleculeswith high solubility into the mix with the other components. When the voltage is increased, the ionic species supportincreasing values of electrical current intensity. Since the voltage used is AC, electrochemical reactions are avoided andthe ionic species in the active layer are not wasted.Proc. of SPIE Vol. 9286 92865C-5Downloaded From: http://proceedings.spiedigitallibrary.org/ on 11/13/2014 Terms of Use: http://spiedl.org/terms
7060DE (%)50403020B10A0020406080100120140Vrms (V)Figure 5. Diffraction efficiency as a function of RMS voltage. Graph A: device without post-exposure treatment. Graph B: device withpost-exposure treatment.3.2. Bleaching post-exposure treatmentIn order to minimize the effect of the ionic species of this photopolymer, we use a bleaching post-exposure treatment bymeans of a halogen light. The devices are exposed to halogen light (90 W, 5 minutes) after hologram recording. Thistreatment has two effects. First the YEt concentration is reduced since the dye placed in the dark zones during hologramrecording reacts with NPG. Second, the monomer placed in the dark zones is polymerized and therefore the mobility ofthe ions is reduced. Figure 5 graph B shows the diffraction efficiency as a function of the RMS voltage for device B withthe bleaching post-exposure treatment. Figure 6 shows the electrical current intensity through the device as a function ofthe RMS voltage for the two devices.Proc. of SPIE Vol. 9286 92865C-6Downloaded From: http://proceedings.spiedigitallibrary.org/ on 11/13/2014 Terms of Use: http://spiedl.org/terms
1210-120100 -80 -Z.E 60 -áE40 20 -Ans0o105152025Vrms (V)0e0,20,4t406080t100B120140Vrms (V)Figure 6. Electrical current intensity as a function of RMS voltage for both devices.The device A reaches an electrical current intensity of 100 mA with a very low voltage of 22 V. Therefore, thediffraction efficiency decreases only from 62% to 59% (Figure 5). The diffraction efficiency starts to increase againwhen the amplifier automatically switches off (last dot of graph A in Figure 5). The voltage can be increased up to 132 Vfor the device B. The diffraction efficiency decreases from 66% to 39% when the voltage increases.The electrical current intensity increases from zero at voltages higher than 123 V as can be seen in graph B. When thevoltage of the amplifier is set at 125 V, i 7 mA and with this current between the electrodes of the H-PDLC cell thevoltage starts to decrease. Therefore the DE starts to increase from the minimum value (Figure 5).CONCLUSIONThis photopolymer formulation obtains a high value of diffracted intensity during hologram recording (DE 60 %) butthe device shows high electrical conductivity and the voltage only can be increased up to 60 V and at this voltage theelectro-optical response is very poor. We have identified several ionic components of the photopolymer formulation thatcould be related to the high electric current intensity obtained at that voltage.We use a bleaching post-exposure treatment that obtains a better result. Thus, the voltage can be increased up to 125 Vand the device has a better electro-optical performance. The bleaching treatment has two effects: dye and initiatorconcentration decrease and mobility decrease of the ionic species. Therefore, we can conclude that the poor response ofthe untreated device is due to the high electrical conductivity of this formulation due to the molecules with ioniccharacteristics: YEt, NPG and OA.Proc. of SPIE Vol. 9286 92865C-7Downloaded From: http://proceedings.spiedigitallibrary.org/ on 11/13/2014 Terms of Use: http://spiedl.org/terms
ACKNOWLEDGMENTSThe work was supported by the “Ministerio de Economía y Competitividad” of Spain under projects FIS2011-29803C02-01 and FIS2011-29803-C02-02 and by the “Generalitat Valenciana” of Spain under projects PROMETEO/2011/021and ISIC/2012/013.REFERENCES[1] Yan, J., Rao, L., Jiao, M, Li, Y., Cheng, H. C., Wu, S. T., “Polymer-stabilized optically isotropic liquid crystals fornext-generation display and photonics applications,” J. Mater. Chem. 21, 7870-7877 (2011).[2] Bunning, T. J., Natarajan, L. V., Tondiglia, V. P., Sutherland, R. L., “Holographic polymer dispersed liquid crystals(H-PDLCs),” Annu. Rev. Mater. Sci. 30, 83-115 (2000).[3] Ren, H., Xu, S., Wu, S-T., “Gradient polymer network liquid crystal with a large refractive index change,” Opt.Express. 20, 26464-26472 (2012).[4] Hsiao, V. K. S., Lu, Ch., He, G. S., Pan, M., Cartwright, A. N., Prasad, P. N., Jakubiak, R., Vaia, R. A., Bunning, T.J., “High contrast switching of distributed-feedback lasing in dye-doped H-PDLC transmission grating structures,”Opt. Express. 13, 3787-3794 (2005).[5] Massenot, S., Kaiser, J., Perez, M. C., Chevallier, R., Tocnaye, J. B., “Multiplexed holographic transmissiongratings recorded in holographic polymer-dispersed liquid crystals: static and dynamic studies,” Appl. Opt. 44,5273-5280 (2005).[6] Li, M. S., Wu, S. T., Fuh, A. Y-G., “Sensor for monitoring the vibration of a laser beam based on holographicpolymer dispersed liquid crystal films,” Opt. Express. 18, 26300-26306 (2010).[7] Infusino, M., Luca, A. D., Barna, V., Caputo, R., Umeton, C., “Periodic and aperiodic liquid crystal-polymercomposite structures realized via spatial light modulator direct holography,” Opt. Express. 20, 23138-23143 (2012).[8] Gallego, S., Márquez, A., Riquelme, M., Neipp, C., Ortuño, M., Beléndez, A., Pascual, I., “Analysis of PEAphotopolymers at zero spatial frequency limit.” Proc. SPIE. 8429, 1-8 (2012).[9] Liu, Y. J., Sun, X.W., “Holographic polymer-dispersed liquid crystals: materials, formation, and applications,” Adv.Optoelectron. 2008, 1-52 (2008).[10] Ortuño, M., Riquelme, M., Gallego, S.,Márquez, A., Pascual, I. and Beléndez, A., “Overmodulation Control in theOptimization of a H-PDLC Device with Ethyl Eosin as Dye,” Int. J. Polym. Sci., 2013, 1-8 (2013).Proc. of SPIE Vol. 9286 92865C-8Downloaded From: http://proceedings.spiedigitallibrary.org/ on 11/13/2014 Terms of Use: http://spiedl.org/terms
PROCEEDINGS OF SPIE Volume 9286 Proceedings of SPIE 0277-786X, V. 9286 SPIE is an international society advancing an interdisciplinary approach to the science and application of light. Second International Conference on Applications of Optics and Photonics Manuel Filipe P. C. Ma
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