Browsing by Author "Marinova, Vera"

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All-optically controlled light valve assembled by photorefractive crystal and PDLC hybrid structure
(2015-01-01)
Marinova, Vera
;
Liu, Ren Chung
;
Chen, Ming Syuan
;
Lin, Shiuan Huei
;
Lin, Yi Hsin
A light-valve device, assembled by Ru-doped Bi12SiO20 (BSO) photoconductive substrate and polymer dispersed liquid crystal layer is proposed, in which all the processes are controlled by the near infrared light. Laser beam illumination (Gaussian shape) on BSO:Ru crystal caused charge carriers generation, which migrate and form an inhomogeneous distribution and subsequent space charge field. This surface-localized electromagnetic field penetrates into the PDLC layer and modulate the orientation of the liquid crystals, that caused reverse of the device initial opaque state to the highly transparent one. The proposed structure is simple and easy to fabricate, without requirements of ITO contacts and alignment layers and opens further possibilities for near-infrared applications.
Atomic Layer-Deposited Al-Doped ZnO Thin Films for Display Applications
(2020-06-01)
Dimitrov, Dimitre
;
Tsai, Che-Liang
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Petrov, Stefan
;
Marinova, Vera
;
Petrova, Dimitrina
The integration of high uniformity, conformal and compact transparent conductive layers into next generation indium tin oxide (ITO)-free optoelectronics, including wearable and bendable structures, is a huge challenge. In this study, we demonstrate the transparent and conductive functionality of aluminum-doped zinc oxide (AZO) thin films deposited on glass as well as on polyethylene terephthalate (PET) flexible substrates by using an atomic layer deposition (ALD) technique. AZO thin films possess high optical transmittance at visible and near-infrared spectral range and electrical properties competitive to commercial ITO layers. AZO layers deposited on flexible PET substrates demonstrate stable sheet resistance over 1000 bending cycles. Based on the performed optical and electrical characterizations, several applications of ALD AZO as transparent conductive layers are shown-AZO/glass-supported liquid crystal (LC) display and AZO/PET-based flexible polymer-dispersed liquid crystal (PDLC) devices.
Chemical vapor deposition growth of bilayer graphene via altering gas flux geometry
(2019-11-30)
Petrov, Stefan
;
Rafailov, Peter M.
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Marinova, Vera
;
Lin, Shiuan-Huei
;
Lai, Yi-Chun
Graphene films with high content of bilayer graphene are obtained by chemical vapor deposition technique on copper (Cu) foil by means of suitably designing the flux geometries of the reactant gases. First single-layer graphene growth is optimized using a preliminary oxygen passivation of the Cu substrate which facilitates the formation of larger graphene grains with low defect density. Then, in order to enhance the transport of reactant species to the catalyst substrate, the gas flux geometry is modified in two ways: (i) fixing a graphite holder next to the Cu substrate perpendicular to the stream of the flux gases or (ii) positioning the Cu foil into a graphite shelter. It is found that both modifications facilitate the growth of a second graphene layer leading to increased formation of bilayer graphene. The obtained graphene layers are characterized by Raman spectroscopy (with special focus on the overtone (2D) of the disorder-induced band), scanning electron microscopy, transmission electron microscopy, atomic force microscope analysis and optical transmission measurements. Narrow symmetric 2D Raman peaks with linewidths ranging down to 22 cm(-1) but blue-shifted with respect to that of single-layer graphene are obtained from graphite holder- and shelter-grown samples indicating high-quality bilayer graphene.
Electro-optically and all optically addressed spatial light modulator devices based on organic-inorganic hybrid structures
(2017-01-01)
Marinova, Vera
;
Lin, Shiuan Huei
;
Hsu, Ken Yuh
;
電子物理學系
;
光電工程學系
The paper reviews two types of organic-inorganic hybrid structures: electro-optically addressed and all optically addressed that can be used as spatial light modulator devices, operating in a transmission mode. Both hybrid devices are assembled by inorganic Bi12SiO20 (BSO) crystals and organic liquid crystals (LC). The electro-optically controlled device demonstrates very high beam-amplification values at Raman-Nath regime of diffraction whereas all optically controlled device operates at Bragg matched regime of diffraction allowing sub-micron spatial resolution. Phase modulation ability has been demonstrated supporting possibilities for applications in adaptive optics, information processing and display technologies.
FLEXIBLE AND STRETCHABLE OPTOELECTRONIC DEVICES USING GRAPHENE
(2019-01-01)
Chiou, Chung Chin
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Marinova, Vera
;
Petrov, Stefan
;
Fidanova, Cvetelina
;
Angelova, Ina
In this paper we demonstrate flexible polymer dispersed liquid crystal (PDLC) devices using graphene as transparent conductive electrodes on polyethylene terephthalate (PET) substrate. Graphene was grown by Low Pressure Chemical Vapor Deposition (LPCVD) technique and characterized by Raman analysis, optical and electrical measurements. Several graphene-based PDLC devices have been fabricated and their electro-optical characteristics, response time and bending ability were measured and discussed. The results support the graphene promising features for integration in flexible optoelectronics.
Flexible light valves using polymer-dispersed liquid crystals and TiO2/Ag/TiO2 multilayers
(2019-06-10)
Chiou, Chung Chin
;
Hsu, Fan Hsi
;
Petrov, Stefan
;
Marinova, Vera
;
Dikov, Hristosko
The era of flexible optoelectronics demands development of wearable and bendable structures, foldable touch screens, paper-like displays, and curved and flexible solid-state lighting devices. Here, we demonstrate the fabrication of highly flexible light valves using polymer-dispersed liquid crystal (PDLC) and TiO2/Ag/TiO2 transparent conductive films. TiO2/Ag/TiO2 multilayers were prepared by magnetron sputtering technique on polyethylene terephthalate (PET) substrates at room temperature. By keeping the equivalent TiO2 layers and varying the deposition time of the Ag layer, proper metal nanograins on TiO2 planar plane were formed, providing the best tradeoff between the transmittance, sheet resistance and bending ability. The results are validated by numerical simulations that suggest the best match between the deposition time and individual layer thickness. Based on the performed characteristics of TiO2/Ag/TiO2/PET structures, several flexible light valves are fabricated and characterized. The sheet resistance values of TiO2/Ag/TiO2/PET remain unchanged over 1000 bending cycles. The measured driving voltage and response time values open great potential of TiO2/Ag/TiO2/PET for integration into next-generation ITO-free flexible and stretchable devices. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
Graphene oxide doped PDLC films for all optically controlled light valve structures
(2016-01-01)
Marinova, Vera
;
Tong, Zhon Fang
;
Petrov, Stefan
;
Karashanova, Daniela
;
Lin, Yi Hsin
We study the effect of graphene oxide (GrO) on the switching voltage of polymer dispersed liquid crystal (PDLC). The threshold voltage decreases with addition of GrO nanoparticles. Scanning electron microscopy (SEM) supported that the size of LC droplets in GrO-doped PDLC increase in comparison with non-doped one. PDLC:GrO layer was combined with Bi12SiO20 (BSO) inorganic substrate into a hybrid structure and based on the surface activated photorefractive phenomena typical for BSO, it allows the opaque-transparent states to be all optically controlled, operating faster and requiring less intensity due to the GrO addition in PDLC.
Graphene-based spatial light modulator operating at near infrared spectral range
(2019-04-01)
Marinova, Vera
;
Lin, Shiuan Huei
;
Petrov, Stefan
;
Chen, Ming Syuan
;
Lin, Yi Hsin
In this paper, a near infrared operating spatial light modulator is demonstrated, assembled in a way to combine the excellent photoconductivity of Ru-doped Bi12SiO20 (BSO:Ru) crystal, strong birefringence of liquid crystal (LC) and exceptionally high transparency and conductivity of graphene. A photo-alignment method instead of mechanical rubbing is used to simplify the fabrication procedure and to prevent detachment of the graphene layer from the substrate. The proposed device operates at low driving voltage (competitive to a reference device using ITO electrodes) moreover requires much less near infrared intensity for the light modulation. It is assumed the effect is due to the photo-induced space charge exchange between BSO:Ru and graphene allowing charge redistribution and optical doping effect resulting in a modulation of graphene's properties. The voltage-dependent transmittance and phase retardation show high contrast ratio with the response time of similar to 100 ms at 1064 nm. In addition, by projecting a video image through the proposed structure the response of modulated pump light intensity is demonstrated which supports device ability to work as near infrared optically addressed spatial light modulator (OASLM). The obtained performances reveal great potentials of graphene-based electro-optic devices for near infrared applications.
Near-Infrared Holography in Ruthenium Doped Bismuth Sillenite Crystal
(2010)
Marinova, Vera
;
Lin, Shiuan Huei
;
Liu, Ren Chung
;
Hsu, Ken Yuh
;
電子物理學系
Improvement of the response speed during real-time holographic recoding is demonstrated in Ru-doped bismuth sillenite crystal at 1064 nm after green light pre-exposure. By using gating light significant operation speed of 60 ms is achieved.
Near-infrared properties of Rh-doped Bi12TiO20 crystals for photonic applications
(2013-02-15)
Marinova, Vera
;
Liu, Ren Chung
;
Lin, Shiuan Huei
;
Chen, Ming-Syuan
;
Lin, Yi Hsin
The effect of Rh doping in Bi12TiO20 (BTO) crystals on the photosensitivity and recording speed at 1064 nm is reported. Response time of 0.1 s is measured during real-time holographic recording without any preliminary treatments. Once the crystal is pre-excited with a green light, the detected response time becomes 0.02 s. A possibility to implement BTO:Rh crystal plate with liquid crystals into a hybrid organic/inorganic device is demonstrated, which opens perspectives for further near-infrared applications. (c) 2013 Optical Society of America
Near-infrared sensitive organic-inorganic photorefractive device
(2016-10)
Marinova, Vera
;
Liu, Ren-Chung
;
Lin, Shiuan-Huei
;
Chen, Ming-Syuan
;
Lin, Yi-Hsin
Organic-inorganic hybrid structure, assembled by Rh-doped Bi12TiO20 crystal and liquid crystal (LC) layer, operating at near-infrared range is proposed and demonstrated. Due to the photorefractive properties of inorganic substrate, light illumination caused a space charge field which acts as a driving force for LC molecules re-alignment and subsequent refractive index modulation. All optically controlled phase retardation ability has been demonstrated supporting possibilities for further infrared applications.
Near-infrared sensitive organic-inorganic photorefractive device
(2016-10-01)
Marinova, Vera
;
Liu, Ren-Chung
;
Lin, Shiuan-Huei
;
Chen, Ming-Syuan
;
Lin, Yi-Hsin
Organic-inorganic hybrid structure, assembled by Rh-doped Bi12TiO20 crystal and liquid crystal (LC) layer, operating at near-infrared range is proposed and demonstrated. Due to the photorefractive properties of inorganic substrate, light illumination caused a space charge field which acts as a driving force for LC molecules re-alignment and subsequent refractive index modulation. All optically controlled phase retardation ability has been demonstrated supporting possibilities for further infrared applications.
Near-infrared sensitive photorefractive device using polymer dispersed liquid crystal and BSO: Ru hybrid structure
(2014-06-01)
Liu, Ren Chung
;
Marinova, Vera
;
Lin, Shiuan Huei
;
Chen, Ming-Syuan
;
Lin, Yi-Hsin
A near-infrared sensitive hybrid device, based on a Ru-doped BSO photorefractive substrate and polymer dispersed liquid crystal (PDLC) layer, is reported. It is found that the photoexcited charge carriers generated in the BSO: Ru substrate create an optically induced space charge field, sufficient to penetrate into the PDLC layer and to re-orient the LC molecules inside the droplets. Beam-coupling measurements at the Bragg regime are performed showing prospective amplification values and high spatial resolution. The proposed structure does not require indium tin oxide (ITO) contacts and alignment layers. Such a device allows all the processes to be controlled by light, thus opening further potential for real-time image processing at the near-infrared range. (C) 2014 Optical Society of America
Optical and holographic properties of Fe plus Mn co-doped Bi4Ge3O12 crystals
(2008-01-01)
Marinova, Vera
;
Petrova, Dimitrina
;
Lin, Shiuan Huei
;
Hsu, Ken Yuh
;
電子物理學系
The effect of iron and manganese co-doping on the light-induced, dark- and photoconductivity and holographic properties of Bi4Ge3O12 crystals in comparison with Fe- and Mn-single doping is studied. Fe+Mn co-doped crystals exhibited strong photochromic effect at room temperature, the photochromic effect being fully reversible by thermal annealing. The observed light-induced absorption changes and non-linear dependence of photoconductivity on light intensities indicate deep and shallow photoactive levels contribution to the charge transport mechanism of Fe+Mn co-doped BGO. Holographic gratings are successfully recorded at different wavelengths and a possibility to extend the photorefractive sensitivity into the red spectral range is demonstrated. It is found furthermore that Fe+Mn-doping combination leads to faster response time during holographic recording, especially after a preliminary exposure with ultraviolet light, in comparison with Fe- and Mn-single doping. (c) 2007 Elsevier B.V. All rights reserved.
Optical, magneto-optical and holographic study of Bi4Ge3O12 crystals doped with transition elements
(2006-01-01)
Petkova, Petya
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Marinova, Vera
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Iliev, Ilia
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Dimov, Todor
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Lin, Shiuan H.
Bismuth germanate Bi3Ge4O12 (BGO) single crystals doped with ruthenium, manganese and ruthenium plus manganese are gown by Czohralski technique with automatically diameter-weight control method. The effect of doping on the light-induced, magneto-optical and holographic properties of BGO single crystals is studied. It was found that the optical transmission spectrum of doped samples is modified strongly under thermal annealing and homogeneous illumination with UV light as well as the photochromic effect is fully reversible. The magneto-optical rotation was measured and Verdet constant was calculated at visible spectral range. Holographic grating are successfully recorded at 633 nm.
Organic-inorganic hybrid structures for high-resolution spatial light modulators
(2018-01-01)
Marinova, Vera
;
Lin, Shiuan Huei
;
Hsu, Ken Yuh
;
電子物理學系
;
光電工程學系
The continuing need of improvements governed by the development of all optically controlled devices providing wide broadband sensitivity, high spatial resolution and low energy consumption rapidly increase. In this paper, we review varieties of organic-inorganic hybrid structures that can be used as all optically driven high resolution spatial light modulators. In the proposed structures all optical processes are controlled by the surface activated photorefractive phenomena, typical for highly photoconductive substrates. The performed two-beam coupling measurements at Bragg match regime show prospective amplification values and sub-micron spatial resolution. The structures are easy to fabricate and their operation simple to control.
Phase-modulated ellipsometry for probing the temperature-induced phase transition in ruthenium-doped lead zinc niobate-lead titanate single crystal
(2011-02-28)
Chuang, Chun-I
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Marinova, Vera
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Lin, Shiuan-Huei
;
Chao, Yu-Faye
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電子物理學系
Phase-modulated ellipsometry was applied to measure changes in the refractive index of pure and ruthenium (Ru)-doped 0.9Pb (Zn(1/3)Nb(2/3))O(3)(PZN)-0.1 PbTiO(3) (PT) during the heating process in real time. Both samples were heated from room temperature to 200 degrees C in a thermally insulated chamber. In both samples, the phase transitions were observed to change from tetragonal to cubic. The temperature region at which the phase transition (Curie region) of Ru-doped 0.9PZN-0.1PT occurred not only broadened but also shifted to a lower temperature. The refractive indices were extremely stable in this region, meaning that Ru-doped 0.9PZN-0.117 is a more favorable medium for the fabrication of optical memories. (C) 2011 Elsevier B.V. All rights reserved.
Polymer Dispersed Liquid Crystals Devices on Rigid and Flexible Substrates Using Graphene Electrodes
(2019-01-01)
Angelova, Ina
;
Chiou, Chong Chin
;
Marinova, Vera
;
Lin, Shiuan Huei
;
Petrova, Dimitrina
Polymer Dispersed Liquid Crystal (PDLC) devices on rigid and flexible substrates using graphene as transparent conductive electrodes are fabricated and demonstrated. Graphene is growth by using low pressure Chemical Vapor Deposition (CVD) method on Cu foil and transferred on polyethylene terephthalate (PET) substrates. Electro-optical modulation characteristics of several PDLC devices are measured and discussed. It is found that the transmittance dependence on the driving voltage demonstrates high potential of graphene for next generation ITO-free optoelectronic and display technology.
Quasi-nonvolatile storage in Ru-doped Bi12SiO20 crystals by two-wavelength holography
(2012-08-27)
Marinova, Vera
;
Liu, Ren Chung
;
Lin, Shiuan Huei
;
Hsu, Ken Yuh
;
電子物理學系
Prolonged read-out process of a hologram recorded at near infrared with simultaneous green light exposure is measured in Ru-doped Bi12SiO20 crystal. The experimental results are confirmed by numerical simulations, suggesting two different traps involved in the space-charge transport mechanism. In addition, quasi-permanent holographic recording of image with fast updating speed by using two-wavelength recording is demonstrated. (C) 2012 Optical Society of America
Real-time holographic information processing at near infrared using ruthenium-doped bismuth sillenite crystals
(2011)
Lin, Shiuan Huei
;
Marinova, Vera
;
Liu, Ren Chung
;
Hsu, Ken Y.
;
電子物理學系
In this paper, we report our investigations on real-time holographic recoding at 1064 nm in Ru-doped bismuth sillenite crystal with a green gating light at 532 nm. By using gating light significant improvement of the response time to 80 ms is achieved and the prolonged read-out process of the recorded hologram is observed. We also demonstrate quasi-permanent holographic recording of image with fast speed in Ru-doped BSO crystal using two-wavelength recording.