Showing papers on "Organic photorefractive materials published in 2005"
TL;DR: In this paper, a high-performance photorefractive polymer composite operating at 1550 nm was developed, achieving 40% internal diffraction efficiency with response time of 35 ms and a net gain of 20 cm−1 in four-wave mixing and two-beam coupling experiments, respectively.
Abstract: The development of a high-performance photorefractive polymer composite operating at 1550 nm is reported. We show 40% internal diffraction efficiency with response time of 35 ms and a net gain of 20cm−1 in four-wave mixing and two-beam coupling experiments, respectively. This is more than an order of magnitude improvement in the diffraction efficiency and net two beam coupling gain and two orders of magnitude in the response time than the previously reported photorefractive polymer operating at this technologically important wavelength. The improvement in photorefractive characteristics is accomplished by an enhanced orientation of the nonlinear optical chromophore in the present composite.
38 citations
TL;DR: Direct measurements of UV photo-induced volume densification demonstrates that glass compaction accounts for large part of the refractive index change, and highly efficient photo- induced phase gratings have thus been fabricated in the waveguide.
Abstract: We present the characterization of highly photorefractive Er3+/Yb3+-doped 75SiO2-25GeO2 planar waveguides, single mode at 1550 nm, deposited by radio-frequency-magnetron-sputtering (RFMS) technique. Details of the deposition process are reported. The material presents an intense absorption band (α≈103÷104 cm-1) in the UV region. Irradiations by a KrF excimer laser source at λ=248 nm have produced large positive (up to 3·10-3) refractive index changes, without the need of particular sensitization procedures. Direct measurements of UV photo-induced volume densification demonstrates that glass compaction accounts for large part of the refractive index change. Highly efficient photo-induced phase gratings have thus been fabricated in the waveguide.
35 citations
TL;DR: The photorefractive performance of a polymer composite sensitized by CdSe/ZnS core/shell nanoparticles, and also comprising poly(N-vinylcarbazole) and an electro-optic chromophore, constitutes a significant improvement on the performance of previous nanoparticle-sensitized photoreFractive polymer composites.
Abstract: We report the photorefractive performance of a polymer composite sensitized by CdSe∕ZnS core/shell nanoparticles, and also comprising poly(N-vinylcarbazole) and an electro-optic chromophore. The nanoparticles are characterized by absorption and photoluminescence spectroscopy, elemental analysis, transmission electron microscopy, and powder x-ray diffraction. The electro-optic response of the composite is measured independently of the photorefractive effect by transmission ellipsometry. An asymmetric two-beam coupling gain of 30.6±0.4cm−1 is obtained, confirming photorefractivity. Degenerate four-wave mixing is used to assess photorefractive performance and, at a poling field of 70Vμm−1, yields a diffraction efficiency of 4.21%±0.03%, a holographic contrast of 3.05×10−4±1×10−6, a space-charge rise time of 25±2s, and a sensitivity of 4.7×10−5±4×10−6cm3J−1. These results constitute a significant improvement on the performance of previous nanoparticle-sensitized photorefractive polymer composites.
25 citations
TL;DR: In this article, the photorefractivity of liquid crystalline polymers and ferroelectric liquid crystals is described, where the interference of two laser beams in a photore-fractive material establishes a refractive index grating.
Abstract: This paper reviews our recent work on the photorefractive effect in liquid crystalline materials. The photorefractive effect is defined as the optical modulation of the refractive index of a medium as a result of various processes. The interference of two laser beams in a photorefractive material establishes a refractive index grating. This phenomenon enables the creation of different types of photonic applications. Recently, the development of organic photorefractive materials has been attracting great interest. Liquid crystalline materials are a strong candidate for practical photorefractive materials and application. In this paper, the photorefractivity of liquid crystalline polymers and ferroelectric liquid crystals is described.
18 citations
TL;DR: In this paper, a photorefractive polymer composite sensitized by 1-hexadecylamine capped CdSe nanoparticles is reported, which includes the charge transporting matrix poly(N-vinylcarbazole) and the electro-optic chromophore 1-(2-ethylhexyloxy)-2,5-dimethyl-4-(4-nitrophenylazo) benzene.
Abstract: The performance of a photorefractive polymer composite sensitized by 1-hexadecylamine capped CdSe nanoparticles is reported. The polymer composite also comprises the charge transporting matrix poly(N-vinylcarbazole) and the electro-optic chromophore 1-(2-ethylhexyloxy)-2,5-dimethyl-4-(4-nitrophenylazo) benzene. At an applied field of 70 V μ m−1 two beam coupling gain of 13.2 cm−1 was observed, confirming the photorefractive nature of the induced grating. At the same field, a holographic contrast of 9.12×10−4±6×10−6, a photorefractive sensitivity of 5.1×10−4 ±0.2×10−4 cm3 J−1 and a space-charge field rise time of 13±1 s were obtained.
13 citations
TL;DR: In this paper, the photorefractive effect in a photoconducting polymer containing small liquid crystal droplets is studied, and two beam coupling experiments indicate a high optical gain at moderate field strength (>50cm−1 at 10 V∕μm).
Abstract: The photorefractive effect in a photoconducting polymer containing small liquid crystal droplets is studied. Two beam coupling experiments indicate a high optical gain at moderate field strength (>50cm−1 at 10 V∕μm). The writing of photorefractive gratings is reversible. The dynamic behavior can be described by a two step process of the grating formation, the faster time constants being of the order of 100 ms. Modulation of the external voltage indicates that the reorientation of the director in the liquid crystals droplets is faster than the rise and decay times of the space charge field.
11 citations
TL;DR: At a temperature lower than the melting point of pure pentyl-cyanobiphenyl liquid crystal (5CB), the photorefractive effect of 5CB heavily doped with fullerene is studied and a diffraction efficiency of the photOREfractive grating of more than 40%, which is more than twice as high as the best data reported to the authors' knowledge.
Abstract: At a temperature lower than the melting point of pure pentyl-cyanobiphenyl liquid crystal (5CB) we studied the photorefractive effect of 5CB heavily doped with fullerene (C60) and obtained a diffraction efficiency of the photorefractive grating of more than 40%, which is more than twice as high as the best data reported to our knowledge. A quasi-permanent grating was observed with a diffraction efficiency of 11.2% after the grating was kept in the dark for a month.
10 citations
TL;DR: By monitoring the effect of local grating disruption, the distribution of power transfer is spatially resolved throughout the crystal, and the results are found to be in agreement with the theoretical predictions.
Abstract: The spatial distribution of the power transfer achieved by contradirectional two-beam coupling using self-pumped photorefractive reflection gratings is investigated in two materials with different photorefractive gain coefficients, LiNbO3:Fe and KNbO3:Fe. Incremental portions of the volume grating are erased optically by inducing thin optical damage planes, reducing the overall two-beam coupling efficiency. By monitoring the effect of local grating disruption, the distribution of power transfer is spatially resolved throughout the crystal, and the results are found to be in agreement with our theoretical predictions.
6 citations
TL;DR: In this paper, two monolithic organic materials exhibiting high photorefractive (PR) performances at a wavelength of 1064 nm were prepared and characterized, and it was found that thiophene-based molecule T6 demonstrated better PR properties than benzene based molecule B6.
Abstract: Two monolithic organic materials exhibiting high photorefractive (PR) performances at a wavelength of 1064 nm were prepared and characterized. It was found that thiophene-based molecule T6 demonstrated better PR properties than benzene based molecule B6. A net optical gain of 139.1cm−1 at a low applied field of 43.7V∕μm and a diffraction efficiency of 45.6% at 35.3V∕μm were observed for materials made from T6. Net optical gain at 1300 nm was also observed for T6. The differences in PR behavior between two materials with similar structures were explained based on dipole moment and photoconductivity differences.
5 citations
15 Aug 2005
TL;DR: In this paper, interference imaging of refractive index distribution in photorefractive records in the LiNbO3 sample is presented, which shows that an easily readable image can be obtained when refractive indices are modulated only in direction parallel with interference fringes.
Abstract: Short analyze and some results of interference imaging of refractive index distribution in photorefractive records in the LiNbO3 sample are presented. The presented result shows that an easily readable image can be obtained when refractive index is modulated only in direction parallel with interference fringes. For this purpose, it is useful to use Mach-Zehnder interferometer what allows adjusting the interference fringes to desired position. Obtained images of records of a light field with aperiodic distribution of intensity show that refractive index profiles do not correspond to profile of light intensity or intensity of internal electric field (which is formed by the sample illumination). It is more like the profile of distribution of carrier concentration trapped on the donors or profile of square of the electric field when gradient of refractive index is parallel or perpendicular to c axis of the crystal, respectively. This result leads to necessity of modifying explanation of mechanism of photorefractive record creation. At least in investigated LiNbO3:Fe.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
5 citations
TL;DR: In this article, the crystal orientation dependence of optical properties in InxGa1−xN∕GaN multiple quantum wells was investigated and the spectral peaks and intensity of the microphotoluminescence signal for different crystal orientations were found to have sixfold symmetry.
Abstract: We have investigated the crystal orientation dependence of optical properties in InxGa1−xN∕GaN multiple quantum wells. The spectral peaks and intensity of the microphotoluminescence signal for different crystal orientations were found to have six-fold symmetry. Quite interestingly, the refractive index, obtained from the interference pattern, also varies with the crystal orientation. The 60° periodic anisotropy of electronic transitions as well as optical parameters was interpreted in terms of the Pockels effect induced by the strong built-in field in nitride heterojunctions. The linear dependence of the change of the refractive index on electric field is consistent with the prediction of the Pockels effect. Our result provides an alternative solution to improve the designs of photonic and electronic devices based on nitride semiconductors.
TL;DR: The influence of chromophore solubility enhancements on photorefractive grating rise time and device lifetime was investigated in this article, where three azo chromophores differing primarily in compatibility with a polyvinyl carbazole host polymer were synthesized.
Abstract: The influence of chromophore solubility enhancements on photorefractive grating rise time and device lifetime is investigated. Three azo chromophores differing primarily in compatibility with a polyvinylcarbazole host polymer were synthesized. Aromatic substitutions to the chromophore increased the device lifetime from several days to years although electric-field-induced poling experiments indicated that chromophore orientational mobility is severely hindered, resulting in photorefractive grating rise times approaching several hours. The incorporation of a flexible butyl chain to the aromatic substituted chromophores significantly enhanced the orientational mobility. These chromophores could be loaded as high as 60wt% with no degradation in transparency for one year following fabrication.
TL;DR: In this paper, the photorefractive effect (optical damage) is enhanced by the electric field applied to the waveguide, and resistance to the effect is increased when the samples are heated at temperatures as high as 80°C.
Abstract: The temperature and electric field dependences of the photorefractive effect in proton-exchanged (PE) waveguides formed on MgO-doped lithium niobate (LN) are investigated in detail for the first time. As a result, the photorefractive effect (optical damage) is found to be enhanced by the electric field applied to the waveguide. On the other hand, resistance to the photorefractive effect is markedly increased when the samples are heated at temperatures as high as 80°C. We should take these properties into consideration in designing optical devices such as electrooptic modulators and parametric devices.
Journal Article•
19 Jul 2005
TL;DR: In this article, the surface structure of a photorefractive grating that is formed with the use of a bulk interference pattern by photovoltaic effect in X-cut lithium niobate crystal short-circuited along z-axis was theoretically investigated.
Abstract: We theoretically investigate the surface structure of a photorefractive grating that is formed with the use of a bulk interference pattern by photovoltaic effect in X-cut lithium niobate crystal short-circuited along z-axis. The steady-state gratings with the wave vector directed along the z-axis in the samples with dielectric and metallized (shortcircuited) x-boundaries are considered. The amplitude of the surface relief grating in the sample with metallized boundary exceeds one for the case of dielectric boundary. The existence near such metallized surface the x-component of electric space-charge field causes here the predominance of perturbation for off-diagonal component ?B
13=?B
31 of the dielectric impermeability tensor at optical frequency.
TL;DR: By using split-step beam propagation method, self-pumped contra-directional two-beam coupling is simulated in a photorefractive medium for arbitrary shaped beams in this article, where the role of diffusion, photovoltaic effect and dark conductivity is investigated for a LiNbO3:Fe crystal.
Abstract: By using split-step beam propagation method, self-pumped contra-directional two-beam coupling is simulated in a photorefractive medium for arbitrary shaped beams. The role of diffusion, photovoltaic effect and dark conductivity is investigated for a LiNbO3:Fe crystal.
14 Jul 2005
TL;DR: In this paper, an image cross connector with multiple-layered photorefractive polymers is proposed to arbitrarily change and interconnects vertically-disposed input images into horizontally without blur.
Abstract: We propose an image cross connector with multiple-layered photorefractive polymers that arbitrarily changes and interconnects vertically-disposed input images into horizontally without blur We verify its fundamental operation with a photorefractive polymer PATPD experimentally
19 Jul 2005
TL;DR: The photorefractive properties of high performance PR organic monolithic glasses containing dicyanomethylenedihydrofuran (DCDHF) chromophores are reviewed in this article.
Abstract: The photorefractive (PR) properties of high performance PR organic monolithic glasses containing dicyanomethylenedihydrofuran (DCDHF) chromophores are reviewed. Two-beam coupling net gain coefficients of ~200-400 cm-1 were obtained at the wavelengths of 676 nm and 830 nm. Beam self-focusing and defocusing observed in DCDHF glasses are discussed. Beam guiding in the optically induced waveguide is demonstrated.
19 Jul 2005
TL;DR: In this paper, the authors investigated the high-frequency mode of space charge wave (SCW) in crystals of the sillenite family Bi12SiO20, Bi12GeO20 and Bi12TiO20.
Abstract: This paper presents investigations of the high-frequency mode of space-
charge waves (SCW) in crystals of the sillenite family Bi12SiO20, Bi12GeO20 and
Bi12TiO20.
19 Jul 2005
TL;DR: Based on the angle selectivity of photorefractive volume holographic grating (PVHG), the corresponding refractive index modulation depth and effective thickness are measured in this article.
Abstract: Photorefractive volume holographic grating (PVHG) is predicted to have attractive applications in optical communications and optical sensors due to its flexibility for fabricating, easy erasure and repeatable use. In this paper, we present some theoretical analyses and experimental results on the diffraction properties and applications of PVHGs in LiNbO3:Fe crystal. Based on the angle selectivity of PVHG, the corresponding refractive index modulation depth and effective thickness are measured. Using these calculation values in addition to recording parameters, some special diffraction properties of PVHG can be designed. In order to avoid the polarization dependent diffraction efficiency due to the anisotropy of photorefractive crystals, double PVHGs are suggested to record in the same position of the crystal with two ordinary and extraordinary recording beams, respectively. As a filtering device, the PVHG can be well used to demodulate the wavelength reflected by a fiber Bragg grating. And the corresponding wavelength demodulation experiment is demonstrated in this paper.
30 Aug 2005
TL;DR: In this article, an all-optical switching device, photorefractive connection module (PRCM), with an organic photore-fractive polymer PATPD was proposed, which can be branched by illuminating matrix patterned control beams.
Abstract: We propose an all-optical switching device, photorefractive connection module (PRCM), with an organic photorefractive polymer PATPD. Spatially multiplexed time-series signals propagating in optical bus line can be branched by illuminating matrix patterned control beams.
30 Aug 2005
TL;DR: In this paper, the photorefractive properties in barium titanate crystal are associated with the concentration variation, and the change of the shallow concentration can be estimated through the light-induced absoption, but the relation between oxygen partial pressure also.
Abstract: In this report, the photorefractive properties in barium titanate() crystal are associated with the concentration variation. Not only the change of the shallow concentration can be estimated through the light-induced absoption, but the relation between oxygen partial pressure also. A correlation between measurement of photoconductivity and light-induced absorption yields the concentration variation is a function of oxygen partial pressure. Otherwise, the wavelength dependent photorefractive properties of the are investigated and discussed.
15 Sep 2005
TL;DR: In this article, a theory of higher-order diffraction order images properties in photorefractive liquid crystal polymer composites has been developed, which is in good agreement with experimental work.
Abstract: About forty years ago, Ashkin found that the refractive index was changed when laser transmits some materials', then photorefractive(PR) phenomenon was found. During the past four decades, photorefractive nonlinear optics has received great attention due to its real-time operation, high sensitivity, and high holographic storage capacity 2.3 . The interbeam angle between signal and reference beam usually is large than ten degrees when people storage information, so we can use fundamental photorefractive grating and avoid the influence of higher-order diffraction. However, higher-order diffraction can be used to realize image processing .It has not been well studied because higher-order diffraction images are usually blurry for crystal. With research expanding, photorefractive polymer materials are being paid much attention because of the properties of easy processing, fast response and material flexibility 4 . In this paper, we firstly report some novel photorefractive higher-order diffraction phenomena of polymer material (PVK:5CB:C 60 )at small interbeam angle. The photorefractive composite consists of polymer poly[N-vinylcarbazole](PVK)doped with 4,4'-n-pentylcyanobiphenyl (5CB) and C 60 . The weight ratio is 55.45%:44.45%:0.10%(PVK:5CB:C 60 ). The higher-order diffraction images are clear. The experiments testify the feasibility of optical image processing. In two-wave coupling experiments, signal beam is interfered with a mutually coherent reference beam within composites. Results are given respectively when signal beam was focused behind the composites, in front of the composites, in the composites. Higher diffraction order images are amplificatory or inverse. A theory of higher diffraction order images properties in photorefractive liquid crystal polymer composites has been developed .The theory is in good agreement with experimental work.
12 Jun 2005
TL;DR: In this article, the photorefractive two-beam coupling in semi-insulating GaN thin crystal was observed and compared with paraelectric and ferroelectric crystals, or organic materials.
Abstract: Most of semi-insulating compound semiconductors show photorefractive effect. Its photorefractive response is quite fast compared with paraelectric and ferroelectric crystals, or organic materials. Sometimes the effect is enhanced by the band edge effect such as the electroabsorption. However, photorefractive effect has not been reported in nitride semiconductors, which are intensely studied as promising nonlinear optical materials for the blue and ultra-violet wavelength region. In this paper, we report the observation of the photorefractive two-beam coupling in semi-insulating GaN thin crystal.
TL;DR: In this article, the effect of polarization of light on photorefractive grating formulation with any light modulation in birefringent photore-fractive material is studied in detail.
Abstract: In this paper, effect of polarization of light on photorefractive grating formulation with any light modulation in birefringent photorefractive material is studied in detail. The diffraction efficiency with various modulations and different polarization mode is calculated. Theoretical analytic results are presented. It is shown that both the ratio of the initial intensity and the incident angle of the writing waves are selective when the polarization of mode of the readout wave and that of diffracted wave are different. But these two recording conditions are not selective for the isotropic diffraction. On the other hand, it is also found that the length of the grating is selective for anisotropic diffraction.
19 Jul 2005
Abstract: In a planar aligned photorefractive liquid crystal light valve we show the appearance of optical structures induced by a single mirror feedback. We report the typical responses of the valve as a function of the pump intensity. We observe that the length scale of the structures scales with the light free propagation length, according with a diffractive feedback model.
12 Jun 2005
TL;DR: Tin thiohypodiphosphate (Sn/sub 2/Pn/Sub 2/S/sub 6/) is a wide bandgap semiconductor ferroelectric with interesting nonlinear optical properties and large electro-optical coefficients as mentioned in this paper.
Abstract: Tin thiohypodiphosphate (Sn/sub 2/Pn/sub 2/S/sub 6/) is a wide bandgap semiconductor ferroelectric with interesting nonlinear optical properties and large electro-optical coefficients. In addition it is also a very attractive photorefractive material showing fast photorefractive grating recording times and large refractive index change in the red and near infrared spectral region. These properties make Sn/sub 2/Pn/sub 2/S/sub 6/ an interesting material for several applications where laser diodes are employed (laser stabilization, beam cleanup, optical phase conjugation). The wide optical transparency range extending from /spl lambda/=0.53 /spl mu/m to /spl lambda/=8 /spl mu/m also allows optical parametric generation of infrared wavelengths not accessible with standard nonlinear optical crystals.
12 Jun 2005
TL;DR: In this article, the authors have succeeded in generating stable self-focused states in an optically active photorefractive (PR) crystal (Bi/sub 12/TiO/sub 20) at 633 nm with a lifetime of several hours.
Abstract: Spatial solitons in photorefractive (PR) crystals have attracted great interest in the last two decades because they represent a model scheme for solitons in other materials which are more complicated to obtain experimentally. In our presentation, we show that we have succeeded in generating stable self-focused states in an optically active PR crystal (Bi/sub 12/TiO/sub 20/) at 633 nm with a lifetime of several hours.
TL;DR: An electro-optic wavelength demultiplexer using photorefractive orthogonally polarized four-wave mixing with writing by ordinary rays and readout by extraordinary rays is proposed in this article.
Abstract: An electro-optic wavelength demultiplexer using photorefractive orthogonally polarized four-wave mixing with writing by ordinary rays and readout by extraordinary rays is proposed. The demultiplexing characteristics based on the phase-matching properties are theoretically studied. A refractive index grating is induced within a photorefractive crystal by optical interference of the wavelength-multiplexed signal and the forward pump light with the same channel wavelengths. An external electric field is applied to the crystal in such a way that the phase match condition (Bragg condition) is satisfied for the diffracted light of the backward pump by means of the refractive index grating. As a result, the desired channel signal can be converted to a diffracted signal for demultiplexing by scanning of the external electric field and of the input and output angles of the forward pump and the diffracted signal. As a specific crystal, BaTiO3 is considered. Numerical calculations are used to investigate the demultiplexing characteristics when the signal light is incident normally on the crystal surface. It is found that demultiplexing by spatial separation with a sufficient crosstalk level is achievable with wavelength spacings up to about 0.2 nm, near the wavelength of 0.5145 µm for a crystal size of 4 mm × 4 mm. Since the external electric field is applied only in the direction affecting the refractive index of the read-out signal, the formed refractive index grating is not disturbed and high-speed response is possible. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 88(10): 19–27, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20177
19 Jul 2005
TL;DR: In this article, the photorefractive ferroelectric material Sn2P2S6 was modified with Te to improve its photore-fractive properties. But the results showed that the improvement was limited to about 2 cm-1.
Abstract: Sn2P2S6 is a fast responding photorefractive ferroelectric material with very attractive properties for applications in the near infrared. It exhibits high electro-optic coefficients up to r T 111 = 174pm/V at 633nm and room temperature, large transparency range in the infrared (530–8000 nm), and a high photorefractive sensitivity. We show that modifying the growth conditions and doping with Te can efficiently improve the photorefractive properties of Sn2P2S6. Photorefractive two-beam coupling gain at 860 nm increases from about 2 cm-1 in conventional