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Holographic display has attracted widespread interest because of its ability to show the complete information of the object and bring people an unprecedented sense of presence. The absence of ideal recording materials has hampered the realization of their commercial applications. Here we report that the response time of a bismuth and magnesium co-doped lithium niobate (LN:Bi,Mg) crystal is shortened to 7.2 ms and a sensitivity as high as 646 cm/J. The crystal was used to demonstrate a real-time holographic display with a refresh rate of 60 Hz, as that of the popular high-definition television. Moreover, the first-principles calculations indicate that the electron mobility while Bi occupying Nb-site is significantly greater than that in Li-site, which directly induces the fast response of LN:Bi,Mg crystals when the concentration of Mg is above its doping threshold.

We have conducted numerical examinations on the characteristics of off-shooting solitons (OSS) arising from optical Airy beams in a biased centrosymmetric photorefractive medium, along with their relationship with conventional spatial solitons in such medium. As a result of this study, OSS exhibits qualities resembling those of photorefractive spatial solitons. The existence of OSS is found to be slightly shifted from the center of the propagation axis and varies with the intensity of the Airy beam sent into the medium. Under fixed nonlinear conditions, there exists a range of intensity values for which the characteristics of OSS most closely resemble those of photorefractive spatial solitons. At low-intensity regimes, OSS exhibit lower amplitudes and wider widths compared to the spatial soliton. The OSS profile is lost and displays spatial breathing along the propagation axis under strong power or nonlinear conditions. Subsequently, diffusive nonlinearities cause OSS to undergo deflection, resembling the self-deflection recently observed in photorefractive spatial solitons. The characteristics of OSS found in this study suggest that OSS can be classified as novel spatial solitons in the biased centrosymmetric photorefractive medium. [ABSTRACT FROM AUTHOR]

Copyright of Arquivos Brasileiros de Oftalmologia is the property of Arquivos Brasileiros de Oftalmologia and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The photorefractive glass-ceramics of Na2O-ZnO-Al2O3-SiO2 system were prepared by high temperature melting method. The effects of different components on the photorefractive properties of glass samples were studied by absorption spectroscopy and XRD. The results show that lanthanum ions, bromide ions, silver ions, and fluoride ions are crucial to the photorefractive properties of photorefractive glass-ceramics, and the absence of any of these elements does not result in photorefractive phenomena. [ABSTRACT FROM AUTHOR]

Aim The aim of this work was to study the changes that occur in the posterior corneal surface after photorefractive keratectomy (PRK) in moderate myopia using pentacam. Patients and methods This prospective study included 30 myopic eyes of 17 patients with spherical equivalent −2.00–6.00 D who underwent PRK using Visx S4 Excimer Laser. Pentacam examination was carried out for all our eyes at preoperatively, and 1 week and 3 months postoperatively. Pentacam was used to compare preoperative and postoperative measurements of the anterior and posterior corneal curvatures, and asphericity of the posterior corneal surface. Results This study included 30 myopic eyes of 17 patients, seven women and 10 men. Patients’ ages ranged from 28 to 40 years; the mean age was 30.3±3.03 years. No statistically significant changes were found in the posterior horizontal corneal curvature. A statistically significant change in the posterior vertical corneal curvature from 6.1±0.3 to 6.06±0.2 mm 1 week after PRK was found, but it increased after 3 months to 6.2±0.3 mm. No statistically significant changes in the posterior mean corneal curvature were observed either at 1 week or 3 months after PRK. A significant change in the Q-value (asphericity) was found both at 1 week and 3 months postoperatively. Conclusion After PRK, changes in the posterior corneal surface affect mainly the vertical curvature asphericity with forward elevation of the posterior corneal surface.

Photorefractive holograms have received great attention for decades due to their transmissive geometries and dynamic nature. The PR mechanism involves charge generation, charge transport, charge trapping, and modulation of the refractive index. So far, photorefractive hologram is regarded as one of the most important holographic materials with dynamic features. Since the first PR mechanism was described about 50 years ago, extensive investigations have been undertaken by many researchers and it is anticipated that PR materials will be the center of optoelectronic material research in the near future. This article reviews the current understanding of the mechanism responsible for the PR effect and current research trends, and briefly introduces recent progress in applications and material design. [ABSTRACT FROM AUTHOR]

With respect to digital holography, techniques in suppressing noises derived from reference arm are maturely developed. However, techniques for the object counterpart are not being well developed. Optical phase conjugation technique was believed to be a promising method for this interest. A 0°-cut BaTiO 3 photorefractive crystal was involved in self-pumped phase conjugation scheme, and was employed to in-line digital holographic microscopy, in both transmission-type and reflection-type configuration. On pure physical compensation basis, results revealed that the image fidelity was improved substantially with 2.9096 times decrease in noise level and 3.5486 times increase in the ability to discriminate noise on average, by suppressing the scattering noise prior to recording stage. [ABSTRACT FROM AUTHOR]

We investigate the formation or time evolution characteristics of bright and dark optical spatial solitons in novel photorefractive media with linear and quadratic electro-optic effects. This study was carried out at low amplitude. By the application of low amplitude approximation to the time-dependent wave (soliton) propagation equation, bright soliton solution (BSS) and dark soliton solution (DSS) were each obtained analytically, and both are exact solutions. The change in soliton width or the intensity full width at half maximum (FWHM) of two soliton types can also be calculated directly from the BSS and the DSS, providing a suitable description of the bright and dark solitons time evolution in novel photorefractive media. Only steady state solitons are formed in low amplitude, and the quasi-steady state soliton does not exist as reported at high saturation values. We compare analytical BSS with numerical calculation results of previous studies and find good agreement between analytics and numerics on the amplitude limit. In contrast to bright solitons, which can arise in the dominant linear or quadratic electro-optic effect, dark solitons in novel photorefractive media always exist under the dominant quadratic electro-optic effects only. We found that the time evolution of dark solitons from the DSS corresponds with time-independent optical spatial solitons studies in a similar media. Lastly, BSS and DSS found at low amplitude limits are fundamental soliton solutions or initial state soliton (at low peak intensity ratio regime) that can play an important role in further investigations of optical spatial solitons formation in novel photorefractive media. [ABSTRACT FROM AUTHOR]

We live in a complex world where revolutionary progress has been and continues to be made in communications, computer memory, and data processing. There is a growing need for new technologies that rapidly detect and treat diseases at an early stage or even pre-stage. As we are accustomed to these advances, our expectations will demand more compact, energy-efficient, rapidly responding, and environmentally safe technologies. Since the discovery of the photorefractive effect in organic polymers, carbazole-containing polymers have also attracted much attention because of their photoconductivity. In this context, multicomponent polymers with structural units containing both photoconductive and electro-optic functionalities in the side chain can be regarded as potentially suitable materials for photorefractive applications. Azobenzene photochemistry is a fascinating area of investigation, on one hand, because it is fairly well known, and on the other hand, because it has produced and continues to reveal completely unexpected phenomena, some of them still unexplained. When the azobenzene group is incorporated into a polymer, its photoisomerization can have a wide range of unexpected possible consequences. Connecting the carbazole sequence with azo sequence, using en spacer with  electrons, can enhance the electro-optical properties of the polymer materials based on carbazole. That can be realized first by (co)polymerization of the monomers with the azo-carbazole sequences. Secondly, the chemical transformations of the polymers contented by (co)polymerization of the known monomers with the carbazole monomers will be used. In these ideas the goal of this paper is an investigation of the scientifically literature regarding the new electro-active materials, peculiarly photorefractive alongside of our results in this field.

In this paper, we investigate the Optical Bistability (OB) resulting from a degenerate two-wave mixing process in a single layer of Kerr nonlinear ferroelectric material. The nonlinear process is mathematically described by a nonlinear coupled-wave (CW) equations propagating across the nonlinear medium. The system is solved numerically with and without employing the Slowly Varying Envelope Approximation (SVEA). The effects of layer thickness, operating frequency, and the intensity of the probe beam on the bistable response are investigated in both cases with and without SVEA. We have found that there is a significant difference between both solutions (with and without SVEA) in the analysis of the CW theory of two-wave mixing for OB. The SVEA solution fails to predict the bistable response for various combinations of the input parameters. Furthermore, the solution with SVEA overlooks the detection of several bistable response periods, reduces the switching contrast of the detected OB, and shows only higher threshold values of bistable response. A comparison between our theoretical results and some available experimental data is also shown. [ABSTRACT FROM AUTHOR]

Aim: The aim of this work was to study the changes that occur in the posterior corneal surfaceafterphotorefractivekeratectomy (PRK)inmoderatemyopiausingpentacam. Patients and methods: This prospective study included 30 myopic eyes of 17 patients with spherical equivalent -2.00-6.00 D who underwent PRK using Visx S4 Excimer Laser. Pentacam examination was carried out for all our eyes at preoperatively, and 1 week and 3 months postoperatively. Pentacam was used to compare preoperative and postoperative measurements of the anterior and posterior corneal curvatures, and asphericity of the posterior corneal surface. Results: This study included 30 myopic eyes of 17 patients, seven women and 10 men. Patients' ages ranged from 28 to 40 years; the mean age was 30.3±3.03 years. No statistically significant changes were found in the posterior horizontal corneal curvature. A statistically significant change in the posterior vertical corneal curvature from 6.1±0.3 to 6.06±0.2mm 1 week after PRK was found, but it increased after 3 months to 6.2±0.3 mm. No statistically significant changes in the posterior mean corneal curvature were observed either at 1 week or 3 months after PRK. A significant change in the Q-value (asphericity) was found both at 1 week and 3 months postoperatively. Conclusion: After PRK, changes in the posterior corneal surface affect mainly the vertical curvature asphericity with forward elevation of the posterior corneal surface. [ABSTRACT FROM AUTHOR]

Enhancement in the photorefractive (PR) performance of organic composites photosensitized by CdSe quantum dots (QCdSe) passivated with the charge-transport ligands, sulfonated triphenyldiamine (STPD), is reported. This enhancement is primarily attributed to the ability of the passivating ligand, STPD, to facilitate the charge-transfer process between the QCdSe and the triphenyldiamine (TPD) charge-transport matrix. The PR composites exhibited a maximum photocharge-generation efficiency of 0.9% and two-beam coupling gain coefficient of 110 cm −1 . These figures of merit represent a significant improvement over similar composites photosensitized with more conventional trioctylphosphine oxide-passivated QCdSe (TQCdSe). Moreover, composites photosensitized with SQCdSe had a faster response time of τ = 128 ms at an electric field of 60 V/ μ m compared with τ = 982 ms for those containing TQCdSe. Because of the molecular similarity between the STPD passivating groups and the TPD-based charge-transport matrix, concentrations of up to 1.4 wt% of SQCdSe are achieved in PR composites without any detectable phase separation, a considerable improvement over the 0.7 wt% for TQCdSe. [ABSTRACT FROM AUTHOR]

Commonly used diffraction method of photorefractive effect investigation does not give the complete information about properties of photorectrative record. Thus, the legitimate assumption aries that such a way of investigation cannot register manifestation of the all-possible mechanisms contributing to formation of the record in photorefractive medium. therefore, the combining of various ways of registering the record is required. In order to do so, except the classical diffraction investigation of photorefractive effect we used also imaging of refractive index distribution in the record by means of interference as well as imaging the transmittance of the sample in the place of the record. This contribution also presents some results obtained by methods of photorefractive record registration mentioned above. As the photorefractive mediumwas used Fe:LiNbO3 crystals.

There are some results of investigation of photorefractive record of interference field created by two planar wave of Ar laser (488 nm) in LiNbO3:Fe presented in this work. Such record behaves as a phase diffraction grating. The time dependence of diffracted beam intensity informs about process of the record creation. To read this record a weak beam of He-Ne laser (632.8 nm) was used. During recording and erasure process of the record, the intensities of the zero and intensities of higher orders on both sides of reading beam were detected. Experimentally obtained time dependences of intensities of diffracted beams were compared with dependences following from diffraction integral integral for harmonic phase grating. Quite small differences between measured and calculated dependences occurred. The differences show that there are some non-linear processes taking place at the record creation.

Purpose: To describe symmetry of response in fellow eyes of patients undergoing photorefractive keratectomy (PRK) for myopia, analyse the risk factors leading to asymmetry in response and to determine if delayed treatment of the second eye increases safety and predictability of PRK. Methods: Retrospective review of case records of 133 patients who underwent bilateral myopic PRK and had a minimum follow up of 6 months in both eyes. Results: Postoperative uncorrected visual acuity, spherical equivalent (SE) refraction within ±1D of emmetropia, best-corrected visual acuity (BCVA) and corneal haze were not significantly different in fellow eyes of patients undergoing PRK for myopia. Of 87 eyes in group 1 (myopia Conclusion: This study demonstrates that considerable symmetry of response exists in fellow eyes of patients undergoing myopic PRK. Early PRK in the fellow eye of patients with < 6 D myopia is safe and allows quick visual rehabilitation of the patient. In patients with myopia ≥6D, a 3-month interval before treating the second eye may improve the safety of the procedure.

This work presents a holographic method based on active feedback techniques for determining the sign of the dominant charge carriers in photorefractive materials. A two-step procedure is proposed: first off a stationary phase-locked hologram is recorded; an electric field normal to the grating layers is then applied to the material, thus producing a running hologram. The sign of the charge carriers is determined by comparing the direction of the applied field with the direction of the hologram movement, which is known through the automatically attached light pattern. The method can be applied from highly photoconductive to highly insulating materials. Furthermore, no information on any material parameter is required. The method is validated by a set of holographic experiments using a Bi 12 TiO 20 crystal that has electrons as the majority photocarriers. [ABSTRACT FROM AUTHOR]

We fabricate several different photonic lattice microstructures in iron-doped lithium niobate photorefractive crystal using single step projection method by a spatial light modulator. Wavy photonic lattice and several lattice structures with different defects were one-step induced inside the crystal. This method makes up the weakness of the conventional multiple beams interference method. The experimental setup is very flexible and easy to operate without complicated programming. Induced photonic structures can be fixed or erased and re-recorded in the crystal. The method can be easily extended to fabricate diverse photonic microstructures by drawing different structural patterns on a computer. [ABSTRACT FROM AUTHOR]

Visible and Infrared Optical Absorption and Electron Paramagnetic Resonance (EPR) techniques have been used to characterize the intrinsic defects in sillenite type crystals: nominally pure Bi12TiO20 (BTO) and doped with vanadium (BTO:V). Optical quality crystals, with the composition Bi12.04±0.08Ti0.76±0.07V0.16±0.02O20, have been grown. Results obtained by these different techniques have shown unambiguously the 5+ valence state of the vanadium ion in BTO:V crystals. In pure BTO samples, the EPR and optical spectra show strong evidence of the presence of the intrinsic defect BiM3+ + ho+, which consists of a hole h+, mainly located on the oxygen neighbors of the tetrahedrally coordinated Bi3+ ion. After doping with vanadium, results have shown that the characteristic bands, associated to this hole defect center, disappear, suggesting its transformation in single Bi3+. Anisotropy of the EPR spectra , at 20 K, is related to Fe3+ impurities.

Some new photorefractive polymers containing indole groups were synthesized and characterized by IR, H NMR, and UV techniques. The Gibbs free energy changes (Δ G) of corresponding reactions were predicted by density functional theory to be 4.19 and −9.71 kcal mol for -H, and 4.12 and −11.93 kcal mol for -OCH, respectively. The glass transition temperature ( T) of the polymers were about 96-111 °C. The nonlinear second-order optical susceptibility was predicted to be 2.84 × 10 and 1.04 × 10 esu by theoretical quantum calculations. [ABSTRACT FROM AUTHOR]

Photorefractive performances of the composites using two kinds of photoconductive triphenylamine-based polymer have been compared and investigated. One polymer is poly(4-(diphenylamino)benzyl acrylate) (PDAA). The other is newly synthesized one of photoconductive acrylate polymer with methoxy substituted triphenylamine pendant, poly(4-((4-methoxyphenyl)(phenyl)amino)benzyl acrylate) (PMPAA). The methoxy substituent in PMPAA does not only shift the highest occupied molecular orbital (HOMO) level of the polymer, but also effectively enhances the chromophore orientation. Larger phase shift is confirmed by using the modified photoconductive polymer of PMPAA. The plasticizer of (4-(diphenylamino)phenyl)methanol (TPAOH) (IP = -5.64 eV) works as an effective trap in the PDAA (IP = -5.69 eV)-based composite, resulting in higher diffraction efficiency. Diffraction efficiency of 70% and fast response time of 25 ms (dominant) is measured at 532 nm under the moderate electric field of 45 V/µm. [ABSTRACT FROM AUTHOR]

In this paper, the measurement of grating period in photorefractive anisotropic self diffraction by using digital holography technique is proposed. In our experimental setup, He –Ne laser beam with wavelength of 632.8 nm has been separated and then incident on photorefractive cerium doped barium titanate crystal to produce photorefractive index grating. The transmitted probe beam, which contains phase and amplitude has been expanded and recorded on digital camera. To explore the grating periods, both phase and amplitude of the images are reconstructed by numerical process using computer. Then the grating periods in photorefractive anisotropic self diffraction have been measured. The results show grating periods, holograms and their reconstruction. [ABSTRACT FROM AUTHOR]

Abstract: Three-dimensional Penrose-type photonic quasicrystal lattices are optically induced inside an iron-doped lithium niobate photorefractive crystal for the first time using a single multi-pinhole plate. The setup of this method is simple and compact dispense with complex optical adjustment system. Induced Penrose-type photonic quasicrystal lattices are analyzed and verified by plane wave guiding and far field diffraction pattern imaging. The quasicrystal microstructures can be maintained for a long time inside the crystal in a dark room. Other more complex three-dimensional photonic quasicrystal structures can be fabricated with this method by designing the multi-pinhole plate flexibly. [Copyright &y& Elsevier]

Carbazole-based bi-functional photorefractive polyacrylates were prepared via free radical polymerization and post-azo-coupling reaction. The structure of polymers was characterized by Fourier transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance (H-NMR) spectroscopy. The differential scanning calorimetry (DSC) and the thermal gravimetric analysis (TGA) were used to characterize the thermal property of polymers. The results indicate that though the glass transition temperature ( T) of polymers increases with increasing the ratio of NLO groups, the polymers with different ratios of NLO groups still all show low glass transition temperatures around 60 °C, and good thermal stability, which are favorable to the practical application of these polymers. The gel permeation chromatographic (GPC) result indicates that these polymers all have high-molecular-weight which is favorable to the long term stability of the material. Further, these polymers have good solubility in chloroform solvent, and the solutions can easily be fabricated into optically transparent films. Gain coefficients of 75 cm, 185 cm and 66 cm can be observed at zero external electric field without any addition agent or pre-poling for polymers P-2, P-3 and P-4 respectively. The different contents of NLO groups result in the different properties of polymers P-2, P-3 and P-4. [ABSTRACT FROM AUTHOR]

We fabricate two-dimensional elliptic photonic lattices in iron-doped lithium niobate photorefractive crystal for the first time with optical induction method. The experimental setup of our method is very simple and flexible without complicated optical adjustment system. We analyze and verify the two-dimensional elliptic photonic lattices by plane wave guiding, far field diffraction pattern imaging, and Brillouin-zone spectroscopy. Induced elliptic photonic lattices can stably exist for a long time in the iron-doped lithium niobate crystal. The induced two-dimensional elliptic photonic lattices might offer an easy method to study generic band gap phenomena in anisotropic periodic structures. [ABSTRACT FROM AUTHOR]

Abstract: We investigated the photorefractive performance of the polymer dissolved liquid crystalline composite (PDLCC), in which liquid crystalline polymer and low-molar-mass liquid crystal are miscible without phase separation, doped with three kinds of fullerene derivatives with different length of alkyl groups. The photorefractive performance was improved for the photorefractive PDLCC doped with fullerene derivatives with long length of alkyl groups. The photorefractive grating formation originates in the cooperative reorientation of the liquid crystalline director and the space charge field was estimated using the elastic continuum theory and the field for the PDLCC doped with the functionalized fullerene with longer alkyl side groups was larger than that for the PDLCC doped with conventional fullerene C60. [Copyright &y& Elsevier]

Abstract: A study of the speckle photo-electromotive force (PEMF) in a photorefractive sensor of amplitudes of micro-oscillations is presented. The experimental behavior of the first harmonic of the photocurrent generated as a function of the average speckle diameter and the oscillation amplitude of the speckle pattern is analyzed for a sensor implemented with a Bi12SiO20 (BSO) crystal. For a given light intensity, a nearly constant value of the maximum amplitude of the first harmonic was experimentally observed for the range of speckle sizes considered. This experimental result and the linear dependence of the vibration amplitude yielding the maximum of the photocurrent as a function of the speckle diameter were appropriately described by the mathematical model considered. Results show the possibility of adequately selecting the speckle size to optimize the output of speckle PEMF-based sensors depending on the oscillation amplitude to be measured. [Copyright &y& Elsevier]

Copyright of Bistua: Revista de la Facultad de Ciencias Básicas is the property of Facultad de Ciencias Basicas de la Universidad de Pamplona and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

With excellent photo-electric and electro-optical effects, the photorefractive spatial light modulators can work as optically addressed modulators in optical information processing systems and parallel optical computing systems. The photo-induced current pulses of the photorefractive spatial light modulator observed in the experiments are analyzed to conclude the characteristics, and to find the relationship between the properties of the current pulse and the structural parameters. Furthermore, the origin of the photo-induced current pulse is analyzed, and the methods to improve the operation speed of the spatial light modulators are proposed. The research results will be significant for extending the applications of the photorefractive spatial light modulators, and pushing ahead the research of all-optical modulation materials and devices for optical supercomputing. [ABSTRACT FROM AUTHOR]

Organic all-optical photorefractive (PR) materials will soon become an interesting topic owing to the convenient signal-writing without the application of external electrical field and poling, even without any photosensitizer. In this paper, organic all-optical PR materials synthesized in our laboratory have been systematically summarized including organic monolithic PR molecular glasses with a linear or hyperbranched chemical structure such as organic carbazole/triphenylamine-based amorphous compounds, and PR polymers with a non-conjugated main chain (NCMC) such as polymethacrylates, polyphosphazenes and polynorbornenes. Much progress has been made not only in the synthesis strategy of organic all-optical materials but also in understanding the primary mechanism of all-optical PR effect in organic materials. It is believed that the outcoming of organic all-optical PR materials will broaden the application fields of organic PR materials. [ABSTRACT FROM AUTHOR]

In this work the evanescent space-charge field generated in semi-insulating GaAs semiconductor substrates was used to reorient the liquid crystals molecules sandwiched between them to study the energy exchange in two-wave mixing experiments. We show that the two-beam coupling gain coefficient in hybrid devices is enhanced by a factor of ∼36 as compared to GaAs alone. The photorefractive gain coefficient reported here is the largest ever reported in semiconductors without the need of space-charge enhancing techniques such as externally applied fields or running gratings. [ABSTRACT FROM PUBLISHER]

Abstract: Tuning of the dynamic range of a micro-displacement fiber specklegram sensor based on two-wave mixing on a photorefractive material Bi12SiO20 (BSO) and self-correlation operations of speckle patterns is experimentally demonstrated. The high modal interference present in a standard plastic optical fiber (POF) allows generating a Gaussian pattern of subjective speckle, which is recorded in the volume crystal. The volume characteristics of the fiber speckle are changed using a pupil aperture adjacent to the imaging lens of the speckle. A notorious effect of the three dimensional structure of the speckle on the dynamic range of the metrological system is observed, such that, the performance of the sensor can be improved by a simple mechanical action on the pupil aperture. The behavior of the self-correlation loss of the sensor can be adequately described by a squared normalized Bessel function. [Copyright &y& Elsevier]

Abstract: In this work, we show that it is possible to change the properties of an optical vortex formed in a speckle pattern by the control of an external electric field applied to a sillenite-type photorefractive material in a non-holographic configuration. To show it, a scheme that allows the recovering of both, the polarization state and the phase distribution of an optical field was implemented. Changes in the polarization state of the light in the neighborhood of the vortex were observed with the application of an external electric field. Likewise, changes in the phase structure around the vortex and displacements of the vortices themselves were measured. These displacements have a fairly linear dependence on the applied field to the photorefractive crystal. Experimental results are qualitatively explained with the theoretical treatment of non-holographic recording in photorefractive crystals. [Copyright &y& Elsevier]

Abstract: In this work, the improvement of the dynamic range of a micro displacement sensor based on fiber specklegrams holographically stored in a photorefractive BSO (Bi12SiO20) crystal is reported. In our experimental setup, a plastic optical fiber (POF) was used to generate a subjective speckle pattern that was recorded in the crystal using a two-wave mixing arrangement. The speckle size was controlled by modifying the diameter of a pupil aperture adjacent to a lens producing the image of the speckle. Fringe patterns were obtained at the output of the system by producing micro displacements of the fiber output end. An increase in the visibility of the fringe patterns was appreciated when the pupil aperture diameter decreased even without controlling the average modulation of the intensity of the light pattern, i.e. when the speckle length increased and the average light modulation simultaneously decreased. This behavior allowed recovering the autocorrelation functions of fringe patterns associated with displacements that initially led to decorrelation, and therefore, significantly to improve the dynamic range of the metrological system. To the best of our knowledge this is the first report about the influence of speckle size on the dynamic range of fiber specklegrams sensors recorded on photorefractive materials. [ABSTRACT FROM AUTHOR]

Abstract: In this work, the dependence on the speckle size in the performance of a micro displacement sensor based on fiber specklegrams stored in a photorefractive BSO (Bi12SiO20) crystal is experimentally demonstrated. In our experimental setup, a plastic optical fiber (POF) was used to generate a subjective speckle pattern which was recorded in the crystal by using a four-wave mixing arrangement in transmission geometry. The speckle size was controlled by modifying the diameter of a pupil aperture adjacent to a lens producing the image of the speckle. The signal speckle beam was mixed into the crystal with two counter propagating pump beams to generate a fourth beam which is proportional to the conjugate of the original speckle beam. Real time fringe patterns were obtained at the output of the system by producing micro displacements of the fiber output end. Increases of the phase conjugation reflectivity and the visibility of the fringe patterns were appreciated when the speckle length was increased by decreasing the pupil aperture diameter. This behavior allowed recovering the autocorrelation functions of fringe patterns associated to micro displacements that initially led to decorrelation, and therefore, to improve the dynamic range of the metrological system. Until the best of our knowledge this is the first report about the influence of the speckle size on fiber specklegrams sensors recorded on photorefractive materials by four-wave mixing. [ABSTRACT FROM AUTHOR]

Abstract: We present a physical and computational procedure to calculate the gain in a two-wave mixing process in a thick optically active photorefractive BSO crystal under diffusion regime. The procedure is based on the integration of the amplitude of the signal beam through the sample. In the model, the effects of self-diffraction are taken into account by using the more general expression of the diffraction efficiency for the case of dynamic gratings. It allows also including the effects of the optical activity on the coupling factors and not only on the rotation of the optical field vectors when the waves are propagated along the crystal. The <001> crystallographic configuration is used. The model is used to predict the behavior of the gain as a function of the beam polarization angle. Numerical and experimental results using crystals with thickness of 5mm and 10mm are presented. A good agreement between the proposed model and the experimental measurements is observed. [ABSTRACT FROM AUTHOR]

Abstract: We theoretically studied photorefractive surface waves supported by polymers with orientationally enhanced photorefractive effect. We find that the orientational enhancement and the dependency of the quantum efficiency of generating mobile holes on the electric field make the diffusion nonlinearity in photorefractive polymers dependent not on only the variation of light intensity but also on external electric field, which is very different from the external electric field independent diffusion nonlinearity in inorganic photorefractive crystals. Consequently the profile, frequency and especially the penetration depth of polymeric photorefractive surface waves strongly depend on external electric field, which makes it more controllable than that in photorefractive inorganic crystals. The stability of polymeric photorefractive surface waves, the effects of birefringence component and electro-optic component of orientationally enhanced photorefractive nonlinearity on the formation of x or y-polarized polymeric photorefractive surface waves are also discussed. [Copyright &y& Elsevier]

The relations between conversion stabilities and photo-excited electron-depletion effects have been experimentally evaluated in a Zn-indiffused lithium niobate polarization converter, for the first time.A simple method with a biased voltage and laser trimming was performed to observe these phenomena. The results show that the stable conversions for both polarities of applied polarization-conversion voltages are achievable due to the depletion of photo-excited electrons in the waveguides. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1937–1941, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25384 [ABSTRACT FROM AUTHOR]