Showing papers on "Organic photorefractive materials published in 2009"
TL;DR: In this article, the photorefractive behavior of optical waveguides fabricated in LiNbO3 by swift heavy ion irradiation is investigated, and the electro-optic coefficient r r is measured for 33 of these guides.
Abstract: The photorefractive behaviour of a novel type of optical waveguides fabricated in LiNbO3 by swift heavy ion irradiation is investigated. First, the electro-optic coefficient r
33 of these guides that is crucial in the photorefractive effect is measured. Second, two complementary aspects of the photorefractive response are studied: (i) recording and light-induced and dark erasure of holographic gratings; (ii) optical beam degradation in single-beam configuration. The main photorefractive parameters, recording and erasing time constants, maximum refractive-index change and optical damage thresholds are determined.
22 citations
TL;DR: An interferometric Mach-Zehnder technique very recently developed is applied to measure photorefractive index changes in different types of z-cut proton-exchanged planar waveguides in LiNbO, comparing well with the predictions of a recent work, that uses a two-center model to explain the optical damage.
Abstract: An interferometric Mach-Zehnder technique very recently developed has been applied to measure photorefractive index changes in different types of z-cut proton-exchanged planar waveguides in LiNbO3 These measurements are complemented by determining the intensity-threshold for the onset of optical damage with a standard single-beam setup In the intensity region just below the threshold-intensity obtained in the single-beam experiment the refractive index change is found to saturate at values around 1×10-4 Furthermore, we measure the dark conductivities of proton-exchanged waveguides by monitoring the decay of the light-induced index changes Via the time constant of the decay we obtain dark conductivities of the order of about 5 × 10-16 Ω-1 cm-1, that are negligible compared with the photoconductivity within the light intensity range used The results of the measurements compare well with the predictions of a recent work, that uses a two-center model to explain the optical damage
11 citations
TL;DR: By using soluble fullerene derivative, this work improved photorefractive efficiency in polymer-liquid crystal composites in comparison to previous works on similar materials and proposed an approach for designing composites with higher grating efficiency and resolution.
Abstract: By using soluble fullerene derivative [60]PCBM, we improved photorefractive efficiency in polymer-liquid crystal composites in comparison to previous works on similar materials. We show the effect of polymer network results in resolution and bandwidth improvements compared to pure liquid crystals. This is explained by the introduction of a charge trapping mechanism, providing a memory effect for the composite. Based on this effect, we propose an approach for designing composites with higher grating efficiency and resolution.
10 citations
TL;DR: In this paper, the gain factor for counter-propagating two-beam coupling was measured at both wavelengths for CdTe:Ge at λ = 1.064 μm and λ=1.55 μm.
Abstract: Recording of efficient reflection holograms is achieved in CdTe:Ge at λ=1.064 μm and λ=1.55 μm. The gain factor measured at both wavelengths for counterpropagating two-beam coupling considerably exceeds the absorption constant and transcends all values previously reported for semiconductors with no external field. The dependences of the gain factor on intensity and grating spacing are studied. Some crystal characteristics are estimated in the frame of a single band, one mobile species approximation of space-charge formation. The homogeneity of photorefractive properties in the crystal volume is demonstrated.
8 citations
Patent•
18 Sep 2009TL;DR: In this article, the photorefractive composition is formulated such that a grating that is irradiated into a photore-fractive composite can be read out of the same composition without applying an external bias voltage.
Abstract: Described herein are optical devices comprising a photorefractive layer and at least two inert layers, such that the photorefractive layer is sandwiched between the two inert layers. The photorefractive layer may include a photorefractive composition that is photorefractive upon irradiation by a laser beam. In some embodiments, the photorefractive composition is formulated such that a grating that is irradiated into the photorefractive composition can be read out of the photorefractive composition without applying an external bias voltage. Furthermore, a grating that is written into the composition may be controlled using thermal treatment.
5 citations
TL;DR: In this article, an improved mathematical model for photorefractive materials exhibiting hole-electron competition where the constants accounting for electrical coupling between holes and electrons are independently adjusted for each one of them is presented.
Abstract: We describe an improved mathematical model for photorefractive materials exhibiting hole-electron competition where the constants accounting for electrical coupling between holes and electrons are independently adjusted for each one of them. Experimental results from photorefractive titanosillenite crystals with hole-electron competition, and particularly from a vanadium doped sample, are shown to be better described by this modified model than by the classical one already reported in the literature.
5 citations
TL;DR: A tunable color filter with surface plasmon resonance (SPR) excited by a photorefractive diffraction grating, modified by alteration of the optic configuration, where the wavelength at which the SPR excitation led to a reflection minimum changed and the spectrum of the reflected light also changed.
Abstract: We report on a tunable color filter with surface plasmon resonance (SPR), excited by a photorefractive (PR) diffraction grating When a white light was incident at the diffraction grating formed by a PR effect, the SPR generated at a metal-dielectric material interface was absorbed, and the reflected light showed a complementary color When the period of the PR diffraction grating was modified by alteration of the optic configuration, the wavelength at which the SPR excitation led to a reflection minimum changed and the spectrum of the reflected light also changed A well-known equation was used to help us understand the experimental results All experimental results are in good agreement with the calculation predictions This result could lead to a new type of tunable color filter
3 citations
30 Oct 2009
Abstract: The process of refractive index grating formation in a photorefractive crystal, used as the self-adapting spectral filter in an external cavity laser, is studied with a self-consistent model The model is based on the Finite Difference solution of the Kukhtarev equations The results obtained are compared with approximate analytical models
TL;DR: In this paper, a technique for measuring the saturated amplitude of the photorefractive index grating Δn0 with a precision of 2%, by measuring the diffraction efficiency as a function of time, was proposed.
Abstract: The saturated photorefractive index determines the information storage capacity of a photorefractive crystal. Therefore, it is important to be able to measure this quantity precisely. We report a technique for measuring the saturated amplitude of the photorefractive index grating Δn0 with a precision of 2%, by measuring the diffraction efficiency as a function of time. We also report the measurement of the half-growth time τ of the grating. The Δn0 and τ are also verified by substitution into the theoretical formula derived from the coupled wave theory. The resulting theoretical prediction is shown to be consistent with the experimental data. The results also show that Δn0 is almost linearly proportional to light modulation up to unit light modulation for 0.01% Fe doped LiNbO3, which may be understood from the work of Vaveliuk et al. [Phys. Rev. B59, 10985 (1999)] work for the nonlinear regime. We will now be able to quantify the photorefractive effect of those crystals for which this method is applicable.