Effect In LiNbO3 Research Articles

Photorefractive effects in LiNbO 3:Fe, Me at high light intensities

In LiNbO 3:Fe,Me (Me = K, Mg, Zn) holograms are recorded and erased with frequency-doubled pulses of a Q-switched Nd:YAG laser. At high light intensities contributions of higher order to the holographic quantities appear. Effects are diminished by increasing the lithium content of the crystals or by doping with magnesium or zinc. All results can be described by a two-center model, which is the Fe 2+/3+ model supplemented by shallow traps, namely niobium ions occupying lithium sites.

Bulk photovoltaic effect of LiNbO3:Fe in the liquid-He temperature range

Abstract The linear photovoltaic effect in LiNbO3:Fe has been measured in a broad interval below room temperature. The temperature dependence of the G22 photovoltaic tensor component was measured up to 6 K. The results obtained are interpreted in terms of the ballistic mechanism for nonthermalized electrons.

Fourier spectroscopy of elastic modes and anharmonic effects in LiNbO3

Elastic vibrational thickness modes in LiNbO3 crystal were studied in the frequency range 20–100 MHz using a modified Fourier transform pulsed nuclear-magnetic-resonance spectrometer. The phase discrimination capability, absence of baseline distortions and drifts, and the excellent spectral resolution permit a very accurate determination of the elastic constants and the observation of subtle anharmonic coherent effects in the fine structure of the overtones of several modes.

SHG CHARACTERISTIC OF Co-DOPED LiNbO3 SINGLE CRYSTAL

In order to investigate the doping effect of LiNbO 3 by cobalt ion, LiNbO 3 single crystals doped with CoO, 0.02, 0.05, 0.2, and 1 mol% were synthesized. SHG characteristics were measured using CW YAG:Nd laser in the temperature range from 120 to 310 K. Optical absorption measurements were carried out in the wavelength between 300 and 1800 nm in the y direction. The largest conversion efficiency of SHG was observed in the 0.02 mol% doped crystal, which is due to harmonic effect. Microscopic observation of domain structure was also carried out. It is found that the domain layers of positive and negative orientation lie on top of another in the direction of the c axis, the thickness of which is of the order of microns. SHG intensity is discussed based on the relation between laser beam diameter and the thickness of domain layers.

Light-climbing effect in LiNbO_3:Fe crystal

The light-climbing effect in a LiNbO(3):Fe crystal sheet was experimentally studied, and the mechanism for light climbing proposed was proved to be correct. The relevant optical properties were investigated.

OPTICAL LIMITING BASED ON DETERMINISTIC BEAM FANNING IN PHOTOREFRACTIVE MATERIALS

We propose passive optical limiting based on the photorefractive effect-induced asymmetric deterministic beam fanning in BaTiO 3, and symmetric deterministic beam fanning due to a combination of photovoltaic and thermal effects in LiNbO 3.

The bulk photovoltaic effect in LiNbO3, crystals under X-ray synchrotron radiation

Abstract In LiNbO3, crystals the Bulk Photovoltaic Effect (BPE) under X-ray synchrotron radiation has been revealed. We observed this effect in LiNbO3,: Fe both in visible light and under synchrotron irradiation for energies 4-10 KeV. The photovoltaic current in the visible and X-ray region has opposite directions. It may be connected with two different mechanisms of the BPE: ballistic and shift. The combined effect, caused by light and X-ray, is investigated.

High-temperature photorefractive effects in LiNbO3:Fe

Photorefractive effect has been measured in LiNbO3:Fe at high temperature in the range 180–300 °C. At temperatures higher than 230 °C only transient effects can be observed. The kinetics of the diffraction efficiency is explained in terms of two kinds of mobile charges; electrons and protons. From the analysis of the final decay of the curves, an activation energy of 1.33±0.02 eV is obtained for the diffusion of protons in lithium niobate.

The Photorefractive Effect in LiNbo3 at High Light Internsity

The Photorefractive Effect in LiNbo3 at High Light Internsity

Photorefractive fixing and related thermal effects in LiNbO3

The thermal and optical stability of photorefractive holograms written in iron-doped LiNbO3 have been measured over the temperature range from 50 to 165 degrees C. In each case the decay proceeded as a non-simple exponential process exhibiting several more or less resolvable stages. For optically erased holograms the activation energy of the two observed stages was 0.15+or-0.01 eV. Thermal erasure revealed at least four stages with activation energies ranging from 0.85 to 0.95 eV. Homogeneous illumination at room temperature gave rise to a fixed-developed hologram whose diffracted signal was about 1% of that shown by the initially light-recorded hologram. The developed signal was approximately the same after four successive erasing-developing cycles. Thermal erasure results are interpreted in terms of only proton migration, within the framework of recent models for photorefractive fixing. Thermal electron detrapping proceeds at higher temperatures (t>170 degrees C) in lightly reduced samples.

Simulation studies of silicon electro-optic waveguide devices

Several silicon-on-insulator guided-wave structures have been analyzed as potential electro-optic waveguide modulators using the pisces-ii two-dimensional (2D) device simulation program. From the electron and hole concentration data, the 2D refractive index profile is obtained. The profile is then spatially averaged with respect to a 2D cosine representation of the guided-wave E field to obtain the effective modal index changes at 1.3 and 1.55 μm. The channel-waveguide devices studied include the metal-oxide-semiconductor (MOS) diode, and the one or two-gate metal-oxide-semiconductor field-effect transistor (MOSFET) with single-or double-transverse injection. The single-gate double-injection MOSFET modulator offers the most promise with 10−3 refractive index changes possible, changes comparable in size to the Pockels effect in LiNbO3 or GaAs.

Space charge field limitations in photorefractive LiNbO3:Fe crystals

We use holographic techniques for the investigation of strongly oxidized LiNbO3:Fe crystals with small Fe2+ concentrations and compare the results with theoretical predictions. Experimental evidence is presented for enhanced phase shifts between light intensity pattern and refractive index grating and for limitations of optically induced space charge fields in photovoltaic crystals due to the low concentration of filled traps. Our findings do not support the model of a nonlocal photovoltaic effect in LiNbO3.

Studies of absorption spectra and the photovoltaic effect in LiNbO3:Mg:Fe crystals

The absorption spectra, photoconductivities and photovoltaic currents of LiNbO3:Fe crystals with different Mg doping levels and Li/Nb ratios in the oxidized state have been investigated at room temperature. The Fe2+ ions in LiNbO3:Mg:Fe with Mg content above a critical value are more easily oxidized than in crystals with Mg content below a critical value. The photoconductivity of LiNbO3:Mg:Fe crystals with Mg content above a critical value is one order of magnitude higher than those with Mg content below a critical value, however, the photovoltaic current of the former is one order of magnitude lower than the latter. The differences are postulated to be due to different sites of Fe in these two classes of crystals.

Dispersion of the linear electro-optic effect in lithium niobate

The linear electro-optic effect in LiNbO3 has been investigated in the wavelength range from 0.4 to 1.15 mu m at applied field frequencies of 200 Hz and 9.45 GHz. The dispersion of clamped (rs22) and unclamped (r22T) electro-optic coefficients is measured. The values of the clamped electro-optic coefficients (rs22) are determined. Based on the results of measurements and reported data of the second harmonic generation coefficient, an attempt has been made to estimate the value and dispersion of the electronic and ionic contributions to the clamped electro-optic effect.

Threshold effects in LiNbO3:Mg caused by change of electron-lattice coupling

Abstract X-ray induced luminescence, dark conductivity and fundamental absorption of LiNbO3 containing between 0 and 9% Mg show marked changes near 4% Mg. These features can consistently be explained as due to changes in the electron-lattice coupling for higher Mg concentrations. This is supported by the behavior of below bandgap absorption and lattice frequencies when the Mg concentration increases. A microscopic model explaining these effects is discussed.

Trading coupling loss for modulation efficiency in electrooptic modulators

Phase modulators utilizing the electrooptic effect in Li-NbO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> are most efficient if the waveguide, and hence the guided mode, is positioned as closely as possible to the modulation electrode which is located at the surface of the crystal. However, placing the guided wave near the crystal surface tends to deform its shape so that the coupling loss between the waveguide mode and an optical fiber is increased. In this paper, we study the tradeoffs between coupling loss and modulation efficiency that result from moving the waveguide further below the crystal surface.

Photorefractive effects in LiNbO3:Cr induced by two-step excitation

With the help of a Q-switched ruby laser elementary volume phase holograms are recorded in LiNbO3:Cr crystals via stepwise two-photon excitations. Readout experiments are performed with lower intensity and unwanted erasure effects are largely reduced. The light induced charge transport is investigated and the following model is proposed: The crystals contain essentially Cr3+ ions and presumably a small number of Cr4+ ions. By two-step processes electrons of Cr3+ ions are excited to the conduction band. These electrons are then captured by Cr4+ ions forming Cr3+ ions again or by other unknown traps forming colour centers. The model describes the principal experimental results. Mit Hilfe eines Rubinlasers im „Q-Switch”︁-Betrieb werden elementare Volumenphasenhologramme in LiNbO3:Cr-Kristallen über schrittweise Zwei-Photonen-Anregungen geschrieben. Beim Auslesen mit Pulsen geringerer Intensität kann man unerwünschte Löscheffekte weitgrehend vermeiden. Der lichtinduzierte Ladungstransport wird untersucht und folgendes Modell vorgeschlagen: Die Kristalle enthalten hauptsächlich Cr3+-Ionen und vermutlich eine kleine Anzahl von Cr4+-Ionen. Mit Hilfe von Zwei-Schritt-Prozessen werden Elektronen von Cr3+-Ionen in das Leitungsband angeregt. Diese Elektronen werden dann entweder von (Cr4+-Ionen eingefangen, die dadurch wieder Cr3+-Ionen bilden, oder von anderen unbekannten Elektronenfallen, die dadurch Farbzentren entstehen lassen. Das Model! beschreibt die wesentlichen experimentellen Ergebnisse.

Circuit effect in LiNbO_3 channel-waveguide modulators

An RC circuit is used to model transient effects that occur when dc or quasi-dc voltages are applied to channel waveguide modulators. These effects are believed to be due to the anisotropic redistribution over time of charge stored in the LiNbO(3). The anisotropy arises from the anisotropic material properties and the inhomogeneity induced when channel waveguides are formed. The transient effects measured are not caused by photorefractivity.

Photovoltaic Effect in LiNbO3:Mg

Photovoltaic Effect in LiNbO3:Mg

Optical Devices Based on Ferroelectric Single Crystals

Optical devices based on the electrooptic effect of the ferroelectric crystals are described for the application to the information processings, including the analog to digital converter using the electrooptic light modulators, the distributor and demultiplexer of optical signals and the electrooptic bistable device. The spatial light modulators are also discussed. Finally, the microscopic mechanism of the electrooptic effect in LiNbO3 and LiTaO3 is introduced through the observation of the ionic and electronic contributions by the X-ray diffraction method.