According to optical absorption spectra the width of the forbidden band of nominally pure congruent and stoichiometric lithium niobate crystals, as well as a series of congruent crystals doped with ...cations of Mg2+(0.35wt.%), Zn2+(2.05), B3+(0.12), Gd3+(0.26, 0.44, 0.51), Y3+(0.46), Gd3+(0.23):Mg2+(0.75), Mg2+(0.86):Fe3+(0.0036), Ta5+(1.13):Mg2+(0.01), Y3+(0.24):Mg2+(0.63), Er3+(3.1) is determined. The photorefractive effect in crystals, their structural and optical homogeneity was studied by photo induced and Raman scattering methods, laser conoscopy.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
We fabricated a periodically poled and ZnO-doped LiNbO 3 ridge waveguide by employing direct bonding and dry etching techniques. We obtained a second-harmonic generation (SHG) conversion efficiency ...of 2400%/W, and converted 92% of the pump light into SH light at a pump power of 160 mW. We developed a fiber-coupled module using the fabricated ridge waveguide. The high conversion efficiency and high damage resistance of the ridge waveguide result in the parametric amplification of the signal and converted signal lights. The low insertion loss of the module (-4 dB) and sufficient parametric conversion gain (+8 dB) enable us to achieve a wavelength converter with + 4 dB fiber-to-fiber gain, which means the wavelength converter operates without loss.
In this paper, for enhancement of the nonlinear optical properties of photorefractive gain, a novel plasmonic waveguide is proposed. The geometry of the proposed structure is optimized to reach the ...highest photorefractive gain. The proposed structure is based on bimetallic structure and it includes a graphene layer. It is shown that a strong mode can be coupled to a weak mode by means of photorefractive effect. It is found that comparing with the conventional symmetric and asymmetric metal-insulator-metal plasmonic waveguides, the proposed structure with different metals and a graphene layer with an optimized notch has higher photorefractive gain and longer propagation distance, the distance for which a net photorefractive gain exists. The effect of the crystal thickness and amplitude inputs are also analyzed. It is found that there is an optimum crystal thickness that yields the maximum photorefractive gain.
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BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
The remarkable photorefractivity enhancement was observed and investigated in copper-doped (K0.5Na0.5)0.2(Sr0.75Ba0.25)0.9Nb2O6 (Cu:KNSBN) crystals due to charge accumulation on the surface, stemming ...from electrostrictive effect. This electrostatic modification to the surface was studied with conventional two beam coupling experiment and over 17 high diffraction orders were observed. To estimate the amount of charge accumulation, the surface charge density was measured through direct current measurement using a close loop circuit. It was believed that a thin phase grating was responsible for the diffraction pattern, which was confirmed by the related reading experiment. Corresponding calculation and analysis were given to highlight the strong refractive index modulation of the gratings.
•A method of photorefractive performance enhancement is proposed.•It based on the electrostatic modulation of charge accumulation.•High diffraction efficiency was achieved.•Generation of thin phase grating was confirmed.•The enhanced photorefractive performance was studied upon different high voltages.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
We investigate the separate spatial soliton pair supported by both the linear and quadratic electro-optic effects. The numerical solutions of the bright-bright, dark-dark and bright-dark separate ...spatial soliton pairs are deduced from the coupling equations. The intensity profiles, coupling effects and dynamical evolutions of three types of separate spatial soliton pairs are analysed by numerical method. The two solitons in bright-bright separate spatial soliton pair can affect each other only by adjusting the background beam intensity. In dark-dark soliton pair, the two solitons can affect each other by adjusting the soliton beam intensity besides the background beam. And in bright-dark soliton pair, the bright soliton can affect the dark soliton only by the background beam intensity but the dark soliton can affect the bright soliton by both the background beam and soliton beam intensity.
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Ordered defective structures in lithium niobate crystals have been established. The phenomenon is a result of non-equilibrium processes of a different nature: photo-induced light scattering, laser ...ablation, and creation of cracks during relieving mechanical stresses. The shape of such structures depends on the nature and energy that affect a crystal. A number of concentric areas with a different density of laser-induced defects with a changed refractive index appear during photoinduced light scattering. Concentric clusters of microdomains appear in a macrodomain of another sign at laser ablation as a result of local switching under impulse laser radiation. A number of microcracks with a fractal structure appear near main macro-crack during cracking under mechanical stress. Thus, appearance of ordered defective structure occurs not only in the local spot of direct exposure to laser radiation, mechanical stress, etc., but also in some volume of a crystal around it.
•Defects appear in lithium niobate crystal under laser radiation and mechanical stress.•Defects form ordered structures: rings, “stars”, fractal cracks.•Defects appear at some distance from the point of the outer force action.•Type of structure and distance of its propagation depend on type, power of the force.•Defect structures also depend on a crystal type and chemical composition.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
A theory on incoherently coupled soliton pairs for photorefractive solitons is developed that gives rise to incoherently coupled soliton pairs and multi-component spatial solitons in biased ...centrosymmetric photorefractive crystals in all three realizations, bright-bright, dark-dark and grey-grey. The properties and characteristics of these soliton pairs are studied under different conditions like the bias field strength, external and internal resistance, and the intensity of the beams. This theory is extended to incorporate incoherently coupled multicomponent solitons. The stability of the soliton pairs is investigated by the modulation instability theory. A quantitative assessment is made out for the MI gain in all three realizations of the incoherently coupled soliton pairs. These can be established provided the incident beams have the same polarization, wavelength and are mutually incoherent. Relevant examples are also provided to illustrate our results.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The dielectric property of ferroelectric barium titanate (BaTiO3) thin film with optical field was investigated by terahertz time-domain spectroscopy at room temperature. Experimental results showed ...that dielectric constant of BTO film was increased with the optical pump powers, and tunability of the real part of dielectric constant could be reached to74%. The reason of realizing high modulation depth could be explained as photorefractive and photothermal effects. Furthermore, the variation of refractive index displayed a monotonically increase with the optical powers.
•The dielectric property in the THz range of BaTiO3 thin film on Si substrate was tuned by optical pump powers.•Dielectric constant of BTO film was increased with the optical pump powers, and the real part could be tuned to 74%.•The phenomenon could be explained as the photorefractive effect and the photothermal effect.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
We demonstrate a simple technique to create a large number of arbitrary optical structures in photorefractive Fe-doped lithium niobate (Fe:LN). The technique consists in directly writing with a ...focused laser beam at visible wavelength the desired optical structures on a sample, taking advantage of the photorefractive effect. Using a computer-controlled translation stage, arbitrary 1D patterns can be recorded allowing diffraction gratings or waveguide arrays to be realized. In contrast to other laser-writing approaches, our method exploits solely the large photorefractive sensitivity of Fe:LN as the mechanism to induce the refractive index change. Thanks to this, commonly available, low power cw lasers are sufficient to obtain the desired structures. The resulting refractive index modulations are characterized by an interferometric technique and positively compared with the one-center photorefractive model. The proposed method offers interesting advantages in terms of simplicity, flexibility and cost effectiveness, making it very interesting for rapid prototyping of complicated diffractive optical elements.
The slowing down of light in photorefractive SBN:61 and SBN:61:CeO₂ as a function of input pulse width via two wave mixing is presented theoretically. Optical delay has been found to vary from ...0.106 s to 4.411 s in SBN: 61 and from 0.212 s to 6.852 s in SBN:61:CeO₂ on varying the pulse width from 0.25 s to 7 s respectively. Cerium doping resulted in enhancement of optical delay at low pulse width. At higher pulse width optical delay was stabilized.
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