J.A. Sanz-García

Red, green, and blue simultaneous generation in aperiodically poled Zn-diffused LiNbO3:Er3+/Yb3+ nonlinear channel waveguides

In this work, continuous-wave broadly tunable simultaneous generation of red (650–690 nm), green (520–575 nm), and blue (425–495 nm) light in aperiodically poled Zn-diffused LiNbO3:Er3+/Yb3+ channel waveguides is reported after Ti:sapphire excitation in the 850–990 nm range. The red and green emissions arise from energy transfer and upconversion mechanisms between Yb3+ and Er3+ ions, while the blue light with a maximum efficiency of 0.04% W−1 cm−1 is produced by quasi-phase matching processes.

Yb3+ to Er3+ energy transfer in LiNbO3

The energy transfer between and ions in lithium niobate is investigated and modelled using the rate equation formalism. An efficient energy transfer from to is found and the transfer and back-transfer coefficients have been determined ( and , respectively). Using the rate equation formalism it is shown that population inversion of the level (upper laser level at ) is attainable at sufficiently low pumping levels, making this material suitable for laser applications. The effective transfer efficiency is also calculated, showing good agreement with the experimental values obtained from the increase of the emission.

Single polarized Tm3+ laser in Zn-diffused LiNbO3 channel waveguides

In this work, laser operation at 1.76μm in Tm3+:LiNbO3 Zn-diffused channel waveguides is reported. The laser emission is single polarized with the electric field parallel to the optic axis(π-polarization) and operates in continuous-wave regime, at room temperature. The threshold of laser oscillation is in the range of 40mW, the slope efficiency is around 1%, and both magnitudes are dependent on the channel width, in accordance with the mode overlap between the pump and signal modes within the waveguides.

Zn-diffused LiNbO3:Er3+/Yb3+ as a waveguide laser material

In this work we present the preparation and optical studies of waveguides in LiNbO 3 :Er/Yb formed by Zn-diffusion. In relation to crystal growth it is found that both impurities incorporate to the crystal, with a segregation coefficient of K eff = 1.5. Spectroscopic measurements have shown an effective energy transfer from Yb 3+ to Er 3+ , increasing the absorption cross section in the InGaAs-diode laser pump region. Waveguides prepared by Zn diffusion show the possibility of Er 3+ pumping via Yb 3+ absorption within in the waveguide, without degrading the optical characteristics of the 1.5 μm emission of the Er 3+ ions.

Redistribution of Cr3+ ions from Li+ to Nb5+ sites in ZnO codoped LiNbO3:Cr crystals

Abstract This Letter reports on the optical spectroscopy properties of Cr 3+ ions in codoped ZnO:LiNbO 3 :Cr crystals. Experimental techniques such as optical absorption, luminescence, time-resolved spectroscopy and electron paramagnetic resonance have been used to investigate the site occupied by the Cr 3+ ions. Two Cr 3+ centres located in Li + and Nb 5+ sites (Cr Li 3+ and Cr Nb 3+ centres, respectively) were observed, depending on its relative concentrations of the ZnO content in the samples. For ZnO concentrations below 4.7%, the majority of centres correspond to Cr Li 3+ centres, whereas, for a ZnO concentration above this threshold both centres coexist, but with the Cr Nb 3+ centres being more predominant. The emission bands, excitation spectra and lifetimes associated with both centres are reported.

Concentration dependence of refractive index in Zn-doped LiNbO3 crystals

Abstract This paper reports the concentration dependence of the ordinary (no) and extraordinary (ne) refractive indices in congruent ZnO-doped LiNbO3 crystals. The Zn2+ concentration in the crystals was varied from 0% to 5.9%. Although the dependencies of no and ne with the Zn2+ content are very different, both showed singularities for ZnO concentrations in the crystal at around 4.6%. The no and ne values measured in ZnO doped crystals doped from the melt are compared with the data reported in the literature for post-growth thermal diffusion of Zn2+ ions in LiNbO3 crystals. Both sets of data are well described by a generalised Sellmeier equation which takes into account a different Zn2+ ions sites location depending on the Zn2+ concentration and the method used for doping the crystals.

Site-selective spectroscopy of Er3+ ions in the Bi12SiO20 piezoelectric crystal

Site-selective spectroscopy fluorescence experiments (emission and excitation) in the near-infrared region associated with the 4I15/2↔4I11/2 transitions of Er3+ ions have been successfully used to show the presence of two different Er3+ centres in the Bi12SiO20 piezoelectric crystal. Green (545-570 nm), red (650-690 nm) and near-infrared (850-890 nm) up-converted emissions have been observed and resolved for each type of centre under excitation up to the 4I11/2 state. The Stark energy level schemes of the three lower energy states of Er3+ ions have been determined and compared for both centres, showing two quite different crystalline field environments. The mechanisms responsible for the up-conversion process (excited state absorption and/or energy transfer up-conversion) are also analysed.

Compositional effect on site distribution in MgO or ZnO codoped congruent and stoichiometric crystals

In this letter optical and electron paramagnetic resonance (EPR) techniques are used to investigate the effect of stoichiometry changes on the site distribution of ions in crystals with (or without) MgO or ZnO codoping. In congruent crystals codoped with MgO (ZnO) the ions begin to enter into the site for concentrations higher than 4.5% (4.7%). Below this MgO (ZnO) threshold ions enter only into the sites. However, for nominally stoichiometric crystals, the threshold concentration is much lower (between 0 and 0.2% in our crystals). The use of ions as an optical and paramagnetic probe to evaluate the grade of stoichiometry is considered.

Fabrication of photorefractive damage-resistant active waveguides based on Zn-indiffused LiNbO 3

Fabrication characterization and operation stability of Zn-indiffused integrated optical devices in lithium niobate are described. Two examples of the operation of active waveguides fabricated by this technique are presented: laser operation of Nd3+ doped channel waveguides, and blue light generation by Quasi Phase Matching (QPM) using periodically structured substrates. In both cases ne-polarized high power denstiy CW-optical beams are involved and stable room temperature operation is sustained.