R. Nevado

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.

Characterization of index profiles of Zn-diffused LiNbO 3 waveguides

We characterize the refractive-index profiles of Z-cut and X-cut Zn-diffused LiNbO3 substrates from the vapor phase. We obtained these profiles by reflectivity measurements of the samples, using the prism coupling technique at each step of a systematic polishing, and then fitting the data with a program that models a multilayer optical structure. For diffusions performed at 800 °C, four different layers were clearly distinguished in the LiNbO3:Zn diffused samples, the first one being a very thin layer of polycrystalline ZnO. Two step-index layers were also detected: One was isotropic, and the other showed birefringence depending on the crystal cut. These two layers were correlated with Zn-rich phases previously detected in Zn-diffused LiNbO3 by x-ray techniques. The fourth layer detected presents a graded-index profile and corresponds to the formation of a Zn-containing solid solution with a LiNbO3-likestructure. These results are discussed and compared with the phases reported for Ti-diffused LiNbO3.

Modelling of optical amplification in Er/Yb co-doped LiNbO3 waveguides

The optical amplification of LiNbO3:Er3+/Yb3+ channel waveguides has been modelled in the small signal regime using the overlapping integrals method and the rate-equation formalism. It has been found that Yb3+ -sensitisation improves the pump efficiency at 980 nm and a higher gain is achievable in the high power-limit compared to singly-doped LiNbO3:Er3+ amplifiers.

Preservation of Periodically Poled Structures in Zn-Diffused LiNbO 3 Waveguides

In this work, the formation of optical waveguides in periodically poled lithium niobate (PPLN) substrates by Zn-diffusion from vapour phase is studied. It has been found that the diffusion of the Zn ions is homogeneous in the PPLN substrates and the optical waveguides can be fabricated with the same parameters used in single-domain lithium niobate. The periodic ferroelectric domain pattern initially present in the substrate is preserved in the waveguides.

Correlation between compositional and refractive index profiles in LiNbO3:Zn diffused optical waveguides

Waveguides fabrication in Z- and X-cut LiNbO3 crystals by vapor zinc diffusion has been studied by secondary ion mass spectrometry and optical measurements. Compositional analysis of diffused substrates shows the formation of a Zn rich superficial layer, followed by a deeper region with decreasing Zn concentration. A subsequent thermal annealing process has been performed to let zinc ions further diffuse into the substrates. The composition profiles have been correlated with the refractive index profiles, reconstructed by optical reflectivity measurements. The results and the nature of the detected layers are discussed and correlated with previous x-ray studies obtained in the same samples.

Modelling of 980 nm pumped EDWAs: Spectroscopic variations associated to fabrication process

In this work the optical amplification, in the small signal regime, at 1.5 μm in Zn-diffused, proton exchange and reverse proton exchange Er3+-doped waveguide amplifiers (EDWAs) based on LiNbO3 under 980 nm excitation has been modelled, including the dominant up-conversion channel activated by this pumping wavelength. The overlapping integrals method has been used to investigate how the spectroscopic changes, induced by the waveguide fabrication technique, affect the optical amplifier performance. In particular, it has been found that either the amplifier threshold and the maximum gain achievable are spectroscopy-dependent and therefore fabrication-dependent.

Photorefractive Damage Resistant Zn-Diffused Optical Waveguides in LiNbO 3 : Nd 3+ and Laser Operation

This work reports the fabrication of photorefractive damageresistant channel waveguides by a two-step Zn-diffusion technique in LiNbO 3 :Nd 3+ crystals and the demonstration of laser operation at room temperature at u =1.085 w m.