Vanessa D. Del Cacho

Giant third-order nonlinearity of lead and germanium based films in the visible and in the infrared

The nonlinearity of lead and germanium based films with thickness of 1.5μm was studied using a mode-locked picosecond Nd:YAG laser at 1064nm and its second harmonic at 532nm. Nonlinear refractive indices of ≈10−16m2∕W and two-photon absorption coefficients varying from ≈102cm∕GW at 1064nmto≈103cm∕GW at 532nm were measured. The results show that the films have potential applications in optical limiting devices.

Blue cooperative emission in Yb3+ - doped GeO2 - PbO glasses

Investigation of the blue cooperative luminescence in a binary composition of GeO2-PbO glasses with different Yb3+ concentrations is reported. High refractive index (1.96) and large transmission window (0.4 up to 5.0 µm) are characteristics of this vitreous system. Luminescence and lifetime measurements in the visible and near infrared regions were performed to investigate the spectroscopic characteristics of the glasses. Visible emission around 507 nm was detected in all samples. The visible emission intensity increases with the Yb2O3 content at least up to 2.0 wt. (%), that represents the maximum Yb2O3 concentration possible for this glass system. The visible lifetimes are about half of their respective near infrared ones, and the blue luminescence comes from a cooperative process. A rate equation was used to describe the behavior of the cooperative emission intensity as a function of Yb2O3 concentration; a good agreement with the calculated and measured cooperative luminescence was achieved.

Semiconductor Characteristics of Nd Doped PbO-Bi2O3-Ga2O3 Films

In this work optical and semiconductor characteristics of gallium oxide based thin films are studied. This material has important electro-optic applications and offers possibilities for semiconductor applications in heavy metal oxide semiconductor technology. In this study thin films of PbO-Bi 2O3-Ga2O3 were deposited by reactive sputtering. Two targets with different concentrations of Nd 2O3 (0.2 and 1.0 wt%) were prepared. Thin films were deposited by pure Ar plasma, at 5 mTorr pressure and RF power of only 20 W. Films were deposited on three inch diameter substrates of (100) silicon wafers. Optical UV-Vis-Nir transmittance and FTIR analyses showed that the films are transparent in the visible and middle infrared region of the electromagnetic spectrum. The refractive index of the films was of about 2.3, as measured by ellipsometry; Rutherford Backscattering Spectroscopy (RBS) analyses were employed for the compositional analysis of the films. For the electrical characterization it was used metallic electrodes, and the final structure obtained is a capacitor structure where the gallium oxide film plays the role of a dielectric. In the current versus voltage (IxV) analyses, the samples with 1.0 wt% of Nd2O3 show semiconductor characteristics similar to the ones obtained for the degenerated transistors. The electric characteristics of these films allow applications with electro-optic devices (phototransistors and photo detectors).

Tellurite Thin Films Produced by RF Sputtering for Optical Waveguides and Memory Device Applications

The development of new materials is very important for integrated optics and optical communications technology. In this perspective, tellurite glasses are promising materials, since they have interesting properties as high linear refractive index (~2.0), low phonon energy (600–800 cm−1), and wide transmission window (0.4–6 μm) that make them potential candidates for several applications; they are adequate hosts for rare-earth ions and for the nucleation of metallic nanoparticles. Recent results of tellurite thin films, produced by RF sputtering for optical waveguides and memory device applications, are presented. Results of pedestal waveguides fabricated using optical lithography followed by plasma etching for integrated photonics and integrated optical sensors applications are reported. Optical amplifiers were obtained based on Yb 3+ /Er 3+ codoped Bi 2 O 3 –WO 3 –TeO 2 thin films. The internal gain measured at 1530 nm was 5.6 dB (~3.7 dB/cm), under 980 nm excitation, and demonstrated the possibility of providing gain in short length waveguides. Also pedestal waveguides, using Bi 2 O 3 –WO 3 –TeO 2 thin films, as core layer, were employed for optical device applications, as Mach–Zehnder interferometers; low propagation losses were obtained at 633 and 1050 nm for waveguides in the 20–100 μm width range. Recently, a bistable current mechanism in Au nanoparticles embedded in TeO 2 –ZnO thin films was demonstrated. The nucleation of the metallic nanoparticles was performed with an adequate heat treatment, and the influence of the film thickness and of the gold nanoparticle size on the bistable properties is reviewed showing the feasibility of using TeO 2 –ZnO composition for memory device applications.

Yb3+/Er3+ codoped Bi2O3-WO3-TeO2 pedestal type waveguide for photonic applications

This work presents, for the first time to our knowledge, experimental results on pedestal waveguides produced with Yb3+/Er3+ codoped Bi2O3-WO3-TeO2 thin films deposited by RF Sputtering.

Fabrication and Characterization of GeO2-PbO Optical Waveguides

Departamento de Engenharia de Sistemas Eletronicos Escola Politecnica Universidade de Sao Paulo, Sao Paulo, SP