Luis C. Barbosa

Ultrafast processes in semiconductor doped glasses

We review studies of resonant and nonresonant ultrafast optical processes in semiconductor doped glasses, made at the University of Campinas. First we discuss measurements done in CdTe quantum-dots in glass, excited resonantly. In this case we observe a fast recombination, that depends on the size of the quantum-dot. For the smallest dots, with 3.2 nm average radius, the recovery time constant was found to be 360 fs. Then we describe the observation of the Optical Stark shift in CdSxSe1−x semiconductor-doped glass (SDG) excited under nonresonant below gap condition and probed with femtosecond optical pulses. An ultrafast and pure light-induced shift of the band edge is observed. For a pump intensity of 3 GW/cm2 the band shifts by 11 meV. The response of the shift tracks the profile of the pumping pulse.

High Verdet constant Ga:S:La:O chalcogenide glasses for magneto-optical devices

The magneto-optical rotation at room temperature was mea- sured for three Ga:S:La:O chalcogenide glasses at several laser lines in the visible. The first sample was a binary system constituted by 70 mol % Ga2S3 and 30 mol % La2O3, whereas in the second and third ones the lanthanum oxide was partially substituted by lanthanum sulfide, keeping the amount of gallium sulfide fixed. A pulsed magnetic field between 50 and 80 kG was used for the Faraday rotation measurements. The Verdet constant for one of the ternary samples was found to be as high as 0.205 min G 21 cm 21 at 543 nm, indicating that these chalcogenide glasses are very promising for magneto-optical applications. The data for each sample were fitted using the expected analytical expression for the magneto-optical dispersion. Measurements of the refractive index of the glasses at 632.8 nm are also reported. Data on the magneto-optical properties of two high Verdet constant, heavy-metal oxide diamagnetic glasses are also included for comparison.

Tellurite microstructured optical fibers doped with rare-earths for optical amplification

We present experimental results of optical amplification by using Er3+-doped tellurite MOFs. Also, a study of broadband near infrared emission in Pr3+ single-doped and Pr3+/Yb3+ codoped tellurite-tungstate glasses to perform new MOFs is presented.

Sm3+ effects in the Tm3+ doped tellurite glass for S-band amplification

Thulium doped Samarium codoped tellurite-tungstate glasses were produced. Luminescence properties in the infrared region were investigated looking to observe improved properties for S-band amplification in the co doped samples. Thulium is well-known by the 3H4-3F4 radiative transition emitting around ~1.47μm, which is a self-terminating transition in tellurite hosts due the longer lifetime of the lower level in relation to the upper level of this transition. Analysis of absorption and emission spectra showed that we could quench the 3F4 level significantly, what improved the intensity of the emission at 1.49μm. However, the state 3H4 were also quenched due the cross relaxation process due the absorption bands of Sm3+ around 1.5μm.

Spectroscopic investigation of the glass system TeO2-WO3-Na2ONb2O5 for mid-infrared amplifiers

Tellurite glasses following the molar concentration 71.5% TeO2, 22.5% WO3, 5% Na2O and 1.5% Nb2O5 have been investigated. Samples doped with Tm2O3, Pr2O3, Yb2O3 or Bi2O3 were fabricated by the conventional melt quenching process. Rare-earth (RE) 3+ ions have well defined emission bands. On the other hand, Bismuth emission in the infrared region have been found in some glasses and even that emission laser have been already obtained, the mechanism behind its luminescence is still misunderstood[1]. The Bismuth emission is sometimes referred as a “superbroadband” emission around 1.3um, which is very promising for an optical amplifier, but, to the best of our knowledge a bismuth based optical amplifier have not been produced yet. Our purpose is to investigate the mechanism behind this misunderstood “superbroadband” luminescence, and compare it with the rare-earths properties in the same range. The characterization consists in measurements of optical absorption spectra, optical emission spectra and life-time decay. Differential thermal analysis (DTA) was also performed, to identify changes in Tg and Tx as function of the doping concentration, which is important to the drawing process of a fiber.

Optical Amplifier based on a Er3+- doped Tellurite Microstructured Optical Fiber

Optical gain from 1530 up to 1570 nm by using an Er3+-doped tellurite microstructured fiber is presented. A maximum optical gain of ~27 dB at 1554 nm is obtained for a 980/1480 nm pump scheme.

Auger recombination process in CdTe quantum dots

Electron-hole recombination was theoretically and experimentally studied in CdTe quantum dots. A dependence of recombination times with pump pulse intensity was observed dots and it was attributed to the Auger recombination process. The rate equation model can describe completely the experimental data.

Supercontinuum generation in photonic crystal fibers made from borosilicate glasses

Supercontinuum generation in optical fibers has found applications from optical frequency metrology to telecommunications [1]. In this work, we present results of supercontinuum generation in photonic crystal fibers (PCFs) made from borosilicate glasses and pumped by nanosecond pulses from a Q-switched microchip laser. These PCFs were fabricated by the stack-and-draw technique and consist of five hollow ring periods with their solid core composed of lead-doped borosilicate glass. They have external diameters ranging from 3.8 to 6 microns and were excited by a commercial Q-switched laser (1064 nm, average power of 60 mW, repetition rate of 144 kHz). The PCF lengths were inferior to a meter. Optical attenuations for these PCFs were measured with the cut-back method and their dispersion curves were calculated from the scanning electron microscope images. The lead-doped core borosilicate PCFs with short lengths can provide high nonlinear properties and dispersion control, and therefore can be well suited for supercontinuum generation. Figure 1 details the PCF structure and presents some of the generated spectra.

Supercontinuum generation by using photonic crystal fibres made from borosilicate glasses

In this work, we present results of broadband emissions ranging from 800 to 1500 nm generated by using Photonic Crystal Fibres (PCFs) made from borosilicate glasses. The borosilicate PCFs, fabricated by the Stack-and-Draw technique, consist of five hollow ring periods around the solid core. The solid core is based on the lead-doped borosilicate glass. The PCFs with their external diameters ranging from about 3.8 to 6 microns were excited with a commercial pulsed diode laser (wavelength at 1065 nm, Power <100mW). The PCF length used to generate broadband emissions was less than a meter. The Optical Attenuation of these PCFs was measured via the Cut-Back method and their Dispersion Spectra were calculated by using the Finite Element Method (FEM) and the scanning electronic microscope images. Finally, we believe that short borosilicate PCFs with lead-doped cores (related to high non-linear properties) may be used in broadband emissions, supercontinuum generations or other non-linear applications.

Luminescence of PbS quantum dots on a silica microstructured fiber

In this work, we report results of lead sulfide (PbS) quantum dots (QDs) luminescence spectra evolution during the QDs spread process around the core of silica micro-structured (MS) fibers. These QDs are excited, via evanescent field effect, with a 532nm or 785nm laser guided by the MS-fiber cores. The PbS-core QDs of different sizes (originally immersed in Toluene) with emission bands around 877 nm (PbS877), 1160 nm (PbS1160) and 1474 nm (PbS1474) were inserted inside the silica MS-fiber structure by using an N2 gas pressure system. The broadband luminescence spectra varying from around 1000 nm to 1600 nm were obtained by using QDs mixtures impregnated around MS-fiber core surfaces. This QDs spread technique and the PbS QDs broadband luminescence spectra results could have potential applications in optical amplifier,sensor and nonlinear optical fiber loop mirror devices.