C. H. Brito Cruz

Microstructured-core optical fibre for evanescent sensing applications

The development of microstructured fibres offers the prospect of improved fibre sensing for low refractive index materials such as liquids and gases. A number of approaches are possible. Here we present a new approach to evanescent field sensing, in which both core and cladding are microstructured. The fibre was fabricated and tested, and simulations and experimental results are shown in the visible region to demonstrate the utility of this approach for sensing.

Lateral access to the holes of photonic crystal fibers – selective filling and sensing applications

A new, simple, technique is demonstrated to laterally access the cladding holes of solid-core photonic crystal fibers (PCFs) or the central hole of hollow-core PCFs by blowing a hole through the fiber wall (using a fusion splicer and the application of pressure). For both fiber types material was subsequently and successfully inserted into the holes. The proposed method compares favorably with other reported selective filling techniques in terms of simplicity and reproducibility. Also, since the holes are laterally filled, simultaneous optical access to the PCFs is possible, which can prove useful for practical sensing applications. As a proof-of-concept experiment, Rhodamine fluorescence measurements are shown.

Liquid-core, liquid-cladding photonic crystal fibers

We experimentally demonstrate a simple and novel technique to simultaneously insert a liquid into the core of a hollow-core photonic crystal fiber (PCF) and a different liquid into its cladding. The result is a liquid-core, liquid-cladding waveguide in which the two liquids can be selected to yield specific guidance characteristics. As an example, we tuned the core-cladding index difference by proper choice of the inserted liquids to obtain control over the number of guided modes. Single-mode guidance was achieved for a particular choice of liquids. We also experimentally and theoretically investigated the nature of light confinement and observed the transition from photonic bandgap to total internal reflection guidance both with the core-cladding index contrast and with the PCF length.

PROBING OF THE QUANTUM DOT SIZE DISTRIBUTION IN CDTE-DOPED GLASSES BY PHOTOLUMINESCENCE EXCITATION SPECTROSCOPY

We studied confinement effects in CdTe quantum dots by means of photoluminescence excitation spectroscopy. We show that by changing the detection energy we can resolve the spectrum of quantum dots of different sizes inside their much broader size distribution in CdTe‐doped glass. The spectra obtained show several well‐resolved lines. There is excellent agreement between the photoluminescence excitation spectra peak energies and calculations of the confined energy transitions based on a modified multiband envelope function model.

Ultrafast optical switching with CdTe nanocrystals in a glass matrix

This letter describes a principle demonstration of an ultrafast optical switch operating at 1Tbit∕s using CdTe-quantum-dots-doped glasses. Using a three-beam pump and probe experiment, we showed that thermal effects are responsible for a baseline in the pump and probe graphs and the nonexistence of carrier accumulation effects. After eliminating the thermal effects, we showed that, when two pump pulses are delayed by 1 ps, each pump pulse modulates the probe pulse independently, making this material highly promising for ultrafast all optical switching.

Recombination processes in CdTe quantum-dot-doped glasses

Electron-hole recombination in CdTe quantum dots was studied by photoluminescence and resonant femtosecond pump–probe measurements. A dependence of recombination times with pump pulse intensity was observed and we attribute this to the Auger recombination process. The overall kinetic processes that we observed are a fast decay from the initial excited state to surface trap states, the Auger recombination, the recombination of electrons from the surface states, and a longer time recombination which we attribute to electrons in the deep traps states.

Coherent acoustic phonons in PbTe quantum dots

Femtosecond pump-probe studies at 1.5 μm of PbTe quantum dots in a glass matrix have revealed oscillations due to a spheroidal acoustic mode. The wavelength dependence of the observed frequencies indicates size selectivity. The frequency and damping of the mode as a function of wavelength agree with the predictions of an acoustic continuum model that suggests that the dominant damping mechanism is radiative loss from the dots to the surrounding glass.

Positive and negative chirping of laser pulses shorter than 100 fsec in a saturable absorber

We present a calculation of the chirp generated in laser pulses shorter than 100 fsec on propagation through a saturable absorber (DODCI in ethylene glycol). The calculation takes into account the absorber saturation and the solvent nonlinear refractive index. At pulse energies greater than 10 nJ the chirp tends to be predominantly positive, and it increases rapidly as the pulse duration becomes shorter than 50 fsec. At pulse energies in the 1–7-nJ range the chirp is mostly negative for pulses longer than 30 fsec.

High power subnanosecond pulse generation in Nd YAG lasers

Abstract We describe the application of the self-injection and cavity dumping techniques to a Nd YAG laser. Single or double, highly stabilized nanosecond pulses are obtained with large efficiency.

Nonlinear interaction between two different photonic bandgaps of a hybrid photonic crystal fiber

Nonlinear interaction between spectral components in two different photonic bandgaps is experimentally demonstrated by launching femtosecond pulses near a zero-dispersion wavelength of a hybrid photonic crystal fiber, which guides by a combination of total internal reflection and bandgap effects. It is demonstrated that the initial pulse becomes spectrally broadened, and narrowband resonant radiation is generated in a different bandgap from the one responsible for guiding at the pump wavelength. The spectral intensity of the resonant radiation peaks at 2.7 dB below that of the broadened pulse in the pump-guiding bandgap.