Davor Ristić

In this letter, we present an experimental and theoretical study of the radiation pressure-induced periodic and quasi-periodic routes to chaos in silica microspheres. We demonstrate that the Kerr effect is essential for correct interpretation of the experimental results both quantitatively and qualitatively and propose a new system of equations to describe opto-mechanical phenomena. Quantitatively, we observe chaotic behaviour for very small values of threshold pump power. Qualitatively, we report a novel double torus behaviour that is not possible in the absence of Kerr effect.

We review the works performed on whispering gallery mode (WGM) micro-optical resonators made in rare-earth (RE) doped glasses for implementing low threshold and narrow line coherent sources. These types of micro-lasers, because of their small size and ease of fabrication can be a useful tool for the characterization of laser glasses and have several applications, especially as sensors.

We present a theoretical analysis of the refractometric sensitivity of a spherical microresonator coated with a porous sensing layer performed for different whispering gallery modes. The effective refractive index of the modes is also calculated. The calculations are also made for a system which has an additional high-refractive index layer sandwiched between the microsphere and the porous sensing layer. The results of the calculation are discussed in regards to the applicability of the studied systems for gas sensor construction.

We report the effects of thermal oxidation on the sensing properties of porous silicon. Porous silicon substrates were prepared by electrochemical etching and thermally oxidized at different temperatures. A comparative EDS analysis shows that porous surfaces oxidized at higher temperatures have higher oxygen-to-silicon ratios. Our results indicate that the chemoresistive response due to the presence of isopropanol vapors at room temperature also increases with an increasing oxidation temperature. The presence of oxygen atoms in the PS layer could both protect the sensor from further atmospheric oxidation and increase its sensitivity.

Low threshold coherent emission at 1.5 µm is achieved using Er³⁺-doped dielectric 1D microcavities fabricated with a Radio Frequency-sputtering technique. The microcavities are composed of a half-wavelength Er³⁺-doped SiO₂ active layer inserted between two Bragg reflectors consisting of ten, five, and seven pairs of SiO₂/TiO₂ layers, also doped with Er³⁺ ions. The morphology of the structure is inspected using scanning electron microscopy. Transmission measurements show the third and first order cavity resonance at 530 nm and 1.5 µm, respectively. The photoluminescence measurements are obtained using the optical excitation at the third order cavity resonance using a 514.5 nm Ar⁺ laser or Xe excitation lamp at 514.5 nm, with an excitation angle of 30°. The full width at half maximum of the emission peak at 1535 nm decreased with the pump power until the spectral resolution of the detection system was 2.7 nm. Moreover, the emission intensity presents a non-linear behavior with the pump power and a threshold at about 4 µW.