Narrow Results

In this paper we report the detailed fabrication and experimental characterization of porous silicon one-dimensional photonic bandgap structures for specific photonic applications. These structures have been prepared on silicon substrate as well as free standing and can be proven useful for a large variety of applications such as high quality dielectric mirrors and filters.

In this paper, we present the theoretical analysis on how the wavelength of the localized surface plasmon resonances of gold nanoparticle can lead shift for the resonance wavelength. In our results, we calculate the scattering cross-section, the absorption cross-section and the field enhancement due to the nanoparticle. Numerical simulation were done using the finite element method (FEM). The work that we do here is different from the previous work because we use the Bragg reflector as a substrate. The Bragg reflector has a property of high reflectivity in some certain frequency bandwidth because of its periodic structure. The coherence interference of the Bragg reflector contributes to the plasmon resonances and results in some special character for a wide variety application, from sensing to photovoltaic. The periodic number of the Bragg reflector substrate and shapes of the nanoparticles are also discussed that result in a shift of the resonance wavelength.

The low and medium frequency - 1 Hz ≤ f ≤ 100 kHz - amplitude noise characteristics of 840 nm proton-implanted VCSELs (Vertical Cavity Surface Emitting Lasers) have been investigated. Experiments clearly show that the DBR (Distributed Bragg Reflector) structure represents the main electrical noise source of VCSELs. Furthermore, the electrical noise is somehow linked to the optical noise when the laser shows a "disturbed" optical spectrum with competition between very close modes.

At first, the single-layer Al₂O₃ and Nb₂O₅ films were deposited to find their refractive indices. After the indices of the single-layer Al₂O₃ and Nb₂O₅ films were measured, the thickness of 1/4 wavelength ($\lambda )$ for each layer of the Al₂O₃–Nb₂O₅ bi-layer Bragg reflectors of blue (450-nm) and green (550-nm) lights could be obtained. E-beam was used to deposit the bi-layer Al₂O₃–Nb₂O films (called as one period) with two, four, and six periods on glass substrates to fabricate the Bragg reflectors of blue and green lights. The measured results had proven that the reflectance ratio increased and the bandwidth and full-width at half-depth (FWHD) decreased with the increase of number of periods. The measured results had also proven that as the designed central wavelength increased (changed from blue to green light) and same periods were deposited, the reflectance ratio decreased and the bandwidth and FWHD values increased.

Sol–gel technology was applied to fabricate Eu-doped BaTiO₃/SiO₂ multilayer structures by spinning on silicon and fused silica substrates. Eu photoluminescence (PL) was investigated depending on the annealing temperature of these structures. The samples demonstrate the room temperature luminescence corresponding to ⁵${\text{D}}_0\to {}^7$F_J ($J=1$, 2, 3, 4) transitions of trivalent europium with the most intensive band at 615 nm. For the structure on fused silica with Eu in the BaTiO₃ cavity, increase of the annealing temperature from $450^{\circ }$C to $700^{\circ }$C results in modification of the luminescence indicatrix and lowering of the luminescence intensity in the direction along the surface normal. For BaTiO₃/SiO₂ multilayer structure generated on silicon, scanning electron microscopy (SEM) analyses reveal disordering after annealing at $1000^{\circ }$C. This heat treatment provides also an increase of the Eu luminescence intensity.