We report on a novel organic/inorganic hybrid waveguide approach, which is composed of a cladding of extremely low
refractive index oxidized porous silicon formed on a bulk silicon substrate and of it, a polymeric
(polymethylmethacrylate) core doped with a visible laser dye (Nile-Blue) was deposited by spin coating.
The waveguiding properties of the structures have been characterised by means of the m-line technique, demonstrating
that the use of oxidized porous silicon as a cladding can considerably improve the mode confinement factor of single-mode
waveguides. The low refractive index achievable in the cladding (n=1.16) allows forming waveguides with a low
index polymer cores.
Variable stripe length (VSL) measurements have been also performed in order to characterise the amplification
properties of the waveguides. We demonstrate a clear transition from losses to gain at 694nm with a pump threshold of
28mJ/cm<sup>2</sup>. Values of net optical gain up to 104dB/cm have been measured at this wavelength.
Stimulated emission and light amplification have been observed in Ho<sup>3+</sup>-doped transparent oxyfluoride glasses and glass-ceramics.
A pump and probe experiment has been designed to show this result. A doubled-frequency Nd-YAG pulsed
laser oscillating at 532nm was used as the pump source to strongly populate the Ho<sup>3+ 5</sup>S<sub>2</sub>:<sup>5</sup>F<sub>4</sub> level. Low power laser
radiation at 750nm was used as the probe beam to stimulate the Ho<sup>3+ 5</sup>S<sub>2</sub>:<sup>5</sup>F<sub>4</sub> → <sup>5</sup>I<sub>7</sub> electronic transition at the same
The high power pump pulses provide population inversion between the Ho<sup>3+ 5</sup>S<sub>2</sub>:<sup>5</sup>F<sub>4</sub> and <sup>5</sup>I<sub>7</sub> electronic levels and a net
positive gain in the 750nm signal is observed both in the precursor glass and in the glass-ceramic. The highest optical
gain was obtained for the glass-ceramic sample and corresponds to about 3.7cm<sup>-1</sup> (~16dB/cm). The dynamics of the gain
is also investigated.
We present an experimental work on porous silicon-based optical devices. Notch filters and planar waveguides are fabricated and characterized. Three different types of filters are shown, the first one is a stop band filter in the 1.5 micron region, where improvements have been performed (smoothing of the index profile, apodization and index matching). The second is a double Notch filter in the IR range, which blocks two different frequencies. Finally Notch filters in the visible range are shown, where porous silicon has been completely oxidized. Double layer waveguides are fabricated and characterized by atomic force microscopy, luminescence and prism coupling techniques. All the results shown are compared with numerical calculations. The photoluminescence changes and the refractive index variations for different annealing times are modeled in terms of oxidation of silicon and slow condensation of the porous structure.
Laser-excited site selective spectroscopy of the Eu<sup>3+</sup> ions has been used in malonate crystals to detect a structural phase transition. From room temperature (RT) to 236 K a unique crystal-field site around the Eu<sup>3+</sup> ions is observed. However, two different sites are clearly identified below this temperature indicating a structural phase transition.
Room temperature intense green upconversion emission under excitation at 749 nm in a fluoroindate glass doped with 2.5 mol% of Ho<sup>3+</sup> has been observed. Analysis of spectral measurements suggest a photon avalanche mechanism with emissions from the <sup>5</sup>S<sub>2</sub> and <sup>5</sup>F<sub>4</sub> levels of Ho<sup>3+</sup> ions.